The Preparation And Alcohol-selective Performance Study Of Polysiloxane/Polyphenylene Oxide Copolymer Membranes

The coupling of fermentation and pervaporation for bio-fuel has been proven asan efficient and low energy consumption technology route. Researchers are alwaysfocus on the design of membrane which has high separation performance and stability,and the development of novel membrane materials with perfect separationperformance and good mechanical properties is the key point in pervaporation. Basedon the ground of ethanol and butanol in bio-fuel, this study synthesized thepolydimethylsiloxane-block polyphenylene oxide （PDMS-b-PPO） copolymers withdifferent composition, through the modification of PDMS by PPO. PDMS-b-PPOhomogeneous membranes were prepared by solvent evaporating method, and then thedifferent solubility and diffusion of ethanol and water in the membrane were studied.High flux PDMS-b-PPO asymmetric membranes were prepared by phase-inversionmethod, and the morphologies and pervaporation performance were studied.Furthermore, bromide-substituted polyphenylene oxide （BPPO） was synthesized,althernately assembled PDMS and BPPO on ceramic membrane for preparing thecross-linked-PDMS/BPPO membranes. This study is benefit to the design ofmembrane material for alcohol concentration.First, amido-terminated polydimethylsiloxane were synthesized by the methodsof positive ion ring-opening reaction and substitution reaction, the effect oftemperature, ratio of raw materials and the amount of end-capping reagent onsynthesis of amido-terminated polydimethylsiloxane were studied, and the productwas characterized by FTIR and element analysis.Orientation reaction between amidoor amine groups on PDMS chains and the hydroxyl groups on PPO chains wereconducted for obtaining the PDMS-b-PPO copolymers with different composition.The effects of temperature, ratio of raw materials and the amount of end-cappingreagent on synthesis of amido-terminated polydimethylsiloxane were studied, thePDMS-b-PPO copolymers were characterized by FTIR,1H-NMR, DSC, and thereaction between PPO with two different PDMS was compared.Second, a series of PDMS-b-PPO membranes with different PDMS content wereprepared by solvent evaporation method with suitable conditions. The permselectivityof these membranes were discussed as the variety of PDMS content. According to theFlory-Huggins principle, the solubility parameters of PDMS-b-PPO membranes, theinteraction parameters of ethanol and water with membrane, the diffusion parameterswere calculated, and the morphologies of PDMS-b-PPO membrane werecharacterized by AFM, EDX, SAXS and DSC, the relationship of PDMS content withthe thermodynamic of PDMS-b-PPO membranes was studied. Third, a series of PDMS-b-PPO asymmetric membranes with different PDMScontent have been prepared by phase-inversion process, the morphologies of thesemembranes were characterized by SEM, EDX, XRD and AFM, and the effect ofPDMS content on the morphology, hydrophobility and crystallization of themembrane, and the effect of operation conditions on the pervaporation performance ofPDMS-b-PPO asymmetric membranes with different PDMS content were studied.The differences of separation performance of PDMS-b-PPO homogeneous andasymmetric membranes were discussed by comparing the morphologies andthermodynamics of these two membranes. The results showed that the PDMS-b-PPOasymmetric membrane shows better flux than that of PDMS-b-PPO homogeneousmembrane. When polymer concentration in casting solution was11wt%, operatingtemperature was60℃, feed concentration was5wt%and the flux was1400g·m^-2·h^-1.At last, a series of BPPO with different bromide-substituted ratio were firstlysynthesized through Wohl-Ziegler reaction, and the bromide-substituted ratio ofBPPO was controlled by illumination time. An in-situcross-linked-polydimethylsiloxane/brominated polyphenylene oxide（c-PDMS/BPPO） membrane on ceramic tube has been prepared for the recovery ofbutanol by pervaporation. BPPO and PDMS were sequentially assembled and in-situcross-linked to form the final c-PDMS/BPPO membrane. As the results shown, theseparation factor increased and the flux decreased as the increase of dipping time. Onthe other hand, the separation factor increased first and then decreased as the increaseof bromide-substituted ratio of BPPO. The pervaporation experiments ofbutanol-water mixture indicated that the c-PDMS/BPPO membrane exhibited anacceptable flux of220g·m^-2·h^-1and high separation factor of35towards butanol,when the bromide-substituted ratio was34wt%and the dipping time was1.33h.Moreover, the c-PDMS/BPPO membrane performed excellent stability in an about200h continuous butanol recovery, as compared to the PDMS membrane.