Green Reactions and Technologies for Biomass Valorisation

This research project has focussed on the upgrading of biomass derivatives, particularly glycerol derivatives and lignin, to higher added-value chemicals by means of green and sustainable technologies. The fundamental principle of sustainability is that waste is not an old useless substance that needs to be disposed of, but is rather an important and multicomponent feedstock that can be exploited to produce new chemicals, materials and energy sources, thus re-entering the material cycle. The valorisation of waste must be done in a sustainable way, i.e. using environmental friendly technologies. These concepts have been the guidelines by which methods and chemical transformations have been conceived in this Thesis work. The experimental work was divided into three main areas, which were all commonly aimed at combining green technologies and biobased compounds for the development of sustainable protocols. 1) OH-bearing bio-based compounds (O-BBs), as glycerol acetals/carbonates and furfuryl alcohol derivatives, are suitable for a number of derivatisation processes. Of particular note, alkylation protocols allow the potential of O-BBs to be expanded through the synthesis of intermediates, solvents and biologically active molecules as glycerol ethers and carbonates, and additives for biodiesel blends based on furanyl ethers. In this context, an innovative alkylation protocol was implemented in this Thesis (cfr. Chapter 2) using dialkyl carbonates, which are green and safe compounds, as alkylating agents under continuous-flow (CF) conditions. Different classes of catalysts were compared: Na-exchanged Y- and X-faujasites and Mg-Al hydrotalcites. Calcined hydrotalcites (c-HTs), particularly c-HT30 (Mg:Al ratio=30), proved to be the most effective system for highly chemoselective transformations: functionalised bio-based alcohols and dialkyl carbonates were activated preferentially towards O-alkylations over the competitive transesterifications and other side-reactions. 2) The synthesis of symmetrical dialkyl carbonates is a highly desirable target since symmetrical DAlCs are of great interest as eco-friendly solvents and intermediates. Symmetrical DAlCs can be synthesised via catalytic transesterification/disproportionation reactions starting, for example, from methyl alkyl organic carbonates. These products in turn, can be obtained via a transesterification of OH-bearing bio-based derivatives with the non-toxic dimethyl carbonate. In this Thesis (cfr. Chapter 3), carbonate interchange reaction strategies have been investigated and a continuous-flow protocol for the disproportionation of four different methyl alkyl carbonates was optimised, using c-HT30 as a heterogeneous catalyst. 3) Lignin constitutes around 25-30% of lignocellulosic biomass and it is the most abundant source of renewable aromatic compounds in the terrestrial biosphere. Of the many target compounds that can be produced from the conversion of lignin, phenol(s) and BTX-type arenes are economically attractive due to their large market volumes. In this Thesis (cfr. Chapter 4), the catalytic depolymerisation of Kraft lignin in supercritical ethanol (which acted as both the solvent and the H-donor) was explored in the presence of eight different Mo-based catalysts. 4) Nitrogen-based compounds are commonly found in biocrude oils when they are generated from biomass containing some residual protein, e.g. algae, seaweed or municipal green waste. These N-containing residues interfere with traditional refining methods and need to be removed. Ionic liquids have previously been suggested as useful and green extractants of aromatic N-containing compounds from fuel oils. In this thesis, twelve ILs based on common cations and anions were synthesised and used for the selective extraction of two archetypical N-compounds, pyridine and indole, from a model oil, consisting of n-decane and toluene. The performance of these ILs was compared and rationalised