Thermal decomposition of dichloromethane in hydrogen/oxygen/argon mixtures and in pure oxygen

Author

Wen-Pin Ho, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

5-31-1989

Degree Name

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

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Arthur Greenberg

Third Advisor

Gresheng Dai

Abstract

The thermal decomposition of Dichloromethane in hydrogen/oxygen mixtures and argon bath gas was carried out at 1 atmosphere total presure in tubular flow reactors of varied surface to volume (S/V) ratio. The thermal degradation of dichloromethane was analyzed systematically over temperature ranges from 610 to 820°C, with average residence times in range of 0.1 to 2.0 seconds. Five reaction sets in three different size flow reactors were studied.

It was found that the complete decay ( 99% ) of the dichloromethane at 1 second residence time occurs at about 810°C for all the reactants ratio sets. The major products for dichloromethane decomposition are methyl chloride, methane, CO, and HCI. The quantity of chlorinated products decrease with increasing temperature and residence time. Oxygen has almost no effect on the decay of dichloromethane when conversion is below 50% (less than 750°C) and/or the initial oxygen concentration is below 5%. Formation of CH3C1 as one of the major products from CH₂Cl2 increases to a maximum when conversion of dichloromethane is at 80%; and this is observed for all reactants ratio sets. It then drops quickly with increasing temperature and increased oxygen. The higher the ratio of O₂ to H₂, the lower the temperature needed to observe the formation of CO and CO₂. The major products when conversion is above 90% are HCI and non—chlorinated hydrocarbons : CH₄, C₂H₂, C₂H₄, CO, and CO₂.

An increase in surface to volume ratio of the reactor was observed to accelerate the decomposition process in this study, but it had no effect on the relative distribution of principal products.

First order plug flow model was utilized to analyze the experimental data. In addition the homogeneous and wall rate constants were decoupled and separately evaluated. The following overall rate equations were found to fit the reaction systems studied.

Ar : O₂ : H₂ : DCM = 97 : 1 : 1 : 1

k = 3.76 x 10¹⁴ x exp(-69.98/RT) (1/sec)

Ar . O₂ : H₂ : DCM = 95 : 2 : 2 : 1

k = 5 00 x 10¹² x exp(-60.41/RT) (1/sec)

Ar O₂ : H₂ : DCM = 95 : 3 : 1 : 1

k = 2.25 x 10¹⁵ x exp(-72.65/RT) (1/sec)

Ar : O₂ : H₂ : DCM = 95 : 1 : 3 : 1

k = 4.25 x 10¹³ x exp(-64.97 I RT) (1/sec)

A detailed kinetic reaction mechanism was developed and used to model results obtained from the experimental reaction system. A sensitivity analysis of the model was done to show the most important reactions in the mechanism. The kinetic reaction mechanism was based on thermochemical principles and Transition State Theory.

The rate constant obtained by optimization of the model to the experimental data for initially important decomposition of dichloromethane over the temperature range 700 ~ 800°C is :

CH₂Cl₂ ---> CH₂Cl+ Cl k = 3.76 x 10¹⁶ x exp(80.6/RT)

Recommended Citation

Ho, Wen-Pin, "Thermal decomposition of dichloromethane in hydrogen/oxygen/argon mixtures and in pure oxygen" (1989). Theses. 2787.
https://digitalcommons.njit.edu/theses/2787