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Correspondence to: RH Venderbosch, BTG Biomass Technology Group B.V., Josink Esweg 34, 7545 PN Enschede, The Netherlands.
E-mail: [email protected]
178
Review
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd
Fast pyrolysis technology developmentRH Venderbosch, BTG Biomass Technology Group BV, Enschede, the Netherlands
W Prins, Faculty of Bioscience Engineering, University of Ghent, Belgium and BTG Biomass Technology Group BV,
Enschede, the Netherlands
Received October 21, 2009; revised version received November 30, 2009; accepted December 14, 2009
Published online in Wiley InterScience (www.interscience.wiley.com); DOI: 10.1002/bbb.205; Biofuels,
Bioprod. Bioref. 4:178-208 (2010)
Abstract: While the intention of slow pyrolysis is to produce mainly charcoal, fast pyrolysis is meant to convert bio-
mass to a maximum quantity of liquids (bio-oil). Both processes have in common that the biomass feedstock is
densifi ed to reduce storage space and transport costs. A comfortable, more stable and cleaner intermediate energy
carrier is obtained, which is much more uniform and well defi ned. In this review, the principles of fast pyrolysis
are discussed, and the main technologies reviewed (demo scale: fl uid bed, rotating cone and vacuum pyrolysis;
pilot plant: ablative and twin screw pyrolysis). Possible product applications are discussed in relation to the bio-oil
properties. General mass and energy balance are provided as well, together with some remarks on the economics.
Challenges for the coming years are (1) improvement of the reliability of pyrolysis reactors and processes; (2) the
demonstration of the oil’s utilization in boilers, engines and turbines; and (3) the development of technologies for the
production of chemicals and biofuels from pyrolysis oils. One important conclusion in relation to biofuel production
is that the type of oxygen functionalities (viz. as an alcohol, ketone, aldehyde, ether, or ester) in the oil should be
controlled, rather then merely focusing on a reduction of just the oxygen content itself. © 2010 Society of Chemical
Industry and John Wiley & Sons, Ltd
Keywords: pyrolysis, technology, review, bio-oil, biomass
Introduction
Environmental concerns and possible future short-
ages have boosted research into alternatives for fos-
sil-derived products. Biomass is abundantly available
worldwide and considered to be renewable. Despite its com-
plexity, the use of biomass is rapidly expanding. Agriculture,
petrochemical industries, and individual entrepreneurs,
meanwhile, have developed a signifi cant production of so-
called fi rst-generation biofuels from vegetable oils (biodiesel),
sugar and starch (bioethanol). Th e scale of production of
these fi rst-generation fuels (<100 MWth) appears to be sig-
nifi cantly lower than that of unit operations in traditional
petroleum refi neries (several GWth’s). Obviously the pro-
duction of fi rst-generation biofuels is in competition with
the food/feed industry. Th is is a non-ethical situation with
a limited CO2 reduction potential that is acceptable only
to get started while developing the techniques for second-
generation biofuels derived from lignocellulosic biomass
(residues like wood thinning, bagasse, rice husks, straw, etc.).
Second-generation biofuels can be made by (1) hydrolysis and
fermentation of cellulosic materials to ethanol; (2) gasifi cation
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 179
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
of lignocelluloses to syngas and further conversion to metha-
nol or gasoline/diesel, for example; and (3) liquefaction of
lignocelluloses with further upgrading, either by gasifi cation
(see 2), or by hydro-de-oxygenation (CO2 and H2O removal).
Large-scale implementation of biomass technologies is hin-
dered by a number of adverse biomass properties causing
diffi culties or excessive costs in its processing. Such problems
are in the highly distributed occurrence of biomass and its
low annual yields (usually less than 10 ton per hectare (dry
and ash-free), as well as in the wide variety in biomass struc-
ture and energy density (compare, for example, wood logs
with rice husks). To overcome these disadvantages of bio-
mass, one could include a pre-treatment process as a fi rst step.
In the overall conversion chain, fast pyrolysis, being such a
pre-treatment process, creates a uniform, liquid intermedi-
ate that is virtually ash-free and has a signifi cantly increased
energy density. It can be produced at a scale matching the size
of cost-effi cient biomass collection, stored until transport to
the nearest harbor, and fi nally shipped together with the pro-
duction of many other pyrolysis plants to a central site (e.g.,
a refi nery or a power station) for further conversion to heat,
electricity, chemicals, or fuels at any desirable time.
Th e handling and processing of liquids has many advan-
tages in comparison with processing solid or gaseous feed
streams. Interest in the production of pyrolysis liquids from
biomass has grown rapidly in recent years, due to the poten-
tial possibilities of:
• de-coupling liquid fuel production (scale, time, and loca-
tion) from its utilization;
• separating minerals on the site of liquid fuel production
(to be recycled to the soil as a nutrient);
• producing a renewable fuel for boilers, engines, and tur-
bines, power stations and gasifi ers;
• secondary conversion to motor-fuels, additives or special
chemicals (biomass refi nery); and
• primary separation of the sugar and lignin fractions in
biomass with subsequently further upgrading (biomass
refi nery).
An interesting aspect here is that pyrolysis could connect
(conventional) agricultural business to (petro)chemical
processes. Besides, fast pyrolysis can be integrated with bio-
logical processes in many ways, to form dedicated biorefi n-
eries (e.g., conversion of lignin residues to bio-oil (and bio-
char), fermentation of the fast pyrolysis sugar fraction, etc.).
Many reviews on pyrolysis can be found in the literature1–4
and in three handbooks edited by Bridgwater,5–7 while the
PyNe website and PyNe (now Th ermalNet) newsletters show
the state-of-the-art. Th e reviews should be read with some
care, as the data presented do not always refl ect the actual
case due to a lack of precise information on actual feedstock,
processing conditions, variations in feeds used, and a lack of
detail on the (usually proprietary) technologies.
Pyrolysis processes are carried out in the absence of oxy-
gen, at atmospheric pressure and temperatures ranging from
300 to 600°C. Charcoal is the main product of the tradi-
tional slow pyrolysis process, in which the biomass (usually
wood) is heated slowly to temperatures between 300 and
400°C. To the contrary, fast pyrolysis processes are char-
acterized by a high rate of particle heating to temperatures
around 500°C, and a rapid cooling of the produced vapors
to condense the liquids. Th is yields a maximum quantity
of dark-brown mobile liquid with a heating value roughly
equal to that of wood, which is approximately half the heat-
ing value of fossil fuel oil. Th e earliest recorded use of this
technique was in Egypt, where the product was used for
sealing boats.8 In more recent times, a number of chemicals
were derived from the liquids as well (e.g., methanol, acetic
acids, etc., and liquid smoke). While the function of slow
pyrolysis is to produce mainly charcoal and gas, fast pyroly-
sis is meant to convert biomass into a maximum quantity
of liquids. Th ey are both meant to pre-treat the biomass to
facilitate transport, storage, and utilization.
Principles
Th ermal decomposition of biomass results in the production
of char and non-condensable gas (the main slow pyrolysis
products) and condensable vapors (the liquid product aimed
at in fast pyrolysis). It is realized by rapid heat transfer to
the surface of the particle and subsequent heat penetration
into the particle by conduction. For fast pyrolysis condi-
tions, meant to maximize the liquid yield, the temperature
development inside the particle, and the corresponding
intrinsic reaction kinetics dominate the conversion rates and
product distributions. Principally, biomass is decomposed to
a mixture of defragmented lignin and (hemi)cellulose, and
180 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
fractions derived from extractives (if present). Th e intention
of fast pyrolysis is to prevent the primary decomposition
products (1) to be cracked thermally or catalytically (over char
formed already) to small non-condensable gas molecules on
the one hand; or (2) to be recombined/polymerized to char
(precursors) on the other. Such conditions would then lead
to a maximum yield of condensable vapors and include the
rapid heating of small biomass feed particles. Besides, it is also
essential to create a short residence time for the primary prod-
ucts, both inside the decomposing particle and in the equip-
ment before the condenser. For chemicals or fuel application,
an additional target would be to control the chemical compo-
sition of the condensables; for instance, by applying catalysts.
First reactor developers adopted the concept of fl ash
pyrolysis in which small particles (<1 mm) were used to
achieve high oil yields. Later research showed that the oil yield
is much less dependent on biomass particle size and vapor
residence times than originally assumed.9,10 Th e composition
of the oil, however, is sensitive for these parameters. High
external heat transfer to the biomass particles can be realized
by mixing the cold biomass feed stream intensively with an
excess of pre-heated, expectedly inert, heat carrier (e.g., hot
sand). A number of reactor designs have been explored that
may be capable of achieving high heat transfer rates, such
as fl uidized beds and mechanical mixing devices. For an
effi cient heat transfer through the biomass particle, though,
a relatively small heat penetration depth is required, which
limits the ‘size’ of biomass particles to, typically, 5 mm. ‘Size’
here refl ects a distance of two times the actual (heat) penetra-
tion depth of the particle. For such particles, the decomposi-
tion rate is controlled by a combination of intra-particle heat
conduction and the decomposition kinetics. Oil yield values
observed in continuously operated laboratory reactors and
pilot plants, for wood as a feedstock material, are usually in
the range of 60 to 70 wt.% (dry-feed basis). Although generally
reported in reviews, oil yields over 70% are exceptional and
only for well-defi ned feedstocks as cellulose. Energetic yields
are a bit lower, approx. 55 to 65%. It is obvious that the energy
left in the byproducts should be used as well; for example, for
drying the feedstock and/or steam-electricity production. If
the objective is to derive chemicals from the pyrolysis liquid,
it is essential to operate the process at the proper conditions
(temperature, residence time, feedstock type, and feedstock
pre-treatment) in order to maximize the yield of the specifi c
component aimed at. When fuels are required, less stringent
criteria must be met; the conversion of as much biomass
energy as possible to the liquid product is then decisive. Until
recently, most R&D work has been focused on maximizing
the overall oil yield, without paying suffi cient attention to the
product composition and quality. Next to water, the major
components of biomass are:
- cellulose (mostly glucans), with a composition roughly
according to (C6H10O5)n, and n = 500 to 4000;
- hemicellulose (mostly xylans), with an average composi-
tion according to (C5H8O4)n, and n = 50 to 200; and
- lignin, consisting of highly branched, substituted, mononu-
clear aromatic polymers, oft en bound to adjacent cellulose
and hemicellulose fi bers to form a lignocellulosic complex.
Cellulose, hemicellulose, and lignin all have a diff erent ther-
mal decomposition behavior, and each individually depends
also on heating rates and the presence of contaminants.11 A
typical temperature dependence of the decomposition through
thermo-gravimetric analysis (TGA) for reed, carried out by
the University of Groningen is given in Figure I. Th e total
mass loss rate is plotted versus the temperature in Figure
IA, while the TGA data are interpreted in terms of cellulose
(almost 30%), hemicellulose (25%), and lignin (20%) in lB. Th e
diff erential plot for these fractions is given on the left hand
side against the original biomass data. Hemicellulose is the
fi rst component to decompose, starting at about 220°C and
completed around 400°C. Cellulose appears to be stable up
to approx. 310°C, where aft er almost all cellulose is converted
to non-condensable gas and condensable organic vapors at
320–420°C. Th ough lignin may begin to decompose already
at 160°C, it appears to be a slow, steady process extending
up to 800–900°C. At fast pyrolysis temperatures of around
500°C, the conversion of lignin is probably limited to 40%. In
general, for fast pyrolysis, a solid residues remains (char, not
shown in Fig. 1), which is then mainly derived from lignin and
some hemicellulose fractions, respectively 40 and 20 wt-% of
the original sample.12 A conclusion from such TGA data can
be that the oil is derived mainly from cellulose, and only par-
tially from hemicellulose (depending on the heating rate up
to approx. 80% conversion to oil and gas) and lignin (roughly
50% conversion to oil and gas). Th e explanation is that in the
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 181
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
biomass structure, lignin and hemicellulose are linked through
covalent bonds (ester and ether) and cannot be released that
easily upon pyrolysis; cellulose and hemicellulose are linked
by much weaker hydrogen bonds.13 Indirect evidence for this
hypothesis is given by the composition of the pyrolysis-derived
char, which has an elemental composition close to that of
lignin. Th e pyrolysis of biomass can be either endothermic or
exothermic, depending on the temperature of the reactions
and the type of feed. For (hemi)cellulosic materials, the pyroly-
sis is endothermic at temperatures below about 450°C, and
exothermic at higher temperatures. As argued already, vapors
formed inside the pores of a decomposing biomass particle
are subject to further cracking, leading to the formation of
additional gas and/or (stabilized) tars. Th e sugar-like fractions
especially can be readily re-polymerized, increasing the overall
char yield (mostly ex-bed of the pyrolysis process). Th is may
be the purpose of slow pyrolysis but should be avoided in fast
pyrolysis. For the small particles used in fast pyrolysis, second-
ary cracking inside the particles is relatively unimportant due
to a lack of residence time. When the vapor products enter the
surrounding gas phase, however, they will further decompose
if they are not condensed quickly enough.
