| Forward osmosis(FO) is a new type of membrane technology, which has shown its valueor is showing the potential value in the field of seawater desalination, wastewater treatment,food processing, pharmaceutical and energy, due to the fact that it is energy-efficient, lowlypolluted, capable of being operated at normal temperatue, exempted from pressure and easilyoperated. However, in practice, this technology is still at experimental stage. Tocommercialisation of FO, it is pivotal to find the proper membrane and draw solution, whichcould reduce the impact induced by the concentration polarization to water flux. Although it isstill a challenging task, researchers all over the world are working on this in order to improvethe performance of the membrane.This dissertation suggests a method that uses threecellulose acetate and cellulose diacetate as permeable membrane material,1,4-dioxane,acetone and methanol as solvent, lactic acid as the additives, and producesmembrane byadopting phase transformation method, meanwhile, it characterises the membraneperformance.This thesis examines the influencing factors during the process of producing FOmembrane, including the system of solvents,polymer concentration, content of additive, waterbath temperature, polyester screen mesh, the proportion of CDA and CTA, blend temperature,heat treatmenttemperature, casting solution temperature on the membrane structure andperformance.This paper concludes the most favorable conditions for producing CDA/CTA FOmembrane, specifically, this include dissolved system of1,4-dioxane, polymer concentrationof8.96%, additives content of3.5%, water bath temperature of15℃, blend mesh of120,CDA: CTA=7:1, blend temperature of60℃, heat treatment temperature of70℃, polymertemperature of30℃. Accordingly, the water flux is approximately5L/m2·h and the retentionrate is about98%.The process of FO does not need external pressure, instead, it is powered by osmoticpressure difference. In practice, membrane water fluxis below the calculated value, whichiscaused by the concentration polarization.Thus, how to reduce the concentration polarizationand increase membrane water fluxes, is becoming one of the difficulties and hotspots in theresearch. This thesis examines the influencing factors in three aspects with respect to the process of membrane separation, including semi-permeable membrane supporting layer,concentrations and peristaltic pump of driving fluid speed, and concludes the mostfavourableconditions for membrane separation, i.e. facing support layer, glucoseoptimumconcentration of4M and the peristaltic pump speed of100rpm.The experiment also made cellulose acetate/dioxide FO membrane to alter performanceof membrane, and examined theirinfluences in three aspects:blend temperature, nano-titaniumconcentration and water bath temperature, which identified the conditions of preparingdioxide/cellulose acetate FO membrane: blend temperature at70℃, nano-titaniumconcentration at0.1%，water bath temperature at15℃. Meanwhile, the water flux wasapproximately5L/m2·h and the retention rate was98%.Finally, by testing the performance of the FO membrane made in the experiment, andcomparing with the three cellulose acetate produced by American HTI company, it was foundthat the former has some deficiency. The experiment did a preliminary study on thepollution-resistance of the prepared FO membrane, and analysed the principle of thatpollution. Furthermore, the dissertation embarks a preliminary test on sea water desalinationby using FO membrane, which may offer some reference for further research. |
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