High-Sulfur vs. Low-Sulfur Petroleum Coke: How to Choose for Different Applications?

The sulfur content of petroleum coke is the core indicator for measuring its quality grade and application range. According to current industry standards, petroleum coke with a sulfur content of less than 1% is called low-sulfur coke (corresponding to 1#, 2A), with a sulfur content between 1% and 3% is called medium-sulfur coke (corresponding to 2B, 2C, 3A, 3B, 3C), and with a sulfur content greater than 3% is classified as high-sulfur coke. This classification directly determines the downstream destination and market price of petroleum coke.

In practical applications, more refined classification standards are also widely used. According to the Chinese delayed petroleum coke quality standard (ZBE44002-86), raw coke is classified into No. 1, No. 2, and No. 3, each further divided into A coke and B coke. No. 1 A coke has a sulfur content of no more than 0.5%, No. 1 B coke no more than 0.8%, No. 2 A coke no more than 1.0%, and No. 2 B coke no more than 1.5%. The earlier the letter and the smaller the number, the lower the sulfur content and the better the quality.

It is worth noting that there is currently no national standard for petroleum coke with a sulfur content of 3% or higher. Although the enterprise standard previously issued by Sinopec has been abolished, it is still used in the high-sulfur coke market.

Low-sulfur coke, with its superior quality, has become the preferred raw material for high-end carbon products, playing an irreplaceable role in graphite electrodes, lithium-ion battery anode materials, and high-end prebaked anodes.

• Graphite Electrodes

Graphite electrodes are one of the most important applications of low-sulfur coke. The main raw material for producing graphite electrodes is petroleum coke. A small amount of pitch coke can be added to ordinary power graphite electrodes, but the sulfur content of both petroleum coke and pitch coke cannot exceed 0.5%. For the production of high-power or ultra-high-power graphite electrodes, needle coke is required. The sulfur content has a particularly critical impact on the performance of graphite electrodes-during the high-temperature graphitization process, sulfur cannot be completely released. When the electrode is exposed to temperatures above 1500℃, sulfur decomposes, causing the crystals to expand. Upon cooling, the crystals contract, leading to electrode cracking. This phenomenon, known as "gas expansion," severely affects the quality and performance of the graphite electrode.

Ultra-high-power graphite electrodes not only require low resistivity but also low thermal expansion coefficients, good oxidation resistance, and good thermal shock resistance after graphitization. High-performance needle coke is used to produce high-quality graphite electrodes for high-power and ultra-high-power electric furnaces, while petroleum coke containing approximately 1% sulfur is mainly used in the aluminum smelting industry for the production of anode paste or carbon anodes.

• Lithium-ion Battery Anode Materials

In recent years, with the explosive growth of new energy vehicles and energy storage industries, the application of low-sulfur coke in the field of lithium-ion battery anode materials has rapidly emerged. Low-sulfur coke has a low coefficient of thermal expansion, low porosity, low ash and metal element content, high conductivity, and is easily graphitized, making it an ideal raw material for preparing artificial graphite anode materials.

Currently, commercially available petroleum coke used in large quantities is all low-sulfur coke, and the tight supply of low-sulfur coke leads to high costs. In the demand structure of low-sulfur coke, lithium-ion battery anodes account for 29%, and its crowding-out effect on demand from traditional fields is becoming increasingly prominent. Anode material companies maintain their expansion pace, and the demand for low-sulfur coke continues to grow well.

• High-end Prebaked Anodes

Prebaked anodes are key components in aluminum electrolysis cells, conducting current and participating in electrochemical reactions, and are crucial in aluminum electrolysis production. Low-emission anodes use petroleum coke with stricter control over sulfur content and trace element indicators, which can effectively reduce carbon dioxide emissions in aluminum electrolysis operations, contributing to energy conservation and emission reduction under the "dual carbon" goals of the aluminum electrolysis industry. Petroleum coke used for prebaked anodes typically requires a sulfur content below 1.5%.

• Other High-End Applications

In the field of carbon raisers, the foundry industry usually requires extremely low sulfur content, often using "semi-graphitized" or "fully graphitized" petroleum coke with a fixed carbon content of over 98% and a sulfur content below 0.05%. Furthermore, the production of high-purity graphite products requires raw material ash content to be as low as possible (e.g., below 0.15%).

