New insight into micromixing in supercritical CO2 using a chemical method

Competing reactions have been studied in order to characterize micromixing efficiency in supercritical medium. A new chemical reaction test has been developed because the current systems involving ionic species are not suitable for a supercritical medium (CO2). The system is based on two competitive reactions: the esterification of phenylacetic acid by ethyl alcohol using paratoluenesulfonic acid monohydrate as a catalyst and the neutralization of paratoluenesulfonic acid monohydrate by tributylamin. The neutralization reaction is faster than the esterification reaction. The test procedure consists in adding, in stoechiometric defect, paratoluenesulfonic acid monohydrate to a mixture of ethyl alcohol, phenylacetic acid, tributylamin and carbon dioxide under 17 MPa and 50 degrees C. The ester yield is directly linked to the micromixing efficiency. Preliminary studies such as miscibility or analytical method (GPC) studies have been carried out in order to test the reactions' system in batch reactor. The sensitivity to micromixing effects has been investigated in a 0.5 L stirred reactor. Final composition in the vessel is dependent on the stirring speed. This new system is efficient to characterize micromixing effects in a supercritical medium, which are particularly important in the Supercritical AntiSolvent precipitation processes but also for chemical reactions. (c) 2005 Elsevier B.V. All rights reserved.