双极膜电渗析清洁制备NaOH和H_2SO_4的试验研究

CLEANER PREPARATION OF NaOH AND H_2SO_4 BY Na_2SO_4 SPLITTING USING BIPOLAR MEMBRANE ELECTRODIALYSIS

采用双极膜、阴离子交换膜和阳离子交换膜交替排列构成的五隔室双极膜电渗析(BMED)构型,以Na2SO4为原料制备NaOH和H2SO4。研究了电流密度和原料液浓度对膜堆操作性能的影响,并对2种不同的均相阳膜进行了对比考察。结果表明,在电流密度50 mA/cm2,Na2SO4原料液浓度10%的条件下,试验范围内NaOH的收率可达79.63%,其收率和能耗随电流密度的增大而增加;电流密度恒定时,较高的原料液浓度利于保持更小的膜堆电阻,过程能耗相应降低。将BMED制得的稀NaOH和H2SO4溶液直接用于饱和阴、阳离子交换树脂的再生处理,并将其与经常规酸碱试剂化学再生的树脂均用于反渗透产水的深度除盐制备纯水,结果前者所获水质纯度显著优于后者,表明BMED所制备的酸碱纯度更高,树脂再生更为彻底。

A bipolar membrane electrodialysis （BMED） stack with five compartments was adopted to directly produce sodium hydroxide and sulfuric acid by sodium sulfate splitting. Effects of current density and feed concentration on the BMED performances were well investigated. Also the influences of two different kinds of cation-exchange membranes were compared with each other. The results show that with current density of 50 mA/cm2 and 10% Na2SO4 solution, the conversion rate of NaOH could achieve 79.63%. The conversion rate and energy consumption increased as the current density increased. At the constant current density, the resistance of the stack reduced as Na2SO4 concentration increased, and the energy consumption reduced accordingly. The dilute NaOH and H2SO4 solutions produced by BMED were then used for regeneration of anion and cation ion-exchange resin, and further to process RO water to obtain pure water compared with the usuat ＂RO/IE＂ processes whose ion-exchange resins were chemical regenerated. The results showed that the product water quality obtained in the former experiment using NaOH and H2SO4 produced by BMED was significantly superior to the latter, which demonstrated that the resins were more thoroughly regenerated since the acid and alkali with higher purity were obtained by BMED process.