Study Of PPESK Hollow Fiber Composite Nanofiltration Membrane And Fundamental Application

Poly(phthalazinone ether sulfone ketone) (PPESK) is a novel membrane material for ultrafiltration membrane and nanofiltration membrane with high glass-transition temperature, good solubility, well membrane-forming ability, good mechanical performance and chemical stability.The phase separation behavior of different nonsolvent additives (methyl ethyl ketone, glycol methyl ether and diethylene glycol) on PPESK casting solution was studied at 20℃according the linerized cloud point (LCP) correlation. It was found that the phase separation behavior of PPESK, ie., PPESK/NMP/H₂O and PPESK/NMP/NSA, all agree with the LCP correlation. The binodal lines of the three systems were calculated according LCP correlation. Therefore, the maximum content of NSA in the casting solution can be calculated according to the binodal lines of the system, which is a scientific solution for the establishment for the composition of casting solution. It can be concluded that NSA has the stronger ability of coagulation, the larger the intercept when the slope of the simulated LCP is the same. The coagulation ability of the nonsolvent additives increased as the follows: water> diethylene glycol> glycol methyl ether> methyl ethyl ketone at 20℃according to the disparity of solubility parameters and ternary phase diagram. Hollow fiber ultrafiltration membranes were prepared successfully from Poly(phthalazinone ether sulfone ketone) with a dry/wet phase inversion technique. Organic substances (diethylene glycol, glycol methyl ether and methyl ethyl ketone) were used as nonsolvent additives and N-methyl-2-pyrrolidone (NMP) used as a solvent in membrane preparation. The effects of PPESK concentration, the type of additives and the NSA concentration in casting solution on the morphology and performance of the PPESK hollow fiber ultrafiltration membrane were systematically investigated. A series of hollow fiber ultrafiltration membranes with different pore size and flux have been successfully prepared. At the same time, they supply substrate membranes for the preparation of hollow fiber nanofiltration composite membrane.A hollow fiber poly(piperazineamide) nanofiltration composite membrane was prepared by interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on the surface of PPESK substrate membrane. The effects of the performance of PPESK substrate on that of composite membranes were studied. PPESK ultrafiltration membrane with 94.1% rejection for PEG2000 and a flux of 200 L/m²h when tested at 0.1MPa was chosen as the support membrane. The effects of preparation conditions (such as concentration of the monomers, residence time of monomer solutions etc.)>on the performance of the hollow fiber composite membranes were systematically studied. When tested at 0.35MPa, room temperature, the composite hollow fiber membrane had a Na₂SO₄ rejection of 99.0% and a pure water flux of about 54 L/m²h. The effect of operating parameters, such as operating pressure, operating temperature, feed flow rate etc., on the performance of composite nanofiltration membrane were investigated. The PPESK hollow fiber composite nanofiltration membrane exhibits good thermal stability. The inorganic electrolytes rejection of nanofiltration membrane ranks: MgCl₂> MgSO₄> NaCl> Na₂SO₄, which is typical characteristics of a negatively charged membrane. The rejection for organics increases as their molecular weight increases.The membrane parameters (σand p) can be determined by a best-fit method employing irreversible thermodynamic model according to permeate experimental data. The structure parameters and effective volume charge density of the three series( PIP, TMC and Time) hollow fiber membranes were calculated based on Pore and TMS model. It was found that the structure parameters and effective volume charge density were influenced strongly by concentration of monomers. The pore size decreases while the thickness and charge density increase with the increase of monomer concentration. the pore size of Na₂SO₄ rejection ranges negligibly when reaction time prolongs, while thickness and charge density increase.The separation properties of the membrane for NaCl solution with various concentrations were studied. It was found that both of the flux and rejection decreased as the concentration of the tested solution increased. The prepared hollow fiber composite membrane exhibited good separation property and fouling resistance for dye KN-R. the flux of composite membrane decreased slightly in the first 60 min, and then reach a plateau when tested at 0.5MPa for 200min. part of flux lose could be recovered by rinsing of hollow fiber membrane. Composite membrane was applied in the desalination-purification for dye KB-R, and the rejection for KN-R was kept at nearly 100% and the flux waved about 45L/m h. The dye KN-R was almost desalinized through 8 times cycle.The separation properties of three hollow fiber composite membranes for nucleotide containing phosphate were tested at 0.6MPa, room temperature. CMc was selected for the separation of nucleotide because of its highest rejection and good flux. The factors of nanofiltration separation process were studied systematically. The influence of the parameters, such as operating pressure, concentration of feed, feed flow rate and operating time on the performance of hollow fiber membrane were investigated. It was found that naofiltration membrane could reject nucleotide effectively and let phosphate partly pass through. The flux and rejections increased with increase of velocity of feed. On the other hand, they decreased when the concentration of feed increased. The rejection for inorganic p decreased when increase of PH of feed. The rejection for nucleotide was kept at more than 95%, and that for inorganic salt maintained at about 50%. The performance of hollow fiber nanofiltration composite membrane is stable during the operating time in lab.