Thermochemical methylation of lignin to produce high value aromatic compounds

摘要

ABSTRACTTechnical lignin, the byproduct from cellulosic ethanol production, is a potential feedstock for producing coumaric and ferulic acids. These biorenewable aromatic hydroxycinnamic acids can be upgraded to high value chemicals for the manufacture of cosmetics, flavoring agents, and sunscreens. We hypothesize that during the fast pyrolysis of lignin, aromatic acid esters can be recovered from coumaric, ferulic and other hydroxycinnamic acids using a methylation agent. In this study, technical lignin from cellulosic ethanol production was pyrolyzed in a micropyrolyzer with a methylation agent to produce gas chromatography (GC) detectable aromatic acid esters. Corn stover lignins from enzymatic hydrolysis and the organosolv processing were combined with different methylation agents to produce, identify and quantify the hydroxycinnamic acid esters. High performance liquid chromatography (HPLC) with a diode array detector (DAD) was used to separate and quantify the extracted hydroxycinnamic acids from lignin for determination of yield recoveries.To determine the actual total extractable yields of coumaric and ferulic acid in the lignin an alkaline extraction method was used. The yields on a mass basis of coumaric and ferulic acid in the enzymatic hydrolysis lignin was 5.6% and 1.9%, respectively. The yields on a mass basis of coumaric and ferulic acid in the organosolv lignin was 7.7% and 2.9%, respectively.The recovery of hydroxycinnamic acids from enzymatic hydrolysis and organosolv lignin with different loading of methylation agent were compared using a micropyrolyzer at 500°C and the pyrolysis cup method. Using tetramethylammonium hydroxide (TMAH) or tetra-methyl carbonate of pentaerythritol (PEMC) at concentrations of 1µL – 10µL produced high yields of coumaric and ferulic acid that can be recovered at concentrations up to 89% and 97%, respectively.The recovery of hydroxycinnamic acids from enzymatic hydrolysis and organosolv lignin with different loading of methylation agent were compared using a micropyrolyzer at 500°C and the micro reaction method. Using tetramethylammonium hydroxide (TMAH) or tetra-methyl carbonate of pentaerythritol (PEMC) at concentrations of 1µL – 10µL produced high yields of coumaric and ferulic acid that can be recovered at concentrations up to 97% and 90%, respectively.Overall, both techniques and methylation agents produced a significantly high concentration of biorenewable chemical intermediates from the lignin byproduct of corn stover cellulosic ethanol production. The hydroxycinnamic acids that are produced can be further upgraded into high value chemical products. Utilizing lignin valorization could provide a substantial effect on the economics of cellulosic ethanol production via precursors or intermediates of high value commodity chemicals.