Preparation Of Superhydrophobic PP Composite Membrane And Application Of Membrane Distillation In High Saline Solution

The shortage of water resources has become a global problem to be solved,and technologies such as seawater desalination and wastewater treatment have attracted attention.With the development of ultrafiltration,nanofiltration,reverse osmosis and other water treatment technologies becoming increasingly mature,much high saline wastewater has been produced.How to treat it with high-efficiency,energy-saving and environmentally-friendly methods is a research hotspot in recent years.Membrane distillation is a new membrane separation technology,which is advantageous to high salinity treatment compared with other methods.Hydrophobic microporous membrane,as the core component of membrane distillation,restricts the development of membrane distillation technology.At present,the commonly used hydrophobic microporous membranes are difficult to meet the requirements of membrane distillation process.Therefore,it is significant to fabricate superhydrophobic membranes with excellent anti-wetting,anti-pollution and high-flux capabilities.In view of the above-mentioned problems,this paper investigates the preparation of superhydrophobic membrane and its performance in vacuum membrane distillation for the treatment of high-salt systems,making full use of the characteristics of superhydrophobic membranes to improve the processing efficiency of the membrane distillation.This paper explores and optimizes the conditions for the preparation of superhydrophobic membranes by surface modification of PP microporous membranes.The superhydrophobic PP composite membranes with modified surface roughness were successfully fabricated through a facile modification process of hydroxylation,loading of SiO₂ nanoparticles and coating of low surface energy material 1H,1H,2H,2H-perfluorodecy-ltriethoxysilane on the PP membrane.The surface wettability can be adjusted by the particle size and quantity of SiO₂ nanoparticles.The water contact angle of the prepared superhydrophobic F/SiO₂/PP-OH composite membrane can reach up to 159°.The impact of loading nanoparticle size on the surface roughness,critical nucleus size versus the loading nanoparticle size(d*_nuclear/d)and heterogeneous nucleation barrier were simulated by the model combining the surface roughness and superhydrophobility with the critical nucleation energy.With the optimized loading nanoparticles size to maintain the proper roughness,nucleation energy barrier and d*_nuclear/d to ensure the desire performance of antifouling,the resulting modified membrane possessed good anti-wetting ability and stable anti-fouling performance during the long-term continuous and batch operation of vacuum membrane distillation?VMD?treating high saline solution?3.5 wt%,15.0 wt%NaCl solution?.The fouling rate of the fabricated superhydrophobic membrane was decreased to 20%of the fouling rate of the original membrane under the 15.0 wt%high saline feed conditions.This paper also studied the effect of different feed concentration and feed flow rate on permeation flux and wettability under high concentration NaCl/MgCl₂ solution.The results showed that,with the concentration of MgCl₂ increasing,the permeation flux of the superhydrophobic membrane and the original PP membrane showed a tendency to decrease.However,the superhydrophobic membrane demonstrated a smaller degree of attenuation.The permeation flux of the superhydrophobic membrane is more stable than original PP membrane at the same condition.With the increasing of flow rate,the concentration and difference polarization problems can be effectively restrained and thus,the permeation flux of original PP membrane and F/SiO₂/PP-OH membranes can be significantly improved.More importantly,the prepared superhydrophobic F/SiO₂/PP-OH membranes still exhibit excellent anti-wetting and anti-fouling performance under high concentration NaCl/MgCl₂ solution.