| With the development of pervaporation membrane,industrial production on the performance requirements of pervaporation membrane is getting higher and higher.Because the comprehensive performance of the composite membrane is affected by both the separation performance of the composite membrane and the base membrane properties,it is the key to improve the separation performance of the pervaporation membrane in order to find a better separating layer material and the base membrane material.In this paper,using the properties of polytetrafluoroethylene?PTFE?,such as high temperature resistance,strong acid and alkali resistance,solvent corrosion resistance and the properties of polyimide?PI?,such as heat resistance,solvent resistance,chemical stability and high mechanical strength,to prepare a PI/PTFE composite pervaporation film.The performance of pervaporation separation in 95% ethanol/water solution was investigated using a laboratory self-made cross-flow membrane module.The main contents are as follows:?1?Hydrophobic PTFE microporous flat membrane was modified by hydrophilicity firstly,and hydrophilic microporous PTFE membrane was used as base membrane of composite membrane.Pyromellitic dianhydride?PMDA?and 4,4?-diadmacodiphenylether?ODA?were used as the main raw materials to prepare the PI precursor polyamic acid?PAA?by solution polymerization.After conducting the doctor blade coating process,The PAA was coated onto the hydrophilic PTFE base film,and the PI/PTFE composite film was prepared by thermal imidization method.It was concluded that the PI / PTFE composite membrane could be prepared by the method of imidization,imidization temperature and time during preparation of PI/PTFE composite membrane.The selection of liquid temperature and the selection of the lateral pressure of the PI/PTFE composite membrane were studied in the separation of 95% ethanol/water solution,and the optimum conditions of PI/PTFE composite membrane were obtained.Research indicates: In the preparation of PI/ PTFE composite membrane,thermal imidization,thermal imidization temperature and retention time conditions for 80 ?? 150 ??0.5 h??200 ??0.5 h??250 ??0.5 h?,the optimum PI / PTFE composite membrane preparation process,the PI / PTFE composite membrane PI layer contact angle test for the 80 °.Fourier transform infrared spectroscopy?FTIR?showed that PAA was completely imidized to PI after thermal imidization,and the surface and cross-sectional morphology of PI/PTFE composite films were observed by field emission electron microscopy?SEM?the lower layer is a microporous and other PTFE layer.When the test liquid was selected at 30 ? and the permeate side pressure was 200 Pa,the separation effect was better under the optimal conditions,the permeation flux of the permeate was 1.96 Kg·m-2·h-1,and the separation factor reached 38.23 under the optimum conditions of PI/PTFE composite membrane.?2?In order to further improve the performance of PI/PTFE composite membranes,the PI/PTFE composite membrane was modified by hydrophilicity.SiO2/PI was prepared by adding hydrophilic gas-phase nano-silica to PI precursor PAA/PTFE composite film.The best hydrophilic SiO2/PI/PTFE composite membrane was prepared by discussing the doing amount of hydrophilic gas-phase nano-silica,and the pervaporation test was carried out.Research indicates: The hydrophilic effect of SiO2/PI/PTFE was best when the content of hydrophilic silica was 3%,the contact angle of the 3%-SiO2/PI/ PTFE composite film showed a contact angle of 47.1 °.SEM observation of the surface and cross-sectional morphology of the 3%-SiO2/PI/PTFE composite film showed that the surface of the composite film after physical doing changed from the original smooth and compact morphology to the rough roughness of the physical morphology,the morphologies of the particles become disordered morphology of the "groove-convex" organic-inorganic continuous phase.The weight loss of SiO2/PI/PTFE composites after the physical doing was little changed at 479 ?,and the weight loss temperature was about 30 ? higher than that of PI/PTFE composites.When the temperature of the feed solution was 30 ? and the permeation pressure was 200 Pa,the permeation flux of 3%-SiO2/PI/PTFE composite membrane was reduced by the introduction of inorganic nano-particles.0.352 Kg·m-2·h-1,but the separation factor increased from the original 38.23 to 62.90.The results show that the permeation selectivity of 3%-SiO2/PI/PTFE composite membranes is further enhanced when the permeation flux is maintained at a relatively high level after hydrophilization.?3?After the physical modification of SiO2/PI/PTFE composite membrane,the permeation separation effect of the composite membrane was further improved,but the separation factor was still lower than that of the same type.The results showed that SiO2/PI/PTFE composites could improve the selectivity of SiO2/PI/PTFE composites,and they were used as chemical crosslinking reagents.The effect of the PI layer of the composite film was cross-linked by chemical diadmace.The cross-linking efficiency and cross-linking concentration of different diadmaces and cross-linking time were studied.Research indicates: FTIR tests showed that the diadmaces had some crosslinking effect on the PI layer of the SiO2 / P I/ PTFE composite film,but the crosslinking efficiency of ethylenediadmace was the highest,and the crosslinking reaction of ethylenediadmace occurred during the same crosslinking time the greatest degree.SEM observation of the surface and cross-sectional morphology of the SiO2/PI/PTFE composite film showed that the surface of the composite membrane became rough after crosslinking,and the surface layer of the PI layer formed a dense layer crosslinked layer.The contact angle test showed that the contact angle of the composite membrane was 49.07 ° after crosslinking with ethylenediadmace.The permeation flux of 3%-SiO2/PI/PTFE composite membrane was 0.179 Kg·m-2·h-1 at 30 ?,osmotic pressure 200 Pa,ethylenediadmace crosslinking concentration 5% and crosslinking time 8 h,which is higher than that of other types of composite membranes,and the separation factor increased from 62.90 to 112.94. |
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