Sugar production by dilute acid hydrolysis of oat bagasse with three different acids: kinetics and thermodynamics

Acid hydrolysis is used as a treatment method to hydrolyze the polysaccharides present in biomass to fermentable sugars. In this research the hydrolysis of oat bagasse was studied employing different inorganic acids (HCl, H$_2$SO$_4$ and H$_3$PO$_4$) at low temperatures (90 - 110 °C) in a long-term process. Sulfuric acid showed a high potential to produce reducing sugars reaching the maximum production yields at 110°C, while hydrochloric acid at 110°C was the most catabolic acid promoting sugars transformation into furfural. FTIR and relative transmittance analyses suggested that major impact on lignin polymer was made by phosphoric acid hydrolysis at Combined Severity Factors (CSF) higher than 1.5. Kinetic constants calculated from conventional Saeman model allowed to determine thermodynamic parameters for each inorganic acid. Decomposition of sugars occurred most frequently when the Activation Energies (Ae) were low than calculated for sugar production, being aldehydes, the most stable products obtained during hydrolysis. Thermodynamic parameters show an endothermic and non-spontaneous oat bagasse hydrolysis reaction for different inorganic acids.

Keywords: kinetics, thermodynamics, oat bagasse, reducing sugars, acid hydrolysis.