Alternative technologies for ethanol and pullulan production in sugarcane bagasse biorefineries using hydrodynamic cavitation reactors and systems for simultaneous hydrolysis and fermentation

Abstract

The production of fuels from renewable sources is among the most important current research topics. In Brazil, the development of ethanol production process from sugarcane bagasse is particularly relevant, considering the high availability of this raw material in the country. However, the economic feasibility of producing 2G ethanol requires the integral use of the raw material in a biorefinery context, and current research has been directed towards the production of this alcohol from the glucose present in cellulosic hydrolysates obtained by enzymatic route. The hemicellulose fraction, which can represent up to one third of the mass of the bagasse, can be hydrolyzed to pentoses, which can be converted to ethanol or other products with higher added value. Among the products that can be obtained from hexoses and pentoses, pullulan corresponds to a biopolymer with applications of interest in food and pharmaceutical industries. The utilization, in bioprocesses, of the carbohydrates present in biomass, has been performed using an initial pretreatment step, which results in higher enzymatic digestibility of the cellulose present in the material in a subsequent hydrolysis step. Several alternatives have been studied and, recently, innovative pretreatment methods assisted by hydrodynamic cavitation systems have been evaluated and have shown promising results. Initial experiments carried out at the Laboratory of Biopolymers, Bioreactors and Process Simulation (LBBSIM) of the Engineering School of Lorena / University of São Paulo (EEL / USP) also indicated that the enzymatic hydrolysis of the pretreated material can be enhanced if assisted by hydrodynamic cavitation. In addition, the hydrolysis and fermentation steps can be carried out separately or simultaneously, and the development of studies in bioreactors that can be scaled up is fundamental. Recently, a system with interconnected column reactors and immobilized cells was proposed to allow the development of biological steps simultaneously, but using separate reactors, thus allowing the use of optimized conditions for each bioprocess. Therefore, the present project is proposed aiming at the development of innovative technologies using hydrodynamic cavitation reactors and interconnected column systems to obtain products of interest in sugarcane bagasse biorefineries. Initially, the sugarcane bagasse will be pretreated by oxidative processes assisted by hydrodynamic cavitation, evaluating the influence of important variables such as concentration of oxidant and iron (III) oxide, besides pH and temperature. The solid material obtained in the pretreatment will be used as raw material in an enzymatic hydrolysis process catalyzed by commercial preparation of cellulases in a cavitation reactor and, also in this case, the influence of variables such as enzymatic charge, initial solid:liquid ratio and temperature of process will be evaluated. The hydrolysates obtained will be used for production of ethanol and pullulan in bubble column bioreactors, using, respectively, cells of Scheffersomyces shehatae and Aureobasidium pullulans. The material pretreated by process assisted by hydrodynamic cavitation will also be used in simultaneous hydrolysis and cofermentation systems, in which interconnected column bioreactors will be used. Of them, one bioreactor will be used for the enzymatic hydrolysis of the carbohydrate fractions of the material, while the other column bioreactor will contain immobilized S. shehatae cells for ethanol production. Alternatively, A. pullulans cells will be used in this system to produce pullulan. Thus, the project contributes with innovative approaches for viabilization of bioprocesses of interest for the use of lignocellulosic raw materials, resulting in the generation of sustainable national technology. (AU)