| Ionic liquids (ILs) are composed of an organic cation (imidazolium, pyridinium,tetraalkylammonium, etc.) and an anion such as halide, tetrafluoroborate,hexafluorophosphate, triflate, amidotriflate, dicyanamide, etc. One of the mostsignificant features of the ILs is that it can be tunable. The chemical composition andphysical properties of ILs can be modulated by selecting the appropriate cation, anionand ligand, or fine-tune the alkyl chains of the cation, and thus obtain a lot of(Task-specific) multi-functional ILs. Another remarkable feature of ILs is that it hasan excellent ability of selective dissolution in a variety of organic solvents and water,and therefore it is referred to as "liquid Zeolite". These two characteristics of ILshighlight their potential applications in the field of separation. However, smallmolecule ILs are generally liquid at room temperature, and have poor film-formingability which limiting their applications as a membrane separation material. As a solidpolymer poly (ionic liquid)s (PILs) can improve these deficiencies to a certain degree.Meanwhile, PILs has the same functional groups as ionic liquids, so that a variety ofPILs with different structures and properties could be synthesized by selectingdifferent cation and anion. This means that it is easy to adjust the structures of theseobtained PILs by changing its chemical composition, and those polymers often exhibitdesirable mechanical strength which the ILs do not have. With these features PILs isexpected to be a new and promising separation material. However, PILs has poorability of film-formation, and thus can not withstand the greater pressure differentialin the pervaporation （PV） process. Therefore, it is of great importance to developPV membranes with desirable separation properties by combing the ILs’ excellentlyadjustable performance and membrane separation technology with an appropriatemethod.In this thesis, a series of imidazolium-based ionic liquid monomers and theircorresponding polymers (PILs) were synthesized. Then, the adsorption behavior ofPILs in different organic solvents was studied, and associated with the ILs structure,composition, morphology, as well as the solution properties. On this basis, the characteristics of the ILs such as the controllability was introduced into the PVAmembrane by chemical surface modification, and its PV performance of theorganic/water mixtures was investigated.1. A series of dialkyl imidazoles ILs monomer with different alkyl chain length oncationic imidazole ring([VBMI][BF4],[VBEI][BF4],[VBBI][BF4],[VBMI][PF6],[VBEI][PF6],[VBBI][PF6],) and their corresponding polymers(P[VBMI][BF4],P[VBEI][BF4], P[VBBI][BF4], P[VBMI][PF6], P[VBEI][PF6], P[VBBI][PF6])were synthesized by free radical polymerization, and were characterized by IR,and1HNMR.2. The adsorption behavior of the PILs film in different solution was investigated bya DCA method. It was found that the amount of adsorption of all PILs samplesincreased dramatically, and then an equilibrium state was attained, which followsthe conventional adsorption behavior. Some different adsorption equations wereused to fit the absorption behavior, and it was found that all adsorption behaviorcould be well fitted by the Bangham pore diffusion model. PILs structure isknown to have a great influence on its adsorption properties. Whether pure solventor a mixed solvent was absorbed by PILs, the longer the alkyl chains substitutedon the imidazole ring of PILs anion were, the fewer the adsorption amount of thesolution was. With the identical cation, the adsorption amount decreased withincreasing the hydrophobicity of anion of PILs. Furthermore, when PILs adsorbedpure solvent, the amount of its equilibrium adsorption of PILs was enhanced withthe increase in the polarity of the pure solvent (water> methanol> ethanol). As amixed solvent was absorbed by PILs, the equilibrium adsorption amount was thatbetween the two pure solvents included in the mixed solvent.3. A series of ILs with different cation and anion were introduced onto PVAmembrane surface by the chemical graft modification, and the modified PVAmembrane were characterized by ATR-FTIR and water contact angle, etc. Twoaqueous solution of90wt%acetic acid and90%wt methanol were permeatedthrough the ILs modified PVA membrane. It was found that after grafting with theILs, the permeate flux of the modified PVA membrane for both two feed solution was increased significantly, while the separation factor decreased to a certaindegree. In addition, the ILs’ cations and anions have a certain impact on the PVperformance of modified PVA membrane. The PV performance of the two feedsolution through the modified PVA membranes had the same changing trend withanion, and the permeation flux and selection factor decreased with the decrease inanionic hydrophilicity ([Br]->[BF4]->[PF6]-). When the90%acetic acid/watermixture was separated, increasing the length of alkyl chain on the ILs cationimidazole ring would reduce the imidazole ring’s adsorbability towards acetic acid,and accordingly the permeation flux of acetic acid decreased and the water contentin permeate was slightly increased. When90%methanol/water mixtures wereused as feed solution, both the permeation flux and the water content in permeatewere decreased.The present work provides a new method to control the separation property ofPV membrane, and have played important role in the preparation and application ofhigh-performance membrane. |
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