Production and Physicochemical and Structural Characterization of a Hydrochar Derived from Agave Leaves and Tequila Vinasse with Potential Agricultural Applications

The generation of agro-industrial waste necessitates the search for viable, sustainable alternatives for its utilization; therefore, Hydrothermal Carbonization (HTC) is proposed as a means to transform waste into carbonaceous products that can improve soil quality. To this end, conditions in the HTC process were evaluated for the production of hydrochar from tequila vinasse and Agave tequilana Weber leaves. Different reaction times (8, 12, and 16 h) and catalyst concentrations (0%, 5%, and 10%) of citric acid were evaluated at 200 °C, using fresh agave leaves and raw vinasse. The hydrochars were characterized using various instrumental analyses (XPS, FTIR, SEM-EDS, and XRF) to determine their structure, functional groups, and elemental composition. The highest yield was obtained at 8 h without a catalyst (44.6%), decreasing with increasing process time. The vinasse served effectively as an aqueous medium and natural catalyst, with its acidic pH (3.8), thereby eliminating the need for water and acid addition. With longer processing times, microspheres form within the hydrochar structure due to carbohydrate degradation. The hydrochar produced without a catalyst and with a shorter reaction time exhibited functional groups (carboxyl and hydroxyl) that enhance Cation Exchange Capacity (CEC), thereby increasing the contact surface area. Under the evaluated conditions, the HTC process is suitable for producing hydrochar from agave leaves and vinasse.