Renewable fuel additives from depolymerized lignin

Lignin is an abundant, arom. biopolymer which constitutes up to 25​% by wt. of lignocellulosic biomass. Unlike the cellulosic components of the biomass, lignin is highly resistant to chem. degrdn., 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 arom. functionality, lignin contains a large amt. of untapped chem. potential and thus there has been much interest in its depolymn. to form higher value products. The phenolic lignin monomers are structurally related to the com. antioxidant butylated hydroxytoluene (BHT) and it was therefore anticipated that depolymd. lignin could be useful as an antioxidant. Lignin depolymn. viaozonolysis in the presence of ethanol was found to produce a low conversion of oxygenated arom. species over short reaction times of up to 2 h. Over longer reaction times of 24 h, these arom. species were further broken down and a range of satd. 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 arom. compds. produced over short ozonolysis reaction times might behave as antioxidants. Model lignin depolymn. compds. 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 oxidn. tests. While 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.