Fundamental insight into pyrolysis and oxidation process of ferric(III) stearate

Abstract

Recently, metal organic complexes have attracted a lot of attention as oil-dispersed catalysts for in-situ combustion and upgrading of heavy oil. As a relatively new topic, their catalytic mechanism has not been clearly understood. The pyrolysis and oxidation process of metal organic complexes is very important for their catalytic function. In this work, we investigated the pyrolysis and oxidation process of ferric(III) stearate by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Mössbauer spectroscopy analysis. The results indicated that the pyrolysis and oxidation of ferric(III) stearate is a multistage process. Isothermal treatments experiments show that ferric(III) stearate begins to decompose at about 200 °C and produce ferrous(II) stearate. From 200 to 300 °C, there are three processes that may occur simultaneously: ferric(III) stearate → ferrous(II) stearate; ferrous(II) stearate → Fe3O4; and ferric(III) stearate → Fe3O4. At 300–350 °C, iron(II) oxide (FeO) is formed with a complete decomposition of ferric(III) stearate. A further heating up to 500 °C leads to the oxidation of FeO to Fe3O4, and Fe3O4 is the final solid-state product. The degradation kinetics of ferric(III) stearate were analyzed by both isoconversional model and reaction-order model. For reaction-order model, five contributions with the activation energy values in the range of 110–250 kJ/mol were identified and compared with isothermal experiments results. The findings in this work are of great value for understanding the catalytic mechanism of ferric(III) stearate as oil-dispersed catalysts for in-situ catalytic upgrading of heavy oil as well as in-situ combustion for heavy oil recovery.