Research On Mass Transfer Behavior Of Fluoropolymer Hollow Fiber Membranes

The energy consumption of separation and purification greatly in the total energy consumption of industry.Green and efficient separation technology is the key to sustainable economic development.The recycling of lubricating oil is mainly achieved through pretreatment,purification and re-refining and can create environmental and economic benefits.Advanced technology is urgently needed due to traditional regeneration technology has some problems such as high energy consumption and secondary pollution.Membrane separation technology has gained in popularity due to its advantages such as high separation efficiency,low energy consumption and easy to be combined with other technologies.At present,the commercial polymer membrane is mainly used in water treatment and there are few reports about the organic solvents.Compared with water,lubricating oil has higher viscosity and more complex composition.So mass transfer efficiency and stability of polymer membrane need to be solved when using polymer membrane to treat waste lubricating oil.According to the Hagen-Poiseuille equation,reducing viscosity can promote mass transfer,while increasing temperature is an effective way to reduce viscosity.For years,our group has been committed to develop high-performance membrane materials,among which PVDF and FEP hollow fiber membranes have strong thermal and chemical stability,which are expected to be used in the regeneration of waste lubricating oil.Kerosene,lubricating oil and water were selected as feed solution to study the effect of viscosity on the mass transfer behavior of liquid in fluoropolymer hollow fiber membranes.A continuous 8-hours membrane permeation flux test was carried out under the operating pressure of 0.06 MPa at different temperature.The mass transfer behavior was explained by analyzing the feed,membrane material and membrane structure of the hollow fiber membranes,as well as the.the interaction.The results showed that the kerosene and lubricating oil flux of the hydrophobic PVDF hollow fiber membranes could be increased by increasing the operating temperature.The PVDF hollow fiber membranes can maintain excellent hydrophobicity below 65℃and the damage happened when the temperature rose to 85℃.After 120 min,its water flux begun to gradually increase to 2.92 L·m^-2·h^-1,and the trend would continue.The sample test results indicated that the pore size of PVDF hollow fiber membranes tended to decrease with increasing operating temperature.When coupled with pressure,the membrane hole would become smaller due to the swelling effect of organic liquid,while in aqueous solution,the water would squeeze the pore wall,resulting in the increase of the pore diameter.Porosity did not change significantly.Roughness was an important factor on the change of contact angle.Moreover,the capillary pressure was used to explain the difference of mass transfer behavior on the membrane surface.The kerosene flux of FEP hollow fiber membranes was much higher than that of lubricating oil.The water flux was similar to the kerosene flux,which was due to the presence of large strip holes on the membrane surface which can reduce capillary pressure and reduce the mass transfer resistance of water.For the same feed liquid,increasing the operating temperature did not significantly promote mass transfer.Finally,the membrane hole was regarded as a cylindrical hole perpendicular to the membrane surface.By using OpenFOAM to simulate the mass transfer behavior within a single membrane hole,the influence of contact angle,surface tension,aperture and kinematic viscosity was analyzed and quantified.The mass transfer can be divided into two stages,the gas-liquid two-phase flow of the exhaust and the single-phase flow.For the wetting phase,the influence of gas-liquid two-phase flow was negligible.When the flow developed into a single-phase flow,the main influencing factors were pore diameter and viscosity.For non-wetting phase（water）,there was a critical water contact angle.At room temperature,when the water contact angle was greater than 96°,water cannot penetrate a membrane pore with diameter of 0.26μm.The simulation results were closed to the experimental values and validated the interpretation of mass transfer behavior in Chapter 2 and Chapter 3.