Novel lignosulfonated polyester membranes with remarkable permeability and antifouling characteristics

Polyamide thin film composite (TFC) membranes are the most common nanofiltration and reverse osmosis membranes for wastewater treatment and desalination. Even though polyamide membranes excel in these applications, they can be fouled easily. In this work, we used an alternative approach for these applications: polyester membranes made via interfacial polymerization of terephthaloyl chloride (TPC) and sulfonated kraft lignin (SKL). The novel polyester TFC membranes had much higher negative surface charges than a reference polyamide TFC membrane, helping them reject negatively-charged solutes such as reactive red, reactive black, methyl orange, and most foulants like proteins. The polyester TFC membrane prepared with 7 wt% SKL and 0.2 wt% TPC reached a water flux greater than 50 LMH (liter per square meter per hour) and over 90% dye rejection, which is more than 3 times the water flux of a polyamide TFC membrane at almost the same dye rejection. We propose that compared with more reactive monomers, such as piperazine (PIP) and trimesoyl chloride (TMC), the slower polymerization rate between SKL and TPC increased the free volume in the polyester membrane, which, in turn, increased the membrane permeability while keeping the dye rejection constant. Our findings indicate a promising pathway for developing non-polyamide membranes with competitive separation performance and antifouling properties that could rival current commercial nanofiltration membranes.