Although other mechanisms have been proposed as well,
Fig. 2 shows a possible reaction pathway for biomass pyroly-
sis. Schemes like these, including three lumped product
classes, were originally proposed by Shafi zadeh et al.14,15
and start with a reaction that is fi rst order in the decompos-
ing component. Unfortunately, there is great variety in the
results of reaction rate measurements, even for a ‘single’
biomass type, such as wood. Published rate and selectivity
expressions maybe useful in describing trends, but they can
hardly be used for reliable quantitative predictions.10,16–18 It
should be realized here that biomass is a natural material,
with widely varying structural and compositional proper-
ties. Despite all such uncertainties in the required input
data, many scientists still propose single particle models
based on fundamental chemical and physical phenomena
taking place inside the particles. Kinetic data are proposed
for the pyrolysis of wood, but a small variation in ash con-
tent seriously aff ects these reaction rates, and probably the
pyrolysis pathways themselves. Already stated in 1991, ‘it
should not be expected that any simple one-step kinetic
scheme can account for all the facts concerning the pyrolytic
behavior of [just] carbohydrates’.19 Although the predictive
power is limited, and insuffi cient for scaling-up purposes,
modeling is still useful to create a better understanding.18
0
0.01
0.02
0.03
0.04
0 100 200 300 400 500
Temperature (°C)
Mas
s Lo
ss R
ate
(wt.%
/°C
)
lignin
cellulose
hemicellulose
water
0
0.01
0.02
0.03
0.04
0 100 200 300 400 500
Temperature (°C)
Mas
s Lo
ss R
ate
(wt.%
/°C
)
Figure 1. Thermogravimetric analysis curve for Reed (A) and the differential plot interpreted in terms of
hemicellulose, cellulose and lignin (B). TGA curves are prepared by the University of Groningen.
Wood (s)
bio-oil (l)
Char (s)
Wood vapors (g)
Gas (g)(CO,CO2,CH4)
Char (s) + gas (CO2)+ ‘bio-oil (l)’
Primary phasedecomposition
reactions
Secondary phasecracking + condensation
Re-polymerisation
Gas (g)(CO,CO2,CH4)
450 – 550°C<1 s
400 – 500°C>1 s
atmosphericweeks / months
Figure 2: Representation of the reaction paths for wood pyrolysis.
182 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
Effect of ash
A photograph of bio-oil is given in Figure 3. Th e maximum
possible oil yield thus depends on various parameters, and
this includes feedstock properties, water content, tempera-
ture and vapor residence time. Th e maximum possible oil
yield thus depends on various parameters, and this includes
feedstock properties, water content, temperature, and vapor
residence time. In addition, ash in the biomass can have a
dominant eff ect on the oil yield and composition.20,21 Th e
trend line in Fig. 4 is based on published data points.
In general, the yields of char and gas increase signifi cantly
for higher ash contents in the biomass, viz. at the expense of
oil yields.
Sodium and potassium will have a large impact, but sul-
fur- and phosphorus-containing ammonium salts can also
dramatically aff ect oil yields and promote char formation.22
Although there is evidence that ash (including metals) can
have a catalytic eff ect on the thermal degradation of biomass
during pyrolysis, data like in Fig. 4 should be interpreted
with care as they are derived for diff erent types of biomass
as well. Figure 4 may suggest otherwise, but not all ash-like
materials are detrimental for the oil yield; silicon and metals
other than the alkalis appear quite inactive in the pyrolysis
process. It has been suggested that alkali metals have the
potential to lower the optimal pyrolysis temperature as well.
Consequently, for biomass types with high ash content,
which is generally the case for the technological interesting
low-valued residues, the oil-yield can drop to values, some-
times below 50 wt.%. Th ough extremely relevant for both the
oil yield and oil quality, limited research has been carried out
to understand the eff ects of ash on the pyrolysis reactions.
Oil properties
Representative values for wood-derived pyrolysis oil proper-
ties are collected from various resources and listed in Table 1.
It is a liquid, typically dark red-brown to almost black, a
color that depends on the chemical composition and the
presence of micro-carbon (Fig. 3). Th e density of the liquid is
Table 1. The range of elemental composition and properties for wood-derived pyrolysis oil.1–3
Physical property Pyrolysis conditionsWater content
(wt.%)15–30 Temperature (K) 750–825
pH 2.8–3.8 Gas residence time (s) 0.5–2
Density (kg/m3) 10500–1250 Particle size (µm) 200–2000
Elemental analysis Moisture (wt.%) 2–12
(wt.% moisture free) Cellulose (wt.%) 45–55
C 55–65 Ash (wt.%) 0.5–3
H 5–7
N 0.1–0.4 Yields (wt.%)
S 0.00–0.05 Organic liquid 60–75
O Balance Water 10–15
Ash 0.01–0.30 Char 10–15
Gas 10–20
HHV (MJ/kg) 16–19
Viscosity (315 K, cP) 25–1000
ASTM vacuum
Distillation (wt.%) 430 K ~10
466 K ~20Solubility
(wt.%)Hexane ~1
492 K ~40 Toluene 15–20
Distillate ~50 Acetone >95
Acetic acid >95
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 183
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
about 1200 kg/m3, which is signifi cantly higher than that of
fuel oil. It has a distinctive acid, smoky smell, and can irritate
the eyes. Th e viscosity of the oil varies from 25 up to 1000 cP,
depending on the water content and the amount of light
components in the oil. It is important to note that oil proper-
ties depend on feedstock and operating conditions, but may
change during storage, a process indicated as ‘ageing’, which
(by lack of defi nition) is usually noticed by an increased vis-
cosity in time and a possible phase separation of the oil in a
watery phase and a viscous organic phase. Due to the pres-
ence of large amounts of oxygenated components, the oil has
a polar nature and does not mix readily with hydrocarbons.
In general, it contains less nitrogen than petroleum prod-
ucts, and almost no metal and sulfur components. However,
some of the nitrogen is transferred to the oil product as well:
feed materials with a high nitrogen contents yield oil with
higher pH-values and larger amounts of nitrogen in the oil.
Degradation products from the biomass constituents include
organic acids (like formic and acetic acid), giving the oil its
low pH of about 2 to almost 4. Th e oil attacks carbon steel,
and storage of the oils should be in acid-proof materials like
stainless steel or poly-olefi ns. Water is an integral part of the
single-phase chemical solution. Th e (hydrophilic) bio-oils
have water contents of typically 15–35 wt.%, and water can-
not be removed by conventional methods like distillation.
Th is high water content is a serious drawback if considering
the heating values: the higher heating value (HHV) is below
19 MJ/kg (compared to 42–44 MJ/kg for conventional fuel
oils). Above a certain water-content level, viz. in the range
of 30 to 45 wt.%, phase separation may occur. Depending
on the type of feedstock and process conditions the ratio of
oil over aqueous phase varies from 50:50 to 30:70, and the
presence of these two phases can complicate the oil’s applica-
tion. In many cases, suffi cient drying of the biomass feed-
stock material prior to pyrolysis prevents phase separation.
Applying diff erent condensation temperatures will yield oils
with diff erent water contents (aff ecting the oil yield as well),
and there is quite some room for optimization.23
Usually the choice of the feedstock and process (char-
acteristics) will determine the ‘oil’ quality and possible
phases. Benefi cial eff ects of the water content have also been
reported, viz. in case of combustion. It causes a decrease
in viscosity of the oil (facilitating transport, pumping, and
atomization); it improves ‘stability’; it lowers the combustion
0
10
20
30
40
50
60
70
80
0 3 5 6 7 8
Ash content (wt.%)
Oil
an
d c
ha
r y
ield
(w
t.%
)
oil
char
gas
Trendline oil (Chariamonti et al. 2007)
1 2 4
Figure 4. Relationship between oil yield and ash content in the
biomass. The solid lines represent trend lines taken from literature,20
while the broken line is a trend line based upon more than 20 data
point for wood.21Figure 3. Fast pyrolysis oil.
184 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
temperature and, as a consequence, it may cause a reduction
of the NOx emission. Generally speaking, the (organic) oil
yield achieved in fast pyrolysis should be as high as possi-
ble. Besides, the oil should have a much higher (volumetric)
energy content than the original biomass, and must be more
stable towards biological degradation.
Composition and stability
Pyrolysis oils are produced by the rapid quenching of frag-
mented biomass, these fragments being derived from the
biomass constituents, cellulose, hemicellulose, and lignin.
Th e largest fragments that are conveyed to the condenser in
the vapor phase have a molecular mass that is far too high
for being a gas component at temperatures around 500°C.
Th ey may be present in the vapor phase as aerosols, or are
produced upon ‘freezing’ the vapors. Th is liquid product
collected in the condenser includes the complete spectrum
of oxygenated compounds, with molecular weights rang-
ing from 18 to over 10 000 g/mol, the higher values prob-
ably caused by repolymerization of the biomass fragments.
Whereas some researchers think the oil is a (micro-)emulsion
of these compounds, there is also reason to believe the oil
is a mixture of soluble components, likely with water as the
solvent and polar sugar constituents behaving as bridging
agents in the dissolution of hydrophilic lignin material.24
GC-analysis (including 2D-GC, GC-MS etc) appears, to a
certain extent, valuable in the interpretation of the oil qual-
ity. However, the usefulness of GC data is limited due to
the (unknown) destructive eff ect of the technique on the oil
composition. GC injection includes vaporization of the feed,
which is known to be diffi cult for pyrolysis oils and causing
some coking in the injection part of the system. Moreover,
chemical reactions occurring in the GC column cannot be
excluded either, and it is questionable whether the compo-
nents actually detected are really present in the feed oil. Other
techniques of which the potentials for pyrolysis-oil analysis
are being investigated are Gel Permeation Chromatography
(GPC) and High Performance Liquid Chromatography
(HPLC), but both methods need to be handled with great
care. Fortunately, development of new techniques to footprint
the oils is ongoing. As the oil can not be distilled without
severe repolymerization and thus chemical degradation, a
solvent fractionation technique, illustrated in Fig. 5, is devel-
oped to analyze the oil in an alternative way, and reveal the
presence of certain fractions present in the oil:25
• water solubles (acids, alcohols, diethylethers);
• ether solubles (aldehydes, ketones, lignin monomers, etc.);
• ether insolubles ((anhydo)sugars, hydroxyl acids);
• n-hexane solubles (fatty acids, extractives, etc.);
• DCM solubles (low molecular lignin fragment, extrac-
tives); and
• DCM insolubles (degraded lignins, high molecular lignin
fragments, including solids)
Th e ether insolubles in particular (the sugar components, a
syrup-like fraction) appear to have high oxygen contents (up
to 50%) if compared to, for example, the DCM solubles and
insolubles (25 to 30% oxygen). Ongoing research is aimed at
BIO-OIL
WATER-SOLUBLES WATER INSOLUBLES
ETHER INSOLUBLESETHER SOLUBLES
DCM SOLUBLES DCM INSOLUBLES
water extraction
ether extraction DCM extraction
Ether solubles:(Aldehydes, ketons,lignin monomers)
Sugars (anhydrosugars,anhydro-oligomers,Hydroxyacids (C<10))
LMM lignin (low molecularlignins, extractives)
HMM lignin (high molecularlignins, solids)
N-HEXANE SOLUBLES
Extractives
Water (by KF titration)Solids (by MeOH-DCM extraction)
Figure 5. Fractionation scheme for chemical characterization.25
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 185
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
revealing the various components in each fraction, and their
eff ects on storage, stability, upgrading, etc. Th e results from
solvent fractionation and GC-MS can be combined.25 Th e
main part of GC-eluted compounds is in the ether-soluble
fraction of the fractionation scheme, with the DCM (in-)solu-
bles not being detected in a GC. Table 2 shows the combined
results of solvent extraction, GC/MSD and CHN analyses for
reference pine liquid. Although this method may not be the
future standard for bio-oil analysis, it could be an important
technique relevant to understanding how the oxygen is actu-
ally bound to the carbon (alcohol, keton, or as an ether/ester).
