Management of de-oiled coffee beans biomass through pyrolysis process: Towards a circular bioeconomy

Abstract

In this work, we proposed the pyrolysis process for the valorization of de-oiled defective coffee beans (DCB) residual biomass provided by the pressurized fluid extraction (PFE) process after the recovery of coffee oil. The proposal to subsequent thermoconversion of the de-oiled biomasses focuses in an integrated biorefinery concept to obtain value-added products, what fits into the circular bioeconomy strategy. DCB biomasses showed the highest coffee oil recovery yields (∼10%) from the PFE processes and presented yields of the pyrolysis condensate fraction (bio-oil + aqueous fraction) in the range between 53.7% and 59.4%. On the other hand, the yields of biochar and pyrolysis gas increased, with values from 23.6% to 27.3%, and from 17.0% to 19.5%, respectively, when compared to the yields from pyrolysis of the raw DCB. The biochars showed very similar compositions, with HHV between 24.7 and 25.3 MJ kg−1. Overall, the bio-oils showed same constituents with variation in the concentrations of some species detected by GC/MS. Among them, the main classes with such alterations were phenolic compounds and carboxylic acids, in which the relative contents ranged from 19.7% to 39.0% and 11.3–46.1%, respectively. The findings demonstrated the potential of using pyrolysis as a sequential step to add value to the de-oiled DCB biomass remaining after the extraction of coffee oil, which could contribute to a sustainable circular economy with zero waste generation.