Two-step hydrogen peroxide-acetic acid and sodium hydroxide-urea pretreatment for saccharification of lignin-rich poplar

Abstract

Pretreatment using high concentration (>60 %, v/v) of hydrogen peroxide-acetic acid (HPAA) exhibits highly selective and strong delignification capacity. However, the utilization of high concentrations of HPAA is costly and potentially explosive. Although low HPAA concentration is safer, it limits the improvement of the hydrolyzability of poplar. Herein, after the production of xylo-oligosaccharides from poplar by acetic acid (AC) hydrolysis, the obtained lignin-rich (35.6 %) poplar was pretreated with low concentration (10–20 %) of HPAA followed by sodium hydroxide-urea (SU) to enhance the hydrolyzability of AC-hydrolyzed poplar. Firstly, 37.0 % lignin and 93.2 % acetyl groups were removed from AC-hydrolyzed poplar via pretreatment using 10 % HPAA at 120 °C for 10 min. Then, SU pretreatment removed 35.2 % lignin of HPAA-pretreated poplar, which enhanced the glucose yield of the poplar from 21.4 % to 95.5 %. This HPAA-SU process saved 90 % HPAA loading and largely improved the hydrolyzability of lignin-rich poplar in a relatively short time. • The concentration of hydrogen peroxide-acetic acid (HPAA) in pretreatment was 10 %. • HPAA pretreatment removed 93.2 % acetyl group of acetic acid-hydrolyzed poplar. • Sodium hydroxide-urea treatment removed 35.2 % lignin in HPAA-treated poplar. • SU pretreatment enhanced glucose yield of HPAA-pretreated poplar to 95.5 %. • SU pretreatment saved 90 % HPAA dosage in HPAA pretreatment.