Hidrólise em água subcrítica de bagaço de malte: um pré-tratamento sustentável para produção de produtos de valor agregado e bioenergia em um conceito de biorrefinaria

Author(s)

William Gustavo Sganzerla

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos
• Defense date: 2023-04-19

Examining board members

Tânia Forster Carneiro; Mauro Donizeti Berni; Rosana Goldbeck; Montserrat Pérez Garcia; Miriam Tena Villares

• Advisor: Tânia Forster Carneiro

Abstract

The management of lignocellulosic biomass and the production of bioenergy and biobased products is a constant demand in the industry. Brewer’s spent grains are the main lignocellulosic by-product generated by the beer industry, accounting for 20 kg per 100 L of beer produced, being a suitable feedstock for potential application in a biorefinery. However, the production of biofuels and biobased products from biomass requires a pretreatment to break down the lignocellulose structure. A comprehensive review and bibliometric analysis elucidated that the sustainable pretreatment of brewer’s spent grains is one of the most limiting steps in lignocellulosic biomass conversion into biobased products and bioenergy. Therefore, the objective of this PhD thesis was to evaluate the application of subcritical water pretreatment of brewer’s spent grains as a sustainable technological process to produce biobased products and bioenergy in a biorefinery concept. The pretreatment of brewer’s spent grains was optimized in a semi-continuous subcritical water hydrolysis process operated with a single and two sequential flow-through reactors to obtain a hydrolysate containing sugars, xylo-oligosaccharides, and amino acids. The subcritical water hydrolysis was carried out at 15 MPa, 5 mL water min–1, and at different temperatures (80 – 180 °C). Experiments integrating subcritical water hydrolysis and anaerobic digestion were conducted to produce bioenergy (biomethane, electricity, and heat) and agricultural fertilizer. In a biorefinery concept, the techno-economic assessment of the designed bioprocesses was studied to identify the most profitable option for industrial implementation. The results obtained demonstrated that subcritical water hydrolysis attacked the brewer’s spent grains structure, releasing monosaccharides (47 mg g–1 carbohydrate), amino acids (42 mg g–1 proteins), and xylo-oligosaccharides (204 mg g–1 hemicellulose). The economic analysis of sugar production revealed that the separation of monosaccharides obtained by subcritical water hydrolysis is an advantage for the profitability of the industrial-plant process. In the case of xylo-oligosaccharides, the gross profit of the process with two sequential reactors was 30% higher when compared to the single subcritical reactor. In addition, the pretreatment was demonstrated to be profitable for recovering xylo-oligosaccharides. The hydrolysate obtained by subcritical water hydrolysis was applied in anaerobic digestion to elucidate the production of methane-rich biogas and bioenergy. The results demonstrated that the integration of subcritical water hydrolysis and anaerobic digestion increased the methane yield (747 L CH4 kg?1 TVS) when compared to the anaerobic process without pretreatment (53 L CH4 kg?1 TVS). For the process with pretreatment, the generation of electricity (134 kWh ton–1) and heat (604 MJ ton–1) were responsible for the mitigation of 44 kg CO2-eq ton–1. The industrial scale of anaerobic digestion without pretreatment was also found to be a feasible option to recover bioenergy and fertilizer, with payback lower than 5 years, internal return rate around 20%, and net present value up to 1 million USD. Finally, the application of subcritical water hydrolysis of brewer's spent grains is a sustainable pretreatment to produce value-added products and bioenergy, supporting the circular economy transition by reducing the carbon footprint of the beer industry (AU)

• FAPESP's process: 19/26925-7 - Development of an automated system for biofuel precursor production using sub-critical technology
• Grantee: William Gustavo Sganzerla
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)