Institute of Paper Science and Technology / Thesis (Ph. D) -- Institute of Paper Science and Technology, 1998.

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A previously proposed kinetics equation describing the delignification of wood in soda-anthraquinone (AQ) liquors was shown to be valid under isothermal conditions, and was extended to describe variation in initial alkali charge. Kinetics expressions were derived for soda-amine, kraft (soda-hydrosulfide ion) and soda-ethanol delignification under isothermal conditions over various ranges of additive charge. In each case, the total delignification observed after a given time of pulping could be described as the sum or two contributions: (i) that due to the sodium hydroxide alone, and (ii) that due to the additive (AQ, amine, hydrosulfide ion or ethanol). Rate constants were determined at various temperatures and apparent Arrhenius activation energies were calculated for soda-AQ, soda-amine and kraft delignification. Although the calculated activation energies were found to be similar, the forms of kinetic expressions obtained suggested that the role of AQ in alkaline delignification may differ from that of an amine or hydrosulfide ion. The effects of various combinations of additive pairs on delignification were investigated and the results suggested that interactions occur. Under certain conditions, delignification in soda-AQ-amine and kraft-AQ liquors, respectively, could be described as the sum of the effects of the sodium hydroxide alone, the amine or hydrosulfide ion, and a term dependent upon the anthraquinone.

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When high yield chemimechanical sulphite pulp fibres were suspended in water, both lignin and carbohydrate were leached out of the pulp. The rate of leaching fitted a theory developed previously for the diffusion of macromolecules through the water-swollen fibre wall. The average intrafibre diffusion coefficients for lignin and carbohydrate were several orders of magnitude lower than the free diffusion of these macromolecules in solution. Leaching over a long period indicated a polydispersity of diffusion coefficients. This was related to an increase with time in the molecular weights of macromolecules removed from the fibre. Although the rate of leaching increased markedly with temperature, the diffusion coefficient of lignin decreased, while that of carbohydrate increased by a factor higher than that predicted by the Stokes-Einstein equation. These contrasting results were interpreted in terms of the molecular weights of the diffusing species and hydrogen bonding of carbohydrate to the fibre wall. The rate of leaching decreased with an increase in pulp yield, increasing cationic strength and pH of the wash water, decreasing refining energy, pretreatment of pulp with formaldehyde, and the use of polyethyleneoxide/alum retention aid in the wash water. Decreasing pH of the cooking liquor and the use of anthraquinone in the pulping increased the leaching of lignin but did not affect the leaching of carbohydrate. The effects observed could be related either to swelling or degradation of the fibre wall.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1936. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The important role of black liquor in the pulp and paper industry has, been addressed and a review of conventional and potential alternative technologies has been made. Black liquor combustion properties and its combustion within a conventional recovery boiler, the principle of vortex combustion, and methods of computational fluid dynamics were summarized. In order to use the commercially available computational fluid dynamics package, PHOENICS, to simulate black liquor combustion in a vortex combustor, the black liquor combustion process was simplified and modelled and additional software programs were developed and attached to the commercial package. The developed module is capable of tracking trajectory paths of black liquor particles during combustion. A 250 kW vortex combustor was used for some experimental work. The combustor was first tested with natural gas and kerosene. The - combustion conditions were satisfied and their characteristics were presented. Atomization was the main technical problem in the combustion of black liquor. However, the environmental problem was also severe. The results were presented and discussed. Improvements of the system and further studied were suggested. Selection of a suitable turbulence model was made by comparing experimental data with the simulations from various turbulence models. Prandtl mixing length model gave closer predictions than k-? and k-1 model and therefore, it was used for the entire simulations. Simulations of natural gas combustion in a vortex combustor were made to establish skill and confidence in using the package, PHOENICS, to deal with combustion process. A series of black liquor combustion models were performed afterward using the particle tracking module developed. This led to the suggestion of a potential suitable geometry of a vortex combustor for black liquor incineration. The results were presented and discussed. Further simulation studies are also suggested.

In order to gain insights into ultrastructural changes taking place during the conversion of hardwoods into mechanical pulps, refiner pulp fibres were studied in detail using several microscopical techniques. Aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.) wood chips were used to produce thermomechanical (TMP), chemithermomechanical (CTMP) and chemimechanical (CMP) pulps. Following the hypothesis that there are fundamental differences in the surface and state of the fibres due to species and processing conditions, four pulps for each species and process were analyzed. Trends in fibre characteristic development were obtained within each group, based on the detailed optical analysis of 300 fibre cross-sections for each pulp. Fibre surface quality was the most important aspect of this study. Retention of middle lamella and of the layer, as well as the extent of exposure of the S₂ layer were evaluated. It was found that TMP processing of wood chips produced fibres with more exposure of the S₂ layer. Chemical pretreatment did not improve the extent of S₂ layer exposure nor the extent of fibrillation. However, the TMP fibres remained stiff, producing pulp sheets of low density and strength. Birch fibres showed a marked tendency to produce separation at or near the S₁/S₂ boundary. This resulted in high exposure of S₂ layers in TMP fibres, but produced a sheath of S₁ and ML around fibres from chemically-treated chips. This sheath was sometimes rolled back, exposing the fibre S₂ layer. Aspen TMP pulps showed high proportions of fibres with partially exposed S₂ layer. The application of chemical pretreatments to aspen chips resulted in fibres of similar levels of S₂ exposure than those achieved by TMP processing of this species, but only after reaching freeness levels of about 100 mL CSF. Fibres that showed radial failure were frequent in TMP but not in CTMP nor CMP pulps. The breakdown pattern of tension wood fibres (G-fibres) was also studied. TMP processing showed preferential breakdown of G-fibres, from which the G-layers were freed. This was not the case in the G-fibres from chemically-treated chips, in which the G-layer generally remained inside the fibres. Other categories discussed in the analysis of fibre cross sections included fibres with delamination of the S₂ layer and proportion of fibres distorted due to chemical impregnation. The breakdown of vessel elements (VE) was studied by comparing VE size frequency distributions and the proportion of whole VE that survived refining. TMP reduced VE into small fragments showing virtually no whole VE, while wood softening due to chemical pretreatment was responsible for a high proportion of whole VE in CTMP and CMP pulps. The VE from birch tend to be destroyed more easily than those from aspen, due to the intervessel pitting arrangement of the former. It is concluded that despite superior bonding potential of TMP fibres due to: - large S₂ exposure in fibres on account of separation at or near the S₁/S₂ boundary, - increased fibrillation, - longer fibrils in fines, and - release and exposure of highly cellulosic G-layers from tension wood in the case of aspen, the lack of conformability of TMP fibres, which translates into low sheet density, negates the promising benefits that otherwise would be obtained. / Forestry, Faculty of / Graduate

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No description available.