Jean-Philippe Torré

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 CO2 and CH4 as guest molecules for potential use in practical applications for the separation of a CO2/CH4 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 CH4 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 CO2-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 CO2/CH4 gas mixture is put in contact with either the α-HQ or the guest-free β-HQ, the CO2 is preferentially captured. Moreover, the guest-free β-HQ can retain the CO2 quicker and more selectively.

Hydrate-Based Removal of CO2 from CH4 + CO2 Gas Streams

This chapter is concerned with CO2 separation from CO2 + CH4 mixtures by means of gas hydrates. It describes and discusses the laboratory experimentation and the metrics of CO2 separation, which define, for given gas mixture and experimental conditions, the various parameters that describe the efficiency of the capture process. A review is then presented of the few available experimental results obtained with CO2 + CH4 mixtures, emphasizing the role of additives, whether water‐soluble or ‐insoluble molecules. The chapter points out possible directions worth being pursued to enhance this selectivity, such as that consisting in forming hydrate in some moist mesoporous materials. It presents and discusses the performance indicators and some of the routes explored for improving selectivity. These routes combine the use of chemical promoters with “non‐chemical” methods investigated so far mainly for increasing the rate of formation of gas hydrate.