Abstract 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 1-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.

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