Date of Award

Spring 1991

Document Type

Dissertation

Degree Name

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

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Robert Benedict Barat

Third Advisor

Barbara B. Kebbekus

Fourth Advisor

Henry Shaw

Fifth Advisor

Arthur T. Poulos

Abstract

Chloroform decay and product distributions were distinctly different in the absence and presence of added O2 and/or CH4. Increases in O2 concentration were observed to speed reagent loss, with a slower decay of chloroform observed for the CHCl3/CH4/Ar pyrolysis system. In CHCl3/CH4/O2, the major products were C2Cl4, CH2CCl2, C2HCl3, CO and CO2 over a wide temperature range. Minor products included CH2Cl2, CH3Cl, and C2H3Cl. When CH4 reactant was not present, C2Cl4 and CCl4 levels increased significantly.

A detailed kinetic reaction mechanism to describe the important features effecting product formation and reagent loss was developed. The mechanism, consisting of 121 species and 426 elementary reactions, is based on fundamental thermochemical principles and Transition State Theory.

The mechanism includes bimolecular QRRK analysis of the chemically activated adduct formed in recombination reactions of chlorinated hydrocarbon radicals with OH, O, HO2, CIO and from addition reactions with O2 to correctly describe the temperature and pressure dependence of plausible reaction pathways. Unimolecular reactions are analyzed with unimolecular QRRK analysis for the proper treatment of fall-off dependencies. Model predictions for loss of reagents and product distributions show good agreement with the experimental observations.

We conclude that the primary decomposition reaction pathway for chloroform is: CHCl3 > HCl + :CCl2. High pressure limit rate constants obtained in this work for the important initial decomposition of Chloroform were determined to be: A (1/sec.) Ea (Kcal/mol) CHCl3 ----> CCl2+ HCl 1.6E14 56.0 CHCl3 ----> CHCl2 + Cl 2.5E16 74.6

We also postulate the major pathways for O2 interaction with CCl2 and CCl3 radicals, and present estimates of kinetics and mechanistic pathways for these reactions.

Section II: Thermal Decomposition of Dichloromethane/1,1,1-Trichloroethane Mixture Diluted in H2

Dichloromethane/1,1,1-trichloroethane mixture was used to investigate pyrolysis reactions and the conversion of chlorocarbons in the presence of excess hydrogen. Profiles for the formation and subsequent loss of intermediates and the formation of final products are presented as functions of both time of reaction (0.05 to 2.0 sec.) at fixed temperature and of temperature (475 - 810 °C) at uniform reaction time in tubular flow reactors of three different surface to volume ratios and 1 atm pressure.

The major products observed were dichloroethylene, vinyl chloride, methyl chloride, dichloroethane and HCl at 572 °C and l.0 second. Ethylene, methane, ethane, methyl chloride and HCl were the major products at this time and 810 °C.

A detail kinetic reaction mechanism was developed and used to model results obtained from the experimental reaction system. The mechanism, consisting of 42 species and 97 elementary reactions, is based on thermochemical principles and Transition State Theory, and describes the overall reaction process. Model predictions for the loss of the reagents and the formation product distributions show good agreement with the experimental observations.

Rate constants obtained in this work for the important initial decomposition of dichloromethane and l,l,l-trichloroethane over the temperature range 475 to 810 °C were determined to be: A (1/s) (Kcal/mol) CH2CI3 ------> CH2CI + Cl 1.15E+14 75.6 CH3CCI3 ------> CH2CCI2 + HCl 4.20E + 13 51.0 CH3CCI3 ------> CH3CCI2 + Cl 1.44E + 15 65.2

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