Molecular separation with organic solvent nanofiltration: A critical review

Separation processes play a remarkable role in the chemical and pharmaceutical industries, where they account for 40-70% of both capital and operating costs.1 Organic syntheses in the chemical and pharmaceutical industry are frequently performed in organic solvents and consist of products with high added value that should be removed from the organic solvents. Additionally, organic solvents, used as raw materials, for chemical syntheses, and as cleaning agents, have to be recovered or discarded at the end of the process. According to the transport mechanism, membrane separation is based on both size exclusion and additional effects, characteristic of the molecular level. UF and MF are characterized by a sieving transport mechanism through pores of significant dimension, therefore described by the pore-flow theory, while RO is characterized by the solution diffusion transport mechanism, because the free volume is so small, that it is in the range of thermal motion of the polymer chains that form the membrane.