Studying the thermal conversion of acetone lignin in supercritical butanol in the presence of NiCuMo/SiO2 catalysts

Abstract

Existing and emerging technologies for the chemical processing of wood are mainly aimed at transforming its cellulose component into target products. In these processes, lignin is produced on a large scale as a waste product, but there are no advanced ways of processing it. This work investigates the effect NiCuМо/SiO₂ catalysts have on the thermal transformation of acetone lignin in supercritical butanol at temperatures of 280, 300, and 350°C. The resulting liquid products are studied via gas–liquid chromatography mass spectrometry, and 13С NMR spectroscopy. It is found that butanol undergoes almost no thermochemical conversions at temperatures below 300°C. Catalysts raise its level of conversion to 36–40 wt %. Under the effect of NiCuМо/SiO₂ catalysts, the yield of hexane-soluble products of acetone lignin thermal conversion at 300°C increases by a factor of 2.4, while the yield of solid residue falls by approximately a factor of 3.3. Catalysts reduce the relative content of methoxyphenols in hexane-soluble products: the content of syringol in particular falls by a factor of 14. According to ¹³С NMR spectroscopy, the catalytic transformation of acetone lignin to liquid acetone-soluble products is accompanied by the breaking of β–О–4 chemical bonds between the structural fragments of lignin and a reduction in the content of methoxyl groups, primarily in the syringyl structural units of the resulting products.