The work described in this thesis was aimed at obtaining a better understanding of the neutral sulphite semichemical pulping process employed by Mondi Kraft's Piet Retief mill, and to investigate ways to improve this process. The unique feature of the process in this mill is that hardwood and softwood species are pulped simultaneously in a continuous digester. The pulping trials described were carried out in a laboratory batch digester which was build as a part of this project. Pulps were evaluated for yield, Hypo number as an indication of the residual lignin content and strength properties. The first part of the experimental work focused on the effect that different pulping variables have on the process and the resulting pulp. Variables investigated were the chemical charge, pulping temperature, chip composition and anthraquinone dosage. The second part of the work was to investigate ways in which the process can be improved. In particular it was investigated whether it would be advantageous to pulp hardwood and softwood separately and mix the two pulps together after pulping. The effect of changing to an alkaline sulphite process was also briefly investigated. It was found that the current process is optimized as far as the chemical charge and pulping temperature is concerned. Increasing the softwood percentage used to 50 % (from current value of 41 %) increases the tear strength, whilst decreasing it to 30 % increases the tensile strength of the resulting pulp. It was also determined that increasing the AQ dosage from 0.1 % to 0.5 % might bring savings in chemical costs. It is suggested that this is investigated in a mill trial. It was further found that pulping the two species separately improves the tear strength of the pulp by about 20 % compared with that which was pulped simultaneously. The results indicate that no benefits concerning the chemical costs, pulping temperature, pulp yield, burst strength or tensile strength are to be gained from separate pulping. Preliminary results indicated that significant strength increases and possible chemical cost savings are to be gained by changing from a neutral sulphite to an alkaline sulphite process. Further work to determine the reproducibility of these results, as well as the effect of different chemical charge and ratios is suggested. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Submitted in fulfillment of the requirements of the degree of Master of Technology (Biotechnology), Durban University of Technology, Durban, South Africa, 2014. / Microbial enzymes are gaining worldwide attention due to their potential industrial applications. Microorganisms producing thermostable -xylanase and their associated hemicellulases have significant application in the paper and pulp, food, animal feed, and textile industries. The potential of partially purified xylanase from Thermomyces lanuginosus MC 134, Luminase PB 100, Luminase PB 200 (a commercial xylanase) and T. lanuginosus DSM 5826 (Sigma Aldrich) was evaluated in bleaching of bagasse pulp. The temperature and pH optima for all the enzymes were 60°C and pH 6, respectively. The temperature (50- 80°C) and pH (5-8) stability of the enzymes were also assessed. All the enzymes were relatively stable at 60°C and pH 6 for 180 min. T. lanuginosus MC 134 retained 80% of its activity at 60°C and pH 6 for 180 min and PB 200 retained 75% of its activity at 80°C for 180 min. T. lanuginosus MC 134 also exhibited good alkaline stability at pH 8. The commercial xylanases Luminase PB 100, Luminase PB 200, T. lanuginosus DSM 5826 (Sigma Aldrich) were purified to homogeneity using a gel filtration column packed with sephadex G-100 and characterized for Km and Vmax. However extracellular crude xylanases from T. lanuginosus MC 134 was purified to homogeneity using (N )2S04 precipitation and gel filtration column, packed with sephadex G-100. The purified xylanases exhibited a molecular mass of- 26 to 24 kDa, given range as determined by SDS page. The Km and Vmax values of Luminase PB 100, Luminase PB 200, T. lanuginosus MC 134, and T. lanuginosus DSM 5826, xylanases were determined by the Michaelis-Menten equation using birchwood xylan as the substrate. The Km value for Luminase PB 100, Luminase PB 200, T. lanuginosus DSM 5826 and T. lanuginosus MC 134 were, 8.1 mg/mL, 11.7 mg/mL and 14.3 mg/mL respectively. The Vmax for Luminase PB 100, Luminase PB 200, T lanuginosus DSM 5826 and T lanuginosus MC 134 were 232.6, 454.6 and 74.6 !Jl11ol/min/mg. Biobleaching conditions of the xylanases were also optimised and the release of reducing sugars and lignin derived compounds showed that an enzyme dosage of 50U/g of pulp was ideal for biobleaching at pH 6 and 60°C for 180 min. This brightness for T lanuginosus MC 134, Luminase PB 200, Luminase PB 100 was 45.5 ± 0.11%, 44.1 ± 0.007% and 42.7 ± 0.03% respectively at pH 6, compared to untreated samples. Reducing sugars and UV-absorbing lignin-derived compound values were considerably higher in xylanase-treated samples. All the enzymes analysed exhibited similar trends in the release of lignin derived compounds and reducing sugars which indicated their potential in the pulp and paper industry. / PDF Full-text unavailable. Please refer to hard copy for Full-text / M

