Lignocellulosic materials as new renewable resourcesextraction, purification and potential use of hemicelluloses

Resumen

In recent years, the uncertainty in the supply, price of fossil fuels and generatedenvironmental pollution, make necessary the investigation of new alternatives. As aresult, the lignocellulosic materials become an important resource to provide andsupport a sustainable and environmentally friendly system.These renewable materials (consisting mainly of cellulose, hemicellulose andlignin) can be processed to produce energy, fuels, chemicals products and precursors ofbiopolymers with high added-value. Today, cellulose is the main polysaccharideactively used in commercial products. In biorefinery concept, which the objective is theefficient use of biomass components and its conversion for obtaining energy, fuels,chemicals and materials, the isolation of hemicelluloses as valuable compounds, can bean important aspect for optimal biomass usage.Therefore, one of the objectives of this work was the evaluation of differentagricultural residues as new renewable resources, in this case, as hemicellulosefeedstocks. The main goal was the extraction, purification and characterization ofhemicelluloses for various potential uses, namely, as hemicellulosic monomeric sugars(useful to value-added products obtention, e.g. xylitol, ethanol etc.), and as biopolymer,for new materials production.In order to achieve these objectives, in this work, different agricultural residueswere used as hemicellulose source, such as corn stalks, grape stalks, corncob, cottonwaste, olive and apple tree pruning, pepper and chilli wastes; most of them recoveredfrom the available residues in the local area.Corn stalks and grape stalks were used separately as raw materials forhemicellulosic monomeric sugars extraction. For that, autohydrolysis process wasselected as environmental friendly process. The optimization of autohydrolysisextraction process was performed through experimental design, observing the optimumconditions for maximum sugar monomeric extraction for each material.In case of corn stalk autohydrolysates, several purification processes wereapplied in different autohydrolysis liquors, i.e. precipitation, liquid-liquid extraction andultrafiltration, with the aim to refine the obtained hemicelluloses in the liquors.Following the biorefinery concept, the by-products extracted from liquid-liquidpurification process from corn stalk autohydrolysates, i.e. phenolic compounds, wereassessed as valuable products with antioxidant capacity.On the other hand, for grape stalks sugars monomers recovery, the optimizationof autohydrolysis process was performed. Besides that, the washing step of the rawmaterial prior to autohydrolysis and the effect of sulphuric acid as optimumautohydrolysis catalyst were evaluated. In this case, activated charcoal was proposed forgrape stalks hydrolysates purification. Non-purified, purified and prepared sameconcentration synthetic liquors were tested as fermentation substrates by D. nepalensysfor value-added products production.In the last part of the work, the extraction of hemicelluloses as biopolymer fornew materials productions was performed using delignification and alkaline extractionfrom corncob, cotton waste, olive, apple tree pruning, pepper and chilli wastes. Thephysicochemical characteristics of obtained hemicelluloses (with and without lignin)with respect to their film forming capacities were evaluated. As the last section of thiswork, corncob hemicellulose was selected and treated to improve its material propertiesthrough purification and acetylation processes, until a suitable matrix was obtained forfuture materials applications