Role of excess molar enthalpies in supercritical antisolvent micronizations using dimethylsulfoxide as the polar solvent

The role of excess molar enthalpies ( H m E ) in the supercritical antisolvent (SAS) micronizations using dimethylsulfoxide (DMSO) as the polar solvent was investigated. Excess molar enthalpies for CO2 + DMSO mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in SAS micronizations. In most cases, mixtures showed very exothermic mixing. A local temperature increase can be expected in the precipitation chamber as a consequence of the heat evolved when CO2 dissolves in DMSO. Based on the H m E measurements, local temperature increases were calculated and shown to explain immiscibility of CO2 and DMSO and agglomerated or irregular particles for average temperature and pressure conditions where complete miscibility and uniform particles could have been expected. H m E data were also discussed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for CO2 + DMSO.