ارزيابي روش‌هاي الكتروشيميايي در كلرزدايي از كلرواستيك اسيدهاي موجود در پساب كارخانه‌ي توليد مونوكلرواستيك اسيد يزد

eva‎luation of electrochemical methods in the dechlorination of chloroacetic acids in wastewater of Yazd monochloroacetic acid production plant

شيمي تجزيه

In this research, the efficiency of electrochemical methods for the dechlorination of chlorinated compounds in the wastewater of the Nirou Chlor Yazd Company was investigated to convert the wastewater into valuable products. The results show that electrochemical methods can be used to dechlorinate the wastewater of this company, which is a mixture of acetic acid (AA), monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) (in very small amounts). After the dechlorination process, the wastewater turns into a mixture of AA and MCAA. This conversion changes the wastewater from a complex, unusable, and environmentally harmful mixture into a simple mixture consisting of water, AA (the raw material for the factory), and MCAA (the factoryʹs product). The operational conditions for the electrochemical dechlorination process of DCAA and TCAA present in the wastewater were examined using two types of cells: a two-compartment cell where the cathodic and anodic half-cells were separated by a cation exchange membrane, and a single-compartment cell. The results obtained from both setups were compared. For the two-compartment cell process, sulfuric acid solution was used as the anodic half-cell solution, and a lead electrode served as the anode. The cathodic solution consisted of wastewater diluted with sulfuric acid. The effect of the cathode material on the coulombic efficiency was studied. The results showed that among the electrodes examined, silver and lead electrodes provided the highest efficiencies. When using the silver electrode at a voltage of 3 volts, the conversion of DCAA to MCAA achieved a coulombic efficiency of 87%. In the single-compartment cell, conventional electrodes cannot served as anode because they are unstable and prone to corrosion under experimental conditions. Therefore, a mixed metal oxide (MMO) electrode was necessarily employed as the anode. Investigations were conducted using silver and lead electrodes as cathode. The effect of applied voltage and electrolyte type on coulombic efficiency was analyzed. The findings revealed that reducing the acidity of the medium and lowering the voltage significantly increased efficiency. Using lead as the cathode at a voltage of 3 volts for a sample diluted with water yielded a coulombic efficiency of 76% for converting DCAA to MCAA. This efficiency increased to 80% for a sample diluted with sodium hydroxide solution. Due to the unavailability of conventional measurement methods for chlorinated acetic acids, part of the work was dedicated to developing an electrochemical method based on square wave voltammetry for quantitatively measuring DCAA concentration.

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