Sorption-enhanced reforming of methane is an attractive option for the combined production of electricity and capture of CO2. In this process, the steam-reforming catalyst is mixed with a CO2 sorbent. During the reaction, CO2 is adsorbed, leading to an increase of the hydrogen production rate. Once the sorbent is saturated, it must be regenerated using purge gas, usually steam. The amount of steam needed for CO2 removal from the saturated sorbent determines the system efficiency of the process to a large extent. In this paper, several potassium-promoted hydrotalcite samples, both obtained commercially and prepared in-house, are tested for their suitability as a CO2 sorbent for sorption-enhanced reforming of methane. In particular, the purge gas to adsorbed CO2 ratio is determined under various operation conditions. It is shown that this ratio is still too large under the investigated conditions. Mixed with steam-reforming catalyst the hydrotalcite sorbent can adsorb sufficient CO2 to enhance the CH4 conversion to almost 100%.

No abstract

A one-dimensional reactor model has been developed to describe the performance of a sorption-enhanced steam-methane reforming and water-gas shift reactor. In part I of this paper, the model is verified using the analytical solution for the breakthrough curve and validated using the results of laboratory-scale CO 2 sorptiononly experiments. Langmuir and Freundlich isotherms are fitted to an experimentally derived adsorption isotherm, while a linear driving force model is used to describe the sorption kinetics. The breakthrough profile is accurately described using the Freundlich isotherm. This holds also when the purge flow or duration of the desorption step are decreased, provided the mass transfer coefficient is changed accordingly during the desorption step. A sensitivity analysis shows that the breakthrough profile is sensitive to the adopted isotherm model and its parameters. The molecular diffusion coefficient affects the slope of the breakthrough curve, while particle size and heat of adsorption show hardly any effect. In part II, the model will be applied to laboratory-scale sorption-enhanced steam-methane reforming experiments.

In this paper, the reactor model introduced in part I will be verified using the results of an analytical solution for the increase of CH 4 conversion over the bed and validated using the results of sorption-enhanced steammethane reforming laboratory-scale experiments. An experimentally derived rate equation for the steammethane reforming reaction is used, a literature rate equation for the water-gas shift reaction. An overview of modeling work on the sorption-enhanced reaction process for steam-methane reforming performed by other groups is presented. The CH 4 and CO 2 profiles obtained from laboratory-scale experiments are quite satisfactorily described using a Freundlich isotherm. A sensitivity analysis shows that both the CH 4 and CO 2 profiles are sensitive to the adopted isotherm model and its parameters. In addition to that, the CH 4 and CO 2 profiles are sensitive to the diffusion coefficient. Neither profile is sensitive to the particle size or the heat of adsorption.

No abstract