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Properties

Petroleum coke is a hard solid petroleum product in black or dark gray, and is characterized by metallic luster and porosity. It is carbon-shaped stuff composed of tiny graphite crystals formed into granules, columns or needles. The composition of petroleum coke is hydrocarbons, containing 90-97% carbon, 1.5-8% hydrogen, and elements such as nitrogen, chlorine, and sulfur.

Petroleum coke is the carbonized product of heavy residue produced by crude oil processing (atmospheric and vacuum distillation, catalytic cracking, etc.). The main production techniques include delayed coking and fluidized coking.

Quality standards

Generally speaking, petroleum coke refers specifically to sponge coke. Currently, domestic manufacturers mainly produce it in accordance with the industry standards NB/SH/T 0527-2019 formulated by Sinopec (see Table 1 for details). The standards apply to both imported and domestic petroleum coke, which are used as common-power graphite electrodes, carbon raw materials and fuels for aluminum, etc. Needle-shaped coke meets the requirements of the standards of GB/T 37308-2019 for “Oil-based Needle Coke” and T/ZGTS 002-2019 for “Oil-based Needle Coke for Graphite Electrodes”.

Main uses

Petroleum coke products can be divided into needle coke, sponge coke, shot coke and powder coke based on its structure and appearance:

1.Needle coke has an obvious needle structure and fiber texture, and is mainly used as high-power and ultra-high-power graphite electrodes in steelmaking after calcination, and some of it is used as cathode materials.

2.Sponge coke is of high chemical reactivity and low impurity content, and is mainly used in aluminum industry and carbon industry.

3.Shot coke or spherical coke is spherical in shape and 0.6-30mm in diameter, generally produced by high-sulfur and high-asphaltene residual oil, and can only be used as industrial fuels such as power generation and cement.

4.Fluid coke is produced by fluidized coking, with fine particles (0.1-0.4mm in diameter), high volatile component and high thermal expansion coefficient. It can’t be directly used in electrode preparation and carbon industry.

Sponge coke is mainly used to produce pre-baked anode and anode coal paste for electrolytic aluminum, carbon addictive used in carbon industry, graphite electrode, silicon used in smelting industry, fuel, etc. When pre-baked anodes are used for aluminum smelting and graphite electrodes are used for steelmaking, the raw coke must be calcined in order for petroleum coke (green coke) to meet the requirements. The calcination temperature is generally about 1300 ℃ in order to remove the volatile components of petroleum coke and improve the physical and chemical properties such as strength and conductivity. Green coke can be directly used to produce silicon carbide, silicon metal and other materials without calcination.

Needle coke has a series of advantages such as low thermal expansion coefficient, low porosity, low sulfur, low ash, low metal content, high conductivity and easy graphitization. Its graphitized products feature good chemical stability, corrosion resistance, high thermal conductivity, good mechanical strength at low and high temperatures and good electrochemical performance. Needle coke is therefore a high-quality raw material for ultra-high power graphite electrode and artificial graphite cathode materials. Its downstream industry is electric arc furnace steelmaking and new energy vehicles, which are encouraged by national industrial policies. The supply of needle coke plays an important supporting role in ensuring “peaking CO₂ emissions” and “carbon neutrality” for downstream industries.