Review of Microreactors

Radmila Jevtic (graduate student)and

Professors Muthanna Al-Dahhan andMilorad P. Dudukovic

Outline

Background and features Review of gas-liquid microreactors Scale-up methodology Conclusions

Background and Features Micro-structured reactor channel diameters: sub mm

to mm range Surface/Volume area: 1,000-50,000 m2/m3

Sources: 1) A. Günther at al., Langmuir, 21, 1547 (2005); 2) www.imm-mainz.de/; 3) http://www.mikroglas.com/

Features: Advantages

High surface-to-volume area; enhanced mass and heat transfer

Laminar flow conditions

Uniform residence time, backmixing minimized (increased precision and accuracy)

High-throughput and use of very small amounts of materials

Low manufacturing, operating, and maintenance costs (if mass produced), and low power consumption

Minimal environmental hazards and increased safety

“Scaling-out” or “numbering-up” instead of scaling-up

Type of conventional reactor

Specific interface area

[m2/m3]

Type of microreactor Specific interfacearea

[m2/m3]

Packed columnCountercurrent

flowCo-current flow

10-35010-1700

Micro bubble column

(1100μm x 170 μm)

5,100

Bubble columns 50-600 Micro bubble column

(300 μm x 100 μm)

9,800

Spray columns 10-100 Micro bubble column

(50 μm x 50 μm)

14,800

Mechanically stirred bubble columns

100-2000 Falling film microreactor

(300 μm x 100 μm)

27,000

Impinging jets 90-2050

Features: AdvantagesSpecific interfacial area (S/V)

Source: Oroskar, A. R et al. Proceedings of the IMRET-5: 5th International Conference on Microreaction Technology, 27.-30. 5. 2001, Strasbourg, (Berlin, Heidelberg, New York: Springer,

2002), 153.

Features: Advantages Mass and heat transfer

Source: J.C. Schouten, Symposium on Micro Process Engineering for Catalysis & Multiphases, Eindhoven University of Technology, February 2006

Features: AdvantagesG

L

L

G

10-8

10-7

10-6

10-5

10-4

0.001 0.01 0.1 1 10 100

Mass transfer coefficient, KLa (s-1)

Re

ac

tio

n R

ate

(m

ol/

s/g

ca

taly

st)

Conventional

equipment

Cyclohexene Hydrogenation

Microreactor Results

Mass transfer

Source: Klavs Jensen’s Group, MIT. Reference: M.W. Losey, et al., I&EC Research, 40, 2555 (2001)

Cyclohexane hydrogenation was performed in micro packed bed reactor. The catalyst was standard platinum supported on alumina powder. It was determined that overall mass transfer coefficient (KLa) was 5-15 s-1 as opposed to 0.01-0.08 s-1 for laboratory trickle bed reactors

Features: Drawbacks

Fast reaction rates are required due to the short residence times

Fouling and clogging Maintenance, ageing, regeneration Lack of experience with commercial processes Catalyst deactivation, life on stream unknown Only few technology providers

Potential application for microreactors

Synthesis of hazardous gases: chlorine, iso-cyanates, hydrogen cyanide, phosgene…

Hydrogen production via steam reforming, partial oxidation of methane, from higher alkanes and alcohol to syngas

Synthesis of ethylene oxide, propylene to acrolein, oxidative dehydrogenation of alcohols to aldehydes

Oxidation of ammonia

Source: Dupont et al , Minisymposium on Micro Process Engineering for Catalysis & Multiphases, Eindhoven University of Technology, February 2006

Potential application for microreactors

Type A are very fast reactions with a reaction half time of less than 1 s. Type B are also fast reactions with reaction times between 1s and 10 min.Type C reactions are slow (reaction times greater than 10min).

63% are not well suited due to solids present as reactant, catalyst, or products.

Almost 50% of reactions could benefit from a continuous process in microreactors:

Source: Roberge, D. et al Chem. Eng. Tech. 2005, 28, 318.

Review on G-L microreactors: Falling Film Microreactor (FFM)

Cross-section of a microchannel: 100micronx300micron Reaction used: direct fluorination of aromatic compound

using elemental fluorine Specific interfacial area: 33,000m2/m3 and 27,000m2/m3

corresponding to film thickness of 30 and 37 microns

Source: 1) Jähnisch, K. et al. Fluorine Chem. 2000, 105, 117. 2) Zanfir, M. et al. Ind. Eng. Chem. Res. 2005, 44, 1742. 3) www.imm-mainz.de/

Review of G-L microreactors:Micro-bubble Column (MBC)

Dimensions: 50μmx50μm (narrow rectangular channels) and 300μmx150μmx50μm (wide channels)

Measured interfacial area: 9,000m2/m3; calculated: 14,000m2/m3

Taylor flow Reaction of direct fluorination of aromatics used

Source: 1) Jähnisch, K. et al. Fluorine Chem. 2000, 105, 117. 2) www.imm-mainz.de/

Review of G-L microreactors:MMB and FFR Performance

100,0,

RTolueneToluene

tolueneFmono

nn

nSSelectivity:

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60

Conversion of toluene (%)

Se

lec

tiv

ity

(%

)

FFMR

MBC(I)

MBC(II)

LBC

Poly. (FFMR)

Poly. (LBC)

Poly. (MBC(II))

Poly. (MBC(I))

LBC- laboratory reactor

MBC (I) 300μmx100μm

MBC (II) 50μmx50μm

Source: 1) Jähnisch, K. et al. Fluorine Chem. 2000, 105, 117.

