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- Acid sulfite pretreatment in the enzymatic hydrolysis of Cytisus striatus: optimization strategyPublication . Vaz, Álvaro; Gomes, Tânia; Simões, RogérioEthanol production from lignocellulosic material includes three major steps: biomass pretreatment, which fragments the lignocellulosic matrix to facilitate the enzymes access to the substrate; hydrolysis, where the polysaccharides are converted into fermentable sugars (e.g. glucose and xylose); and finally, fermentation that produces ethanol or other biologically based chemicals (e.g. lactic acid, succinic acid). The aim of the present work was to study the effect of some operative variables of the pretreatment stage, namely sodium hydrogen sulfite and sulfuric acid loadings, temperature and time, on the release of sugars in the enzymatic hydrolysis of Cytisus striatus, performed applying a Novozymes® cocktail, with fixed charges and operating conditions. Wood branches were chipped and submitted to different reaction conditions, with a central composite experimental design 2^4+star, exploring the following variables: sulfuric acid charge (0-3%, on wood), sodium bisulfite charge (0-4 %, on wood), maximum temperature (150-190ºC) and time at maximum temperature (0-30 minutes). After pretreatment, the acid hydrolysates were recovered, the solid residues were mechanically disintegrated and thereafter subjected to enzymatic hydrolysis with an enzymatic cocktail from Novozymes®. Sugars and by-products released in the sulphite pretreatment and enzymatic treatment hydrolysates were analyzed by HPLC.
- Energy efficiency in low consistency refining: a study using a Valley beaterPublication . Vaz, Álvaro; Espírito-Santo, António; Araújo, Pedro; Simões, Rogério; Silvy, JacquesThe purpose of this work was to study the influence of pulp fiber suspensions refining operating variables on energy efficiency coefficient. Three chemical pulps with different average morphological characteristics were used, obtained from bleached kraft Pinus sylvestris, Eucalyptus globulus and Betula verrucosa. The final objective was to establish the chemical pulps refining efficiency parameters. Refining hydromechanics and energy consumption profiles were analyzed. Average normal and tangential forces on pulp suspension in the gap clearance, resulting rotor-stator distance and no-load and refining conditions power consumption were obtained. The refining trials took place in a laboratory Valley beater, and the manipulated variables were charge on the roll and rotor rotation speed. Global relationships for tangential stress and energy efficiencies in terms of rotation speed and rotor-stator gap were obtained. A relationship between energy efficiency and shear stress was obtained. The results have shown that in a Valley beater increased rotor-stator gaps reduce energy efficiency, concomitantly increasing apparent viscosity and reducing shear stress. No-load power was seen to increase with crowding factor, and thus with flocculation. Inversely, crowding factor and ultimately flocculation had an adverse effect on energy efficiency.
- Optimization of acid sulfite pretreatment in the enzymatic hydrolysis of Cytisus striatusPublication . Vaz, Álvaro; Gomes, Tânia; Simões, RogérioEthanol production from lignocellulosic material includes three major steps: biomass pretreatment, which fragments the lignocellulosic matrix to facilitate the enzymes access to the substrate; hydrolysis, where the polysaccharides are converted into fermentable sugars (e.g. glucose and xylose); and finally, fermentation that produces ethanol or other biologically based chemicals (e.g. lactic acid, succinic acid). The aim of the present work was to study the effect of some operative variables of the pretreatment stage, namely sodium h ydrogen sulfite and sulfuric acid loadings, temperature and time, on the release of sugars in enzymatic hydrolysis, performed applying a Novozymes® cocktail, with fixed charges and operating conditions. Cystisus striatus wood branches were chipped and submitted to different reaction conditions, with a central composite experimental design 2^4+star, exploring the following variables: sulfuric acid charge (0-3%, on wood), sodium bisulfite charge (0-4 %, on wood), maximum temperature (150-190ºC) and time at maximum temperature (0-30 minutes). After pretreatment, the acid hydrolysates were recovered and the solid residues were mechanically disintegrated and thereafter subjected to enzymatic hydrolysis with an enzymatic cocktail from Novozymes®. Sugars and by-products released in the sulfite pretreatment and enzymatic treatment hydrolysates were analyzed by HPLC. The percentage of material released in the acid hydrolysates was between 7 and 29.1%. Temperature and sulfuric acid load were the most important tested variables. The inhibition products represented less than 0.9% of the initial wood mass, even for the most severe reaction conditions. Enzymatic hydrolysis of polysaccharides on solid residues resulted in conversions from 6.0 to 68.9%, depending on the reaction conditions used in biomass pretreatment with sulfite and sulfuric acid. The rate of sugars release proved to be high at the beginning, gradually decreasing with contact time. The experimental data analysis using Statgraphics®Plus5 enabled us to obtain correlation expressions and conclude that all study variables influence this phase of the process, mainly temperature and sulfuric acid load. For a given sulfite load, more acidic conditions led to higher sugar release and greater fragmentation of the material, but also higher production of degradation products; moderate sodium bisulfite (1%) and sulfuric acid (2.25%) loads released practically all hemicelluloses in the raw material.
