Produção de bioetanol via hidrólise ácida de Eucalyptus urograndis utilizando os concei-tos de uma biorrefinaria: abordagem teórico experimental
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Data
2021-06-07
Autores
Camargo, Sâmique Kyene de Carvalho Araújo [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Os combustíveis fósseis, além de serem recursos limitados na natureza, aumentam os níveis de dióxido de carbono e outros gases causadores do efeito estufa na atmosfera, neste aspecto os biocombustíveis surgem como uma alternativa sustentável. A produção de bioetanol a partir de materiais de origem renovável é uma proposta importante para o desenvolvimento econômico do país e desafia pesquisadores a buscar tecnologias mais eficientes que viabilizem esse processo. O objetivo deste trabalho foi otimizar o estágio de hidrólise ácida durante a produção do bioetanol a partir da madeira. Para obtenção do bioetanol foi necessário a hidrólise da celulose em monômeros de glicose, portanto, seguem as etapas para separação da matriz de celulose e lignina interligadas pelas hemiceluloses: pré-tratamento ácido para remoção das hemiceluloses, seguida de tratamento alcalino para remoção da lignina e, por fim a hidrólise ácida das ligações glicosídicas do tipo -(1→4) entre os carbonos C1-C4 da celulose liberando os monômeros de -D-glicose a serem fermentados em bioetanol. Com o intuito de avaliar a reatividade das estruturas presentes no processo foi também realizado o cálculo de estrutura eletrônica IFCA (Índice de Fukui condensados aos átomos) partindo de modelos pré definidos para simulação, visando verificar também sua interação com os reagentes utilizados. Também foi necessária uma abordagem PCM (Polarizable Continuum Model) para avaliar a influência do solvente na reatividade das estruturas. Com os cálculos de IFCA pode-se comprovar que a parte amorfa da celulose tem maior susceptibilidade no pré-tratamento e na hidrólise ácida e, que os monômeros de glicose presentes na etapa de hidrólise podem sofrer oxidação e, causar a formação de hidroximetilfurfural (HMF), ácido acético, ácido fórmico e ácido levulínico. Também foi observada a mesma reatividade elucidada na literatura com relação às hidroxilas do C2, C3 e C6 e hidrólise por despolimerização do grupo terminal, no entanto, quando se realiza o cálculo de interação entre orbitais das estruturas com os reagentes do processo nota-se que não há interação, ou seja, a hidrólise, pode estar relacionada a outro tipo de interação que não a maciez química. Com isso, foi necessário verificar a influência da constante dielétrica na reatividade das estruturas, aumentando ou diminuindo seu valor em relação à da água, nota-se rotações que aumentam a reatividade da estrutura, principalmente no oxigênio da ligação glicosídica β1-4 tanto das extremidades quanto do centro da estrutura, vantagem para o processo de hidrólise ácida. Após as análises experimentais realizadas pode-se observar que na hidrólise ácida o tratamento de 70 mL e 80 mL não diferem estatisticamente com relação à produção de glicose, mas aumentando o volume de ácido sulfúrico para 90 mL, houve um aumento na produção de açúcares fermentescíveis à bioetanol, 63,7%, decrescendo em seguida, pois o excesso de ácido também causou a degradação dos açúcares em HMF, sendo que no tratamento de 100 mL houve maior produção de HMF e menor produção de glicose e bioetanol. A fermentação se mostrou uma etapa complexa, devido a variabilidade obtida em seus resultados, mas em todas as bateladas de análises de fermentação maior produção de bioetanol foi obtida com o tratamento de 90 mL, também pode-se observar um aumento na produção de ácido acético conforme maior produção de bioetanol nos tratamentos, no entanto, a produção do mesmo através de reações secundárias devem ser evitadas, pois os açúcares que poderiam ser convertidas em bioetanol estão sendo consumidos na produção de ácido acético, e isto ocorreu devido a fatores externos que causaram a oxigenação durante esta etapa sensível.
