Competing Occupation of Guest Molecules in Hydroquinone Clathrates Formed from Binary C₂H₄ and CH₄ Gas Mixtures

Abstract

When reacted with pure ethylene (C₂H₄) and pure methane (CH₄) at 2.0 and 4.0 MPa, respectively, pure hydroquinone (HQ) was converted into β-form clathrate compounds. Experimental solid-state ¹³C NMR spectra and powder X-ray diffraction patterns provided direct evidence of C₂H₄ and CH₄ enclathration in the β-form HQ clathrates. On the basis of cage occupancy from the solid-state ¹³C NMR spectra, C₂H₄ (cage occupancies of 0.81–0.88) molecules are more likely to occupy the clathrate cages than CH₄ molecules (cage occupancies of 0.38–0.39). The selective occupation by C₂H₄ was also observed for HQ clathrates formed from C₂H₄ and CH₄ gas mixtures of 10, 30, 50, 70, and 90 mol % concentrations of C₂H₄. The experimental results from this study could be applied to a clathrate-based process for separating and concentrating C₂H₄ from gas mixtures