Study On Improvement Of Resin Layer Structure Of Membrane-free EDI

Membrane-free electrodeionization(MFEDI)is a novel deionization for high purity water production.MFEDI in previous research using double layers filed with mixed weak-acid and strong-base resins in the lower,strong-acid and strong-base resins in the upper was restricted due to the poor performance and high regeneration voltage.This thesis was aimed at improving the resin layer structure of MFEDI with double layers and increasing its purification and regeneration performance.Major research works were:improvement on the ratio of the strong-acid and strong-base resin layer;improvement on the variety of the strong-acid and strong-base resin layer;stability and economy of improved MFEDI in long last running.The results showed that changing the ratio of strong-acid and strong-base resin from single 1:1.75 into 1:1,1:2,1:3 could effectively inhibit cationic reverse migration and decrease regeneration voltage.MFEDI with improved layers had better performance for high purity water production.Examined in 30 operational cycles,the effluent conductivity of improved MFEDI was 0.058?0.060ps/cm,the average regeneration voltage was 620V,the concentrate conductivity kept in 69.5?s/cm,pH maintained at 6.8-7.0,and the system energy consumption was only 0.39 kWh/m3.Changing the variety of the strong-acid and strong-base resin layers of MFEDI by adding some of weak resins into the strong resin layer of the ratio 1:1 could effctiveiy promote the regeneration of strong resin and improve its performance for high purity water production.By investigating their influence on the performance of MFEDI,the optimal regeneration parameters were obtain:processing velocity at 50 m/h,regeneration duration 20min,regeneration velocity of 40 m/h,regeneration current density of 175 A/m2,cation and anion of resin absorbed both got good regeneration,MFEDI system had the lowest energy consumption of 0.20 kWh/m3 and the highest water recovery rate at 93.3%.The improved MFEDI system had strong operation stability by testing.Running continuously for 700 hours,the effluent conductivity maintained at 0.057?0.059?s/cm,pH was kept from 6.8 to 7.0,near to neutral.Electrodes and resin also had good stability,the breakage rate of resin was sharely short,their impact on the overall system can be neglected.Compared to RO/RO/EDI,MFEDI system had obvious economic advertange in industrial application with the lower energy consumption,none of ion exchange membrane,simple device,easy for automation control.Therefore,MFEDI system had a stronger market competiviveness and a bright industrial prospect.