Experimental and ReaxFF molecular dynamic study on pyrolysis of phenylalanine

Abstract

Amino acids are building blocks of protein, which is an important constituent in biomass such as algae, sewage sludge, animal manure, and food waste. Phenylalanine (Phe) is the most abundant amino acid in the amino acids with the benzene group. The pyrolysis mechanism of phenylalanine through experimental study and Reactive Force Field (ReaxFF) molecular dynamic (MD) was studied. Some gaseous products were found in both experiments and simulations, including inorganic compounds such as H2O, CO2, NH3, CO as well as organic compounds such as phenethylamine and toluene. The peak concentrations of these inorganics and organics were observed at 305 °C during the experiments, while the numbers of most of these inorganics peaked within only several picoseconds in the pyrolysis simulations, except that CO at 800 K and 1000 K increased gradually. By comparing with Phe pyrolysis mechanisms from previous studies, major Phe pyrolysis mechanisms such as decarboxylation, dehydration, and deamination as well as the concerted rupturing of CC bonds were verified, and several new pathways were identified: (1) dimerization of Phe to produce diketopiperazines (DKPs), (2) dimerization of phenethylamine to produce α-benzylphenethylamine, (3) deamination of Phe to cinnamic acid, and (4) dimerization of cinnamic acid or trans-cinnamic acid to 2-phenethyl-β-phenylpropionate or 3-phenylpropanoic anhydride.