Enhancement of lignin removal from pre-hydrolysis liquor for saccharide recovery via horseradish peroxidase treatment in the presence of Ca2

Abstract

The removal of lignin is important to the recovery of saccharides from the pre-hydrolysis liquor (PHL) in kraft-based dissolved pulp production. A one-step process for lignin removal from PHL via treatment with horseradish peroxidase (HRP) in the presence of Ca²⁺ was proposed, and its principle was studied. The results demonstrated synergy between HRP and Ca²⁺ in lignin removal from PHL, whereas NH₄⁺ had little effect on lignin removal. HRP treatment in the presence of 60 mmol/L of Ca²⁺ resulted in a lignin removal of 64.8% accompanied by a saccharide loss of 14.2%. HRP catalyzed both the polymerization and depolymerization of the lignin in the PHL. The HRP-catalyzed lignin polymerization rendered some lignin insoluble enabling it to be directly removed. The HRP-catalyzed depolymerization of lignin decreased its molecular weight with an evident increase in its carboxyl content. The insoluble complexes formed between the lignin with carboxyl and the Ca²⁺ facilitated the removal of the depolymerized lignin.

Keywords: Ca(2+); Horseradish peroxidase; Lignin; Pre-hydrolysis liquor; Saccharide.