Isotherm model for high-temperature, high-pressure adsorption of CO2CO2 and H2OH2O on K-promoted hydrotalcite

• We measured breakthrough curves for CO2CO2 and H2OH2O adsorption at 400 °C, up to 24 bar.
• Surface adsorption occurs at specific sites for CO2CO2 or H2OH2O up to 5 bar.
• CO2CO2 and H2OH2O adsorb competitively in nanopores at higher partial pressures.
• Adsorption isotherm and sorption kinetics have been validated with a reactor model.

Sorption-enhanced water-gas shift (SEWGS) combines the water–gas shift reaction with in situ adsorption of CO2CO2 on potassium-promoted hydrotalcite (K-HTC) and thereby allows production of hot, high pressure H2H2 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 CO2CO2 and H2OH2O on K-HTC at 400 °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 CO2CO2 or H2OH2O. 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.

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