Preparation Of PVDF Hydrophobic Membrane And Study On Ultrasonic Field Combined Membrane Distillation

With the rapid development of the economy,the dual problems of water shortage and water pollution have become increasingly serious.The increasingly diverse types of pollutants have challenged traditional water treatment processes.Membrane distillation technology is a new technology that uses hydrophobic membranes for membrane separation in recent years.It has the advantages of simple equipment,easy process automation,energy saving and high efficiency,and no new pollutants will be produced during the process.However,it also has some shortcomings,such as high cost,short life,and easy membrane fouling.In this paper,a hydrophobic polyvinylidene fluoride(PVDF)membrane was used for membrane distillation experiments.And ultrasonic technology was used to construct ultrasonic combined membrane distillation reactor.The optimum technological parameters were determined by experiments,and the effects of various pollutants on membrane flux were studied in order to solve the membrane fouling problem in the process of membrane distillation,and the effect and mechanism of ultrasound field on the mitigation of membrane fouling were explored.The main contents and results are as follows:The characterization of the self-made PVDF hydrophobic membrane,including the porosity,average pore size,contact angle measurement and membrane structure analysis of the membrane.The results show that the self-made membrane has good membrane flux and hydrophobicity,and is suitable for subsequent membrane distillation experiments.The variation of membrane flux in direct contact membrane distillation experiments was studied by controlling different parameters,including hot side liquid temperature,feed liquid concentration and flow rate.The results showed that the increase of hot side temperature and hot side flow increased the membrane flux.The decrease of the cold side temperature and the increase of the cold side flow have no effect on the membrane flux,and the membrane flux decreases as the concentration of the feed liquid increases.After adding the ultrasonic field,the effects of different process parameters on membrane flux and relative flux were investigated,and the effect of membrane distillation mass transfer and membrane anti-pollution performance was explored.The results show that the addition of ultrasonic field has a significant effect on the membrane flux,and is positively correlated with the ultrasonic power and negatively correlated with the frequency.The ultrasonic enhancement effect is enhanced as the concentration of the liquid solution increases,and decreases as the temperature on the hot side and the flow on the hot side riseMembrane distillation experiments were carried out on some inorganic pollutants and organic pollutants,including sodium chloride,calcium carbonate,calcium sulfate and bovine senim albumin(BSA)solutions.The membrane was observed by scanning electron microscopy(SEM)before and after the experiment,and the separation performance and microstructure of the membrane were discussed under the condition of ultrasonic or not.The results show that the improvement of membrane flux decrease caused by NaCl membrane fouling caused by ultrasonic is very limited.CaCO3 can hardly cause membrane fouling due to its extremely low solubility.The addition of ultrasound effectively alleviated the decrease of membrane flux caused by crystallization and precipitation of CaSO4.Because of the hydrophilicity of BSA molecules,it is difficult to adhere to the PVDF hydrophobic membrane.Therefore,the membrane flux almost did not decrease before and after the addition of ultrasound.