A biopolpação consiste no biotratamento de madeira por fungos degradadores de lignina como etapa prévia à produção de polpa celulósica. De uma forma geral, as madeiras biotratadas facilitam os processos posteriores de polpação. Entretanto, ensaios anteriores que avaliaram a biopolpação em escala piloto mostraram que é difícil estabelecer os cultivos de basidiomicetos de interesse livre de bolores contaminantes, já que não é fácil controlar perfeitamente a assepsia durante a inoculação. Para contribuir com o avanço do processo de biopolpação, este trabalho avaliou os cultivos mistos de Ceriporiopsis subvermispora e Phanerochaete chrysosporium sobre madeira de Eucalyptus grandis e Eucalyptus urograndis em regimes de incubação em temperaturas variáveis e em condições não assépticas. A estratégia de iniciar os cultivos em temperatura mais elevada (37°C) e depois manter as culturas em temperaturas variáveis de 27°C e 37°C se mostrou eficiente para inibir o crescimento de contaminantes indesejáveis tanto nos cultivos mistos como nos individuais de cada espécie avaliada. Para avaliar o efeito do biotratamento da madeira numa etapa subsequente de polpação quimiotermomecânica (CTMP) foi feito um estudo preliminar de ajuste de variáveis de polpação por refinamento mecânico de cavacos pré-digeridos com licor alcalino contendo sulfito de sódio. Os dados mostraram que é possível simular o rendimento e as características fisico-mecânicas de polpas industriais empregando uma etapa de pré-digestão dos cavacos com 6% de Na2SO3 e 3% de NaOH a 120°C por 2 h, seguida de desfibramento e refino em refinador de discos. As curvas de refino nesse processo CTMP mostraram que os cavacos biotratados deram origem a polpas com 300 mL de Freeness (CSF) consumindo menos energia do que o observado para o refino da madeira controle. As economias de energia chegaram a 60% em alguns casos, porém não foram maximizadas pelo efeito sinérgico do cultivo misto dos dois basidiomicetos em questão. Experimentos adicionais foram desenvolvidos empregando as espécies fúngicas Pycnoporus sanguineus e Trametes versicolor que foram eficientes para competir com contaminantes mesmo a 27oC. Neste caso, as economias de energia no processo CTMP subsequente somente foram obtidas com tempos mais longos de biotratamento (30 dias) e ainda assim os valores obtidos foram inferiores àqueles obtidos com as madeiras biotratadas por C. subvermispora e P. chrysosporium. Também a combinação das espécies C. subvermispora e Pleurotus ostreatus foi avaliada. Neste caso havia informação prévia da literatura indicando um efeito sinérgico da ação das duas espécies no que diz respeito a secreção da enzima manganês-peroxidase (MnP) e na degradação de lignina. Os resultados corroboraram que os cultivos mistos de C. subvermispora e P.ostreatus proporcionam maior produção de MnP do que os cultivos individuais de cada espécie. Por outro lado, P. ostreatus foi ineficiente para promover a redução do consumo de energia no processo CTMP subsequente. Os cultivos mistos também não proporcionaram efeito superior àquele observado com o cultivo individual de C. subvermispora. / Biopulping involves the wood biotreatment by selected white-rot fungi as a pretreatment step of conventional pulping processes. In general, the biotreated wood facilitates the subsequent pulping processes. However, previous studies on pilot scale showed that the process is susceptible to contamination by molds when the inoculation and biodegradation steps are carried out under non-aseptic conditions. To contribute with the biopulping progress this study evaluated the use of mixed cultures of Ceriporiopsis subvermispora and Phanerochaete chrysosporium acting on Eucalyptus grandis and Eucalyptus urograndis wood under non aseptic conditions where incubation was performed at varied temperatures. The simple strategy of initiating the incubation at 37°C for 3 days followed by a non-controlled step where the temperature could oscillate in the range of 27°C to 37°C proved to be efficient to inhibit the growth of contaminants. To evaluate the wood biotreatment effect in a subsequent step of chemithermomechanical pulping (CTMP), a preliminary study to adjust pulping variables was performed. Wood chips were predigested with alkaline-sulfite liquor, fibrillated and refined in a disk refiner. It was possible to simulate the yield and physico-mechanical properties of industrial CTMP pulps using a pre-digestion stage with 6% of Na2SO3 and 3% of NaOH at 120°C for 2 h. The refing