Crystal engineering of reticular materials for gas-and liquid-phase hydrocarbon separation

Crystal engineering focuses upon the design, properties, and applications of crystals, whereas reticular chemistry involves linking molecular building blocks to create network structures. The intersection of these areas is evident in the number of systematic studies of structure/function relationships concerning porous coordination networks (PCNs) and covalent organic frameworks (COFs). PCNs and COFs are inherently modular in nature and therefore amenable to systematic fine-tuning of both pore size and chemistry in a manner that is infeasible for other classes of porous solid. This review highlights how this exquisite control over pore size and chemistry has enabled the development of a new generation of physisorbents that are effective in the context of industrially relevant hydrocarbon (HC) separations. The motivation behind such reticular sorbents is the need to replace today's energy-intensive HC separation methods with more sustainable alternatives. Physisorbents are attractive in this context as they can offer the high selectivity needed for trace removal of impurities along with relatively low energy of recycling. This review details how crystal engineering strategies offer precise control of pore size and chemistry to enable HC selectivity to reach hitherto unprecedented levels. Nevertheless, despite these property advances, challenges remain to be addressed before commercial adoption becomes feasible.