甲苯的光氧化降解试验研究

以气相甲苯为对象,研究其在波长为254 nm紫外光下的光氧化降解反应.同时,考察了甲苯初始浓度、光强和相对湿度对甲苯转化率的影响,分析了甲苯降解中间产物的生成机理.结果表明,随着甲苯初始浓度的增加,甲苯转化率缓慢下降;随着光照强度的增强,甲苯转化率逐渐增加;而提高相对湿度,甲苯转化率则为先升高后降低.在甲苯降解动力学分析中发现其光氧化降解过程符合伪一级反应动力学,且表观速率常数与光照强度成正比.通过对甲苯降解中间产物的分析,发现随着光照强度的增加,含苯环物质的降解更为充分,乙醇、乙酸等的相对含量逐渐增加,苯甲醇、苯甲醛缩二甲醇等的含量逐渐降低,在此基础上提出了甲苯生成含苯环产物及开环生成2-戊酮等的降解机理.

Experimental study on the degradation of toluene by photo-oxidation

An investigation was performed on the photo-oxidative degradation of toluene under irradiation by 254 nm UV light. The effects of the initial toluene concentration, illumination intensity and relative humidity on the toluene degradation were studied, as well as the degradation mechanism of toluene into its intermediates. The results showed that the toluene conversion efficiency decreased slightly with increase of initial toluene concentration, whereas the conversion efficiency improved with an increase of illumination intensity. As the relative humidity increased, the toluene conversion efficiency improved at first with a subsequent decline as humidity level increased further. The toluene degradation demonstrated pseudo first-order chemical kinetics, and the apparent constant was proportional to the intensity of UV light. According to the intermediates produced during the toluene degradation process, an increase of light intensity favored complete degradation of aromatic compounds. The relative fraction of small molecular products such as ethanol and acetic acid increased, while those of phenylcarbinol and benzaldehyde dimethyl acetal reduced gradually. Speculation was made of kinetic pathways for the degradation of toluene to intermediate aromatic compounds and ring-opening reaction pathways to form small molecular products like 2-pentanone.