High-purity hydrogen production through sorption enhanced water gas shift reaction using K 2 CO 3 -promoted hydrotalcite Hyun Min Jang a , Ki Bong Lee a,n , Hugo S. Caram b , Shivaji Sircar b a Department of Chemical and Biological Engineering, Korea University, Seoul 136-713, Republic of Korea b Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA article info Article history: Received 9 September 2011 Received in revised form 16 January 2012 Accepted 9 February 2012 Available online 16 February 2012 Keywords: CO 2 adsorption Hydrogen production Sorption enhanced water gas shift reaction K 2 CO 3 -promoted hydrotalcite Packed bed Numerical analysis abstract Sorption enhanced water gas shift (SEWGS) reaction is a process concept, which simultaneously carries out the gas phase water gas shift (WGS) reaction (CO þH 2 O2CO 2 þH 2 ) and selective chemisorption of the byproduct CO 2 from the gas phase reaction zone for direct production of essentially pure H 2 in a single unit operation. A packed bed sorber-reactor containing an admixture of a WGS catalyst and a CO 2 chermisorbent is used in the process. The concept circumvents the thermodynamic limitation of the WGS reaction and enhances the rate of reaction for H 2 production. In this study, the SEWGS reaction concept was successfully demonstrated by both experiment and numerical simulation using K 2 CO 3 - promoted hydrotalcite as the CO 2 sorbent. Numerical model simulations were also carried out to investigate the effects of various operating conditions of SEWGS reaction on the process performance. In general, higher H 2 O/CO feed ratio, higher fraction of sorbent (chemisorbent ratio in the sorber- reactor), and lower operating temperature favor both H 2 productivity and CO conversion. Higher reaction pressure increases H 2 productivity but decreases CO conversion. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Worldwide demand for hydrogen has steadily increased in the recent years. More than 50 million tons of hydrogen is currently produced annually in the world. More than 80% of this production capacity is met by conventional steam methane reforming route (CH 4 þ 2H 2 O2CO 2 þ 4H 2 ) because of technology maturity and favorable economics (Ngˆ o and Natowitz, 2009; Ritter and Ebner, 2005). Production of hydrogen by gasification of coal, which is more abundant and cheaper than natural gas, is another technically and economically feasible route (National Research Council and National Academy of Engineering, 2004). Use of renewable carbon sources such as biomass and bio-derived feed- stock for hydrogen production is also promising and its technical development is progressing (Bulushev and Ross, 2011; Florin and Harris, 2008; National Research Council and National Academy of Engineering, 2004). Fig. 1 shows a conventional process scheme to produce hydrogen by coal gasification (Bell et al., 2011). A synthesis gas containing CO, H 2 , CO 2 , and H 2 O is produced by reacting coal with H 2 O and O 2 above 1000 1C. CO in the synthesis gas is then reacted with H 2 O in a water gas shift (WGS) reactor to produce CO 2 and H 2 (Kim et al., 2009; Twigg, 1989). The reversible WGS reaction is moderately exothermic CO þ H 2 O2CO 2 þ H 2 DH ¼ 41.1 kJ/mol (1) The product gas from the WGS reactor, after water condensa- tion, goes to purification processes such as a pressure swing adsorption (PSA) process to produce high purity H 2 . The thermo- dynamics of the equimolar WGS reaction controls the conversion of CO to CO 2 and the reactor effluent gas composition. There are significant amounts of CO and CO 2 in the equilibrium composition of the conventional WGS reactor (Twigg, 1989). Consequently, the reactor effluent gas requires extensive purification by the PSA process in order to produce pure H 2 . The H 2 recovery of such a typical PSA process is 75–90% because a part of the H 2 product is used to regenerate the adsorbent in the cyclic PSA process. Therefore, a considerable amount of H 2 produced by the upstream WGS reaction is lost. The above-described thermodynamic limitations of the conventional WGS reaction can be circumvented by the ‘‘sorption enhanced reaction (SER)’’ concept. The SER concept is based on the Le Chatelier’s principle and combines a reversible gas phase reaction with selective removal of a reaction product from the gas phase of the reaction zone by selective sorption in a single unit operation, thereby, driving the reaction more to the product side (Carvill et al., 1996). The SER concept has been applied to and studied in the steam methane reaction (Derevschikov et al., 2011; Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2012.02.015 n Corresponding author. Tel.: þ82 2 3290 4851; fax: þ82 2 926 6102. E-mail address: kibonglee@korea.ac.kr (K.B. Lee). Chemical Engineering Science 73 (2012) 431–438