화학공학소재연구정보센터
Chemical Engineering Journal, Vol.369, 686-693, 2019
Kinetic CO2 selectivity in clathrate-based CO2 capture for upgrading CO2-rich natural gas and biogas
Upgrading CO2-rich natural gas or biogas through CO2 capture is essential to reduce greenhouse gas emissions and to increase its energy density. In this study, clathrate-based CO2 capture from CO2-rich natural gas or biogas was investigated with a primary focus on kinetic CO2 selectivity. The time-dependent CO2 selectivity during clathrate formation for pure water, tetrahydrofuran (THF, 5.6 mol%) solution, and tetra-n-butylammonium chloride (TBAC, 3.3 mol%) solution was examined through direct composition analysis and in situ Raman spectroscopy. In pure water, the CO2 composition in the clathrate phase was much higher at the early stage of clathrate formation than that at equilibrium, indicating that CO2 is kinetically and thermodynamically selective. For both the THF (5.6 mol%) and TBAC (3.3 mol%) solutions, the CO2 composition in the clathrate phase was almost constant during clathrate formation. However, the TBAC (3.3 mol%) solution showed significantly higher CO2 composition (similar to 74%) throughout the reaction, whereas the THF (5.6 mol%) solution exhibited enrichment of CH4 in the clathrate phase. The experimental results clearly demonstrate that CO2 selectivity is dependent on both kinetics and equilibrium of clathrate hydrates and that the addition of thermodynamic promoters, such as THF and TBAC, can affect kinetic CO2 selectivity as well as equilibrium CO2 selectivity in the clathrate phase.