Study on the mechanisms and kinetics of complex's thermal decomposition getting anhydrous magnesium chloride

摘要

This paper investigated the preparation of anhydrous magnesium chloride (MgCl_2) from bischofite (MgCl_2·6H_2O) by complex thermal decomposition method. In this process, the thermal properties of complex compound MgCl2·C_6H_5NH_2·HCl·6H_2O, an intermediate to produce anhydrous MgCl_2, was studied using thermogravimetry-differential thermal analysis (TG-DTA) and simultaneous thermogravimetry-mass spectrometry (TG-MS). The results showed that the thermal decomposition process of the complex combination can be divided into four stages, of which the first two stages belong to the evaporation of crystal water in the complex while the last two ones attribute to the elimination of aniline hydrochloride (C_6H_5NH_2HCl) from the complex. The weight loss for each stage of thermal decomposition was in good agreement with the existing theory. The kinetic analysis of the thermal decomposition process was performed using Coats-Redfern method and Malek method. Results suggested that the first three stages submit to 2-dimentional phase boundary mechanism (model R_2) while the last stage rule follows 3-dimensional diffusion (D_3) kinetics. The apparent active energies of four stages are 127.4,124.8,142.3 and 329.0 kJ mol~(-1), respectively. The frequency factors arel.28 × 10~(18),7.94 × 10~(15),5.98 × 10~(16)and 4.39 × 10~(34) s~(-1), respectively. This study provides a valuable theoretical basis for industrializing the MgCl_2·C_6H_5NH_2·HCl·6H_2O decomposition process.