Study On The Performance Of Microwave-assisted Catalytic Oxidation Of Volatile Organic Compound

Volatile organic compounds (VOCs) are easier to volatilize in ambient temperature, and its toxicity, pungentness and odor can arouse headache, nausea and intoxication, even damage human tissue and result in cancer while contacting for long terms. The omnipresent VOCs are dangerous and have been caused air pollution, so it has been paid more and more attentions at home and abroad. The paper briefly describes the current processes which are more commonly used to remove VOCs, and points out their shortcomings. Meanwhile, microwave technology and its research and application in the field of environmental engineering are reviewed in this dissertation.A new technology, named microwave assisted catalytic oxidation, is adopted in this research and an experimental setup has been established. The study takes silicon carbide as the microwave-absorbing material, and zeolite supported copper oxide (CuO/zeolite) as the catalyst, and selects toluene to be target VOC that treated continuously under conditions of microwave irradiation and air flow. The adsorption effects of CuO/zeolite catalysts were investigated, and surface morphology of the catalysts was characterized and analyzed. The microwave-absorbing property of silicon carbide was checked, and the experimental parameters for toluene catalytic oxidation under microwave heating were optimized, and the degradation and mineralization efficiencies of toluene under optimal conditions were also measured. The course products in the process of toluene degradation were determined by GC-MS and infrared spectrum, and the possible degradable pathway of toluene by microwave assisted catalytic oxidation was predicted based on the analytical results. Finally, a simple economic analysis of the new technology of microwave assisted catalytic oxidation was discusced in the dissertation. The experimental results showed that green silicon carbide had strong microwave-absorbing ability, and the temperature could be raised quickly up to 600℃within 30s under microwave irradiation while the microwave power was 117.3W. CuO/zeolite catalyst that prepared by impregnation method had poor adsorption ability to toluene, and its adsorption belongs to langmuir single-layer adsorption, and the adsorption amount for toluene was 11mg.g^-1. The analysis of surface morphology showed that copper oxide particles were dispersed uniformly on the surface of zeolite, and CuO/zeolite catalyst performed good catalytic capacity in experiment. However, sinter phenomenon could be observed on the surface of the catalyst when reaction temperature was too high. Under microwave irradiation, the bed temperature rise quickly and reached 460 oC in one minute for CuO/zeolite catalyst mixing with SiC. The blank experiment indicated that, silicon carbide itself did not have the obvious removal to toluene under microwave irradiation, and zeolite and CuO/zeolite catalyst respectively had certain elimination efficiencies to the target, but removal efficiency of toluene by microwave assisted catalytic oxidation was extremely remarkable compared with those above mentioned.The optimal parameter conditions confirmed in this study were that mixing ratio of CuO/zeolite catalyst to silicon carbide 10:1, microwave power 117.3W, air velocity 0.08 m3.h^-1, bed height 18.5 cm, toluene flow rate 40μL.min^-1, as well as zeolite loaded copper weight ratio 20:1. Under the optimal conditions, synergistic effects of the catalyst and silicon carbide on the removal of toluene by microwave assisted catalytic oxidation were remarkable after 10 hour continuous run, and removal of toluene reached 93.5%, and mineralization rate of toluene was 86%.The degradable intermediates of toluene included benzoic acid, benzaldehyde, benzyl alcohol, and small molecule organic compounds such as acetic acid and butyric acid were determined by GC-MS and FTIR analysis. The economical analysis indicated that, energy consumption by microwave assisted catalytic oxidation was lower than catalytic oxidation with conventional electric stove heating, which showed certain practical application prospect for the process of microwave assisted catalytic oxidation.