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

Biomass pyrolysis has the potential to be transformed into valuable chemicals and fuels. Nitrogenous chemicals exert a substantial influence on the quality of bio-oil. Studying the impact of lignin on the transformation of nitrogen-containing elements in biomass during biomass pyrolysis is crucial for achieving efficient and effective utilization of biomass resources. In this study, tube furnace experiments, thermogravimetric infrared experiments (TG-FTIR), and gas chromatography-mass spectrometry (Py-GC/MS) were used to investigate the interactions of typical lignins (vanillin and syringol), nitrogenous components (glutamic acid), and the effect of lignin on the pyrolysis gas release of glutamic acid and the pyrolysis products during the co-pyrolysis process. In addition, the impact of lignin on the effect of pyrrolidone formation from glutamic acid was investigated in this study in conjunction with quantum chemical calculations. The experimental findings demonstrated that the co-pyrolysis of lignin and glutamic acid resulted in a reduction in the pyrolysis temperature. This reduction facilitated the release of HCN, NH₃, and CO₂ while notably impeding the formation of nitrogen-containing compounds in the oil. The nitrogen concentration in the pyrolysis oil declined from 97 % to a range of 51.06–79.63 %, and the inhibitory impact decreased as the pyrolysis temperature increased. At an elevated pyrolysis temperature of 800 °C, lignin facilitated the decarboxylation process of glutamic acid, resulting in an increased production of pyrrolidone.Simulation results demonstrated that the lowest energy barrier paths were the dehydration condensation process and the Maillard reaction involving glutamic acid and lignin and their pyrolysis intermediates, with a particular competitive connection between the two pathways. The results explained the interaction mechanism between the two pyrolysis products and provided a fundamental theoretical basis for nitrogen conversion in biomass pyrolysis.