The effect of additive molecular diameters on the hydrate-based CO2 capture from simulated biogas

Lots of thermodynamics and kinetics accelerators have been used in the process of mixture gas separation by hydrate method, but there is still lack of valid screening method for seeking reliable and effective hydrate promoters. In this work, the effects of additive molecular diameter on the hydrate phase equilibrium condition and the quantity of hydrogen bond donor and accepter of additive on the separation efficiency during CO2 (40.0 mol%)/CH4 hydrate formation process were investigated. The results demonstrated that the larger molecular diameter of additive in cyclopentane (CP), tetrahydrofuran (THF) and tetrahydrothiophene (THT) systems, the phase equilibrium promotion effect of additive is more significant. And the empirical equations were proposed for predicting the phase equilibrium condition of CO2/CH4 hydrate under the impact of additive with different molecular diameters. Moreover, on account of the quantity of hydrogen bond donor and acceptor of additive were different, the degree of mutual dissolution between additive molecule and aqueous solution was different, so that the number of additive molecules that could participate in the formation of hydrate was different, which had a certain impact on the separation efficiency.