Co-production of hydrochar and bioactive compounds from Ulva lactuca via a hydrothermal process

Abstract

This study investigates the simultaneous production of hydrochar and bioactive compounds from Ulva lactuca via a hydrothermal process. The experiment was carried out using a batch reaction vessel at different reaction temperatures of 180–220 °C and various holding times of 30–90 min. As expected, both temperature and time vigorously influenced hydrochar and bioactive compound production. The maximum hydrochar yield was at 32.4 wt%. The higher heating value (HHV) of hydrochar was observed in the range of 17.68–21.07 MJ kg⁻¹, near the energy content of low-rank coals. The hydrochars exhibited contact angles higher than 90° (i.e., 94-108°) for a longer time, confirming their hydrophobic surfaces. The scanning electron microscope analysis (SEM) showed that the hydrothermal process enables cracks in the spherical shape of raw U. lactuca into small and porous particles. Besides producing hydrochar, the hydrothermal process of U. lactuca also gives promising antioxidants and phenolics as bioactive compounds. The highest total phenolic content and antioxidant activity could be achieved in hydrolysate at 200 °C and 30 min with the value of 1.20 ± 0.12 mg/g and 71.6 ± 1.3%, respectively.