curves in the CTMP process showed that the biotreated chips required less energy to reach 300 mL of Freeness (CSF) in the pulps than energy required to refine the control wood chips. Energy savings reached 60% in some cases, but were not maximized by the eventual synergic effect of the mixed cultures of the two basidiomycetes. Additional experiments were developed using the fungal species Trametes versicolor and Pycnoporus sanguineus that were efficient to compete with contaminants even at 27°C. In this case, the energy savings in the subsequent CTMP process were obtained only after long biotreatment times (30 days) and these values were lower than those obtained with the biotreated wood by C. subvermispora and P. chrysosporium. The combination C. subvermispora and Pleurotus ostreatus was also evaluated. In this case, previous literature information indicated some synergic effect of the two species regarding secretion of manganese peroxidase (MnP) and lignin degradation. The results corroborated that the mixed cultures of C. subvermispora and P.ostreatus provided an increased production of MnP compared to the individual cultivation of each species. On the other hand, P.ostreatus was not efficient to promote energy savings in the subsequent CTMP process. The mixed cultures did not provide increased energy savings as compared with the individual biotreatment with C. subvermispora.

A indústria de papel e celulose convive com questões de adequação da oferta à demanda que influenciam na tomada de decisão em vários elos da cadeia produtiva. A pressão por baixos custos requer novos investimentos em tecnologia, normalmente associados ao processo e ao produto. Neste cenário, o objetivo do presente trabalho envolve o estudo da influência de variáveis de processo sobre a composição química da polpa e do licor preto, bem como sobre a formação de ácidos hexenurônicos, na polpação Kraft industrial de Eucalyptus. A metodologia proposta contemplou a realização de 36 polpações (em duplicata), sendo 3 níveis de álcali ativo (14, 17 e 19%), 2 níveis de sulfidez (20 e 30%) e 3 níveis de temperatura (150, 160 e 170oC). As polpas obtidas foram analisadas quanto à composição química, alvura e viscosidade. Os licores gerados no processo foram analisados quanto à composição química e por espectroscopia no infravermelho. Os resultados obtidos indicaram que uma maior sulfidez gera um menor teor de ácidos hexenurônicos na polpa independentemente da carga de álcali empregada. A temperatura exerce forte influência na geração destes ácidos, sendo que a 160°C foram geradas as maiores concentrações de ácidos hexenurônicos na polpa. Ainda com relação à temperatura, observou-se que o número kappa da polpa é reduzido quando a temperatura é elevada. A carga de álcali ativo leva a um aumento na quantidade de ácidos hexenurônicos gerados na polpa e a uma redução do número kappa. A alvura da polpa foi mais elevada para menores teores de ácidos hexenurônicos. A utilização da técnica de espectroscopia no infravermelho não se mostrou aplicável para a determinação dos teores de lignina nos licores de cozimento. / The pulp and paper industries have to manage issues concerning the offer of their products and the needs of different markets. To get this goal several important aspects of the productive chain has to be considered. The achievement of low costs of production requires investments in technologies for both processes and products. In this context, the aim of the present work involves the study of the influence that process parameters exerts in the chemical composition of the pulps and liquors, as well as hexenuronic acids generated in the industrial kraft pulping of Eucalyptus. The experimental work consisted in a factorial planning designed pulping reactions. 36 cookings were performed (in duplicate) with 3 levels of active alkali (14, 17 e 19%), 2 levels of sulfidity (20 e 30%) and 3 levels of temperature (150, 160 e 170oC). The obtained pulps were analyzed in relation to their chemical composition, brightness and viscosity. The black liquors were also analyzed by infrared spectroscopy. The results indicated that the higher sulfidity produced pulps with the lower content of hexenuronic acids, independently of the charge of active alkali employed in the process. The temperature of the pulping process exerted a strong influence in the production of hexenuronic acids, mainly at 160°C. Still considering the temperature, it was observed that occurs a reduction of the kappa number at higher temperatures. The active alkali charge produced an increase in the amount of hexenuronic acids and a decrease in the kappa number of the pulps. It was also observed an increase in the brightness for the pulps with lower amount of hexenuronic acids. Infrared spectroscopy showed not feasible results considering the determination of lignin content in the pulping liquors.

