Hydrothermal decomposition of rapeseed straw in subcritical water. Proposal of three-step treatment

We have investigated the three-step hydrothermal decomposition of rapeseed straw, rich in lignocellulosic components, as a batch process. The effects of the reaction temperature and holding time on the composition of the reaction products were studied. After the first step of the treatment there prevailed products of the hydrolytic depolymerization of hemicellulose. The highest yield of xylose (5.87% (w/w)) was obtained at a temperature of 210 °C and a holding time of 10 min. In the second step of the process as a result of depolymerization of cellulose, glucose was obtained, with the largest yield (17.4% (w/w)) at a temperature of 270 °C after 5 min. Unreacted lignin was used in the third step of the treatment. Its decomposition was performed at a temperature of 330 °C. The highest yield of guaiacol (11.56% (w/w) and catechol (5.61% (w/w)), was obtained after a holding time of 0 min and 60 min, respectively, whereas the highest yields of phenol (4.11% (w/w)), m,p-cresol (4.09% (w/w)) and o-cresol (2.71% (w/w)), were obtained after 150 min. The solid residue obtained in the third step of the process consisted mainly of phenolic biochar.