Environmentally friendly route for the preparation of solvent resistant polyimide nanofiltration membranes

Organic Solvent Nanofiltration (OSN) is an emerging membrane separation process with the potential to replace traditional separation techniques. Its advantages include lower energy consumption than alternatives such as distillation, easy up scaling and flexibility. However, manufacturing OSN membranes involves a number of stages contributing towards the discharge of hazardous chemicals as waste. Thus the environmental advantages of employing OSN are to some extent cancelled out by the waste released during OSN membrane production. This paper describes a process for the preparation of polyimide integrally skinned asymmetric OSN membranes with adjustable molecular weight cut off (MWCO). Previously reported methods for producing polyimide based OSN membranes are modified in the presented work without compromising the performance of the membranes. The toxic solvents used to form polymer dope solution, i.e. dimethylformamide (DMF)/1,4-dioxane are replaced by an environmentally friendly dimethyl sulfoxide (DMSO)/acetone solvent system. In order to further diminish the environmental impact, isopropanol was successfully replaced with water in the crosslinking step. Scanning electron microscope images revealed that membranes with spongy matrix without macrovoids were obtained regardless the DMSO/acetone ratio.