Initially the group began looking at membrane reactors for enhancing the intermediate product selectivity of series reaction networks. The idea was to selectively remove the intermediate product before it had time to react further. In the course of studying this application, we measured the permeability/permselectivity of polyimide membranes. We also did some dimensionless modeling work to identify the parameter space that was most favorable to this mode of operation. The reaction systems we were studying at the time all required temperatures sufficiently high that polymer membranes weren't feasible. This left porous membranes and dense membranes as the major options. Dense membranes are fantastic with respect to their permselectivity, but they are typically permselective for either hydrogen (Pd based membranes) or oxygen (silver or perovskites, for example). Producing hydrogen or oxygen as the intermediate product of a series reaction might demonstrate feasibility, but it doesn't make any practical sense. This left porous membranes as the remaining choice. Porous membranes can be permselective for a wider range of materials, but generally the permselectivity is based upon molecular size. Smaller molecules typically permeate faster than larger ones. If you think about it, most series reaction networks other than oxidations involve making molecules bigger, not smaller. One adds a functional group to a molecule, then a second functional group, etc. We did look at some oxidations, but the problem was that the reaction kinetics were too different from the permeation kinetics. In the end, we did find one application where porous membranes could be used to decrease catalyst deactivation by selective removal of an intermediate.

At the time, membrane reactors were being touted more as a means of bypassing equilibrium limitations in reversible reactions. The idea is that by removing the products from the reaction environment, the reaction never reaches equilbrium in the reaction zone. Consequently the overall conversion is greater than the equilibrium conversion one would observe is the same feed was used in a conventional non-membrane reactor. We did some analysis and modeling of this situation and showed that this only works when the membrane is highly permselective. We showed that in cases where mildly permselective membranes were used with an inert gas sweeping the effluent side of the membrane, the increased conversion was really a dilution effect and not due to selective removal of the product. That is, we showed that apart from a very small parameter space, one could realize the same increase in conversion if the sweep gas was co-fed with the reactants to a conventional reactor. Similarly we showed that membrane reactors with no sweep gas could be mimicked using two reactors operating at the high and low pressures of the membrane reactor.

Having shown that a permselective membrane is necessary to truly enhance conversion, we next considered running water-gas shift in a membrane reactor. If a palladium membrane were used, then only hydrogen would be removed. At the time of these studies, there were many groups working on developing better membranes that allowed more rapid permeation of hydrogen. It seemed to be implicitly assumed that since shift was a decades old technology, the existing catalysts would be a drop-in component of a membrane reactor. However, our studies showed that commercial high temperature shift catalysts are known to be inhibited by the product carbon dioxide, and use in a membrane reactor exacerbates this problem. Our analysis led to a new project, described elsewhere on this site, focused upon developing shift catalysts specifically for use in a membrane reactor.

“Assessing High-Temperature Water-Gas Shift Membrane Reactors.” D. Ma and C. R. F. Lund, Ind. Eng. Chem. Res., 42 (4), 711-717 (2003). [more info]

“Preliminary Assessment of Membrane Reactors as a Means to Improve the Selectivity of Methylamine Synthesis,” Chimin Sang, Chen-Chang Chang and C. R. F. Lund, Ind. Eng. Chem. Research, 38 (12), 4552-4562 (1999). [more info]

“The Effect of a Membrane Reactor upon Catalyst Deactivation during Hydrodechlorination of Dichloroethane,” Chen-Chang Chang, Christopher M. Reo, and C. R. F. Lund, Appl. Catal. B: Environ., 20, 309 (1999). [more info]

“Defining Conditions Where the Use of Porous Membrane Reactors Can be Justified Solely on the Basis of Improved Yield,” C. M. Reo, L. A. Bernstein, and C. R. F. Lund, Chem. Eng. Sci., 52 (18), 3075 (1997). [more info]

“Cocurrent Membrane Reactors Versus PFRs for Shifting Dehydrogenation Equilibrium,” C. M. Reo, L. A. Bernstein, and C. R. F. Lund, AIChE J., 43 (2), 495 (1997). [more info]

“A Batch Membrane Reactor for Laboratory Studies,” L. A. Bernstein, C. M. Reo, and C. R. F. Lund, J. Membrane Sci., 118, 93, (1996). [more info]

