CO2 capture from flue gas using clathrate formation in the presence of thermodynamic promoters

Tetrahydrofuran (THF) as a water-soluble sll clathrate former, cyclopentane (CP) as a water-insoluble slI clathrate former, and tetra n-butyl ammonium chloride (TBAC) as a water-soluble semiclathrate former were used to investigate their thermodynamic promotion effects on clathrate-based CO2 capture from simulated flue gas. The phase equilibria of CO2 (20%) + N-2 (80%) + promoter clathrates at different promoter concentrations revealed that the presence of THF, CP, and TBAC could significantly reduce the clathrate formation pressure. THF solutions provided the highest gas uptake and steepest CO2 concentration changes in the vapor phase, whereas TBAC solutions showed the highest CO2 selectivity (-61%) in the clathrate phase. CP solutions exhibited a slower formation rate, but their final gas uptake and CO2 selectivity in the clathrate phase were comparable to the THF solutions. Raman spectroscopy confirmed the enclathration of both CO2 and N-2 in the clathrate cages and a structural transition due to the inclusion of promoters in the clathrate phase. The overall experimental results indicate that TBAC is a viable thermodynamic promoter for clathrate-based CO2 capture from simulated flue gas, considering the lower pressure requirement for clathrate formation, higher CO2 enrichment in the clathrate phase, non-toxicity, and non-volatility. (C) 2016 Elsevier Ltd. All rights reserved.