| Capacitive deionization(CDI)has attracted a lot of attention due to its unique advantages of eco-friendliness and cost-effectiveness.Membrane capacitive deionization(MCDI),combining the advantages of CDI and ion-exchange membrane,can effectively eliminate the co-ion effect and improve the desalination efficiency of the MCDI cell simultaneously.In order to solve the problems of the flow dead zone and uneven distribution of the fluid which are caused by the scale-up of the CDI/MCDI cell,we designed an innovative two-level liquid distributor.The fluid flow distributions under different flow conditions were simulated with CFD to obtain the optimal structure of the liquid distributor and achieve the good uniform distribution of the fluid in the CDI/MCDI cell.In the structure optimizing CDI cell,graphite cloth was used as the electrode material.Effects of the technological conditions such as the operating voltage,the flow rate and the thickness of the spacer on the desalination performance of the CDI cell were discussed and analyzed.The results indicate that the desalination efficiency and the specific adsorption capacity both increase at first and then tend to be stable as the operating voltage increases from 0.8 V to 2.0 V;Along with the increase of the flow rate from 48 mL/min to 238 mL/min,the desalination efficiency and the specific adsorption capacity both increase firstly and then decrease;From no spacer to three layers of spacers,the specific adsorption capacity reduces firstly and then increases.When the operating voltage is 1.6 V,the flow rate is 142 mL/min and the thickness of the spacer is 1.8 mm,the CDI cell has a better desalination performance.Under the same optimal technological conditions,the desalination performances and the energy consumptions of the CDI and MCDI cell were studied and compared after 16 h of multiple adsorption/desorption experiments.The experiment results show that during the adsorption stage of the first cycle,the desalination efficiency and the current efficiency of MCDI are about a 31.68 % and 36.16 % increase compared to CDI,respectively.After 16 h of cyclic test,the MCDI cell has a high regeneration rate of 99.01 %.However,the regeneration rate of CDI cell is just 73.54%.Under the same optimal technological conditions,the saturated adsorption and recyclability of the MCDI cell were investigated under different feed concentrations.The results show that MCDI displays good cycle stability and recyclability under different feed concentrations.Both the saturated adsorption capacity and the surface area utilization of the positive electrode increase with increasing feed concentration.The largest saturated adsorption capacity of 23.84 mg/g is achieved under the concentration of 2000 mg/L(about 4000 μS/cm),which is more than 3 times that of 500 mg/L.It turns out that MCDI can be used to deal with a high concentration of the feed solution.In addition,the desalination processes with different series-parallel connections of multiple pairs of MCDI cells were investigated and optimized under the feed concentration of 2000 mg/L.The results show that process 1(both adsorption and desorption in parallel)shows the best desalination performance.Compared to process 3(both adsorption and desorption in series),the growth rates of the current efficiency of process 1 are 27.5% and 37% during the adsorption and desorption stage,respectively.After 5 cycles of cyclic test,process 1 has good cycle stability and a high regeneration rate of 97.37%. |
