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Title: Soda-AQ delignification of hardwoods: Reactions, mechanisms, and dissolved lignin characteristics

Abstract

Alkaline pulping of Populus deltoides performed in a flow through reactor shows the formation of coniferyl alcohol (CA), sinapyl alcohol (SA), and other low molecular weight (LMW) compounds in different phases of delignification. During the heating-up period, the rate of formation of these compounds increases until the maximum cooking temperature (170C) is reached. Afterward, their concentration in the spent liquor decreases sharply. This decrease is accompanied by dissolution of high molecular weight lignin fractions. Comparison between soda and soda-AQ delignifications shows a higher production of LMW compounds when the AQ-AHQ redox system is present. During the heating-up period the cinnamyl alcohols apparently originate from unetherified {beta}-aryl ether units in lignin and their formation is accompanied by solubilization of lignin fragments with relatively low molecular weights. A lignin core having {beta}-aryl ether bonds as major hydrolyzable interunit linkages remains in the fiber and it is solubilized as high molecular weight fragments at later delignification stages. Lignin fragments, especially those formed during the heating-up period, undergo further degradation after they are dissolved in the liquor. Low molecular weight fragments are degraded to oligomers at the end of the cook, while the fragments formed by degradation of the lignin core are more resistant.more » Pulps with low kappa number can be produced by maintaining alkali concentrations higher than those found in normal cooks during the last delignification phase. Replacing in this stage the cooking liquor by a liquor with a higher alkali concentration results in extended delignification, elimination of lignin redeposition and creates the possibility of producing technical lignins with higher {bar M}w.« less

Authors:
Publication Date:
Research Org.:
North Carolina State Univ., Raleigh, NC (United States)
OSTI Identifier:
5642466
Resource Type:
Miscellaneous
Resource Relation:
Other Information: Thesis (Ph. D.)
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; LIGNIN; ACID HYDROLYSIS; WOOD; DELIGNIFICATION; CHEMICAL FEEDSTOCKS; MOLECULAR WEIGHT; POPLARS; CARBOHYDRATES; CHEMICAL REACTIONS; DECOMPOSITION; HYDROLYSIS; LYSIS; MAGNOLIOPHYTA; MAGNOLIOPSIDA; ORGANIC COMPOUNDS; PLANTS; POLYSACCHARIDES; SACCHARIDES; SOLVOLYSIS; TREES; 090900* - Biomass Fuels- Processing- (1990-)

Citation Formats

Venica, A D. Soda-AQ delignification of hardwoods: Reactions, mechanisms, and dissolved lignin characteristics. United States: N. p., 1989. Web.
Venica, A D. Soda-AQ delignification of hardwoods: Reactions, mechanisms, and dissolved lignin characteristics. United States.
Venica, A D. Sun . "Soda-AQ delignification of hardwoods: Reactions, mechanisms, and dissolved lignin characteristics". United States.
@article{osti_5642466,
title = {Soda-AQ delignification of hardwoods: Reactions, mechanisms, and dissolved lignin characteristics},
author = {Venica, A D},
abstractNote = {Alkaline pulping of Populus deltoides performed in a flow through reactor shows the formation of coniferyl alcohol (CA), sinapyl alcohol (SA), and other low molecular weight (LMW) compounds in different phases of delignification. During the heating-up period, the rate of formation of these compounds increases until the maximum cooking temperature (170C) is reached. Afterward, their concentration in the spent liquor decreases sharply. This decrease is accompanied by dissolution of high molecular weight lignin fractions. Comparison between soda and soda-AQ delignifications shows a higher production of LMW compounds when the AQ-AHQ redox system is present. During the heating-up period the cinnamyl alcohols apparently originate from unetherified {beta}-aryl ether units in lignin and their formation is accompanied by solubilization of lignin fragments with relatively low molecular weights. A lignin core having {beta}-aryl ether bonds as major hydrolyzable interunit linkages remains in the fiber and it is solubilized as high molecular weight fragments at later delignification stages. Lignin fragments, especially those formed during the heating-up period, undergo further degradation after they are dissolved in the liquor. Low molecular weight fragments are degraded to oligomers at the end of the cook, while the fragments formed by degradation of the lignin core are more resistant. Pulps with low kappa number can be produced by maintaining alkali concentrations higher than those found in normal cooks during the last delignification phase. Replacing in this stage the cooking liquor by a liquor with a higher alkali concentration results in extended delignification, elimination of lignin redeposition and creates the possibility of producing technical lignins with higher {bar M}w.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1989},
month = {1}
}

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