Development and Integration of Sustainable Processes for Biomass Fractionation

Industrial practices and technological processes require a fast reformulation to meet the demands while preventing the horrible consequences of reaching limit global temperatures. Lignocellulose biomass is widely produced worldwide and holds a great potential to substitute fossil-based fuels and materials. Its implementation into biorefinery processes can be a key contributor to the transition to a circular and biobased economy, in which waste fractions are considered a resource rather than a burden. A major constraint of biomass conversion processes is the high recalcitrance of its structure, that is difficult to depolymerize and partition into simpler units which can subsequently be used as a product or as a raw material for conversion. This issue could be solved by using an efficient and sustainable fractionation method, in which the three main components of the biomass (cellulose, hemicellulose and lignin) could be obtained for conversion, however it has still not been achieved.
This thesis addresses the topic with the utilization of sugarcane bagasse and the introduction of a novel and mild pretreatment approach using carbon dioxide. When applying it to low moisture sugarcane bagasse, it has shown to increase the release of sugar monomers in the subsequent hydrolysis step compared to the untreated biomass. Results also showed that the chemical composition of the structure remained almost constant after pretreatment, which proves the potential of this pretreatment to use cellulose, hemicellulose, and lignin for the conversion of valuable compounds.
The optimization of the enzyme cocktail formulation was also covered with the supplementation of enzymes and additives to the commercial enzyme cocktails Cellic®Ctec 2 IV and Cellic®Ctec 3 HS. The addition of hydrogen peroxide, lytic polysaccharide monooxygenases, cello-oligosaccharide dehydrogenase, surfactants and hemicellulases were some of the approaches that showed a great potential for the enhancement of sugar monomers production during hydrolysis of the mildly pretreated sugarcane bagasse.
The sustainability of two systems for bioethanol production, one using the CO₂ pretreatment method and other diluted acid pretreatment, were evaluated and compared using life cycle assessment. Results showed that the CO2 emissions of the production of bioethanol using one tonne of bagasse were substantially lower for the system that used CO₂ pretreatment method.
The results obtained through this thesis provide a profound knowledge of the potential that the utilization of a mild and sustainable fractionation has and paves the way for future research studies focused on reducing the environmental impact of biomass conversion processes.