| Summary: | The main purpose of this dissertation is to scrutinise the potential of two distinct high-pressure technologies - CO2/H2O mixture and ammonia – for lignocellulosic biomass processing following the biorefinery concept. High-pressure CO2/H2O mixture took benefits from the formation of in-situ carbonic acid and involved the integration of both pre-treatment and hydrolysis steps. Due to its acidic effect, this technology was able to selectively hydrolyse the hemicellulosic fraction of biomass producing C5-oligomeric sugar-rich aqueous stream. Later, the C5-sugars present in this stream were successfully converted into furfural with high yield and selectivity using the same catalytic effect of high-pressure mixture of CO2/H2O. Additionally, the leftover materials enriched in cellulose demonstrated to be highly susceptible for enzymatic hydrolysis leading the production of highly concentrated solution of upgradable glucose. High-pressure ammonia relied on the development of a new ammonia-based technology called “Compacted Biomass with Reduced Ammonia” to pre-treat pelletised biomass, at reduced ammonia loadings. This process combined the advantages of conversion of native crystalline cellulose Iβ into highly digestible cellulose III and the benefits of ammonolysis of cell wall ester cross-links. Besides, the proposed process allowed obtaining fermentable sugars, either C5 or C6-sugars, and ethanol yields comparable to industrially relevant technologies i.e. AFEXTM (Ammonia Fiber Expansion) and steam explosion. Additionally, the proposed approach demonstrated to be a feedstock-independent technology capable to handle different types of biomasses, regardless of their macromolecular composition and morphological structure, to produce high yields of fermentable sugars. Both explored technologies demonstrated to be highly effectives for lignocellulosic biomass valorisation, showcasing their potential as sustainable technologies applicable in the biorefinery approach.
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