Energy & Fuels, Vol.33, No.7, 6634-6640, 2019
Swapping and Enhancement of Guest Occupancies in Hydroquinone Clathrates Using CH4 and CO2
In this study, we investigated guest behaviors of CO2 and CH4 molecules during the initial formation of hydroquinone (HQ) clathrates and then the swapping reactions of guest-loaded HQ Two experimental pressures of 3.0 and 5.0 MPa were selected for both formation and swapping reactions at room temperature, both of which are known to be in the stability region of HQ clathrates. Prepared samples were analyzed by a series of spectroscopic measurements to obtain qualitative and quantitative information on guest molecules in clathrate cages. After the initial formation, CO2 molecules showed higher cage occupancies of 90.1 +/- 3.9 and 99.4 +/- 2.7%, with full conversion into the clathrate form, compared to the values of 61.9 +/- 4.2 and 64.6 +/- 4.5% with incomplete conversion for CH4 molecules at 3.0 and 5.0 MPa, respectively. In the subsequent swapping reactions, 72-77% of CH4 molecules in guest-loaded HQ clathrate are replaced with CO2, while only 6-9% of CO2 molecules are replaced with CH4 molecules. The experimental results demonstrated that kinetic behaviors of CO2 molecules are better favored than CH4 molecules in HQ clathrates, even though their thermodynamic equilibria are almost identical.