Valorization of Posidonia oceanica balls: from waste to versatile raw material in an integrated biorefinery perspective

In recent years, the replacement of fossil resources with renewable ones to produce alternative fuels has received great interest. In this regard, the marine waste Posidonia oceanica balls (POb) is a promising feedstock that accumulates in an uncontrolled manner on Mediterranean beaches, thus causing environmental problem. For this reason, up to now most of POb are conferred in landfills but an integrated chemical conversion of POb into added value products could represent a more sustainable and innovative solution [1]. In this work, according to a biorefinery approach, the exploitation of POb, previously subjected to ethanol extraction, has been developed aiming at the conversion of the cellulose fraction (23.7 wt% of biomass) to n-butyl levulinate (BL), one of the most promising bio-fuel additives for Diesel engines [2]. BL synthesis was conducted under microwave heating, an alternative and more efficient system than the traditional one, using a one-pot alcoholysis approach employing n-butanol as the reactant/solvent and sulfuric acid as the homogeneous acid catalyst. The highest BL yield of 54.6 mol% was ascertained working at 180 °C for 30 minutes adopting 5.2 wt% of H2SO2 loading and 14 wt% of biomass loading. Furthermore, due to the recalcitrance demonstrated by POb, the alkaline delignification (AD) with NaOH was performed to increase the biomass reactivity and the highest delignification yield of 40.3 wt% was ascertained under the optimized conditions. Noteworthy, the AD allowed the fractionation of the biomass leading to the production of a polysaccharide enriched residue (PER), a pure acid insoluble lignin and an acid soluble lignin. PER was subjected to alcoholysis reaction, achieving the same BL yield under milder reaction conditions, in particular adopting a lower H2SO2 loading of 2.6 wt%. In conclusion, the biorefinery process proposed in this work not only addresses the urgency of a sustainable managing of POb, but also offers the opportunity to produce several bio-based compounds.