Effects of temperature and atmosphere on the formation of oligomers during the pyrolysis of lignin

Abstract

Here the effects of pyrolysis temperatures and atmospheres on content and characteristics of the oligomer-rich fractions obtained after sequential extraction of alkali lignin (AL)-derived pyrolysis oil (PO) were investigated to obtain effective regulation pathways for the reduction of the oligomers content in PO. The results showed that the content of oligomers and main monophenols produced by AL under a pyrolysis temperature of 600 °C was relatively low and high, respectively. Additionally, the functional group strength of oligomer-rich fractions was affected to a lesser extent by pyrolysis temperature. By contrast, the nitrogen and argon atmosphere exerted a slightly different effect on the composition and characteristics of oligomer-rich fractions. However, in comparison with argon, the presence of a certain amount of hydrogen (H2/Ar = 1:9, v/v) promoted the preferential hydrogenation of unsaturated bonds during AL pyrolysis, and was beneficial to reduce the content of oligomers and enhance the yield of monophenols by inhibiting the occurrence of secondary reactions. In view of these findings, an effective regulation pathway featuring a pyrolysis temperature of 600 °C and the presence of a certain amount of hydrogen is recommended for reducing the content of oligomers and enhancing the content of monophenols.