The oxidation of methylene chloride over manganese dioxide catalyst

Author

Jun Du, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

Spring 5-31-1990

Degree Name

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

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Henry Shaw

Second Advisor

Joseph W. Bozzelli

Third Advisor

Robert J. Farrauto

Abstract

This research presents results from a study with the goal of using a transition metal oxidation catalyst, manganese dioxide (MnO₂) I to convert low concentrations of methylene chloride (CH₂Cl₂) in air and in a methane/air stream into CO₂, H₂O and HCl. Our objectives were to determine the oxidative effectiveness of the catalyst and its durability under the corrosive exposure to chlorine, HCl and other likely stack gas contaminants.

Experiments were carried out in a tubular packed bed integral reactor using gas chromatographic (FID and TCD) analysis for chlorocarbons and non-dispersive infrared analysis for CO and CO₂. The results indicate:

1. The light-off temperature for oxidation of the CH₂Cl₂/air mixture over MnO₂ is on the order of 500 K for space velocities from 1.67 to 6.67 v/v/sec.

2. There are two regions where rate is controlling: (i) in the range of 513-625 K, rate is controlled by kinetics, where higher temperatures increase conversion of CH₂CL₂ and selectivity to CHCl₃ and CCl₄, and (ii) above 675 K, the rate is controlled by bulk mass transfer, where the reaction rate is an insensitive function of temperature.

3. A typical material balance at 708 K shows that 100 ppm CH₂CL₂ are converted to 8.4 ppm CO₂, 32.7 ppm CHCl₃ 9.2 ppm CCl₄, 3.7 ppm HU (determined by titration) , and 34.4 ppm CH₂CL₂ come through unreacted.

4. The overall rate constant is: k = 9,600 (±600) Exp[-12.7(±0.2)/RT] in 1/sec where, activation energy is 12.7 kcal/mol and gas constant 1.987 cal/(mol K).

5. Increased residence time changes selectivity from CHCl₃ to CCl₄.

6. Oxychlorination (the catalytic conversion of HCl to Cl₂ in the presence of O₂) apparently effectiveness of MnO₂ to produce CHCl₃ and CCl₄.

7. Since MnO₂ converts CH₂Cl₂ to higher chlorinated products rather than just CO₂ and HCl, it is not suitable as an incinerator catalyst.

Recommended Citation

Du, Jun, "The oxidation of methylene chloride over manganese dioxide catalyst" (1990). Theses. 1333.
https://digitalcommons.njit.edu/theses/1333