Preparation Of Modified Poly (vinyl Alcohol) Membranes And The Dehydration Of 2-Methyltetrahydrofuran/Water Mixtures Using Them

Energy shortages and environmental pollution are becoming more and more serious,and the development and utilization of sustainable,safe,and environmentally friendly production of transportation fuels and chemical raw materials is essential.2-Methyltetrahydrofuran(2-Me THF)is made from renewable oat hulls and corn cobs.It can be used as a gasoline additive,a multi-functional new solvent,an organic metal reaction drying solvent,and a pharmaceutical intermediate.In the use of 2-Me THF,an aqueous mixture will be generated,and recycling 2-Me THF can reduce environmental pollution and turn waste into treasure.However,2-Me THF and water will form an azeotropic mixture,which is difficult to separate by rectification.Pervaporation membrane separation technology has low energy consumption and no pollution,and is especially suitable for the separation of azeotropes.In this paper,PVA-g-AA membrane was prepared by grafting reaction of polyvinyl alcohol(PVA)and acrylic acid(AA).The prepared PVA-g-AA was blended with polyvinylpyrrolidone(PVP),and maleic anhydride was used as a cross-linking agent to prepare a PVA-g-AA/PVP membranes.The as-synthesized membranes were characterized by ATR-FTIR,X-ray diffraction(XRD),water contact angle(WCA),thermogravimetry(TG),differential scanning calorimetry(DSC),and scanning electron microscope(SEM).The dehydration process of these two membranes on 2-Me THF/water mixture by pervaporation was studied.The specific research content is as follows:1.The effect of the mass ratio of AA to PVA on the structure and performance of membranes was investigated.Increase the mass ratio of the two matrials(5:1～10:1),the amount of acrylic acid grafted onto PVA increases first and then decreases.The crystallinity and water contact angle of the PVA-g-AA membranes showed opposite trends,first decreasing and then increasing.When the mass ratio of AA to PVA was 8:1,the above physical quantities obtained the extreme value.This was because as the mass ratio of the two increased,more AA was grafted onto the PVA molecule,but when the concentration of AA was above some level,too much AA monomer was adsorbed on the PVA surface,hindering the initiation of active center on PVA,the amount of AA grafted onto PVA is reduced.The PVA-g-AA membrane with the mass ratio of AA to PVA8:1 showed the highest dehydration efficiency of 2-Me THF solution.Change the concentration of the initiator from 1.5 mmol/L to 3.5 mmol/L with the mass ratio of acrylic acid to PVA of 8:1,the obtained membranes was used to dehydrate the 2-Me THF solution,the separation factor increased first and then decreased.The best separation effect was achieved when the initiator concentration was 2.5 mmol/L.2.On the PVA-g-AA membrane prepared with the initiator concentration of2.5 mmol/L and the mass ratio of AA to PVA of 8:1 changing the feed water content from 1.9 wt.%to 3.9 wt.%,the total flux,water flux,and 2-Me THF flux all increased,while the separation factor increased first and then decreased.When the operating temperature(20℃～50℃)increased,the total flux,water flux,2-Me THF flux and separation factor increased at the same time.When the operating temperature was above 50℃,the membrane trended to break.Increasing the membrane thickness from 30μm to 60μm,the operating temperature from 20℃to 70℃,the total flux,water flux,2-Me THF flux and separation factor still increased with increasing temperature.Increasing the feed flow rate(20 L/h～60 L/h),the total flux,water flux,2-Me THF flux,and separation factor increase D simultaneously.At an operating temperature of70℃,a feed flow rate of 60 L/h,and a membrane thickness of 60μm,a2-Me THF/water mixture with a water content of 3.9 wt.%was separated,and its water flux was 619.58 g/(m~2·h),and the corresponding separation factor was637.75.3.Prepared PVA-g-AA/PVP membranes by mixing 5 wt.%PVA-g-AA and PVP solutions,according to the volume ratio from 10:0 to 6:4,using maleic anhydride as the cross-linking agent.The crystallinity and thermal stability of the PVA-g-AA/PVP membranes increased,the contact angle and glass transition temperature decreased,compared with those of PVA-g-AA membranes.increasing the volume ratio of the two materials,the crystallinity and thermal stability of the membranes decreased.The PVA-g-AA/PVP membrane with 9:1volume ratio of PVA-g-AA to showed the highest effect of dehydration of2-Me THF solution.4.Using PVA-g-AA/PVP membrane(9:1)with the thickness of 30μm as the separation membrane,changing the feed water concentration(1.5 wt.%～3.9wt.%),the total flux,water flux,2-Me THF flux increased,and the separation factor decreased.The operating temperature increased from 20℃to 50℃,the total flux,water flux,2-Me THF flux and separation factor all increased.On the membrane with 60μm thickness,the operating temperature increased from20℃to 70℃,the total flux,water flux,2-Me THF flux and separation factor still increased,but the total flux,water flux,2-Me THF flux on the thicker membrane were decreased,and the separation factor increased compared with those on the thinner membrane.On the PVA-g-AA/PVP membrane with thickness of 60μm at an operating temperature of 28℃,a feed flow rate of 60L/h,the feed water concentration increased from 1.5 wt.%to 3.9 wt.%,the water permeation flux increased from 7.79 m g/(m~2·h)to 527.13 g/(m~2·h),and the separation factor decreased from infinity to 989.39.