Fabrication of lithium silicates from zeolite for CO2 capture at high temperatures

Li4SiO4 has been regarded as one of the most promising high-temperature CO2 sorbents. However, for practical applications, its CO2 sorption kinetics, cycling stability and sorption properties at lower temperatures or lower CO2 concentrations have to be improved. In this contribution, four Li4SiO4 sorbents were synthesized from zeolite precursors MCM-41, MCM-48, TS-1, and ZSM-5. The CO2 uptake, cycling stability and the optimal CO2 sorption conditions were investigated. Among the samples, MCM-41-Li4SiO4 showed the best cycling stability at 650 degrees C, with a stable reversible CO2 uptake of 29.1 wt% under 100 vol% CO2 during 20 cycles. But its sorption kinetics and CO2 uptakes at lower temperatures and lower CO2 concentrations need to be improved. We then demonstrated that the sorption kinetics can be improved by modifying the MCM-41 precursor with metals such as Al, Ti, Ca, and Na. The Na-MCM-41-Li4SiO4 sample exhibited the highest sorption rate, and reached the equilibrium sorption capacity close to the theoretical value of 36.7 wt% within 20 min. In addition, we proved that coating the MCM-41-Li4SiO4 with Na2CO3 and K2CO3 can significantly increase the CO2 uptakes at lower temperatures (e.g. 550 degrees C) and lower CO2 concentrations (10-20 vol%). At 550 degrees C and under 20 vol% CO2, 15 wt% K2CO3 -MCM-41-Li4SiO4 and 10 wt% Na2CO3 -MCM-41-Li4SiO4 sorbents resulted in a CO2 uptake of 32.2 wt% and 34.7 wt%, respectively, which are much higher than that of MCM-41-Li4SiO4 (11.8 wt%). These two sorbents also showed good cycling stability. The promoiting mechasnim by alkali carbonate coating was discussed by a double-shell model. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.