Heat Capacities and Nonisothermal Thermal Decomposition Reaction Kinetics of d-Mannitol

Abstract

The low-temperature heat capacity Cp,m of d-mannitol was measured in the temperature range from (80 to 390) K by means of a fully automated adiabatic calorimeter. The dependence of heat capacity on the temperature was fitted to a polynomial equation with the least-squares method. The thermodynamic functions (HT − H298.15 K) and (ST − S298.15 K) were derived from the heat capacity data in the temperature range of (80 to 390) K with an interval of 5 K. The melting temperature, molar enthalpy, and entropy of fusion were determined to be (437.25 ± 0.12) K, (54.69 ± 1.64) kJ·mol−1, and (125.08 ± 3.75) J·K−1·mol−1 by DSC measurements. The thermal stability and nonisothermal thermal decomposition kinetics of the compound were studied by the TG-DTG technique under atmospheric pressure and flowing nitrogen gas conditions. The thermal decomposition process had one mass loss stage, and the apparent activation energy Ea was obtained to be (120.61 ± 1.85) kJ·mol−1 by the Kissinger, Friedman, and Flynn−Wall−Ozawa methods. The Malek method was used to identify the most probable kinetic model SB(m, n). The kinetics model function and the pre-exponential factor A were expressed to be: f(α) = α0.306(1 − α)0.381; ln A = 17.88, respectively.