Topochemical studies applied to etanol production from bagasse and straw sugarcane

Author(s)

Priscila Maziero

• Document type: Doctoral Thesis
• Press: Lorena.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI)
• Defense date: 2013-05-10
• Advisor: Adilson Roberto Gonçalves

Abstract

Studies of fuels from renewable sources are a topic of fundamental importance. Taking into account, the production of ethanol from biomass, such as bagasse and straw sugarcane, offers benefits to sustainable production and energy security. Biomass conversion technologies are mainly developed empirically, based on chemical and biological properties of biomass and many studies include variations of parameters of process. But there are difficulties to understand the changes of the lignocellulosic material during reactions. In this context, topochemical studies are a tool of significant importance to elucidate these characteristics. This study aims to evaluate different conditions of hydrothermal pretreatment followed by a fixed condition of alkaline delignification of straw and bagasse sugarcane. Additionally, this work deals the evaluation of plant cell wall modification during hydrothermal pretreatment an alkaline delignification in the optimized condition, considering the best cellulose digestibility at enzymatic hydrolysis process of bagasse. Results reveal a different behavior of bagasse and straw from sugarcane at the end of its processing. There was a greater morphological change of sugarcane bagasse compared to straw, which presented exposure of the fibers, but also aggregated. This fact can be explained by less removal of lignin and hemicellulose of this biomass compared to the same processing conditions of bagasse. The exposure of fibers contributed to increase the cellulose of bagasse digestibility, since there was a greater area of contact of the enzyme with the substrate and a minimization of interference from inhibitors, such as lignin. The conditions of pretreatment most promising for bagasse and straw sugarcane were 180oC for 20 and 30 min. respectively, showing that the straw requires longer treatments to reach a higher digestibility in the enzymatic hydrolysis process. The optimal condition for the sugarcane bagasse was used to characterize the changes in parenchyma cells and vascular bundles from stalk of sugarcane at different growth regions, after its processing. The results showed a variation of cell size depending on growth of the plant. The top of sugarcane stalk presented the more pronounced difference between parenchyma cells from pith and rind region. Furthermore, it was observed that after processing these cells and vascular bundles lost its structural conformation and become more fragile after drying. This result indicated the significant removal of the structural components for all growth region of sugarcane stalk analyzed. Differently from vascular bundles, which presented lignin mainly located in the cell corners, the lignin from parenchyma cells was completely removed after delignification. Regarding the orientation of cellulose, determined by SAXS and Raman microscopy, the parenchyma cells from initial part of stalk presented two preferential directions of orientation, one parallel and other perpendicular to the axis of plant growth. This feature may be associated with maturation phase of sugarcane which appears incomplete, since the middle and top part of the stalk showed only one preferred direction, indicating that the contribution of the layer S1 is prominent, and the S2 layer is not deposited. Another indication of incomplete maturation process may be associated with porosity of parenchyma and vascular bundles, which have the top of the cane more porous that indicates an incomplete lignification process. The results showed that the pretreatment can be considered the most important treatment which affects this variable, since promotes an increase of up to 54% in porosity, differently of alkaline delignification process which no presented significant changes in the porosity of the cells. (AU)

• FAPESP's process: 09/00874-5 - Topochemical studies during cellulosic ethanol production from sugarcane bagasse and straw
• Grantee: Priscila Maziero
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)