An important property of pyrolysis oil is its chang-
ing characteristics over time. Such an ‘instability’ can be
observed by a viscosity increase during storage, some for-
mation of carbon dioxide, an increased water content, and
eventually by phase separation. Defi nitions to address this
unstable character are lacking. Th e detailed mechanism
of this ‘ageing’, the causes of it, and the consequences for
further use are still unclear, and will depend highly on the
various oxygen functionalities in the oil (and therefore
feedstock type, operating conditions, initial quality, stor-
age temperatures, etc.). At room temperature, the ageing of
bio-oil occurs over periods of months or years, depending
on the type of feedstock, and its ‘initial quality’. At elevated
temperatures, however, the polymerization reactions are
enhanced signifi cantly, and it is therefore recommended
to avoid (long) storage at temperatures above 50°C. Recent
work indicates that recombination/polymerization of oil
fragments, accompanied by separation and evaporation
of small molecules (including CO and CO2), could be an
important cause.25 Although the reasons for instability may
be unclear, the major chemical change in wood-derived oil
is due to an increase in the DCM insoluble fraction and a
signifi cant decrease in the ether insoluble constituents (‘sug-
ars’). Th e increase in the average molecular weight in time,
the viscosity (of the organic fraction) and pour point, and/or
changes in the molecular structure cause phase separation.
Th e instability of the oil and the varying quality of oils
produced worldwide could be hurdles to further develop-
ment of oil applications. Much depends on the eventual
Table 2. Chemical composition of reference pine oil and its fractions.25
Reference Pine Oil wet dry C H N O
Water wt-% 23,9 0
AcidsFormic acid Acetic acid Propionic acid Glycolic acid
wt-%wt-%wt-%wt-%wt-%
4,3 5,61,53,40,20,6
40,0 6,7 0 53,3
AlcoholsEthylene glycolIsopropanol
wt-% wt-%wt-%
2,23 2,90,32,6
60,0 13,3 0 26,7
Aldehydes and ketonesNonaromatic AldehydesAromatic AldehydesNonaromatic KetonesFuransPyrans
wt-%wt-%wt-%wt-%wt-%wt-%
15,41 20,39,72
0,0095,363,371,10
59,9 6,5 0,1 33,5
Sugars Anhydro-ß-D-arabino-furanose, 1,5 Anhydro-ß-D-glucopyranose(Levoglucosan)Dianhydro-a-D-glucopyranose, 1,4:3,6
wt-%wt-%wt-%wt-%
34,44 45,30,274,010,17
44,1 6,6 0,1 49,2
LMM lignin Catechols Lignin derived PhenolsGuaiacols (Methoxy phenols)
wt-%wt-%wt-%wt-%
13,44 17,70,060,093,82
68 6,7 0,1 25,2
HMM lignin wt-% 1,950 2,6 63,5 5,9 0,3 30,3
Extractives wt-% 4,35 5,7 75,4 9,0 0,2 15,4
186 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
end application: although technologies are being demon-
strated already at a signifi cant scale (up to a 100 ton biomass
throughput per day), standards and specifi cations are still
underdeveloped. Some progress has been made however in
recent years.26 Various physical and chemical methods for
the characterization and analysis of pyrolysis liquids in rela-
tion to their future applications have now been identifi ed.
Th is applies to properties such as the viscosity, water con-
tent, pH, density, elemental composition, LHV, ash content,
char content, surface tension, solubility in diff erent solvents,
ageing characteristics, and pour and fl ash points.
Catalytic pyrolysis
It has been recognized already in the early days of fast
pyrolysis R&D that application of catalysis could be of major
importance in controlling the oil quality and its chemical
composition.27,28 Without any catalyst involvement, the bio-
oil derived from fast pyrolysis is a mixture of hundreds of
diff erent, highly oxygenated chemical compounds. Catalysis
could be applied for a number of reasons, and at a number
of diff erent positions in the process. Lower pyrolysis tem-
peratures, a higher chemical and physical stability, high
yields of target components, and an improved miscibility
with refi nery streams, are all goals strived for. Bio-oils can
be upgraded by either applying catalysts in the production
process (‘catalytic pyrolysis’), or by post-treatment of the
bio-oil over a catalyst bed. Th is post-treatment may be the
thermal cracking of re-evaporated bio-oil in a hot fl uidized
bed of Fluidized Catalytic Cracking (FCC) catalyst parti-
cles (‘bio-oil FCC’), or the catalytic hydrodeoxygenation at
elevated temperatures and hydrogen pressures (‘hydrotreat-
ment’). When, in catalytic pyrolysis, the catalyst particles
are mixed into the reactor together with the inert heat car-
rier (oft en sand), there is an immediate contact between
the catalyst and pyrolysis products. Besides, in pyrolysis
processes with a separate char combustor, the catalyst can
be regenerated continuously (coke burn off ). Requirements
are then that the particle properties of the catalyst should
match those of the inert heat carrier while its activity should
be maximal at the optimal fast pyrolysis temperature. More
fl exibility regarding the design of the catalyst and the condi-
tions of the catalytic treatment is created when a separate
reactor is installed in the pyrolysis vapor stream to the
condenser. Th e latter procedure is mostly applied in research
projects. Results of laboratory investigations are, until now,
quite poor regarding the understanding of what is actually
taking place. Mostly, the approach is to carry out catalytic
pyrolysis experiments for selected types of biomass and ana-
lyze the liquids obtained for their contents of alkanes –
alkenes and aromatics. Yield numbers remain oft en unclear,
but obviously the yield of the desired liquid is far below the
theoretically maximum possible value. Signifi cant amounts
of coke, water, and carbon oxides are produced.29,30
Fast pyrolysis technologies
Th e aim of the slow pyrolysis process is to produce mainly
charcoal, whereas the fast pyrolysis process should convert
the biomass into a maximum quantity of liquid. As men-
tioned in the introduction, both processes have in common
that the energy in the biomass feedstock is concentrated in a
smaller volume by which transport costs and storage space
can be reduced. Also benefi cial is that a more uniform, stable,
and cleaner-burning product is obtained, that could serve as
an intermediate energy carrier and feedstock for subsequent
processing. In an industrial process, the byproducts char or
gas (both 10 to 20 wt.%) would be used primarily as a fuel for
the generation of the required process heat (including feed-
stock drying). But the byproducts left could also be applied
otherwise. Active carbon, carbon black, or a pelletized fuel
could be produced from the char. Th e char is also proposed
as a soil improver (‘biochar’).31 For specifi c purposes, such as
entrained fl ow gasifi cation (syngas production), recombina-
tion to a char-oil slurry is sometimes considered. Th e gaseous
byproduct, essentially a mixture of CO and CO2, could also
be used for electricity production in an engine, if cleaned
properly. Apart from possible fl ue gas emissions resulting
from the char combustion, there are no waste streams. Th e
ash in the original biomass will be largely concentrated in the
char product and is separated when the char is combusted in
the process for drying and heating the biomass feed stream.
It allows recycling of the minerals as a natural fertilizer to
the site where the biomass was grown originally.
Th e essential characteristics of a fast pyrolysis reactor for
maximal oil production are the very rapid heating of the bio-
mass, an operating temperature around 500°C, and a rapid
quenching of the produced vapors. Crucial in the pyrolysis
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 187
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
reactor is the ability to have high heat transfer rates to (and
preferably also inside) the solid particles. On an average
basis, it can be estimated that 1.5 MJ/kg is required, mainly
for heating the biomass (which is 2/3 of that of water evapo-
ration). Moreover, the time and temperature profi les of the
vapors produced aff ect the composition of the oil as well. In
small laboratory reactors, where very rapid transfer rates are
achieved, and vapor residence times of only a few tenths of a
second can be realized, oil yield can be maximized. For heat
transfer limited systems, and longer residence times of the
pyrolysis vapors at higher temperatures, occurring especially
in real-scale installations, the consequences of secondary
cracking can become quite signifi cant. In practice, high
external medium-to-solid heat transfer rates are required
(say >500 W/m2K); intraparticle biomass heat transfer limita-
tion should be avoided (requiring particles <5 mm to limit
the heat penetration depth); and vapor phase residence times
should be kept below a few seconds in order to maintain
the oil yield. In case a pyrolysis plant is meant to produce a
liquid fuel for combustion or gasifi cation, the process could
be designed in a way that maximizes the energy conversion
to the liquid product. When the bio-oil product is meant to
derive biofuels or chemicals from it, however, factors other
than just the vapor residence time should also be considered.
Th e composition of the oil can be steered by process condi-
tions, equipment dimensions, and the application of catalysis.
Th e latter is an ongoing research item at various laboratories.
Although laboratory studies regarding the thermal decom-
position of various organic substances have been carried
out for a much longer period, the technology development
of ‘fl ash’ and ‘fast’ pyrolysis started only some 20 years ago
when the advantages of liquefying biomass in such a simple
way were gradually recognized. During the 1980s and the
early 1990s, research was focused on the development of
special reactors, such as the vortex reactor, rotating blades
reactor, rotating cone reactor, cyclone reactor, transported
bed reactor, vacuum reactor, and the fl uid bed reactor. Since
the late 1990s, the process realization emerged, resulting in
the construction of pilot plants in Spain (Union Fenosa),
Italy (Enel), UK (Wellman), Canada (Pyrovac, Dynamotive),
Finland (Fortum) and the Netherlands (BTG). In the USA
and Canada, Ensyn’s entrained fl ow bed process is applied
at a scale of around 1 ton/hr for commercial production of
a food fl avor called ‘liquid smoke’. Dynamotive and BTG
designed and operated demonstration installations of 2 to 4
tons’ biomass throughput per hour for utilization of bio-oil
in energy production primarily. Meanwhile, many pilot-
plant projects stopped, sooner or later aft er the initial test-
ing. At the time of writing, the plants of Union Fenosa, Enel,
Wellman, Fortum, and Pyrovac’s large-scale installation in
Jonquiere, Canada, are no longer in operation. Th is may be
caused by a lack of confi dence in economic prospects and
markets at the time, or by legislative limitations.
On refl ection, the state-of-the-art in the development of
pyrolysis seems comparable with the situation in 1936 in
the petrochemical industry, when the Houdry (FCC) proc-
ess was fi rst demonstrated on a scale of 2000 barrels per
day. Today, fast pyrolysis is attracting increased interest.
