Optimization of sequential alkaline–acid fractionation of pine sawdust for a biorefinery

• Report of the optimization of alkali and acid fractionation of slash pine sawdust.
• Maximum removal of extractives (90.7% sms) was reached at 90 °C, 1 h and 5% NaOH.
• Alkali concentration was the most influential factor in alkaline stage.
• Maximum hemicelluloses extraction was 57% at 150 °C, 30 min and 7.5 g/L H2SO4.
• Temperature was the most influential factor in acid stage.

The aim of this work was to apply an alkaline–acid sequence for the fractionation of slash pine sawdust, to obtain a solid lignocellulosic material (which can be subsequently delignified to obtain pure cellulose), and separate liquid fractions containing extractives and hemicelluloses. Processes were optimized using a central composite design of two variables for the alkaline extraction stage (NaOH concentration and temperature), and another of three variables for the acid treatment (H2SO4 concentration, time and temperature). Yield and contents of extractives, lignin, carbohydrates and degradation products, all by NREL Standards were determined. Maximum removal of extractives in the alkaline stage (90.7%) was reached using 5% NaOH (oven dry basis, od) at 90 °C for 1 h, and maximum hemicelluloses extraction in the acid stage (57%) was obtained using 7.5 g/L H2SO4 at 150 °C for 30 min The alkaline–acid sequence has shown to be effective for the sequential extraction of resin and hemicelluloses from slash pine sawdust, making possible its use for the production of high value products.

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