(417f) Modeling and Characterization of Organic Solvent Nanofiltration PDMS Membranes for the Separation of Organic Mixtures

Permeation rates and solute rejection are key factors in organic solvent nanofiltration processes and were investigated for two different PDMS-based membranes, both through an extensive experimental campaign and a model-based analysis. The characterization was done using different n-alkane solutes with variable chain length, corresponding to molecular weight in the range from 170 to 310 kg/kmol and several solvents with different properties (toluene, n-hexane, ethanol and butanol). In addition, the corresponding alkane/alcohol mixtures were investigated; all the tests were conducted at 25°C and 35 bar as transmembrane pressure. Significant differences in fluxes and rejection behavior for the OSN processes were measured for the case of different solvent composition, in both membranes. The results are interpreted in terms of the solution-diffusion model, also utilizing the results from sorption experiments of pure solvents performed ad hoc at 25°C for the investigated membranes. The model was developed to calculate the organic-solvent fluxed through a dense OSN membrane in ternary and quaternary systems. To quantify the solubility of the organic solvents/solutes in the membrane in the feed and permeate side, the â??Perturbed Chain-Statistical Associating Fluid Theoryâ? (PC-SAFT) equation of state was used modified through a term that binds the elastic contribution to the free energy , induced by the extension of the polymer chains between cross-linking points by â??affine-networkâ? model. The thermodynamics properties were explained for both membrane using the PC-SAFT parameters of uncrosslinked PDMS and diversifying the contribution of elastic energy , through the degree of crosslinking values. The binary interaction parameters were evaluated using the sorption experiments results. The thermodynamic approach used allows to represent the permeability and rejection as a function of solvent composition. The diffusion-coefficients (membrane-solvent/solute) are in agreement with the literature data. The solution-diffusion theory is able to describe the flux and most of the time the rejection of solute in the mixtures.