| Salinity gradient power(SGP),also referred to as "Blue Energy",is contained between sea water and fresh water,which is known as a completely clean and sustainable energy source.Reverse electrodialysis(RED)technology,based on ion exchange membrane(IEM),is one of the core technologies to realize the conversion and utilization of SGP.Once bringing seawater and fresh water into the reverse electrodialysis system,Donnan potential will be generated due to the salinity gradient of two solutions on both sides of the membrane.Therefore,the ions in high salinity solutions migrate through corresponding membranes to low salinity ones based on the selective permeability of membrane,and induce ionic current generation between membranes.Through coupling the paired electrode and the special electrode solution,the ionic currents are converted to an electron current by electrode reactions.This is the construction of an effective RED system and the process of converting SGP into electrical energy.RED technology has the advantages of high integration,low membrane fouling and high energy conversion efficiency,and has great application potential in conversion and utilization of SGP at the river estuary.Nevertheless,the overall recovery efficiency of SGP based on the process of RED remains to be improved.Besides,the low voltage and low power density of RED process may not match with the grid power demand and limit its direct use.In order to improve the process economy and reliability of the RED process and achieve the goal of direct conversion and utilization of SGP,efficient internal integration of different electric drive membrane processes were proposed in this dissertation by focusing on the optimization of the process model and the in-depth exploration of the advantages of SGP resources,and the efficient conversion and storage of SGP were realized.The main research contents are concluded as follows:1)Hydrogen production by internal integrated RED and membrane electrolysisTo solve the disadvantages of low energy recovery efficiency in the process of converting SGP into electric energy and difficulty in direct grid connection,a process intensification of internal integrated reverse electrodialysis and membrane electrolysis was proposed in this study,and strong acid/alkali were used as supporting solutions inside electrodes instead of Fe2+/Fe3+buffer solutions.The performance of energy recovery and hydrogen production rate of the internal integrated system were evaluated.The results showed that the asymmetric electrolyte system of acid catholyte and alkali anolyte was helpful to reduce the potentials of hydrogen evolution reaction and oxygen evolution reaction at the electrode ends.Meanwhile,the hydrogen production rate and energy recovery efficiency of integrated process increased with the increasement of salinity gradient.And the conversion of hydrogen energy form was conducive to improve the overall recovery efficiency of SGP and realize the effective storage of energy.2)Hydrogen production by internal integrated bipolar-membrane-assisted RED technologyThe internal integrated RED and membrane electrolysis system is helpful to the effective conversion and storage of SGP,but the acid and alkali consumed in the membrane water electrolysis process need to be continuously supplemented to maintain a stable hydrogen production rate,which affects the economy and operability of the process.In order to solve the above problems,bipolar membrane-assisted reverse electrodialysis process was proposed by introducing bipolar membrane into internal integrated RED and membrane electrolysis system and focusing on the effective design of the innovative internal integrated membrane stack structure.The results showed that this internal integrated membrane system could maintain the SGP?hydrogen energy conversion process in a stable electrochemical operation environment without the supplement of the acid/alkali electrolyte(pH value of cathode chamber before and after reaction was fixed),and effectively promote the process economy and reliability of conversion and storage process of SGP.Furthermore,bipolar membrane with lower limiting current density,such as BP-1E,should be selected for this internal integrated membrane system.While the real hydrogen production rate increased as the initial acid concentration increased.3)CO2 sequestration and storage by internal integrated bipolar-membrane-assisted RED technologyIn order to realize the direct conversion and utilization of SGP,an efficient method using internal integrated bipolar-membrane-assisted reverse electrodialysis was described and optimized for extracting CO2 by the in-depth exploration of the advantages of SGP resources.The process of decarbonization of seawater by this integrated system was deeply studied in order to realize the transformation of renewable SGP to carbon dioxide separation and storage.Two kinds of operation models,batch operation and continuous operation,were systematically explored.The results indicated that this system had feasibility and practicability for decarbonization of seawater based on the reaction of proton generated by BM and DIC in seawater.It should be noted that the current supplied by simulated seawater was lower than that of the formulated solution under the same salinity gradient.Furthermore,the proton production rate by bipolar membrane dissociation could match the content of bicarbonate in the input seawater,and the suitable flow rate of seawater in acid and alkali chambers depended on stack current in continuous operation mode.The appropriate flow rate of the seawater in acid and alkali chambers was about 65 mLˇmin-1 if the current was fixed on 0.18 A. |
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