article · Biomass Conversion and Biorefinery
This research investigates the pyrolysis kinetics and thermodynamics of tea-waste to evaluate its viability for thermochemical processes. Raw tea-waste was compared against samples torrefied at 200 degrees Celsius and 600 degrees Celsius. Using thermogravimetric analysis across seven heating rates from 27 to 1000 degrees Celsius under a nitrogen environment, the study established kinetic parameters through model-fitting and model-free methods. Natural mineral presence was evaluated using X-ray fluorescence and Fourier transform infrared spectroscopy. The results reveal that tea-waste has the potential to yield syngas, with torrefaction at 600 degrees Celsius boosting energy content by 53 percent compared to raw biomass. Furthermore, the Coats-Redfern method proved more reliable than the direct Arrhenius model, with activation energy increasing alongside heating rates.
Agricultural residues such as tea-waste represent an underutilised resource for clean energy generation. By mapping the precise thermodynamic and kinetic properties during thermal breakdown, this work provides the baseline calculations necessary to understand how agricultural by-products behave during heating, demonstrating that high-temperature pre-treatment substantially improves their energy value for bioenergy systems.
This research informs syngas generation and bioenergy applications, offering foundational kinetic parameters for thermochemical process designers, biomass plant operators, and energy equipment manufacturers. Given that the investigation is based on laboratory-scale thermogravimetric analysis of small samples under controlled nitrogen flows, the work is at an early stage of research and requires pilot-scale validation before real-world commercial processing can occur.
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Abstract This study aimed to investigate waste-tea’s pyrolysis kinetics and thermodynamics to assess its potential for thermochemical processes. In this study, three primary samples of tea-waste are prepared for investigation: raw, torrefied at 200 °C, and torrefied at 600 °C. Under a nitrogen environment, thermogravimetric analyses (TGA) were conducted at seven heating rates (10, 15, 20, 25, 30, 35, and 40 °C/min) to investigate the effect of heating rates on the kinetic parameters at temperatures ranging from 27 to 1000 °C. Using seven heating rates was beneficial to take advantage of multiple heating rates techniques alongside single heating rate techniques. These heating rates were combined, forming four heating rate groups (HRG). The pyrolysis kinetic parameters are determined using two model-fit-methods, direct Arrhenius and Coats-Redfern methods, and two model-free methods, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. Thermodynamic data comprising Δ H , Δ G , and Δ S are addressed. The X-ray fluorescence (XRF) and Fourier transform infrared (FTIR) spectrum are used to assess the presence of natural minerals in tea-waste. The results indicated that the tea-waste material has the potential to produce syngas. The torrefaction process at 600 °C shows a 53% increase in the energy content compared to the raw biomass. The Coats-Redfern is shown to be more reliable than the direct Arrhenius method. The activation energy ( E a ) witnesses rising with the heating rate ( β ) from E a = 55.27 kJ mol −1 at β = 10 °C min −1 to 60.04 kJ mol −1 at β = 40 °C min −1 for raw tea-waste using Coats-Redfern method. For model-free approaches, the minimum activation energy values of the raw tea-waste samples are 82 kJ/mol for FWO and 78 kJ/mol for KAS, whereas the peak values are 420 kJ/mol for KAS and 411 kJ/mol for FWO. A comparison of the effect of heating rate groups for FWO method in raw material case indicated that HRG1 has the maximum activation energy average value. The resulting values of HRG1, HRG2, HRG3, and HRG4 were 269 kJ/mol, 145 kJ/mol, 174 kJ/mol, and 202 kJ/mol, respectively.
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DOI: 10.1007/s13399-023-04017-y
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