Bio-inspired Preparation Of Pervaporation Composite Membrane By Interfacial Polymerization For Ethanol Dehydration

As the energy saving and low-carbon environmental protection becoming a worldwide topic, new renewable clean energy has become the focus of the research around the world. Fuel ethanol has become the representative of alternative energy sources. However, the ethanol dehydration is a critical step in the industrial production. In the industrialization of ethanol dehydration, pervaporation technology has the advantages of mild conditions, simple process, low energy consumption, environment friendly and so on.The core of pervaporation process is the development of appropriate membrane material.This dissertation focuses on the easy stripping and even coming off the separation layer of composite membrane from the supporting layer due to as the low adhesion strength. Based on the bionic dopamine auxiliary method of surface modification, thin film composite(TFC) membranes were prepared by interfacial polymerization on a microporous polyethersulfone(PES) substrate. These membranes were studied for ethanol dehydration by pervaporation.1. On the basis of dopamine self-polymerization and strong adhesion feature, the surface hydrophilicity of hydrophobic PES membrane were improved by coating dopamine via the dopamine spontaneously oxidative polymerization and adherring firmly to the membrane surface in mild aqueous solution. The membrane surface hydrophilicity was investigated by water contact angle measurement. The results showed that the water contact angle of PES membrane decreased from 74.2±1.2° to approximately43±1°. The optimum conditions were dopamine solution of concentration of 2.0g/L, modified time of 24 hours. Chemical and morphological changes of membrane surfaces before and after hydrophilic modification were examined by Fourier transform infrared spectroscopy(ATR-FTIR) and scanning electron microscopy(SEM). It was found that the hydrophilic polydopamine coating layers containing carboxyl,hydroxyl and amino groups were substantially attached onto the PES membrane surfaces.2. The PEI-TMC/PDA/PES polyamide composite membrane was prepared by interfacial polymerization of polyethylenimine(PEI) and trimesoyl chloride(TMC) on a modified microporous polyethersulfone(PES) substrate. The effects of interfacial polymerization conditions on the pervaporation performance of the PEI-TMC/PDA/PES composite membrane were studied. including molecular weight of PEI, concentration of reactants, reacting time. The surface composition, chemical structure and morphology of composite membranes were studied by ATR-FTIR spectroscopy and XPS, SEM. The ATR-FTIR analysis indicated that acyl amide existed in the surface of polyamide composite membrane. The SEM images showed an active layer formed on the PES membrane.The optimal preparation conditions of polyamide composite membrane were as follows: molecular weight of PEI is 600, 4 wt% PEI solution in water, 2.5 wt% trimesoylchloride in hexane, reacting time 10 minute at room temperature.3. The PEI-TMC/PDA-TMC/PES high-performance pervaporation membrane was fabricated by interfacial polymerization for ethanol dehydration. Polydopamine was first explored as a monomer inaqueous solution to prepare composite membrane by interfacial polymerization. The effects of interfacial polymerization conditions on the pervaporation performance of the PDA-TMC/PES membrane and PEITMC/PDA-TMC/PES composite membrane were studied. including concentration of TMC, reacting time in the first interfacial polymerization, molecular weight of PEI, concentration ratio of reactants in the second interfacial polymerization. The surface composition, chemical structure and morphology of composite membranes were studied by ATR-FTIR spectroscopy and XPS, SEM. The ATR-FTIR analysis indicated that acyl amide existed in the surface of polyamide composite membrane. The result of highdeconvolution XPS data indicate that the O=C-O species were formed after the first interfacial polymerization, which was produced by catechol of PDA reacting with acyl chloride of TMC. The SEM images showed an active layer formed on the modified PES membrane.The optimal preparation conditions of polyamide composite membrane were as follows: 3.6 wt%trimesoylchloride in hexane, reacting time 10 minute at room temperature for preparing PDA-TMC/PES composite membrane; molecular weight of PEI is 1800, the concentration ratio of PEI/TMC is 5:1(0.8 wt%trimesoylchloride in hexane). The PEI-TMC/PDA-TMC/PES membrane showed good pervaporation performance with a flux of 1667g/(m2·h), separation factor of 886 for dehydration of 90 wt% ethanol at30 ℃.