Combined pretreatment of malic acid and kraft pulping for the production of fermentable sugars and highly active lignin.

The separation and utilization of cellulose, hemicellulose, and lignin in lignocellulosic biorefineries present significant challenges. This study proposes a pretreatment method for biomass refining by combining acid and kraft pulping. Firstly, the biomass was pretreated by malic acid, resulting in the isolation of xylo-oligosaccharides (XOS) with a yield of 86.26 % with optimized conditions of 180 °C, 1 wt% concentration, 40 min. Secondly, a mixture of 12.98 wt% NaOH and 1.043 wt% Na 2 S is employed to achieve lignin removal efficiency up to 63.42 %. Physical refinement techniques are then applied to enhance the enzyme digestion efficiency of cellulose, resulting in an increase from 55.03 % to 91.4 % for efficient cellulose conversion. The reacted samples exhibit a lignin composition rich in β-O-4 ether bonds, facilitating their high-value utilization. The results indicated that the combined pretreatment approach demonstrates high efficiency in separating cellulose, hemicellulose, and lignin while obtaining XOS, highly active lignin, and enzyme-digested substrates. Graphical abstract [Display omitted] • Towards the separation of hemicellulose, cellulose and lignin in poplar wood • The rate of XOS isolation from poplar wood biomass was 86.26 %. • Enzymatic digestibility of the substrate reached 91.04 % after pretreatment. • The combined pretreated samples were enriched with highly active lignin. [ABSTRACT FROM AUTHOR]