The Preparation And Application Of Pervaporation Membrane For Deep Deh Ydration

With the continuous development of aerospace,new energy,pharmaceutical and chemical industries,petrochemicals and other fields,the quality of liquid organic solvents is becoming more and more demanding,especially for the deep removal of water.The presence of micro water in industry has a great impact on organic solvent applications,catalytic cracking,organic synthesis reactions,chemical component separation and detection systems.At present,the technologies used for deep dehydration mainly include special distillation,molecular sieve method and gas extraction method,etc.However,each of these technologies has its own disadvantages,such as high energy consumption and low dehydration depth of special distillation,and the use of additives in the distillation process is likely to cause environmental problems.Therefore,the need to develop a low energy consumption,environmental protection,efficient and durable of the depth of dehydration process has important application value and market demand.Pervaporation,as a new membrane separation technology,is increasingly used in the field of organic solvent dehydration for its advantages of high efficiency,enegy saving,environmental protection and simple operation.Based on the many advantages of pervaporation technology,this paper proposes to apply pervaporation technology to the process of dehydration of solvents to achieve deep dehydration.In this study,polyvinyl alcohol was selected as the main deep dehydration membrane material based on the affinity of the system to be separated and the membrane making material,and the PES ultrafiltration membrane was prepared by the phase conversion method,and the PVA/PES composite membrane was prepared by using the PES ultrafiltration membrane as the support layer and dip-coating the PVA solution on the surface of the PES membrane,and a series of physical and chemical properties of the prepared PVA/PES membrane were characterized.The effects of the membrane preparation conditions such as polyvinyl alcohol concentration,times of dip coating,cross-linking conditions and post-treatment conditions on the properties of the composite membranes were investigated with the ethanolwater system.The experimental results showed that the pervaporation membrane separation layer and the support layer were tightly bonded.Under the optimal membrane making conditions,the prepared PVA/PES composite membrane has the best separation performance for 95 wt.%ethanol/water solution with total flux of 145 g·m-2·h-1 and separation factor of about 600.Finally,the 99.7 wt.%isopropanol-water system was used as a probe to study the effect of PVA/PES composite membrane for deep dehydration.The effects of feed liquid temperature,feed liquid water concentration,flow rate of membrane surface and post-membrane absolute pressure for total flux and separation factor of PVA/PES membrane were systematically investigated.The optimal operating conditions were determined as follows:feed liquid temperature of 70℃,post-membrane absolute pressure of 0.67 kPa,and membrane surface flow rate of 2.0 cm·s-1;deep dehydration of isopropanol was carried out under the optimal operating conditions.The water content in isopropanol decreased from 2987.5 ppm to about 85.3 ppm.The conventional dehydration process is far from such depth of dehydration.The isopropanol obtained through the pervaporation meets therequirements of high-purity electronic grade chemicals,indicating that pervaporation technology can be used for deep dehydration of organic solvents,expanding the technology of deep dehydration and having certain guiding significance for its industrial application.