enhanced rates of gas-liquid reactions in a piston oscillating monolith reactor (pomr) k.m. dooley*,...
TRANSCRIPT
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
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