Preparation And Performance Of Forward Osmosis Membrane With High Water Flux

Low water flux is still one of the important issues limiting the application of Forward Osmosis(FO)membrane separation technology.In view of this,the preparation of high water flux forward osmosis membranes has become the core of forward osmosis technology research.In this paper,surface pore structure reconstruction method and co-solvent assisted interface polymerization process were used to optimize the FO membrane preparation process respectively.Firstly,A support surface pore structure re-construction method was developed to modify the support layer and regulate the porosity of the support layer,thereby improving the water flux of the FO membrane.The effects of solvent categories(N,N-Dimethylformamide,N,N-Dimethylacetamide,and N-Methyl pyrrolidone)and non-solvent categories(water,ethanol,and isopropanol)on the forward osmosis membrane water flux were researched in the re-constructing agent.The results show that,the FO membrane has higher water flux when DMAc was used as the solvent and water as non-solvent.Furthermore,when the re-constructing agent is aqueous solution of DMAc,the porosity of the support layer and the water flux of the forward osmosis membrane were mainly investigated,as the function of the volume ratio of the DMAc/water in the re-constructing agent and the contact time of the re-constructing agent.The results show that,with increasing the volume ratio and the contact time,the porosity of the support layer and the water flux of the forward osmosis membrane increase firstly and then decrease.Under the conditions that the re-constructing agent is aqueous solution of DMAc with volume ratio of 30/70,and the contacting time is 3 s,the support porosity achieves the largest value,and the water flux of the prepared forward osmosis membrane is optimal.When using 1mol/L Na Cl as draw solution and deionized water as feed solution,the water flux of the modified forward osmosis membrane reaches up to 20.06 L/(m~2·h),exhibiting a50%higher flux compared to the unmodified membrane.By adding a co-solvent to the organic phase to assist the interfacial polymerization process,a FO membrane having a thinner dense layer was obtained,which improved the water flux.The effect of the categories and content of co-solvents on water flux was explored.The results showed that,when the 2 wt%acetone,ethyl formate and ethyl acetate were added as co-solvents to the organic phase to prepare the FO membrane,the water flux was increased by 1.18,1.22 and 1.27 times,respectively.It is indicated that all three solvents can be used as a co-solvent for the preparation of FO membrane;and the FO membrane prepared by using ethyl acetate as a co-solvent has the highest water flux.Based on this,the effect of the addition amount of ethyl acetate as the co-solvent on the water flux was investigated.Studies have shown that with the increase of ethyl acetate addition,the water flux increases,but the permeation selectivity increases first and then decreases.Comprehensive evaluation,when the ethyl acetate is added in an amount of 4 wt%,the prepared FO membrane has a higher water flux and optimal permeation selectivity.Therefore,the optimum addition amount of ethyl acetate was 4 wt%.When using 2 mol/L Na Cl as draw solution and deionized water as feed solution,the water flux of the modified forward osmosis membrane reaches up to 26.75 L/(m~2·h),which was 1.46 times that of the unadded FO membrane.