- Enzymatic hydrolysis of Cytisus striatus: acid sulfite pretreatment optimizationPublication . Vaz, Álvaro; Gomes, Tânia; Simões, RogérioEthanol production from lignocellulosic material includes three major steps: biomass pretreatment, which fragments the lignocellulosic matrix to facilitate the enzymes access to the substrate; hydrolysis, where the polysaccharides are converted into fermentable sugars (e.g. glucose and xylose) [1]; and finally, fermentation that produces ethanol or other biologically based chemicals (e.g. lactic acid, succinic acid) [2]. The aim was to study the effect of pretreatment operative variables, namely sodium bisulfite and sulfuric acid loadings, temperature and time, on released sugars in Cytisus striatus enzymatic hydrolysis with a Novozymes® cocktail. Pre-treatment intends lignin and hemicelluloses removal, reduced cellulose crystallinity and lignocellulosic network porosity increase in order to facilitate enzyme access.
- The effect of shear rate on apparent viscosity for different pulp suspensionsPublication . Vaz, Álvaro; Simões, Rogério; Silvy, JacquesThe goal of this work was to study the relationship between chemical pulps suspensions rheology and the operating variables of refining for three different paper fibres, namely Pinus sylvestris, Eucalyptus globulus and Betula verrucosa. The intention was the establishment of the best conditions for the refining of chemical pulps for paper production. In order to obtain that, the hydromechanics of the beating was analysed for the three pulps. So, the normal and tangential forces were evaluated, the distance between rotor and stator was measured and the pulp apparent viscosity evolution during refining was calculated. The refining essays took place in a laboratory Valley refiner, and the studied variables were the charge on the roll, the rotor speed of rotation and the specific applied energy. A global relationship between the apparent viscosity and the shear rate was finally obtained.
- Refining rheological response of chemical pulp fibre suspensionsPublication . Vaz, Álvaro; Simões, Rogério; Silvy, JacquesThe purpose of this work was to study the influence of the refining operating variables on the rheological response of chemical pulp fibre suspensions using a Valley beater. Pinus sylvestris, Eucalyptus globulus and Betula verrucosa bleached pulps were used. The normal and tangential average forces exerted on the pulp suspension in the gap clearance were evaluated, the gap between rotor and stator was measured and the apparent viscosity evolution during refining was obtained. The refining essays took place in a laboratory Valley beater, and the studied variables were the load on the roll, the rotor speed of rotation and the specific applied energy. Relationships between apparent viscosity and shear rate were tested for the three species fibre suspensions, which showed shear-thinning behaviour (Fig.1). The results were analysed in terms of fiber and flock properties. The computed crowding factors, Nc, (Kerekes and Schell) decrease from pine to eucalypt to birch. Thus, flock dimensions and resistance are significantly higher for pine. Pine had significantly wider gap, due to its greater and more resistant flocks. This produced smaller shear rate and thus higher apparent viscosity. The smaller and weaker eucalyptus and birch flocks induced smaller gaps, higher shear rates and smaller apparent viscosity. For each pulp suspension, the apparent viscosity diminished with refining time due to increased fibre flexibility and shortening, which promoted smaller flocks and reduced gap clearance (producing higher shear rates). The different rheological behaviors under the same operating conditions for different pulps lead to the inference that from the hydrodynamical point of view one should treat pulps with different morphological characteristics separately, considering the optimization of the energy transfer efficiency in pulp refining.
