| In the paper, hydrophobic zein was used as the raw material, combined with itsspecial solubility behavior and the hydrophobic properties of silicalite-1, four kinds ofmembranes with different structures were designed for separation, such as zein single(ZS) membrane and zein composite (ZC) membrane, modified zein membrane,zein/silicalite-1composite membrane. The pervaporation process was applied forevaluating the separation performance of the membranes for low concentrationsethanol aqueous solution, which stimulate the bio-ethanol fermentation solution.Zein single (ZS) membrane was developed by spin coating zein solution ontoporous asymmetric alumina tablets. Whereas, the zein composite (ZC) membraneconsisted of two layers, where the inner layer was a microsphere film cast fromsolution of zein-based microspheres, which is prepared by phase separation and basedon the characteristic solubility of zein. And the outer layer was a continuous zein filmjust similar to ZS membrane. The separation membrane had an average thickness of10μm, single gas permeation confirmed that the membranes were free of defects andmaintained their integrity during pervaporation. The ZS and ZC membranes caneffectively concentrate ethanol from a3wt%feed to8.73wt%and9.51wt%,respectively after8h of pervaporation at298K. The permeation flux increased as thetemperature increased, and the separation factor decreased as the temperatureincreased. The good ethanol permselectivity of ZS and ZC membranes can beexplained by the Switch Effect.Zein was modified by hexadecanoyl chloride via Friedel-Crafts acylationreaction to improve the hydrophobicity. Then, a modified zein membrane supportedon porous alumina substrate was prepared by spin-coating process. The modifiedmembrane had an average thickness of10μm and showed better separation abilitythan unmodified one. The modified membrane effectively concentrated ethanol from3wt%ethanol/water feed to11.74wt%by pervaporation at303K. The separationfactors (α) of ethanol and the total permeate fluxes (J) at298K were3.4~3.7and0.65~0.70kg/m2hr. The permeation flux increased and the separation factor decreasedas the concentration increased. Compared with the ZS membrane, the modified zeinmembrane is more hydrophobic, which makes a great of contribution for the selectiveadsorption on the surface of membrane step of solution-diffusion mass transfermechanism.In order to develop membrane with favorable separating efficiency, the zein/ silicalite-1composite membranes were designed by absorbing and profiting the gooddesign thought of silicalite-1/PDMS organic-inorganic hybrid membrane. Firstly,mesoporous silicalite-1membrane supported on porous alumina substrate wasprepared by double hydrothermal synthetic process, then, a continuous compact zeinfilm just as ZS membrane was spin-coated on it. The silicalite-1membrane made ofelongate plate crystal oriented growth by b axis is the best, the thickness is about10μm, and the composite membrane has an average thickness of15μm. Hydrophobiczeolite membrane offsets the loss of poor separation selectivity of zein membrane,simultaneously; good membrane forming properties of zein compensate the innatedrawback of crack and poor film-forming of rigid silicalite-1membrane.Themechanism of zein/silicalite-1composite membrane is about of coordinating andenhancing the hydrophobicity of both materials.Compared with pure silicalite-1membrane, the separation performance of composite membrane is improved. Ethanolseparation factors (α) of7.3~7.4with total fluxes of0.41~0.44kg/m2hr were obtainedby pervaporation at298K for ethanol feed composition of3wt%, the membraneconcentrated ethanol from3wt%ethanol/water feed to18.62wt%by pervaporation. |
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