Characterization and modeling of organic solvents sorption and transport in PDMS membranes for organic/organic separations

This study is mainly focused on the investigation of which are the main characteristics affecting the membranes’ performances and how they are influenced by the presence of different organic solvents. Two different PDMS membranes were prepared and studied, the two materials have the same chemical structure but different number of active sites for the cross-linking process. This choice was made to investigate how the swelling of a polymer can affect membrane characteristics. The first experiment performed with these PDMS membranes was the dynamic vapor sorption of organic solvents. Both hydrocarbons and alcohols were tested in order to understand how the polymeric material interacts with the different chemical species. It is evident from the results, the higher affinity between polymer and hydrocarbons with respect to alcohols. The sorption isotherms so obtained were modelled using different theories, trying to estimate the strengths and limits of each of them. From the same sorption experiments, kinetic data for the evaluation of transport phenomena were obtained and Fick’s law was applied to calculate values of the diffusion coefficient. In the second part of this study, the same membranes were tested in presence of pure liquid organic solvents, performing some filtration experiments. Fluxes through the membranes were measured and an evaluation of rejection and Molecular Weight Cut Off were given. In the end, the membranes were tested in presence of organic solvents binary mixtures. As before, fluxes through the membranes were measured and selectivities were calculated. It was possible to observe how these membranes are not able to separate hydrocarbons but they show higher selectivity in presence of a mixture of a hydrocarbon and an alcohol. In conclusion, this research provides a guidance on which experiments can be performed to characterize a membrane material and help to understand how many different parameters can affect the separation process.