Smart valorization of waste biomass: Exhausted lemon peels, coffee silverskins and paper wastes for the production of levulinic acid

In recent years, the replacement of fossil resources with renewable ones has focused great interest, expecially as regards the production of new valuable bio-products and bio-fuels, in progressive replacement of the traditional petroleum-based ones.The Waste Management Policy strongly encourages the valorization of waste biomasses into added-value bio-chemicals, instead of their traditional combustion for energy recovery or, even worse, of their landfill disposal. In this context, the acid-catalysed hydrothermal conversion of negative-value bio-wastes into levulinic acid (LA) represents a smart exploitation possibility, already developed and optimized on pilot-scale, and widely adaptable to different kinds of feedstocks. In this work, the LA production was investigated starting from two bio-wastes deriving from industrial Italian food-processing, e.g.exhausted lemon peels and coffee silverskins, together with that of a clean cellulose powder, which derives from the cutting operations occurring during the tissue paper production. The effect of the main reaction parameters on the LA synthesis, in particular the concentration of the acid catalyst, the biomass loading, the reaction temperature/time and, additionally, the effect of an upstream milder acid pretreatment, was investigated and discussed. Moreover, in the case of coffee silverskin, a preliminary extraction step of the water-soluble phenolics has further improved the fractionation and exploitation of this waste biomass. These compounds have been proposed as natural antioxidants, which represent very valuable niche products for nutraceutical uses. The described examples confirm the feasibility of an integrated valorization of the waste biomass, well in agreement with the Biorefinery concept.