21 May 2014 www.hnei.hawaii.edu

The Fundamentals of BiocarbonFormation at Elevated Pressure:

From 1851 to the 21st CenturyMichael J. Antal Jr, Charissa Higashi,

Phacharakamol Phothisantikul, Sam Van Wesenbeeck, Simon Williams

Hawaii Natural Energy InstituteUniversity of Hawaii at Manoa

Exponential Growth in PV MarketIsland of Maui

(Source: Maui Electric Company, Ltd.)

Integrating High Penetrations of PV on Distribution FeedersIs a Challenge in Hawaii Today 2

• In both 2011 and 2012, the installed PVon Maui doubled the total installed PVcapacity of the prior year

• July, 2013 PV @ 37+ MW

Silicon – Basic processProduction (overview)

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SiC

C(Coal / Coke / Charcoal)

SiO2(Quartz)

Silicon

SiO(g) + 2C = SiC + CO

O2(air)

2SiO + O2 = 2SiO2

SiO2(Microsilica)

2SiO(g) =SiO2 + Si

SiO(g)

SiO2 + Si= 2SiO(g)

SiO2 + C + SiC =Si + SiO(g) + CO

CO2

2CO + O2 = 2CO2

Surface

Inner reductionzone

Charge

courtesy of Dr. Viktor Myrvagnes, Elkem

Courtesy of Dr. Scott Turn, HNEI 4

Metallurgical charcoal production in Brazil

1) Antal et al., Ind. Eng. Chem. Res. 2003, 42, 3690-3699 5

Thermochemical equilibrium predictions for the products of cellulose pyrolysis at 400 C1

• C, H2O, CO2, (H2,) and CH4 are the only significant products.

• The theoretical charcoal (i.e. C) yield is 28 wt%.

• The gas contains significant energy (i.e. CH4). Pressure (MPa)

0.001 0.01 0.1 1 10

Mas

s fr

actio

n (%

)

0

10

20

30

40

50

C(s)

CO2

H2O(g)

CO

CH4

(a)

1) Antal et al., Ind. Eng. Chem. Res. 2003, 42, 3690-3699 6

Energy balance for cellulose pyrolysis following thermochemical equilibrium1

0 5000 10000 15000 20000

input

output

Energy [kJ/kg-cellulose]

cellulosespecific heat

carbongas

worksensible heat

exotherm

0 5000 10000 15000 20000

input

output

Energy [kJ/kg-cellulose]

cellulosespecific heat

carbongas

worksensible heat

exotherm

1) Antal et al., Ind. Eng. Chem. Res. 2000, 39, 4024-4031 7

Useful definitions:1

1. ychar = mchar / mbio

2. 100 = % VM + % fC + % ash; where

%VM = volatile matter;

%fC = fixed carbon

3. yfC = ychar {% fC / (100 - % feed ash)}

1) Wang et al., Energy Fuels 2013, 27, 2146-2156 8

Parity plot of fixed-carbon yields from various oak wood feedstocks1

• Flash Carbonization at elevated pressure attains yfC = 82% of the “theoretical” yield

• Muffle furnace yields in N2 at 1 bar are lower.

• TGA yields at 1 bar are much lower.

• Proximate analysis yields are very much lower.

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Themes of my presentation:

1. Is it possible to realize the “theoretical”

yfC from biomass?

2. If it is possible, must the carbonization

process be “slow” (and boring)?

3. Can such a carbonization process be

practical (i.e. commercial)?

1) Gronli et al., Ind. Eng. Chem. Res. 1999, 38, 2238-2244 10

Effects of Avicel cellulose sample mass on char yield and TGA pyrolysis kinetics1

• Char yields at 400 C are VERY LOW

• Decreasing sample mass reduces char yield

• We hypothesize that in the limit of small sample mass, the char yield would be negligible.

1) Mok and Antal, Thermochim. Acta. 1983, 68, 165-186. 11

Charcoal yield from cellulose pyrolysisvs. pressure1

• Pressure strongly favors formation of charcoal.

• Low gas flow rates also favor the formation of charcoal.

• Elevated pressure and low flow rates together double the yield of charcoal.

Violette, M. Memoire sur les Charbons de Bois. Ann. Chim. Phys. 1853, 32, 304. 12

1) Violette, M. Memoire sur les Charbons de Bois. Ann. Chim. Phys. 1853, 32, 304. 13

Highlights of Violette’s 2nd series of runs using sealed vessels:1

1. DRY wood (1 g) carbonization from “150” to “350” °C in sealed glass tubes (4 at each temperature with little void volume).

2. Each tube held in a metal safety container because carbonization created “enormous” gas pressures.

3. ychar = 78.7% at 320 °C in a sealed vessel with %C = 65.6% (vs. ychar = 29.7% at 1 bar)!

