Thermal desorption and decomposition of hazardous organic compound I: Mass transfer of benzene and chlorobenzene in soil matrices II: Oxidation and pyrolysis of 1,1,1-trichloroethane in methane/oxygen/argon

Author

Yo-Ping Wu, New Jersey Institute of Technology

Document Type

Dissertation

Date of Award

Spring 5-31-1992

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Dana E. Knox

Third Advisor

Gordon Lewandowski

Fourth Advisor

Henry Shaw

Fifth Advisor

Jay N. Meegoda

Abstract

I: Mass Transfer of Benzene and Chlorobenzene in Soil Matrices

Experimental measurements on several apparatus were used in conjunction with chromatographic theory to study the thermal adsorption and desorption of organic vapors on soil with different particle sizes for analysis mass transfer parameters and heat of adsorption. Benzene (C₆H₆) and chlorobenzene (C₆H₅Cl) were tested on soil with 0.55, 0.46, 0.36, and 0.225 mm average particle sizes. Sample injection volumes for organic compounds were studied to ensure linearity of gas chromatography. Equilibrium constants were strongly dependent on temperature but not on particle size. Heats of adsorption, determined from the slope of the plot of Van't Hoff's equation, were -16.08 for C₆H₆ and -19.48 kcal/mole for C₆H₅Cl. An analysis of second central moment showed that mass transfer resistance of larger molecules like C₆H₆ and C₆H₅Cl was not strongly dependent on temperature within the ranges of this study and for this soil matrix.

Results from continuous adsorption and desorption experiments showed that temperature and inlet flow rate affect effluent concentration. The temperature effect on the effluent concentration of C₆H₆ became less significant for temperatures above 220 °C.

The results from an analytical solution and numerical analysis using orthogonal collocation method showed excellent coincidence. The numerical approach was therefore chosen to model experimental results. This model includes axial dispersion coefficients, intraparticle diffusion coefficient, film mass transfer coefficients plus the adsorption equilibrium constant and shows good agreement at higher temperatures; but shows slower transfer through the bed for the effluent concentration of organics on soil at lower temperature.

H: Oxidation and Pyrolysis of 1,1,1-Trichloroethane in Methane/Oxygen/Argon

The thermal decomposition of 1,1,1-trichloroethane in methane/oxygen mixtures and argon bath gas was carried out at 1 atmosphere total pressure in tubular flow reactors. The thermal degradation of 1,1,1-trichloroethane and methane was analyzed systematically over the temperature range of 500 to 800°C, with average residence times of 0.05 to 2.5 seconds. Five reactant ratio sets, in three different diameter flow reactors, were studied.

It was found that the 99% decay of the 1,1,1-trichloroethane at 1 second residence time occurs at about 600°C for all the reactant ratio sets. The major products for 1,1,1-trichloroethane decomposition were 1,1-dichloroethylene and HCl. Oxygen (maximum 4.5%) had almost no effect on the initial decay rates of 1,1,1-trichloroethane in our study. Formation of CH₂CCl₂ as a major product from CH₃CCl₃ increased with increasing temperature to a maximum near 600°C at 1.0 sec residence time, and was independent of O₂/CH₃CCl₃ reactant ratio from 0 to 9. It then drops quickly with increasing temperature and increased O₂ partial pressure. Faster decay of compounds, such as C₂H₃CI, C₂H₂, C₂H₄ and C₂HCl which were formed at lower temperatures, occurred when the reactor temperature was increased above 650°C, and higher oxygen levels were present in the mixture. At higher ratios of O₂ to CH₄, it was observed that lower temperatures were needed to form CO and CO₂. The major products at temperature above 750°C are HCl, C₂HCl, and non-chlorinated hydrocarbons C₂H₂, C₂H₄, CO and CO₂.

Increasing the surface to volume ratio of the quartz reactor accelerated the decomposition of the reactants, but had no effect on distribution of major products.

A detailed kinetic reaction mechanism was developed and used to model the experimental results. The mechanism consists of 339 elementary reactions with both forward and reverse rate constants based on thermochemical principles. A sensitivity analysis of the model was done to show the most important reactions in the mechanism.

Rate constants obtained for initially important decomposition of 1,1,1-trichioroethane over the temperature range 500 -1000°C are:

A(sec-1) Ea (kcal/mole)
CH₃CCl₃ --> CH₂CCl₂ + HCl 3.35E+ 13 51.2
CH₃CCl₃ --> CH₃CCl₂ + Cl 4.59E+ 14 66.6

Transition state theory was utilized for isomerization reactions and Quantum Kassel theory was used to account for fall-off in unimolecular dissociation reaction and in reactions of adducts formed from addition, combination or insertion reactions.

Recommended Citation

Wu, Yo-Ping, "Thermal desorption and decomposition of hazardous organic compound I: Mass transfer of benzene and chlorobenzene in soil matrices II: Oxidation and pyrolysis of 1,1,1-trichloroethane in methane/oxygen/argon" (1992). Dissertations. 1165.
https://digitalcommons.njit.edu/dissertations/1165