| As an emerging membrane separation technology,forward osmosis(FO)has gained considerable attention in recent years with potential application in the area of wastewater treatment,seawater desalination,pharmaceutical products,food processing,power generation and so forth.However,the lack of proper FO membranes with high performance has impeded the further development of this emerging process.The actual water flux is often far lower than expected value when the traditional reverse osmosis membranes are applied in the forward osmosis process.Commercial cellulose acetate FO membrane have many drawbacks such as weak thermal stable,easy to hydrolysis,low resistance to acid and alkali,easy to biodegradation,etc.In addition,the application temperature of FO membrane materials is generally lower than 50 ℃.Therefore,it is urgent to develop a novel forward osmosis membrane with high water flux,low Js/Jv ratio,good thermal stability and high chemical stability by choosing a suitable material.Copoly(phthalazinone biphenyl ether sulfone)(PPBES)is a novel copolymer which was previous synthesized in our group.The unique rigid phthalazinone and aromatic groups in the main chain endowed PPBES membrane material with superior physicochemical stability,good solubility and excellent thermal stability,while the flexible ether linkages gave it good flexibility,which is a suitable candidate for membranes.Compared with flat-sheet membranes,hollow fiber(HF)mode has many obvious advantages such as excellent self-support,ease of module fabrication and high packing density.So far,the application of PPBES as forward osmosis membrane has not been reported in the literature.In current work,the novel PPBES material with excellent comprehensive properties was used as membrane materials.A series of PPBES hollow fiber substrates were prepared by changing the polymer dope formulation and fiber spinning condition.The effects of fiber spinning conditions on the substrate morphologies and the performance of PPBES HF substrate membranes were investigated.Experiments results revealed that the increase of PPBES concentration in the dope solution could change the HF substrate morphologies from loose finger-like macro-voids into dense sponge-like structures.The porosity decreased from 83.4%to 60.4%.The water flux inclined from 340 L/m2h to 114 L/m2h while the rejection increased from 79.2%to 97.2%.Different types and contents of additives have different influence on the structures and performance of HF substrates.With the increase of EGME contents from 8 wt%to 20 wt%,substrate structures changed from loose macro-voids into dense sponge-like,water flux decreased from 300 L/m2h to 100 L/m2h,while the rejection improved from 75%to 98.5%.The increase of glycol or propanol contents could significantly increase water flux and incline the rejection of substrates.With the increase of PVP content,water flux of substrates decreased obviously while the rejection changed slightly.With the increase of LiCl contents,substrate porosity and water flux increased obviously while the rejection declined slightly.The coagulation bath temperature rising from 10 ℃ to 30 ℃ could improve water flux of substrates and changed the rejection slightly.The increase of air gap distance from 7.5 to 20 cm had no significant influence on the structures and rejection of substrates.The novel PPBES HF substrate membranes prepared exhibited good separation performance and mechanical strength as well as thermal stability.With the feed solution temperature increased from 20 ℃ to 95 ℃,water flux of substrates improved from 155 L/m2h to 428 L/m h while the rejection changed less.The performance of PPBES HF substrates kept stable in the solution at 90 ℃.Novel PPBES thin film composite forward osmosis(TFC-FO)hollow fiber membranes were successfully fabricated via interfacial polymerization on the lumen side of PPBES hollow fiber substrates.Effect of dope formulations and spinning conditions of PPBES substrates on the morphologies and performance of TFC-FO membranes was investigated.The results indicate that FO water flux and Js/Jv ratio deceased with the increase of PPBES concentrations.The increase of EGME contents could decrease the water flux and Js/Jv ratio of TFC-FO membranes.FO water flux and Js/Jv ratio increased obviously with the addition of glycol or propanol.With the increase of LiCl from 0.5 wt%to 1.5wt%,FO water flux improved from 18.3 L/m2h to 25.1 L/m2h while the Js/Jv ratio increased slightly.The increase of coagulation bath temperature could significantly improve FO water flux while slightly change the Js/Jv ratio.The increase of air gap distance had no significant influence on the Js/Jv ratio of TFC-FO membranes.The decrease of substrate thickness could improve the performance of PPBES TFC-FO membranes.It is beneficial to prepare a novel PPBES composite FO membrane with high performance by adopting the hollow fiber membrane with a ultra-thin,high porosity,direct finger holes and dense layer structure.Influence of interfacial polymerization conditions on the morphologies of polyamide active layer and performance of PPBES TFC-FO membranes was investigated.The composite FO membrane prepared with hexane as the organic solvent exhibited the best comprehensive properties.FO water flux and Js/Jv ratio firstly decreased obviously and then increased slightly when MPD or TMC concentrations increased.The increase of immersion or IP reaction time could change the polyamide active layer from loose to dense morphologies,which resulting in the FO water flux and Js/Jv ratio decreased quickly.Heat curing treatment could change the densification of polyamide active layer,which could reduce the water flux of TFC-FO membranes.Water flux and Js/Jv ratio of TFC-FO membrane reduced significantly as the flushing time increased.The performace of PPBES TFC-FO membrane was relatively good when IP temperature at 25℃.The optimal choose parameters of PPBES composite FO membranes are as follows:An aqueous solution of 2 wt.%MPD is brought into contact with the lumen side of PPBES hollow fiber membrane for approximately 3min.The unabsorbed amine solution is removed by purging it gently with nitrogen gas for 6 min following by the reaction with a solution of 0.1 wt./v%TMC in hexane for 60 s,and then the nascent polyamide membrane are cured by heating in an oven at 50 ℃ for 5min.The additional of the presence of phase transfer catalyst,DMSO,Acetone,TEA as additives in the aqueous/organic phase systems could improve the performance of PPBES TFC-FO-HF membranes.Different test conditions were employed to study their effect on the performance of PPBES TFC-FO-HF membranes.The change of solution flow rate had a little influence on the performance of TFC-FO membranes.With the increase of draw solution concentration,FO water flux improved significantly while the JS/JV ratio changed slightly.FO water flux reduced significantly with the increase of feed solution concentration.The water flux and Js/Jv ratio in the AL-DS mode were better than the values in the FO mode.PPBES composite FO hollow fiber membrane exhibited excellent thermal stability.Water flux of PPBES TFC-FO membranes was enhanced more than twice without significant change of the Js/Jv ratio when draw solution temperature increased from 23 ℃ to 85 ℃.The water flux and Js/Jv ratio of PPBES composite FO membrane were change slightly during the 1500 min of experiment.Comparing with other FO membranes,PPBES composite FO hollow fiber membrane displayed a relatively high water flux and low Js/Jv ratio... |
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