Date of Award

Spring 1990

Document Type

Thesis

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.

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