Investigation of the interaction and nitrogen conversion mechanism during lignin/phenylalanine co-pyrolysis

Abstract

Nitrogen-containing compounds become a bottleneck in the conversion of biomass pyrolysis oil into high-value chemicals and fuels, and they are easily oxidized to nitrogen oxides in the subsequent utilization process, causing serious pollution to the environment. Lignin, a biomass component, has an important influence on nitrogen migration during biomass pyrolysis. In this study, we investigated the interaction of lignin model compounds (vanillin and Syringol) with nitrogen-containing components (phenylalanine) during lignin/amino acid co-pyrolysis using tube furnace experiments, thermogravimetric infrared (TG-FTIR) experiments, and gas chromatography-mass spectrometry (Py-GC/MS), as well as the effect of lignin on the pyrolysis gas release and pyrolysis products of phenylalanine, in conjunction with quantum chemical calculation The effect of lignin on the pyrolysis of phenylalanine to styrene was explored. The experimental results showed that during the co-pyrolysis process, lignin modulators (vanillin and Syringol) dramatically reduced the temperature of the first stage of phenylalanine pyrolysis; promoted the pyrolysis oil generation and inhibited the pyrolysis gas generation; vanillin and Syringol promoted the fracture of oxygen-containing and nitrogen-containing functional groups of the side chain of phenylalanine, which resulted in a significant increase in the yields of aromatic hydrocarbons in the pyrolysis oils, with an increase of 32.07 % and 23.41 %, respectively. The simulation results showed that the hydrogen radicals generated by lignin modulators would promote the carbon ring breakage, decarboxylation and intermolecular ring-forming reaction of phenylalanine side chain to generate 1,2-diphenylethene, styrene and NH₃, and promote the nitrogen-containing carbon chain to undergo intramolecular hydrogen transfer to form HCN, which was converted into styrene pathway showing strong competitiveness.