Selection of CO 2 chemisorbent for fuel-cell grade H 2 production by sorption-enhanced water gas shift reaction Michael G. Beaver, Hugo S. Caram, Shivaji Sircar* Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA article info Article history: Received 23 November 2008 Received in revised form 23 January 2009 Accepted 26 January 2009 Available online 25 February 2009 Keywords: Hydrogen Fuel-cell grade Water gas shift Sorption-enhanced reaction Promoted alumina Promoted hydrotalcite Chemisorption Carbon dioxide abstract New experimental data are reported to demonstrate that high purity H 2 can be directly produced by sorption-enhanced water gas shift (WGS) reaction using synthesis gas (CO þ H 2 O) as sorber-reactor feed gas. An admixture of a commercial WGS catalyst and a proprietary CO 2 chemisorbent (K 2 CO 3 promoted hydrotalcite or Na 2 O promoted alumina) was used in the sorber-reactor for removal of CO 2 , the WGS reaction by-product, from the reaction zone. The promoted alumina was found to be a superior CO 2 chemisorbent for this application because (a) it could directly produce a fuel-cell grade H 2 product (<10–20 ppm CO) at reaction temperatures of 200 and 400  C, and (b) it produced w45.6% more high purity H 2 product per unit amount of sorbent than the promoted hydrotalcite at 400  C. Furthermore, the specific fuel-cell grade H 2 productivity by the promoted alumina at a reaction temperature of 200  C was w3.6 times larger than that at 400  C. These striking differences in the performance of the two CO 2 chemisorbents were caused by the differ- ences in their CO 2 sorption equilibria and kinetics. ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction The advent of hydrogen economy and concern with global warming by CO 2 emission to the atmosphere has initiated research and development of new technologies on simulta- neous production of fuel-cell grade H 2 by coal gasification and sequestration of the CO 2 by-product [1,2]. A novel process concept called ‘‘thermal swing sorption enhanced reaction (TSSER)’’ was recently proposed which could simultaneously produce (a) a fuel-cell grade H 2 product stream containing less than 20 ppm CO at the feed gas pressure and (b) a compressed by-product stream containing 99.9þ% CO 2 from a synthesis gas (primarily CO þ CO 2 þ H 2 O) feed produced by coal gasifi- cation (after removal of trace contaminants such as sulfur impurities) [3–5]. The concept uses a set of parallel fixed-bed sorber-reactors packed with an admixture of a water gas shift (WGS) reaction catalyst and a reversible CO 2 selective chem- isorbent and undergoes a five-step cyclic process described by Fig. 1. A detailed description of the TSSER concept and its potential advantages can be found elsewhere [3–5]. The concept is based on the following key principles:  Removal of CO 2 from the reaction zone of a WGS reactor by selectively chemisorbing the gas on a solid sorbent, thereby circumventing the thermodynamic limit of the reaction and directly producing a fuel-cell grade H 2 product as reactor effluent (step a). * Corresponding author. Fax: þ1 610 758 5057. E-mail address: sircar@aol.com (S. Sircar). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.01.065 international journal of hydrogen energy 34 (2009) 2972–2978