Reactions of gas phase amino acids with the prevailing radicals in biomass thermal treatments

Abstract

Amino acids, N‐containing compounds, hold a significant importance in various field. Within the biomass energy sector, amino acids constitute a large fraction of the biomass's nitrogen content. As such, it is essential to comprehend their combustion chemistry; most specifically their biomolecular interactions with governing radicals in the pyrolytic and combustion media that prevail during thermal utilization of biomass. Herein, we have employed quantum chemical calculations and reaction rate theory to investigate reactions of a selected set of amino acids with H, CH3, NH2, OH, HO2, and HS radicals. Thermo‐kinetic calculations have been performed to determine the rates of hydrogen abstraction by these six radicals across all possible reaction channels for three specific amino acids: alanine, cysteine, and methionine. The investigation of other amino acids like glycine, threonine, and other models have been carried out for α‐C positions as the most probable abstractable sites. The study also examines the individual effects of different substituents (COOH, NH2, HS, and CH2) and uncovers significant insights. Notably, the presence of the COOH group introduces polar effects that counterintuitively deactivate the thermodynamically favored α‐abstraction pathway. Presented thermo‐kinetic values are anticipated to complement existing biomass kinetic models and to improve current understanding of chemical events that participate in the complex nitrogen transformation reactions in biomass.