Assessment of the thermal pyrolysis characteristics and kinetic parameters of spent coffee waste: a TGA-MS study

ABSTRACT

The present study aimed to investigate the pyrolysis characteristics and kinetics of spent coffee waste (SCW) at different heating rates (5–40 °C/min) at a temperature ranging from 30 to 800°C in a thermogravimetric analyzer (TGA). First, the physicochemical properties of the SCW were characterized using X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy, and elemental analysis. Then, the thermal decomposition kinetic profiles were modeled using the Coats–Redfern, Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink models. All the tested models provided accurate fits of the thermogravimetric analysis data with acceptably high R² values. The mean activation energy of the coffee waste was 101.8, 96.7, and 97.1 kJ/mol for the FWO, KAS, and Starink models, respectively. Finally, the evolved gases detected during the decomposition by TGA coupled with a mass spectrometer (MS) primarily consisted of water, methane, and carbon dioxide.

Graphical Abstract

KEYWORDS:

• Spent coffee waste
• pyrolysis
• kinetics
• gas analysis
• TGA-MS

Nomenclature

A	=	Pre-exponential or frequency factor (min−1)
E	=	Activation energy (kJ/mol)
f(x)	=	Reaction model
g(x)	=	Integrated reaction model
n	=	Reaction order
R	=	Ideal gas constant (8.314 J/mol.K)
t	=	Time
T	=	Absolute temperature (K)
x	=	Conversion
β	=	Heating rate (K/min)

Article highlights

Pyrolysis kinetics of SCW were studied at various heating rates.

SCW was characterized by using FTIR, XRD, and SEM.

Both model-free and model-fitting methods were used to calculate the activation energy.

Evolved gases of CH₄, CO₂, and H₂O were detected simultaneously using TGA-MS.

Additional information

Notes on contributors

Sevgi Polat

Sevgi Polat is currently a research assistant of chemical engineering at Marmara University. She received her Ph.D. degree in chemical engineering from Marmara University, in 2018. Her main research interests focus on thermal analysis, polymorphism, and experimental design.

Perviz Sayan

Perviz Sayan is the Professor of Chemical Engineering at Marmara University. He received his PhD in the Department of Chemical Engineering from Istanbul Technical University, in 1995. Prof. Sayan’s interests are focused on seperation techniques including crystallization, polymorphism, adsorption, filtration and thermal characterization.