(621cc) The Effectiveness of Sorption Enhanced Reaction Processes

Abstract: The conversion of equilibrium reaction can be carried to completion using an adsorbent that selectively removes one of the reaction products.  It has been found experimentally that it is possible to produce fuel cell grade hydrogen from water gas shift and steam conversion of methane by selective adsorption of CO₂.  While it is know that the presence of a selective adsorbent will improve a reversible reaction, complete conversion requires more complex interaction of convection, reaction and adsorption. In this work the reactant and product concentration profiles are simulated in sorption enhance reaction processes. By neglecting the mass transfer resistance for both reaction and adsorption, the effects of the reaction kinetics and shape of isotherm are investigated. The proposed model with instant local equilibrium and isothermal and isobaric operating conditions was applied to two different cases with different reaction stoichiometric parameters, the water gas shift reaction and the hydrogen sulfide decomposition reaction. It was found out that in order to obtain high purity product with sorption enhanced reaction processes all the key parameters, including the reaction equilibrium constant, the reaction kinetics constant and the adsorption isotherm parameter, need to be appropriate. To have a sharp breakthrough curve the adsorption isotherm needs to be the favorable shape according to the range of adsorbate concentration in the reactor. For reactions with slow kinetics increasing the reactor length may help improving the purity of the product, however, the shape of the breakthrough curve won’t be changed. The stoichiometric parameters affect the product concentrations as shown in the case the hydrogen sulfide decomposition where the initial molar fraction of sulfur inside the reactor needs to be as low as 1E-10 to produce high purity hydrogen.