Kinetic and thermodynamic evaluation of almond shells pyrolytic behavior using Coats–Redfern and pyrolysis product distribution model

ABSTRACT

Rigid environmental regulations and the energy crisis are pursuing researchers to investigate eco-friendly and more energy-generating alternatives to conventional resources. Biomass has the required potential and is drawing keen attention, especially in the field of energy. This work includes the thermal decomposition of almond shells under pyrolysis (N₂) conditions in a thermogravimetric analyzer (TGA) and estimated pyrolysis product gas composition and thermo-kinetic parameters. Pyrolysis experiments were conducted at heating rates of 10°C/min, 20°C/min, and 30°C/min. Using 11 reaction models, the Coats–Redfern method was applied to determine kinetic and thermodynamic parameters. The pyrolysis product gas composition was estimated using correlations based on elemental composition and pyrolysis temperature. Thermal decomposition mainly occurred in the temperature range 150–550°C with a peak temperature of 292°C, 310°C, and 321°C for the three heating rates, i.e. 10°C/min, 20°C/min, and 30°C/min, respectively, and 99.40% total weight loss. High regression coefficients (R²) in the range of 0.90–0.99 were obtained for the Coats–Redfern models. High mean relative reactivity (0.04%min⁻¹°C⁻¹) and low activation energies showed a high tendency to degrade thermally. The overall activation energy Eα range for almond shell was 2–84 kJ/mol at all heating rates. The pyrolysis gas composition showed good agreement with the experimental results of similar biomass.

Graphical Abstract

KEYWORDS:

• Almond shell
• pyrolysis
• reactivity analysis
• kinetic analysis
• thermodynamic analysis
• pyrolysis products

Highlights

• Thermal and pyrolysis gas analysis of almond shells has been performed.

• Characterization shows low ash content, high volatility, and high HHV.

• Reactivity analysis gives high Rm and PF.

• Eα decreases at elevated temperature

• Pyrolysis gas analysis shows an increase in CO, H_2, and a decrease in CO₂ in the range 400°C–700°C.

List of Abbreviations

TGA	=	Thermogravimetric analysis
$\mathit{E\alpha }$	=	Activation Energy
A	=	Pre-exponential factor
$\mathrm{\Delta }\mathit{H}$	=	Change in enthalpy
$\mathrm{\Delta }\mathit{G}$	=	Change in Gibbs free energy
$\mathrm{\Delta }\mathit{S}$	=	Change in Entropy
HHV	=	High heating value
$\mathit{\alpha }$	=	Degree of conversion
$\mathit{g}\left(\mathit{\alpha }\right)$	=	Function related to reaction mechanism
${\mathit{R}}_{\mathit{m}}$	=	Mean reactivity
${\mathit{P}}_{\mathit{f}}$	=	Pyrolysis factor
${\mathit{K}}_{\mathit{B}}$	=	Boltzmann constant
h	=	Planks constant
R	=	Gas constant
VM	=	Volatile matter
FC	=	Fixed carbon
${\mathit{Y}}_{\mathit{char}}$	=	Char yield

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to acknowledge the management of the Coal Research Centre (CRC) for providing us the financial support in carrying out this research work.

Notes on contributors

Rumaisa Tariq

Rumaisa Tariq is currently pursuing Ph. D. in Monash University, Malaysia. She has completed her Master of Science in Chemical Engineering from National University of Science and Technology, Pakistan. She has authored/co-authored 13 research papers in high impact-factor research journals. Her research interests are thermochemical conversion of biomass and nanotechnology.

Sana Saeed

Sana Saeed is working as an Assistant Professor in chemical engineering department of NFC Institute of Engineering & Technology Multan. She has obtained her Ph. D. degree in chemical engineering from University of the Punjab, Lahore. Her research interests are ionic liquids, energy, heat & mass transfer operations.

Muzaffar Riaz

Muzaffar Riaz is working as a Lecturer in chemical engineering department of NFC Institute of Engineering & Technology Multan. He has obtained his Master of Science degree in chemical engineering from NFC Institute of Engineering & Technology Multan. His research interests are thermochemical conversion processes, energy, and biomass pretreatment.

Saad Saeed

Saad Saeed is working as a Lecturer in chemical engineering department of NFC Institute of Engineering & Technology Multan. He has obtained his Ph. D. degree in chemical engineering from University of the Punjab, Lahore. His research interests are ionic liquids, energy, and chemical reaction engineering.