Fields of science other than engineering (e.g., agriculture,
organic chemistry, catalysis, separation technology) are
getting involved, together accelerating the developments in
bio-oil applications. Oil companies and food/feed industries
are building biofuel departments and looking for existing
knowledge matching their strategies and targets regarding
renewable resources. Also, new developers of fast pyrolysis
technology are showing their intentions with the construc-
tion of pilot plants based on proprietary technology. A selec-
tion of historical developments aiming at demonstration-
scale pyrolysis technologies will be discussed later, with an
emphasis on the rotating cone technology of BTG.
Entrained down-fl ow
Early attempts of fast pyrolysis have been carried out in
entrained fl ow reactors, where biomass particles (1 to 5 mm)
were fed to a hot, down-fl ow reactor. Th e reaction was sup-
posedly complete within a residence time <1 s, if the reactor
tube was held at temperatures in between 700 and 800°C.
Unlike many other fast pyrolysis reactors later on, no extra
hot solid material was used to transport and heat the bio-
mass particles. An early process was developed at Georgia
Tech Research Institute (USA) and a fi rst unit transferred to
Egemin (Belgium) for further development and scale up in
a project funded partly by the European Commission. Th e
plant was dismantled in 1993. It appeared that the feedstock
was incompletely pyrolyzed in the reactor, particularly when
larger particles were used (6 mm). Insuffi cient heat transfer
188 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
to the solid biomass particles during their short travel in the
reactor was the likely cause.32 Th is resulted in total liquids
yields of less than 40 wt.% on dry feed basis.
Ablative reactor
Ablative pyrolysis was then considered as a possible alter-
native to entrained fl ow reactors. Th e principle of ablative
pyrolysis is given in Fig. 6. Th e surface, heated by hot fl ue
gas, is rotating, and biomass is pressed onto the hot surface
(approx. 600°C). Th e fl ue gas is produced by combustion
of pyrolysis gases and/or produced char. In the 1990s, BBC
(Canada) demonstrated an ablative fl ash pyrolysis technique
for the disposal of tires at a 10–25 kg/hr capacity.33
Th e process was licensed to Castle Capital (a holding com-
pany of several companies involved in the fabrication of
pressure vessels, military vehicle modifi cation etc.) for the
erection of a 50 t/d plant in Halifax, Nova Scotia, using solid
wastes. It is unknown to the authors what happened to these
plans. Much of the pioneering work on ablative pyrolysis was
carried out by NREL (Golden, CO, USA, formerly known as
SERI).34 In their approach, the forces to press the biomass to a
hot surface are centrifugal forces in a so-called vortex reactor.
Th e biomass, though, appeared to be insuffi ciently converted,
requiring the solids to be redirected back to the entrance. In
1989, NREL entered a consortium with Interchem Industries
Inc. (USA) to develop and exploit NREL’s ablative pyrolysis
for the production of phenol adhesives and alternative fuels.
However, the construction of a demonstration plant was never
completed. NREL is no longer contractually involved with
this fi rm, and abandoned the vortex design concept in 1997.
oil
excess
Biomass
recycle gas
char / sand loop
char combustionsand
air
gas
biomass
Oil
hot disc
air
char gas
gas
oil
vacuumvessel
char
biomass
molten salt
air
biomassbiomass
fluid bed
recyclegasrecyclegas
char excessexcess
oil
air
gas
char
sand loop
biomass
oil
air
gassand
oil
char combustion
char/sand loopbiomass
sand
air
air
gas
(a) (b)
Figure 6A. Ablative, CFB and vacuum technologies. Figure 6B. Fluid bed, screw (auger) and rotating
cone technologies.
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 189
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
In the 1990s, Aston University (Birmingham, UK), built
and tested a prototype rotating blade reactor for ablative
pyrolysis on a small scale of 3 kg/hr.35 Oil samples were pro-
duced in yields of up to 80 wt.%.
Work in a cyclone reactor continued at CNRS (France) in
this century, yielding up to 74% bio-oil.36 At present, the
German company Pytec is the only company developing
ablative pyrolysis technology, with a pilot plant of 250 kg/hr
in operation near Hamburg and plans for demonstration of a
2 t/hr unit in Mecklenburg-Vorpommern.37–39
In general the following limitations for this ablative tech-
nology can be expected:
• Limited heat transfer rates to the hot surface due to the
indirect heating principle. Th is is caused by both a rela-
tively small temperature diff erence between hot fl ue gas
(likely around 800oC) and the pyrolysis reactor (around
500oC), and a low heat transfer coeffi cient. Experiments
in which electricity is used as a heat source (quite usual
in R&D work) can be misleading in designing a large
scale process.
• Restrictions in feedstock morphology (particle shape,
structure and density), the particle size and its free-fl ow-
ing characteristics, because the material needs to be
pressed against a hot surface.
Finally, although strictly speaking not an ablative type
of reactor, TNO operated a 30 kg/hr pilot plant at the
University of Twente in the Netherlands. Th eir PyRos-
reactor integrates pyrolysis and high- temperature gas
cleaning in one unit, and consists of a cyclone with a rotat-
ing particle separator. Th e biomass is fed to the cyclone
by an inert transport gas, with a solid acting as a heat car-
rier.40 So far no yield data have been presented in the open
literature.
Fluid bed
A simple method for the rapid heating of biomass parti-
cles is to mix them with the moving sand particles of a
high- temperature fl uid bed. High heat transfer rates can be
achieved, as the bed usually contains small sand particles,
generally about 250 μm. Th e heat required is generated by
combustion of the pyrolysis gases, and/or char, and is even-
tually transferred to the fl uid bed by heating coils. While the
sand-to-biomass heat transfer is excellent (over 500 W/m2K),
the heat transfer from the heating coils to the fl uid bed will
be low, due to the resistance inside the coils (gas-to-coil wall
heat transfer estimated 100–200 W/m2K), and the limiting
driving force of around 300°C as a maximum (800 down
to 600°C in coils versus 500–550°C in the fl uid bed). In an
optimistic case, at least 10 to 20 m2 surface area is required
per ton/hr of biomass fed.
Th e University of Waterloo in Canada reported early work
in the beginning of the 1980s on fl uid bed pyrolysis. In 1990,
a 200 kg/hr demonstration plant was built by Union Fenosa, a
utility company in Spain for the generation, transmission, and
distribution of electricity. (Th is plant has since been disman-
tled).41 Another 200 kg/hr fl uid bed system was developed and
constructed by Enco Enterprises Inc., on a standard trailer in
the late 1980s and early 1990s, with the intention of convert-
ing peat moss into liquid fuel. Aft er extensive testing, how-
ever, it became clear that scale-up opportunities were limited.
Th e project was abandoned and a heated auger system (screw
conveyor) was adopted (more details later in this review).42
Th e Canadian company, Dynamotive Corporation, how-
ever, further commercialized the fl uid bed technology of the
University of Waterloo. Design and development of the fi rst
commercial plant at West Lorne started in 2002. A process
scheme has been presented elsewhere.43,44 Th e plant started
operations in early February 2005 with a design capacity of
100 tons per day of waste sawdust. At the beginning of 2008,
the plant was not in full production and did not reach the
designed bio-oil production capacity, presumably due to
design and construction problems. Th e company did not wait
for the West Lorne plant and started to build a second plant
in Guelph in 2006 with a design capacity of 200 tons per day.
Operational performances for both plants cannot be found
in the open literature. Th e oil of the West Lorne facility was
meant originally for combustion in Orenda’s GT 2500 gas
turbine to produce electricity. Figure 7 shows a photograph
of the West-Lorne plant. Th e Orenda turbine is an industrial
Mashproekt-designed engine, with nine axial, and one radial
stage compressor. Due to variations in the oil quality (per-
haps off -spec) and a limited supply of the oil, the turbine has
hardly been used.
Scale-up of fl uid bed pyrolysis seems thus limited in case
the heat is indirectly transferred through submersed coils
190 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
or alike, as in the case of Dynamotive, but the application
of a twin fl uid bed with solids exchange (and separation of
biomass pyrolysis and char-gas combustion) could solve
this problem (see Table 3 for mass and energy balances
of a twin fl uid bed process). An example of such a sys-
tem is a fl uid bed designed and constructed by Wellman
Process Engineering in an EU project coordinated by Aston
University in Birmingham, UK. Here the fl uid bed was sur-
rounded by the char combustor, with heat transfer through
the separating wall and by exchange of solids. Th e con-
struction of the pilot plant was indeed completed in early
1999, but due to permit problems it could never be started.
Th e installation has not been used since then. Biomass
Engineering Ltd is now erecting a similar (250 kg/hr)
installation. Improvements include the collection system
for the pyrolysis liquids, hot gas fi ltration, the handling and
combustion of the char (to provide process energy inter-
nally), and so on.
Vapo Oil and Fortum Oil together undertook another
initiative from 2001 onwards and developed a new-patented
principle for fl uid bed pyrolysis.45 Pictures of the plant are
presented in Fig. 8. Th e project was abandoned, presumably
for economic reasons.
Although fl uid bed operation seems a pretty well under-
stood technology for pyrolysis,1 experimental experiences
in fl uid bed pyrolysis still indicate a number of serious
technical problems to overcome. Referring to Fig. 6, the fol-
lowing remarks can be made:
• Cyclones are applied to separate the vapors and solids,
and thus avoid large quantities of char and bed mate-
rial ending up in the bio-oil. Char fi nes in the oil cause
increased instability, problems in pumping and, more
importantly, diffi culties in the end-use applications (tur-
bines, engines, boilers). Perhaps because of the diffi culties
in char separation, as the char is pyrophobic and easily
catches fi re, Dynamotive now deliberately leaves the char
in the oil, naming it Intermediate Bio-oil (BioOil Plus).46
Figure 7. The Dynamotive’s West Lorne plant: wood
feed hopper on left, char product hopper on right.
Figure 8. ForesteraTM pilot: reactor and product
storage area.
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 191
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
Table 3. Mass and energy balances for 2000 kg/hr (daf) fluid bed pyrolysis.
Input Reactor feed
Air Inert carrier gas
Pyrolysis vapours
Heat carrier
Bio-oil Surplus char
Flue gas
Stream no. 1 2 3 4 5 6 7 8 9
Organics 2,000 2,000 1200
Water 900 200 400 740
O2 600 250
N2 2,400 2,400
CO2 470
Pyrolysis gas 1,000 200
Char 155 245
Ash 20 20 12 8
Sand 66,600
Total 2,920 2,220 3,000 1,000 1,200 257 3,860
Temp. (K) 291 291 291 326 304 804 317 804 400
Pressure (bar) 1 1 1 1.2 1 1 1 1 1
Chem. heat (MW) 10.4 10.4 2.1 0.42 1.3 6.6 2.1
Heat (MW) 7.41 0.05 0.33
Water
70x70x70 mm30% moisture
<10 mm<10 %moisture
1
2
3
4
5
6
7
8
9
• Inert gas used for fl uidization of the reactor bed logically
is the non-condensable part of the pyrolysis gas. Th is gas
needs to be reheated and compressed, which requires
careful cleaning to avoid blockage of heat exchangers,
blowers, etc. For comparison, gas cleaning appears to be
one of the main hurdles in ‘conventional’ gasifi cation. A
similar problem can be noted for CFB operation.
Circulating fl uid bed (CFB)
The first CFB process was developed at the University
of Western Ontario in the late 1970s and early 1980s.
Biomass could be converted to bio-oil at yields of over
70 wt.%. The principle is shown in Fig. 6: Biomass is
screwed into a (riser or fast f luidization) reactor, where
extensive contacting between inert particles (sand) and
biomass takes place. Together with the char, sand is
entrained out of the reactor, and sent to a combustor
chamber where the char is combusted. The main
advantage of the CFB system compared to f luid bed
and ablative is the direct heat supply to the biomass by
recirculation of sand, reheated by combustion of
pyrolysis char.
