Investigation on standard molar enthalpy of combustion, specific heat capacity and thermal behavior of methionine

The standard molar enthalpy of combustion of methionine was determined to be − 6661.03 kJ mol−1 by XRY-1C microcomputer oxygen bomb calorimeter. The standard molar enthalpy of formation was calculated to be 3121.35 kJ mol−1 based on the standard molar combustion enthalpy. The thermal stability behavior of methionine was studied by the thermal gravimetric analysis. The results show that melting process of methionine was accompanied by the decomposition reaction in the temperature range of 500.15–520.15 K, displayed one-stage decomposition process. The absorb heat of methionine was obtained to be 974.34 kJ mol−1 (6530.00 J g−1) at 550.51 K by DSC-60 differential scanning calorimetry. Moreover, the specific heat capacity of methionine from 373.15 to 453.15 K in the solid state was measured, and then the relationship between the constant pressure specific heat capacity Cp and the temperature has been established. These data provide a thermodynamic basis for process development, engineering design and industrial production of methionine.