Formation and characterization of (melamine–TMC) based thin film composite NF membranes for improved thermal and chlorine resistances

Numerous efforts have been made to improve the thermal resistance and chlorine resistance of nanofiltration (NF) membranes. In this work, interfacial polymerization (IP) is selected for preparing TFC membranes because TFC membranes prepared with the IP method can provide high fluxes. Poly(melamine/trimesoyl chloride (TMC)) with all aromatic rings and triazine rings is used to fabricate the functional layer of the composite NF membrane and a reinforced polyetherimde (PEI) ultrafiltration (UF) membrane is used as the support layer. The effects of the reaction time and the effects of the monomer concentration on the membrane performance are studied in detail in this work. When the melamine concentration is 2.0%, reaction time is 40 s and the curing temperature is 70 °C, the optimized preparation conditions of the composite membrane are reached. The flux of the composite NF membrane is about 34 L/m2 h and its Na2SO4 rejection is about 77.8% when it is tested at 1.0 MPa and 20 °C. The surface morphologies of the composite membrane and substrate membrane are observed by scanning electron microscopy (SEM). The prepared composite membrane shows excellent thermal resistance and chlorine resistance compared with the poly(piperazine amide/TMC) amide NF membrane prepared at the same condition. The flux of poly(melamine/TMC) composite membrane increases from 32 to 138 L/m2 h while the rejection of Na2SO4 does not decrease when the operation temperature is elevated from 18 °C to 95 °C. The performance of poly(melamine/TMC) amide does not decline during 96 h immersion in chlorine solution (NaClO, 200 ppm).

► Melamine with triazine ring structure was used to prepare composite membranes.
► Monomer structure affects the chlorine resistance of composite membrane.
► The composite membrane has excellent thermal resistance and chlorine resistance.