PVDF Hydrophobic Membrane Wetting Process Control

With the increasing pollution of water resources,the application of hydrophobic membrane separation technology is more and more widely.But at the same time,in the process of using hydrophobic membrane,the drying problem of membrane pore cannot be ignored.In order to solve the problem for the hydrophobic membrane,based on the former research results by our group,the critical wetting depth of hydrophobic membrane was further studied.The continuous operation of hydrophobic membrane separation process was achieved at room temperature through the VMD-cleaning experiment.Moreover,this paper presented a method of using room temperature air to clean and dry the hydrophobic membrane.And then the effect of the two kinds of gas with different moisture content on the hydrophobic membrane in the process of gas purging is explored.According to the previous research results,the further study testified the existence of the critical wetting depth of hydrophobic PVDF hollow fiber membrane in VMD process,which was 19.5±0.5μm.Then the hydrophobic membrane separation experiments were performed using another surfactant,and the critical wetting depth value of the hydrophobic membrane was 20μm.Because this depth value is in the range of 19.5±0.5μm,the critical wetting depth value for a particular hydrophobic membrane material can be determined as a certain value.Through the experiments of VMD-cleaning,the drying of hydrophobic membrane materials can be achieved at room temperature,and the continuous operation of membrane separation process is realized.In this paper,the hollow fiber membrane module was swept by purging gas with different flow rate,and found that there was a limit value of purging gas pressure which was between 0.108MPa and 0.144MPa.The water in the membrane pore can be discharged completely,and the hydrophobic membrane can be recovered to the dry state when the purge gas pressure is in the above range.The effect of the two kinds of gas with different moisture content on the hydrophobic membrane is explored.And the main performance of the gas in the purge process is the mechanical shearing force of the purge gas,rather than the role of gas absorption of water,which is different from the principle of conventional heating drying methods.