A critical look at reactions in class I and II gas-expanded liquids using CO2 and other gases

Abstract

This short review aims to give a summary of the publications on reactions in class I and II gas-expanded liquids (GXLs) (those with organic or aqueous liquid components), and to draw conclusions from the trends in the current literature.

Hydrogenation of phenol with supported Rh catalysts in the presence of compressed CO2: Its effects on reaction rate, product selectivity and catalyst life

“…The volume increased slightly with the pressure up to 6 MPa and significantly at higher pressures. The expansion is caused from the dissolution of CO 2 molecules into the liquid phase [26,[32][33][34][35][36]. CO 2 -expanded liquid phase has recently been gaining considerable attention, because it will facilitate the dissolution of other coexisting gases of H 2 , O 2 , CO, and so on and may accelerate the reactions involved with these gaseous reactants although CO 2 is not a reactant but rather a diluent [26][27][28][32][33][34][35][36].…”

“…The molecular interactions between carbonyl group and CO 2 were shown to depend significantly on the structure of the carbonyl compounds [31]. It is known that an organic liquid phase expands when it is pressurized by CO 2 and the extent of volume expansion may change with the kind of organic liquid and the CO 2 pressure [32][33][34][35][36]. These CO 2 -dissolved expanded liquid phases are demonstrated to be interesting reaction media for reactions including gaseous reactants like O 2 , H 2 , and CO.…”

Phase equilibrium of the CO2/glycerol system: Experimental data by in situ FT-IR spectroscopy and thermodynamic modeling

“…The interest of these biphasic systems is maximum when the partner solvent is a biosourced solvent because such systems become then environmentally friendly. Such biphasic systems are useful to overcome the limited solvating power of pure scCO 2 , especially in respect to homogeneous catalysis where in this case catalysts can be more easily solubilized in the liquid solvent. They can also alleviate the drawback of the conventional use of biosourced solvents whose low volatility usually handicaps easy recovery of the reaction products.…”

“…However, drawbacks in the utilization of non-volatile solvents, such as glycerol, are still the uneasy recovery of products and recycling of catalysts. In this context, biphasic systems using supercritical CO 2 (scCO 2 ) as a partner phase make it possible the solubilization of the catalyst in the glycerol phase while products are extracted by scCO 2 [9,11,12].…”

“…Recently, interest in biphasic systems, which couple supercritical CO 2 and a conventional liquid solvent have been highlighted [1,2], as they can provide innovative reaction media. The interest of these biphasic systems is maximum when the partner solvent is a biosourced solvent because such systems become then environmentally friendly.…”