Este trabalho teve como objetivo avaliar a eficiência do processo de polpação Lo- Solids® em relação ao processo de polpação convencional para obtenção de polpa celulósica não branqueável (número kappa 58±2). A espécie de madeira utilizada foi Pinus taeda com 9 anos de idade, que se constitui na principal espécie utilizada no Brasil para obtenção de polpa de fibra longa. Para isso foram realizados cozimentos convencionais com fator H de 2300 e carga alcalina variável visando a obtenção do número kappa especificado. Devido a complexidade de simulação do processo Lo- Solids®, utilizou-se nesse trabalho um conjunto de cozimentos Lo-Solids® com fator H de 2000 e diferentes níveis de carga alcalina visando a obtenção de polpas com diferentes números kappa. Para efeito de comparação os parâmetros relacionados as polpas referentes ao processo Lo-Solids® foram interpolados para número kappa obtido experimentalmente para processo convencional. Também foi realizado um estudo do licor negro ao longo do cozimento, para isso amostras de licor foram coletadas dos processos a cada 20 minutos; foram analisados o teor de lignina, sólidos totais, sólidos orgânicos, sólidos inorgânicos, pH e álcali ativo residual, os resultados obtidos permitem uma melhor avaliação desses parâmetros durante o processo de polpação. A análise de lignina no licor negro ao invés do método tradicional realizado na polpa se constitui em um método prático, rápido e confiável que permite um monitoramento online do processo. Os resultados da curva alcalina realizada para o processo Lo-Solids® mostraram grande sensibilidade do processo em relação a carga alcalina; o aumento de álcali no cozimento proporcionou grande redução do número kappa, decréscimo do rendimento da polpa e da formação de ácidos hexenurônicos e aumento da seletividade. Os resultados de polpação mostraram que o processo convencional apresentou maior rendimento bruto comparado ao Lo-Solids®, porém quando comparado ao rendimento depurado ambos os processos apresentaram valores similares, sem diferença significativa. Assim o teor de rejeitos foi maior para o processo de polpação convencional. Foi observado também, maior formação de ácidos hexenurônicos no processo Lo-Solids®. Em relação ao estudo do licor ao longo dos processos de polpação, foi possível a identificação das distintas fases de deslignificação: inicial, principal e residual para ambos os processos. Para o processo convencional 23% da lignina inicial da madeira foi removida durante a fase de impregnação, enquanto que aproximadamente 55% da lignina da madeira foi removida na fase de cozimento; a fase de deslignificação principal teve início ainda durante o período de impregnação. No processo de polpação Lo-Solids® com diferentes cargas alcalinas a deslignificação da madeira apresentou a mesma tendência, sendo que aproximadamente 16% da lignina inicial da madeira foi removida durante a impregnação, 46 a 56% na fase de cozimento e 6 a 12% na etapa de lavagem. A deslignificação na fase inicial de cozimento se mostrou mais eficiente para o processo Lo-Solids® quando comparado ao convencional. / The present study aimed to evaluate the efficiency of the Lo-Solids® pulping process in relation to conventional pulping process to obtain unbleachable pulp (kappa number 58±2). Pinus taeda wood with 9 years old was used, for being the main specie used in Brazil for obtaining long fiber pulp. Conventional cooking was performed with H factor of 2300 and changeable alkali charge in order to obtain specified kappa number. Due to complexity in simulating Lo-Solids® process, a set of Lo-Solids® cooking was used in this study with H factor of 2000 and several alkali charges levels in order to obtain pulps with different kappa numbers. For comparison the parameters related to pulps from Lo-Solids® process were interposed to kappa number experimentally obtained for conventional