Mass transport modeling in a gas antisolvent process

We present a theoretical investigation on thermodynamic and transport phenomena taking place in a gas antisolvent precipitation process for binary and ternary systems containing an organic solvent, a compressed gas antisolvent, and a solute, for both dilute and concentrated solutions. A mathematical model for mass transfer between a droplet of a polymeric organic solution and a compressed gas antisolvent is solved under fully miscible conditions. The generalized Maxwell-Stefan diffusion equation is used. To describe the thermodynamics of chainlike solutes, such as polymers, both volumetric and equilibrium properties are accurately represented by a perturbed-hard-sphere-chain theory. Finite-volume numerical discretization is applied to conserve the mass balance for a ternary system. Simulations are carried out for both spherical and cylindrical geometries. The results show the influence of temperature, pressure, and polymer concentration on the mass transfer. In particular, the evolution of the precipitation front within the droplet is followed for different types of solvents commonly used in gas processes. The particle-formation lifetime is correlated with transport properties of the mixture. Mass-transfer pathways for a droplet of solvent mixtures and of a dilute or concentrated polymeric solution in a compressed gas antisolvent environment are reported. Organic solvent transport properties and solute solubility may play a fundamental role in determining the final particle morphology.