ENHANCED RATES OF GAS-LIQUID REACTIONS IN A PISTON OSCILLATING MONOLITH REACTOR (POMR)

K.M. Dooley*, F. C. Knopf, A.G. Bussard, Y.G. Waghmare, D. Liu, and R.V. Forest

Cain Department of Chemical Engineering

Louisiana State University

*dooley@lsu.edu

Microreactor for GLS Reactions

Gas-liquid-solid diffusion –limited reactions – hydrogenation /dehydrogenation – desulfurization, denitrogenation, polymer modifications, bio-fuel processing, edible oils.Problems: Mass transfer, surface wetting distributions, activity vs. selectivity tradeoffs.

Want control other than T, P, space velocity, particle size, G/L ratio

Liquid film

Gas film

Liquid solution

Liquid film

H2

PorousCatalyst

Advantages of Pulsed Flows in Gas-Liquid Reactors

• Enhance gas mass transfer; alternate gas- and liquid-rich conditions1 – with optimal average external surface environment, can improve both activity and selectivity2,3

• Effects of pulsing on intraparticle diffusion???– For polymeric systems, typically use large pore (380

nm), low surface area supports (16 m2/g). 4 What are pulsing effects on diffusion of larger molecules?

1. Boelhouwer, J.G.; Piepers, H.W.; Drinkenberg, A.A.H. Chem. Eng. Sci., 2002, 57, 3397-3399.

2. Cybulski, A.; Stankiewicz, A.; Edvinsson Albers, R.K.; Moulijn. Chem. Eng. Sci., 1999, 53, 2351-2358.

3. Khadilkar, M. R.; Wu, Y. X.; AlDahhan, M. H.; Dudukovic, M. P.; Colakyan, M. Chem. Eng. Sci. 1996, 51 2139-2148.

4. Hucul, D.; Hahn, S. Adv. Mater., 2000, 12(23), 1855-1858.

Piston Oscillating Monolith Reactor (POMR)

– Gas distributor similar to monolith (5 x 5 x 1.2 cm, 1.3 mm holes)– HX/monolith “sandwich” stack– Up to 17.5 Hz and 2.5 mm (LARGE) amplitude from piston– Gas booster recycles hydrogen , 0.5 Hz at 170 mL/s – semibatch

recycle mode

POMR - Single capillary experiments

Slug velocity plot

• Expulsion and suck-back cycle1

Flow regime map

• Mainly slug flow even during oscillations

• Amplitude = 1.36 mm

• Frequency = 17.5 Hz

• Gas flow rate = 0.18 mL/s

Superficial gas velocity (m/s)

0.01 0.1 1 10Su

pe

rfic

ial liq

uid

velo

city (

m/s

)

0.01

0.1

1

10

Bubbly

Slug

Churn

Slug-annular

Time, t (ms)

0 10 20 30 40 50

Plu

g v

elo

city,

(cm

/s)

-600

-400

-200

0

200

400

600

800Cycle 1Cycle 2Cycle 3Cycle 4Cycle 5Cycle 6

1. Knopf et al. AIChE J, 2006, 52, 1103-1115.

POMR Visualization Studies – Air/Water

• Microchannel assembly, without (a) and with oscillation (b, c); (b) top of stroke, (c) bottom of stroke

• 121 channels, A = 2.5 mm, F = 2 Hz; gas flow = 0.09 m/s

– Piston oscillations induce gas and liquid rich conditions - ability to control gas fraction over wide range

POMR Rheology – Viscous Fluid

Flow of N2/glycerol (1260 mPa•s, 0.09 m/s) in monolith with (L)and without (R) oscillation. A = 2.5 mm, F = 1 Hz.

• POMR gives high interfacial areas and good gas distribution even with viscous solutions

Typical Catalyst

• γ-Al2O3 washcoated (2.7 wt%) on 200 cpsi cordierite monoliths or pressed into pellets

• Impregnated with 0.5 wt% Pd• 290 m2/g, 74% dispersion (H2), pore size 10 nm (average),

monolith washcoat ~100 μm

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.4E-02

1.6E-02

1 10 100 1000 10000

Log (Pore Diameter) (A)

(cc/A/g)

dD

dVads

Test Reaction - -Methylstyrene Cumene

• Extensive previous work in trickle beds and monoliths• Batch mode, typical conditions 40-50 °C, 0.34-1.0 MPa, 13

mol% AMS in cyclohexane

• Superficial velocities: Ug = 0.18 m/s Ul = 0.28 m/s• Side reactions – disproportionations (minimal, less with

pulsing)

H2

0.5 wt%Pd Al2O3

AMS Cumene

AMS Hydrogenation- Activity Results

• POMR enhances gas-liquid mass transfer

• P/VPOMR (8 Hz) ~ P/Vtank (520 rpm)

46°C, 0.44 MPa, ug=0.18 m/s, A = 2.5 mm

5

10

15

20

25

30

35

0 5 10 15 20

Ra

te (m

mo

l/s/g

Pd)

Frequency (Hz) or Speed (RPM/100)

POMR

stirred tank, powder cat.stirred tank, monolith cat.

