Study On Preparation Of PTFE-based Membrane And Its Distillation Performance

Membrane distillation offers wide application prospects in the field of seawater desalination because of the advantages of low operating pressure,low operating temperature gradient,high salt rejection and simple equipment,etc.Electrospinning is a method used to manufacture nanofibers by stretching a polymer solution or melting under the action of static electricity.This technique has several advantages such as the fact that a wide variety of raw materials are applicable,the fiber structure is very adjustable,and the device is simple.This article focuses on the outstanding issues of current membrane in distillation technology,such as low permeate flux and poor hydrophobicity,which limit the larger-scale application of membrane distillation technology.The new type of Polytetrafluoroethylene(PTFE)-based superhydrophobic membrane was developed based on electrospinning technology by using PTFE with advantages of high hydrophobicity,low heat transfer coefficient and good chemical stability as the raw material and combining nano-doping and structural design methods.The prepared PTFE-based superhydrophobic membranes were used for membrane distillation.The main research results are:(1)Based on electrospinning technology,Polyhedral Oligosilsesquioxane(POSS)rigid nanoparticles were introduced into PTFE nanofiber membranes to prepare PTFE&POSS hybrid nanofiber membrane.The SEM,EDS,XRD,tensile mechanics test,contact angle test and other methods were used to characterize the structure and performance of PTFE&POSS electrospun membrane,and explore the effect of different POSS doping amount on the membrane used in direct contact membrane distillation.The results show that the morphology of PTFE&POSS nanofiber membrane is optimized when the POSS content is 2%.The addition of organic/inorganic hybrid POSS effectively improves the crystallinity and roughness of the PTFE nanofiber membrane,thereby improving its mechanical and hydrophobic properties.The unique beaded structure of PTFE&POSS nanofibers helps to increase the porosity of the membrane.When it is used for membrane distillation,the permeation flux can reach 40±2 L m^-2h^-1.Over than 200h of operating,the permeate flux was still basically stable,and the salt rejection rate was always kept above 99.9%,showing good long-term stability.(2)Based on electrospinning-electrospraying technology,PTFE nanospheres were prepared by electrospraying process and high-strength PI nanofiber membrane was introduced through electrospinning technology to design and prepare super-hydrophobic electrospun PTFE/PI blended nanofiber membrane with interlayer lotus leaf structure for direct contact membrane distillation.The SEM,EDS,XRD,tensile mechanics test,contact angle test and other methods were used to characterize the structure and properties of PTFE/PI-BCNM in order to explore the effect of different PTFE/PI ratios on PTFE/PI composite membranes,and its direct contact membrane distillation performance was tested.The results show that when the PTFE/PI ratio is 2:1,the morphology of the PTFE/PI composite membrane is the best,which presents a porosity of 78±3%,an average pore size of 1.00±0.05 um,a contact angle of 150±2°,and a strength of 3.1±0.4 Mpa.The maximum permeate flux in the membrane distillation test could reach 45±3 L m^-2.h^-1,and the salt rejection rate was almost 99.9%.