High-temperature CO2 capture by doped Li4SiO4 sorbents: Scaling up adsorption and regeneration in a fixed bed reactor

The urgent need to reduce CO2 emissions has prompted increased interest in carbon capture technologies, particularly for applications in energy-intensive industries using fossil fuels. This study explores the performance of potassium carbonate (K2CO3)-doped lithium orthosilicate (Li4SiO4) sorbents for high-temperature CO2 capture in a fixed bed reactor to simulate a real adsorption process. Li4SiO4 sorbents were produced through a solid-state synthesis, and different amounts of K2CO3 were added as alkali promoter. Cylindrical pellets were fabricated via mechanical compression and tested for CO2 capture in a lab-scale packed bed system at low CO2 concentration. The effect of the adsorption temperature, the gas flow velocity, and the CO2 concentration on the pellets adsorption and regeneration capacities was investigated. The breakthrough profiles evidenced that pellets containing 30 wt% of K2CO3 achieved the highest CO2 adsorption capacity of 205.5 mg/g sorbent and a breakthrough time of approximately 80 min at 515 °C with 4 vol% CO2 concentration thanks to the formation of a molten carbonate mixture that greatly enhanced CO2 diffusivity. Long-term stability tests in the fixed bed reactor demonstrated that the pellets maintained a CO2 removal efficiency above 96 % for over 20 consecutive adsorption/desorption cycles. Additionally, a recycling method was developed, restoring macro-porosity in spent cycled pellets, which led to improved adsorption capacity (244.8 mg CO2/g sorbent) and breakthrough time (up to 120 min). These findings highlight the feasibility of using K2CO3-doped Li4SiO4 pellets in fixed bed applications for high-temperature CO2 capture, indicating their potential for scalable implementation in industrial settings.