The complete and mild-condition fractionation of woody biomass without the energy-intensive size reduction still remains a significant challenge. This study reports an innovative and scalable cellulose-centred fractionation process based on...

The development of an energy-efficient fractionation process as well as the preservation of the fractionated cellulose, hemicellulose sugars, and lignin are the key to the valorization of lignocellulose. This study presents a mild-condition fractionation process based on a recyclable and bifunctional 4-chlorobenzenesulfonic acid (4-Cl-BSA). The aqueous (e.g., 72%) 4-Cl-BSA solution near-completely fractionated unmilled poplar chips at 50–80 °C for 18–180 min and successively preserved the theoretical maximum yields and key structures of the fractionated cellulose, lignin, and hemicellulose sugars. Around 21.3–27.8% lignin was hydrotropically dissolved at a mesoscale level through accumulation by and complexation with 4-Cl-BSA and its aggregates. The solubilized lignin preserved about 24.7–50.7% of the 61% β-O-4 linkages in the native lignin and about 48.3–82% aromatic units uncondensed. About 72.2–78.7% lignin was insolubilized and quickly deposited on the surfaces of cellulose fibers. Remarkably, the deposited lignin preserved about 61.9–81.1% of the β-O-4 linkages in the native lignin and about 78.2–86.2% aromatic units uncondensed. Hemicellulose sugars and cellulose (millimeter-size, CrI: 71–75, DPv: 910–1022) had high purity and high quality. Compared to the other selected aryl sulfonic acids whether they have or do not have substituents (dichloro, bromo, hydroxyl, and methyl) and mineral acids, 4-Cl-BSA performed better in fractionating unmilled poplar chips and preserving the β-O-4 linkages and aromatic units of lignin. The results indicate that both acidity and hydrophobicity of aryl sulfonic acid greatly influence its fractionation and preservation performances.

An interpretation of solid surfaces is generated based on physical considerations and the laws of thermodynamics. Like the widely used Owens–Wendt (OW) method, the proposed method uses liquids for characterization. Each liquid provides an absolute lower bound on the surface energy with some uncertainty from measurement variations. If multiple liquids are employed, the largest lower bound is taken as the most accurate, with uncertainty due to measurement errors. The more liquids used, the more accurate is the greatest lower bound. This method links generalizations of the Good–Girifalco equation with a general thermodynamic inequality relating the three‐interfacial tensions in a three‐phase equilibrium system. The method always satisfies this inequality with better than a 65% certainty. However, the OW seldom, if ever, conforms to this inequality and even then, the degree of satisfaction is insignificant. A reconciliation of the two methods is proposed based on rescaling the OW surface energies to conform to the inequality. This enables interpretations of dispersion and polar components of the surface energy, which are thermodynamically self‐consistent. The proposed method is also capable of dealing with material exchange between liquid and solid phases, when the surface tension and contact angle of the saturated liquids can be measured.

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