Absorption of Carbon Dioxide at High Temperature with Molten Alkali Carbonate Using Bubble Column Reactor

The purpose of this study is to examine the possibility of establishing a novel CO2 absorption process with molten alkali carbonate using a bubble column reactor. In our previous study, a hot CO2 recovery process using Li4SiO4 suspended in molten Li2CO3–K2CO3 was developed. In the process, molten alkali carbonate itself showed great potential for CO2 absorption at high temperature. If a hot CO2 absorption process were established using only molten alkali carbonate, it could make the system simpler and the operating temperature range could be extended without the limitation of reaction temperature of solid absorbent. In the study, molten Li2CO3, Na2CO3, K2CO3 and its eutectic mixture were selected as CO2 absorbent. A bubble column was chosen as the device for gas absorption at high temperature. First, the CO2 absorption performance of each single molten alkali carbonate was investigated. The result showed that the molten Li2CO3 had a great ability to absorb CO2 at high temperature. Li2O was thought to be produced by decomposition of Li2CO3 during the melting and purging process and a reaction of CO2 with Li2O occurred during the absorption process. Further, the CO2 absorption performance of eutectic mixture increased exponentially with increasing the ratio of Li2CO3 in composition. Second, the possibility of establishing a CO2 absorption process using molten Li2CO3 was examined. The overall CO2 absorption process in the bubble column was investigated and the experimental results showed that the mass transfer of CO2 into molten Li2CO3 was the rate-controlling step. The operational conditions of the bubble column were optimized. The super cial gas velocity was an important operational parameter that a ected both the CO2 absorption rate and total amount of CO2 nally absorbed in the bubble column. The operating temperature also greatly a ected the amount of absorbed CO2.