Grape stalks as a renewable source for the production of value-added products: application of hydrothermal carbonization, analysis of the process and products

Abstract

Biomass from agro-industrial waste is a vital renewable resource for addressing energy and environmental challenges. Hydrothermal carbonization (HTC) is utilized to produce hydrochar from various materials, including these wastes, for environmental remediation and other industrial applications. In this work, the effects of temperature and treatment time on the solid and liquid obtained from the application of the HTC process to grape stalks, were assessed. The energetic properties of the hydrochar, its physico-chemistry and that of the activated carbons prepared with it, were evaluated by proximate analysis, higher heating value (HHV), BET area, pore volume, FTIR and SEM. Temperature significantly impacted the hydrochar´s mass yield (50%), while time had minimal effect. The hydrochars´ energy yield was about 70%, with an HHV value of 26.21 MJ/kg. The activated carbons produced from grape stalk hydrochar, using KOH and H3PO4, exhibited BET areas of 1630 and 1800 m2/g, respectively, highlighting their potential as adsorbents and or energetic applications. Meanwhile, the liquid fraction emerged as a potential source of antioxidant compounds due to the presence of phenols and flavonoids. The highest concentration of phenolic compounds (TPC) was obtained at 240°C for 10 hours TPC (1310.17 mM GAE/100 g dw), and the highest of flavonoids (TFC) at 180 °C for 2 h (39 mm QE/100 g dw). Antioxidant capacity was determined by DPPH scavenging activity and Ferric-reducing antioxidant power assay (FRAP). These results present genuine possibilities for the technological application of the products derived from this simple process, pending completion of complementary studies.