Microwave-assisted conversion of lignocellulosic biomass to platform chemicals and bio-oligomers

The diminishing availability of fossil sources has stimulated the search for alternative energy and chemicals sources. Lignocellulosic biomass is the most abundant renewable source of biofuels and biochemicals [1]. Agricultural waste represent a valuable source of platform chemicals as they do not compete with food feedstock. Several attempts have been studied in the last three decades to make processes more sustainable. From this point of view, new technologies such as microwaves strongly promote chemical modifications reducing the reaction time and temperatures [2]. In this work, the microwave-assisted flash conversion of agricultural waste into levulinic, lactic and glycolic acid is reported. Levulinic acid was obtained with high selectivity in acidic conditions [3] and was then hydrogenated to γ-valerolactone (GVL) through a new solvent-free protocol under microwave irradiation. GVL is renewable and biodegradable, and it can be used as an intermediate or directly as a green solvent and food additive. GVL was used for the deconstruction of the lignocellulosic biomass itself, promoting the separation of lignin and hemicellulose from levulinic acid under acid conditions. Lactic and glycolic acids were obtained by flash catalytic conversion using divalent metal cations under microwave irradiation. The batch protocol was then adapted to a flow process, paving the way to scale up. The C2 and C4 units thus obtained were directly used for a microwave-assisted polycondensation affording oligomers in good yields with a solvent and catalyst free protocol [4]. Novel microwave-assisted sustainable processes for biomass valorisation were reported.