<p>Over the years, hydrogen peroxide has been used to improve the brightness of pulp at the end of a bleaching sequence. However, the degree of delignification achieved by a hydrogen peroxide stage is usually modest. That is because in alkaline condition the hydroperoxy anion reacts with chromophores in pulp as a nucleophile that does not oxidize residual lignin to a significant extent. In order to enhance the reactivity of hydrogen peroxide as an oxidant, a binuclear manganese complex Mn(IV)2-Me4DTNE was added. As a result, the degree of delignification was significantly improved, while at the same time, the strength properties of the pulp were better preserved compared traditional in hydrogen peroxide delignification. In order to better understand the mechanism of this delignification process, lignin model compound oxidation and kinetics of pulp delignification were studied. In addition, residual lignin was isolated from the pulp before and after delignification and then characterized by GPC, FTIR, and 1H-13C 2D NMR. Shown by the model compound study, hydrogen peroxide is able to oxidize 1-(3,4-dimethoxyphenyl)ethanol, E-diphenylethene, and 1-(3,4-dimethoxyphenyl)-1-propene to a considerable extent when catalyzed by Mn(IV)2-Me4DTNE, indicating that the reactivity of hydrogen peroxide as an oxidant is significantly improved. Indeed, as shown by the kinetic study of pulp delignification, the degree of delignification as well as the rate of delignification were greatly improved when the catalyst was applied. In addition, the catalyzed delignification process benefits from the concerted reaction mechanism that regulates the formation of hydroxyl radicals responsible for the severe damage to the fibers. As a result, the strength properties were well preserved. Shown by the characterization of residual lignin before and after the delignification, residual lignin was oxidized to a good extent which accounts for the significant degree of delignification. The process simulation of this catalyzed delignification process by WinGEMS4.0 showed that this process was profitable if the cost of the catalyst was kept below $330/kg.<P>
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-20000203-202106 |
| Date | 10 February 2000 |
| Creators | Cui, Yu |
| Contributors | Josef S. Gratzl, Chen-Loung Chen, Adrianna G. Kirkman, Carol A. Haney |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-20000203-202106 |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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