Inorganic acid-catalyzed hydrogen peroxide-acetic acid pretreatment for selective delignification of poplar

Effects of different inorganic acids as catalysts on the delignification ability of hydrogen peroxide-acetic acid (HPAA) pretreatment were unclear. Herein, the oxidizability of HCl, HBr, H₂SO₄, and H₃PO₄-catalyzed HPAA on the delignification of poplar were investigated. The ionized H⁺ from inorganic acids catalyzed the synthesis of peracetic acid and improved the oxidizability of HPAA. The anion of inorganic acids caused ineffective decomposition of peroxides and inorganic acids. After the addition of poplar, the H₂SO₄-catalyzed HPAA pretreatment exhibited the lowest pH than other inorganic acids catalyzed systems. After the catalysis by inorganic acid, HPAA removed 78.1–91.4 % poplar lignin. Compared with other inorganic acids, the H⁺ of H₂SO₄ exhibited superior retention in HPAA pretreatment of poplar. After poplar pretreated with the same initial pH value of inorganic acid-catalyzed HPAA, the H₂SO₄-catalyzed HPAA showed the strongest delignification ability of poplar. The presence of free radicals in inorganic acid-catalyzed HPAA was unnecessary for the delignification of poplar. This paper elucidated that the ionized H⁺ of inorganic acid mainly enhanced the oxidizability of HPAA for the selectively delignification of ability of HPAA pretreatment.