Study On The Influence Of Base Membrane Pore Size Adjustment On The Permeability Of PDMS/PVDF Membrane

Wastewater containing volatile organic compounds(VOC)causes serious harm to human health and the environment.Existing treatment methods such as steam stripping,oxidation,and biological methods have different shortcomings.As a new treatment method,pervaporation is environmentally friendly and highly efficient.It has the advantages of low consumption,recycling of organic matter,and improved resource utilization.It can be applied to VOC wastewater treatment.PV membranes are mostly used in the separation of organic matter/water systems,and there are few studies on their applications in VOC wastewater treatment.The researches on PV membranes are mostly focused on the modification of the separation layer,but the base membrane that affects the permeation resistance of composite membranes is rarely studied.In this paper,a phase inversion method is used to prepare PVDF ultrafiltration membrane as the base membrane of the composite membrane,and the influence of the base membrane preparation parameters(polymer PVDF concentration,non-solvent additive type and concentration,and air bath time)on the pore structure of the base membrane is systematically investigated,and refer to the idea of pervaporation series resistance model to analyze the reasons for its influence on the pervaporation performance of the composite membrane.Furthermore,the surface structure and physical and chemical properties of the composite membrane were analyzed through serial characterization(SEM,AFM,XRD,TGA,etc.).Finally,systematically investigate the influence of various parameters(including feed liquid concentration and temperature,membrane surface flow rate,absolute pressure on the downstream side of the membrane,etc.)on the separation performance of the composite membrane during the operation process,and provide theoretical guidance for the actual industrial application of PDMS/PVDF membrane.The experimental results show that the membrane preparation conditions of the base membrane are:polymer concentration is 18 wt.%,the type of non-solvent additive is LiCl,the LiCl concentration is 3 wt.%,and the air bath time is 30 s.The pore size and porosity of the composite membrane prepared therefrom has better pervaporation performance.Investigate the preparation conditions of the separation layer.When the amount of polymer PDMS is 5 g,the ratio of polymer amount to solvent n-heptane is 5:35,the amount of crosslinking agent TEOS is 0.5 g,the amount of catalyst DBTL is 0.2 g,and the membrane forming temperature is 70℃,the membrane formation time is 5 hours,and the thickness of the separation layer is 20 μm.The separation layer has an excellent separation effect.And through the characterization results,it can be seen that the surface of the prepared composite membrane is compact and flat,and the stability is good.Investigate the influence of various operating conditions on the separation performance of the composite membrane.As the concentration of the feed liquid increases,the acetone flux and total flux increase,and the water flux is basically unchanged,but the separation factor gradually decreases.The acetone flux,water flux and total flux increase with the increase of the temperature of the feed liquid.But the separation factor gradually decreases,and the flux is affected by temperature and satisfies the Arrhenius equation.Ea(acetone)<Ea(water)is obtained,indicating that the permeation flux of water is more affected by temperature.As the flow rate of the membrane surface increases,the flow conditions is improved,the acetone flux and total flux increase,and the separation factor also increases.As the pressure on the downstream side of the membrane increases,the flux and total flux of each component gradually decrease,while the separation factor remains unchanged.Through long-term stability experiments,the permeation flux is stable at 820-840 g·m-2·h-1,and the separation factor is 44-48.