Extraction of hemicellulosic sugars from coffee silverskin: process optimization, prospects, and sustainability assessment

Coffee silverskin (CS), a major byproduct of the coffee industry, is typically incinerated for disposal. However, its composition makes it a valuable feedstock for biorefinery valorization. This study investigated dilute acid pretreatment to extract sugars from CS. Statistical designs identified optimal conditions (14 g/g CS liquid-to-solid ratio, 100 mg H 2 SO 4 /g CS, 165 °C, 59 min) for hemicellulosic sugar release, achieving extraction efficiencies of 75.4%, 36.6%, 43.9%, 97.5%, and 62.4% for galactose, mannose, xylose, arabinose, and hemicellulose, respectively. Potential sugar stream applications were then discussed. Three scenarios (Sc) for CS biorefinery valorization were proposed, each incorporating ethanol production from cellulose and electricity generation from lignin/remaining solids. The scenarios differed in hemicellulose utilization: Sc1) ethanol production; Sc2) xylitol production; Sc3) 2,3-butanediol production. All scenarios were found to be unprofitable, with high energy consumption for hydrolysate concentration significantly impacting operating costs. Sc2, however, showed the most promising economic potential (−1049.56 thousand USD/year). Ethanol, xylitol, and electricity production (Sc2) had a notable environmental impact, emitting 115.1 kg CO2eq/L ethanol. Hydrolysate concentration (67.3%) and dilute acid pretreatment (19.8%) were the primary contributors to emissions. While this study confirms CS's potential for biorefinery valorization, addressing hydrolysate concentration and pretreatment methods was found to be crucial for achieving profitable and environmentally sustainable processes. • Dilute acid pretreatment was used to extract sugars from coffee silverskin (CS). • Optimal pretreatment conditions resulted in 62.4% hemicellulose extraction efficiency. • High energy costs negatively affected the economic potential of biorefinery scenarios. • Hemicellulosic hydrolysate concentration was the main emission contributor in the GWP.