Benito A. Stradi, J. P. Kohn, M. Stadtherr
Apr 1, 1998
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Influential Citations
31
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Journal
Journal of Supercritical Fluids
Abstract
Abstract The possible phase behavior of a reaction mixture is an important consideration when evaluating CO 2 as an alternative solvent to replace traditional organic compounds. To address this issue we present phase equilibrium measurements and modeling of primarily binary mixtures with CO 2 of the reactants, products and catalysts present in the allylic epoxidation of trans -2-hexen-1-ol to (2R,3R)-(+)-3-propyloxiranemethanol. This reaction occurs with very high enantiomeric selectivity in liquid CO 2 , yields a high value product, and would normally be carried out in an organic solvent like benzene. Thus, it is a promising candidate for CO 2 solvent replacement. The systems studied are trans -2-hexen-1-ol-CO 2 , tert -butyl hydroperoxide (in decane)-CO 2 , (2R,3R)-(+)-3-propyloxiranemethanol-CO 2 , tert -butyl alcohol-CO 2 , diisopropyl L-tartrate-CO 2 , vanadium(V)tri- i -propoxy oxide-CO 2 and titanium(IV) isopropoxide-CO 2 . The compositions of the liquid phases were determined as a function of pressure, at temperatures between 303.15 and 323.15 K and pressures between 31.5 and 110.2 bar. Liquid/liquid immiscibility regions were found for the trans -2-hexen-1-ol-CO 2 and (2R,3R)-(+)-3-propyloxiranemethanol-CO 2 binaries. This region is located between 310.9 K (the l ower c ritical e nd p oint) and 315.3 K (a type-k point) and the corresponding pressures of 79.5 and 86.7 bar for trans -2-hexen-1-ol-CO 2 . The (2R,3R)-(+)-3-propyloxiranemethanol-CO 2 liquid/liquid immiscibility region ranges from 315.1 K (a type-k point) to below 293.7 K, at the corresponding pressures of 86.1 to 55.8 bar. All of the other binaries exhibited simple vapor/liquid equilibrium (VLE). Modeling with the Peng-Robinson equation of state (PREOS) gave reasonably good results for the two phase regions for all of the systems, using just one temperature-independent parameter for each binary system. The PREOS did predict LLV three phase regions for the trans -2-hexen-1-ol-CO 2 and (2R,3R)-(+)-3-propyloxiranemethanol-CO 2 binaries, but generally at conditions different from those observed experimentally. Finally, we present some preliminary predictions of the multicomponent phase equilibria based on the binary measurements and models.