Preparation Of Thermo-responsive Polymer Hydrogels And Their Performance Evaluation As Draw Solution In Forward Osmosis Process

Forward osmosis(FO)is an spontaneous membrane separation process driven by the osmotic pressure difference between the feed solution and the draw solution across membrane.As no impressed pressure is involved in,FO is a 'Green' purification technology featuring the characteristics of low energy consumption and low cost etc.,and it has been applied in many industrial fields including food processing,pharmaceutical industry,power generation,sewage sludge treatment and desalination so far.However,the'Green' characteristics of FO depend on the development of highly efficient FO membrane,draw solution and the corresponding recycling system,and the exploring of highly efficient draw solution has become one research focus.In this paper,N-isopropylacrylamide(NIPAM),y-polyglutamic acid(y-PGA)and polyvinyl alcohol(PEG)were used to prepare two types of temperature-responsive hydrogels,i.e.PNIPAM/?-PGA hydrogel and PNIPAM/y-PGA/PEG hydrogel.First,the prepared hydrogels were applied as the draw solutions in FO process,and their physical and chemical properties,FO performances(e.g.water flux)as well as recyclability were investigated.Then,the reaction is added on the basis of PNIPAM/y-PGA hydrogel extractor to improve the water absorption and dehydration properties of the hydrogel.The interaction between the reactants were studied and the optimal hydrogel preparation scheme were optimized using the response surface methodology.Finally,the optimal hydrogel was applied as FO draw solution for brine desalination to investigate its practical efficiency.The research results showed that PNIPAM/y-PGA hydrogel has obvious pore structure,y-PGA was successfully introduced into PNIPAM/y-PGA,and its equilibrium swelling rate increased with the addition of y-PGA.When the ratio of NIPAM to y-PGA was 5:1,the equilibrium swelling rate was 40.3 g/g and the dehydration rate reached up to 80%after dehydration at 40? for 6 h.When being used as the draw solution,the water flux of the hydrogel has a water flux of 1.1-1.4 Lm-2h-1 within 0.5 h and a good recyclability,the recycle effect is better.The water absorption and dehydration properties of PNIPAM/y-PGA/PEG hydrogel were significantly improved after the addition of PEG,and the pore structure of the hydrogel has increased and the initiators and y-PGA were found to have interacted.According to the response surface methodology,the optimal hydrogel preparation scheme was that the ratio of NIPAM and y-PGA,the ratio of NIPAM and PEG,the ratio of initiator and monomers and the ratio of crosslinking and monomers were 5:1,1:1,1:100 and 1:100,respectively.The results of PNIPAM/y-PGA and PNIPAM/y-PGA/PEG hydrogels as the FO draw solutions for brine desalination showed that the water flux decreased with the increase of the feed NaCl concentration,when the NaCl concentration was 2 g/L,the FO water fluxes provided by PNIPAM/y-PGA hydrogel and PNIPAM/?-PGA/PEG hydrogel were about 0.8 and 1.1 Lm-2h-1 respectively within 0.5 h.The low critical solution temperature(LCST)of the two kinds of hydrogels is about 35?,and the dehydration rate of PNIPAM/y-PGA/PEG hydrogel up to 90%after dehydration at 40? for 30 min.Water recovery rate is higher and easy to operate.The hydrogel recyclability test results showed that the variation of the water fluxes provided by the hydrogel before and after regeneration was small,indicating the good stability and recyclability of the prepared hydrogels.