- A refinabilidade de pastas químicas papeleiras: um contributo para a sua avaliação utilizando o refinador ValleyPublication . Vaz, Álvaro Frederico Campos; Silvy, Jacques; Simões, Rogério Manuel dos SantosO objectivo desta tese é o estabelecimento de uma metodologia que permita relacionar as propriedades da suspensão fibrosa, nomeadamente as morfológicas e físicas, assim como as do papel, designadamente as estruturais, ópticas e de resistência, com as variáveis operacionais de refinação e as características físicas e químicas da matéria-prima. Visa-se assim efectuar um contributo para a análise da refinabilidade de pastas químicas para papel. As refinações realizaram-se num refinador Valley laboratorial, tendo-se utilizado como variáveis de estudo a carga sobre o cilindro, a velocidade de rotação do rotor e a energia específica aplicada. Para a sua consecução adaptou-se ao equipamento um variador de velocidade no rotor, um sensor para medição da distância entre o rotor e o estator e um medidor de potência eléctrica. Estudaram-se estes efeitos para diferentes matérias-primas, tendo-se incluído na análise três pastas Kraft branqueadas, uma de pinho silvestre, uma de eucalipto e outra de bétula. Ao nível da fibra, analisou-se a sua morfologia por análise de imagem, especificamente o seu comprimento médio e a sua distribuição, a sua largura, massa linear, curvatura, teor em dobras, fibrilação e proporção de finos; determinou-se ainda a sua resistência intrínseca, o seu nível de hidratação e a sua flexibilidade em estado húmido. Ao nível do papel analisou-se a massa volúmica das folhas, a resistência à tracção, a resistência ao rebentamento, a resistência ao rasgamento, a brancura, a opacidade e os coeficientes de dispersão e absorção da luz. Implementaram-se metodologias para a medição da área relativa de ligação e para estimar a energia de ligação entre as fibras da folha de papel através de métodos ópticos e mecânicos. Fez-se igualmente a análise hidromecânica das condições de refinação para estas três matérias-primas. Desta forma estudou-se o efeito das condições de refinação sobre a carga específica de aresta, estimaram-se as forças tangenciais e forças normais desenvolvidas, determinou-se a viscosidade aparente da pasta ao longo da refinação, quantificou-se a distância entre o rotor e o estator (ou seja, o entreferro) e a eficiência energética do processo. Consequentemente, estabeleceu-se uma relação entre a viscosidade aparente da pasta e o valor do entreferro, assim como entre a primeira variável e o gradiente de velocidade. Os resultados experimentais são explorados de forma a desenvolver relações de controlo das propriedades das pastas para a produção do papel. Foi possível tentarse uma optimização das condições de refinação para cada uma das matérias-primas estudadas para tipos específicos de papéis industriais, respectivamente em termos das propriedades do papel e do consumo de energia no refinador Valley. Pode-se concluir que a suspensão de pasta apresenta um comportamento reofluidificante e que a viscosidade aparente da pasta diminui com o progresso da refinação. Observaram-se igualmente diferentes comportamentos reológicos das diversas pastas, o que permite inferir que do ponto de vista de uma análise hidrodinâmica é preferível a refinação de pastas com diferentes características morfológicas em separado. As equações de ajuste obtidas para as diferentes propriedades estudadas permitem que se comparem as diferentes pastas e que se estude os efeitos das condições operatórias sobre as mesmas. Desta forma, foi possível comprovar que o pinho silvestre exibe melhores propriedades mecânicas, enquanto que o eucalipto apresenta as melhores propriedades ópticas. No entanto, a bétula supera o eucalipto em termos de desempenho mecânico. Relativamente à análise das condições operatórias, pode-se verificar que a velocidade de rotação tem um efeito preponderante sobre as propriedades da suspensão e do papel. Pode-se ainda aferir que a bétula revela um comportamento inverso do pinho e do eucalipto face à velocidade de rotação e da carga específica de aresta.