What are the differences between graphite petroleum coke and ordinary petroleum coke? A comprehensive explanation.

Petroleum coke is a black solid coke produced after petroleum is distilled, separating light and heavy oils. The heavy oil undergoes cracking and coking at a high temperature of approximately 500-550℃. It is a byproduct of petroleum refining, and its main component is carbon. Petroleum coke is black or dark gray, irregularly shaped, and porous on the surface; it is an amorphous carbon material.

Petroleum coke produced directly from a refinery's delayed coking unit without further heat treatment is commonly referred to as "raw coke" or "green coke." This raw coke contains a high amount of volatile matter (up to 10% or more), has low mechanical strength, and high sulfur and metallic impurity content. It is usually classified as "ordinary petroleum coke" or "fuel-grade petroleum coke" and is primarily used as fuel.

Ordinary petroleum coke and graphite petroleum coke are not two completely independent raw materials; they are actually products of different stages in the petroleum coke processing chain. The following diagram clearly illustrates this evolution path:

• 1. Ordinary Petroleum Coke (Raw Coke)

This is the most primitive form, produced directly from the delayed coking unit. Based on sulfur content, petroleum coke can be classified into high-sulfur coke (sulfur content >3%), medium-sulfur coke (sulfur content 1%–3%), and low-sulfur coke (sulfur content <1%). Low-sulfur petroleum coke with a sulfur content of less than 0.5% is considered a high-quality raw material and can be used to produce graphite electrodes and carbon raisers. High-sulfur coke is mostly used as fuel in cement plants and power plants, but its use will be significantly restricted due to increasingly stringent environmental policies.

• 2. Calcined Petroleum Coke (CPC)

Ordinary petroleum coke is heat-treated in a rotary kiln or pot furnace at approximately 1200–1350℃ to remove most of the volatile matter and moisture, increasing the fixed carbon content to over 98.5%. Calcined petroleum coke has increased density, improved conductivity, and enhanced chemical stability, making it a key raw material for manufacturing aluminum electrolytic anodes, graphite electrodes, and other products. However, the carbon atoms in calcined petroleum coke are still in a relatively disordered state and have not yet formed a graphite crystal structure.

• 3. Graphite Petroleum Coke (GPC)

Graphite petroleum coke is obtained by further graphitizing calcined petroleum coke at higher temperatures (2800-3000℃). This process is typically carried out in an Atchison graphitization furnace for 48-72 hours. At such high temperatures, carbon atoms transform from a random arrangement to an ordered hexagonal lattice structure, forming a graphite-like crystal arrangement. During graphitization, most of the residual sulfur, nitrogen, and other impurities also volatilize and escape, resulting in graphite petroleum coke with extremely low sulfur content (typically controllable below 0.03%-0.05%) and high fixed carbon content (up to 99% or more).

The core changes are concentrated at two key points: calcination mainly removes volatiles, increasing density and strength, laying the foundation for subsequent processes; graphitization is the watershed moment where carbon atoms undergo a qualitative change from disorder to order, directly determining the order-of-magnitude improvement in the material's electrical conductivity, thermal stability, and chemical stability.

Regarding sulfur content, ordinary petroleum coke (especially high-sulfur coke) can have a sulfur content exceeding 3%, while graphitized petroleum coke, after high-temperature graphitization, can have its sulfur content reduced to below 0.03%. This difference is particularly significant in today's increasingly stringent environmental regulations.

Regarding true density, ordinary petroleum coke typically has a low true density (approximately 1.3–1.4 g/cm³), which can increase to over 2.07 g/cm³ after calcination, and further increase to approximately 2.20 g/cm³ after graphitization, reflecting a significant change in the material's density.

In terms of appearance, calcined petroleum coke appears as black, blocky granules with a strong metallic luster and transparent carbon pores; graphite petroleum coke, on the other hand, is even darker and shinier with an even stronger metallic luster, and can even leave a smooth mark on paper, a characteristic unique to graphite materials.

Typical uses of ordinary petroleum coke:

High-sulfur coke (sulfur content > 3%): Primarily used as fuel in cement plants and power plants, or in the manufacture of chemical products such as calcium carbide and silicon carbide. However, due to carbon peaking and carbon neutrality policies, the market space for high-sulfur coke as fuel is gradually shrinking.

Medium-sulfur coke (sulfur content 1%–3%): Can be used in the aluminum smelting industry to produce anode paste or prebaked anodes, and is also used in the metallurgical industry.

Low-sulfur coke (sulfur content < 1%): Can be used to manufacture ordinary power graphite electrodes, carbon products, etc. High-quality low-sulfur coke with a sulfur content < 0.5% is a superior raw material for the production of graphite electrodes and carbon raisers.

Typical applications of graphite petroleum coke:

Carbonizer in the steel and foundry industries: Graphite petroleum coke is characterized by low sulfur, low nitrogen, and high carbon content, making it particularly suitable for gray cast iron casting and ductile iron casting with strict sulfur content requirements.

Prebaked anodes in electrolytic aluminum: Used as aggregate in prebaked anodes in aluminum electrolysis cells, it offers good conductivity and low energy consumption. Globally, approximately 70%–80% of calcined petroleum coke is used in the aluminum industry.

Lithium-ion battery anode material: Due to its high purity and stable crystal structure, graphite petroleum coke is becoming an important precursor for lithium-ion battery anode materials. With the rapid development of the new energy industry, the demand for its application in this field is growing rapidly.

Graphite Electrodes and Refractory Materials: Used in the manufacture of graphite electrodes for electric arc furnace steelmaking, and in advanced refractory materials and coatings in the metallurgical industry.

Understanding the difference between ordinary petroleum coke and graphite petroleum coke is essentially about understanding the evolution of carbon materials from "fuel" to "high-end functional materials." For foreign trade companies and buyers, the key is to accurately select the appropriate coke type based on the application scenarios, performance requirements, and cost budgets of their products. Only by truly understanding the entire process of raw materials-"where they come from, what they go through, and where they go"-can companies take the initiative in upstream material selection within the carbon industry chain.