Li Tao

Date of Award

12-2005

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Joseph M. Genco

Second Committee Member

Barbara J. W. Cole

Third Committee Member

Raymond C. Fort, Jr.

Abstract

The kinetics and selectivity of the oxygen delignification process were investigated for southern softwood Kraft pulps at high lignin content. The process variables investigated were the initial kappa number, the temperature, alkali application rate, oxygen pressure and the reaction time. The experimental data were fit to mathematical models that describe the decrease in the kappa number of the lignin, the molecular weight of the cellulose and the selectivity of the process. A comparison was made between the selectivity of Kraft pulping and oxygen delignification processes over the kappa number range from 90 to 25 mL KMn04. Experimentally, the alkali application rate, temperature and initial kappa number were found to significantly affect the rate and extent of the oxygen delignification reactions. By contrast, the reaction pressure was found to have a considerably lesser effect upon the reaction. A five-parameter, one region, power-law model proved to be a realistic mathematical representation for the delignification data. A zero-order model in the moles of cellulose could be used to adequately correlate the experimental data for the molecular weight of the cellulose. It was concluded that the Kraft pulping process was more selective than the oxygen delignification process for removing lignin from southern softwood Kraft pulps. The oxygen delignification process was found to be more selective for the higher kappa number pulps. It is recommended that work be done to determine why the Kraft process is more selective than the oxygen delignification process at high kappa number values.

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