Design of an industrial autohydrolysis pretreatment plant for annual lignocellulose

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Three concepts for a 3000 t/a continuous autohydrolysis plant aiming at a full fractionation of agricultural residues (wheat straw as model substrate) into streams rich in xylose, glucose, and lignin, respectively, are developed. For this purpose, two kinetic models based on batch liquid-hot water experiments (30 mL, 170–230 °C, 10–60 min) were investigated. The solid hemicellulose conversion was described with a first-order rate model. The concentration and conversion profile investigation of the solid and liquid phases using the severity factor resulted in a linear equation describing the hemicellulose solubilization: XHC = (0.5839 ∗ log(R0) − 1.7027) ± 0.06. Here, specific process parameter boarders for the maximal hemicellulose concentration and furfural formation at log(R0) = 4.0 considering the liquid phase were identified. These findings were used to propose a multi-step hydrothermal processing approach, with intermediate sugar extraction, tailored to the compositional requirements of the product streams. Seven reactor types were evaluated for its feasibility; in this regard, the screw conveyor reactor (SCR) was evaluated as most promising. For the concepts, the SCR reactors were scaled, based on the generated data. It was found that the process temperature is a major parameter determining the reactor size. It is considered more important than the number of autohydrolysis treatment steps. In brief, the fractionation of agricultural residues using a multi-step continuous plant is evaluated to be very promising for the industrial application, regarding selectivity, handling, investment, and process costs.