Production of xylose and glucose from rapeseed straw in subcritical water – Use of Doehlert design for optimizing the reaction conditions

The hydrothermal depolymerization of the hemicellulosic and cellulosic fractions of rapeseed straw was carried out in a batch reactor in subcritical water. The experimental design methodology (Doehlert matrix) was used to model the hydrothermal process and to optimize operational parameters reaction temperature and holding time for highest yields of saccharides: xylose and glucose, obtained in experimental series 1 and 2, respectively. In good agreement with experimental results, the model predicts an optimal yield of xylose (60.4 g kg−1 ± 2.1 g kg−1) at a temperature and a holding time of about 203 °C and 13 min. The optimal yield of glucose (180.7 g kg−1 ± 2.8 g kg−1) required higher temperatures but shorter times and was obtained at a temperature 255 °C and a holding time of 9 min. A further increase of both reaction parameters would lead to the undesirable transformation of the saccharides: their dehydration, retro-aldol condensation, isomerization and tautomerization. The obtained results confirm that the hydrothermal treatment of rapeseed straw in optimal reaction conditions might be an alternative route for the production of xylose and glucose. -- Highlights: • Utilization of rapeseed straw rich in hemicellulose and cellulose agricultural residue from the pressing of oil. • Subcritical water hydrolysis of rapeseed straw as a new method of its conversion. • Saccharides: xylose and glucose as valuable main products of studied reaction. • Optimal experimental design for optimizing the conditions for saccharides production. • Undesirable transformation of reaction products at highest temperatures and times