Novel Hydroquinone-Alumina Composites Stabilizing a Guest-Free Clathrate Structure: Applications in Gas Processing

Organic clathrates formed by hydroquinone (HQ) and gases such as CO₂ and CH₄ are solid supramolecular host-guest compounds in which the gaseous guest molecules are encaged in a host framework of HQ molecules. Not only are these inclusion compounds fascinating scientific curiosities but they can also be used in practical applications such as gas separation. However, the development and future use of clathrate-based processes will largely depend on the effectiveness of the reactive materials used. These materials should enable fast and selective enclathration and have a large gas storage capacity. This article discusses the properties and performance of a new composite material able to form gas clathrates with hydroquinone (HQ) deposited on alumina particles. Apart from the general characterization of the HQ-alumina composite, one of the most remarkable observations is the unexpected formation of a guest-free clathrate structure with long-term stability (>2 years) inside the composite. Interestingly enough, in addition to a slight improvement in the enclathration kinetics of pure CO₂ compared to powdered HQ, preferential capture of CO₂ molecules is observed when the HQ-alumina composite is exposed to an equimolar CO₂/CH₄ gas mixture. In terms of gas capture selectivity toward CO₂, the performance of this new composite exceeds that of pure HQ and HQ-silica composites developed in a previous study, opening up new opportunities for the design and use of these novel materials for gas separation.