1995 Fiscal Year Final Research Report Summary
Pretreatment with Nitrous Acid for Oxygen Bleaching of Kraft Pulp
| Project/Area Number |
06660203
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
林産学
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| Research Institution | University of Tsukuba |
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Principal Investigator |
OHI Hiroshi The University of Tsukuba, Institute of Agricultural and Forest Engineering, research associate, assistant professor, 農林工学系, 助手 (20201965)
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| Project Period (FY) |
1994 – 1995
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| Keywords | nitrous acid / oxygen bleaching / kraft pulp / lignin / veratraldehyde |
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| Research Abstract |
A pretreatment method with nitrite and nitric acid for oxygen bleaching of kraft pulp has been proposed as one of the possible methods for the reduction of organic chlorine compounds from bleaching process. Effects of the nitrous acid pretreatment were compared with those of the nitrogen dioxide pretreatment proposed by Swedish researchers, and their delignification mechanism was compared to each other on the basis of reactions of lignin model compounds. The problems and advantage of the nitrous acid treatment were discussed to carry out it on an industrial scale in the near future.
(1) Softwood (Pinus densiflora Sieb.et Zucc.) kraft pulp was delignified under the conditions at 90ﾟC for 3 hours with nitrite (0.3% on pulp) and nitric acid (4% on pulp), whereas it was slightly done in the absence of the nitrite.
(2) Phenolic lignin model compounds were rapidly degraded under the conditions compared with nonphenolic lignin models. However, the nonphenolic models (veratrylglycerol-beta-guaiacyl ether.VG,alpha-ethyl ether of VG : VGE,veratrylglycerol-beta-syringyl ether : VS,alpha-ethyl ether of VS : VSE,dehydrodi-isoeugenol methyl ether : DIM) were distinctly degraded through cleavage of their Calpha-Cbeta bonds giving veratraldehyde.
(3) Z-, E-isoeugenol methyl ether, IME was rapidly degraded even at 0ﾟC,giving veratraldehyde. It suggests a possible mechanism involving acid-promoted conversion of the nonphenolic lignin units into ring-conjugated structures, followed by the oxidative cleavage of the Calpha-Cbeta bonds.
(4) Compared with the nitrogen dioxide treatment, the nitrous acid treatment has the advantage. The latter does not need the gas-phase chemical and the two-stages treatment, and gives similar results to the former. However, an environmental issue of disposal of the spent liquor including nitrogen compounds may be made. Development of the process which would recover it and regenerate nitrite and nitric acid may solve the problem.
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