| A large amount of acidic wastewater is discharged in industries such as chemical fiber factory,electroplating factory,coal processing and metal pickling plant,and a lot of alkaline wastewater is produced in industrial processes such as printing and dyeing,tanneries and oil production.The wastewater contains acid or alkali,as well as some metal ions.Direct discharge of the wastewater not only wastes recyclable resources,but also constitutes a threat to the environment.Therefore,acidic and alkaline wastewater must be pretreated,including recycling of useful resources.Diffusion dialysis(DD)is one of membrane separation processes,which is characterized by low energy consumption and environmental friendliness.At present,the polymeric materials used for the preparation of diffusion dialysis membranes mainly include polysulfone,polyphenylene ether,and polystyrene-diethylbenzene,and most of the membranes are of dense structure,which is unfavorable to the transmission of ions.Therefore,a series of porous P84 co-polyimide anion exchange membranes with different pore structures are prepared to replace the traditional dense membranes for diffusion dialysis to recover acid,but the water penetration from the low concentration to high concentration side can be also increased.Hence,another important point of this thesis is to study the water osmosis of the porous membranes at different operating temperatures.In this way,a new type of micro-pressure diffusion dialysis device was developed,which was to apply certain micro pressure on the liquid side to suppress the water osmosis.In the first part,a series of porous P84 co-polyimide anion exchange membranes(hereinafter referred to as P84 co-polyimide AEMs)were prepared by phase inversion,and the properties of these membranes were characterized,mainly including thermal stability,chemical stability and mechanical stabilities.Changing the types of non-solvent(isopropanol or water)in phase inversion process yields membranes with different micro-structures.This series of porous P84 co-polyimide AEMs were used for diffusion dialysis to recover sulfuric acid and experimental temperature was increased from 15,25,35 to 45 ?.The results showed that porous P84 co-polyimide AEM had high permeability and selectivity to the acid system,so that they could effectively separate the acid/salt mixture and show higher separation efficiency than the traditional dense membrane.The dialysis coefficient of H2SO4(UH)was 0.00584-0.00781 m/h at 25 ? higher than that of commercial S203 membrane and DF-120 membrane,and the separation factor(S)at 25 °C can be as high as 51.3.Finally,the optimized membrane was used for diffusion dialysis to explore the permeability of pure acetic acid(HAc).The dialysis coefficient of HAc(UHAc)increased from 0.00239 m/h to 0.0133 m/h as the temperature increased from 15 °C to 45°C.In addition,the water osmosis of porous P84 co-polyimide AEMs was studied at different temperatures.The results showed that the water osmosis volume(VH2O)was affected by the membrane structure and the operating temperature.What's more,water osmosis was mainly caused by the different concentrations of metal salts across the membrane.The VH2O values of porous P84 co-polyimide AEMs were in the range of 15-47.5 mL as the temperature increased from 15 ? to 45°C.Therefore,the second part systematically studies the phenomenon of water osmosis in the process of diffusion dialysis.By applying nitrogen to the traditional static diffusion dialysis side,the water osmosis was effectively inhibited and the operating flux was increased,and thus the processing capacity was enhanced.The porous P84 co-polyimide AEMs,commercial anion cation exchange membrane(AEM)and commercial cation exchange membrane(CEM)were used to separate not only the mixture of acid and salt,but also a mixture of alkali and salt,so that the feasibility of the "concentration-pressure" double driven diffusion dialysis process was explored and confirmed. |
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