process. It was also performed a black liquor study during cooking, liquor samples were collected from the processes every 20 minutes; lignin amount, total solids, organic solids, inorganic solids, pH and residual active alkali were analyzed, the results allowed a better interpretation of these parameters during pulping process. The analysis of lignin in black liquor performed in pulp instead of the traditional method consisted of a practical, fast and reliable method, which allows on-line monitoring of the process. The results of the alkali curve performed for Lo-Solids® process showed great sensibility of the process in relation to alkali charge. Alkali increase during cooking provided great kappa number reduction, decline in pulp yield and hexenuronic acids formation, and selectivity increase. Pulping results showed that the conventional process presented greater total yield compared to Lo-Solids®, however, when compared to screened yield both process presented similar values, without significant difference. Therefore rejects amount was greater for conventional pulping process. It was also observed greater hexenuronic acids formation during Lo-Solids® process. Regarding liquor study along pulping processes, identification of the different delignification phases was possible: initial, principal and residual for both processes. For conventional process 23% of the wood initial lignin was removed during impregnation phase, while approximately 55% of the wood lignin was removed during cooking phase; the principal delignification phase initiated during impregnation period. At Lo-Solids® pulping process with diverse alkali charges wood delignification presented the same tendency; about 16% of the wood initial lignin was removed during impregnation, 46 to 56% during cooking phase and 6 to 12% at washing phase. Delignification at initial cooking phase was more efficient for Lo-Solids® process when compared to the conventional process.

Este trabalho teve como objetivo avaliar a eficiência do processo de polpação Lo- Solids® em relação ao processo de polpação convencional para obtenção de polpa celulósica não branqueável (número kappa 58±2). A espécie de madeira utilizada foi Pinus taeda com 9 anos de idade, que se constitui na principal espécie utilizada no Brasil para obtenção de polpa de fibra longa. Para isso foram realizados cozimentos convencionais com fator H de 2300 e carga alcalina variável visando a obtenção do número kappa especificado. Devido a complexidade de simulação do processo Lo- Solids®, utilizou-se nesse trabalho um conjunto de cozimentos Lo-Solids® com fator H de 2000 e diferentes níveis de carga alcalina visando a obtenção de polpas com diferentes números kappa. Para efeito de comparação os parâmetros relacionados as polpas referentes ao processo Lo-Solids® foram interpolados para número kappa obtido experimentalmente para processo convencional. Também foi realizado um estudo do licor negro ao longo do cozimento, para isso amostras de licor foram coletadas dos processos a cada 20 minutos; foram analisados o teor de lignina, sólidos totais, sólidos orgânicos, sólidos inorgânicos, pH e álcali ativo residual, os resultados obtidos permitem uma melhor avaliação desses parâmetros durante o processo de polpação. A análise de lignina no licor negro ao invés do método tradicional realizado na polpa se constitui em um método prático, rápido e confiável que permite um monitoramento online do processo. Os resultados da curva alcalina realizada para o processo Lo-Solids® mostraram grande sensibilidade do processo em relação a carga alcalina; o aumento de álcali no cozimento proporcionou grande redução do número kappa, decréscimo do rendimento da polpa e da formação de ácidos hexenurônicos e aumento da seletividade. Os resultados de polpação mostraram que o processo convencional apresentou maior rendimento bruto comparado ao Lo-Solids®, porém quando