Converting coffee silverskin to value-added products by a slow pyrolysis-based biorefinery process

This work aims to transform coffee silverskin (CSS), the only waste from the coffee roasting process, that worldwide amounts to about 76 million kg/year, into value-added products within an integrated slow pyrolysis process. The study, performed at 280 degrees C, 400 degrees C and 500 degrees C, determined the potential applications of the resulting fractions. Biochar has been studied as an adsorbent of organic pollutants in water, using methylene blue (MB) and methyl orange (MO), which are respectively cationic and anionic aromatic dyes, as model compounds, and with 400 degrees C biochar giving the highest removal values, at 98% with MB and 40% with MO. Moreover, CSS biochar could be used to obtain renewable energy from its combustion, with 22.6-24.2 MJ/kg calorific values. The liquid fraction could be a potential source of caffeine, among phenolics, with 400 degrees C aqueous phase presenting the highest concentration of caffeine (14.3 g/L). Concerning the gas fraction, it could be used to obtain heat for biomass drying before pyrolysis. Hence, use of the pyrolysis products as described would allow zero waste to be achieved in the coffee roasting industry, thus promoting the green and circular economy and production of green chemicals and materials in a biorefinery context.

Automated summary

This study aims to transform coffee silverskin (CSS) waste into value-added products through an integrated slow pyrolysis process, producing biochar as an organic pollutant adsorbent and liquid fraction for caffeine extraction. The pyrolysis process also generates gas for biomass drying, achieving zero waste in the coffee roasting industry and promoting green chemicals production in a biorefinery context.