ABSTRACT The time development of the polysaccharide content in the wood residue and the black liq... more ABSTRACT The time development of the polysaccharide content in the wood residue and the black liquor during kraft pulping for softwood is the focus of this study. The degradation process falls into two distinct categories: the chain element type and the chain fragment type. In the chain element reactions, a single element in the polymer chain can be removed, whereas in the chain fragment reaction a longer piece of the polymer is dissolved into the black liquor. The element-wise process consists of the subreactions peeling, stopping, and alkaline hydrolysis. A mathematical model considering peeling, stopping, and alkaline hydrolysis of the polymer chains as well as the dissolution of the wood components into the black liquor is presented and tested for the experimental data obtained from kraft cooking of Scots pine wood meal. As a novelty, the model distinguishes between primary peeling originating in the initial reducing end groups and secondary peeling following alkaline hydrolysis. Four series of cooking at high (1.55 M) hydroxide ion concentration were conducted at temperatures ranging from 130 to 160 °C. The reaction rates connected with the various processes were assumed to obey the Arrhenius equation, the frequency factor, and activation energy of which could be estimated while fitting the model to the data. Another series of cooking was executed at moderate (0.5 M) hydroxide ion concentration and at a temperature of 160 °C. The reaction rates associated with the different hydroxide ion concentrations were compared. Further, the effect of adding anthraquinone (AQ) to the cooking was modeled. The amounts of degradation attributed to the different subprocesses (primary peeling, secondary peeling, alkaline hydrolysis, and dissolution) were compared with each other for glucomannan, xylan, and cellulose.
ABSTRACT In this study three different modeling approaches, with varying levels of sophistication... more ABSTRACT 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.
ABSTRACT The purpose of this study was to review some of the existing models for delignification ... more ABSTRACT The purpose of this study was to review some of the existing models for delignification in kraft cooking. Data and results from earlier studies were utilized to evaluate the performance of the models of Gustafson (M-G), Purdue (M-P), Andersson (M-A) and Bogren's method "continuous distribution of reactivity" (M-Bcdr) in terms of their ability to give a realistic description for delignification of softwood and hardwood. The M-G, M-P and M-Bcdr were tested on lignin data obtained from cooks of Eucalyptus globulus. In this case, M-P seemed to perform best, whereas the M-Bcdr failed in the range of low residual lignins. M-A considers the lignin subunits with various reaction speeds, and this feature improves the performance in the case of low residual lignins and helps to reflect sudden changes in cooking conditions, but the difference to the ordinary M-P is moderate.
... E-mail: herbert.sixta@tkk.fi Abstract ... Introduction The chemical composition of the pulp t... more ... E-mail: herbert.sixta@tkk.fi Abstract ... Introduction The chemical composition of the pulp together with the cell wall microstructure are crucial factors affecting the proper-ties of the pulp and its paper and board end products (Connors and Sanyer 1975). ...
The present study reports on a revised kinetic model for alkaline degradation of cellulose accoun... more The present study reports on a revised kinetic model for alkaline degradation of cellulose accounting for primary peeling/stopping reactions as well as for alkaline hydrolysis followed by secondary peeling. Oxalic acid pretreated cotton linters was utilised as the model substrate for the prehydrolysis-soda anthraquinone process. The main emphasis was investigating the effect of end-group stabilising additives such as sodium borohydride (BH), anthraquinone (AQ), and anthraquinone-2-sulphonic acid sodium salt (AQS) on the rates of the yield loss reactions. BH and AQS ensured a cellulose yield gain of 13% and 11%, respectively, compared to the reference. Both stabilisation agents decreased the content of the reducing end groups in the samples, while in the case of AQS stabilisation a 25% increase in carboxyl group content compared to the reference was also observed. As expected, the addition of end group stabilisers resulted in a significant decrease in the peeling-to-stopping rate constants ratio.
ABSTRACT The time development of the polysaccharide content in the wood residue and the black liq... more ABSTRACT The time development of the polysaccharide content in the wood residue and the black liquor during kraft pulping for softwood is the focus of this study. The degradation process falls into two distinct categories: the chain element type and the chain fragment type. In the chain element reactions, a single element in the polymer chain can be removed, whereas in the chain fragment reaction a longer piece of the polymer is dissolved into the black liquor. The element-wise process consists of the subreactions peeling, stopping, and alkaline hydrolysis. A mathematical model considering peeling, stopping, and alkaline hydrolysis of the polymer chains as well as the dissolution of the wood components into the black liquor is presented and tested for the experimental data obtained from kraft cooking of Scots pine wood meal. As a novelty, the model distinguishes between primary peeling originating in the initial reducing end groups and secondary peeling following alkaline hydrolysis. Four series of cooking at high (1.55 M) hydroxide ion concentration were conducted at temperatures ranging from 130 to 160 °C. The reaction rates connected with the various processes were assumed to obey the Arrhenius equation, the frequency factor, and activation energy of which could be estimated while fitting the model to the data. Another series of cooking was executed at moderate (0.5 M) hydroxide ion concentration and at a temperature of 160 °C. The reaction rates associated with the different hydroxide ion concentrations were compared. Further, the effect of adding anthraquinone (AQ) to the cooking was modeled. The amounts of degradation attributed to the different subprocesses (primary peeling, secondary peeling, alkaline hydrolysis, and dissolution) were compared with each other for glucomannan, xylan, and cellulose.
ABSTRACT In this study three different modeling approaches, with varying levels of sophistication... more ABSTRACT 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.
ABSTRACT The purpose of this study was to review some of the existing models for delignification ... more ABSTRACT The purpose of this study was to review some of the existing models for delignification in kraft cooking. Data and results from earlier studies were utilized to evaluate the performance of the models of Gustafson (M-G), Purdue (M-P), Andersson (M-A) and Bogren's method "continuous distribution of reactivity" (M-Bcdr) in terms of their ability to give a realistic description for delignification of softwood and hardwood. The M-G, M-P and M-Bcdr were tested on lignin data obtained from cooks of Eucalyptus globulus. In this case, M-P seemed to perform best, whereas the M-Bcdr failed in the range of low residual lignins. M-A considers the lignin subunits with various reaction speeds, and this feature improves the performance in the case of low residual lignins and helps to reflect sudden changes in cooking conditions, but the difference to the ordinary M-P is moderate.
... E-mail: herbert.sixta@tkk.fi Abstract ... Introduction The chemical composition of the pulp t... more ... E-mail: herbert.sixta@tkk.fi Abstract ... Introduction The chemical composition of the pulp together with the cell wall microstructure are crucial factors affecting the proper-ties of the pulp and its paper and board end products (Connors and Sanyer 1975). ...
The present study reports on a revised kinetic model for alkaline degradation of cellulose accoun... more The present study reports on a revised kinetic model for alkaline degradation of cellulose accounting for primary peeling/stopping reactions as well as for alkaline hydrolysis followed by secondary peeling. Oxalic acid pretreated cotton linters was utilised as the model substrate for the prehydrolysis-soda anthraquinone process. The main emphasis was investigating the effect of end-group stabilising additives such as sodium borohydride (BH), anthraquinone (AQ), and anthraquinone-2-sulphonic acid sodium salt (AQS) on the rates of the yield loss reactions. BH and AQS ensured a cellulose yield gain of 13% and 11%, respectively, compared to the reference. Both stabilisation agents decreased the content of the reducing end groups in the samples, while in the case of AQS stabilisation a 25% increase in carboxyl group content compared to the reference was also observed. As expected, the addition of end group stabilisers resulted in a significant decrease in the peeling-to-stopping rate constants ratio.
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