comparado ao rendimento depurado ambos os processos apresentaram valores similares, sem diferença significativa. Assim o teor de rejeitos foi maior para o processo de polpação convencional. Foi observado também, maior formação de ácidos hexenurônicos no processo Lo-Solids®. Em relação ao estudo do licor ao longo dos processos de polpação, foi possível a identificação das distintas fases de deslignificação: inicial, principal e residual para ambos os processos. Para o processo convencional 23% da lignina inicial da madeira foi removida durante a fase de impregnação, enquanto que aproximadamente 55% da lignina da madeira foi removida na fase de cozimento; a fase de deslignificação principal teve início ainda durante o período de impregnação. No processo de polpação Lo-Solids® com diferentes cargas alcalinas a deslignificação da madeira apresentou a mesma tendência, sendo que aproximadamente 16% da lignina inicial da madeira foi removida durante a impregnação, 46 a 56% na fase de cozimento e 6 a 12% na etapa de lavagem. A deslignificação na fase inicial de cozimento se mostrou mais eficiente para o processo Lo-Solids® quando comparado ao convencional. / The present study aimed to evaluate the efficiency of the Lo-Solids® pulping process in relation to conventional pulping process to obtain unbleachable pulp (kappa number 58±2). Pinus taeda wood with 9 years old was used, for being the main specie used in Brazil for obtaining long fiber pulp. Conventional cooking was performed with H factor of 2300 and changeable alkali charge in order to obtain specified kappa number. Due to complexity in simulating Lo-Solids® process, a set of Lo-Solids® cooking was used in this study with H factor of 2000 and several alkali charges levels in order to obtain pulps with different kappa numbers. For comparison the parameters related to pulps from Lo-Solids® process were interposed to kappa number experimentally obtained for conventional process. It was also performed a black liquor study during cooking, liquor samples were collected from the processes every 20 minutes; lignin amount, total solids, organic solids, inorganic solids, pH and residual active alkali were analyzed, the results allowed a better interpretation of these parameters during pulping process. The analysis of lignin in black liquor performed in pulp instead of the traditional method consisted of a practical, fast and reliable method, which allows on-line monitoring of the process. The results of the alkali curve performed for Lo-Solids® process showed great sensibility of the process in relation to alkali charge. Alkali increase during cooking provided great kappa number reduction, decline in pulp yield and hexenuronic acids formation, and selectivity increase. Pulping results showed that the conventional process presented greater total yield compared to Lo-Solids®, however, when compared to screened yield both process presented similar values, without significant difference. Therefore rejects amount was greater for conventional pulping process. It was also observed greater hexenuronic acids formation during Lo-Solids® process. Regarding liquor study along pulping processes, identification of the different delignification phases was possible: initial, principal and residual for both processes. For conventional process 23% of the wood initial lignin was removed during impregnation phase, while approximately 55% of the wood lignin was removed during cooking phase; the principal delignification phase initiated during impregnation period. At Lo-Solids® pulping process with diverse alkali charges wood delignification presented the same tendency; about 16% of the wood initial lignin was removed during impregnation, 46 to 56% during cooking phase and 6 to 12% at washing phase. Delignification at initial cooking phase was more efficient for Lo-Solids® process when compared to the conventional process.

