Presentation on theme: "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,"— Presentation 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 H2H2 Porous Catalyst
Advantages of Pulsed Flows in Gas-Liquid Reactors Enhance gas mass transfer; alternate gas- and liquid-rich conditions 1 – with optimal average external surface environment, can improve both activity and selectivity 2,3 Effects of pulsing on intraparticle diffusion??? – For polymeric systems, typically use large pore (380 nm), low surface area supports (16 m 2 /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, Cybulski, A.; Stankiewicz, A.; Edvinsson Albers, R.K.; Moulijn. Chem. Eng. Sci., 1999, 53, Khadilkar, M. R.; Wu, Y. X.; AlDahhan, M. H.; Dudukovic, M. P.; Colakyan, M. Chem. Eng. Sci. 1996, Hucul, D.; Hahn, S. Adv. Mater., 2000, 12(23),
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 cycle 1 Flow regime map Mainly slug flow even during oscillations Amplitude = 1.36 mm Frequency = 17.5 Hz Gas flow rate = 0.18 mL/s 1. Knopf et al. AIChE J, 2006, 52,
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 N 2 /glycerol (1260 mPas, 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-Al 2 O 3 washcoated (2.7 wt%) on 200 cpsi cordierite monoliths or pressed into pellets Impregnated with 0.5 wt% Pd 290 m 2 /g, 74% dispersion (H 2 ), pore size 10 nm (average), monolith washcoat ~100 μ m
Test Reaction - -Methylstyrene Cumene Extensive previous work in trickle beds and monoliths Batch mode, typical conditions °C, MPa, 13 mol% AMS in cyclohexane Superficial velocities: U g = 0.18 m/s U l = 0.28 m/s Side reactions – disproportionations (minimal, less with pulsing)
AMS Hydrogenation- Activity Results POMR enhances gas-liquid mass transfer P/V POMR (8 Hz) ~ P/V tank (520 rpm) 46°C, 0.44 MPa, u g =0.18 m/s, A = 2.5 mm
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 H 2 at external surface. – Observed rates computed from mass transfer correlations consistent with experimental observations (both stirred tank and POMR).
Soybean Oil Hydrogenation – Why? –Serial pathway and stereo selectivity issues –Tradeoff between activity and selectivity - optimal C s H2 –Both intraparticle and film concentration gradients important
Soybean Oil Hydrogenation - Kinetics H2H2 H2H2 H2H2 C18:3 C18:2 C18:1 C18:0 k3k3 k2k2 k1k1 j = C 16, C 18 etc. IV = iodine value = measure of total double bonds T = 110ºC, P = 0.41 MPa H 2, 2000 rpm(stirred tank), u g = 0.18 m/s (POMR)
Diffusion-Limited – in Liquid and Solid f (Hz)u L (cm/s)k ov a (s -1 )C H2 s /C H2 * H2 Hzcm/s1/s monolith
Calculation of Mass Transfer 1.Irandoust, S.; Andersson, B. Ind. Eng. Chem. Res. 1989, 28, Kreutzer, M.T.; Du, P.; Heiszwolf, J.J.; Kapteijn, F.; Moulijn, J.A. Chem. Eng. Sci., 2001, 56, Bercic, G.; Pintar, A. Chem. Eng. Sci., 1997, 52, u L based on volume per stroke k gs a gs – Irandoust and Andersson (1989) 1 k ls a ls – Kreutzer et al. (2001) 2 k gl a gl – Bercic and Pintar (1997) 3
Serial Pathway Selectivity S 21 = k 2 /k 1 Even at high L, S 21 range OK. 110°C, 0.41 MPa, stirred tank rpm.
Effects of Frequency POMR: T = 110 °C, P = 0.41 MPa, A = 2.5 mm; max. P fluctuations 0.08 MPa. At 8 Hz, (P v ) POMR ~ (P v ) stirred tank at 520 rpm; pulsing enhances both interfacial and intraparticle mass transfer.
Comparison to Shear-Enhanced Transport Theory 1,2 (D enh /D e ) = 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), Chandhok, A.; Voorhies, N.; McCready, M. J.; Leighton, D. T. AIChE J. 1990, 36,
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 IGERT – NSF GOALI People – Cassidy Sillars, Paul Rodriguez, Joe Bell, Kevin Kelly (Mezzo Systems, Heat Exchangers) – Sasol and BASF for material donations