Preparation And Performance Of Polyamide Nanofiltration Membranes Based On Zwitterionic Piperazine

Nanofiltration is a novel type of pressure-driven membrane seperation process, where its pore size is between reverse osmosis membranes and ultrafiltration membranes. Nanoflitration has attracted great research interest due to its low cost, energy saving characters, and broad applications in desalination, drinking water production, waste water treatment, industrial substances separation, and more. However, some performance of nanofiltration membranes still needs to be improved to meet more complicated applications. In this paper, the zwitterionic monomer was designed, synthesized, and utilized in interfacial polymerization to prepare polyaimde nanofiltration membranes. The systematic study about the influence of zwitterionic monomer on membrane structure, separation performance and antifouling property was made.Firstly, the zwitterionic monomer AEPPS was synthesized by the ring-opening reaction of AEP with 1,3-PS. The chemical strcture of AEPPS was characterized by Fourier transform infrared infrared spectrum and nuclear magnetic resonance spectrum. The interfacial polymerization between AEPPS and Trimesoyl chloride (TMC) was studied to confirm its feasibility and determine the optimum reactiom. The results show that the interfacial polymerization between AEPPS and TMC can poceed. A macroscopically visible membrane can be obtained by increasing the monomer concentration in interfacial polymerization.The interfacial polymerization conditions of composite nanofiltration membranes prepared by PIP and TMC were optimized. The optimal preparation conditions as following are determined:the monomer concentration of PIP and TMC is respectively 0.35 wt% and 0.2 wt%, the post-processing temperature is 50℃, and the aqueous phase pH is 12. Based on this, AEPPS was utilized in conjunction with PIP to perform the interfacial polymerization with TMC, producing polyamide nanofiltration membranes (NFMs). Chemical structures and compositions of the NFMs were characterized by (attenuated total reflectance) fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface morphology and hydrophilicity of NFMs were examined by field emission scanning electron microscopy, atomic force microscopy, dynamic water contact angle. The water permeability and antifouling property of nanofiltration membranes are improved by introducing AEPPS into membranes. Moreover, the performance of NFMs is stable during a long term operation process. When tested with 1 g L-1 K2SO4 aqueous solution, the water flux of NFM-4, in which the AEPPS content is 3.2 mol%, is 43.1 L m-2 h-1. It is almost as twice as NFM-0 which does not have AEPPS. When tested with 0.1g L-1 BSA+1g L-1 K2SO4 solution, the relative water flux recovery ratio of NFM-4 is 93%, higher than NFM-0. Compared with NFM-0, NFM-4 has a 50% reduction in S.epidermidis adsorption and a 98% reduction in S.maltophilia adsorption.The post polymerization between AEPPS and pristine PIP-TMC thin composite NFM was performed to introduce zwitterionic AEPPS moieties into the NFM. Effect of monomer concentration, inmmersion time, aqueous phase pH and the interval time between the interfacial polymerizations on the performance of nanofiltration membrane was studied to optimize the polymerization condition. The optimal preparation conditions as following are determined:the monomer concentration of AEPPS is 2.4 wt%, the aqueous phase pH is 12, immersion time is 120s, and the interval time between the interfacial polymerizations is 20 s. When tested with 1 g L-1 K2SO4 aqueous solution, the water flux and K2SO4 rejection of nanofiltration membranes are 60 L m-2 h-1 and 98%, respectively. Notably, the membrane exhibits a stable and good separation performance in a 25 h filtration.