An experimental and theoretical study of pyrrolidine pyrolysis at low pressure

Pyrrolidine serves as a model substance for a series of saturated nitrogenated heterocycles in plants, including certain amino acids such as proline and hydroxyproline. Thus the pyrolysis of this compound was investigated regarding the increasing interest on biofuels. The pyrolysis of pyrrolidine diluted with 95% argon was studied in a flow reactor at 40 mbar over the temperature range from 950 to 1450 K. Isomer-specific assignment and quantification was performed using molecular-beam mass spectrometry and ionization with tunable synchrotron vacuum ultraviolet radiation. The prominent decomposition pathways were analyzed based on the quantified mole fractions of pyrolysis species. Computations including an ab initio calculation and kinetic modeling for the primary fuel decomposition were used to refine the analysis and reveal the combustion chemistry of this saturated heterocyclic compound. Based on the theoretical calculation, a new pathway for the isomerization reaction pyrrolidine → CH₂=CHCH₂CH₂NH₂ via a diradical intermediate was proposed. The rate constant calculations showed that this channel has a large contribution to pyrrolidine pyrolysis.