Solution Behavior Of Small Molecular Permeates In Polyimide Membrane

In pervaporation process, the separation performance primarily depends on the membrane materials selected for the separation. Polyimides can be applied to the dehydration of organic solution and the separation of organic compounds. Polyimde(PI) is now emerging as a promising material for the pervaporation dehydration of alcohol because of its super chemical resistance and mechanical properties and lower hydrophilicity. In pervaporation, Solution process has great effect on membrane performance. In this thesis, nineteen kinds of homogeneous polyimide membranes were prepared by five kinds of diamines and four kinds of dianhydrides. The swelling characteristics of these polyimide membranes immersed in pure solvent and dual-solution were measured. The influences of these diamine, dianhydride chemical structures, different solutions and different solution temperature on the membrane swelling characteristics were discussed.The experiment results show that alcohol is preferentially absorbed in polyimides membrane in pure solvent while swelling separation fators show that water is preferentially absorbed in 88wt% aqueous alcohol solutions. The swelling performance is also affected by polymer structure. Polymers with big side group, low chain packing density and weak chain mobility have high swelling ratio and low swelling separation fator. The swelling separation fator of polyimide membrane for ethanol/water separation increases with the introducing of hydrophilic group to the monomer structure. Moreover, with the rising of temperature, the increase of membrane swelling ratio and the decrease of swelling separation factor. In addition, with the rising of temperature, the increase of swelling ratio of polyimides membrane with strong rigid molecular chain is larger than those with weak rigid molecular chains.The membrane hydrophilicity increases with the introducing of hydrophilic group to the monomer structure. Among all the polyimide membranes discussed in this paper, PMDA-ODA ODPA-ODA ODPA-MDA BTDA-ODA membranes have better swelling performances in aqueous feed which contains 88wt% ethanol aqueous solutions.The solution fator were calculated and Flory-Huggins models were established to compare with the swelling data. The results show that experiment data and the theory fator have high accordance.