| Global oil spills and industrial oily wastewater introduce various toxic compounds into clean water systems,thereby threatening global ecological system.Compared with the traditional burning of oil,high-effective separation of oily wastewater should be the first choice to solve such global environmental problems.High-efficiency separation technology not only helps reduce environmental pollution,but also saves energy and resource recycling.Traditionally,gravity separation,flotation and filtration can successfully separate oil/water mixtures,but these technologies still need improvement in terms of efficiency and operating costs.Due to the strong oil-water interface energy of oil-in-water emulsions,traditional techniques face huge challenges in the separation of oil-in-water emulsions.Membrane separation technology has the characteristics of low energy consumption,high efficiency,and strong versatility,and has been widely studied in the oil-water separation process.However,the separation efficiency of membrane separation technology is limited by internal factors such as the anti-fouling and chemical stability of the membrane and external factors such as the form of membrane modules and operating conditions.The separation of oily wastewater requires the membrane not only to have high porosity and easy handling,but also to have super wettability and low adhesion to oil on the membrane surface.Due to the high separation efficiency and good reusability,compared with traditional separation methods,the high porosity,super hydrophilic membrane has great advantages and has broad prospects in the field of oil/water treatment.In this context,this article is dedicated to the study of high-porosity,super-hydrophilic and super-oleophobic oil-water separation membranes.The high porosity base membrane is designed and prepared,and the chemical groups on the surface of the membrane are adjusted to endue the membrane with special properties.The specific work is as follows:(1)Design and preparation of PTFE fiber composite membrane.To prepare a high-performance PTFE fiber composite membrane for oil-water separation,a PTFE fiber membrane with high porosity and uniform pore size distribution was prepared by the biaxial stretching method.The parameters in the biaxial stretching process were optimized and the final porosity was 80.3%,average pore size was 0.23?m and maximum pore size was 0.24?m.To maintain the stability of the pore size and facilitate the preparation of the membrane module in the application,the PTFE fiber membrane and the polypropylene non-woven fabric are composited by the thermal composite method,and the composite temperature,pressure and speed are optimized,and the final preparation has a peel strength of 7.5N/2.5cm,PTFE fiber composite membrane with an average pore diameter of 0.22?m.High porosity and uniform pore size distribution provide the foundation for membranes for oil-in-water emulsion separation.(2)Preparation of PTFE-PDA/PEI-PEMA fiber composite membrane and study of oil-water separation performance.Use dopamine(DA)and polyethyleneimine(PEI)as the intermediate adhesion layer to give PTFE fiber surface active groups of amino and hydroxyl groups,and poly(ethylene-co-maleic anhydride)(PEMA)as the negative hydrophilic group provider,through the amidation reaction of acid anhydride and amino group,the PEMA was fixed on the surface of the fiber composite membrane,and then the unreacted anhydride was further hydrolyzed and ionized to prepare a hydrophilic PTFE-PDA/PEI-PEMA fiber composite membrane.This membrane not only has negative electricity underwater,but also has super oleophobic properties.The surface zeta potential of this membrane is-18.45m V,the permeation flux of pure water is2663L·m-2·h-1under the transmembrane pressure of 0.05MPa,and the contact angle is 23.6°.The membrane has high separation efficiency for vegetable oil,toluene,petroleum ether and cyclohexane oil-in-water emulsion containing cationic surfactant,and the oil rejection ratio is98.6%,97.9%,98.1%and 98.9%,respectively.In the separation process,the underwater super-oleophobicity of the membrane and the low adhesion to oil make the membrane difficult to be adhered and contaminated by oil,and it has a lower flux reduction ratio and a higher flux recovery ratio.The membrane was subjected to continuous water rinsing experiments,and it was found that the membrane has good hydrophilic stability,making the recycling of the membrane simple and feasible.(3)Preparation of PTFE-PGAL/PEI-KH560 fiber composite membrane and study of oil-water separation performance.The gallic acid(GAL)can be self-polymerized by laccase catalyst under acidic conditions.Under alkaline conditions,the PGAL and PEI was co-deposited on the surface of the PTFE fiber composite membrane,and then a stable acid-resistant micro-nano structure hydrophilic layer was formed on the surface of the fiber composite membrane via the hydrolysis and condensation of?-(2,3-epoxypropoxy)propytrimethoxysilane(KH560)to prepare a hydrophilic PTFE-PGAL/PEI-KH560 fiber composite membrane.This membrane has strong oleophobicity and oil-resistant adhesion underwater,and the pure water permeation flux of 7799.3L·m-2·h-1under transmembrane pressure of 0.1MPa,and water contact angle of 38.36°.The separation efficiency of the membrane for oil-in-water emulsions containing Tween-80 can reach more than 98%,and the permeation flux is as high as 1747.2L·m-2·h-1under0.05MPa.Repeated filtration experiments show that the membrane is reproducible usability.Stability analysis of the membrane found that the membrane has strong physical stability,and its hydrophilicity remains basically unchanged under acidic conditions.(4)Preparation of PTFE-PGAL/CS-KH550 fiber composite membrane and study of oil-water separation performance.The GAL can be self-polymerized by laccase catalyst under acidic conditions.The PGAL and chitosan(CS)are cross-linked through the esterification reaction with citric acid(CA)to form a three-dimensional network structure on the surface of the PTFE fiber composite membrane,which gives the PTFE fiber composite membrane antibacterial and hydrophilic properties,and then a stable hydrophilic layer of micro/nano structure was formed on the surface of the fiber composite membrane via the hydrolysis and condensation of?-aminopropyltriethoxysilane(KH550),thereby preparing an antibacterial and hydrophilic PTFE-PGAL/CS-KH550 fiber composite membrane.This membrane has anti-protein pollution performance,antibacterial performance and strong oleophobicity underwater,and the pure water flux of 6861.2L·m-2·h-1under a transmembrane pressure of 0.1MPa,and a surface water contact angle of 45.65°.The membrane not only has contact pollution resistance to bovine serum albumin,but also the combined action of PGAL and CS makes the membrane have outstanding antibacterial properties.The separation efficiency of the membrane for oil-in-water emulsions containing Tween-80 can reach more than 97%,and the permeation flux is as high as 1596L·m-2·h-1under 0.05MPa.Repeated filtration experiments show that the membrane has a reusability.The stability analysis of the membrane found that the membrane has strong physical stability,and its hydrophilicity is basically unchanged under the conditions of p H=3,p H=12solution and ethanol. |
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