Xylan solubilisation from oil palm frond and sago palm bark via in-situ reductant-aided alkaline peroxide pretreatment

Black liquor (BL), a byproduct of biomass pretreatment, serves as a key medium for xylan recovery but contains inhibitory compounds that affect its purity. This study focuses on maximizing xylan solubilization in BL while minimizing inhibitor formation by evaluating different pretreatment methods and alkaline hydrogen peroxide (AHP) pretreatment with in-situ reducing agents using sodium borohydride (NaBH 4 ) and sodium dithionite (Na 2 S 2 O4) as the most effective approach for enhancing xylan solubilization from oil palm frond (OPF) and sago palm bark (SPB) into BL. The optimal conditions were identified using mixture of 2 % NH 4 OH: 1 % H 2 O 2 : 1 % Na 2 S 2 O4 for OPF and 2 % NH 4 OH: 1 % H 2 O 2 : 1 % NaBH 4 for SPB, both at 100°C for 60 minutes. Compositional analysis of pretreated OPF and SPB confirmed substantial xylan removal, reducing OPF’s xylan content from 22.0–1.9 % and SPB’s from 25.2–2.9 %. Correspondingly, black liquor analysis demonstrated high xylan solubilisation, reaching 91.4 % for OPF and 88.5 % for SPB, and the inhibitor content in BL, specifically furfural and 5-hydroxymethyl furfural (HMF) was efficiently reduced by up to 71.7 %, reinforcing the effectiveness of in-situ reducing agents in xylan solubilization. Interestingly, the efficacy of reducing agents was substrate-specific, with sodium dithionite performing best for OPF and sodium borohydride for SPB, likely due to differences in lignocellulosic composition, such as differences in lignin structure and hemicellulose linkages, which influences the effectiveness of reductive during pretreatment. The study demonstrates that in-situ reducing agents significantly enhance xylan solubilization while reducing inhibitor formation, offering a promising approach for improving biorefinery efficiency. • Inhibitors present in the black liquor from biomass pretreatment hinder efficient bioconversion. • Pretreatment with sodium borohydride and sodium dithionite effectively reduced these inhibitors. • This approach utilizes in-situ reducing agents during pretreatment, eliminating the need for additional process steps. • Black liquor analysis revealed high xylan solubilization, achieving 91.4 % for oil palm frond and 88.5 % for sago palm bark. • The inhibitor content in black liquor, particularly furfural and 5-hydroxymethylfurfural (HMF), was significantly reduced by up to 71.7 %.