Measurement and modeling of supercritical fluid extraction from polymeric matrices

Extraction of low-molecular weight solutes by supercritical fluids (SCFE) is often rate-limited by the interaction of the solute with a polymer. In typical applications, the effect of the SCF on the matrix through swelling is paramount. Both the equilibrium of the solute between polymer and SCF and its rate of mass transfer are affected by this polymer-solvent interaction. Experimental data for situation where the SCF swells the polymer strongly (CO2/ethylbenzene/polystyrene) are presented; for this system the extractions are neither close to equilibrium nor are they completely diffusion-limited. This results in unusual variations in the amounts of ethylbenzene extracted versus temperature and pressure, in particular a much stronger dependence on temperature than on density. We found roughly a 10(6)-fold increase in the experimental ethylbenzene diffusivity in the polymer phase when SCF-CO2 was present. A model used to estimate the solute's diffusivity in the swelled polymer is presented.