Preparation Of Oxidation Resistant PP Hollow Fiber Membrane And Membrane Distillation Process Application

Membrane distillation technology is much suitable for the concentration/purification treatment of inorganic industrial wastewater.However,some industrial wastewater contains a variety of metallic cations,nitrate ions and oxidizing ions.Due to the hot operation of membrane distillation,the membrane materials are easy to be oxidized,leading to decrease in contact angle and structural aging failure.Thus,this affect the long-term separation performance,limiting the practical application of membrane distillation technology.Therefore,it is necessary to the preparation of a hydrophobic hollow fiber membrane with good mechanical properties and oxidation resistance,which is great significance for the concentration and purification treatment of industrial wastewater.In this work,based on the previous research in our laboratory(PP and POE blending modification and preparation of blend hollow fiber membrane),three antioxidants are chosen to be added in the blending system,improving the ductility and antioxidant ability of membrane.In the immersion vacuum membrane distillation,the operation stability and service life of the hollow fiber membrane are greatly improved.First,based on the previous research,dibutyl phthalate(DBP)and soybean oil with a mass ratio of 7:3 are used as the mixed diluent of casting solution,the solid polymer content of casting solution is set to be 30%,and liquid paraffin wax and DBP with a mass ratio of 1:1 are used as the core liquid(pore-forming agent)to prepare hollow fiber membrane.Under 60℃coagulation bath,n-hexane and anhydrous ethanol are used as extraction agents,the traction rate and core liquid temperature are further optimized to be20 m/min and 150℃,respectively.An optimized PP/POE blended hollow fiber membrane with high ductility is prepared by blending 15%POE into PP.The results show that the outer surface has uniform pore structure,while the inner wall presents uniform filamentous pores,and the cross-section is honeycomb with uniform pore structure distribution.The average pore size is 0.16μm with the pore size distribution of 0.10～0.20μm.The permeability of optimized PP/POE blended hollow fiber membrane is 27 L/(m~2·s),with the porosity of 62%,the fracture strength of 8 N,the tensile strength of 4.7 MPa and the elongation of 190%and water contact angle>110°.At the same time,the oxidation resistance of PP/POE blended hollow fiber membrane is studied.When adding 0.4%1076 antioxidant or 0.3%1010 antioxidant into the casting solution,the oxidation resistance of the membrane is significantly enhanced.In the oxidizing environment(1000 mg/L Na Cl O,p H=5-6),the anti-oxidizing PP hollow fiber membrane exhibits a very stable hydrophobicity,the water contact angle is stable over 100°.In comparison,the water contact angle of the hollow fiber membrane without oxidation modification is only 60°.Furthermore,the anti-oxidant polypropylene hollow fiber membrane is applied to separate mixed solution(60 g/L aluminum nitrate and 0.1 mol/L nitric acid)in the immersion vacuum membrane distillation.The rejection rate of the hollow fiber membrane with 1076 and 1010 antioxidants a remaines above 99.7%after 30 h running.The average flux finally stabilized at 2.3 kg/(m~2·h)and 2.7 kg/(m~2·h),respectively.By comparison,the rejection rate of hollow fiber membrane without antioxidant decreased to below 99.7%after10 h running.thus,the addition of antioxidant improves the structural stability and service life in membrane distillation application.