چكيده به لاتين
With its performance at voltages of 1 to 2 volts, as well as the disuse of chemicals, Capacitive Deionization (CDI), is considered as an efficient green electrochemical water treatment technology. Recently an important modification to the process is proposed which adds ion exchange membranes to the corresponding process.
Considering the importance of synthesis and modification of capacitive deionization membranes as well as the existence of a research gap on the development of homogeneous nitrate-selective membranes, in this study by firstly preparing 11 polysulfone-based anion exchange membranes with different chloromethylation and amination conditions. By changing the reaction time, in the process of chloromethylation, two kinds of chloromethylated polysulfone with degrees of 83 and 122 were prepared. At the amination step, trimethylamine, triethylamine, and tetramethylhexanediamine were used as aminating and cross-linking agents to investigate the effects of HLB and crosslinking on nitrate selectivity. After preparation of the anion exchange membranes, ex-situ and in-situ analysis were performed. Ex-situ evaluations include HNMR to determine the degrees of chloromethylation, FTIR to confirm amination, FESEM to assure the placement of membrane layers on each other. Furthermore, ion exchange capacity, ionic conductivity, water uptake and transport numbers of nitrate and chloride were also measured by experimental methods. Ion conductivity values which represent the state of electrochemical properties of the membranes were at the range of 1.1-9.5 mS/cm. Meanwhile, values of selectivity which is the ratio of nitrate to chloride transport number were measured to be between 0.96 and 1.52. Among the prepared membranes, due to higher selectivity and other suitable electrochemical properties, the one that was aminated by triethylamine and the double-layer membrane which was aminated by trimethylamine and tetramethylhexanediamine were selected to be investigated by an in-situ analysis in a capacitive deionization module. When using a feed containing sodium nitrate, utilization of these membranes in the capacitive deionization module increased the nitrate removal efficiency by 20% compared to the typical capacitive deionization without membranes. Moreover, the amount of nitrate adsorption was about 1.4 times higher than chloride adsorption which confirms nitrate selectivity at process conditions.
Keywords: Water treatment, Capacitive deionization, Anion exchange membrane, Polysulfone, Nitrate removal
