Study On Poly(Phthalazinone Ether Sulfone) (PPES) Hollow Fiber Nanofiltration Membrane

Nanofiltration (NF) is a pressure-driven separation process with a low operating pressure and high permeability compared with the Reverse Osmosis (RO) process. Due to its unique ability to separate and fractionate ionic and low molecular weight organic species from 200 to 1000 Da of the neutral solutes, NF has grown rapidly in the last few decades. However, most NF membranes are composite membranes produced via sophisticated fabrication processes, such as coating or interfacial polymerization. And the commercial composite NF membranes were mostly based on the Flat-Sheet module. Since hollow fiber configuration has the advan-tage of self-support and provides a higher ratio of membrane area over module volume, it has the potential advantage in the industries application. In this work, a new type of hollow fiber nanofiltration membrane is reported based on the poly(phthalazinone ether sulfone) (PPES) as membrane material.The thermodynamics of casting solution is the basic theory for the formation of polymeric membrane via the phase inversion process. In this paper, the phase separation behavior of different non-solvent additives (NSAs) on the PPES casting solution was studied by the turbidity measurements and theoretical calculations. And the binodal lines in the ternary phase diagram were obtained by combining the experimental data of turbidimetric titration measurements in a wide concentration range according to the linerized cloud point (LCP) correlation. According to the binodal lines of the system, the maximum content of NSA in the casting solution can be calculated. On the other hand, effects of different non-solvent additives on the polymer conformation in the PPES solution were evaluated by the measurement of intrinsic viscosity with different additives in the polymer solution. Therefore, the dope composition of PPES casting system could be established scientifically.The PPES hollow fiber membranes were prepared by the dry/wet phase inversion technique. Effects of PPES concentration, different non-solvent additives (NSAs) and the NSA content in casting system on the morphologies and performance of PPES hollow fibers were systematically investigated by using N-methyl-2-pyrrolidone (NMP) as solvent. On the basic of single solvent system (PPES/NMP/NSA), a fourth component THF was introduced to the casting solution. And serials of PPES membranes with good permeability and high temperature-resistance could be obtained by optimized the PPES/(NMP/THF)/NSA system. Under the operating pressure of 0.1MPa, flux of the PPES fibers increased from 597 L/(m2-h) to 1420 L/(m2-h) with the operating temperature increased from 20℃to 90℃, while the relative change ratio for membrane rejection is lower than 2%. Moreover, under the operating temperature of 90℃, the membrane rejection was about 75.6% for polyethylene glycol 20,000 (PEG20,000) and the rejection for PEG30,000 is above 99%.The SPPES/PPES composite NF membrane was successfully prepared by using PPES fibers as support and SPPES as the outer active layer. The coating process was more efficiency and stability by using the self-design coating equipment. Effects of the substrate performance, the pretreatment of PPES fibers, dope composition of SPPES coating solution, the post-treatment temperature and time on the performance of the composite membrane were systematically studied. It is shown that inorganic electrolytes rejection of the SPPES/PPES composite nanofiltration membrane ranks:Na2SO4>MgSO4>NaCl>MgCl2, which is typical characteristics of the negatively charged membrane. Under the operating pressure of 1.0MPa and the operating temperature of 20℃, flux of SPPES/PPES composite membrane can be up to 43.5 L/(m2-h), while rejection for Na2SO4 solution(1000mg/L) was about 87.4%. With the operating temperatre increased to 90℃, flux of the SPPES/PPES composite membrane increased to 114 L/(m2·h). Accordingly, the rejection for Na2SO4 (1000mg/L) solution was 87%. And it was shown that the SPPES/PPES hollow fiber composite nanofiltration membrane had a good high temperature-resistance.By using the compatibility difference of the components in the PPES/(NMP/THF)/NSA system, two NSAs in terms of dimethyl sulfoxide (DMSO) and Y-butyrolactone (GBL) were selected to fabricate integrally skinned asymmetric NF membranes via the phase inversion method. Effects of different ratio for NMP/THF, polymer concentration, air-gap, NSA content and composition of the bore fluid on the perforamce and structure of PPES asymmetric NF fibers were studied. When DMSO was used as the additive and the ratio of NMP/Water (95/5) used in the bore fluid, NMP/THF(4/6) in the casting solution, flux of PPES fibers can be 87.2 L/(m2-h) under the operating pressure 0.6MPa. Accordingly, the membrane rejection for PEG600 (1000ppm) were above 98%. Under the operating pressure of 0.6MPa and the operating temperature of 80℃, integrally skinned asymmetric PPES NF membranes was applied in the desalination-purification for the mixed solution of dye KB-R (10 g/L) and NaCl (2g/L) by the continuous batch diafiltration desalting process. By concentration the solution in half, the dye KN-R can be desalinized through 7 times cycle. And the permeate solution conductivity was decreased to 100μs·cm-1, which meant the PPES asymmetric hollow fiber NF membranes was suitable for the desalination of KN-R solution.