192 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
In the beginning of the 1990s, Ensyn Technologies Inc., in
Ottawa, Canada developed industrial applications for their
so-called Rapid Th ermal Processing (RTP), in which woody
biomass is converted to pyrolysis liquids as a source of valu-
able chemicals and fuel.47–49 Commercialization was enabled
through the granting of an exclusive license to Red Arrow
Food Products Company Ltd of Wisconsin for certain prod-
uct applications in the food industry, mainly wood fl avors.
Ensyn and Red Arrow have been producing large quanti-
ties of bio-oil for the production of specialty products since
1990. A fairly large circulating fl uid bed pilot plant of 625
kg/hr throughput capacity has been built in Bastardo, Italy.
Th e plant is stated ‘running on demand’, which is in practice
never or hardly ever.50 A 100 kg/hr, a 40 kg/hr and a 10 kg/
hr R&D unit were available at Ensyn’s site in Ottawa, while a
20 kg/hr PDU-unit is built for research purposes at VTT in
Finland. By 2007, eight RTP™ plants are in commercial oper-
ation, ranging from 1 to 100 t/day. Details of the operation
(or operational performance) are unknown. Recently, Ensyn
went into a Joint Venture (JV) with UOP, under the name
Envergent Technologies LCC to commercialize the pyrolysis
technology for fuel substitution and electricity generation.51
Another JV was announced by Finnish companies Metso
and UPM to develop bio-oil production combined with
(preferably existing) CFB biomass combustion units. Th e
technology is based on the integration of conventional bio-
mass-based fl uidized bed boilers with a (non-disclosed)
pyrolysis reactor (in cooperation with VTT). Th e pyrolysis
unit utilizes the circulating hot sand from the boiler as a
heat source. Test production will begin at Metso’s test unit in
Tampere (Finland) in June 2009.52
Just as for fl uid bed technology, CFB technology is said to be
well understood,42 but actual operation in pyrolysis appears
problematic with substantial erosion problems, and complica-
tions due to operational parameters, such as the use of seals
between various vessels (‘dip legs’). Th is is a problem solved
in the chemical industry (see FCC Fluid Catalytic Cracking
processes). Nevertheless, and similar to fl uid bed technology,
the large amounts of gas needed for fl uidization of the reactor
should be the non-condensable part of the pyrolysis gas. Th is
gas must be reheated and compressed, which requires careful
cleaning to avoid blockage of heat exchangers, blowers, etc.
As already mentioned, gas cleaning appears to be one of the
main hurdles in ‘conventional’ gasifi cation. Finally, for real-
izing the rather low solids hold-up in riser systems at solid
fl uxes of 100 to 200 kg/m2s, the gas fl ow rate in the riser is
high, in the order of 1000 m3/hr (ton/hr biomass).
Vacuum moving bed
Th e biomass vacuum pyrolysis process was developed by Roy
at Pyrovac Institute Inc., between 1988 and 2002, aft er hav-
ing carried out R&D work at the Université de Sherbrooke
(1981–1985) and Université Laval (1985–1988), both in
Canada. Th e process includes a combination of slow and
fast pyrolysis conditions. Course solids are heated relatively
slowly to temperatures higher than those of slow pyrolysis,
while the gas is removed from the hot temperature zone rela-
tively quickly by applying a reduced pressure of less than 20
kPa in the process. An attempt to commercialize the proc-
ess was carried out by Pyrovac International by the end of
the 1990s. In this concept, biomass material was conveyed
over a long horizontal grate, which was heated indirectly by
a mixture of molten salts composed of potassium nitrate,
sodium nitrite, and sodium nitrate.53 Th e salt itself was
heated by a gas burner fed with the non-condensable gases
produced by the pyrolysis process. Limitations in external
heat transfer were avoided as much as possible by applying
a patented internal agitation raking mechanism, but obvi-
ously internal heat transfer limitations could not be avoided.
A 3.0 t/hr demonstration plant for bark residues was erected
in the City of Saguenay Quebec, Canada, and taken into
operation between 1999 and 2002 (Fig. 9). Crumb rubber
was also successfully tested in 2002. Th e system proved to be
functional except for a limitation encountered at one of the
two condensing packed towers, which somehow impaired
the organic vapor condensing performance. Th at condens-
ing tower was on its way to be modifi ed when the joint
partner of Pyrovac Group, UNA B.V. (now NUON B.V.) was
acquired by Reliant Energy Inc., in Houston. Because the
pyrolysis project did not fi t into the core business, Reliant
Energy withdrew from the JV and Pyrovac was subsequently
brought to an end in June 2002. Th e process equipment
and the building were purchased by a third party from the
bankruptcy in 2003 and the assets were kept in good shape
till today. A group of investors led by US-based NewEarth
Renewable Energy is now planning to restart the plant in
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 193
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
2010 for industrial production of torrefi ed wood, wood char-
coal, and bio-oils. 54–55
Auger systems
Aft er concluding that design limitations precluded the scale
up of their fl uid bed, ABRI-Tech the former Encon Enterprise
Inc., and Advanced BioRefi nery Inc. started working with
heated augers systems using a hot, high-density heat carrier
(e.g., metal beads, see Fig. 6).56 ABRI-Tech is a JV between
Advanced BioRefi nery Inc., and Forespect Inc., the latter
being a forest products company located in Namure, Quebec,
Canada. Th e system has evolved to the point where the com-
pany builds, for sale, a 1 t/d unit and a 50 t/d unit. Th e fi rst
commercial 50 t/d system is presently (October 2009) being
commissioned in Iowa and will produce bio-oil and bio-char
from agricultural residues (Fig. 10).57
Forschungszentrum Karlsruhe (FZK) developed a fast
pyrolysis reactor to convert straw to pyrolysis oil and char
to serve as a high-energy slurry feedstock for entrained
fl ow gasifi cation (the ‘Bioliq Process’).58 Th e reactor design
is adopted from the Lurgi-Ruhrgas twin-screw mixer reac-
tor that was developed decades ago for oil shale, tar sand,
and refi nery vacuum residues (LR coking). Chopped bio-
mass is mixed with hot sand in the double-screw reactor
and decomposed to vapors and char. Th e hot sand loop
is maintained pneumatically or mechanically. Just like in
BTG’s rotating cone technology, heat transfer to the bio-
mass particles takes place by intimate contact with a heat
carrier, with no need for an inert carrier gas. At the time of
Figure 9. The Pyrovac installation in Jonquière, Canada
(© Christian Roy).48
Figure 10. ABRI-Tech’s Auger pyrolysis system of 50 t/d plant. The left side of the
picture is the dryer/pulverizer. The reactor and condenser are the two modules on
the right side of the photo. (© Peter Fransham).
194 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
writing (October 2009), the construction of a 500 kg biomass
per hour pilot plant was completed but no test runs were
reported yet. Th e pilot plant uses sand as a heating medium,
whereas the R&D work was carried out while testing diff er-
ent heat carriers including metal beads.
BTG’s technology: Rotating cone reactor
Fast pyrolysis has been a continuous research item in
the Netherlands at Twente University for a few decades.
Researchers started with the principle that intense mixing
of biomass and hot inert particles is the most eff ective way
to transfer heat to the biomass, but that fl uid bed mixing
requires too much ineff ective inert carrier gas. A high-
intensity reactor for the pyrolysis of biomass was developed
where no inert gases were required, while simplifying the
reactor parts and peripheral equipment as oil condenser, gas
cleaning, etc. Th e original idea in 1989 to rely on a merely
ablative principle without inert sand was later modifi ed to
a sand-transported-bed rotating cone reactor (RCR).16 Th e
concept is depicted in Fig. 6. Instead of mixing the biomass
in a hot sand fl uidized bed driven by inert gas, the pyrolysis
reactions take place upon mechanical mixing of biomass and
sand. Similar to the CFB operation, the sand and char are
further transported to a separate fl uid bed where the com-
bustion of char takes place. Th e RCR enables a high solids
throughput and short vapor residence times.
R&D work was continued by BTG Biomass Technology
Group.59,60 Figure 11 shows the fi rst prototype built by BTG
and Royal Schelde in Vlissingen as part of a test unit for
Shenyang Agricultural University. It was shipped to China
in 1994. Biomass particles are fed near the bottom of the
rotating cone together with an excess fl ow of heat-carrier
material like sand, and then transported upwards along the
cone wall in a spiral trajectory by the centrifugal forces (up
to 600 rpm). An electrical oven in which the sand and char
are trapped surrounds the RCR. Th e produced vapors pass
through a cyclone before entering the condenser, in which
the vapors are quenched by re-circulated oil.
Subsequently, the University of Twente constructed a novel
reactor system (throughput capacity of up to 20 kg/hr).61 In
contrast with Wagenaar’s original reactor, where sand is fed
at the top, this rotating cone had a number of holes near the
bottom, through which the sand was sucked into the cone. To
compensate for heat losses and provide both the energy for
heating the biomass particles and consequently the overall
endothermic pyrolysis reactions, the char produced during
pyrolysis was burnt in a fl uid bed around the rotating cone
(‘combustion chamber’). Experiments with sand and cata-
lysts demonstrated that autothermal operation can indeed be
achieved with this system, but unfortunately, the operational
fl exibility of this advanced concept appeared to be poor,
and therefore the concept was not considered for further
scale-up.
BTG scaled up Wagenaar’s RCR technology, fi rst to about
50 kg/hr in 1997. Th e cone reactor was integrated in a circu-
lating sand system composed of a riser, a fl uid bed char com-
bustor, the RCR reactor, and a down comer. Char is burnt in
the combustor to generate the heat required for the pyrolysis
process, viz. by (re-)heating the inert sand that is re-circu-
lated to the reactor. Oil is the only product of this lab facility,
and gases were fl ared. In 2001, the system was further scaled
up to 250 kg/hr. Th rough the past ten years, about 100 tons
of bio-oil has been produced from over 50 diff erent materi-
als. Oil is partially sent out to universities, institutes, and
industrial companies for application research. In addition
Figure 11. Photo of the rotating cone reactor.
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 195
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
to this pilot plan installation, a smaller (5 kg/hr) test unit
has been erected in BTG’s laboratories, for quick screening
of potential feedstock materials in a continuously operated
system. Initially, researchers reported that the RCR principle
would be limited to particles < 1 mm in diameter. Over the
years, however, the method of mixing in the cone and the
pyrolysis system were improved considerably. Th e overall
effi ciency of the process has increased, the acceptable particle
diameter demonstrated to be up to 10 mm, and product qual-
ity and consistency for diff erent feedstocks have improved
considerably. In 2001, a fi rst detailed design for a 1 t/hr dia-
per sludge pyrolysis unit was prepared under a license for the
company Bio-Oil Nederland (BON). BON is now a wholly
owned subsidiary of Bio-Oil Holding N.V. (BOH), with no
relation to BTG anymore. Th e company ambitiously plans to
start up the fi rst of four, 5 t/hr installations in 2010, inten-
tionally on SRF, in Delfzijl (the Netherlands). No informa-
tion is publicly available on the technology at the moment,
but it is likely deviating from the original BTG design.
In 2004, BTG sold the world’s fi rst commercial unit of 50
t/d on so-called Empty Fruit Bunch (‘EFB’) in Malaysia.
EFB is a left over from palm oil mills. In the Malaysian
plant, EFB is taken directly from a nearby palm mill,
pressed, shredded, dried, and converted to bio-oil. From
reception to oil delivery takes about 1 h, time that is con-
sumed almost entirely by the pre-treating process. Genting
Bio-Oil Sdn Bhd (GBO) commissioned its bio-oil pilot plant
in Ayer Itam, Johor (Malaysia) in 2006. While undergoing
some engineering upgrades, full commercial operations
have been targeted for 2009.62
Th e overall (simplifi ed) scheme is given in Fig. 12, which
includes the complete chain from EFB reception, storage,
pre-treatment (pressing, shredding, and drying), storage
(approx. 4 ton) and conversion.63 Th e heat required for the
drying of the EFB (up to 70 wt.% moisture upon reception)
is taken from the pyrolysis unit, and a steam production
system is fully integrated in the production unit. Pictures
of the EFB and the pyrolysis plant are given in Fig. 13. From
mid-2005, the plant was running on a daily basis, showing
the potentials but also the shortcomings. Th e main achieve-
ments over the last years are listed below:
■ Over a thousand tons of bio-oil have been produced from
more than 5000 tons of wet (up to 70% moisture) EFB.
