ABSTRACT
Compressibility is a fundamental property of all materials. For fluids, that is, gases and liquids, compressibility forms the basis of technologies such as pneumatics and hydraulics and determines basic phenomena such as the propagation of sound and shock waves. In contrast to gases, liquids are almost incompressible. If the compressibility of liquids could be increased and controlled, new applications in hydraulics and shock absorption could result. Here, it is shown that dispersing hydrophobic porous particles into water gives aqueous suspensions with much greater compressibilities than any normal liquids such as water (specifically, up to 20 times greater over certain pressure ranges). The increased compressibility results from water molecules being forced into the hydrophobic pores of the particles under applied pressure. The degree of compression can be controlled by varying the amount of porous particles added. Also, the pressure range of compression can be reduced by adding methanol or increased by adding salt. In all cases, the liquids expand back to their original volume when the applied pressure is released. The approach shown here is simple and economical and could potentially be scaled up to give large amounts of highly compressible liquids.
ABSTRACT
We assess the potential for formulating a porous liquid that could be used as a selective solvent for the separation of ethane and ethene. Ethane-ethene separation is performed on very large scales by cryogenic distillation, but this uses large amounts of energy. Solvents that are selective to ethane or ethene could potentially enable more efficient liquid-based separation processes to be developed, but to date such solvents have been elusive. Here, Type 3 porous liquids, which consist of microporous solids dispersed in size-excluded liquid phases, were tailored toward the separation of ethane and ethene. A high selectivity for ethene over ethane (25.6 at 0.8 bar) and a high capacity was achieved for zeolite AgA dispersed in an Ag-containing ionic liquid. Unusually for liquid phases, the selectivity for ethane over ethene (2.55 at 0.8 bar) could also be achieved using either the metal-organic framework (MOF) Cu(Qc)2 (Qc = quinoline-5-carboxylate) dispersed in sesame oil or ZIF-7 in sesame oil, the latter showing gated uptake. The efficiency of the Cu(Qc)2 synthesis was increased by developing a mechanochemical method. The regeneration of Cu(Qc)2 in sesame oil and ZIF-7 in sesame oil was also demonstrated, suggesting that these or similar porous liquids could potentially be applied in cyclic separation processes.
