Product compositions from pyrolysis of some aliphatic α-amino acids

Abstract

The pyrolysis of aliphatic α-amino acids, glutamine, glutamic and aspartic acids, and formation of heterocyclic and polycyclic aromatic hydrocarbons ( N-PACs and PAHs) were studied. Each amino acid was first pyrolyzed at 300 °C to obtain a low-temperature tar (LTT) and a low-temperature char (LTC). The LTC was then pyrolyzed at 625 °C to obtain the corresponding high-temperature tar (HTT) and high-temperature char (HTC). The tars were separately subjected, in some cases, to temperatures in the range 700–870 °C to study secondary reactions. Oligomers of aspartic acid and glutamic acid were also pyrolyzed. The tars were analyzed by gas chromatography/mass spectrometry. Glutamic acid and glutamine underwent significant decomposition to volatile products at 300 °C but aspartic acid required higher temperature. The heterocyclic compounds were primarily single-ring compounds comprised of five- or six-member heterocycles in the absence of secondary reactions, and up to four rings after the secondary pyrolysis. The PACs included nitriles from glutamine and glutamic acid and PAHs from aspartic acid. For aspartic acid, the results from oligomers were similar to those from the monomer, whereas the results from the glutamic acid oligomer were slightly different from glutamic acid. All three acids appeared to break down to smaller “building blocks” and then pyrosynthesize the N-PACs and PAHs.