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Determining the kinetics of sunflower hulls using dilute acid pretreatment in the production of xylose and furfural

Abstract Pretreatment of sunflower hulls was conducted under varied dilute acid concentrations (0.5–2.0 wt%), reaction temperatures ranging between 140°C and 160°C and the reaction time up to 30 min. The conversion of xylan into xylose and furfural was investigated. The maximum xylose and furfural recoveries, 54.5±0.7 and 24.0±1.1 wt%, respectively, were obtained at different reaction times with 2.0 wt% acid concentration at 160°C. The experimental data were fitted into a two-step kinetic model based on irreversible pseudo-first-order kinetics at each step. The model was successfully validated using the F-test. Sunflower hulls showed a greater recalcitrance to acid pretreatment than other agricultural crops, such as kenaf, sorghum and sunn hemp. This feature was ascribed to the occurrence of a wax layer on the cell wall surface with a high lignin content, which may act as a barrier hindering the acid access to acetyl linkages in xylan.