Effect of quaternary ammonium salts on the separation efficiency of nanofiltration membranes Original Research Article

The separation of inorganic and organic ions by membrane filtration of aqueous solutions through NF-(PVDI, MPF-34) membranes was investigated. In our experiments, the measured ionic transmissions varied in the range of 44%–56% in case of alkali metal salicylates, and as for alkali metal bromides, in the range of 90%–95%. We detected that the addition of tetrabutylammonium bromide or chloride salt increases the transmission of alkaline metal salicylate through NF membranes. The higher the concentration of TBAB or TBAC, the smaller is the transmission of salicylate anion. The transmission of coion cations increased due to TBAB or TBAC addition. The transmission of salicylate anions decreased in time, reaching the equilibrium. In the course of the experiments we found that during the creation of the multicomponent solution (NaSal, NaCl and TBAB or TBAC) a ligand exchange happened between NaSal and TBAB or TBAC. The measured ionic transmissions decreased with the addition of quaternary ammonium salt ion to bromide. In case of salicylate, the decrease was significant, onto values in the range of 12%–22% for salicylate, and to the range of 86%–91%, regarding bromide. This observed phenomena could cause a new possibility of increasing the separation efficiency of monovalent ions from a multicomponent system with the aid of nanofiltrating membranes.