Date of Award

1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Abstract

A study of the effect of variable solid properties on the kinetics of the reaction of spherical manganous oxide pellets with hydrogen sulfide gas was performed. This study resulted in a major modification of the grain model to allow for radial solid property variations due to reaction and/or sintering. It was shown that this new model did the original constant property grain model. A complete experimental study was made of the effects of exposure to high temperatures (sintering) and the effects of the reaction itself on the structural properties, notably the specific surface area and porosity, of the solid reactant (MnO) and solid product (MnS). It was determined that sintering resulted in drastic changes in the solid properties as exposure temperature increased. It was also shown that sintering was negligible below 500(DEGREES)C and caused significant variations only at or above 600(DEGREES)C. These structural variations were correlated as a function of time and temperature for use in the reaction model. Variations in solid properties were also noted due to the effects of the reaction itself. The porosity change was determined to be a function of the molar volumes of solid reactant and product and the extent of reaction. A ratio of the molar volume of solid product to that of solid reactant greater than unity results in porosity decrease and a slower rate of reaction. In the present case, this ratio was 1.59. The surface area change with reaction, however, could not be correlated with molar volume. An empirical correlation was developed for inclusion in the model. The experimental kinetic study was carried out with the two-fold purpose of determining the kinetic pararmeters of the reaction and providing data for comparison with model predictions. All kinetic data were collected on a thermogravimetric analyzer, which measured weight change in a single pellet during reaction as a function of time. Reactions were carried out at temperatures of 200(DEGREES)C to 800(DEGREES)C for gas streams containing 1.0 to 2.0 mole percent H(,2)S. In general, it was observed that the fastest rate of reaction was obtained at 500(DEGREES)C with reactions at higher temperatures exhibiting, in many cases, much slower rates. The data were compared to the predictions of the constant property grain model and the variable property model developed herein. In all cases, except at 500(DEGREES)C, the proposed model exhibited far better predictive capabilities. At 500(DEGREES)C the two models were approximately equal in matching experimental data.

Pages

442

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