Miscanthus x giganteus, a source of biobased productscharacterización, organosolv fractionation and TCF bleaching

Résumé

Many national governments worldwide have already perceived the importance of biomass in a model of sustainable socio-economic development. For this reason, its use is being stimulated and a wide variety of bioproducts, bioenergy and biofuels are being introduced in markets competing with oil-based products for quality, prices and consumers interest. A biorefinery is a process facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass. The achievement of replacing petroleum- for bio-based products will mean a great challenge and aspects like adequate selection of plant species, productivity increase with a rational use of soil, fertilizers, pesticides and water, the use of genetically modified organisms and logistics, among others, will have to be directed. Furthermore, it will be essential that biobased products do not come from part of the food production, particularly when the world population is expected to reach 9-10 billion by the middle of the XXI century. In this complex scenario, a deep knowledge and thorough understanding of the composition of each plant species and the development of efficient processing and chemical/biochemical transformation/fractionation technologies will be essential for the development of future biorefineries. The main objective of this work was to evaluate the potential of Miscanthus x giganteus as a source of organic chemicals for processes in biorefineries. In order to achieve this, lipophilic extractives obtained from bark and core, were analyzed by gas chromatography-mass spectrometry (GC-MS), showing that several compounds with useful nutraceutical and pharmacological applications (sterols and aromatic compounds) are abundant especially in the core extractives and that they could be a source of added value in a future biorefinery, using this species as raw material. Optimization studies were carried out on two organosolv fractionation processes, viz., Acetosolv and Formosolv, and evaluated with the help of appropriate kinetic models, achieving suitable pulps to initiate a bleaching process (with kappa numbers near 20). Besides, the lignins from black liquors were isolated, purified and characterized. The physico-chemical changes with respect to milled wood lignin (MWL) were analyzed using analytical techniques such as nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC) and thioacidolysis, observing that these lignins are probably acylated at the carbon of the side-chain. The influence of the main operational variables in the bleaching of M. x giganteus Acetosolv pulps with hydrogen peroxide/acetic acid (in aqueous alkaline media and in acetic acid media) was also evaluated, using factorial designs of experiments, and pulps fulfil the requirements for forthcoming stages. This methodology was also used to optimize the bleaching of Acetosolv pulps, with a new sequence free of chlorine [EPabO(PO)P], introducing peroxyacetate ion as bleaching species (Pab-stage). The sequence was tested with Formosolv and Milox pulps (brightnesses near 90% ISO were obtained with good intrinsic viscosities). The necessity of carbohydrate protectors was analyzed: no beneficial effect was observed until the last two stages, where addition of DTPA and MgSO4 preserved the cellulose chains.