The pyrolysis chemistry of a β-O-4 type oligomeric lignin model compound

Abstract

The pyrolysis behavior of a β-O-4 type oligomeric lignin model compound is studied at a temperature range from 250 °C to 550 °C. Thermogravimetric analysis (TGA) indicates the model compound has three distinct thermal decompositions peaks when a slow temperature ramp is applied while only one decomposition peak is observed when a higher temperature ramp is used. The pyrolysis behavior of this model compound is similar to that of lignin prepared by enzymatic hydrolysis of Maplewood. ¹H-NMR shows that the β-O-4 linkage thermally decomposes at a temperature between 250 °C and 350 °C with the formation of solid products at 350 °C. This solid product undergoes transformation to a polyaromatic from 350 °C to 550 °C. Around twenty five volatile compounds are quantified by pyroprobe-GC-MS with vanillin and 2-methoxy-4-methyl phenol being the most abundant monomeric products. A free radical reaction pathway is proposed to explain the product chemistry for pyrolysis of the lignin model compound. Char is most likely formed by random repolymerization of the radicals.