No Brasil o etanol é considerado a melhor escolha para reduzir as dependências dos combustíveis fósseis. Para atender as metas de produção desse combustível renovável, fontes de materiais lignocelulósicos podem ser utilizadas com o intuito de se aproveitar a fração celulósica para obtenção de açúcar fermentável. Contudo, é preciso desenvolver métodos de pré-tratamento eficientes e economicamente viáveis custo para reduzir a recalcitrância da biomassa vegetal in natura, aumentando dessa forma a eficiência da etapa de hidrólise enzimática. Este trabalho teve como objetivo avaliar o efeito do pré-tratamento por explosão a vapor e do pré-tratamento com ácido diluído, seguidos ou não de uma etapa de deslignificação alcalina, na hidrólise enzimática da palha de cana-de-açúcar. O pré-tratamento por explosão a vapor foi realizado em reator de 2,5 m3 sob temperaturas de 180 °C, 190 °C e 200 °C, por 15 min. O pré-tratamento com ácido diluído (1% m:m) foi feito em reator rotatório de 20 L a 180 °C, 185 °C, 190 °C e 195 °C, por 10 min. A etapa de deslignificação com NaOH (1% m:v) foi feita a 100 °C, por 1 h, em reator de 350 L para a palha pré-tratada por explosão a vapor e em ampolas de 500 mL para a palha de cana pré-tratada com ácido diluído. Amostras de todos os tratamentos foram analisadas por FTIR e MEV. Foram feitos ensaios de hidrólise enzimática utilizando Celluclast 1.5L (15 FPU/g de amostra) e β-Glucosidase (10 UI/g de amostra). Os hidrolisados enzimáticos foram usados em testes de fermentabilidade conduzidos a 30 °C por 48 h utilizando S. cerevisiae UFPEDA 1238. Através de ambos pré-tratamentos foi possível remover mais de 90% de hemicelulose. O pré-tratamento com ácido diluído provocou uma maior degradação da celulose em relação ao pré-tratamento por explosão a vapor, bem como uma maior solubilização da lignina. A etapa de deslignificação alcalina somada ao pré-tratamento contribuiu para a remoção de até 80% da lignina. Análises de FTIR e MEV revelaram alterações das bandas de vibração dos grupamentos químicos e mudanças morfológicas das amostras tratadas em relação à palha in natura. O pré-tratamento por explosão a vapor a 200 °C promoveu a maior conversão enzimática (80%) e esse percentual foi aumentado para 85% pela aplicação da deslignificação alcalina. A fermentação dos hidrolisados enzimáticos se mostrou satisfatória, apresentando percentuais de eficiência acima de 70%. / In Brazil, ethanol is considered the best alternative to reduce dependence on fossil fuels. In order to enhance the production of this renewable fuel, lignocellulosic materials must be used with the goal of harnessing the cellulosic fraction to obtain fermentable sugar. However, an efficient pretreatment method to reduce recalcitrance of raw material is required for increasing the efficiency of enzymatic hydrolysis. This study aimed to evaluate the effect of two pretreatments, steam explosion and dilute acid, followed or not by an alkaline delignification, on enzymatic hydrolysis of sugarcane straw. Steam explosion was conducted in 2.5 m3 reactor at temperatures of 180 °C, 190 °C and 200 °C for 15 min. Dilute acid pretreatment was carried out in 20 L reactor at 180 °C, 185 °C, 190 °C and 195 °C for 10 min, using H2SO4 (1% w:w). Alkaline delignification was made with NaOH (1% w:v) at 100 °C for 1 h. Samples of all treatments were analyzed by FTIR and SEM. Enzymatic hydrolysis was performed with commercial cellulase Celluclast 1.5L (15 FPU/w of sample) and β-Glucosidase (10 IU/w of sample). Alcoholic fermentation by S. cerevisiae UFPEDA 1238 was conducted at 30 °C for 48 h. The pretreatments studied were able to remove over 90% of hemicellulose fraction. Higher degradation of cellulose and lignin fractions was observed during diluted acid pretreatment. Alkaline delignification contributed to the removal of more than 80% of lignin. FTIR and SEM analysis revealed changes in the vibration bands of chemical groups and morphological variation of the treated samples compared to raw material. Steam explosion at 200 °C promoted the higher enzymatic conversion (80%) and this percentage was increased to 85% by application of alkaline delignification. Fermentation tests efficiency was above than 70%.

