Systematic investigation on the influence of solutes on the separation behavior of a PDMS membrane in organic solvent nanofiltration

Organic solvent nanofiltration (OSN) offers a great potential to save energy and increase product quality in chemical production. Although the numbers of publications increased in the last years, the transport mechanism in OSN has not yet been clarified due to the complex interactions among membrane, solvent and solute. To simplify membrane selection and accelerate process development for industrial applications, parameters which affect the separation behavior and help to predict rejection have to be determined. In this work, experimental investigations concerning the interactions among membrane–solvent–solute and the influence of functional groups in the solute molecules on the rejections in OSN are presented. Therefore, the rejection of two, three or four ring-type core substances with different functional groups like fluorination, polar endgroups or different side chain lengths were measured in different solvents. The chosen solvents are ethanol (polar), n-heptane (nonpolar) and tetrahydrofuran (polar aprotic), which resemble the solvents used in the various synthesis steps in the production of those specialty chemicals.The results show that rejections vary widely in the three solvents. Rejection in THF varied between 55% and 95% and in n-heptane between 20% and 80% while in ethanol negative values in a range between −10% and −45% were measured. To explain these results a comparison of the solubility parameter of the solute, the membrane and the solvent has been used here, which gives good correlations with the measured data.Incorporating the functional groups into a Design of Experiments, in particular the groups that influence the polarity of the molecules show a significant influence on the rejection depending on the polarity of the solvent.

► Comprehensive investigation of the separation behavior of a PDMS OSN-membrane.
► It concerns the membrane–solvent interactions and the influence of functional groups.
► Comparison of the solubility parameters of the membrane, the solvent and the solute.
► Polar functional groups show a significant influence on the separation behavior.
► This allows for the prediction of rejection and accelerate process development.