Thermal degradation kinetics and structural characterization of sodium bentonite

ABSTRACT

The thermal-decomposition behavior of a sodium-bentonite sample was investigated in this study. Non-isothermal pyrolysis tests were performed through simultaneous thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis to characterize the thermal-behavior of the bentonite sample in a temperature range from ambient to 750°C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) were used to determine the changes in mineralogy, structural features and morphology of bentonite before and after pyrolysis at 750°C. Iso-conversional methods were used to obtain kinetic-parameters such as the activation energies whereas Coats-Redfern (CR) method was used to find the most probable reaction mechanisms involved on the bentonite pyrolysis. XRD analysis showed that bentonite sample was mainly composed of sodium montmorillonite and a minority of other minerals such as quartz, plagioclase, alkali feldspar, cristobalite and calcite. Structural collapse of the clay mineral due to the thermal treatment was confirmed through XRD, FT-IR and SEM. Results indicated that thermal-decomposition of bentonite is carried out in two stages: a dehydration following a diffusion-controlled kinetics with an average activation energy of 72.23 kJ/mol, and a dehydroxylation characterized by a second-order kinetics with an average activation energy of 228.28 kJ/mol.

KEYWORDS:

• Na-bentonite
• TGA-kinetics
• pyrolysis
• dehydration
• dehydroxylation

Supplemental Material

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Nomenclature

λ, wavelength of Cu Kα radiation (Å)

θ, Bragg angle (º)

d, interplanar distance (Å)

α, conversion degree

β, heating rate (°C min⁻¹ or K min⁻¹)

E_α, activation energy (kJ mol⁻¹)

A, pre-exponential factor (min⁻¹)

R, gas constant (kJ/mol K)

T, temperature (°C or K)

Acknowledgments

This work was supported by the IMP and Sectorial Fund SENER (Secretary of Energy)-CONACyT (National Council of Science and Technology in Mexico)-Hydrocarbons through the “Center of Technology for Deep Water (CTAP)” project. Guerrero-Hernández J. thanks both UNAM and CONACyT for the financial support granted during her Master of Engineering Studies. C. Chacon thanks Cátedras CONACyT for its support.

Disclosure statement

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Additional information

Notes on contributors

Luis A. Alcázar-Vara

Luis A. Alcázar V completed his PhD degree in physical chemistry of hydrocarbons at the postgraduate program from the Mexican Institute of Petroleum (IMP). He is currently a scientist researcher at the Center of Technologies for Exploration and Production working in upstream research areas such as drilling fluids, enhanced oil recovery, flow assurance, formation damage, rheology of complex fluids, etc. He is currently a member of National System of Researchers (SNI) at the Mexican National Council of Science and Technology (CONACYT).

Jacqueline Guerrero-Hernández

Jacqueline Guerrero-Hernández is a candidate to obtain a M.Eng. degree in petroleum engineering at the postgraduate program from the National Autonomous University of Mexico (UNAM).

Cecilia Chacon

Cecilia Chacón completed her PhD degree in Advanced Technology at the Research Center in Applied Science and Advanced Technology (CICATA) from the National Polytechnic Institute (IPN). She is currently a scientist researcher (Cátedras-CONACYT program) at the Center of Technologies for Exploration and Production.

Ignacio R. Cortés-Monroy

Ignacio R. Cortés-Monroy completed his M.Eng degree in chemical engineering at the postgraduate program from the National Polytechnic Institute (IPN). He is currently project leader in drilling fluids and the ahead of the Laboratory of Drilling, Completion Fluids and Cementing of Wells at the Center of Technologies for Exploration and Production.