Highly efficient separation of organic substances from high salinity brine by nanofiltration

Efficient separation of organic compounds from the high salinity brines during the treatment of reverse osmosis concentrate (ROC) is highly desirable and also very challengeable for the purpose of zero liquid discharge (ZLD). For the general treatment process, the efficient removal of organic compounds from the NaCl rich solution before the evaporation-crystallization stage is one of the key challenges. In this work, separation of N-(2-hydroxypropyl) morpholine (NMH), 4-morpholineacetate (MHA), the major organic components of ROC in refinery, and monovalent/divalent ions from the high salinity brines by three commercial nanofiltration (NF) membranes, i.e. Desal-5DK, Desal-5DL and NF270 were systematically investigated. The effects of various parameters on the rejection performance of these three NF membranes were experimentally investigated. The results showed that the retentions of NMH and MHA were dominated by flux and pH. Single stage filtration experiments showed that the rejection to NMH and MHA with various operating parameters was high and stable for DK. In comparison, DL and NF270 had higher separation efficiency for monovalent and divalent ions. The experiments determined that the rejections of NMH and MHA were 99.16% and 98.42% under the optimized conditions, respectively, indicating that NF membranes were highly efficient for separating organic compounds from the high salinity brine.