Solvolytic Liquefaction of Bark: Understanding the Role of Polyhydric Alcohols and Organic Solvents on Polyol Characteristics

Abstract

Bark was liquefied in polyhydric alcohols of various functionality, equivalent weight, and hydroxyl type, and organic solvents of varying polarity to determine how these features impact liquefaction behavior and polyol characteristics. It was found that the liquefaction yield was highly tunable with the use of polyhydric alcohols with primary hydroxyl groups, with low equivalent weight alcohols providing the highest liquefaction yield (59.3%). This showed that the highly polar hydroxyls (primary) and short chains created a highly protic solvent that improved conversion and protected the biopolymers from degradation. This was corroborated by 1H NMR analysis that indicated a greater amount of sugar degradation products were observed when polyhydric alcohols with secondary hydroxyl groups were used. Regarding organic solvents, ketonic solvents showed the greatest increase in the liquefaction yield. The composition and carbon content analysis of the residues suggested that the highly polar carbonyl group of ketonic solvents like acetyl acetone and cyclohexanone may have hindered condensation side reactions. These results have shown that selection of polyhydric alcohols and organic cosolvents can be quite impactful on the liquefaction yield and the polyol characteristics.