Domnak Equilibria in Wood-Alkali Interactions Part 3. Theoretical Modeling

Pu, Qiusheng; Gustafson, Richard; Sarkanen, K. V.

doi:10.1080/02773819308020504

Cited by 4 publications

(3 citation statements)

References 8 publications

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“…Also, large differences in the distributions of the anions of the added reactant (X-) inside and outside the fibre wall can be observed. Thus equilibrium in wood-alkali interactions is important when determining the real alkali (and sulphide) consumption during kraft pulping, which has been reported to differ by as much as 58%, due to ionic dissociation equilibrium and the Donnan equilibrium (57,58). If the pKa-values of the COOH and OH groups of the polysaccharides and lignin are known, together with the charged and actual alkali concentrations of the outer solution, the Donnan equation can be utilised to calculate the hydroxyl ion concentration of the inner solution.…”

Section: Influence Of Ionisable Groupsmentioning

confidence: 99%

Physicochemical aspects of fibre processing

Salmén¹,

Ljunggren²

1996

The Chemistry and Processing of Wood and Plant Fibrous Material

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Section: Influence Of Ionisable Groupsmentioning

confidence: 99%

Physicochemical aspects of fibre processing

Salmén¹,

Ljunggren²

1996

The Chemistry and Processing of Wood and Plant Fibrous Material

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“…Pu et al (1993) modeled IE in wood immersed in alkali solution. In another study, Bogren et al (2008) predicted the changes in the molality of OH -, that is, the effective chemical responsible for the formation and degradation of hexenuronic acid (HexA), based on the Donnan theory.…”

Section: Introductionmentioning

confidence: 99%

The role of Donnan effect in kraft cooking liquor impregnation and hot water extraction of wood

2013

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In this article, a phenomenological model is proposed for alkali impregnation and hot water extraction of wood. Elementary reaction kinetics, ion exchange (IE) equilibrium, and mass transfer rates are considered in the model. IE is a consequence of the dissociation of the covalently bound uronic acid and phenolic groups in the wood fiber wall (FW). Due to this effect, the molality of cations is higher in the FW liquid than in the liquid external to the FW, whereas the opposite is true for anions. For the development of kinetic models under the participation of hydroxyl and hydrogen ions, the estimation of their molalities in these two liquid phases is crucial because of their ubiquitous presence in chemical reactions. This study applies a recently developed physicochemical modeling environment in which alkali impregnation and hot water extraction processes are considered. The simulations revealed that the IE effect is significant and affects the chemical reaction kinetics in both processes in focus. Furthermore, the IE effect does not remain constant but varies as a function of treatment time.

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“…Plenty of studies discuss the Donnan effect in pulp suspension or in pulp bleaching operations, but only a few studies discuss the Donnan effect in wood or in cooking. Pu et al − studied experimentally the interactions of wood meal and alkali, and in the analysis of the experimental data, the Donnan theory was applied. To our knowledge, Donnan theory has been considered only in a few studies modeling phenomena in impregnation or kraft cooking, i.e., in the reaction kinetic model for hexenuronic acid formation and degradation, in modeling mass transfer during impregnation of eucalypt wood, and in deacetylation kinetics during alkaline impregnation .…”

Section: Introductionmentioning

confidence: 99%

Novel Insight into Lignin Degradation during Kraft Cooking

Nieminen

Kuitunen

Paananen

et al. 2014

Ind. Eng. Chem. Res.

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In this study three different modeling approaches, with varying levels of sophistication and complexity, on modeling kraft cooking kinetics have been investigated. In the first and second approaches, isothermal conditions were used by converting the heating and cooling times into isothermal time. In the third approach, real temperature and time were used. Donnan theory, accounting for the cation exchange property of the wood fibers, was used in the second and third approaches for estimation of the cooking chemical concentrations in the fiber wall liquid, whereas in the first approach the cooking chemical concentrations in the bulk liquid phase were used. A modification of the Purdue model was used for modeling the delignification kinetics. The parameters of the Purdue model were regressed both with Matlab (commercial software) and Kinfit (in-house software). All three regressions with different modeling approaches provided very good fits to the experimental data. When Donnan theory and real temperature profiles (third approach) were employed, the estimated reaction rates for the faster reacting lignin subcomponent in the Purdue model decreased at all temperatures. On the other hand, the portion of the faster reacting component increased from 24% to 28%. In this way the third modeling approach mimics the reality in the most accurate way. Its implementation is more tedious, but the model should have more predictive capabilities. Furthermore, the effect of anthraquinone on kraft cooking kinetics was studied.

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Domnak Equilibria in Wood-Alkali Interactions Part 3. Theoretical Modeling

Cited by 4 publications

References 8 publications

Physicochemical aspects of fibre processing

Physicochemical aspects of fibre processing

The role of Donnan effect in kraft cooking liquor impregnation and hot water extraction of wood

Novel Insight into Lignin Degradation during Kraft Cooking

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