Fossil fuels, in addition to being limited resources in nature, increase the levels of carbon dioxide and other gases that cause the greenhouse effect in the atmosphere, in this respect biofuels appear as a sustainable alternative. The production of bioethanol from materials of renewable origin is an important proposal for the country's economic development and challenges researchers to seek more efficient technologies that make this process feasible. The objective of this work was to optimize the acid hydrolysis stage during the production of bioethanol from wood. To obtain ethanol, it was necessary to separate the glucose monomers from the wood cellulose chain, therefore, follow the steps for separating the cellulose matrix and hemicelluloses interconnected by lignin: acid pre-treatment to remove the hemicelluloses, followed by alkaline treatment for removal of lignin and, finally, acid hydrolysis separating glucose monomers from cellulose to be fermented in bioethanol. In order to evaluate the reactivity of the structures present in the process, the calculation of the IFCA electronic structure (Fukui index condensed to atoms) was also carried out, starting from predefined models for simulation, in order to also verify their interaction with the reagents used. A PCM (Polarizable Continuum Model) approach was also needed to assess the influence of the solvent on the reactivity of the structures. With the IFCA calculations, it is possible to verify that the amorphous part of the cellulose is more susceptible in the pre-treatment and in the acid hydrolysis and that the glucose monomers present in the hydrolysis stage can suffer degradation and cause the formation of HMF, acetic acid, formic acid and levulinic acid. The same reactivity elucidated in the literature was also observed in relation to the hydroxyls of C2, C3 and C6 and hydrolysis by depolymerization of the terminal group, however, when calculating the interaction between the orbitals of the structures with the process reagents, it is noted that there is no interaction, that is, hydrolysis, may be related to another type of interaction other than chemical softness. With that, it was necessary to verify the influence of the dielectric constant on the reactivity of the structures, increasing or decreasing its value in relation to that of water, it is possible to notice rotations that increase the reactivity of the structure, mainly in the β1-4 bond both at the ends and at the center structure, advantage for the hydrolysis process. After the experimental analyzes carried out, it can be seen that in acid hydrolysis, the treatment of 70mL and 80mL does not differ statistically with respect to glucose production, but increasing the volume of sulfuric acid to 90mL, there was an increase in the production of bioethanol fermentable sugars, 63.7%, then decreasing, since the excess of acid also caused the degradation of sugars in HMF, and in the treatment of 100mL there was greater production of HMF and less production of glucose and bioethanol. Fermentation proved to be a complex step, due to the variability obtained in its results, but in all batches of fermentation analyzes greater bioethanol production was obtained with the 90mL treatment, an increase in acetic acid production can also be observed as greater bioethanol production in the treatments, however, the production of it through secondary reactions should be avoided, because the sugars that could be converted into bioethanol are being consumed in the production of acetic acid, and this occurred due to external factors that caused the oxygenation during this sensitive stage.
Fossil fuels, in addition to being limited resources in nature, increase the levels of carbon dioxide and other gases that cause the greenhouse effect in the atmosphere, in this respect biofuels appear as a sustainable alternative. The production of bioethanol from materials of renewable origin is an important proposal for the country's economic development and challenges researchers to seek more efficient technologies that make this process feasible. The objective of this work was to optimize the acid hydrolysis stage during the production of bioethanol from wood. To obtain ethanol, it was necessary to separate the glucose monomers from the wood cellulose chain, therefore, follow the steps for separating the cellulose matrix and hemicelluloses interconnected by lignin: acid pre-treatment to remove the hemicelluloses, followed by alkaline treatment for removal of lignin and, finally, acid hydrolysis separating glucose monomers from cellulose to be fermented in bioethanol. In order to evaluate the reactivity of the structures present in the process, the calculation of the IFCA electronic structure (Fukui index condensed to atoms) was also carried out, starting from predefined models for simulation, in order to also verify their interaction with the reagents used. A PCM (Polarizable Continuum Model) approach was also needed to assess the influence of the solvent on the reactivity of the structures. With the IFCA calculations, it is possible to verify that the amorphous part of the cellulose is more susceptible in the pre-treatment and in the acid hydrolysis and that the glucose monomers present in the hydrolysis stage can suffer degradation and cause the formation of HMF, acetic acid, formic acid and levulinic acid. The same reactivity elucidated in the literature was also observed in relation to the hydroxyls of C2, C3 and C6 and hydrolysis by depolymerization of the terminal group, however, when calculating the interaction between the orbitals of the structures with the process reagents, it is noted that there is no interaction, that is, hydrolysis, may be related to another type of interaction other than chemical softness. With that, it was necessary to verify the influence of the dielectric constant on the reactivity of the structures, increasing or decreasing its value in relation to that of water, it is possible to notice rotations that increase the reactivity of the structure, mainly in the β1-4 bond both at the ends and at the center structure, advantage for the hydrolysis process. After the experimental analyzes carried out, it can be seen that in acid hydrolysis, the treatment of 70mL and 80mL does not differ statistically with respect to glucose production, but increasing the volume of sulfuric acid to 90mL, there was an increase in the production of bioethanol fermentable sugars, 63.7%, then decreasing, since the excess of acid also caused the degradation of sugars in HMF, and in the treatment of 100mL there was greater production of HMF and less production of glucose and bioethanol. Fermentation proved to be a complex step, due to the variability obtained in its results, but in all batches of fermentation analyzes greater bioethanol production was obtained with the 90mL treatment, an increase in acetic acid production can also be observed as greater bioethanol production in the treatments, however, the production of it through secondary reactions should be avoided, because the sugars that could be converted into bioethanol are being consumed in the production of acetic acid, and this occurred due to external factors that caused the oxygenation during this sensitive stage.
Descrição
Palavras-chave
Bioetanol de segunda geração, Celulose da madeira, Polpação Soda, Modelagem Molecular, Second generation bioethanol, Wood pulp, Pulping soda, Molecular modeling, Etanol, Celulose, Energia - Fontes alternativas