Wet oxidation of lignin model compounds and acetic acid production

Abstract

To investigate the wet oxidation (WO) pathways of acetic acid production from lignin, 2-methoxyphenol, 2,6-dimethoxyphenol, and phenol, as lignin model compounds were oxidized in a batch reactor at a temperature of 300°C, residence times of 10–60 seconds and oxygen supplies of 50–100%. Oxidation experiments using major intermediate products in WO of lignin model compounds, as reactants were also performed.Based on the intermediate products identified by GC/MS and HPLC, WO pathways of lignin model compounds are discussed. Acetic acid production by WO of lignin model compounds is also discussed. It was found that the yield of acetic acid for lignin model compounds was lower, at about 9%. The reason that lignin model compounds cannot produce a large amount of acetic acid may be contributed to the fact that the oxidation of phenols easily forms unsaturated dicarboxylic acids with 4 carbon atoms, which cannot produce a large amount of acetic acid. However, saturated dicarboxylic acids and glutaconic acid can produce a higher yield of acetic acid. Therefore, it is possible to increase the yield of acetic acid from lignin by controlling reaction pathways to increase the formation of saturated dicarboxylic acids and glutaconic acid.