Preraration And Application Of Hydrophilic/Hydrophobic Composite Membranes For Membrane Distillation

The hydrophobic membranes which applied in membrane distillation（MD）are very vulnerable to be fouled by organic compounds.Herin,in order to solve this problem,two types of novel membranes were fabricated with the exceptional anti-oil-fouling property.i.e.Polyacrylonitrile and cellulose acetate（PAN&CA）membranes,and the commercial polyfluortetraethylene（PTFE）was used as the support and selective layer.Moreover,the desalination performance of the prepared membranes was also observed by carrying the directly contact membrane distillation（DCMD）as a model experiment.The results suggested that the membranes which endue with the superhydrophilic function might have a good application prospect of a practical desalination progress.The main results are as these follows:（1）The morphology of the commercial PTFE microporous membrane showed a"node-fiber"substructure.The membrane flux of PTFE could keep stable around 17.2kg/（m²·h）in DCMD while slowly decreased to 0 kg/（m²·h）,when 1 wt‰crude oil were mix with the original NaCl feed.The results indicate that traditional hydrophobic membrane could not maintain dried of its inner pores and use for practical desalination progress when the feed containing organic components and other surfactants.（2）Compared with the PTFE,the thickness of the prepared PAN-PTFE composite membrane increased but pore size distribution got narrow.The nanofiber of the PAN which produced via electrospinning showed a 3D net-work structure and without any beads.In particular,the underwater oil contact angle（OCA）of the PTFE/PAN-NH₂ and PTFE/PAN-OH membranes could reach 153.4±0.1°and 161.7±0.1°after alkaline modifying and amination progress.The membranes which could maintain stable at least for18 h during MD.In addition,the flux of the prepared PTFE/PAN-OH membrane could keep balance in 15.2 kg/（m²·h）.Indicating that compared with the PTFE,the hydrophilic/hydrophobic composite membrane which prepared by electrospinning can be applied to the practical MD desalination progress that could prevent surfactant wet the membrane inner pore.（3）The morphology of the anti-oil-fouling functional layer which prepared via the template method exhibited a honeycomb structure.The OCA increased with the polymer concentration increasing.Especially,the OCA of 9CA-0.2 functional layer could reach at158.1±2.5°.The membrane could maintain stable in practical DCMD progress.