Valorization potential of technical lignins from Norway spruce (Picea abies) via pyrolysis

Abstract

Analytical pyrolysis (Py-GC/MS) on mg-scale of Norway spruce (Picea abies)-derived kraft lignin, ethanosolv lignin, and dried lignin-rich soda-anthraquinone (AQ) black liquors was studied at 500 °C to compare the valorization potential of these materials, focusing on the type and yield of condensable pyrolysis products. Of particular interest was the relatively selective formation of guaiacol (2-methoxyphenol) from the dried soda-AQ black liquors in contrast to the formation of complex phenolic product mixtures from the pyrolysis of the kraft and ethanosolv lignins. It was shown that this finding could be attributed to differences in composition and structure as was assessed by various NMR and 2D-GC/FID analyses. From a comparison between the analytical pyrolysis results and the results of Norway spruce-derived pyrolysis oils that were produced in earlier research with a state-of-the-art kg-scale bubbling fluidized bed pyrolysis reactor, it was concluded that analytical pyrolysis is suitable to predict the pyrolysis behavior of lignin also on a larger scale. However, it was found that the prediction of reliable product yields for larger-scale pyrolysis from the semi-quantitative analytical pyrolysis yield results was less accurate, mainly due to differences in process conditions, such as heating rate and hot-vapor-residence times leading to secondary degradation reaction of the individual monomers.