Development of tuneable polyamine top layer for nanofiltration with high stability in bleach and at extreme pHs

State-of-the-art membranes for nanofiltration are thin film composite membranes, comprising of a thin top layer on top of a porous support. Many separation processes in organic chemistry involve extreme conditions, e.g. aggressive solvents, solvent-water mixtures or extreme pH, e.g. in acid mine drainage or in Cleaning-in-Place cycles. However, the most commonly used thin film composite membranes are polyamides, typically prepared by reaction of a tri(acyl chloride) and a diamine, often trimesoyl chloride and m-phenylenediamine, respectively, which cannot withstand these extreme conditions. This study aims at preparing chemically much more robust membrane based on polyamine. As diamine, 1,2-Diaminocyclohexane is used, due to its high reactivity and in order to mimic PIMs, following its rigidity and twisted structure. Analogous to trimesoyl chloride, 1,3,5-tri(bromomethyl)benzene was used. Unfortunately, no reproducible membranes could be achieved. This was solved by increasing the number of functional groups of the bromomethyl benzene from three to four, resulting in a membrane with both very good separation performance (e.g. 99.6 % Rose Bengal rejection at a permeance of 1.03 L m(-2) h(-1).bar(-1)) and excellent stability in extreme conditions (i.e. bleach and pH 13). Additionally, the formed polyamine membrane is pH-responsive and can be adjusted to the application by post-treatment, i.e. further crosslinking or quaternization.