Avaliação do processo de pré-tratamento do bagaço da cana-de-açúcar com líquidos iônicos próticos para a produção de etanol celulósico

Author(s)

Pedro Yoritomo Souza Nakasu

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química
• Defense date: 2019-10-31

Examining board members

Aline Carvalho da Costa; Simone Coelho Nakanishi; Lívia Beatriz Brenelli; Camila Alves de Rezende; Rafael Ramos de Andrade

• Advisor: Aline Carvalho da Costa; Sarita Cândida Rabelo

Abstract

Using by-products from the agricultural sector to establish a biorefinery is a promising alternative in our society's transition to a biobased economy. Sugarcane bagasse is a lignocellulosic biomass that stands out in the Brazilian scenario due to its production volume and can be converted into second generation ethanol (E2G) in three main steps, pretreatment, enzymatic hydrolysis. and fermentation. In this work, we evaluated the pretreatment process with protic ionic liquids (LIPs) ¿ which can be up to 40 times cheaper than the more commonly known aprotic ionic liquids ¿ for the production of E2G. In the initial stage of the project, 12 LIPs were produced and evaluated in a screening, in which monoethanolammonium acetate, [MEA][OAc], was chosen for the subsequent stages of the studies because due to its great potential as a pretreatment agent. [MEA][OAc] pretreatment has undergone an optimization of operating parameters considering time, temperature, solids loading, water content and anti-solvent type as factors of the experimental design. Such variables were evaluated to ensure maximum carbohydrate conversion and pulp delignification. A study of the acid-base ratio (ABR) of [MEA][OAc] showed that low ABR values provided an almost quantitative yield of cellulose/hemicellulose within 72 h of enzymatic hydrolysis with up to 84% delignification, standing out as one of the best pretreatments available for sugarcane bagasse. The ABR was successfully measured before and after the experiments by NMR-H1 spectroscopy, a pioneering achievement of this work. Thereafter, [MEA][OAc] recycle was assessed over 6 pretreatment cycles. It was observed that the decrease in LIP performance is strongly correlated to its decomposition into an acetamide. This problem was solved by using an excess base mixture, ABR 0.5, which was recycled over 3 cycles and showed that PIL performance was still considerably high with low acetamide formation. Then, quantitative relationships were established between the amount of washing water and its temperature, with the enzymatic saccharification and alcoholic fermentation yields with S. passalidarum, a yeast capable of metabolizing xylose and glucose. Among the partial wash samples (from 13 to 66 g water /g biomass), the wash performed at the highest temperature, 80 °C, and the highest solvent: biomass ratio considered, 66: 1, provided the highest hydrolysis yields. 81% and 64% for cellulose and hemicellulose, respectively, and for fermentation with 85% of the theoretical ethanol yield; while the complete wash (625 g water/ g biomass) yielded 98% and 85% yield of cellulose and hemicellulose, respectively, and 87% of the theoretical yield of ethanol. Although S. cerevisiae did not consume xylose, the fermentation of the complete wash sample had the highest ethanol yield, 1.41 g ·/L·h with approximately the same theoretical ethanol yield, 87%. Mass balances for the complete E2G production process (via S. passalidarum) showed that up to 228 and 300 L of ethanol per tonne of bagasse can be produced with 66 and 625 tonnes of wash water / tonne of bagasse respectively. with the first yield superior to the best pretreatments found in the literature, ie alkaline hydrogen peroxide and sodium hydroxide (AU)

• FAPESP's process: 15/14042-2 - Evaluation of Sugarcane Bagasse Pretreatment Process with Protic Ionic Liquids for Cellulosic Ethanol Production
• Grantee: Pedro Yoritomo Souza Nakasu
• Support Opportunities: Scholarships in Brazil - Doctorate