Key Takeaways & Executive Findings
- •• The oxidation of ethylene tar proceeds in three stages, with the reaction mechanism involving initial side-chain oxidation to alcohols/aldehydes and subsequent polymerization/condensation of aromatic compounds via peroxy-radicals. • Kinetic analysis using the Coats-Redfern method identified a fourth-order reaction model for the first three stages (activation energies 47.33, 18.69, and 9.00 kJ·mol−1) and a three-dimensional diffusion model for the fourth stage (activation energy 88.37 kJ·mol−1). • A high softening point pitch produced from oxidized ethylene tar was applied as a coating on graphite anodes, significantly improving capacity retention after 300 cycles from 51.54% to 79.07%. • The study provides a detailed understanding of the oxidation kinetics and mechanism, enabling the optimization of ethylene tar as a carbonaceous precursor for high-performance lithium-ion battery anodes.
Abstract
The oxidation reaction mechanism and its kinetics for ethylene tar were investigated in order to obtain a suitable anode material for Li-ion batteries. The oxidation of ethylene tar was divided into 3 stages (350–550, 550–700 and 700–900 K) according to the thermogravimetric curve. To reveal the oxidation reaction mechanism, the components of the gases evolved at different stages were analyzed by mass spectrometry and infrared technology. Based on these results the reaction was divided into 4 stages (323–400, 400–605, 605–750 and 750–860 K) to perform simulation calculations of the kinetics. Using the iso-conversion method (Coats-Redfern) to analyze the linear regression rates (R2) between 17 common reaction kinetics models and experimental data, an optimum reaction kinetics model for expressing the oxidation of ethylene tar was determined and the results were as follows. (1) During oxidation, the side chains of aromatic compounds first react with oxygen to form alcohols and aldehydes, leaving peroxy-radicals on aromatic rings. Subsequently, the aromatic compounds with peroxy-radicals undergo polymerization/condensation reactions to form larger molecules. (2) A fourth-order reaction model was used to describe the first 3 stages in the oxidation process, and the activation energies are 47.33, 18.69 and 9.00 kJ·mol−1 at 323–400, 400–605, 605–750 K, respectively. A three-dimensional diffusion model was applied to the fourth stage of the oxidation process, and the activation energy is 88.37 kJ·mol−1 at 750–860 K. A high softening point pitch was also produced for use as a coating of the graphite anode, and after it had been applied the capacity retention after 300 cycles increased from 51.54% to 79.07%.
1. Introduction
Functional carbon materials have been playing an important role in electrical applications, thermal management (e.g., heat conduction and insulation), energy storage (e.g., electrode materials), environmental protection (e.g., gas capture), and various other fields[1–4]. It is well known that high-softening-point petroleum pitch is an important carbonaceous precursor[5]. For example, petroleum pitch with a high softening point can be applied as the coating material to the anode materials of lithium-ion batteries, raw materials for pitch-based carbon fiber and pitch-based spherical activated carbon[6–8].
Among these, ethylene tar is an important resource for preparing high softening point petroleum pitches[9–10]. The raw material for ethylene production is mainly naphtha (atmospheric crude oil fraction with an initial distillation point of ～200 °C). The C―H bond and C―C bond of naphtha are broken at high temperatures (600–800 °C) to produce ethylene and propylene. Meanwhile, olefins can also polymerize and cyclize to produce aromatic hydrocarbons. Therefore, the main components of ethylene tar are monocyclic, polycyclic aromatic hydrocarbons and heavy aromatic distillates, which are valuable resources rich in aromatic hydrocarbons. As the byproduct of hydrocarbons cracking in ethylene production (ca. 15% in yield), ethylene tar is produced in large amounts every year with the increasing demand for ethylene. Thus, it is regarded as an ideal material for producing high-quality pitch.
To increase the softening point and carbon yield of synthetic pitch[11–14], the air oxidation method has been widely applied to prepare high-quality pitch[15–18]. Several researchers[11,13,19] have reported that the air oxidation method can cause polymerization/condensation reactions, leading to increased molecular weight and softening point. However, the detailed oxidation mechanism and kinetics of ethylene tar have not been fully elucidated. This study aims to investigate the oxidation reaction mechanism and kinetics of ethylene tar to optimize its use as a carbonaceous precursor for lithium-ion battery anodes.
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GUO Tian-rui, CHEN Rong-qi, GAO Wei, WANG Yan-li, ZHAN Liang (2025). The oxidation reaction mechanism and its kinetics for a carbonaceous precursor prepared from ethylene tar for use as an anode material for lithium-ion batteries. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2024-39-02-13)
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is the oxidation reaction mechanism of ethylene tar?
The oxidation of ethylene tar proceeds in three stages. Initially, side chains of aromatic compounds react with oxygen to form alcohols and aldehydes, leaving peroxy-radicals on aromatic rings. Subsequently, these aromatic compounds with peroxy-radicals undergo polymerization/condensation reactions to form larger molecules.
What kinetic models describe the oxidation of ethylene tar?
A fourth-order reaction model describes the first three stages (323–400, 400–605, 605–750 K) with activation energies of 47.33, 18.69, and 9.00 kJ·mol−1, respectively. A three-dimensional diffusion model applies to the fourth stage (750–860 K) with an activation energy of 88.37 kJ·mol−1.
How does the oxidation of ethylene tar improve lithium-ion battery performance?
The oxidized ethylene tar produces a high softening point pitch that, when used as a coating on graphite anodes, increases capacity retention after 300 cycles from 51.54% to 79.07%, enhancing battery longevity.
Why is ethylene tar considered an ideal precursor for high-quality pitch?
Ethylene tar is rich in aromatic hydrocarbons, making it suitable for producing high softening point pitch via air oxidation. It is a byproduct of ethylene production, available in large quantities, and its oxidation can be optimized to yield high-quality carbonaceous precursors for battery anodes.
What methods were used to analyze the oxidation kinetics?
The study used thermogravimetric analysis, mass spectrometry, and infrared spectroscopy to analyze evolved gases. Kinetic parameters were determined using the iso-conversion method (Coats-Redfern) by comparing 17 common reaction kinetic models with experimental data.
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