AbstractsEngineering

Lignin is the second most abundant biopolymer available in nature after cellulose. Unfortunately, it is often seen as a hindrance to cellulose isolation for cellulosic ethanol production and paper processing instead of a readily available resource for producing high-value chemicals with an aromatic ring in their structure. Many specialty chemicals can be made from wet aerobic oxidation (WAO) of lignin including the valuable aromatic aldehydes vanillin (3-methoxy-4-hydroxybenzaldehyde) and syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde). Lignin is a heterogeneous polymer which varies in its monomer ratios from one plant species to another and therefore will produce different amounts of aldehydes depending on the nature of the feed that is used in the reaction. Previous research has shown sugar cane bagasse to produce vanillin and syringaldehyde during wet aerobic oxidation and increased yields using a Pd/?-Al₂O₃ catalyst. However, the production of the most economically valuable compound, syringaldehyde, could be increased by using a different lignin feedstock. Corn stover lignin has more syringyl units than sugar cane bagasse and hypothetically should produce more syringaldehyde. Here, we use lignin from corn stover and report different reactivity trends than those for lignin from sugar cane bagasse. To better understand these findings, we examined the composition of corn stover lignin and the influence of wet aerobic oxidation conditions, both in the presence and absence of a heterogeneous catalyst, in order to understand the impact of these parameters on the reactivity of lignin transformation to aromatic aldehydes. In this study, thermogravimetric analysis (TGA) in air was performed on washed lignin feedstock to identify he percentages of lignin, celluloses and ash in the lignin. An EDS study (energy dispersive x-ray spectroscopy) of lignin ash confirmed the presence of Fe, known to be catalytically active in catalytic wet aerobic oxidation (CWAO). To confirm Fe’s catalytic activity, Various amounts of Fe(III) nitrate were impregnated onto the lignin feed stock and used in CWAO to determine how iron concentration affected reaction rates and selectivity of aldehydes. The resulting aldehydes were analyzed by GCMS and residual lignin was quantified by TGA in air. The role of pH was also examined to distinguish the roles of dioxygen and hydroxyl ions in CWAO of lignin. A basic economic analysis was used to determine if using wet aerobic oxidation to produce high-value aldehydes is viable at an industrial level.