Effect of reaction conditions on product distribution from the co-pyrolysis of α-amino acids with glucose

Abstract

The effect of reaction conditions on product distribution from the co-pyrolysis of amino acids with glucose was studied. Three different amino acids, proline, tryptophan and asparagine, were studied. Some experiments were also conducted with aspartic acid, glutamic acid and glutamine. Equimolar binary mixtures of each amino acid and glucose were pyrolyzed at 300 °C to obtain low temperature char (LTC) and low temperature tar (LTT). The LTC in each case was then pyrolyzed further at 625 °C to obtain high temperature char (HTC) and high temperature tar (HTT). In a few experiments, the LTT and HTT were also pyrolyzed at 870 °C (secondary cracking) to obtain the final tars (LTFT and HTFT, respectively) and study the formation of polycyclic aromatic compounds (PACs) via secondary reactions. Experiments were also conducted at different amino acid/glucose molar ratio or at a temperature of 200 °C. All the experiments were performed in an inert atmosphere. The extent of interaction between the amino acids and glucose was determined by comparing the observed results to that calculated from the separate pyrolyses of amino acids and glucose. At 200 °C, the co-pyrolysis led to lower LTC yields relative to the calculated yields. At 300 and 625 °C the yields of LTC and HTC were mostly higher whereas those of LTT and HTT were lower than the calculated yields, except for asparagine and aspartic acid where the observed and calculated LTC yields were comparable. Although proline formed no char in the absence of glucose, it gave a significant amount of nitrogen-containing char when co-pyrolyzed with glucose. The pyrolysis tars contained a number of nitrogenous products not observed from the pyrolysis of amino acids alone. After the secondary cracking, the product changed from mainly single-ring heterocycles to PACs and, in some cases, PAHs.