The Fractionation of Woody Biomass with Bifunctional Aryl Sulfonic Acids at Mild Conditions

Date of Award


Degree Name

Doctor of Philosophy


Chemical and Paper Engineering

First Advisor

Qiang Yang, Ph.D.

Second Advisor

Paul D. Fleming, Ph.D.

Third Advisor

Ruoxi Ma, Ph.D.


Aryl sulfonic acids, fractionation, mild conditions, woody biomass


Fractionation of lignocellulose is a fundamental step in the valorization of cellulose, hemicelluloses, and lignin to produce various sustainable fuels, materials, and chemicals. Over the years, most fractionation processes are cellulose centered or lignin-first. However, regardless of the fractionation strategy, the previous reported fractionation processes either need high temperature and high pressure or intensive size reduction of lignocellulose prior to the process. Therefore, there is a need to develop low energy and rapid delignification with simplistic recovery of chemicals for advanced utilization of renewable and biodegradable lignocelluloses for the future biobased economy.

To address this need, an innovative and scalable cellulose-cantered fractionation process is developed based on the bifunctional, recyclable, inexpensive and lignin-derivable phenol-4-sulfonic acid (PSA). The concentrated aqueous PSA solution can near completely fractionate the centimeter-sized poplar chips into high-quality cellulose fibers, fermentable hemicellulose sugars and lignin fragments in theoretical maximum yields at mild conditions (50-80 °C, 0.5-3h, atm). During fractionation, PSA acts as not only a selective catalyst to depolymerize hemicellulose and lignin but also a hydrotropic solvent to effectively solubilize lignin fragments. The phenolic hydroxyl group in PSA plays the key role in the interaction between PSA and lignin, which presumably facilitates the depolymerization of lignin and fractionation of poplar. In addition to depolymerize lignin, PSA can react with lignin fragments through both the benzene ring and the phenolic hydroxyl group. PSA is adaptable to fractionate other centimeter-sized woody biomasses.

Due to the electron-withdrawing chloro group, 4-chlorobenzenesulfonic acid (4-Cl-BSA) is a stronger acid than PSA, which can easier realize the mild-temperature fractionation of lignocellulose. Given the hydrophobic nature of the chloro group, 4-Cl-BSA trends to easier aggregate in an aqueous environment than PSA does. Owing to the limited mobility, the formed 4-Cl-BSA aggregate might not aggressively approach and not cause severe structural alterations to the deposited lignin particle on the surface of cellulose. Thus, 4-Cl-BSA is expected to perform better in fractionating lignocellulose and especially preserving the fractionated lignin than PSA does. The concentrated aqueous 4-Cl-BSA solution can near-completely fractionate unmilled poplar chips at mild temperatures and preserve key structural properties of cellulose and lignin with the theoretical-maximum yields. Cellulose is effectively preserved without severe depolymerization/decrystallization. Hemicellulose sugars are generated without unwanted dehydration. Lignin is partially solubilized through the formation of the 4-Cl-BSA aggregate/lignin temporary complex and accumulated by unaggregated 4-Cl-BSA due to its hydrophobic effect. The solubilized lignin is physically segregated from the hydrated proton, and its β-O-4 linkage and aromatic unit are preserved accordingly. The preservation of β-O-4 linkage and aromatic unit of the deposited lignin are explained by its coexistence with the adjacent 4-Cl-BSA aggregate. The deposited lignin is better preserved compared with the solubilized lignin.

The acidity of the aqueous aryl sulfonic acid solution directly affects the fractionation performance, while the hydrophobicity influences the fractionation, solubilization and preservation performances.

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