Measurements and modeling of the phase behavior of ternary systems of interest for the GAS process: I. The system carbon dioxide plus 1-propanol plus salicylic acid

As a representative model system for the gas-anti-solvent (GAS) process, the phase behavior of the ternary system carbon dioxide+ 1-propanol + salicylic acid has been studied experimentally. For this purpose, carbon dioxide has been chosen as the anti-solvent gas, 1-propanol as the organic solvent, and salicylic acid (2-hydroxy benzoic acid) as the model drug. In each experiment, a solution of salicylic acid in I-propanol was expanded using carbon dioxide as the anti-solvent. A synthetic method was used for measuring bubble point curves, and the solid (salicylic acid)-liquid boundaries. Three-phase equilibrium data solid (salicylic acid)-liquid-vapor were obtained from intersection of two-phase isopleths vapor-liquid and solid-liquid. Results are reported for this ternary system at carbon dioxide concentrations ranging from 8.0 to 90.6 mol%, and within temperature and pressure ranges of 273-367 K and 1.0-12.5 MPa, respectively. It has been observed that the carbon dioxide concentration significantly affects the optimum operational conditions of the GAS process, i.e. at lower concentrations carbon dioxide acts as a co-solvent, while at higher concentrations it acts as an anti-solvent. Also, it is shown that at a proper temperature, it is possible to precipitate most of the dissolved solute with only a small change of the pressure. The Peng-Robinson equation of state as modified by Stryjek and Vera (PRSV EOS) has been used to model the ternary system. (C) 2002 Elsevier Science B.V. All rights reserved.