Can Reductive Catalytic Fractionation Biorefinery Be a Pathway for Paper-Making Pulp?

Papermaking is traditionally dominated by the kraft process, which produces high-quality fibers while most dissolved lignin is recovered in black liquor and used for chemical recovery that also generates process energy. Reductive catalytic fractionation (RCF), a lignin-first biorefinery strategy, selectively stabilizes high-value lignin while retaining a cellulose-rich pulp. Yet, the potential of the RCF-derived pulp for pulp and paper applications remains underexplored. In this work, RCF of industrial spruce wood chips is evaluated as a pathway to papermaking-grade fibers, with systematic investigation of NaOH concentration (0.2−0.5 M) and solvent effects on delignification, pulp yield, fiber morphology, and mechanical performance. Alkaline-RCF enhanced delignification and fiber liberation while preserving fiber integrity, producing long fibers with low fine content. Aqueous ethylene glycol delivered optimal performance, likely owing to its strong hydrogen-bond-donating capability. Pulp obtained at 0.3−0.4 M NaOH, for instance, exhibited low kappa numbers (20−21), extended fiber lengths (2743−2870 μm), and high tensile strength (28.2−31.9 Nm/g), comparable to unbleached kraft pulp, whereas higher alkali loadings diminished yield and strength. The resulting alkaline RCF pulp also displayed higher brightness (27.2−36.4%) than kraft pulp, indicating reduced bleaching demand. Importantly, this route simultaneously affords lignin oil with a relatively low molecular weight (Mn = 1097 g/mol, Đ = 1.79) and high average-OH functionality (AF OH = 5.3), positioning alkaline RCF as a compelling, integrated biorefinery platform for sustainable pulp and paper production.