■ Oil was co-fi red, replacing conventional diesel in a sys-
tem located 300 km from the site.
■ Drying of de-watered EFB from around 50 wt.% mois-
ture content down to 5 wt.% is possible using the excess
heat from the pyrolysis process.
1st
shredder
press
2e shredder
drier
storage
feeding
boiler
reactor
combustor
condensor
flare
EFBbucket elevator
oil cooling
Oil
water
ash
air
airair
air
Flue gas
wetair
Flue gas
Figure 12. Process scheme of the Malaysian plant for fast pyrolysis of empty fruit bunches
(EFB), including the complete chain from EFB reception, storage, pre-treatment and
conversion.
196 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
■ Oil quality can be controlled by tuning operation
conditions.
■ Any excess energy recovered from the process aft er dry-
ing of the (very) wet EFB, is potentially available to gen-
erate electricity for on site use.
■ Th e maximum capacity of the plant achieved is about 1.7
t/hr (design capacity was 2 t/hr).
■ No problems were observed in the actual reactor system.
Technical problems related to erosion due to high-veloc-
ity sand in riser parts, cyclones, etc., could be overcome.
Some shortcomings of the system at that time should be
mentioned as well:
■ Fluid bed combustion of the char from EFB created a
high risk of blockages, but this appeared to be due spe-
cifi cally to the nature of the EFB ash (a.o. low melting
point).
■ Considerable pre-treatment of EFB is necessary and wear
and tear in pre-treatment equipment is signifi cant (for
instance in presses and shredders).
■ By average, the bio-oil yield on basis of good quality dried
EFB is 50 to 60 wt.%; the oil yield is lower than for wood
(typically 70 wt.%), while the water content is higher.
■ Th e supply rate of wet EFB from the palm mill and the
quality varies considerably, viz. from 2–2.5 t/hr during
daylight, and 1–1.5 t/hr at night with moisture contents
up to 70%. Large amounts of EFB cannot be stored easily.
■ Effi cient heat integration, together with an improved reli-
ability of the total system, will be the challenge for the
coming years.
Considering the status of the pyrolysis process at the begin-
ning of the plant design in 2004, the progress made in
Malaysia is signifi cant. From an initial set of experiments in
Figure 13. EFB Material and the pyrolysis plant in Malaysia. ((use separate
powerpoint fi le))
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 197
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
2003 (8 hours and maximum 100 kg/hr feeding), the system
has been scaled up to a 24 hours/day running factory, where a
direct link has been established between the palm mill and the
pyrolysis plant. In addition, the process is applied here for a
diffi cult type of biomass feedstock as, next to being fl uff y and
wet, the ash of the mineral-rich feed has a very low melting
point (below 650oC). In 2007, BTG established BTG-Bioliquids
with the objective to commercialize the technology.64 On
its website, BTG-Bioliquids announces the construction by
Empyro BV of a 5 t/hr wood based pyrolysis installation on a
site in Hengelo (the Netherlands). Th e project is supported by
the 7th framework program of the European Commission.
Bio-oil fuel applications
A key advantage of producing liquids from biomass is that
its production can be de-coupled in time, scale, and place
from the fi nal application. Th e current status of primary,
secondary, and tertiary processing of pyrolysis liquids is
further presented in Table 4. Due to its high oxygen con-
tent and the presence of a signifi cant portion of water, the
heating value of bio-oil is much lower than for fossil fuel.
Nevertheless, fl ame combustion tests showed that fast
pyrolysis oils can replace heavy and light fuel oils in indus-
trial boiler applications. In its combustion characteristics,
the oil is more similar to light fuel oil, although signifi cant
diff erences in ignition, viscosity, energy content, stability,
pH, and emission levels are observed. Problems identifi ed
in fl ame combustion of bio-oil are related to these deviating
characteristics, but can be overcome in practice. Meanwhile,
bio-oil has been used commercially to co-fi re a coal utility
boiler for power generation at Manitowoc Public Utilities
in Wisconsin (USA). It has also been approved as a fuel for
utility boilers in Swedish district heating applications. Aft er
an extensive boiler test program in Sweden in 1996 and
1997, a commercial project was said to commence in 1998,
but results were never reported. A successful co-fi ring test
with 15 tons of bio-oil was conducted in 2002 in a 350 MWe
natural-gas fi red power station in the Netherlands.65 Some
data are presented in Fig. 14 and Table 5. A four-hour co-fi r-
ing session was carried out at a bio-oil throughput of 1.6 m3
per hour, or an equivalent of 8 MWth. While co-fi ring bio-oil
in the boiler, the power output setting of the plant remained
constant at about 250 MWe, and in the test, the plant control
reduced the natural gas fl ow to the boiler to compensate
for the injection of thermal heat of the bio-oil, indeed cor-
responding to 8 MWLHV (Fig. 14). Low ash deposition rates
were also reported recently for a 100 kW combustion test rig
during the combustion of bio-oil.66
Oil from the Malaysian plant was routinely used to replace
expensive diesel for start-up of a fl uid bed combustor near
Kuala Lumpur International Airport. No results have been
reported in open literature. Since 2006, BTG has been
actively involved in research on the combustion of the oil
in a standard 250 kW hot water generation unit, to replace
Table 4. The status of primary, secondary and tertiary processing of pyrolysis products.
Primary product
Secondary processing
Secondary product
Tertiary processing
Final product
Liquid TransportCombustion2
Engine/turbine1
Stabilization2
Upgrading2
Extraction1,5
Conversion3
Conversion2
FuelHeat/steamElectricity
Stabilized oilHydrocarbons
ChemicalsChemicals
Gas
CombustionSteam turbine5
Engine/turbine1
Refi ning2
Refi ning1,5
Refi ning1,2
Fuel cell1
Heat/steam/electricityElectricity
ElectricityDiesel/gasoline
ChemicalsChemicalsElectricity
Gas CombustionEngine/turbine3
Fuel cell1
Heat/steamElectricityElectricity
Steam turbine Slectricity
(Bio)char transportcombustion5
slurrying2
active carbon
FuelHeat/powerLiquid fuel
Combustion
Combustion3
Heat/steam/electricity
Heat/power
Indices: 1 = conceptual, 2 = laboratory, 3 = pilot, 4 = demonstration and 5 = commercial (Bridgwater, 1997). Indicated in bold are the most promising options on a short time scale.
198 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
diesel and/or natural gas. For this purpose, suffi cient quanti-
ties of palm-derived oil from Malaysia were transported to
the Netherlands, and a dedicated oil lance was developed.
Results derived from a Dutch cooperation between BTG,
Stork-Th ermeq, and ECN will be reported in due course.
A subsequent project is concerned with testing in a larger,
commercial boiler set-up, owned by Stork Th ermeq.
Generally, the production of electricity is more interesting
than the production of heat because of the higher added value
of electricity, and its ease of distribution and marketing.
Diesel engines are relatively insensitive to the contaminants
present in pyrolysis oils, especially in the case of large- and
medium-scale engines, and bio-oil may be used. Tests have
been performed by diesel (re)manufacturers like Ormrod
Diesels and Wärtsilä Diesel, in collaboration with research
institutes such as Aston University, VTT, MIT, and the
University of Rostock.67–69 A review of diesel engines was pre-
pared in 2001 by one of the present authors,70 while another,
very useful review on use of such liquids in engines and gas
turbines was prepared by the University of Florence and VTT
in 2007.21 In general, diesel engine development and testing suf-
fers from insuffi cient quantities of available bio-oil and a lack
HC62 HC61
4
2
3
5
1
6
Air
NG
NG
Gasturbine
Steamcycle
NOx
Flue gas
Bio-oil
90 MWe
Boiler Stack
Stack losses
33 MWth
River cooling
274 MWth
161MWe
Figure 14. Mass and energy balances of Harculo power station.
Table 5. Power settings of Harculo station and the M&E balance as indicated in Fig. 13.
Input Output Effi ciency
Natural gas [MWth]
Heat [MWth]
Power [MWe]
Heat [MWth]
Gas turbine HC62 293.5 0 89.6 203.9 @ 520°C 30.5
Steam turbine HC61 264.8 133.8 161.5 237.2 @ 30°C 40.5
Total plant HC60 558.3 0 251.0 307.2 @ 30°C 45.0
* natural gas LHV: 35.57 MJ/Nm3; 0.808 kg/Nm3
Stream I.D. 1 2 3 4 5 6
Air Natural gas Flue gas Flue gas Natural gas Flue gas
T [°C] 16 16 520 520 16 97
P [bar] 1.00 8.45 1.06 1.02 1.2 1.00
Flow [kg/s] 358 6.67 365 123 6.02 371
LHV [MWth] 0 293.45 0 0 264.80 0
Heat [MWth] 0 0 203.88 70.05 0 32.65
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 199
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
of interest from engine (parts) manufacturers. Nevertheless,
the results obtained indicate that engine deterioration can be
a serious problem. Traditional diesel engines are designed to
operate on acid free fuels, however, and all engine components
are manufactured in such a way and with such (steel) materi-
als as to comply with these fossil fuels. For fast pyrolysis oils,
severe wear and erosion was observed in the injection needles,
due to the fuel’s acidity and the presence of abrasive particles.
Nozzles lasted longer when fi ltered oil was used, but it is clear
that standard nozzle materials are inadequate.
A high bio-oil viscosity and stability loss with rising tem-
peratures are other major problems, already referred to.
Damages to nozzles and injection systems, and buildup of
carbon deposits in the combustion chamber and the exhaust
valves are reported. Engines with larger cylinder bores (i.e.,
medium- and low-speed engines) are expected to be the most
suitable because of less stringent construction tolerances.
For smaller bore engines, reduction of the oil viscosity could
be needed. Injection modifi cation and/or a high turbulence
combustion chamber are required. Because the bio-oil has
poor ignition properties (cetane index below 10), it should be
enriched by the addition of cetane improvers, and the appli-
cation of a dual fuel system is most appropriate.71 Self-clean-
ing injectors are possibly required. At the end of the 1990s,
Wärtsila stopped the development work, mainly due to lack
of quality and quantity of pyrolysis oils at that time. In spite
of all these problems, it has also been reported that modifi -
cations to both the bio-oil and the engine can make pyrolysis
oils quite acceptable for diesels. One option to reduce the
need for adaptations is the use of emulsions of bio-oil in
diesel.72 Th is would not only off er prospects for stand-alone
electricity production units, but potentially for the applica-
tion of fast pyrolysis oils in the transportation sector (ships,
trucks, tractors, or busses) in the future. A substantial RTD
eff ort with involvement of manufacturers is required to
realize this application. German researchers reported a suc-
cessful 12-hour run on bio-oil in a modifi ed Mercedes diesel
engine, but exact details are not provided.73 Recently, a joint
project started between European and Russian partners to
further develop a pyrolysis oil diesel engine/turbine.74
Experience with bio-oil combustion in gas turbines is also
limited. R&D projects known were carried out by Orenda
Division of Magellan Aerospace Corporation (Canada),
ENEL Th ermal Research Center (Italy), and Rostock
University (Germany). Orenda is actively searching for
opportunities to run their Orenda GT2500 on pyrolysis oils.
