Pyrazine Formation from Saccharides and Alanine under Hydrothermal Conditions

Abstract

The reaction products, mechanisms, and kinetics of alanine reacting with saccharides (specifically cellobiose and glucose) under hydrothermal conditions (220–280 °C; 0.5–3 s) have been studied to understand the formation of nitrogen species in biofuels. The nitrogenous species found in the product mixture, including ammonia, ethylamine, and pyrazines, account for 50 to 75% of the total nitrogen balance. The carbonaceous products in the mixture are fructose, glyceraldehyde, dihydroxyacetone, formic acid, acetic acid, and furans. Our kinetic analysis shows that the nature of saccharides and amino acids plays an important role in the Maillard reaction rate. The Maillard reaction involving saccharides and amino acids with larger structures (such as cellobiose and alanine), proceeds more slowly than reactions involving simpler molecules (such as glucose and ammonium). For instance, at 280 °C, we deduce the rate constants of cellobiose–alanine and glucose–alanine = 0.011 and 0.035 s^–1 mM^–1, respectively. We proposed that when cellobiose and alanine are subjected to hydrothermal conditions, the primary pathway for pyrazine formation occurs as cellobiose decomposes into glucose, which then reacts with alanine following the Maillard reaction scheme.