Abstract
Carbon dioxide capture and sequestration is becoming an important means for reducing anthropogenic carbon dioxide emission and global warming. One of the most developed technologies for carbon dioxide capture from post-combustion flue gas is the absorption/stripping process utilizing aqueous alkanolamine solutions. However, this process is still energy intensive. This work explores the feasibility of reducing energy consumption using alternative solvents and process configurations. Firstly, we measured the solubilities of carbon dioxide in the deep eutectic solvent, Reline with different water contents. Water can act as an anti-solvent to strip carbon dioxide from Reline. However, a concentration swing process based on anti-solvent effect is non-competitive due to the low carbon dioxide capacity in Reline. The carbon dioxide loadings in the amino acid salt, [Choline][Pro], with different water contents were measured. High water content results in the formation of bicarbonate ion and increase carbon dioxide loadings. Water acts as a co-solvent rather than anti-solvent. A thermal energy free stripping process was proposed by using ion exchange resin. Chloride form resin was used to convert saturated [Choline][Pro] solution to choline chloride and L-proline, driving out dissolved carbon dioxide. Hydroxide form resin was used to regenerate [Choline][Pro] from the mixture of choline chloride and L-proline. Finally, a simplified method to evaluate the energy consumption of different carbon dioxide absorbents was developed. It was found that [Choline][Pro] in PEG200 solution is the energy-efficient alternative absorbent because of its high capacity and negligible solvent vaporization loss. However, high viscosity of the solution becomes the bottleneck of its application. Based on results of this study, two directions for developing new solvent systems and processes are proposed. One way is to dissolve innovative amino acid salts in non-viscous solvent of low volatility. Alternatively, the thermal energy free stripping process can be applied to aqueous solutions of amino acid salts.