Henrieta Nichipor1, Elena Dashouk1, Svetlana Yacko1, Andrzej G. Chmielewski2, Zbigniew Zimek2, Yongxia Sun2, Steven A. Vitale3
1 IRPCP, Academy of Sciences Republic of Belarus, Minsk-Sosny, Belarus
2 Institute of Nuclear Chemistry and Technology, 16 Dorodna Str., 03-195 Warsaw, Poland
3 Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
New experimental data related to the removal of C2H2Cl2 and C2HCl3 in dry and humid (300 ppm of H2O) air at atmospheric pressure and a temperature of 25°C under the influence of electron beam in the dose range 1 < D < 100 kGy are published. Taking into account these experimental data, theoretical models of the decomposition of both compounds and computer simulations were performed by the present authors to find the kinetics of such processes. The influence of active atoms Cl, O and OH radicals on the VOC degradation process has been established.
The theoretical model of C2H2Cl2 degradation under the influence of electron beam in dry and humid air describes the C2H2Cl2 decay and formation of the main products like Cl2, COCl2, CO, CO2, HCl, HCOCl and C2H2Cl2O. The results of calculation of the kinetics of C2H2Cl2 decomposition were compared with data obtained experimentally for the C2H2Cl2 concentration range 321-2213 ppm. It was established that the relation between the rate constants of intermediate product decomposition:
C2H2Cl3O Þ C2H2Cl2O + Cl; (k1)
C2H2Cl3O Þ COCl2 + CH2C2; (k2)
should be k1/k2 = 40.
The theoretical model of C2HCl3 degradation under the influence of electron beam in dry and humid air describes the C2HCl3 decay and formation of the main products like Cl2, COCl2, CO, CO2, HCl, HCOCl and C2HCl3O. A detailed comparison of experimental and theoretical data for the C2HCl3 concentration 108-3206 ppm shows that the relation between the rate constants of intermediate product decomposition:
C2HCl4O Þ C2HCl3O + Cl; (k3)
C2HCl4O Þ COCl2 + CHCl2; (k4)
should be k3/k4 =10. It was also found that O2+ ions have been formed in a gas mixture as a result of charge transfer process from N2+ ions, partly in excited form, which may lead to charge transfer to C2HCl3 and degradation of those particles.
According to performed calculation, it can be stated that in humid air (300 ppm of H2O) VOC degradation is occurring mainly due to a chain reaction stimulated by Cl atoms, but also OH radicals are playing an important role. In the described gas mixture, the OH radicals are formed in the following reactions:
O2+) + H2O + M Þ (O2+)H2O + M
O2+ (H2O) + H2O Þ O2 + (H3O+)OH
(H3O+)OH + H2O Þ H3O+ + OH + H2O
VOC degradation process under the influence of electron beam is more effective in humid air than in dry air for the same initial VOC concentration level. This conclusion is also supported by experimental data.