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Ž. The Sorption Enhanced Reaction Process SERP is a novel concept for hydrogen production by steam-methane reform-Ž . ing SMR . It uses a fixed-bed reactor packed with an admixture of a SMR catalyst and a chemisorbent for selective re-Ž . moval of carbon dioxide one of the reaction products from Ž . the reaction zone Hufton et al., 1999; Sircar et al., 2000 . The unique steps of the SERP concept allow direct production of ;90qmol. % hydrogen from the reactor at the reaction pressure. The impurities in the hydrogen product consist Ž . Ž primarily of methane -10 mol. % and trace quantities -. 50 ppm level of carbon oxides. The chemisorbent is periodically regenerated by using the principles of pressure swing Ž . adsorption PSA . The reaction can be carried out at a moderate temperature range of 450᎐550ЊC, which is much less Ž . than that of a conventional SMR reactor 800᎐900ЊC packed with reforming catalyst only. The purpose of this article is to describe the actual cyclic performance of the SERP concept for hydrogen production using a pilot-scale apparatus with a Ž . proprietary SMR catalyst noble metal on alumina and a Ž proprietary CO chemisorbent pelletized potassium carbon-2 . ate promoted hydrotalcite , which has been described earlier Ž .The SERP consists of the following cyclic steps:Step a: Sorption-Reaction. The reactants consisting of a mixture of steam and methane at pressure P and tempera-R ture T are passed through the feed end of a packed-bed R reactor containing the admixture of the catalyst and the chemisorbent. The reactor is previously pressurized at temperature T with steam to a pressure level of P . A hydro-R R gen-enriched product stream at pressure P is withdrawn R through the product end of the reactor until the carbon oxide concentration levels in the effluent gas reach a preset level. Ž .Step b: Depressurization. At the end of step a , the reactor is depressurized to near ambient pressure by withdrawing Correspondence concerning this article should be addressed to S. Sircar. desorbed and void gases through the feed end. The effluent gas is vented.Step c: E®acuation with Steam Purge. The reactor is then countercurrently evacuated to a subatmospheric pressure level of P , while introducing ambient pressure steam at D temperature T through the product end of the reactor. The R effluent gas, consisting mostly of desorbed CO and steam, is 2 vented.Step d: Pressurization. Finally, the reactor is countercurrently pressurized from P to P by introducing steam at D R temperature T through the product end while the feed end R is kept closed. The reactor is now ready to repeat a new cycle starting from step a. The reactor is externally heated in order to carry out all four steps of the process under nearly isothermal conditions. Ž . The heat is used to i supply the net endothermic heat of w reaction created by simultaneous endothermic steam Ž . Ž . methane reforming SMR , exothermic water gas shift WGS ,x Ž . and exothermic chemisorption of CO during step a of the 2 Ž . cycle and ii provide the heat...

Variations of perturbation chromatography were used to measure Henry's constants and equilibrium isotherms of various gases on silicalite. Three dgferent adsorbent samples were analyzed ( commercial powder and extruded pellets, and laboratory-synthesized crystals), and no discernable differences among the measured parameters were noted. Henry's constants for the linear alkanes were determined from isobaric and nonisobaric chromatography experiments. They were correlated successfully with temperature and the number of carbon atoms per adsorbate molecule. Isotherms were measured from concentration pulse or tracer/concentration pulse chromatography techniques. The Flory-Huggins version of the vacancy solution model was used to correlate pure gas isotherms and predict binary behavior successfully.

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A novel route for precombustion decarbonization is the sorption-enhanced water−gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water−gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic capacity can be amplified by purging with steam. From previous studies is it known that for SEWGS applications, hydrotalcite-based materials are particularly attractive as sorbent, and commercial high-temperature shift catalysts can be used for the conversion of carbon monoxide. Tablets of a potassium promoted hydrotalcite-based material are characterized in both breakthrough and cyclic experiments in a 2 m tall fixed-bed reactor. When exposed to a mixture of carbon dioxide, steam, and nitrogen at 400 °C, the material shows a breakthrough capacity of 1.4 mmol/g. The sharp adsorption front is accompanied by an exotherm that travels along the bed. Even after breakthrough carbon dioxide continues to be taken up by the bed albeit at a much lower rate. It is shown that the total capacity of this material can exceed 10 mmol/g, which has not been reported before. Desorption curves indicate efficiencies of removing additional carbon dioxide by purging with low-pressure, superheated steam at various flow rates. During cyclic operation for more than 1400 adsorption and desorption cycles, the carbon dioxide slip is very low and remains stable which indicates that carbon recoveries well above 90% can be obtained. The sorbent shows a stable cyclic capacity of 0.66 mmol/g. In subsequent experiments the material was mixed with tablets of promoted iron−chromium shift catalyst and exposed to a mixture of carbon dioxide, carbon monoxide, steam, hydrogen, and nitrogen. It is demonstrated that carbon monoxide conversion can be enhanced to 100% in the presence of a carbon dioxide sorbent. At breakthrough, carbon monoxide and carbon dioxide simultaneously appear at the end of the bed. During more than 300 cycles of adsorption/reaction and desorption, the capture rate, and carbon monoxide conversion are confirmed to be stable. Two different cycle types are investigated: one cycle with a CO2 rinse step and one cycle with a steam rinse step. The performance of both SEWGS cycles are discussed. These experimental results will allow optimization of process conditions and cycle parameters, and especially the reduction of steam consumption needed for sorbent regeneration. The results will provide the basis for scale-up to a pilot unit, which will demonstrate precombustion decarbonization in fossil-fuels-based power generation or hydrogen production.

A novel, high temperature solid absorbent based on lithium orthosilicate (Li(4)SiO(4)) has shown promise for postcombustion CO(2) capture. Previous studies utilizing a clean, synthetic flue gas have shown that the absorbent has a high CO(2) capacity, >25 wt %, along with high absorption rates, lower heat of absorption and lower regeneration temperature than other solids such as calcium oxide. The current effort was aimed at evaluating the Li(4)SiO(4) based absorbent in the presence of contaminants found in typical flue gas, specifically SO(2), by cyclic exposure to gas mixtures containing CO(2), H(2)O (up to 25 vol. %), and SO(2) (up to 0.95 vol. %). In the absence of SO(2), a stable CO(2) capacity of ∼ 25 wt % over 25 cycles at 550 °C was achieved. The presence of SO(2), even at concentrations as low as 0.002 vol. %, resulted in an irreversible reaction with the absorbent and a decrease in CO(2) capacity. Analysis of SO(2)-exposed samples revealed that the absorbent reacted chemically and irreversibly with SO(2) at 550 °C forming Li(2)SO(4). Thus, industrial application would require desulfurization of flue gas prior to contacting the absorbent. Reactivity with SO(2) is not unique to the lithium orthosilicate material, so similar steps would be required for other absorbents that chemically react with SO(2).