Treatment of saturated brine in chlor-alkali process using membranes

Saturated brine in chlor-alkali plant contains some impurities including Mg2+, Ca2+, Fe2+ and SO42− that affect the performance of the process. Membranes may be used in combination with other treatment methods to decrease the impurities to a desirable level. In this work totally seven polymeric membranes (FT30, PVD, DOW-PS, TFC-SR, BW30, 37100 and NF45) were employed to treat the saturated brine. The polyethylene terphetalate PVD membrane at 8 bars and 40 °C showed the best performance with moderate flux, appropriate removal of impurities and minimum NaCl rejection. The hydrophilic polysulfone 37100 membrane exhibited highest flux (300 l/m2 h) without adequate removal of impurities. Nanofiltration polyterphetalate NF45 membrane showed high ability for removal of Fe2+ (98%) with undesirable level (21%)of rejection of NaCl. The DOW-PS membrane demonstrated maximum SO42− removal. The ion rejection depends on the size (hydration radius) and concentration of ions. Larger ions, i.e. with higher hydration radius and lower concentration exhibit the highest rejection.