Thermal decomposition of dichloromethane in absence and presence of added oxygen and/or methane

Author

Hong-Ming Chiang, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

10-31-1992

Degree Name

Master of Science in Environmental Science - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Deran Hanesian

Third Advisor

Paul H. Kydd

Abstract

Thermal decomposition experiments on dichloromethane in absence and presence of added O₂ and/or ₄ and in argon bath gas were conducted in a tubular flow reactor. The thermal reactions were studied at 1 atmosphere pressure with residence times of 0.3 - 2.0 seconds in the temperature range from 680 to 840 °C.

The degradation of dichloromethane and the decomposition product distributions were studied in both oxidative and pyrolytic reaction environments. The slowest decay of dichloromethane occurred when CH₄ was present and 02 was absent. The concentration of all products, (except HCl, CO, and CO₂ in the oxidation), are below 10% in the reaction environments. The chlorinated products, such as C₂HCl₃, CH₃Cl, CHClCHCl, are shown to be more stable in the pyrolysis than in the oxidation. When oxygen is present, the concentration of chlorinated products decreases more rapidly above 780 °C than when no oxygen is present. Carbon mass balance in the CH₂Cl₂/Ar reaction environment was less than 60% at temperatures above 780 °C, and less than 20% at temperatures above 820 °C. This implies that the formation of high molecular species and soot are occur at higher temperatures in the absence of oxygen.

The overall (global) rate constants of CH₂Cl₂ decay in this study were found as:

1. CH₂Cl₂ : CH₄ : O₂ : Ar = 1 : 1 : 4 : 94 k = 6.74 x 1015 x EXP(-75.84/RT) (1/sec)
2. CH₂Cl₂ : O₂ : Ar = 1 : 4 : 95 k = 1.56 x 1024 x EXP(-114.68/RT) (1/sec)
3. CH₂ C:l CH₄ : Ar = 1 : 1 : 98 k = 6.46 x 1013 x EXP(-67.85/RT) (1/sec)
4. CH₂Cl₂ : Ar = 1 : 99 k = 1.21 x 1018 x EXP(-86.92/RT) (1/sec)

A detailed kinetic reaction mechanism consisting of 94 species and 382 elementary reactions based on thermo-chemical principles and Transition State Theory, was modified and used to model results obtained from the experimental system. The results of model prediction for dichloromethane decay were slower than experimental results. Major products (CH₃Cl and C₂HCl₃) distribution below 780 °C match the experimental results well.

Recommended Citation

Chiang, Hong-Ming, "Thermal decomposition of dichloromethane in absence and presence of added oxygen and/or methane" (1992). Theses. 1800.
https://digitalcommons.njit.edu/theses/1800