Post-Combustion Carbon Dioxide Capture using Alumina-Supported Potassium Carbonate

Abstract

The solid sorbent-based CO2 capture process has been studied extensively in recent years as a cost-effective and efficient method for capturing CO2. Among various solid sorbents, K2CO3 has been selected for further investigation and evaluation in this work due to its high theoretical CO2 capture capacity, favorable carbonation/regeneration temperatures, relatively low cost and high selectivity. Firstly, the effect of different synthesis techniques and alumina-based supports was investigated on the capturing performance of K2CO3-based solid sorbents. For this purpose, three types of alumina-based supports and two preparation techniques were employed. It was shown that surface area and hydrophilicity of the supports are important factors in determining the capturing efficiency of the sorbents. In the second paper, a highly-efficient alumina-based support (alumina-aerogel) with a significantly large surface area (over 2000 m2/g) was synthesized. The alumina-aerogel-supported K2CO3 showed a surprisingly high CO2 capture capacity of 7.2 mmol CO2/g K2CO3. The effect of key operating parameters (e.g. carbonation temperature and H2O-to-CO2 flowrate ratio) was studied on the CO2 uptake, and the optimum values were found to be 56.1 ºC and 1.1, respectively. In the third paper, another technique (core-shell) was utilized to improve the cyclic CO2 uptake of K2CO3-based sorbents. In the core-shell technique, the alumina support was shelled with another material (TiO2, SiO2 and ZrO2) to improve the chemical stability and capturing capacity of the sorbents. Among various synthesized samples, K2CO3/Boehmite-TiO2 showed the best performance with a CO2 uptake of 6.61 mmol CO2/g K2CO3. In addition, three kinetic models were applied to investigate the adsorption rate of CO2 in the carbonation step, and Avrami was the best-fit model with a regression coefficient of 0.99. Finally, the last paper investigates the impact of textural properties of the support, including surface area, pore volume and pore size on the capturing capacity of K2CO3-based sorbents. For this purpose, supports with varied textural properties were synthesized by using specific surfactants. It was found that apart from surface area and pore volume, pore size had a significant impact on the CO2 uptake. By increasing the size of mesopores, CO2 uptake improved as well.