Oh-Kyu Lee

Date of Award

12-2003

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Barbara J.W. Cole

Second Committee Member

Raymond C. Fort, Jr.

Third Committee Member

Bruce L. Jensen

Abstract

Oxygen delignification is an environmentally friendly pulp bleaching system. To develop a selective delignification process that results in high DP retention of carbohydrate with lignin being removed, obtaining better knowledge of reactions occurring during oxygen delignification is essential.

In this work, mixtures of guaiacol (model lignin) and methyl-ß-D-glucoside (model cellulose) were reacted in a pressurized oxygen reaction system (pH 12,65 psi O2, and 95°C in a glass reaction vessel). In the results, methyl-ß-D-glucoside degraded only in the presence of lignin. This indicates that hydroxyl radicals, that subsequently react with methyl-ß-D-glucoside, are generated in the system. Unfortunately, we could not develop the degradation mechanisms of methyl-ß-Dglucoside in this study because the identification of products derived from methyl-ß-D-glucoside could not be accomplished. Therefore, we undertook an alternative study of the oxidation reactions of cellulose using a UV/H2O2 system, which is a hydroxyl radical generation system.

For the UV/H2O2 system, the cellulose models used were methyl-ß-D-glucoside, methyl-ß-D-cellobioside, and cellulose fiber. The reactions using hydroxyl radical scavengers in the UV/H2O2 system strongly support the hydroxyl radical reactions proposed in our lab previously. The results, from the qualitative analysis of the organic acids produced during the reaction, suggest that hydroxyl radicals have an important role in the formation of aldonic acids from aldoses.

In the reactions with methyl-ß-D-cellobioside, the reaction chemistry was the same as in the reactions with methyl-ß-D-glucoside. However, the reactivity of methyl-ß-D-cellobioside toward hydroxyl radicals is considered to be larger than that of methyl-ß-D-glucoside. The cellulose fiber (filter paper) was degraded in the W/H202 system. In the presence of hydroxyl radical scavengers, tert-BuOH and 2-propanol, the degradation was inhibited in all three cellulose models used in this study. This supports that cellulose can be protected from the degradation by the hydroxyl radical using scavengers, tert-BuOH and 2-propanol.

Download

Share