Revisiting Lignocellulosic Biomass Pretreatment: Water-Based Deconstruction Using Heterogeneous Solid Acids

Abstract

Dilute acid pretreatment is a widely used strategy to enhance enzymatic digestibility of lignocellulosic biomass; however, its reliance on corrosive mineral acids limits long-term viability. Here, this classical approach is revisited by replacing conventional mineral acids with zirconium phosphate (ZrP), a water dispersible heterogeneous solid acid. Three feedstocks-sorghum, poplar, and pine-were investigated to assess pretreatment performance across varying levels of biomass recalcitrance in water at 120 to 160 °C. The ZrP effectively mimicked the hydrolytic action of dilute (mineral) acids, yielding high sugar recoveries following enzymatic saccharification, with glucose yields up to 94% for sorghum, while xylose recoveries of 80 to 90% were achieved across all feedstocks. Beyond sugar release, the solid acid facilitates subsequent lignin depolymerization and can be recovered by simple centrifugation, highlighting the operational feasibility of solid acid separation. Importantly, ZrP-derived hydrolysates supported bisabolene titers of 800 mg/L, exceeding the YPD control (500 mg/L), without any detoxification step, indicating low inhibitor carryover and high biocompatibility of the pretreatment process. Through integrating a recyclable heterogeneous solid acid into a water-based pretreatment system, this work revitalizes the dilute acid paradigm, offering a versatile and scalable approach for integrated biomass valorization.