Experimental evaluation of Mg- and Ca- based synthetic sorbents for CO2 capture

Hydrogen with high purity can be directly derived from fossil and renewable energy sources, like natural gas, coal and biomass, by the so-called sorption-enhanced reforming (SER) and water gas shift (SEWGS) processes characterized by simultaneous CO2 capture. This paper deals with CO2 capture on a solid sorbent under cyclic (carbonation/decarbonation), industrially relevant conditions. Hydrotalcite-like compounds (double Mg/Al hydroxy-carbonates), in comparison to CaO-based sorbents, are characterized by a comparatively smaller energy demand for regeneration and the operating temperature range is much lower (200–400◦C), making them particularly attractive for SEWGS processes. Different kinds of hydrotalcite were prepared and the Mg2+/Al3+ ratio, the effect of a promoter addition and the substitution of the bivalent cation (Ca instead of Mg) were investigated, with commercial and laboratory synthesized samples. Original and heat-treated hydrotalcite samples were characterized by XRD, BET and SEM-EDX in order to detect composition, crystalline phases and morphology. Sorption capacity was investigated under cyclic conditions by means of TGA-DSC. Step-response experiments were performed in a micro-reactor to evaluate the kinetic behavior, and a first-order-with-dead-time model for gas mixing was used to fit the results and work out the CO2 dynamic load on the solid phase.