A utilização de cana-de-açúcar para geração de açúcar, energia e etanol é uma das atividades mais importantes do Brasil. Esta intensa produção gera grandes quantidades de bagaço que podem ser utilizadas para aumentar a produção de etanol. Neste sentido, é de grande interesse técnico-científico o estudo de pré-tratamentos desta matéria prima, dentre os quais se inserem os processos de polpação. No presente trabalho buscou-se estudar a utilização da polpação hidrotrópica do bagaço de cana-de-açúcar para separação de seus principais componentes macromoleculares. Para tanto foram utilizados dois hidrótropos distintos, o benzoato de sódio e xilenossulfonato de sódio. Como referência, realizaram-se também polpações apenas com água, com soluções etanol/água e com soluções de hidróxido de sódio.O estudo foi realizado a partir de planejamento fatorial de experimentos, utilizando-se a influência das variáveis temperatura e tempo de reação. As respostas consideradas foram o rendimento de polpa e a quantidade de lignina residual. Este estudo exploratório revelou que o xilenossulfonato de sódio foi mais efetivo que o benzoato de sódio. Entretanto, o uso dos agentes hidrotrópicos foram menos eficiente quando comparado aos sistemas etanol/água e hidróxido de sódio. As ligninas extraídas nos processos de polpação hidrotrópica foram analisadas por diversas técnicas de caracterização. As ligninas extraídas na polpação com benzoato de sódio apresentaram menores massas molares quando comparado ao uso de xilenossulfonato de sódio. A análise das polpas obtidas nos diferentes processos revelou que as condições de maiores tempos e temperaturas produziram polpas com maiores índices de cristalinidade. / The production of sugar, energy and ethanol from sugar cane is one of the most important activities of Brazil and generates a enormous quantity of bagasse which can be used to increase the ethanol production. In this sense, the study of sugarcane bagasse is a very important task, in both technical and scientific approaches. Thus, the pre-treatment of sugar cane bagasse by using pulping/delignification processes constitutes a important step to recovery the main macromolecular components of the vegetal tissues of this raw material. In the present work it was studied the utilization of hydrotropic agents to promote the delignification of sugarcane bagasse. The study was carried out by using two different hydrotropes: sodium benzoate and sodium xylenosulfonate. As standard for comparison, it was also studied the pulping of sugarcane bagasse by using only water and ethanol/water and sodium hydroxide solutions. The pulping processes were carried out from factorial planning experiments employing two different levels (and a central point) for reaction time and temperature. As response it was determined the correspondents pulping yield and residual lignin contents. The results indicated that sodium xylenosulfonate was more effective than benzoate sodium in the promotion of the delignification. However, the utilization of hydrotropic systems were less efficient to promote the delignification, when compared with ethanol/water or sodium hydroxide aqueous solution. The lignins extracted in the pulping with sodium benzoate presented lower molar masses when compared with the use of sodium xylenesulfonate. The analysis of the pulps showed that the higher temperatures and reaction times produced pulps with higher crystallinity.

Graduation date: 1997

Fume, sub-micron aerosal particles in the combustion gases, have been identified as a cause of extensive plugging and fouling in the heat transfer section of a kraft recovery boiler in kraft pulp mills. After the deposition on the heat transfer surface, fume deposits will undergo the sintering process which causes densification and hardening, making them hard to remove. There has been relatively little information available on the kinetics of the sintering of fume particles, and no information on the modeling of the sintering process of this particular material. No conclusion about the effect of chloride species on the sintering of fume particles has been made. A series of sintering tests in air at various temperatures were conducted using dense pellets made from a specific fume dust which contains a low amount of chlorides. Each pellet was heated at a constant temperature, ranging from 300��C to 550��C, for a different time interval. By the study of the microstructural change of each sintered specimen, the initial stage, intermediate stage, and final stage of sintering were identified. By the presence of an empirical constant K���, the relative linear shrinkage data in the initial stage sintering fit well with the model proposed by Kingery and Berg��� when volume diffusion is the controlling mechanism. By the presence of an empirical constant K2 and the application of grain growth data, the porosity-time data in the intermediate stage sintering fit well with the model proposed by Coble����� when volume diffusion is the controlling mechanism. The apparent activation energy obtained from the initial stage sintering is equal to 54.5 �� 27.7 kcal/mol which is in good agreement with the apparent activation energy obtained from the intermediate stage sintering which is equal to 56.0 �� 31.3 kcal/mol. A semi-empirical model for the sintering process of this particular well-packed fume dust was formulated. The model does not apply well to the loosely packed fume dust due to some unidentified factors The same experiment was carried out for the other fume dust which contains a high amount of chloride. By the use of the fractional density, the qualitative comparison of the sintering of the low chloride and high chloride dusts was made. At low temperatures, the sintering rate of the high chloride fume dust is lower than that of the low chloride fume dust. At high temperatures, both dusts have the same sintering rate and can sinter close to the theoretical density. It is postulated here that the retarded grain growth rate for the high chloride dust can improve the densification process in the intermediate stage sintering. / Graduation date: 1996

No description available.