Organically-modified ceramic membranes for solvent nanofiltration: Fabrication and transport studies

Solvent resistant nanofiltration (SRNF) is a useful tool for separations in organic media, such as the removal of impurities from used solvents, recycling of solvents or the recovery of products from reaction mixtures in chemical, petrochemical, and pharmaceutical industries. For these kinds of applications, continuous exposure towards organic solvents is expected, giving a need for a robust membrane. Membrane preparation by means of grafting of organic molecules inside the pores of ceramic membranes offers the possibility to tune the membrane pore size and surface wettability or functionality. This thesis deals with the preparation of NF membranes through organic grafting of porous ceramic substrates indicating the potential of grafting as a method to prepare selective and chemically stable membranes. Mesoporous y-alumina UF membranes were grafted by hydrophobic and hydrophilic organic moieties to decrease the membrane pore diameter of the y-alumina UF membrane down to the nanofiltration range. The use of coupling agent to couple the grafted moiety forming a grafted network inside the ceramic pores results in a smaller membrane pores. The solvent and solute transport mechanism of membranes, prepared in this way, has not been described in literature yet. More attention on how these membranes perform in different solvents is important. To enable process modelling and facilitate process design of SRNF processes, this thesis investigates the major parameters which influence the transport of solvents and solutes through the membranes. In this work, the solvent transport behavior of grafted ceramic membranes is described by incorporating solvent sorption terms in the Hagen-Pouiseuille equation. This provides an initial way to predict the performance of grafted ceramic membranes for solvent nanofiltration. Furthermore, the use of three size–based exclusion transport models, namely the Ferry, Verniory, and SHP models, to describe the solute rejection through the grafted membranes indicates a strong effect of the interaction between the membrane and solvent on the membrane rejection behavior. A more closed membrane structure is realized when a solvent is strongly sorbed in the grafted moiety. The findings described in this thesis provide important insights in the material research and modelling of organically-modified ceramic membranes applied for SRNF.