The Woodruff School

SUMMARY

Technology for large scale catalytic hydrogen generation from hydrocarbons is mature; however, miniaturization of these continuous-flow (CF) systems for mobile applications has proven difficult because of the unique application requirements: minimal size/weight, maximum fuel utilization, selectivity to H2, efficient operation over a wide range of throughput, and rapid transient response. The novel CHAMP (CO2/H2 Active Membrane Piston) reactor technology meets these demands and enables precise control of reaction conditions with simultaneous separation of H2 and CO2 streams. In this forced, unsteady-state reactor, a batch of fuel is brought into the reaction chamber and held there as conditions are dynamically controlled to ensure that 1) a maximum reaction rate is maintained even as fuel is consumed, and 2) separation of reaction products through the integrated, selectively-permeable membrane is enhanced even as the permeate species becomes depleted. When both processes are complete, the remaining mixture is exhausted out, and a fresh batch of fuel is brought in. It is demonstrated that the CHAMP-class of reactors is fundamentally capable of pushing the ideal limits of performance beyond where traditional CF reactors may operate. Because the CHAMP reactor is operated in a fundamentally different manner, the traditional reactor design rules are inadequate and a new set of guidelines for optimal operation is required. To this end, a comprehensive, coupled, transport-kinetics model has been developed to simulate the interactions between reaction kinetics, membrane permeation, mass transport, and piston (volume change) dynamics. A timescale analysis serves to identify the transition between rate-limiting steps and operating regimes as the design parameters are varied. Two major modes of operation are studied: fixed-volume mode, wherein the pressure varies throughout the cycle, and constant-pressure mode, where the piston trajectory maintains a constant, elevated pressure in the reactor. Complementary to this theoretical analysis, experimental characterization of a prototype reactor demonstrates the practical feasibility of the reactor and provides validation of the model predictions of performance.

SUBJECT:	Ph.D. Dissertation Defense

BY:	David Damm

TIME:	Wednesday, June 25, 2008, 2:00 p.m.

PLACE:	Love Building, 295

TITLE:	Batch reactors for scalable hydrogen production

COMMITTEE:	Dr. Andrei G. Fedorov, Chair (ME) Dr. William J. Wepfer (ME) Dr. Srinivas Garimella (ME) Dr. Timothy C. Lieuwen (AE/ME) Dr. William J. Koros (ChBE)

SUMMARY Technology for large scale catalytic hydrogen generation from hydrocarbons is mature; however, miniaturization of these continuous-flow (CF) systems for mobile applications has proven difficult because of the unique application requirements: minimal size/weight, maximum fuel utilization, selectivity to H2, efficient operation over a wide range of throughput, and rapid transient response. The novel CHAMP (CO2/H2 Active Membrane Piston) reactor technology meets these demands and enables precise control of reaction conditions with simultaneous separation of H2 and CO2 streams. In this forced, unsteady-state reactor, a batch of fuel is brought into the reaction chamber and held there as conditions are dynamically controlled to ensure that 1) a maximum reaction rate is maintained even as fuel is consumed, and 2) separation of reaction products through the integrated, selectively-permeable membrane is enhanced even as the permeate species becomes depleted. When both processes are complete, the remaining mixture is exhausted out, and a fresh batch of fuel is brought in. It is demonstrated that the CHAMP-class of reactors is fundamentally capable of pushing the ideal limits of performance beyond where traditional CF reactors may operate. Because the CHAMP reactor is operated in a fundamentally different manner, the traditional reactor design rules are inadequate and a new set of guidelines for optimal operation is required. To this end, a comprehensive, coupled, transport-kinetics model has been developed to simulate the interactions between reaction kinetics, membrane permeation, mass transport, and piston (volume change) dynamics. A timescale analysis serves to identify the transition between rate-limiting steps and operating regimes as the design parameters are varied. Two major modes of operation are studied: fixed-volume mode, wherein the pressure varies throughout the cycle, and constant-pressure mode, where the piston trajectory maintains a constant, elevated pressure in the reactor. Complementary to this theoretical analysis, experimental characterization of a prototype reactor demonstrates the practical feasibility of the reactor and provides validation of the model predictions of performance.