Thermal hydrolysis of olive leaves and stems to obtain fermentable sugars

Abstract

Subcritical water hydrolysis was used for the pre-treatment of residues generated in olive groves. Fermentable sugars were produced from the lignocellulosic material found in olive leaves and stems. Firstly, moisture, ash, particle average diameter, and total extracts were measured. Afterward, subcritical water hydrolysis was carried out at 20 MPa in a 50 mL reactor. The influences of two temperatures (180 and 220 °C) and two water flow rates (10 and 20 mL min^-1) on the sugars yields were evaluated. The concentration of sugars was 31.3 g L^-1 at 180 °C and 10 mL min^-1 in a reaction for 3 min, of which glucose was the major sugar (27.64 g L^-1). Statistical analysis was performed using Sisvar^® 5.6 software and the averages were compared through Tukey’s test, considering a significance level of 95% (p<0.05). For the treatments evaluated in this work, only xylose was statistically different in the treatments with different water flow rates. The highest values of xylose were obtained with 10 mL min^-1, which were 1.82 g L^-1 (180 °C) and 2.18 g L^-1 (220 °C). The total inhibitors were high at 220 °C for all water flow rates, with a significant difference from the averages obtained at 180 °C.