Construction And Efficiency Of MCDI With Continuous Water Production Capacity

Capacitive deionization(CDI)is a new technique for efficient removal of salt ions by adsorbed ions to porous electrode under bias.Through introducing anion exchange membrane on the electrode surface and membrane capacitive deionization(MCDI),the problem of repulsed ion at the electrode interface in CDI has been solved,and the energy spent during charging process can be stored in the battery under reasonable operation mode.It can be recovered during discharge.However,the traditional MCDI cannot continuously produce water,and the electrode regeneration process is needed.Moreover,the research on the energy recovery mechanism is not clear,so it cannot be directly utilized.Centered on MCDI technology,this study constructed a new three-membrane MCDI device,combined with evaluation indexes such as desalination rate and charge efficiency,investigated its performance differences with traditional MCDI,and explored the energy recovery and reuse of the device through constant current and constant pressure experiments.The main research contents and results include:(1)A novel dual channel CDI device(CAC-MCDI)with continuous desalination capability and three layers of ion exchange membrane was constructed.The ion adsorption and desorption processes were carried out in the two channels respectively,and continuous desalination was achieved by intermittent voltage reversal.In addition,when the ions reach adsorption saturation on the electrode,the new cell structure is transformed into an electrodialysis like structure,and there is a synergistic effect between the CDI and the electrodialysis.The different adsorption rates of cations and anions were used to optimize the system asymmetrically.By comparing with ACA-MCDI system and traditional MCDI system,the influence of the difference of ion migration rate on the desalination performance of MCDI system was revealed.Taking full advantage of ion diffusion difference and synergistic effect can effectively improve the desalination performance of the system and increase the charge efficiency to more than 100%.(2)The single factor analysis and response surface methodology were used to optimize the operation parameters.The results show that under the optimal operating conditions,the desalination rate is 69.62%,the charge efficiency is up to 103.37%,and the volume and molar energy consumption are 135.38 kJ/mol and 1.63 kJ/m~3,respectively.Both experimental results and model predictions show that the asymmetric adsorption of CAC-MCDI system has excellent desalination performance.The continuous stability experiment shows that the device has good desalination stability,can realize continuous desalination water production,and has a broad application prospect in the field of salt water desalination.(3)The desalination performance of CAC-MCDI under different discharge conditions was analyzed and compared.The results showed that the salt adsorption capacity was the highest under constant current charge and discharge condition of 0.01 A,while the desalination rate was the highest(31%)under charge and discharge condition of 0.01 A and 0.03 A.In CC mode or CV mode,with the increase of discharge current,the energy recovery showed an obvious downward trend,and the energy recovery in CC mode was generally higher than that in CV mode.When charging and discharging under constant current condition of 0.01 A,23.8%of the energy recovery could be recovered.This indicates that at higher charging current,more energy is used to overcome internal resistance rather than stored in EDLs.Both the experimental results and the predicted values of the model in this paper show that the asymmetric adsorption CAC-MCDI system has excellent desalination performance and can achieve continuous desalination water production.The relationship between energy recovery,energy reuse and charge and discharge conditions is discussed in detail,which provides a theoretical basis for practical application.