Soda-AQ delignification of hardwoods: Reactions, mechanisms, and dissolved lignin characteristics
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.
- Research Organization:
- North Carolina State Univ., Raleigh, NC (United States)
- OSTI ID:
- 5642466
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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-)