Overcoming Biomass Recalcitrance Heterogeneity Using a Surfactant-Based CTAB/LA/Cu²⁺ Ternary Pretreatment Mixture for...

The natural structural barriers and resistance of different biomass types are major obstacles to broadly applicable high-efficiency biorefining. This study employed a CTAB/LA/Cu²⁺ ternary pretreatment mixture composed of cetyltrimethylammonium bromide (CTAB), lactic acid (LA), and copper chloride (CuCl₂, as the Cu²⁺ source) at a molar ratio of 1:4:0.012 to pretreat five lignocellulosic feedstocks: agricultural residues (corn stover, CS; sorghum stover, SS), processing by-products (soybean hulls, SH), and forestry hardwoods (maple wood, MW; poplar debris, PD). Under the selected common pretreatment condition of 140 °C for 60 min, the ternary mixture exhibited feedstock-dependent fractionation, with the highest xylan removal of 64.8% observed for MW and the highest lignin removal of 74.2% observed for CS, while increasing the subsequent enzymatic hydrolysis efficiency by 3.0-7.4-fold across the five feedstocks. In addition, total oligomeric xylose and furfural were detected in the crude pretreatment liquors, with maximum concentrations of 5.6 g/L XOSs and 2.8 g/L furfural were detected in the crude pretreatment liquors. These measurements indicate the formation of hemicellulose-derived soluble products but do not represent isolated product yields or purities. Multi-scale characterization using SEM, XRD, and FT-IR clearly indicated the evolution from surface delamination to internal structural collapse of the substrates. Furthermore, based on the hemicellulose models of the five biomass types, qualitative non-covalent interaction patterns between representative hemicellulose oligomers and the pretreatment-mixture components were examined using molecular modeling and IGMH visualization. This study provides a key theoretical paradigm and potentially foundational technical demonstration for the integrated biorefining of multi-source biomass.