环境因素对气相甲苯光氧化反应机制的影响

Effects of Environmental Factors on Photooxidation Mechanism of Gaseous Toluene

以低压汞灯为光源,采用石英管连续流动态反应系统和特氟龙气袋静态反应系统,研究了环境因素〔RH（相对湿度）、温度、光照强度、有氧（空气）/无氧（氮气）气氛条件〕对低浓度（10~20 mg/L）气相甲苯光氧化过程的影响.结果表明：1RH对甲苯光氧化反应影响显著.干燥条件（RH为0%~5%）下甲苯光氧化去除率在8.3%~8.7%之间;当环境中有水蒸气存在（RH为20%）时,甲苯光氧化去除率降至6.5%~7.2%,其后光氧化去除率随着RH的进一步增加而逐渐增大,在RH为60%时达到最大值（9.4%~11.5%）;但当RH继续增至80%时,去除率迅速降至4.4%~5.6%.2甲苯光氧化去除率随着温度、光照强度的增加而提高.3无论是干燥（RH为0%~5%）还是湿润（RH为60%）环境下,甲苯在有氧气氛下的去除率均高于无氧气氛;甲苯在有氧气氛下光氧化产物主要是苯和苯甲醛,在无氧气氛中的产物主要是苯.4在干燥、有氧条件下,O（1D）应是甲苯光氧化的活性物种;在湿润、有氧条件下,甲苯的光氧化主要是通过·OH氧化降解;在无氧条件下,甲苯的光氧化主要是通过甲苯的直接光解完成.

The photooxidation of gaseous toluene using a low-pressure mercury UV lamp as the irradiation source was described. The influence of environmental factors, such as relative humidity （RH）, temperature （T）, light intensity （I） and aerobic/anaerobic atmosphere on the photooxidation efficiency of toluene with low concentrations （ 10-20 ng/L） were studied in a quartz tube reactor using a dynamic experiment system. The intermediate products generated during the photooxidation of toluene were studied in the Teflon reactor using a static experimental system. The experimental results indicated that： 1） RH significantly affected the toluene photooxidation. The removal rates of toluene were between 8.3% and 8.7% under the drying condition （RH -0% -5% ）. When water vapor was introduced into the air, the removal rate of toluene was reduced to 6. 5%-7.2% （RH = 20% ）. With the increase of RH, the photooxidation removal rate of toluene also increased, and the peak removal rates of toluene were between 9.4% and 11.5% under RH = 60%. When RH increased to 80% , the removal rate of toluene was rapidly reduced to 4. 4% to 5.6%. 2） The photooxidation removal rate of toluene tended to improve with the increase of environmental temperature or light intensity. 3 ） The removal rate of toluene in the aerobic atmosphere （air） was higher than that in the anaerobic atmosphere （nitrogen） in both dry （RH = 0%-5% ） and humid environments （RH = 60% ）. The intermediate of photooxidation of toluene in the nitrogen medium was benzene, while the intermediates in the air medium were benzene and benzaldehyde. 4 ） Under the aerobic dry atmosphere, the active species of photooxidation of toluene were perhaps 0 （^1D）, while it was .OH in humid environment. Under the anaerobic atmosphere, the removal of toluene was mainly derived from the direct degradation by UV （ 185 nm） irradiation.