Performance of synthetic CaO-based sorbent pellets for CO2 capture and kinetic analysis

Abstract

Three powdery CaO-based sorbents were synthesized respectively from calcium acetate and three different inert support precursors. Based on these sorbent powder, sorbent pellets without and with pore forming material (cellulose) were fabricated using an extrusion-spheronization method. Cyclic CO2 sorption performance of all powdery sorbents and sorbent pellets were tested in a TGA. It was found that introduction of inert supports was beneficial for enhancing the CO2 capture capacity of CaO. For sorbent powder, sintering was retarded due to high thermal stability of inert supports and good dispersion of CaO particles among inert supports, resulting in better performance of synthetic sorbent than calcined CaCO3. However, CO2 uptake of sorbent pellets deteriorated dramatically owing to damage of pore structure caused in the extrusion process. Cn and Xn was even lower than 0.1 g CO2/g sorbent and 20% for sorbent pellets during the 25th cycle. Adding cellulose was found to be effective for promoting the CO2 sorption capacity of sorbents which was mainly ascribed to enlarged specific surface area and pore volume during cellulose burning. Two kinetic models were used to understand the mechanism of the carbonation reaction and the models were proven to be feasible for analyzing the chemical reaction controlled stage and diffusion controlled stage in the carbonation process. Reaction rate constants obtained from kinetic calculation can also be used to explain the different performance between different types of sorbents.