Relating Dicarboxylic Acid Yield to Residual Lignin Structural Features

Abstract

This study focused on understanding the relationship between dicarboxylic acid (DCA) yields derived from lignin and the structural attributes of their solid residues and corresponding acid-soluble lignin fractions. It is a continuation of the study by the authors on DCA production from bagasse lignin via hydrothermal liquefaction. It characterized the residues derived from the use of H2O2/chalcopyrite and sodium percarbonate for DCA formation, at temperatures between 60 and 300 °C with a reaction time of 3 h. FTIR, GPC, and 2D NMR were used to unravel the functional group changes, molecular weight distribution, and lignin substructures and linkages. The DCA yield correlated well, in a linear fashion, to the aromatic to aliphatic functional group ratio (AAFGR) and the degree of aromatic condensation (DAC). Supporting evidence of lignin depolymerization and repolymerization to explain the DCA yields was provided by GPC. Interestingly, the proportion of the α-oxidized substructure S′ was found to be an indicator of the extent of lignin depolymerization, and its ratio to the S substructure was found to correlate with DCA yield at reaction temperatures up to 200 °C.

Deep Eutectic Solvent Extraction of High‐Purity Lignin from a Corn Stover Hydrolysate

“…A previous study by the authors on lignin structure employed the quantitation of FTIR data as a means of comparing the aromatic to aliphatic functional group ratio (AAFGR), as well as the degree of aromatic condensation (DAC) in lignin samples . This technique allows for a simple quantitative comparison between lignin samples, and assists in elucidating the effect of reaction condition parameters on the prevalence of lignin reactions such as side‐chain cleavage, ring‐opening, and condensation.…”

“…A detailed description of heteronuclear single quantum coherence (HSQC) NMR peak assignments and their associated functional groups and lignin substructure units (based on previous literature studies), is provided in the Supporting Information …”

Oxidative depolymerization of lignins for producing aromatics: variation of botanical origin and extraction methods

“…Several approaches, using or not catalysts, were reported in order to convert lignins into valuable chemicals and were partly reviewed 6,[8][9][10][11][12][13] : they include, hydrolysis [14][15][16][17][18][19][20] , solvolysis 2,[21][22][23][24][25][26][27][28][29] , thermal liquefaction [30][31][32][33][34][35][36] , pyrolysis [37][38][39][40][41] , hydrogenolysis [42][43][44][45][46][47][48][49][50][51][52][53][54][55] , hydrogenation 43,…”

Promising Techniques for Depolymerization of Lignin into Value‐added Chemicals

“…Since C−C bond has higher bond energy than that of β‐O‐4 linkage, which accounts for the most percentage in lignin, repolymerization makes the degradation process tougher and inevitably results in low conversion and yield and complexity of products. Unluckily, repolymerization happened very easily under high temperature, oxidation environment, industrial pulping, acidic hydrolysis, in the presence of radicals or even during extraction of lignin, via radical or carbocation mechanisms . Consequently, there emerged stabilization strategies for suppressing repolymerization during the degradation .…”

“…Small molecular acids can be generated by deeply oxidative degradation of various lignin or lignin‐derived species. From the discussion above, acids are obtained from WAO in non‐caustic solution,, H 2 O 2 oxidization,,, and strongly oxidative degradation (Fenton systems) ,,. Those processes that produce acids show many attractive advantages: (1) high yield.…”