Adsorption of CO₂ on Zeolites at Moderate Temperatures

Abstract

Pressure swing adsorption (PSA) and temperature swing adsorption (TSA) are potential techniques for removing carbon dioxide (CO2) from high-pressure fuel gas streams. Zeolites are suitable candidate sorbents for use in these processes; however, the systems would be even more energy efficient if the sorbents were operational at moderate or high temperatures, especially for the removal of CO2 from high-pressure gas streams, such as those from integrated gasification combined-cycle (IGCC) systems. Competitive gas adsorption tests with gas mixtures representing both coal combustion and coal gasification gas streams were conducted in an atmospheric flow reactor with five zeolites at 120 °C. Promising results of preferential adsorption of CO2 were observed with two of these zeolites. However, the CO2 adsorption capacity was significantly lower at 120 °C than at ambient temperature. Volumetric gas adsorption tests of CO2 and nitrogen (N2) on these two zeolites were conducted at 120 °C, up to a pressure of 300 psi (2 × 106 Pa). Both showed high CO2 adsorption capacity at high pressure. High-pressure flow reactor studies also indicated the preferential adsorption of CO2 from gas mixtures at 120 °C. CO2 adsorption rates were measured utilizing thermogravimetric analysis, and the rates were similar for the two zeolites.