| In recent years,with the development of petrochemical,chemical and pharmaceutical,machinery manufacturing,food processing and textile industries,more and more oily wastewater has been discharged into nature which causes serious problems such as environmental pollution and ecosystem destruction.In the oily wastewater,the existence of oil can generally be divided into four forms:slick oil,dispersed oil,emulsified oil and dissolved oil,and the removal of emulsified oil is the focus and difficulty for oily wastewater treatment.With the rapid development of membrane separation technology,different types of microporous membrane materials have been widely used in the treatment of industrial wastewater.However,the shortcomings including easy pollution,low water flux and high cost limit the large-scale application of membrane materials.Focusing on these problems,series of composite sponges which can be used to separate different types of emulsions were designed.In detail,the polyvinyl alcohol-formaldehyde(PVF)sponge was act as the base material to absorb different types of polyvinyl alcohol(PVA)aqueous solutions,and the pore structure of the composite sponges was adjusted through cross-linking reaction of hydroxyl groups in PVA and PVF.Then,the emulsion separation composite sponges were successfully obtained after the hydrophilic and hydrophobic modification.The relationship between the absorption capacity,pore structure,hydrophilic/hydrophobic properties,mechanical properties,surface potential,separation performance and flux of the composite sponges was systematically studied.The engineering preparation of hydrophilic/hydrophobic composite sponges was carried out,an emulsion separation device for engineering applications was designed,the engineering research for actual industrial wastewater was studied,and the foundation for the application of emulsion separation sponges in the field of industrial wastewater treatment was established.The PVF sponge was acted as the base material to absorb PVA and chitosan(PVA-CS),PVA and diatomite(PVA-Si),PVA and sodium alginate(PVA-SA),carboxyl modified PVA(PVA-COOH)aqueous solution.The hydrophilic composite sponges(PVA-CS/PVF,PVA-Si/PVF,PVA-SA/PVF,PVA-COOH/PVF)were successfully obtained through the cross-linking reaction of hydroxyl groups in PVA and PVF.The as-prepared composite sponges display a broad pore size distribution,interconnected pore structure,and remarkably rough surface structure.With the increasing of extra PVA absorption weight(?30%),the as-prepared composite sponges present a large number of tiny holes(?20?m),nano-scale pores and nano-micro composite structures.The saturated water absorption(Qs)of PVA-CS/PVF,PVA-Si/PVF,PVA-SA/PVF and PVA-COOH/PVF are 6.4 g·g-1 to 9.5g·g-1 in deionized water,the composite sponges show excellent hydrophilic properties with the water contact angle of 0°.Moreover,the as-prepared composite sponges exhibit excellent mechanical property and tough network structure,which could resist against large deformations without any fractures.For oil-in-water emulsions,the separation efficiency of PVA-CS/PVF,PVA-Si/PVF,PVA-SA/PVF composite sponges are greater than 97%,and the flux can be as high as 2.40×104 L m-2 h-1 bar-1.Respectively,the separation efficiency of PVA-COOH/PVF composite sponge is greater than 96%,and the flux can be as high as 3.82×104 L m-2 h-1 bar-1.After 10 cycles of filtration tests,the emulsion separation efficiency of the as-prepared composite sponges does not decrease significantly,which displays the excellent reusability.The polyvinyl alcohol-formaldehyde(PVF)sponge was acted as the base material to absorb PVA aqueous solution.the composite sponge(PVA/PVF)was obtained through the cross-linking reaction of hydroxyl groups in PVA and PVF.Then,the hydrophobic composite sponges(PVA/PVF-CH,PVA/PVF-Si)were successfully obtained after the grafting reaction of stearyl chloride,octadecyltrimethoxysilane with PVA/PVF.The GP and GE values of the composite sponges can be effectively controlled by the reaction conditions such as catalyst amount,reaction temperature,reaction time,and reactant feed ratio.Meanwhile,the as-prepared composite sponges display a broad pore size distribution,interconnected pore structure,remarkably rough surface structure,a large number of tiny holes(?20?m),nano-scale pores and nano-micro composite structures.The PVA/PVF-CH and PVA/PVF-Si composite sponges show the excellent hydrophobicity with the water contact angles of 127°and 130° in the air.Moreover,the saturated absorption capacity for organic solvents of PVA/PVF-CH and PVA/PVF-Si is 3.57g·g-1 to 34.35g·g-1 and 0.76g·g-1 to 5.58g·g-1.The as-prepared composite sponges exhibit excellent mechanical property and tough network structure,which could resist against large deformations without any fractures.For water-in-oil emulsions,the separation efficiency and separation flux of PVA/PVF-CH are 75.85%and 7.65×104 L m-2 h-1 bar-1.Respectively,the separation efficiency and separation flux of PVA/PVF-Si are 99.99%and 7.65×104 L m-2 h-1 bar-1.After 10 cycles of filtration tests,the emulsion separation efficiency of the as-prepared composite sponges did not decrease significantly,which displays the excellent reusability.The engineering preparations of hydrophilic PVA-COOH/PVF composite sponge and hydrophobic PVA/PVF-CH composite sponge were carried out.The emulsion separation device was designed and established for engineering applications.Meanwhile,the engineering experiments on emulsion separation were conducted to explore the suitability of the as-prepared composite sponges and systems in practical applications.For simple emulsion systems,the separation efficiency of the emulsion separation system which is only filled with the PVA-COOH/PVF composite sponge filter layer is greater than 95%,up to 99.52%,and the flux is up to 3.85 ×104 L m-2 h-1.Respectively,for complex emulsion systems,the separation efficiency of the emulsion separation system can reach up to 95.60%,and the flux can reach up to 1.10×104 L m-2 h-1.Moreover,The composite sponge filter layer can be reused after being simply washed with ethanol.After 5 cycles of filtration tests,the separation efficiency curve of the emulsion separation system with the time is basically the same.Meanwhile,the COD value of industrial oily wastewater filtered by the emulsion separation system is significantly reduced,and the lowest value can reach 421.4 mg/L,which has reached the discharge standard for industrial wastewater.The emulsion separation system has the advantages of excellent emulsion separation performance,high water flux and good reusability which has extremely high application value and wide application prospects in the field of industrial wastewater treatment and purification. |
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