Insights into glycine pyrolysis mechanisms: Integrated experimental and molecular dynamics/DFT simulation studies

Understanding pyrolysis pathways of nitrogen-rich biomass is a key to the pyrolytic production of value-added N-rich biochar and bio-oil or the removal of fuel-N to avoid NOX emission. Laboratory pyrolytic experiments referring to horizontal tube furnace pyrolyzer and several real-time analytic instruments, and numerical simulations involving reactive force field molecular dynamics (ReaxFF MD) and density functional theory (DFT) were integrated to explore the pyrolysis of glycine (Gly), which is the simplest amino acid or organic N-carrier in biomass. The major products, reaction pathways, and some theoretical data were obtained and compared with the previous studies to understand the Gly pyrolysis mechanisms. Dehydration of Gly to afford H2O as well as glycylglycine and diketopiperazine (DKP), and decarboxylation of Gly to produce CO2 as well as amines were the dominant reactions at the initial pyrolysis stage, and H free radical transfer was the dominant way to induce these reactions. The pyrolysis of Gly and its derivatives such as glycylglycine and DKP yielded common products such as CO2, NH3, HCN, HNCO, CO, acetic acid, and acetamide; other chemicals including cyclobutanol, propane, alanine, dimethylamine, acetonitrile, and methylamine were also observed, which was different from previous studies. These findings provided a new insight into the pyrolysis mechanisms of Gly, and also showed a great potential of the integrated experiment and simulation on such investigations.