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Thermal Stability and Reaction Mechanism of Chloromethanes in Excess Hydrogen Atmosphere
원양수 한국공업화학회 2007 Journal of Industrial and Engineering Chemistry Vol.13 No.3
The four chlorinated methanes, methyl chloride (CH3Cl), methylene chloride (CH2Cl2), chloroform(CHCl3), and carbon tetrachloride (CCl4), were used as model chlorocarbon systems with Cl/H ratios of 0.021 to 0.083 to investigate the thermal stability and hydrodechlorination of chloromethanes in excess hydrogen. The pyrolytic reactions were studied in an isothermal tubular reactor at a total pressure of 1 atm with reaction times of 0.3∼2.0 s at temperatures between 525 and 900 oC. The thermal stabilities of the chloromethanes, i.e., the temperatures for 99 % destruction within a reaction time of 1 s were 875 oC for CH3Cl, 780 oC for CH2Cl2, 675 oC for CHCl3, and 635 oC for CCl4. The less-chlorinated hydrocarbons were more stable, with CH3Cl the most stable chlorocarbon in this reaction system. This work focused on pyrolysis of CH3Cl in an ex-cess-hydrogen reaction atmosphere. The observed hydrodechlorinated products were CH4, C2H4, and C2H6 at temperatures above 850 oC in the CH3Cl/H2 reaction system. The number and quantities of intermediate chlori-nated products decreased with increasing temperature; the formation of non-chlorinated hydrocarbons in-creased as the temperature rose. One of main pathways for hydrodechlorinated products resulted from H atom cyclic chain reaction by abstraction. Product distributions along with preliminary activation energies and rate constants are reported. The pyrolytic reaction pathways that describe the important features of reagent decay and intermediate product distributions, based upon thermochemical and kinetic principles, are suggested.