AMS Hydrogenation - Conclusions

• POMR - superior activity, selectivity vs. stirred tank at less P/V.

• Observed rate, selectivity increases with frequency, consistent with POMR mass transfer studies - higher rates of gas-liquid mass transfer; more H2 at external surface.

– Observed rates computed from mass transfer correlations consistent with experimental observations (both stirred tank and POMR).

Soybean Oil Hydrogenation – Why?

H2C

HC

H2C

O

O

O

O

O

O

– Serial pathway and stereo selectivity issues– Tradeoff between activity and selectivity - optimal

CsH2

– Both intraparticle and film concentration gradients important

Soybean Oil Hydrogenation - Kinetics

H2 H2H2

C18:3 C18:2 C18:1 C18:0

k3 k2 k1

jjjDB CCCC 321 32

j = C16, C18 etc.

IV = iodine value =measure of total double bonds

T = 110ºC, P = 0.41 MPa H2, 2000 rpm(stirred tank), ug = 0.18 m/s (POMR)

Diffusion-Limited – in Liquid and Solid

f (Hz) uL (cm/s) kova (s-1) CH2s/CH2* H2

Hz cm/s 1/s

0.5 1.1 0.37 0.61 41

8 45 1.14 0.81 45

17.5 97 1.97 0.84 64

sHeH

obscHH

CD

LR

22

2

2

2)(

monolith

Calculation of Mass Transfer

1. Irandoust, S.; Andersson, B. Ind. Eng. Chem. Res. 1989, 28, 1684-1688.2. Kreutzer, M.T.; Du, P.; Heiszwolf, J.J.; Kapteijn, F.; Moulijn, J.A. Chem. Eng. Sci., 2001, 56, 6015-6023.3. Bercic, G.; Pintar, A. Chem. Eng. Sci., 1997, 52, 3709-3719.

111

LSLSGLGLGSGSov akakakak

uL based on volume per stroke

kgs ags – Irandoust and Andersson (1989)1

kls als – Kreutzer et al. (2001)2

kgl agl – Bercic and Pintar (1997)3

NGL

NLS NGS

dchGasLiquid

Lfilm

LUC

uslug

d

Serial Pathway Selectivity

S21 = k2/k1

Even at high L,S21 range OK.

110°C, 0.41 MPa, stirred tank - 2000 rpm.

Effects of Frequency

0

2

4

6

8

0 5 10 15 20

k x

10

3(m

in-1

)

Frequency (Hz) or Speed (rpm/100)

POMR data

Stirred tank, monolith

Stirred tank, powder

POMR: T = 110 °C, P = 0.41 MPa, A = 2.5 mm; max. P fluctuations 0.08 MPa.

At 8 Hz, (Pv)POMR ~ (Pv)stirred tank at 520 rpm; pulsing enhances both interfacial and intraparticle mass transfer.

Comparison to Shear-Enhanced Transport Theory1,2

(Denh/De) =

F(Sc, Wo, x/r)

x = pulse penetration depth

Wo = r( /)

r = 10 μm, x = 30 μm

1. Leighton, D. T.; McCready, M. J. AIChEJ. 1988, 34 (10), 1709-1712.

2. Chandhok, A.; Voorhies, N.; McCready, M. J.; Leighton, D. T. AIChE J. 1990, 36, 1259-1262.

0.5

1

1.5

2

2.5

0 5 10 15 20

De

nh/D

e

Piston Frequency (Hz)

Rate Ratio

Diffusivity ratio, x = 300 micron

Diffusivity ratio, x = 30 micron

• Pulsing enhancements to rates arise from external (gas-liquid) transport, or internal transport in large pores.

• For hydrogenation, serial pathway selectivity increases with POMR frequency, due to modifications in surface wetting .

• Increased observed activities consistent with theory on shear enhanced pulsed transport enhancements in the washcoat.

Conclusions

Acknowledgements• Funding

– NSF-0436759 IGERT– NSF GOALI-0754397

• People– Cassidy Sillars, Paul Rodriguez, Joe Bell, Kevin

Kelly (Mezzo Systems, Heat Exchangers)– Sasol and BASF for material donations

dooley@lsu.edu