The long-term trend regarding wood is an increase in price. Because wood contributes to a large part of production costs, the efficient utilisation of wood is greatly desired to reduce production costs for kraft pulp producers. During the 1990s, the development of improved modified kraft cooking began, which led to higher yields. There was also a trend of terminating kraft cooking at a higher kappa number to maximise the overall yield. For hardwood, the defibration point became a critical setback in allowing this termination at a high kappa number. This thesis discusses how this issue has been tackled in the laboratory by using improved modified kraft cooking combined with extended impregnation to enable a decrease in reject content and shift the defibration point towards a higher kappa number for hardwood. This lab concept is referred to as extended impregnation kraft cooking (EIC), and this thesis reveals that EIC cooking efficiently reduces the reject content for both birch and eucalypt. By using EIC cooking, the defibration point was shifted to a kappa number of ca. 30 from ca. 20 using conventional kraft cooking. This study demonstrates the great potential for achieving a higher overall yield for eucalypt by terminating the EIC cooking at a high kappa number, but with the conditions used in this thesis, no improvement in yield was observed for birch.   An important issue is that the termination of kraft cooking at high kappa number increases the demand for extended oxygen delignification to reach a similar kappa number into bleaching, i.e., due to cost and environmental reasons. Extended oxygen delignification was shown to be possible for both birch and eucalypt EIC pulps (i.e., from kappa number 27 to 10) with an acceptable pulp viscosity number.   The other part of this thesis addresses aspects regarding the limitations in oxygen delignification. It has previously been shown in the literature that a high xylan yield of kraft cooking could negatively affect the efficiency of subsequent oxygen delignification. In this work, the increased xylan content in eucalypt kraft pulp within the range of 8–18% had only a marginally negative impact on the oxygen delignification efficiency after correcting for the HexA contribution to the kappa number. It is also desired to extend the oxygen delignification towards lower kappa number, i.e., below kappa number 10 to decrease the bleaching chemical requirement. In this study, the hypothesis that the reduced efficiency of oxygen delignification at low kappa numbers could partly be due to the formation of oxidisable carbohydrate-related structures (i.e., HexA and/or other non-lignin structures) was also tested. No formation was established. On the other hand, a final oxygen delignification stage in the bleaching could be an attractive alternative for reducing yellowing and enhancing brightness; in fact, this has led to the development of a patent (SE 528066). / Ved står för en stor del av produktionskostnaderna vid framställning av sulfatmassa. Då vedpriserna har ökat genom åren är ett effektivt utnyttjande av veden önskvärt för att kunna sänka produktionskostnaderna. Under 1990-talet förbättrades den modifierade sulfatkokningen vilket innebar möjlighet till högre massautbyte. För att maximera massautbytet styrdes kokningsprocessen mot ett högre kappatal. Detta har visat sig vara svårare för lövved än för barrved, eftersom defibrerbarhetspunkten utgör ett kritiskt hinder. I denna avhandling har laborationsstudier utförts där förbättrad modifierad sulfatkokning kombinerats med förlängd impregnering för att kunna sänka spethalten och därmed förskjuta defibrerbarhetspunkten mot ett högre kappatal. Detta koncept kallas för extended impregnation kraft cooking (EIC). EIC-kokning visade sig vara en effektiv metod för att minska spethalten hos björk och eukalyptus. Med EIC-kokning kunde defibrerbarhetspunkten höjas från cirka 20 till cirka 30. I denna avhandling klarläggs att det finns stora möjligheter att öka massautbytet för eukalyptus genom att avsluta sulfatkoket vid ett högre kappatal. För björk kunde ingen ökning av massutbytet uppnås genom ovanstående metod.   Vid ett högre kappatal efter sulfatkoket ställs även krav på förlängd syrgasdelignifiering, för att kunna behålla samma kappatal in till blekeriet. Det visade sig vara fullt möjligt att förlänga syrgasdelignifieringen för de EIC-kokade björk- och eukalyptusmassorna (d.v.s. från kappatal 27 till 10) med accepterad massaviskositet.   Den andra delen av avhandlingen tar upp aspekter på syrgasdelignifieringens begränsningar. Tidigare studier har visat att ett högre utbyte av xylan vid sulfatkokning kan vara negativt för syrgasdelignifieringens effektivitet.  I denna studie har det påvisats att en ökad xylanhalt i intervallet 8–18 procent i eukalyptusmassa endast har en marginell negativ inverkan på syrgasdelignifieringens effektivitet efter att kappatalet korrigerats för HexA. Det är önskvärt att förlänga syrgasdelignifieringen till ett lägre kappatal än 10 för att minska förbrukningen av blekkemikalier. I den här studien prövades hypotesen att syrgasdelignifieringens begränsningar vid låga kappatal, under 10, delvis skulle kunna bero på bildning av oxiderbara kolhydratrelaterade strukturer (d.v.s. HexA och/eller andra okända ”non-lignin”-strukturer). Ingen bildning kunde dock observeras. Däremot indikerades att ett syrgassteg i slutet av bleksekvensen skulle kunna vara ett eftersträvansvärt alternativ för minskad eftergulning och ökad ljushet, vilket ledde till ett patent (SE 528066). / QC 20120507

