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Doctoral Thesis
DOI
https://doi.org/10.11606/T.97.2018.tde-08062018-184947
Document
Author
Full name
Rafael Cunha de Assis Castro
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Lorena, 2017
Supervisor
Committee
Roberto, Inês Conceição (President)
Dragone, Solange Ines Mussatto
Ferraz, André Luis
Gonçalves, Daniel Bonoto
Pessoa Junior, Adalberto
Title in Portuguese
Produção de etanol a partir da palha de arroz por sacarificação e fermentação simultânea empregando um reator agitado não convencional.
Keywords in Portuguese
Analise tecnico-economica
Desacetilacao
Etanol
Palha de arroz
Reator nao convencional
Abstract in Portuguese
O presente trabalho teve como principal objetivo estudar o processo de producao de etanol por sacarificacao e fermentacao simultanea (SSF) a partir da palha de arroz em um reator agitado nao convencional, denominado Moinho de Bolas Vertical (MBV). Foi também objetivo deste trabalho realizar uma avaliacao tecnico-economica a partir dos resultados experimentais alcancados durante o processamento da biomassa, aplicando o conceito de biorrefinaria. Inicialmente, foi avaliada uma sequencia de pre-tratamentos da palha de arroz que consistiu de uma etapa de desacetilacao alcalina, seguido de hidrolise com acido diluido. Os efeitos destes pre-tratamentos foram analisados com base nas modificacoes estruturais da palha de arroz e no rendimento de conversao de celulose (RCC) em cada solido obtido. Com base nos resultados, foram definidas as condicoes otimas para a etapa de desacetilacao (80 mg de NaOH/g de palha in natura, 70 °C, 45 min), de hidrolise acida (100 mg de H2SO4/g de palha desacetilada, 121 °C, 85 min) e carga de enzimas (21,5FPU e 26,5 UI de ?-glicosidase/g de celulose). Nestas condicoes, foram conduzidos experimentos em reator MBV visando avaliar o efeito das da velocidade de agitacao (100 a 200 rpm), numero de esferas (0 a 30) e temperatura (40 a 46 °C) sobre o RCC na sacarificacao da celulignina desacetilada e sobre a eficiencia da fermentacao por Kluyveromyces marxianus NRRL Y- 6860 em meio semissintetico. Apos definicao das variaveis significativas aos processos, foram realizados experimentos em reator MBV na configuracao de SSF em batelada simples e alimentada. Em batelada simples com 8% de solidos, foi obtida uma concentracao de etanol de 23,1 g/L, com eficiencia (?) de 89,8% e produtividade volumetrica (QP) de 1,6 g/L.h, nas seguintes condicoes operacionais: 200 rpm, 18 esferas e 41,5 °C. No entanto, com o aumento do teor de solidos para 24%, ambos os parametros (??e QP) foram reduzidos em 50%. Visando melhorar os parametros do processo com 24% de solidos, foram realizados ensaios em batelada alimentada e na melhor estrategia de alimentacao do substrato foi produzido 52,3 g/L de etanol (?= 67,5% e QP = 1,1 g/L.h). As fracoes ricas em lignina geradas a partir do licor alcalino e do residuo de fermentacao da batelada alimentada foram caracterizadas fisico-quimicamente, e analisadas quanto ao potencial antioxidante. A partir dos resultados, foram sugeridas possiveis aplicacoes para estes dois residuos ricos em lignina. Finalmente, de posse do balanco de massa de cada etapa do processamento da palha de arroz, foi realizada uma analise tecnico-economica empregando o software SuperPro Designer. As simulações mostraram que, para todos os cenarios avaliados, a etapa de pre-tratamento acido foi a de maior impacto sobre os custos operacionais, seguido pelas etapas de fermentacao (xilose e glicose). Ficou demonstrado ainda que, a conversao de xilose em xilitol proporcionou um melhor retorno financeiro do que a conversao desta pentose em etanol. Para a viabilidade economica da presente proposta de biorrefinaria, alem da diversificacao dos produtos obtidos a partir das fracoes acucaradas, e de fundamental importancia explorar as potencialidades dos residuos ricos em lignina.
Title in English
Ethanol production from rice straw by simultaneous saccharification and fermentation employing a non-conventional stirred reactor
Keywords in English
Deacetylation
Ethanol
Non-conventional reactor
Rice straw
Technoeconomic analysis
Abstract in English
The aim of this work was to study the ethanol production by simultaneous saccharification and fermentation (SSF) from rice straw in a non-conventional agitated reactor, called Vertical Ball Mill (VBM). It was also objective of this study to perform a techno-economic analysis from the experimental results achieved during the biomass processing, using the biorefinery concept. Initially, the rice straw was submitted to a sequential pretreatment consisting of an alkaline step (deacetylation) followed by dilute acid hydrolysis. The pretreatment effects were evaluated based on rice straw's structural modifications and regarding cellulose conversion (CC) from each obtained solid. Based on the results were defined the best conditions for the deacetylation step (80 mg NaOH/g of rice straw in natura, 70 °C, 45 min), acid hydrolysis (100 mg H2SO4/g deacetylated straw 121 °C, 85 min) and enzyme loading (21.5 FPU and 26.5 IU ?-glucosidase/g cellulose). Under these conditions, assays were carried out in VBM reactor to evaluate the effect of stirring speed (100-200 rpm), number of spheres (0-30) and temperature (40-46°C) on saccharification of deacetylated cellulignin and fermentation efficiency by Kluyveromyces marxianus NRRL Y-6860 in semisynthetic media. After defining the significant variables, experiments were carried out in VBM reactor by SSF configuration in batch and fed-batch operational modes. In batch SSF at 8% solids, was obtained an ethanol concentration of 23.1 g/L, with a process efficiency (?) of 89.8%, and volumetric productivity (QP) of 1.6 g /L.h, in the following operating conditions: 200 rpm, 18 spheres and 41.5 °C. However, by increasing solids content to 24%, both parameters (? and QP) were decreased by 50%. In order to improve the process parameters to 24% solids, fed-batch experiments were performed. In the best substrate feeding policy was produced 52.3 g/L ethanol (? = 67,5%) in 48-h process (QP = 1.1 g/L.h). The lignin-rich fractions from the alkaline liquor and from fed-batch fermentation residue were characterized regarding its chemical composition and physical properties and analyzed for antioxidant activity. Based on these results were suggested possible applications for both lignin-rich residues. Finally, considering the mass balance from all rice straw processing steps, a techno-economic analysis was assessed using SuperPro Designer software. The simulation procedures have indicated that, for all evaluated scenarios, the acid pretreatment step had the highest impact on operating costs, followed by the fermentation steps (xylose and glucose). It was also shown that xylose conversion into xylitol provided a better payback rather than its conversion into ethanol. Therefore, to attain a viable and profitable process for this type of rice straw based biorefinery, in addition to the diversification of products obtained from the sugary fractions, it is crucial to explore the potential of lignin-rich streams.
 
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Publishing Date
2018-06-08
 
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