“Permeation Through Kapton® Polyimide at Elevated Temperatures,” M. Hausladen, K. A. Oship, and C. R. F. Lund, Chem. Eng. Comm. 143, 91-97 (1996). [more info]

“Membrane Reactors for Catalytic Series and Series-Parallel Reactions,” L. A. Bernstein and C. R. F. Lund, J. Membrane Sci. 77, 155 (1993). [more info]

“Letter to the Editor,” Lund, C. R. F., Catal. Lett. 13, 423 (1992). [more info]

“Improving Selectivity During Methane Partial Oxidation by Use of a Membrane Reactor,” Lund, C. R. F., Catal. Lett. 12, 395 (1992). [more info]

“Use of a Membrane Reactor to Improve Selectivity to Intermediate Products in Consecutive Catalytic Reactions,” S. Agarwalla and C. R. F. Lund, J. Membrane Sci. 70, 129 (1992). [more info]

“Partial Oxidation Using Membrane Reactors.” L. A. Bernstein, S. Agarwalla, and C. R. F. Lund, ACS Symposium Series 523, “Catalytic Selective Oxidation,” pp 427-437. American Chemical Society, Washington, D.C., 1993. [more info]

“Partial Oxidation Using Membrane Reactors.” L. A. Bernstein, S. Agarwalla, and C. R. F. Lund, Preprints of Papers, Division of Petroleum Chemistry, ACS, 37, 1268, 1993.

“Assessment of Methylamine Synthesis using Membrane Reactor,” AIChE Annual Meeting, Dallas, TX, November 1999.

“Using Membrane Reactors to Enhance Conversion of Large Molecules in Reversible Reactions,” The Procter & Gamble Company, Cincinnati, OH, March 23, 1998.

“An Assessment of Membrane Reactors for Dehydrogenation Reactions,” Annual AIChE Meeting, Chicago, November 1996.

“Using Membrane Reactors for Catalytic Reactions to Improve Selectivity,” Workshop on Advances in Homogeneous and Heterogeneous Catalysis and Surface Science, June 1996, Nanjing, China.

“When Can a Catalytic Membrane Reactor Enhance Dehydrogenation Yields?,” Gordon Conference on Catalysis, June 1996.

“Experimental Studies of the Effect of Membrane Reactors on Selectivity,” Annual AIChE Meeting, Miami, November 1995.

“Membrane Reactors for Consecutive Heterogeneous Catalytic Reactions,” Annual AIChE Meeting, St. Louis, November 1993.

“Engineering Membrane Reactors to Control Selectivity in Consecutive Catalytic Reactions,” 13^th North American Meeting of the Catalysis Society, Pittsburgh, PA, May 1993.

“Partial Oxidation Using Membrane Reactors,” 204^th National ACS Meeting, Washington, D.C., August 1992.

“An Assessment of Catalytic Membrane Reactors for Use in the Partial Oxidation of Methane,” Annual AIChE Meeting, Los Angeles, November 1991.

“Partial Oxidations in Catalytic Membrane Reactors,” SUNY - Buffalo, Chemistry Department Colloquium, April 3, 1991.

Chimin Sang, “Investigations on membrane application to catalytic methylamines synthesis and kinetics of nitrous oxide decomposition on FeZSM-5,” PhD Dissertation, University at Buffalo, SUNY, Dept. of Chemical Engineering (2001). [more info]

Lewis Andrew Bernstein, “Membrane Reactors for Consecutive Heterogeneous Catalytic Reactions,” PhD Dissertation, University at Buffalo, SUNY, Dept. of Chemical Engineering (1996). [more info]

Christopher Reo, “A Study of the Dehydrogenation of Small Hydrocarbons in Membrane Reactors,” M. S. Thesis, University at Buffalo, SUNY, Dept. of Chemical Engineering (1997). [more info]

Michael Hausladen, “Characterization of Polyimides as High Temperature Membrane Material for the Selective Separation of Partial Oxidation Products and Reactants,” M. S. Thesis, University at Buffalo, SUNY, Dept. of Chemical Engineering (1992). [more info]

Kimberly A. Oship, “High Temperature Permeation of CO₂, O₂, CH₄, and CH₃OH in Polyimide Films,” M. S. Thesis, University at Buffalo, SUNY, Dept. of Chemical Engineering (1991). [more info]