Th e GT2500 uses diesel oil and /or kerosene, and unlike
aero-derived turbines, an external silo-type combustor is
adopted. Th is chamber provides a ready access to the main
components. Several modifi cations are reported necessary:75
• A complete low-pressure bio-oil supply system, including
preheating and fi ltering of the bio-oil.
• An improved bio-oil nozzle design to allow larger fuel
fl ows and dual fuel operation.
• Redesign of the hot section, including section vanes and
blades.
• Stainless steel part and modifi cation of polymeric
components.
Despite their involvement in Dynamotive’s plant in West
Lorne, the non-availability of suffi cient quality bio-oil still
remains the main reason why limited test runs are carried
out by Orenda. A 75 kWe nominal gas turbine was tested
in dual fuel mode by Rostock University in 2001, showing
deposits in the combustion chamber and turbine blades, and
higher emissions of CO and hydrocarbons.
Bio-oil may have another suitable end-application, viz.
its use as a fuel for gasifi cation. It should be noted here that
in refi neries, gasifi cation (next to combustion) is merely an
end-of-pipe technique, using (cheap) feedstocks that cannot
be used elsewhere in the process. Regarding co-gasifi cation
of biomass residues, to produce syngas for further process-
ing (e.g., methanol, Fischer-Tropsch), pyrolysis could play
an important role as a pre-treatment technique, facilitating
the cheaper transport and handling of biomass feedstocks
from origin to the site of gasifi cation, over distances that
biomass can never be shipped economically. Use of the
oil in entrained fl ow gasifi cation is the main application
Forschungszentrum Karlsruhe (FZK) is aiming at.76 Residue
gasifi ers can indeed be fed on bio-oil,77 and issues of concern
are mainly the pH (feed train) and alkaline ash content.
R&D on (small-scale) entrained fl ow gasifi cation of pyrolysis
oils have only been reported by BTG.78 Pilot experiments
were performed by BTG in UET’s (now Choren’s) entrained
fl ow gasifi er in Freiberg (Germany) at about 500 kWth with
pure oxygen (results are not yet published).
200 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
Pyrolysis oils could be used (pure or modifi ed) as a feed-
stock for the production of transport fuel, which, with
the growing demand for biofuels, is of strong interest
worldwide. Th e simplest use of bio-oil may be in the diesel
engine, but, as stated before, the oil as such is not suitable
for (even) a stationary diesel engine. Upgrading of the oil to
products more appropriate for further use is being consid-
ered by many organizations and institutes. Bio-oils can be
‘upgraded’ atmospherically using conventional FCC catalyst
in the pyrolysis process itself or, at elevated pressures, by
hydrotreating. FCC-like upgrading dates back to the 1990s,
assuming that, similar to ZSM-5 processing, oxygen will be
rejected from the oil’s structure as CO2.27,79-81 Th ey showed
a limited yield of hydrocarbon products of about 20 wt.% (or
40% energetically), mainly due to charring – coking of the
feed.
Hydrotreating of bio-oils was reviewed in 2007.82 Th e early
work originates from the late 1980s, using the slow pyrolysis
oils derived from carbonization or hydrothermal liquefac-
tion processes.83 It was shown that for deoxygenation, tem-
peratures in the order of 300 to 400oC, and residence times
> 1 hour are required. Until 2000, the real goal remained
unclear. Th e overall objective was to produce transportation
fuels (diesel and gasoline like components), and the target
seemed to be the reduction of the oxygen content in the oil.
Since the use, for instance, of MTBE, butanol and ethanol in
transportation fuels, the common believe of petrorefi neries
shift ed from absolutely no oxygen in the pool of transporta-
tion fuels, toward allowing adding small amounts of oxygen
in the appropriate functionality (viz. alcohol or/and ethers).
Since 2000, the intention of upgrading bio-oil shift ed from
using it directly as a transportation fuel (or blending compo-
nent) aft er upgrading, toward co-refi ning upgraded bio-oil
together with crude oil (derivatives). Hydrotreated bio-oils
can be well co-refi ned, with rather high effi ciencies, in FCC
processes.84 Th e University of Groningen carried out pio-
neering work on the hydrotreatment of such oils revealing
a clear resemblance with hydroprocessing of sugars.85 Aft er
an almost 10-year period of reduced activities in this hydro-
processing area, the concept has recently attracted consider-
able interest again in the USA.86
Co-refi ning in standard refi neries is the main subject
matter of a large European project BioCoup, showing that
‘upgraded’ pyrolysis oils are suitable for such co-refi ning
(Fig. 15). First papers were presented recently.87,88 Complex
chemical process engineering factors such as water evapo-
ration, dry-out phenomena, mass transfer, reaction kinet-
ics, and occurrence of parallel and consecutive reactions,
are considered and quite some progress has been made.
Successful co-refi ning of upgraded oils has been demon-
strated at lab scale,89 and papers will be published in due
course.
Primary fractionation
and liquefaction
Biomassresidues
Co-processingin conventional
petroleum refineryDe-oxygenation
Hydrocarbon-rich bio-liquid
Lignin-rich bio-liquid
ConversionDerivatives of hemicelluloses and celluloses
Conventional fuels and chemicals
Oxygenated products
OVERALL BIOREFINERY CONCEPT
incorporating fractionation with liquefaction
Energyproduction
Process residues
(blending)
Figure 15. Biocoup’s concept of co-refi ning bio-oil in existing refi neries.
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 201
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
Other approaches to arrive at transport fuels include
alcohol treatment (analogous to vegetable oil esterifi ca-
tion), reducing the oil’s acidity and, aft er phase separation,
water content. Th ese studies, initiated by the University of
Groningen are still exploratory in nature.90
Another interesting application may be fermentation.
Anhydrosugars that are produced by pyrolysis of biomass
can be converted by hydrolysis to fermentable solutions as
well.91,92 Feasibility studies show that this route to produce
ethanol from lignocellulose may be an attractive alternative
to acid and enzymatic hydrolysis. A further acid hydrolysis
step of the levoglucosan to free sugars is necessary, and this
should take place at elevated temperatures of around 100oC.
Fermentation of pyrolyzates and their hydrolyzates is under
investigation, and there is much uncertainty about the best
process conditions and the ‘detoxifi cation’ steps required.
Attempts to sustain yeast growth in grass-derived bio-oil
hydrolyzates were unsuccessful, but success was achieved
in fermenting a hydrolyzate from a wood-derived bio-oil
and this supports the concept of pyrolysis with ethanol as
a major product. More research is required to improve the
fermentability of wood-derived bio-oil hydrolyzate and to
establish whether its fermentability is due to the chemistry
of wood vs grass pyrolysis feedstock, the pyrolysis process
conditions existent in the commercial- vs lab-scale reactor
system, or a combination of these two variables.93
Chemicals in bio-oil
Hundreds of compounds have been recognized in (GC) anal-
ysis as fragments of the basic compounds of biomass, viz. the
lignin (amongst others: phenols, eugenols, and guaiacols), and
the cellulose or hemicellulose (sugars, acetaldehyde, and for-
mic acids). Although GC analysis may not be the most appro-
priate analysis tool for bio-oil (as discussed earlier), large
fractions of acetic acid, acetol, and hydroxyacetaldehyde are
identifi ed (Table 2). Until now, approximately 40 to 50% of the
oil’s identity (excluding the water) has been revealed, but the
large, less severely cracked or de-/re-polymerized molecules
(derived from the cellulose and the lignin) in the oils can still
not be identifi ed. Figure 5 shows that all types of (oxygen)
functionalities are present: acids, sugars, alcohols, ketones,
aldehydes, phenols and their derivatives, furans and other
mixed oxygenates. Also (poly)phenols are present, sometimes
in rather high concentrations. Th ese phenolic fractions then
include phenol, eugenol, guaiacols and their derivatives, and
the so-called pyrolytic lignin (poly-phenols) representing the
water insoluble components. It is likely that this ‘pyrolytic
lignin’ which contain the fragments of the original lignin,
also contains polymerized carbohydrate (fractions).
Components in the oil interesting to consider for future
chemicals production are the carbohydrate fragments. Th ese
are sugar derivatives such as all types of anhydrosugars and
oligosaccharides, formaldehyde, furfural alcohols, hydroxy-
acetaldehyde and so on. Due to the principle of GC analysis,
in which only the ‘distillable’ components in the oil can be
identifi ed and quantifi ed, levoglucosan is usually referred
to as an important type of sugar to be isolated (Fig. 5).
However, much more sugars, approx. 30 wt.% of the oil,
must be present.
Aspects to be considered here are that the original feed-
stock, the process conditions, and condensing parameters
are of major importance for the type of chemicals in the oil.
To complicate this further, pre-treatment of wood may result
in an increase of one particular component at the expense
of the other. As mentioned earlier, ash is known to infl uence
the reactions in the pyrolysis process, and may contribute to
higher yields of certain products.
Last but not least, the analysis of bio-oil can also be compli-
cated. As an example of the observed variation in composi-
tion of wood-derived pyrolysis oil, a study published in 1997
indicated that not a single compound of over 100 has been
identifi ed by all 10 laboratories where pyrolysis oils could be
analyzed at that time.94 It should also be repeated that GC
analysis does not reveal the identity or quantity of compo-
nents that do not evaporate in the injection system. Part of the
‘discrepancy’ in the analysis results of the various laboratories
is also caused by the continuous improvements in method-
ology during the last few years, (increased use of GC-MS,
HPLC, etc.) and the factual identifi cation of the various com-
ponents. Th e applications for bio-oil are now further detailed,
starting from application of the unfractionated oil, and appli-
cations in which fractions or isolated compounds are relevant.
Unfractionated bio-oil
Resins for MDF or OSB: Work to examine the potential
use of the pyrolysis oil as a raw material in wood panel
202 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
manufacture is ongoing. Th e use of bio-oil has been inves-
tigated over the years for the replacement of formaldehyde
– phenols in resins for particleboards. Due to the high
cross-linking capability of the lignin-derived compounds
in the bio-oil, a polymer with an improved strength can be
obtained when mixed with conventional urea-formaldehyde
resins. Research in this area published at the end of 2000,
concludes that bio-oils can be used in the manufacture of
resins in phenol substitution rates up to 50%.95 A review of
the production of renewable phenol resins based on pyrolysis
products published recently, concludes that none of the phe-
nol production and fractionation techniques available allows
a complete substitution of the resin.81 Partial substitution
seems more likely though.
Fertilizers and soil conditioners: Reaction of bio-oil
with ammonia, urea, or other amino compounds produces
stable amides, amines, etc. Th ey are non-toxic to plants and
can be used as slow release organic fertilizers. Additional
benefi ts are that the lignin degradation products and their
reaction products are good for soil conditioning, control of
soil acidity, amelioration of the eff ects of excess Al and Fe,
increasing availability of phosphate, and crop stimulation.
Furthermore, they are excellent agents for nutrient metals
such as Mo, Fe, B, Zn, Mn, and Cu. Other functional groups
in the bio-oil-derived fertilizers are nutrients such as Ca,
K and P.96,97 DynaMotive co-operated with two fertilizer
manufacturers on the commercialization of bio-oil-derived
products, but so far no specifi c commercial product outlets
have been demonstrated.
Pure bio-oil can be mixed with lime to form BioLime™,
a trademark of Dynamotive Technologies Corporation in
Canada. Injection of this mixture into fl ue-gas tunnels
should result in complete removal of sulfur oxides, but also
in a signifi cant reduction of nitrogen oxides. Th e research
on this has stopped, and no references have been found in
literature hereaft er.
Fractions derived from bio-oil
In wood-derived pyrolysis oil, specifi c oxygenated com-
pounds are present in quite substantial amounts. Th e
recovery of such pure compounds from the complex bio-oil
may be technically feasible but probably economically unat-
tractive because of the high costs for the recovery of the
chemical and its low concentration in the oil. Th e relevant
chemical components are now presented.
