Li-LSX-zeolite evaluation for post-combustion CO₂ capture

Lithium low silica X type (Li-LSX) zeolite is typically used for industrial N2/O2 separation processes, but its potential as a carbon dioxide capture sorbent has not been fully evaluated yet. In this work, Li-LSX zeolite was investigated as CO2 sorbent under post- combustion conditions in TGA and Fixed-bed configurations. The maximum adsorption capacity and CO2/N2 selectivity were determined to be 4.43 mmol g-1 and 85.7 at 60ºC and in presence of 14% CO2, using a packed bed configuration. The CO2 and N2 adsorption capacity was decreased of 10 mol% when the initial calcination temperature was raised from 60 to 300ºC due to a decreased micropore surface. However, the high calcination temperature increased the CO2 selectivity to 128.1 and increased the adsorption rates due to enhanced basicity (1 order of magnitude) and external surface (+75-80%) in the Li-LSX zeolite.
The sorption stability at 60ºC was found to be excellent during 85 sorption cycles over 35 hour period with Li-LSX showing negligible difference in adsorption capacity throughout the cycles and a working capacity of 2.45 mmolCO2/g after an initial calcination at 550°C (2 min) and cyclic adsorption at 60°C (6 min) and desorption at 420°C (5 min). The Avrami kinetic model shows the coexistence of different adsorption mechanisms. CO2 adsorption rate increased with the increasing CO2 partial pressure, as a result of the facilitated CO2 diffusion processes. Film diffusion was determined as the rate-limiting step for CO2 adsorption. Therefore, based on these findings, Li-LSX represents a promising sorbent for post-combustion carbon capture.