Poly(Ionic Liquid)-Based Membranes:Tunable Hydrophilicity/Hydrophobicity And Application In Oil/Water Separation

Oil exploitation,machine manufacturing,transportation,food processing and frequent oil spills have produced large volumes of oily wastewater every year.Oily wastewater would be a real threat to the environment if it was directly drained into water system without treatment.In these wastewater treatment methods,membrane separation technology characterized by wettability of solid surface has attracted widespread attention in academia and industry due to the low-energy consumption and high-efficiency.Poly?ionic liquid?s?PILs?had the characteristics of ionic liquids?ILs?,specifically the tunable structures/properties.The anions and cations species of ILs would bring about the changes in wettability,which further affected the hydrophilicity or hydrophobicity of PILs modified membranes.This dissertation aimed at preparing a series of PIL-based membranes?PILMs?used for oil/water separation,of which the surface wettability could be controlled by the anions and cations.In this thesis,the main work was carried out as follows:1.General overviews including oil/water separation,surface wettability of ionic liquids?ILs?and poly?ionic liquid?s?PILs?,and the application of PILs in oil/water separation.2.A series of PIL-based membranes?PILMs?were prepared via the facile one-step photopolymerization of N-vinylimidazolium ionic liquid and divinylbenzene?DVB?on the sintered stainless wire meshes.The wettability of PILMs was adjusted by the structures of PILs,specifically the anion species?acrylic anion,Br^-and PF₆^-?and alkyl chain length of imidazolium?butyl and octyl?.The structures and properties of prepared PILMs were characterized by ¹³C MAS NMR,FT-IR,XPS,TGA and SEM.The surface wettability of PILs and corresponding PILMs was quantified by water contact angles?CAs?.It was demonstrated that when the order of anions was acrylic anion,Br^-and PF₆^-,respectively,the hydrophilicity of PILs and PILMs decreased;meanwhile,with the alkyl chain length of imidazolium increased,PILs and PILMs were more hydrophobic.3.The hydrophilic poly?1-vinyl-3-butylimidazolium acrylate?-based membrane?PILM-1?was used as“water-removing”membrane and was fixed into an intermittent oil/water separation device.Water could pass through the membrane while oil could not.PILM-1 could separate different kinds of oil/water mixtures of high and low oil concentration,having the separation efficiency up to 99.99%.During the separation of diesel-1/water mixture at 80°C for 100 times,PILM-1 showed excellent thermostability.Meanwhile,PILM-1 could maintain the chemical stability in the acid-alkali-salt circumstances.On the contrary,the hydrophobic poly?1-vinyl-3-octylimidazolium hexafluorophosphate?-based membrane?PILM-5?was used as“oil-removing”membrane and only oil could permeate the membrane but water could not.PILM-5could separate the variety of oil/water mixtures in batches and the corresponding separation efficiency was up to 99.55%.In the process of 100 cycles,the separation efficiency of PILM-5 for 80°C dichloroethane remained 99.8%.Continuous oil/water separation was also achieved by assembling PILM-1 and PILM-5 on the fabricated continuous devices.A T-type device could separate various oil/water mixtures continuously with the separation efficiency above 99.97%,besides,the purified oil and water could be collected simultaneously;a tank-type device could separate dispersed petroleum ether/water mixture?5%m/m?,with a handling capacity of 46 L within 12 h.