New Insights on Gas Hydroquinone Clathrates Using in Situ Raman Spectroscopy: Formation/Dissociation Mechanisms, Kinetics, and Capture Selectivity

Hydroquinone (HQ) is known to form organic clathrates with different gaseous species over a wide range of pressures and temperatures. However, the enclathration reaction involving HQ is not fully understood. This work offers new elements of understanding HQ clathrate formation and dissociation mechanisms. The kinetics and selectivity of the enclathration reaction were also investigated. The focus was placed on HQ clathrates formed with CO 2 and CH 4 as guest molecules for potential use in practical applications for the separation of a CO 2 /CH 4 gas mixture. The structural transition from the native form (α-HQ) to the clathrate form (β-HQ), as well as the reverse process, were tracked using in situ Raman spectroscopy. The clathrate formation was conducted at 323 K and 3.0 MPa, and the dissociation was conducted at 343 K and 1.0 kPa. The experiments with CH 4 confirmed that a small amount of gas can fill the α-HQ before the phase transition from α- to β-HQ begins. The dissociation of the CO 2 -HQ clathrates highlighted the presence of a clathrate structure with no guest molecules. We can therefore conclude that HQ clathrate formation and dissociation are two-step reactions that pass through two distinct reaction intermediates: guest-loaded α-HQ and guest-free β-HQ. When an equimolar CO 2 /CH 4 gas mixture is put in contact with either the α-HQ or the guest-free β-HQ, the CO 2 is preferentially captured. Moreover, the guest-free β-HQ can retain the CO 2 quicker and more selectively.