Mild-Condition Fractionation of Woody Biomass and Tandem Preservation of Lignin and Carbohydrates

Date of Award

8-2022

Degree Name

Doctor of Philosophy

Department

Chemical and Paper Engineering

First Advisor

Qiang Yang, Ph.D.

Second Advisor

Mert Atilhan, Ph.D.

Third Advisor

Chang Geun Yoo, Ph.D.

Abstract

Various fractionation processes like kraft, sulfite, and organosolv, usually need to be carried out in expensive reactors due to high temperatures (e.g., 160-260 °C) and high pressures (e.g., 5-50 atm). During fractionation, conventional chemicals such as mineral acids (e.g., sulfonic acid and hydrochloric acid), aliphatic organic acids (e.g., formic acid and oxalic acid) and alkalis (e.g., sodium hydroxide and potassium hydroxide) are typically used as catalysts, which could cause structural alterations or even losses to the fractionated components. Recently, aromatic sulfonic acids are expected to in situ solubilize the fractionated lignin through the pronounced hydrotropic effect during fractionation, besides acting as the catalysts for fractionation. Until now, benzenesulfonic acid (BSA) and p-toluenesulfonic acid (p-TsOH) have been widely used to fractionate various milled lignocelluloses at mild conditions (e.g., temperature ≤ 90 °C, time ≤ 3 h, atm). While they are generally ineffective to unmilled lignocelluloses at mild conditions. Phenol-4-sulfonic acid (PSA) and 4-chlorobenzenesulfonic acid (4-Cl-BSA) can near-completely fractionate unmilled wood chips at mild conditions (e.g., 50-80 °C, 0.5-3 h, atm) and well preserve the structures and yields of cellulose and hemicellulose sugar. However, the fractionated lignin is either highly condensed or/and has a low content of β-O-4, which makes it challenge to be further upgraded into high-value aromatics.

To respond to these challenges, this study proposed innovative bifunctional aldehyde sulfonic acids to achieve the mild-condition fractionation of woody biomass (e.g., poplar and aspen chips) and the tandem preservation of the fractionated cellulose, hemicellulose sugars, and lignin. Functionally, the sulfonic acid group can act as a catalyst to selectively depolymerize lignin and hemicellulose; and the aldehyde group can reversibly react with the diol groups of lignin, hemicellulose sugar and cellulose. It is thus expected that the fractionated lignin would be less condensed (or even uncondensed) and water-soluble due to the introduced aldehyde sulfonic acid. The reversibility of the reaction between the aldehyde group and the diol group allows to separate lignin, hemicellulose sugar, and cellulose from the introduced aldehyde sulfonic acid.

First, to verify the expected reaction between aldehyde sulfonic acid and lignin, model study was conducted to see if aldehyde sulfonic sodium salt reacts and modifies lignin to produce water-soluble lignin. Second, aldehyde sulfonic acid sodium salt coupled with phenol-4-sulfonic acid (PSA) was applied to woody biomass to study the preservation performance of aldehyde sulfonic acid sodium salt during fractionation. Third, several aldehyde sulfonic acids with varied structures were developed and tested to achieve the mild-condition fractionation of woody biomass and the tandem preservation of the fractionated lignin and carbohydrates. Their performances in fractionating wood chips and preserving the aromatic structure and β-O-4 linkage of lignin were systematically evaluated. Optimal fractionation conditions were identified for aldehyde sulfonic acid by investigating the effects of experimental variables (temperature, time, acid concentration, etc.). The obtained water-soluble lignin was evaluated as surfactant. The enzymatic saccharification efficiency of the fractionated cellulose and the recoverability and reusability of the spent aldehyde sulfonic acid were evaluated as well.

Access Setting

Dissertation-Open Access

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