High-pressure phase equilibria of some carbon dioxide-organic-water systems

Homogeneous catalysts offer better activity and selectivity than heterogeneous catalysts, but their use is limited by the need to separate them from product and reuse them. Preferential dissolution of gaseous carbon dioxide has been shown to alter phase boundaries and facilitate recovery of such homogenous catalysts. The addition of a polar organic co-solvent to a water/organic biphasic system, coupled with subsequent phase splitting induced by the dissolution of gaseous carbon dioxide creates the opportunity to run homogeneous reactions in an organic/aqueous mixture with a water-soluble catalyst. In homogeneous catalyzed reactions, the catalyst can be tuned to be soluble or insoluble with carbon dioxide present, thus allowing for high catalyst recovery. High-pressure phase equilibria for the systems containing carbon dioxide, an organic (tetrahydrofuran, acetonitrile, or 1,4-dioxane), and water were measured using a variable-volume view cell, by a method capable of rapid and facile measurement of compositions and density in both phases with no sampling or calibration. These systems are well predicted with the Peng-Robinson Equation of State with Huron-Vidal type mixing rules from correlations of the binary systems, with the modified Huron-Vidal 1 (MHV1) and Huron-Vidal-Orbey-Sandler (HVOS) model with UNIQUAC excess energy model performing the best. Applications of the phase behavior on reaction conditions andseparations are addressed. (C) 2004 Elsevier B.V. All rights reserved.