In situ solvent recovery by organic solvent nanofiltration

Reducing solvent consumption in the chemical industries is increasingly becoming a topic of interest. The field of organic solvent nanofiltration (OSN) has markedly evolved in the past decade, and effective membranes are now available that can withstand aggressive solvents while completely rejecting small solutes at the lower end of the nanofiltration range (100-2000 g·mol^-1). With such membranes in hand and the advantages of membrane modularity, it is now possible to design innovative configurations to drastically reduce solvent consumption and enhance sustainability of downstream processes. Notably, a membrane-based solvent recovery configuration reported in our group has opened a new market for OSN membranes. In this work, the current state-of-the-art OSN membranes are screened, and a possible operation window for solvent recovery is identified. In tandem, to tackle the high solvent consumption challenge of membrane-based separation, we improved the solvent recovery configuration by combining both solute separation and solvent recovery in situ. The resultant system effectively performs the desired separation without any addition of extra solvent, thereby reducing solvent consumption to nearly zero. A model system comprising roxithromycin pharmaceutical and triphenylmethanol impurity is employed to illustrate that the proposed configuration allows constant volume diafiltration to be performed without any addition of fresh solvent. Parameters affecting the separation have been identified and validated experimentally or via modeling, and theoretical limitations are critically analyzed. The operability and carbon footprint have been compared with conventional solvent recovery units (e.g., distillation and adsorption). The present work reinforces that OSN is a leading separation technology in the process intensification movement of the fine chemicals sector.