Wood fl avors: Th e only commercial application of wood-
derived bio-oil known to date is that of wood fl avor or liquid
smoke. A number of companies produce these liquids by
adding water to the bio-oil. A red-colored product is then
obtained, that can be sprayed over meat before further cook-
ing. Th e taste, color, and smell of the meat are thus created
‘artifi cially’. A range of food-fl avoring products, based on
pyrolysis oils, has been patented and commercialized by
Red Arrow Products Company (USA)98 and the former
Chemviron, ProFagus (Germany).
Phenolic compounds: A signifi cant part of the oil is
the phenolic fraction, consisting of small amounts of phe-
nol, eugenol, cresols, and xylenols, and larger quantities
of alkylated (poly-) phenols (the so-called water insoluble
pyrolytic lignin). Recoveries of phenolic compounds up to
50 wt.% have been reported, but only for specifi c feedstocks.
Th e amount of the smaller, more expensive, phenolic compo-
nents in bio-oil is usually limited, probably because the orig-
inal lignin in the biomass is only partly cracked. Moreover,
it is likely contaminated by re-polymerized lignin and sugar
fragments (from the hemicellulose) as well. Phenolics have
also been proposed for use as an alternative wood preserva-
tive to replace creosotes.99
Sugars: Levoglucosan, together with levoglucosenone and
HAA, are the few sugars derivatives and detectable in GC
equipment. It seems that this in itself is the main reason that
the fi rst two components especially received a lot of atten-
tion: other sugars which are present cannot be traced back
in the oil using GC. An extensive overview on levoglucosan
is given elsewhere.7 Th e existing market for levoglucosan is
very small (and the product high-priced), but it may well be
an intermediate product suitable for further fermentation,
as indicated earlier. Most pyrolysis technologies could be
adapted for levoglucosan production by pre-hydrolysis of the
feedstock and/or demineralization.100 Levoglucosenone is
said to be applicable in the synthesis of antibiotics/pherom-
ones, rare sugars, butenolide, immuno-suppresive agents,
whisky lactones, and so on, and can be present in amounts
up to 24 wt.%. Progress in the last few years to valorize
bio-oil on the basis of these two interesting products is
limited, though. On the contrary, hydroxy-acetaldehyde is
© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb 203
Review: Fast pyrolysis technology development RH Venderbosch, W Prins
a commercial product. It can be present in relatively large
amounts in the bio-oil (up to almost 20 wt.%), and is used in
browning food (cheese, meat, sausages, and poultry or fi sh).
A possible application is the use as a precursor for glyoxal
OHC-CHO, which is an important chemical produced by
oxidation of ethylene glycol.101
Acids: Components that can also be derived from bio-oil
are mainly the carboxylic acids, from which salts such as cal-
cium acetate and calcium formate can be produced.102,103 In
the aqueous fraction of the bio-oil, these acids are present in
amounts up to 10 wt.%. Th ey have potential applications such
as road or runway de-icing, sulfur dioxide removal during fos-
sil fuel combustion, or as a catalyst during coal combustion.
Furfural-derivatives: Furfural and furfurylalcohol can be
produced from carbohydrates (glucose, maltose, cellobiose,
amylose and cellulose) in amounts up to 30 wt.%.104
Economics
A key factor in the development to commercial implemen-
tation is the economic viability of fast pyrolysis processes.
Currently the main interest in Europe is electricity generation
from biomass. CO2 mitigation, socio-economic benefi ts from
re-deployment of surplus agricultural land, and energy inde-
pendence are driving forces. Th ese have led to signifi cant fi scal
incentives. Apart from such incentives, infl ation, (in)direct
eff ects of oil prices, local costs and labor strongly aff ect the
economics of pyrolysis plants. Th erefore, it does not make
sense to discuss economics in much detail. General data, col-
lected by BTG and confi rmed in other studies, show that the
range of capital costs for the pyrolysis plant alone is in between
€200 and €500/kWth input biomass, depending on the technol-
ogy, scale, degree of heat integration, location, etc. Th e main
parts of the BTG pyrolysis plant are the reactor, riser, combus-
tor, and condenser. Th e costs of pre-treatment, feeding, build-
ings, and infrastructure are not included, but may add up to
another 50 to 100%, depending on the initial feedstock prop-
erties (size, water content, dimensions, free-fl owing behavior,
bulk density, and so on). Costs related to the heat integration
system (heat recovery, steam generation, drying, etc.) are usu-
ally not addressed in the studies of economics.
One of the main challenges of BTG’s process concept is
the effi cient generation and further use of the excess heat
generated in the system. Th e Malaysian plant showed that (1)
the heat required for drying the wet feedstock is delivered
by the process itself; and (2) electricity can be generated
from the excess heat available, even aft er use for drying.
An important aspect to consider in plant economics is the
observation that the cost for the actual pyrolysis reactor is
just a fraction of the overall plant costs. At the same time,
a proper reactor choice in particular off ers the possibility
to reduce costs upfront (i.e., in feeding and pre-treatment)
or in peripheral equipment. Th e rotating cone reactor in
the Malaysian plant, for instance, costs about 2 to 3% of
the complete plant, but reduces the overall costs of the total
plant signifi cantly because the absence of inert gases limits
the costs of secondary equipment.
Studies over the years indicated that pyrolysis oils can be
produced at costs in a range of €4 to €14/GJ (corresponding
€65 to €225/t), with feedstock costing between €0 and €100/t
(€0 to €6/GJ).105,106 Such fi gures match quite well with the
data of the Malaysian plant. But again, it should be noted
that they strongly depend on process technology, the scale of
operation, feedstock, year of construction, and so on.
Generally speaking, it can be stated that the costs of
pyrolysis processes should be rather low, because the oper-
ating conditions are less extreme than for combustion or
gasifi cation (lower temperatures and atmospheric pressure).
Biomass pre-treatment, heat integration and the required
operation reliability, however, can be factors seriously
increasing the overall investment costs.
Concluding remarks
Pyrolysis defi nitely remains an interesting pre-treatment
technique enabling (intercontinental) transport of large vol-
umes of biomass. Th e proof of principle (reactor concept),
and proof of concept (plant set-up) have been demonstrated,
amongst other by BTG (Malaysia), DynaMotive (Canada)
and Ensyn (USA and Canada). Fast pyrolysis is still an
immature technology, of which many aspects are unknown.
Although a number of installations were erected, they all
suff er from a lack of operational hours and no process has
really been ‘demonstrated’. Interested industries like heat
and electricity producers, oil companies and food/feed com-
panies, are waiting for full-scale demonstration including
continuous operation (>7000 hours per year) preferably of
multiple plants on a scale of 5 to 10 tons biomass feedstock
204 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 4:178–208 (2010); DOI: 10.1002/bbb
RH Venderbosch, W Prins Review: Fast pyrolysis technology development
per hour. Here, the problem is that the opportunities for
commercial bio-oil production are limited due to lack of
economic applications. Th e oil should, for the time being, be
used to substitute fossil fuels in heat and power production,
by combustion in conventional boilers or co-combustion in
power stations. Th e focus for the next few years is to produce
oil, and to apply simple and cheap applications. Once the
process and peripherals have been proven, larger amounts of
oil will become available for the development and commer-
cial-scale demonstration of other bio-oil applications, such
as turbines, diesel engines and/or further upgrading to bio-
fuels. Obviously the construction and operation of demon-
stration installations needs to be supported by government
bodies and risk-taking investors, viz. in a sustainable way.
Past failures in biomass demonstration projects were oft en
caused by a serious lack of fi nancing aft er the fi rst period of
plant design and erection.
Challenges within the coming years are related to
improving:
• the operational reliability of demonstration scale pyroly-
sis processes;
• the feedstock fl exibility (accepting all kinds of biomass
residues, instead of only wood);
• the heat transfer to the pyrolysis reactor and from the
char combustor; and
• the process heat integration and its control.
In the meantime, R&D should be directed to improve-
ment of the quality (and stability) of the oil in relation to the
end-application envisaged. Although nice, uniform bio-oil
samples have always been available during the last 20 years,
only limited fundamental know-how has been generated on
the exact composition of the bio-oil. Much attention was paid
to (destructive!) GC analysis techniques, while nowadays it
is gradually being recognized and understood that the com-
ponents quantifi ed are not necessarily (in that concentration)
present in the original oils. In addition, the authors believe
that the compounds or fractions in the oil, causing its specifi c
characteristics (pH, ageing, viscosity, phase separation, and so
on) have not been fully identifi ed nor are the reactions taking
place understood. One particular issue is the exact role of the
various oxygen functionalities in the oil. It is important to
establish which functionalities are desired and which ones
are undesirable, and to understand how to steer the pyrolysis
process itself in this respect, for instance, by catalysis.
With respect to bio-oil upgrading, an important conclu-
sion is that reduction and control of the oxygen functionali-
ties should be the ultimate goal instead of the reduction in
oxygen content itself. Actual demonstration that pyrolysis
oils can be used as a feedstock in refi neries, as aimed at in
the European ‘BioCoup’ project, will certainly boost the fur-
ther development of fast pyrolysis.
For BTG’s system in particular, the progress made in
Malaysia from the beginning of the plant design in 2004 to
date is quite satisfactory. From an initial set of experiments in
2003 (8 hours and maximum 100 kg/hr feeding), the system
has been scaled up to a 24 hours/day running factory, where a
direct link has been established between the palm mill and the
pyrolysis plant. In addition, the process is applied to a very dif-
fi cult biomass feedstock material, which is fl uff y (not free fl ow-
ing) and wet, and has a high ash content (with a very low melt-
ing point). Problems resolved are largely related to boundary
conditions (feeding, pre-treatment, ash-related problems and
heat recovery) instead of to the actual pyrolysis process itself.
All the experiences and knowledge acquired by BTG over the
past 20 years of RTD will be condensed in the design of a new
wood based demo-pant of 125 t/d, to be erected by Empyro
BV in 2010/2011 at a site in Hengelo, the Netherlands. A BTG
daughter company called BTG-Bioliquids takes care of the
future commercialization of BTG’s fast pyrolysis technology.
Acknowledgements
Th e authors would like to thank Erik Heeres and Agnes
Ardiyanti from the University of Groningen for carrying out
the TGA experiments reported in Fig. 1, and Dietrich Meier
for allowing us to use his presentation of pyrolysis technolo-
gies as input for Fig. 6.
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RH Venderbosch, W Prins Review: Fast pyrolysis technology development
Robbie Venderbosch
After his PhD at the Twente University in 1998,
Robbie Venderbosch joined BTG Biomass
Technology Group BV. He has more than ten
years (practical) experience in thermochemi-
cal processes for biomass and its further
use. Robbie Venderbosch has expertise and
responsibilities in the field of engineering and
implementation of fluidized bed system coupled with chemical
reaction, biomass energy processes (ranging from concept to de-
tailed design), construction and operation of laboratory, pilot and
demonstration scale set-ups and process instrumentation, and
process control (both software and hardware). He was responsible
for the delivery of BTG’s commercial pyrolysis plant to a client in
Malaysia.
Wolter Prins
Wolter Prins received his Masters in Chemical
Engineering from the University of Groningen
and his doctoral degree from the University
of Twente in Enschede, the Netherlands. In
1984, he was appointed Assistant Professor
in the Department of Chemical Technology
at the University of Twente. Since 1992, he
has combined his work at the University with a position as head
of R&D in BTG Biomass Technology Group BV in Enschede. In
2008, he was appointed as Professor for Bioresources Processing
in the Bioscience Engineering faculty of the University of Ghent.
Wolter Prins published around a hundred papers in the area of
novel gas-solid reactors, heat and mass transfer in fluidized beds,
and thermochemical conversion of biomass. He participated in
the European Network for Pyrolysis (Pyne) for many years, and
was invited by NEDO and the Chinese Academy of Sciences to
present his work in Japan and China respectively.