The influence of alkali and alkaline earth metals on char and volatile aromatics from fast pyrolysis of lignin

The effect of alkali and alkaline earth metals (AAEM) on fast pyrolysis of polysaccharides has been well documented. This paper examines the effect of AAEM on fast pyrolysis of lignin, which has not been as thoroughly investigated. Acetates of several metals were infused into organosolv cornstover lignin at a concentration of 1.0 mmol AAEM cation per gram lignin followed by pyrolysis at 300–800 °C. One of the most notable effects was an increase in the yield of char with alkali metals producing more char than alkaline earth metals. Char yield was correlated to the electropositivity of the infused metal cations. Alkali metals increased the overall yield of volatile aromatic compounds while alkaline earth metals had the opposite effect. The infusion of AAEMs into lignin led to an increase in methanol and a decrease in alkenyl side chains on the aromatic products. Methanol is hypothesized to result from cleavage of β-carbons from the 3‐hydroxyprop-1-enyl side chains of lignin linkages while the alkenyl side chains are hypothesized to result from cleavage of γ-carbons. Therefore, alkali metals appear to catalyze cleavage of linkages in the lignin structure.