Treatment of a Highly Concentrated Solution of Acetic Acid by Photo-electrochemical Oxidation

• Main Authors: CHANG BO MING, 張博銘
• Other Authors: LO SHANG LIEN
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/04173819475248940688

碩士 === 國立臺灣大學 === 環境工程學研究所 === 90 === Abstract There is a big rise in the yearly production of acetic acid in recent years, so acetic acid now has become one of the top 20 most important industrial chemicals and raw materials that are most extensively used for producing many other industrial products. Therefore, various concentrations of acetic acid can be found in wastewater from many different industrial processes. For wastewater with low concentrations of acetic acid (<1000 ppm), traditional biological processes are sufficient for treatment. For wastewater with high concentrations of acetic acid (>100000 ppm), incineration or recycling can be used. However, for concentrations situated between very high and low ranges, the mentioned methods are insufficient. This study attempts to find an alternative method to treat this medium level of acetic acid. Photo-electrochemical oxidation (PECO) treatment was proposed in this study. It is based on the electrochemical principle to generate H2O2 from the cathodic reduction of oxygen, followed by the generation of hydroxyl radicals (OH‧) from H2O2 by a Fenton-like reaction involving a catalyst of UV radiation and ferrous ion. This study consists of two parts. The first part consists of efficiency experiments of generating H2O2; the second part is an optimization study of treating acetic acid based on conclusions of the first part, and investigating how the relevant factors affect the system. The results of experiments on generating H2O2 under different temperatures (10, 25, 45℃) showed that at the optimum controlling conditions of 0.66 mA/cm2 current density, pH 1, a distance of 1 cm between anode and cathode, and the oxygen flow rate of 0.6 L/min, the maximum concentration of hydrogen peroxide can reach 53 mg/L with a current efficiency of 70% at 10℃. This showed that H2O2 generation is favored at low temperatures. For experiments on the influence of inorganic anions (Cl-, ClO4- and SO42-) on the generation of H2O2, the trials with 0.2 M sulfate attained the highest concentration of H2O2 (64.3 mg/L) with a current efficiency of 80.3%. The results indicated that sulfate is the most effective for generating hydrogen peroxide. The results of experiments on acetic acid treatment efficiency by PECO showed that the initial concentration of 2000 ppm of acetic acid was effectively decomposed and attained 100% conversion after 2 hours and over 90% of TOC mineralization after 3 hours at the following experimental conditions: temperature 25℃; current density 0.66 mA/cm2; pH 2; oxygen flow rate, 0.6 L/min; a distance of 1 cm between anode and cathode; a ferrous ion dosage of 15 mg/L, an UV radiation intensity of 450 W, and a UV radiation wavelength of 254 nm. The results of treating acetic acid by PECO under different temperatures (10, 25, 40℃) showed that the reaction rate slightly increases when temperature increases, but the difference of the result between 25℃ and 40℃ is very small. The difference of TOC mineralization between 25℃ and 40℃ is less than 1%. For experiments on the influence of inorganic anions (ClO4- and SO42-) on the treatment of acetic acid by PECO, the trials showed the addition of anion actually result in a reaction rate slower than that of adding nothing. We concluded that when PECO is applied to the treatment of wastewater with acetic acid, it is not necessary to add inorganic anions to adjust the ionic strength of wastewater. Key words－ Acetic acid, current efficiency, electro-reduction, Fenton method, ferrous ion, hydrogen peroxide, inorganic anion, photo-electrochemical oxidation method, UV radiation