4. Charcoal at 180 °C resembles ordinary “red” charcoal at 280 °C.5. Charcoal at 300 °C resembles coking coal having undergone

melting: glossy, shiny, brittle and bonded to the glass tube. 6. Violette speculates that this is this how coal was formed.7. Ash content of 3-4% vs. 0.5% with ordinary charcoal.8. Also a milky opaque white, or (sometimes) clear yellow liquid

product.

Thanks to Mme. Larence Chevrier, Bibliotheque Nationale de France 14

Who was Jules Henri Michel Violette ??

• Graduate of L’Ecole Polytechnique• Officer of the Legion D’Honneur (1861)• “Commissaire” of Powder & Saltpeter (n.b.

Lavoisier was “Regisseur” of Powder & Saltpeter) • Author of > 20 technical works (e.g. a dictionary

of chemical analysis; experiments with the conservation of eggs; history of his company, etc.)

• Founder of a real estate company for the benefit of factory workers

1) Mok et al., Ind. Eng. Chem. Res. 1992, 31, 1162-1166 15

DSC traces of heat release from cellulose & xylan in closed crucibles1

• At high loadings charcoal formation from cellulose is complete below 300 C.

• The reaction rate is greatly enhanced in a closed crucible

• Xylan is converted to charcoal below 240 C.

• Pyrolysis is exothermic for all cases.

1) Mok et al., Ind. Eng. Chem. Res. 1992, 31, 1162-1166 16

Effects of moisture on heat release & char yield from cellulose in closed crucibles1

• At high moisture content charcoal formation is complete below 300 C.

• The reaction rate is greatly enhanced by high moisture content

• The char yield is greatly enhanced by high moisture content

• Pyrolysis is exothermic for all cases.

1) Varhegyi et al., J. Anal. Appl. Pyrolysis 1997, 42, 73-87. 17

A kinetic model for the observed DSC traces that employs water catalysis1

Cellulose pyrolysis in sealed sample holders:

H2O H2O cellulose intermediates char + H2O + gases k1 k2 char + volatiles + H2O + gases k0

Reaction 0 is the non-catalyzed decomposition observed in open pan TGexperiments. Reaction 1 is the hydrolysis of cellulose in the presence ofwater. Reaction 2 is the secondary reaction of the intermediates in thesealed sample holder. The rates of reactions 1 and 2 depend on the amountof water vapors in the system.

1) Varhegyi et al., J. Anal. Appl. Pyrolysis 1997, 42, 73-87. 18

Fit of the kinetic model to the DSC data for cellulose carbonization in a sealed crucible1

Rat

e of

hea

t rel

ease

(m

W/m

g)

250 260 270 280 290 300 310 °C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Differential scanning calorimetric study of cellulose carbonization in hermetically sealed sample holders at 5°C/min heating rate. The symbols (, ×, ...) represent experiments differing in the initial sample mass and

What does a tubing bomb look like?

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Summary of tubing bomb results

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A liquid “melt” phase precedes the formation of biocarbon with high yfC; linking high pressure phenomena to high heating rate phenomena!

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Conclusions• With >32,000 years of experience, we now understand the

conditions needed to realize the theoretical fixed-carbon yield of charcoal from ash-free cellulose.

• These conditions involve “fast” pyrolysis in a sealed vessel that reaches pressures exceeding 200 psig.

• In 1853 Violette reported amazingly prescient research concerning charcoal production in sealed vessels (but he did not measure the fixed-carbon yield).

• The observation of a liquid phase in charcoal formation links high pressure pyrolysis chemistry to high heating rate pyrolysis chemistry.

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Conclusions (continued)• Numerical simulations of sealed vessel results (e.g.

pressure, temperature gradients, gas and char fC and VM compositions) will reveal much about the mechanism of cellulose pyrolysis.

• It may be possible to build commercial equipment that employs sealed vessels to realize the theoretical fixed-carbon yield of charcoal in a practical situation.

• Advice to young researchers: A year of long days, late evenings and weekends in the laboratory will save you an afternoon of reading interesting papers in the library.

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Acknowledgments• Dr. Maria Burka & Ms. Bonnie Thompson (National

Science Foundation)• Office of Naval Research• Prof. Colomba DiBlasi (Università degli Studi di Napoli

"Federico II)• Jan Piskorz (Resource Transforms Int. Ltd.)• Dr. Gabor Varhegyi, Dr. Piroska Szabo, Dr. Emma Jakab,

Dr. Marianne Blazso (Hungarian Academy of Sciences)• Dr. Morten Gronli, Dr. Oyvind Skreiberg, Dr. Liang

Wang (NTNU & SINTEF)

Three co-authors (Szabo, Varhegyi, and Antal ca. 1990) of the 1992 DSC paper with Emma Jakab,and Linda in the HAS Budapest laboratory

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21 May 2014 Supplementary slides follow this slide

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1) Mok et al., Ind. Eng. Chem. Res. 1992, 31, 1162-1166 30

DSC traces of charcoal formation from woods in closed crucibles1

• Charcoal formation is complete below 350 C for all species.

• Hemicellulose is converted to char-coal below 300 C.

• Pyrolysis is exo-thermic for all species.

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