Low-Temperature Deoxidization of Lignin and Its Impact on Liquid Products from Pyrolysis

Abstract

In this study, low-temperature deoxidization of lignin in the temperature range of 200–390 °C as a pretreatment method had been exploited to gain high-quality pyrolysis products. Two-dimensional infrared correlation spectroscopy (2D-PCIS) was used to analyze the evolution of the functional groups of lignin in the process of low-temperature deoxidization, and the deoxidized samples were pyrolyzed by pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS). The results of 2D-PCIS showed that the decomposition of lignin was accelerated from 320 °C, and it was dominated by the elimination reaction. Notably, the aromatization reaction was intensified at 350 °C, whereas the structure of the lilac aromatic ring was more stable than the guaiac aromatic. It was also found that the alcoholic hydroxyl group was significantly removed, and because of this removal, other functional groups also underwent changes during deoxidization. The results of Py-GC/MS experiments showed that deoxidization treatment at temperatures lower than 230 °C had an insignificant effect on the pyrolysis products. However, when the deoxidization temperature was 230 °C and above, the oxygen-containing compounds in the pyrolysis liquid products (mainly phenols) decreased significantly, and when the deoxidization temperature was above 290 °C, hydrocarbons were the main compounds in the pyrolysis liquid product.