Review of G-L microreactors: CO2 absorption in Falling Film Microreactor

(FFM)

Source: Zanfir, M. et al. Ind. Eng. Chem. Res. 2005, 44, 1742.

Performance of the reactor for CO2 absorption in sodium hydroxide solution compared with the model Model gives good agreement for low concentration of NaOH but poor for higher concentrations due to model simplification and possible liquid maldistribution

Schematic of the single channel in the model

Review of G-L microreactors: Microreactor for direct fluorination of aromatics (MIT)

0

20

40

60

80

100

0 1 2 3 4 5 6

fluorine concentration [vol %]

X, Y

, S [%

]

conversion (X)

yield (Y)

selectivity (S)

Experiments were carried out at room temperature in annular dry flow regime

churnslug

annular

bubbly

0.001

0.01

0.1

1

10

j L (m

/s)

0.1 1 10 100jG (m/s)

wavy annularHeat-

exchangers

Reactors

SlugSlug

Annular

Flow visualizationPerformance

Source: 1) Klavs Jensen group, MIT 2) N. de Mas, et al., Ind. Eng. Chem Research, 42(4); 698-710 (2003)

G

L

Review of G-L microreactors: Using Inert gas to Mix Miscible Liquids

Source: 1) Klavs Jensen group, MIT 2) A. Günther et al., Langmuir, 21, 1547 (2005).

L1

L2

t

t

Review of G-L microreactors: RTD in Fluidic Channels

Source: 1) Klavs Jensen group, MIT 2) F. Trachsel, et al., Chem. Eng. Sci., 60 (2005), 5729

Segmented flow can be understood as sequence of small batch reactors passing through plug flow reactor with very narrow residence time distribution (RTD) curve

Review of G-L microreactors: Colloidal particle synthesis Narrow RTD characteristic of segmented flow in

microchannels can be employed in the synthesis of colloidal particles where size distribution is important. Example: colloidal silica (SiO2)

Alkoxide groups (OR) are first replaced by hydroxyl group (OH)-HYDROLISIS. Siloxane bonds are formed and either alcohol (ROH) or water (H2O) are formed-CONDENSATION

As alkoxide, which can be view as weak ester of silicic acid (Si(OH)4), TOES (tetraehyl orthosilicate) is often used

)(

)(

)(

2

2

oncondensatiOHSiOSiOHSiOHSi

oncondensatiROHSiOSiOHSiORSi

hydrolysisROHOHSiOHORSi

Source: Stöber, W. et al.J. Colloid Interface Sci. 1968, 26, 62.

Review on G-L microreactors: Colloidal particle synthesis

1 µm

1 µm

Gas Gas

SFR enables continuous synthesis with results that mirror those obtained from batch synthesis Wide particle size distribution

at low residence times

Laminar Flow Reactor Segmented Flow Reactor

Source: 1) Klavs Jensen group, MIT 2) S.A. Khan, et al.,” Langmuir 20, 8604-

8611(2004)

Scale up Methodology

Number of channels increases, size of the single channel does not

The concept of scale-up by replication of microreactor units (scale-out) appears to be simple but the areas of reactor monitoring and control become increasingly complex as the parallel array size grows to a large number of reactors.

Source: Lerou, CREL Annual Meeting, St. Louis, MO, November, 2005

Scale up Methodology

Source: Lerou, CREL Annual Meeting, St. Louis, MO, November, 2005

30 ft

100 ft

Scale up Methodology

Reaction: Direct fluorination of ethyl acetoacetate in formic acid by fluorine (10-50% in nitrogen) Cooling and heating is provided by the coils that pass through the steel base of the reactor Production rate: cca 300g of product per day 10 reactors - 3 kg (which is the range of the pilot-plant operation)

Source: Chambers, R. D. et al. Lab Chip. 2005, 5, 191.

Scale up Methodology-Integration

Idea: to standardize interfaces of various microdevices (microreactors, micromixers, etc) available from different manufacturers so that they can be incorporated in a “microplant”Test reaction: the sulfonation of toluene with gaseous SO3. Result: A selectivity of 82% of the target product, toluenesulfonic acid, is achieved at nearly complete conversion (last step, hydration, not performed)

Source: Müller, A. et al. Chem. Eng. J. 2005, 107, 205. 

Conclusions

Promising technology: enhanced mass and heat transfer efficient process intensification inherently safe operation uniform residence time

Some issues still remain: integration with sensors, actuators, and other associated

equipment, such as pumps; reactor monitoring and control; high activity stable catalysts needed.