Although high-sulfur coke has a higher sulfur content, it is significantly competitive in terms of cost and production scale, and still plays an important role in specific application areas.

• Prebaked Anodes

With the rapid development of the electrolytic aluminum industry, the use of high-sulfur coke in the production of prebaked anodes for aluminum is showing an increasing trend. Due to the tight supply of low-sulfur coke, many carbon plants have had to use high-sulfur petroleum coke, leading to an increase in the sulfur content of prebaked anode carbon blocks, which in turn exposes the aluminum electrolysis process to the risk of exceeding sulfur dioxide emission standards.

At the technical level, the use of blended petroleum coke with different sulfur contents has become an important means for aluminum anode manufacturers to balance anode quality, anode consumption, and environmental performance. Through a reasonable blending process, environmental requirements can be met while controlling costs.

• In the fuel sector,

high-sulfur coke has traditionally been widely used as fuel in cement plants and power plants. However, with increasingly stringent environmental policies, the application of high-sulfur coke as fuel is facing significant restrictions. The "Energy Conservation and Carbon Reduction Action Plan" explicitly stipulates that high-sulfur coke cannot be used as fuel. Driven by carbon emission reduction policies, high-sulfur coke faces substitution pressure in applications such as fuel and glass manufacturing.

• New Attempts in Lithium-ion Battery Anode Materials

Although low-sulfur coke remains the mainstream choice for lithium-ion battery anodes, high-sulfur coke, with its cost advantages of cheaper raw materials and higher production volume, is attracting many graphite manufacturers to explore its application in the anode material field. However, excessively high sulfur content in high-sulfur coke leads to a series of problems: during graphitization, sulfur escapes in gaseous form, increasing graphite porosity and specific surface area; simultaneously, sulfur hinders continuous graphite growth, causing crystals to shrink, reducing graphite anisotropy, and resulting in a significant decrease in compaction density, capacity, and initial coulombic efficiency. Currently, the industry is developing technologies such as composite graphite anode materials, attempting to overcome the inherent limitations of high-sulfur coke through raw material formulation and process optimization.

• Chemical Production

High-sulfur ordinary raw coke can be used in chemical production, such as the manufacture of calcium carbide and silicon carbide, or as fuel in metal casting and glass manufacturing.

Based on the above analysis, the selection of petroleum coke for different application scenarios can be summarized as follows:

Graphite Electrodes: Ordinary power graphite electrodes require petroleum coke sulfur content not exceeding 0.5%; high-power and ultra-high-power graphite electrodes require needle coke, with even stricter sulfur content requirements.

Lithium-ion Battery Anode Materials: Currently, the mainstream commercial material is low-sulfur coke (sulfur content less than 1%), and high-quality anode materials have extremely strict sulfur content control.

Prebaked anodes: Sulfur content is typically required to be below 1.5%; low-emission anodes have even stricter requirements, needing to meet environmental standards under the "dual carbon" target.

Carbonizers: Casting-grade carbonizers require extremely low sulfur content (≤0.05%), necessitating the use of "semi-graphitized" or "fully graphitized" petroleum coke.

Chemical production and fuel: High-sulfur ordinary raw coke can be used in chemical production, but its use as fuel is strictly limited.

When selecting petroleum coke, in addition to sulfur content as a core indicator, factors such as ash content, true density, thermal shock resistance, and morphology must be comprehensively considered. Ash content hinders crystallization and affects product performance; true density reflects the degree of crystallinity; and morphology determines the applicability of petroleum coke in specific applications. The industry consensus is: the intended use determines the grade selection-for electrolytic aluminum anodes or high-end graphite products, Grade A coke is preferred; for low-end carbon products or fuel, Grade B and below can be selected.

Against the backdrop of the continued advancement of "dual carbon" goals and the rapid development of the new energy industry, the market positions of low-sulfur coke and high-sulfur coke are undergoing profound adjustments. Low-sulfur coke, with its irreplaceable role in high-end applications, is experiencing continuously rising demand; while high-sulfur coke faces increasingly stringent environmental constraints and urgently needs breakthroughs in technological upgrades and application expansion. For industry practitioners, accurately grasping the quality requirements of petroleum coke for different application scenarios and making scientific decisions based on market supply and demand patterns and price trends will be key to gaining an advantage in the increasingly differentiated petroleum coke market.