Thermal degradation of calcium lactate pentahydrate using TGA/FTIR/MS: thermal kinetic and thermodynamics studies

Abstract

ABSTRACT The objective of this study is to investigate the thermal degradation kinetics and thermodynamics of the calcium lactate pentahydrate (CLP) crystals by means of a thermogravimetric analyzer (TGA) at four different heating rates from 25°C to 1000°C in N2 atmosphere. First, the CLP crystals were precipitated at pH 6 and 25°C in a batch-type crystallizer and the obtained crystals were characterised by X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The XRD result showed that the calcium l-lactate pentahydrate (L-CLP) was the only crystalline phase produced. Then, the activation energy and pre-exponential factor of thermal degradation were determined based on the Coats–Redfern, Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink models. The degradation reaction order was determined as 1.5 by Coats-Redfern model. The average activation energy of the CLP was 34.7, 33.0, and 33.3 kJ/mol for the FWO, KAS, and Starink models, respectively. Thermodynamic parameters as changes in enthalpy, entropy and Gibbs free energy were calculated depending on the conversion degree. Finally, TGA in combination with FTIR and mass spectrometer (MS) was utilised to detect the evolved gases during the degradation of CLP. H2O and CO2 were identified as the main evolved products.