In honor of Arvind Varma's 60th Birthday, I will present ongoing research within my group at the University of Connecticut in the area of microchemical reaction engineering, aimed at realizing biofuel-driven portable power systems. Microchemical systems offer significant advantages over their conventional counterparts in (i) heat and mass transport rates, (ii) system redundancy and safety, and (iii) portability and power densities. This combination of advantages opens the door for realizing commercial, cartridge-based fuel reformers for distributed energy production from biofuels. In order to realize this goal, several reaction engineering problems must be revisited. This talk will highlight reaction and diffusion considerations in non-isothermal microreactor and micro-membrane reformers, and heat integration and stability considerations for multifunctional microreactors.

While conventional catalytic reactors often employ packed-beds of catalyst pellets, presenting the classical problem of reaction and diffusion with symmetric boundaries, microreactors utilize layers of catalytic washcoats, presenting asymmetric boundary conditions for both heat and mass transport. This introduces an interesting variant on reaction and diffusion in the presence of heat conduction and/or catalytic generation, and a significant class of problems in the case of composite-catalytic membranes for combined reforming and purification ¹. In both cases, significant improvement in reactor design can be achieved with appropriate manipulation of reactor and catalyst structures.

Microchemical systems, comprised of large networks of parallel, separate channels promise efficient heat transfer between endo- and exothermic processes (e.g., partial oxidation and water-gas-shift). Selection of appropriate geometries, materials and packaging has significant effects on both thermal efficiency and steady-state multiplicity. Appropriate use of microfabrication techniques further allows coupling of several separate processes in both parallel and series within networks of 10¹ – 10⁶ channels; this level of complexity will require a new generation of design and optimization tools for realizing efficient, integrated microchemical systems.

¹ B.A. Wilhite, S.E. Weiss, J.Y. Ying, M.A. Schmidt and K.F. Jensen, "Demonstration of 23wt% Ag-Pd Micromembrane Employing 8:1 LaNi_0.95Co_0.05O₃/Al₂O₃ Catalyst for High-Purity Hydrogen Generation," Advanced Materials, 18, 1701 (2006).