Catalytic and Ozone-catalytic Oxidation Processes for Treatment of Chlorinated Volatile Organic Compounds
Date Issued
2007
Date
2007
Author(s)
Liao, Wei-Chu
DOI
zh-TW
Abstract
This study investigated the catalytic oxidation for the decomposition of chlorinated volatile organic compounds (CVOCs). The target compounds are 1,2-dichloroethane (DCEA) and vinyl chloride (VC). The former is commonly used as solvents in the industry, and the latter is a main material for manufacturing polyvinyl chloride (PVC) products. CVOCs are difficult to be converted, so they accumulate easily in the environment. Further, CVOCs are hazardous to human health with most of them being proved to cause cancers.
Pt/γ-Al2O3 was used as catalysts in this study. The results indicated that it enchaced the conversions of DCEA and VC via oxidation. The reaction temperatures for 90% conversion (T90) of DCEA and VC are 638 and 580 K, respectively. On the other hand, the values of T90 of DCEA and VC for the traditional thermal oxidation are 925 and 997 K, respectively. Besides, a lower gas hourly space velocity (GHSV) gave a higher conversion. The data with various GHSV were further used to establish the reaction kinetic model of catalytic oxidation of DCEA and VC over Pt/γ-Al2O3. Rideal-Eley model was adopted to simulate the experimental results. The model combining with the Arrhenius equation then yielded the activation energy (Ea) and frequency factor (A). The values of Ea and A were 29.02 kJ mol-1 and 1.02 × 105 s-1 for DCEA, and 43.48 kJ mol-1 and 4.56 × 106 s-1 for VC.
As for the products, the ultimate products of decomposition of DCEA and VC were found to have CO2, Cl2 and HCl. No incomplete combustion product of CO was detected. The main chlorinated product of decomposition of DCEA and VC was Cl2, while VC was also an intermediate of catalytic oxidation of DCEA. The total carbon and chlorine atoms of products after catalytic oxidation reached 70-90% of inlet carbon and chlorine atoms, and these values were higher than those after traditional thermal oxidation. The results showed that catalytic oxidation obviously promoted the conversions of DCEA and VC.
Furthermre, the effect of adding ozone in catalytic oxidation of DCEA was examined. Because VC had a double bond, while ozone showed the selectivity to the double bond. Thus, VC was completely reacted in a short time. When DCEA was treated via the ozone-catalytic oxidation process, about 90% conversion was reached at 610-620 K. The needed reaction temperature to reach the same conversion decreased with the increase of ozone concentration. On the other hand, the conversion of DCEA via the ozone-catalytic oxidation at the same temperature was higher than that of catalytic oxidation. This indicated that the presence of ozone indeed assisted with the efficiency for treating DCEA.
The addition of ozone to the catalytic oxidation of DCEA had distinct effects on yields of products. For CO2, the ultimate yield reached 100%. As to the chlorinated products in ozone-catalytic oxidation of DCEA, VC was also an intermediate, while Cl2 and HCl were the ultimate products. For the chlorine balance, the total chlorine atoms of gaseous products were 40% of inlet chlorine atoms. Thus it indicated a large number of chlorinated products were adsorbed on the surface of the catalyst, standing for a reason for the deactivation of catalyst.
Subjects
含氯揮發性有機物
二氯乙烷
氯乙烯
觸媒氧化
白金觸媒
臭氧觸媒氧化程序
Chlorinated volatile organic compounds (CVOCs)
dichloroethane
vinyl chloride
catalytic oxidation
Pt/γ-Al2O3
ozone-catalytic oxidation process
SDGs
Type
thesis
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