Preparation Of Highly Hydrophobic PVDF Microporous Membrane And Study On Fouling Properties Of Vacuum Membrane Distillation

The new separation process-membrane distillation?MD?is a kind of separation technology with different steam pressure as driving force.Compared with conventional separation technology,MD has many advantages,such as low operating temperature,simple equipment,easy operation,environmentally friendly,et al.However,it was not widely used in reality due to its high cost,poor antifouling property and lack of special membrane,et al.In order to reach the purpose of wetting and polluting resistance,increasing hydrophobicity of membrane,even preparing membrane which can clean itself is a problem to be solved at present.Firstly,we use Hansen solubility parameter prediction method combined with liquid absorption method and Differential Scanning Calorimetry?DSC?to select diluents for preparing PVDF microporous membrane with thermally induced phase separation?TIPS?in the article.So that we can choose some better single diluents from comparing membrane structure,N₂ flux,porosity and mechanical strength,et al.Based on better properties of single diluent,we can also select the best mixed diluents and conditions.The membrane system has 20 wt%PVDF,5 wt%sulfolane?SFL?and95wt%dibutyl phthalate?DBP?,and it has been dissolved in 180?,shaped in 150?and cooled in 60?.Secondly,we use the mixed diluent system and conditions we have chosen to prepare microporous PVDF membrane on the smooth plate,120 mesh and 320 mesh sandblasted stainless steel plate respectively by TIPS.Which that we can get the contact angle of membranes are 116°?X membrane?,131°?Y membrane?,153°?Zmembrane?respectively.It covers three surface infiltration situations:hydrophobic,highly hydrophobic,super hydrophobic.We can see many homogeneous pores on each membrane from the electron microscopy photos,the membranes flux was more than 0.75 m³/?m²·s?,and tensile strength were more than 4.2 MPa.Again,we select typical pollutants sodium chloride?NaCl?,calcium carbonate?CaCO₃?,humic acid?HA?and bovine serum album?BSA?to research static membrane pollution in 60?,70?,80?respectively.We study the influence of antifouling property of membrane for hydrophobicity,temperature,concentration.It turned out that the membrane hydrophobicity is higher,its antifouling property is better.Because the water droplets can roll in high hydrophobic surface to take away some foulings.So that we can achieve the purpose of self-cleaning.And the feed liquid temperature and concentration are higher,the foulings can enter membrane holes easily,the pollution of membrane is more serious.Thus the membrane has been polluted.In the end,we study that the pollutants?NaCl,CaCO₃,HA,BSA?are how to pollute the Z membrane from the change of membrane distillation flux,distillate conductivity?absorbance?,contact angle,SEM-EDS results and membrane cleaning results in controlled condition?vacuum degree is 0.086MPa,the feed rate is 15L/h,operation time is 10h?of membrane distillation.It turned out that inorganic pollutants NaCl crystallizes out on the membrane surface with membrane pores being wetted to lead to the decrease of the flux.And CaCO₃ deposits on the membrane surface in the form of rodlike,but the inner of membrane has almost not been polluted.It can recover high hydrophobicity after being cleaned with hydrochloric acid.Due to organic pollutant-HA has negative electricity after ionizing H⁺in solution,these ions of negative electricity can reject mutually.So HA has been dispersed on the membrane surface in the form of small granular and it not blocks membrane pore seriously,and the hydrophobicity can recover more than 87%after being cleaned in sodium hypochlorite solution with ultrasonic.And BSA is formed gel layer on the membrane surface and the internal structure has been polluted,which can destroy hydrophobicity and reduce the flux.But the hydrophobicity of fouled membrane can recover to 83%and even more than.