Process Intensification in Hydrogen Production from Biomass-Derived Syngas Mitra Abdollahi, † Jiang Yu, † Hyun Tae Hwang, † Paul K. T. Liu, ‡ Richard Ciora, ‡ Muhammad Sahimi, † and Theodore T. Tsotsis* ,† Mork Family Department of Chemical Engineering and Materials Science, UniVersity of Southern California, Los Angeles, California 90089-1211, and Media and Process Technology, Inc., Pittsburgh, PennsylVania 15328 Biomass is a renewable and worldwide-abundant energy resource that shows great potential for environmentally benign power generation by minimizing greenhouse gas emissions. A “one-box” process has been proposed and studied in order to economically produce pure hydrogen from biomass-derived syngas in the presence of its common impurities through the use of the water gas shift (WGS) reaction. The heart of the process is a catalytic membrane reactor making use of carbon molecular sieve (CMS) membranes and an impurity-tolerant commercial Co/Mo/Al 2 O 3 catalyst. CMS membrane stability was investigated in the presence of model tar and organic vapor compounds at experimental conditions similar to the WGS reaction environment. Experimental studies were carried out utilizing simulated biomass-derived syngas containing H 2 S and NH 3 as key impurities, which was fed into the catalytic membrane reactor to produce a contaminant-free hydrogen product using the WGS reaction. The reactor performance has been investigated for various experimental conditions, and has been compared with simulation results from a mathematical model. The model was also used to study the effect of various parameters on system performance. A key observation is that both the membranes and the catalyst show satisfactory stability in the presence of impurities typically encountered in biomass-derived syngas, and that the system shows good performance, delivering higher CO conversion and hydrogen purity than when using a traditional reactor system. 1. Introduction With increasing demand for energy, there is an important need to develop new technologies based on alternative fuels that can substitute for crude oil. There are also significant environmental concerns associated with petroleum use. Hydrogen as a fuel is an important example of a noncarbon energy carrier, which can be produced from various renewable and nonrenewable sources. 1 Hydrogen burns cleanly and produces more energy on a per mass basis than any other fuel; if widely adopted for both mobile and stationary power generation, it would reduce the emissions of pollutants typically associated with power production, and would potentially diminish the prospect of global warming. The abundant availability of coal and biomass in the United States makes them both attractive and comparatively inexpensive energy sources for H 2 production. 2 The possibility of H 2 production from coal-derived syngas in the presence of its impurities has been previously studied by our group. 3 Biomass, however, has several advantages over coal; it is a renewable energy source, abundantly available in the world. It comes in various forms, ranging from agricultural and forestry residues and municipal and industrial waste, to terrestrial and marine crops grown specifically for energy production. 4 It consumes atmospheric CO 2 during growth; therefore, producing hydrogen from biomass has the potential to result in substantially lower net CO 2 emissions than when using coal. Though biological processes have been proposed for H 2 production from biomass, they suffer from low production rates and from process inefficiencies. 5 As a result, as with coal, gasification remains today the main method for H 2 production from biomass. It converts the biomass, in the presence of air (oxygen) and/or steam, into a syngas consisting mainly of H 2 , CO, CO 2 ,N 2 (when air is used), and lower molecular weight (MW) hydrocarbons, principally CH 4 , as well as smaller con- centrations of organic vapors, and high MW compounds known collectively as tars. 6,7 The latter are a major issue in biomass gasification that must be dealt with during process development. Appropriate modifications in gasifier design and operating conditions along with using catalysts and additives, as well as novel technologies such as supercritical water gasification 8-11 help to minimize tar formation, and also to convert the hydrocarbon vapors in the syngas into H 2 and CO via steam reforming. However, their presence in the syngas cannot be completely eliminated and they must, therefore, be taken into account during the design of downstream processes for further syngas cleanup and processing. Maximizing the hydrogen content in the syngas requires cooling it down to remove its contaminants, especially H 2 S and NH 3 , and then heating it up again to further react it with steam in water-gas shift (WGS) reactors. The WGS reaction is exothermic and its equilibrium constant decreases with tem- perature. Therefore, typically two reactors, one operating at high temperature (HTS) using Fe/Cr-based catalysts and another operating at lower temperature (LTS) using Cu/Zn-based catalysts, are used to overcome both kinetic and equilibrium limitations, and to increase the CO conversion. Finally, the gas stream exiting the WGS reactors must be treated further in additional separation units to produce pure hydrogen to be used in both stationary and mobile power applications. Aznar et al., 12 for example, used an HTS followed by an LTS reactor downstream from a fluidized-bed biomass gasifier and a steam- reforming catalytic bed. They obtained CO conversions higher than 90% and H 2 content as high as 73 vol% on a dry basis. The CO conversion and the increase in H 2 content correlated with the steam/CO ratio in the syngas at the inlet of the HTS reactor. Effendi et al. 13 studied the H 2 production from a contaminant-free model biomass-derived syngas through a combination of steam reforming (in excess steam) in a fluidized- bed reactor over a Ni/Al 2 O 3 catalyst, followed by two fixed- * To whom correspondence should be addressed. E-mail: tsotsis@ usc.edu. Phone: 213 740 2069. Fax: 213 740 8053. † University of Southern California, Los Angeles. ‡ Media and Process Technology, Inc. Ind. Eng. Chem. Res. 2010, 49, 10986–10993 10986 10.1021/ie100620e  2010 American Chemical Society Published on Web 09/15/2010