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Sorption-enhanced water-gas shift (SEWGS) is a promising technology for precombustion CO2 capture with high energy efficiency. Hydrotalcite-based adsorbents were studied as possible solid sorbents for pressure swing adsorption under SEWGS conditions. They show high thermal and mechanical stability with sufficiently high cyclic working capacity and fast adsorption kinetics. The regenerations step (desorption of CO2 by feeding steam to the adsorbent) is slower and limits the cyclic working capacity of the adsorbent. It was found that a higher operating temperature is beneficial because of enhanced desorption kinetics. Steam induces the desorption of a second adsorption site available for CO2 which cannot be desorbed with N2. Different adsorption sites are present on the hydrotalcite material. On the basis of a dedicated set of high-pressure breakthrough experiments an adsorption isotherm has been developed which describes the interaction of CO2 and H2O with the hydrotalcite-based adsorbent over the relevant range of partial pressures. Based on the isotherm and a linear driving force approximation for intraparticle mass transfer, a reactor model has been constructed for the simulation and optimization of SEWGS cycles. A parameter study of SEWGS cycles shows that the high-pressure rinse steam improves the CO2 product purity, while the low-pressure steam purge mainly serves to improve the CO2 capture ratio. Finally, a comparative analysis of the required work of precombustion separation of CO2 and H2 shows that SEWGS outperforms conventional technologies for hydrogen-carbon dioxide separation, partly because of its inherently high CO2 capture ratio.

Thermogravimetric analysis (TGA) was used to study the adsorption phenomena of CO2 and H2O on a hydrotalcite-based adsorbent to be used for sorption-enhanced Water-Gas-Shift (SEWGS). The adsorption of CO2 and H2O and the interaction between the two can be described when considering the presence of at least three different sites (2 for CO2 and 1 for H2O) participating in the adsorption phenomena at elevated temperatures. The experiments confirm that the regeneration conditions are crucial for activating more sites for CO2 adsorption and are therefore the limiting factor for the cyclic working capacity of the adsorbent.

Sorption-enhancedwater-gas shift (SEWGS) combines thewater–gas shift reactionwith in situ adsorption of CO2 on potassium-promoted hydrotalcite (K-HTC) and thereby allows production of hot, high pressure H2 fromsyngas in a single process. SEWGS is a cyclic process, that comprises high pressure adsorption and rinse, pressure equalisation, and lowpressure purge. In order to design theSEWGS process, the equilibria and kinetics of adsorptionmust beknownfor the entire pressure range.Here, amulticomponent adsorptionisothermis presented for CO2 and H2O 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 isothermconsists of a lowpartial 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

This paper presents an experimental and modeling investigation for a novel technique of low temperature high purity hydrogen production using sorption assisted catalytic methane reforming in a laboratory – scale fixed bed adsorptive reactor. The performance of methane steam reforming is experimentally tested over a newly developed catalyst – sorbent materials. Rh/CeaZr1-aO2 is employed as an efficient low temperature catalyst for steam reforming and autothermal reforming of methane. K-promoted hydrotalcites, Zr-doped K-promoted hydrotalcites, and lithium zirconate are employed as newly developed candidate sorbents for high purity hydrogen production at temperatures lower than 550oC. Experimental and modeled results are compared to the conventional Ni – based catalytic reforming processes. An enhanced methane conversion of 84%, which is the equilibrium conversion is attained using Hydrotalcites/Ni – based sorption enhanced autothermal reforming at operational conditions of 500oC, 4.47 bar, steam/carbon ratio of 6, oxygen/carbon ratio of 0.45 and space velocity of 3071 hr-1. The corresponding hydrogen yield and purity on dry basis are 3.6 and 95%, respectively. The lithium zirconate – based process demonstrated a gain of enhanced methane conversion of 99.5% and dry basis hydrogen purity of 99.5% achieved at the same conditions. The influence of major parameters of steam/carbon, oxygen/carbon, gas and catalyst temperatures, pressure, gas space velocity, and feed contamination is also examined.