During kraft cooking a significant part of the wood material, especially lignin and hemicelluloses, is degraded and dissolved in the cooking liquor, rendering a broad range of degradation products with different molecular mass and functional groups. The main part of this thesis has been devoted to clarify the role of these dissolved wood components (DWC) during kraft cooking. The investigations have covered their influence on e.g. the delignification rate, pulp yield, point of defibration, unbleached pulp c olour and pulp bleachability, i.e. the amount of bleaching chemicals consumed per kappa number or lignin unit to reach a certain brightness. Both softwood (Picea Abies) and hardwood (Eucalyptus urograndis) have been studied. During kraft cooking, many reactions occur simultaneously. Therefore emphasis has been put on separating the effects of hydroxide ions, hydrogen sulphide ions, sodium ions and DWC. This has been enabled by the use of a so called constant-composition-cooking technique, which enables the use of almost constant concentrations of the cooking chemicals during the cook and also results in a very low concentration of DWC in the cooking liquor. The presence of DWC has been controlled by the addition of industrial black liquor. To further scrutinise the role of DWC, the effect of different molecular mass fractions were studied and representative model substances were used to clarify the origin of the observed effects. A kinetic study showed that the delignification rate was significantly affected by the presence of DWC in the cooking liquor and resulted in a rate increase in the part of the cook where the bulk phase dominates and a decreased delignification rate when the residual phase dominates. The increase in delignification rate was dependent on the concentration of DWC and was observed in softwood as well as hardwood kraft cooks. The rate increasing effect was investigated further by the use of ultra- and nanofiltra tion. This way the DWC was divided into fractions with different molecular mass distributions. The results showed that the increase in delignification rate related more strongly to the content of free phenolic groups in the DWC than on the total amount of DWC. By cooking in the presence of representative model substances the effect was further clarified. Aromatic structures with free phenolic groups gave a rate increasing effect while no visible effect could be seen from other structures. This supports the finding that the delignification rate relates to the amount of free phenols in the cooking liquor and shows that the phenolic functionality take active part in the delignification reactions. Free phenolic groups in the degraded lignin may explain a large part of the rate increasing effect seen from the presence of DWC. Further, the presence of DWC increased the point of defibration in a eucalyptus kraft cook and made it possible to terminate the cook at a higher kappa number with the same amount of reject. By terminating the cook at a higher kappa number it was possible to noticeably increase the fully bleached pulp yield. The content of hexenuronic acids (HexA) in the eucalyptus pulp depends on the H-factor and increases with delignification, providing that the bulk phase still dominates. Therefore, by increasing the rat e of delignification and terminating the cook at a higher kappa number it was possible to significantly decrease the amount of HexA in the pulp. The presence of DWC causes a darkening of the unbleached pulp. Bleachability in a D(EOP)DD sequence was negatively affected by the presence of DWC during pulping of softwood, while no effect was seen on the bleachability of hardwood / QC 20100920

In 1957 Vroom presented an article that dealt with the kinetics of the sulphate cook. He showed that the lignin dissolution exhibited a temperature/time dependency that could be explained by the Arrhenius equation and that the reaction was of first order with respect to lignin. However, even before Vroom introduced the H-factor all wood components were assumed to react according to a first order reaction. In recent years progresses in this area have been made. Lignin for example is nowadays considered to dissolve during three parallel first order reactions, all with differences in activation energies. When the kinetics are evaluated, several cooking series at different temperatures and concentrations of active cooking chemicals are needed. The data points obtained are then fitted into some equation. If the concentration of the active cooking chemicals is constant, the activation energies and the chemical dependency for the dissolution of wood components can easily be found. In order to simplify the evaluations of the kinetics, very high liquor-to-wood ratios are sometimes used, often as high as 50:1 or even 75:1. In this manner, the chemical concentrations are almost constant during the cook. The problem is that in the normal industrial cook where the liquor-to-wood ratio is about 4:1, the chemical concentration is not constant. This is due mostly to the alkali consumption that takes place in the cook for example when neutralising the acidic groups in the hemicelluloses. A disadvantage with high liquor-to-wood ratios is the high dilution of the dissolved organic matter. A high concentration of dissolved lignin boosts the dissolution of the remaining lignin in the wood residue and xylan can redeposit on the fibres when its concentration in the cooking liquor is high. The aim of this project was to describe how different liquor-to-wood ratios influence the kinetics during sulphate cooking of spruce.

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