Platform chemicals recovery from spent coffee grounds aqueous-phase pyrolysis oil

Abstract

Spent coffee grounds (SCG) are a valuable biogenic waste diffused on a global scale, containing a significant amount of extractives. The aim of this study is to characterize the pyrolysis oil fractions, under various process conditions, targeting their potential applications as biofuels and source of valuable chemicals. Pyrolysis tests were carried out in the range of 400–550 °C with a laboratory-scale screw reactor and a two-step solvent extraction process, was conducted for the aqueous bio-oil phase. The results showed that heavy organic bio-oil resulted in a carbon rich biofuel, with a carbon content of up to 63 % (w/w) and HHV up to 34.8 MJ/kg. Chloroform was selective in extracting xantines (68–74 % of the peak area), furans, phenols, and fatty acids from the aqueous phase, while the ethyl acetate extract was abundant in p-benzoquinone (70–83 % of the peak area), a key-player chemical for the petrochemical industry. The residual unextracted water phase is very rich in organic acids i.e. acetic, propionic, and formic-whose concentration is in the range 47 g/L and 87.9 g/L. The results of this study outline how solvent extraction is a promising technique for extracting valuable chemicals to improve the economic potential of spent coffee grounds pyrolysis-based biorefinery.