Reaction Kinetics of Amino Acid Decomposition in High-Temperature and High-Pressure Water

Abstract

Decomposition behavior of five selected amino acids in high-temperature and high-pressure water was studied using a continuous-flow tubular reactor. The reaction was carried out in the temperature range of 200−340 °C at a pressure of 20 MPa. Alanine and its derivatives leucine, phenylalanine, serine, and aspartic acid were used as model amino acids. The effect of temperature on reaction products, pathway, and rate was determined as a function of reaction time. Alanine decomposed into lactic acid and pyruvic acid, then finally mineralized to carbon dioxide with an activation energy of 154 [kJ/mol] at 20 MPa. The degradation rate decreased in the following order: aspartic acid, serine, phenylalanine, leucine, and alanine. The general reaction network of amino acids under hydrothermal conditions takes two main paths: deamination to produce ammonia and organic acids, and decarboxylation to produce carbonic acid and amines. Deamination was the predominant reaction in the decomposition of aspartic acid, an acidic amino acid. Production of glycine and alanine from serine, an oxy amino acid, was also observed.

An investigation of reaction pathways of hydrothermal liquefaction using Chlorella pyrenoidosa and Spirulina platensis

“…The two reactions occurred simultaneously and the competition between the two reactions exists under hydrothermal conditions. Sato et al [46] investigated the characteristics of HTL of five types of amino acids. It was reported that the ratio of decarboxylation/ deamination was affected by the type of amino acid.…”

Hydrothermal Degradation of Fats, Carbohydrates and Proteins in Sunflower Seeds after Treatment with Subcritical Water

“…Already at 160 °C, the content of total amino acids and amines starts to increase with time very slowly, whereas at 190 °C and higher temperatures, this increase becomes quite drastic. At 240 °C, a decrease in amino acids and amine content can be noticed, which probably indicates the formation of other amino compounds, such as ammonia 4 . Because ammonia is a gas at room temperature, it was probably removed in the solvent separation step.…”

“…has been found to be quite useful, especially in waste and biomass processing technologies. Nevertheless, for food processing, these degradation reactions can have a negative effect on the foods structure itself, resulting in an altered structure with lower quality or even formation of toxic compounds 3,4 . It is therefore important, that these hydrothermally induced reactions be studied in more detail in order to know how and when they occur.…”

Gasification Characteristics of Alanine in Supercritical Water

“…A corresponding reduction in carbon monoxide yield supports this idea. Considering that amino groups can produce ammonia or amine molecules, as was observed by Sato et al 39) , the alkalinity of the liquid should also increase with feedstock concentration. This alkali might have functioned as the catalyst for the water gas shift reaction.…”

“…However, Sato et al 39) have analyzed the products from alanine decomposition in high pressure and high temperature condition, and detected ammonia and ethyl amine as nitrogen containing compounds. This behavior of nitrogen will be our next target.…”