Lignin is an abundant, aromatic biopolymer which constitutes up to 25% by weight of lignocellulosic biomass. Unlike the cellulosic components of the biomass, lignin is highly resistant to chemical degradation, and as the native polymer it is a very low value product which is routinely burnt to recover process heat. As the largest source of renewable aromatic functionality, lignin contains a large amount of untapped chemical potential and thus there has been much interest in its depolymerization to form higher value products. The phenolic lignin monomers are structurally related to the commercial antioxidant butylated hydroxytoluene (BHT) and it was therefore anticipated that depolymerized lignin could be useful as an antioxidant.Lignin depolymerization viaozonolysis in the presence of ethanol was found to produce a low conversion of oxygenated aromatic species over short reaction times of up to 2 h. Over longer reaction times of 24 h, these aromatic species were further broken down and a range of saturated esters were produced. These esters were found to be partially miscible with a range of fuels, increasing the bio-content of fossil-derived fuel without dramatically changing the fuel properties.It was suspected that the aromatic compounds produced over short ozonolysis reaction times might behave as antioxidants. Model lignin depolymerization compounds 4-methylphenol, 2-methoxy-4-methylphenol and 4-methyl-2,6-dimethoxyphenol were blended into fuels and the oxidative stability of the fuels was measured via a series of accelerated oxidation tests. Whilst 4-methylphenol was not found to significantly affect the lifetime of the fuels, both the mono and di-substituted phenols demonstrated significant antioxidant properties, with the latter performing at least as well as BHT.

Renewable fuel additives from depolymerized lignin

248th National Meeting (2014)

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