Effects of Thermodynamic Promoters on Clathrate-based CO2 Capture from Flue Gas

Abstract

In this study, tetrahydrofuran (THF) as a water miscible sII hydrate former, tetra-butyl ammonium chloride (TBAC) as a water soluble semiclathrate former, and cyclopentane (CP) as a water immiscible sII hydrate former were used for comparing their thermodynamic and kinetic performance during hydrate or semiclathrate formation and investigating gas separation efficiency. Phase equilibria of CO2 (20%) + N2 (80%) + THF (5.6mol%), TBAC (3.3mol%), and CP (5.6mol%) mixtures were measured to determine stability conditions. These thermodynamic promotors can significantly reduce the equilibrium pressure by filling large cages or partially broken large cages. Gas uptake and CO2 composition changes in the vapor phases were analyzed using gas chromatography. The enclathration of CO2 in small cages was confirmed via Raman spectroscopy. Amount of gas uptake was in the following order: TBAC＜ CP＜ THF. However, the CO2 concentration in hydrate phase after completion of hydrate or semiclathrate formation was found to be approximately 35% for THF and CP hydrate, while 60% for TBAC semiclathrates. From the overall experimental results, TBAC as the semiclathrate former is expected to be a good candidate for clathrate-based CO2 separation process from flue gas.