Evaluation of Transition Metal Catalysts for Biphasic Oxidative Depolymerization of Kraft Lignin

Sammanfattning

To decrease the dependency of fossil-based raw materials in society, and with that, the chemical industry, new and sustainable raw materials need to be investigated. Lignin is an abundant aromatic biopolymer, that can be used to produce, e.g. aromatic fine chemicals through depolymerization. In this master’s thesis, different homogeneous and heterogeneous catalysts were screened for oxidative depolymerization of Kraft lignin in a biphasic system. Iron, copper- and cobalt-salts with different counter ions were screened homogeneously, and iron-copper, iron-cobalt, copper-cobalt and monometallic iron catalysts on zirconia support were screened heterogeneously. Samples were analysed and products quantified using ultra-high performance liquid chromatography coupled with high resolution mass spectrometry. The most abundant identified aromatic product for most catalysts was vanillin, reaching yields of up to 1.1 wt% with iron(III)chloride as homogeneous catalyst, which is an increase of 175% compared to using no catalyst. The difference between the best performing catalysts was not significant, so it is difficult to determine the most suitable catalyst for the system. In general, iron-based catalysts seem to favour a higher selectivity for vanillin, while copper catalysts produce a more diverse product pool. Among the homogeneous catalysts, the chloride salts generally gave higher vanillin yields. When nitrate salts were screened as catalysts, 5-nitrovanillin and other nitrated aromatics were formed, indicating that the catalysts were functioning as reagents.