Utilize este identificador para referenciar este registo: http://hdl.handle.net/10400.6/3192
Título: Effect of physical and physical-chemical pretreatments on the sugar release of lignocellulosic materials through an enzymatic cocktail
Autor: Costa, Vera Lúcia Dias da
Orientador: Simões, Rogério Manuel dos Santos
Palavras-chave: Bioetanol
Hidrólise enzimática
Materiais lenhocellulósicos
Ultroestrutura
Data de Defesa: 2013
Resumo: This work intended to begin an investigation course which aims to deepen the mechanisms that determine the sugar release from lignocellulosic materials, using adequate enzymatic complexes. In this study, it was used an enzymatic complex, kindly provided by Novozymes, which includes a diverse set of enzymes, designed for the hydrolysis of lignocellulosic materials. Provided with this tool, the work began by evaluating the response of two model cellulosic fibrous materials: a chemical bleached pulp (with lignin-free fibers and high specific area) and a mechanical pulp (lignin-rich and also with high specific area). These choices provide high and comparable specific areas, allowing the isolation of the effect of material’s composition. While the chemical bleached pulp is mate exclusively by polysaccharides, the mechanical pulp contains all the lignin from its original wood, apart from the polysaccharides, preserving the wood’s original ultra-structure. In order to distinguish extreme cases, the pulps were also subjected to a beating process in a PFI mill, which additionally increased the material’s specific area, and were afterwards subjected to an enzymatic cocktail. The obtained results revealed completely different answers from both pulps, beaten and unbeaten. The lignin-free pulp has released practically all its carbohydrates, while the mechanical pulp released only about 20% of its potential. The pulp beating had a limited effect on the mechanical pulp and increased the sugar release rate and slightly increased its extension in the chemical bleached pulp. In conclusion, the behavior differences are not due to specific area, but to the chemical composition and/or to the differences in the ultra-structure of both fibrous materials studied. The performed studies point to a combined effect of both factors, which are difficult to isolate due to the fact that the lignin extraction process also induces modifications on the organizational structure of the polymers. The second stage of this work involved non-previously processed prime-matters, namely, pine and eucalyptus wood chips and also broom wood. In these cases, it is essential to submit the material to a pretreatment prior to subject it to enzymatic hydrolysis, aiming its sugars release. In this study, we chose to explore the sodium bisulfite potential, at different pH levels, taking into account the few published studies with this treatment, and the team’s experience on wood coking processes. Based on the literature, the operating conditions of the sulfite stage were chosen, maintaining the enzymatic hydrolysis conditions. After the pretreatment, the material was subjected to a controlled disintegration treatment. The sugars and their byproducts from the pretreatment hydrolysate were analyzed by HPLC and the solid residue was afterwards subjected to enzymatic hydrolysis. The increase on acid charge (H2SO4), for a fixed sulfite level, translated in the increase of sugar release, particularly xylose, and in an increase of byproducts, potentially inhibitors of subsequent bioethanol production stages, and in a darker solid residue with more condensed lignin and higher tendency to fragment in the disintegration step. An attempt of global mass balance was undertaken with consistent results, although they might require adjustments from further investigations. Generally, all the solid residues exhibited a very positive answer on the enzymatic hydrolysis, achieving polysaccharide conversions in the range of 65 to 98%. The sugar release rate proved to be fast in the beginning, gradually decreasing with contact time, until it is annulled. In some cases, a decrease in sugar concentration in the reaction medium takes place, in around 72 hours of enzymatic hydrolysis. Since this decrease is not expectable, it can be related with the existence of microorganisms detected when hydrolyzed samples were observed in an optic microscope. The microscopic observation of samples subjected to different times of enzymatic hydrolysis revealed the enzymes’ ability of fragmenting the fibers; at the end of two days, the fibers were mostly converted to fine elements.
URI: http://hdl.handle.net/10400.6/3192
Designação: Dissertação apresentada à Universidade da Beira Interior para a obtenção do grau de Mestre em Química Industrial
Aparece nas colecções:FC - DQ | Dissertações de Mestrado e Teses de Doutoramento

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