Thermal hydrolysis of olive leaves and stems to obtain fermentable sugars

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.

Assessment of reducing sugars production from agro-industrial wastes by batch and semicontinuous subcritical water hydrolysis

Reducing sugars produced from agro-industrial wastes by means of hydrolysis represent a promising alternative of chemicals and energy. Yet, large scale production still struggles with several factors involving process complexity, sugars degradation, corrosion, enzyme recyclability, and economic feasibility. More recently, sub and supercritical water hydrolysis has been reported for the production of reducing sugars as a readily available alternative to acid and enzymatic biomass hydrolysis. Accordingly, in this work, the results of batch and semicontinuous lab scale subcritical water hydrolysis experiments of agro-industrial wastes of pea pot and corn stover are discussed. Experiments were carried in the temperature range 250 to 300 °C, pressures up to 3650 psi, residence times up to 30 minutes in batch mode operation, or water flowrates up to 12 mL/min in semicontinuous mode operation. Produced sugars were assessed in the effluent of each experimental run by means of dinitrosalicilic acid method (DNS). A maximum total reducing sugar (TRS) yield of 21.8% was measured for batch pea pot subcritical water hydrolysis experiments at 300°C, 15 minutes, 3650 psi, and 1:6 biomass to water mass ratio. Semicontinuous subcritical water hydrolysis of corn stover showed a maximum TRS accumulated yield of 19% at 290 °C, 1500 psi, and water flowrate of 9 mL/min. The results showed the feasibility of producing reducing sugars from agro-industrial wastes currently discarded through subcritical hydrolysis.