Developing a biorefinery from spent coffee grounds using subcritical water and hydrothermal carbonisation

Abstract Spent coffee grounds (SCGs) have been extensively investigated as a feedstock to produce fuels, specialty chemicals and materials. Whilst few reports used cascade processes generate several products from SCG, this work takes the novel approach of using integrated subcritical water extraction (SWE) hydrothermal carbonisation (HTC) derive three products: bioactive extract, protein isolate (SCG PI) solid fuel. SWE HTC were optimized producing an antioxidant rich with chlorogenic acid (CGA) content activity determined. The was quantified via total amino analysis, giving first SCG specific elemental nitrogen-to-protein conversion factor 7.90. then performed on residual solids SWE, raw feedstock. This biorefinery gave higher quality than previously reported in single product systems. For example, pretreatment reduced nitrogen hydrochar ( N = 0.23% wt, HHV 33.30 MJ/kg) relative control (3.03% 31.31 MJ/kg). Limiting preferentially increased (33.0% vs 16.9% wt) yield (53.0% 23.9%) isolate, rendering compared derived following upstream process (33.30 26.92 MJ/kg, 16.3% 14.7%, respectively). goes towards complete utilisation SCGs within biorefinery, highlighting potential processing commercially viable across value chain.