In this study, beech wood was fractionated in lab scale rector by one-stage and two-stage processes. The two-stage processes of the prehydrolysis with no catalyst (only water) and catalyst (sulfuric, phosphoric, oxalic acids), and the subsequent effect on the organosolv process were studied. A one-stage organosolv delignification of beech wood (control experiment) was conducted at 155 degrees C for 160 min in 1:1 ethanol/water mixture with 100 mM sulfuric acid, while the two-stage processes were conducted starting from the uncatalyzed and catalyzed (20-200 mM) prehydrolysis of beech wood at 175 degrees C for 60 min. The results indicate that sulfuric acid enhanced the removal of xylan from beech wood during the prehydrolysis stage. Moreover, the effectiveness of the delignification of beech wood using a one-stage process is more than the two-stage, as well as the enzymatic digestibility of the pulp, which was better than those of the two-stage processes. However, the enzymatic digestibility results of the pulp obtained after sulfuric acid catalyzed prehydrolysis followed by organosolv delignification shown better results than the other two-stage processes. Additionally, high klason content, low sugar content, low M-w, and high phenolic hydroxyl groups of lignin was recovered by a one-stage organosolv delignification. (C) 2020 Elsevier Ltd. All rights reserved.