- 8:55 AM
423b

Harnessing Chemical Energy for Hydrogen Purification In Microreactors

Kishori Deshpande, Engineering and Process Sciences, Dow Chemical Company, B-1603, 2301 N. Brazosport Boulevard, Freeport, TX 77541, Andrea Adamo, Chemical Engineering, Massachusetts Institute of Technology, 66-501, 25 Ames Street, Cambridge, MA 02142, Martin A. Schmidt, Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 39-521, 77 Massachusetts Avenue, Cambridge, MA 02139, and Klavs F. Jensen, Chemical Engineering and Materials Science & Engineering, MIT, Room 66-342, 77 Massachusetts Ave, Cambridge, MA 02139.

 

Hydrogen fed fuel cells are attractive for portable power applications owing to their high conversion efficiency.  However, hydrogen purification is an important step to avoid fuel cell catalyst poisoning and improve fuel cell performance. Palladium membranes which are selectively permeable to hydrogen offer an attractive solution. Besides making the design compact these membranes yield high hydrogen selectivity and are chemically resistant to carbon di oxide and carbon monoxide. While these membranes have been investigated extensively, most studies report using elaborate electrical heating for reactor heating and thus pose issues for systems integration [1-5].

In the current work we propose harnessing chemical energy for sustaining reactor temperature by coupling an exothermic reaction with hydrogen purification. The design imparts flexibility to carry multiple reactions simultaneously and compactness for ease of systems integration. To achieve this goal an integrated hydrogen purification-burner unit is fabricated using bulk micromachining techniques. The purification unit consists of a 200 nm palladium-silver membrane while the burner unit is loaded with platinum catalyst. The palladium membrane separation process implies an equilibrium amount of hydrogen remains in the exhaust gas.  This hydrogen can be burned by catalytic combustion to provide the necessary energy to sustain the reactor temperature and thus impart design compactness.

The performance of this integrated hydrogen purification system in terms of energy efficiency and hydrogen separation is characterized. The minimum hydrogen flow rate at stoichiometric oxygen hydrogen ratio to maintain a specific target temperature is investigated.  Further, the permeate side hydrogen flux dependence for this system is measured. These results compare well with the data obtained using electrical heating. Finally the CO tolerance of the membrane is also tested to check device robustness.

References:

1.      K. Deshpande, M. A. Schmidt, K. F. Jensen “An Integrated Membrane Microreactor for Elevated Pressure Hydrogen Purification – Device Fabrication and Characterization”, In preparation.

2.      B.A.Wilhite, M.A.Schmidt, K.F.Jensen “Palladium-Based Micromembranes for Hydrogen Separation: Device Performance and Chemical Stability” Ind. Eng. Chem. Res, 2004, 43, 7083-7091.

3.      J. Keurentjes, F. Gielens, H. Tong, C. Rijn, M. Vorstman “ High-Flux Palladium Membranes Based on Microsystem Technology” Ind. Eng. Chem. Res, 2004, 43, 4768-4772.

4.      Y. Zhang, J. Gwak, Y. Murakoshi, T. Ikehara, R. Maeda, C. Nishimura “Hydrogen Permeation Characteristics of Thin Palladium Membrane Prepared by Microfabrication Technology” J. Memb. Sci, 2006, 277, 203-209.

5.      S. Ye, S, Tanaka, M. Esashi, S. Hamakawa, T. Hanaoka, F. Mizukami “Thin Palladium Membrane Microreactors with Oxidized Porous Silicon Support and Their Application” J. Micromech. Microeng, 2005, 15, 2011-2018.