Study On The Super-hydrophobic Modification And Membrane Distillation Performance Of Ceramic Membrane

Membrane separation process has the characteristics of simple and efficient,widely used in air or water purification.As an important component of the membrane separation process,membrane distillation provides a new idea for seawater desalination and liquid concentration.The core of the membrane distillation process is hydrophobic membrane.In many membrane materials,ceramic membrane have excellent temperature resistance,high mechanical strength.However,the natural hydrophilicity of ceramic membranes result in their inability to be used in membrane distillation processes,so hydrophobic modification of ceramic membrane is crucial.In this paper,porous alumina flat ceramic membrane was used as the base membrane,and its super-hydrophobicity was modified by different methods,then it was applied to the separation performance of membrane distillation.The surface morphology and chemical structure of super-hydrophobic modified ceramic membranes were studied by Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）and field emission scanning electron microscopy（FESEM）,.The main research contents and conclusions are as follows:（1）In order to improve the hydrophobicity of the ceramic membrane,a super-hydrophobic PS microporous membrane was prepared on the surface of the hydrophilic ceramic membrane by non-solvent phase separation（NIPS）method.The experimental results show that the surface aggregate a large number of PS particles agglomerated and the surface roughness of the ceramic membrane increases after the super-hydrophobic modification.The water contact angle and average pore size of the modified membrane increased first and then decreased with the decrease of PS/EtOH ratio.The water contact angle of the modified membrane increased and then decreased and the average pore size decrease gradually with the increase of the immersion time.The optimum experimental conditions were as follows:the ratio of PS/EtOH was 1:4 and the immersion time was 3 min.The water contact angle of the modified ceramic membrane can be up to 152°.The results show that the modified ceramic membrane can maintain super-hydrophobicity for a long time,the permeation flux is about 1.57kg·m^-2·h^-1,and the desalination rate is higher than 99.5%.With the increase of NaCl solution temperature,the permeation flux and salt rejection of the modified membrane gradually increased.With the increase of NaCl solution concentration,the permeation flux of the modified membrane gradually increased.The surface stable performance test of the modified membrane showed that the modified membrane present good resistance to weak acid and weak alkali.（2）In this study,monodisperse nano-silica（SiO₂）sol was prepared by Sol-gel method,and the SiO₂ particles were hydrophobicly treated with low surface energy silicone ODTMS.The surface of the ceramic membrane was modified by deposition on the surface of the ceramic membrane.The results show that the SiO₂ particles is superimposed on the surface,then the micro-nano rough structure appeared,the surface roughness increased obviously after the super-hydrophobic modification.With the increase of the ODTMS mass fraction,the average pore size of the modified membrane decreased,the water contact angle increased first and then decreased.With the increase of temperature,the average pore size of the modified membrane decreased and the water contact angle increased first and then decreased.With the increase of deposition time,the average pore size gradually decreased and the water contact angle increased first and then decreased.The optimum experimental conditions were as follows:ODTMS mass fraction was 0.4%,reaction temperature was 80℃,deposition time was 10h.The water contact angle of the modified ceramic membrane increased significantly from 72°to 158°.Acid and alkali resistance and chemical stability test results show that:modified membrane resistant to strong acid and alkali,in the common chemical solvent such as water,Na₂CO₃ and NaCl aqueous solution can maintain good stability.In the process of membrane distillation,the super-hydrophobic modified ceramic membrane can maintain the super-hydrophobicity for a long time.When the vacuum degree is-0.10MPa,the permeation flux of the modified membrane is about 15.60kg·m^-2·h^-1,salt rejection reach 99.99%.With the increase of vacuum,the permeation flux of the modified membrane increased,the salt rejection change little.