The core differences in the calcination behavior between oil-based coke and coal-based coke lie in the distinct reaction pathways driven by differences in their raw material chemical compositions, which subsequently lead to significant variations in crystal structure evolution, physical property changes, and process control difficulties. A detailed analysis is as follows:
1. Differences in Raw Material Chemical Compositions Lay the Foundation for Calcination Behavior
Oil-based coke is derived from heavy distillates such as petroleum residue and catalytic cracking clarified oil. Its chemical composition is primarily characterized by short side-chain, linearly connected polycyclic aromatic hydrocarbons, with relatively low contents of sulfur, nitrogen, oxygen, and metallic heteroatoms, as well as minimal solid impurities and quinoline-insoluble matter. This composition results in a calcination process dominated by pyrolysis reactions, with a relatively simple reaction pathway and thorough impurity removal.
In contrast, coal-based coke is produced from coal tar pitch and its distillates, which contain a higher proportion of long side-chain and condensed polycyclic aromatic hydrocarbons, along with significant amounts of sulfur, nitrogen, oxygen heteroatoms, and solid impurities. The complex composition of coal-based coke leads to not only pyrolysis reactions but also significant condensation reactions during calcination, resulting in a more intricate reaction pathway and greater difficulty in impurity removal.
2. Differences in Crystal Structure Evolution Affect Material Properties
During calcination, the carbon microcrystals in oil-based coke gradually increase in diameter (La), height (Lc), and the number of layers within the crystals (N). The content of ideal graphite microcrystals (Ig/Iall) also rises significantly. Although Lc experiences an “inflection point” due to volatile matter escape and raw coke shrinkage, the overall crystal structure becomes more regular, with a higher degree of graphitization. This structural evolution endows oil-based coke with excellent properties such as low thermal expansion coefficient, low electrical resistivity, and high electrical conductivity after calcination, making it particularly suitable for manufacturing large-sized ultra-high-power graphite electrodes.
Similarly, the carbon microcrystal structure of coal-based coke evolves with increasing La, Lc, and N during calcination. However, due to the influence of impurities and condensation reactions in the raw material, there are more crystal defects, and the increase in ideal graphite microcrystal content is limited. Additionally, the “inflection point” phenomenon for Lc is more pronounced in coal-based coke, and the newly added layers exhibit random “stacking faults” with the original layers, leading to significant fluctuations in interlayer spacing (d002). These structural characteristics result in coal-based coke having lower thermal expansion coefficient and electrical resistivity than oil-based coke after calcination, but poorer strength and abrasion resistance, making it more suitable for producing high-power electrodes and medium-sized ultra-high-power electrodes.
3. Differences in Physical Property Changes Determine Application Areas
During calcination, oil-based coke undergoes thorough volatile matter escape and uniform volume shrinkage, resulting in a significant increase in true density (up to 2.00–2.12 g/cm³) and a substantial improvement in mechanical strength. Simultaneously, the electrical conductivity, oxidation resistance, and chemical stability of the calcined material are significantly enhanced, meeting the stringent performance requirements for high-end graphite products.
In contrast, coal-based coke experiences local stress concentration during volatile matter escape due to its higher impurity content, leading to uneven volume shrinkage and a relatively smaller increase in true density. Furthermore, the lower strength and poorer abrasion resistance of coal-based coke after calcination, along with its tendency to expand during high-temperature graphitization, necessitate strict control of the temperature rise rate. These property characteristics limit the application of coal-based coke in high-end fields, although its low thermal expansion coefficient and electrical resistivity still make it irreplaceable in specific areas.
4. Differences in Process Control Difficulties Affect Production Efficiency
Due to its relatively simple chemical composition, oil-based coke exhibits clear reaction pathways during calcination, resulting in lower process control difficulty. By optimizing parameters such as calcination temperature, heating rate, and atmosphere control, the quality and production efficiency of calcined products can be effectively improved. Additionally, the high volatile matter content in oil-based coke provides self-supplied thermal energy during calcination, reducing production costs.
In contrast, the complex chemical composition of coal-based coke leads to diverse reaction pathways during calcination, increasing process control difficulty. Strict raw material pretreatment, precise heating rate control, and special atmosphere adjustment are required to ensure stable product quality after calcination. Furthermore, coal-based coke requires additional thermal energy supplementation during calcination, increasing production costs and energy consumption.
Post time: Apr-07-2026