Quantum yields of decomposition in the photolytic oxidation of methyl mercaptan, dimethyl sulphide and dimethyl disulphide

• Main Author: Sheraton, Donald Frederick
• Language: English
• Published: 2010
• Subjects: Decomposition (Chemistry)
• Online Access: http://hdl.handle.net/2429/22082

The Kraft pulping process produces vast quantities of sulphide vapours which are released to atmosphere. The major components are methyl mercaptan, hydrogen sulphide, dimethyl sulphide and dimethyl disulphide. The fate of these compounds in the atmosphere and the kinetics of their degradation processes in the atmosphere are useful in the modeling of the environment of areas proximate to Kraft pulp mills. The information may also be useful in developing pollution abatement processes. The photolytic oxidation of methyl mercaptan, dimethyl sulphide and dimethyl disulphide was studied in a batch photolysis apparatus. Short wavelength ultra-violet light was provided by a deuterium discharge lamp and monitored by a monochromator equipped with an extended response photo-multiplier tube. Sulphide concentrations were determined on a gas chromatograph equipped with a flame photmetric detector having 365 nm sulphur response. The rate of reaction of methyl mercaptan was found to be a linear function of the photon absorption rate and exhibited a quantum yield of decomposition of 13.9. The methyl mercaptan photo-oxidation rate was found to be unaffected by increased oxygen concentration, decreased atmospheric pressure or the presence of excess sulphur dioxide. The quantum yield of dimethyl sulphide decomposition was found to be dependent upon atmospheric pressure. A pressure of one atmosphere gave a quantum yield of 4 and the yield increased to 8 at one-quarter atmosphere. The quantum yield of dimethyl disulphide.was found to be 1.9 at atmospheric pressure at a concentration of 7.04 x 10⁻⁵M. The apparatus was also operated in a configuration which allowed the detection of light emitted at 90° to the path of illumination. A slow developing emission was found for dimethyl sulphide, hydrogen sulphide and •sulphur dioxide. Only slight emission was found for methyl mercaptan and dimethyl disulphide. The emission from dimethyl sulphide was found to be linearily dependent upon the nitrogen pressure of a dry nitrogen atmosphere. The emission is attributed to aerosol formation and is due to the light scattered from particles in the reaction matrix. === Science, Faculty of === Chemistry, Department of === Graduate