Ionic Liquid-Based Molecular Oxygen Oxidation of Eucalyptus Kraft Lignin to Obtain a Suite of Monomeric Aromatic By-Products

The oxidative degradation of eucalyptus kraft lignin as a function of an oxygen-enriched ionic liquid (IL) medium was investigated as part of a fundamental study to examine its capacity to degrade lignin into a suite of potentially valuable by-products relative to a standard sodium hydroxide solution (control). The variables of temperature, oxygen pressure, reaction time, and catalyst on the aromatic monomer products were controlled, whereas it was found that the yields of various aromatic monomer products were significantly improved when ionic liquid was used as the solvent instead of sodium hydroxide solution. These yields increased more substantially when a mixture of ionic liquid and sodium hydroxide was exploited as the reaction solvent. A quantity of 105.3 mg/g aromatic monomer products can be obtained at a temperature of 150°C, reaction time of two hours, and oxygen pressure of 6 MPa using CuO as the catalyst. In addition to the formation of aromatic monomer products, there were a number of other fascinating functional group and chemical linkage changes observed in the lignin macromolecule within the IL-based reaction system.