Isotherm model for high-temperature, high-pressure adsorption of CO2 and H2O on K-promoted hydrotalcite

Sorption-enhanced water-gas shift (SEWGS) combines the water-gas shift reaction with in situ adsorption of CO2 on potassium-promoted hydrotalcite (K-HTC) and thereby allows production of hot, high pressure H-2 from syngas in a single process. SEWGS is a cyclic process, that comprises high pressure adsorption and rinse, pressure equalisation, and low pressure purge. In order to design the SEWGS process, the equilibria and kinetics of adsorption must be known for the entire pressure range. Here, a multicomponent adsorption isotherm is presented for CO2 and H2O on K-HTC at 400 degrees C and 0.5-24 bar partial pressure, that has been derived from integrated experimentally determined breakthrough curves with special attention being given to the high pressure interaction. The experimental results can be well described by assuming that the isotherm consists of a low partial pressure surface adsorption part and a high partial pressure nanopore adsorption part. Surface adsorption occurs at specific and different sites for CO2 or H2O. In contrast, the nanopore adsorption mechanism is competitive and explains the interaction observed in the capacity data at partial pressures over 5 bar. Based on the characteristics of the sorbent particles, a linear driving force relation has been derived for sorption kinetics. Adsorption isotherm and linear driving force kinetics have been included in a reactor model. Model predictions are in agreement with breakthrough as well as regeneration experiments. (C) 2014 Elsevier B.V. All rights reserved.