Electrolytic smelting of aluminum and electrolysis of aqueous sodium chloride have been used in an industrial scale from the late nineteenth century to the early twentieth century, and the importance of the high purity of the carbon electrode is recognized. Consequently, manufacture of PC nearly free of ash using coal‐tar pitch as a raw material instead of metallurgical coke using a coal as a raw material has started. In the early stage retorts and pot still were used, but the Koppers process has been developed and established by the Koppers Company in Germany in the 1930s and is still used at present in Eastern Europe and China.
Nippon Steel Chemical Industry Co., Ltd. (at present, Nippon Steel & Sumikin Chemical Industry Co., Ltd.) has thereafter used in 1968 the licensing technology from the Lummus Co. in the United States to establish a production process by delayed coking [1], and this process is at present used to manufacture PC in Japan and China. Nippon Steel Chemical Co., Ltd. (at present, Nippon Steel & Sumikin Chemical Industry Co., Ltd.) [2, 3] and Mitsubishi Kasei Corporation (at present, Mitsubishi Chemical Industries Ltd.) [4] have independently succeeded in 1980 scaling up the purification of coal‐tar pitch and initiated industrial scale production of pitch needle coke by the delayed coking process.
An annual production volume of PC in 2009 is estimated to be approximately 900 000 t, and its production is increased particularly in China as the center where extensive economic development is under way. Major production sites for PC are located in China and in the Eastern European region including the former Soviet Union based on the Koppers process and in the East Asian region of China and Japan and the Southern African region based on the delayed coking process.
The majority of PC is processed for making a carbon or graphite electrode. PC is used as a raw material to produce a graphite block followed by machining to form various parts and jigs because it does not melt at high temperature, impurities are easily removed, and it has good lubricity and electrical conductivity.
6.1.3.2. Physical and Chemical Properties
6.1.3.2.1 Physical Properties
PC is blocky, granular, and powdery in shape and black in color and is a porous carbonaceous solid with very little impurities (in general, ash is in a range of <3%). Its appearance depends on a production method and applications. The majority of PC produced using the chamber‐type coke oven is blocky, very hard, and in a shape like a columnar joint or a shape in which the bottom of a cone is protruded convexly. There are pores and cracks elongated in the direction of the major axis and parts of PC appear in silver gray color. There are two types of PC produced by the delayed coking process, needle coke used for a synthetic graphite electrode in electric arc furnace steelmaking and amorphous coke used in aluminum smelting. Needle coke is black and shiny in silver gray color and characterized with the elongated structure with the sharp tip at both ends. Pores and cracks with the cross section in a range of a few millimeters are observed mainly in the direction of the major axis. Amorphous coke is black in color and has the shape close to the rectangular parallelepiped or cube structure with rounded edges or the shape close to the sphere, and pores with the maximum cross section in a range of a few millimeters are observed randomly. The grain size of coke produced by the delayed coking process ranges from a size of fine powder to the dimension of a golf ball as the maximum diameter.
Needle coke is heat‐processed at 2000–3000 °C to convert to the majority of a synthetic graphite electrode and special carbon products as a products, but different cokes are used depending on the degree of graphitization according to the purpose. Coke used in aluminum smelting is used as a carbonaceous substance. Each property differs substantially (see the Section 6.1.3.2.2).
6.1.3.2.2 Chemical Properties
Volatile matter (VM) of PC is around approximately 0.3%, and its ash content is around 0.3% at maximum, whereas in needle coke the ash content generally does not reach to approximately 0.1%. The real density (RD) depends on its application, and it is mostly in a range of 2.13–2.15 in needle coke and mostly in the vicinity of 2.00 in amorphous coke and is adjusted with the calcination temperature in production.
The content of elements in PC is varied with the calcination temperature in production but is generally given as follows. The carbon content is approximately 98% or more in amorphous coke and is further increased in needle coke in which the calcination temperature is higher. The hydrogen content is below approximately 0.5%. The sulfur content is around 0.3% and its value in needle coke is slightly smaller than that in petroleum coke. The nitrogen content is around 0.5–0.8%, and its value in needle coke is higher than that in petroleum coke, and nitrogen is assumed to be the causative agent for an irreversible expansion (puffing) generated in graphitization in the production process of a synthetic graphite electrode. In metal elements as an impurity, the content of V, Ni, and Ti is less in needle coke than that in petroleum coke (see the Chapter 6.1.2).
PC contains little metal impurities and is low in VM so that there is no report specified on the environmental impacts and risks (see Section 6.1.3.5).
6.1.3.3. Production of Pitch Coke
Coal tar used as a raw material for PC is obtained by the dry distillation of coal and produced as a by‐product in the production of metallurgical coke used mainly in steelmaking and in the production of town gas. Useful application of coal tar is important for supporting the steel industries and fuel gas industries.
Production status based on data in 2009 is approximately as follows. In addition to use coal tar generated as a fuel, approximately 16 000 000 t of coal tar is fractionally distilled to produce the naphthalenes, tar acids, tar bases, creosote oil, and soft coal‐tar pitch (boiling point: 300 °C or more). The soft coal‐tar pitch is further distilled to raise the softening point to produce medium pitch (softening point: 60–80 °C) and hard pitch (softening point: higher than 80 °C). The ratio of each product produced is 10% for naphthalenes, 5% for tar acids, 5% for tar bases, 30% for creosote oil, and 50% for coal‐tar pitch including medium and hard pitches. Approximately 90% of pitch produced is used as an anode material for aluminum smelting, a synthetic graphite electrode for steelmaking, or a binder pitch for various carbon products. Remaining 10% of soft pitch (SOP) is used as a raw material for the thermal decomposition polycondensation reaction (carbonization) to produce both PC and creosote oil. The ratio of each product in production of PC is 10% for naphthalenes, 5% for tar acids, 5% for tar bases, 40% for creosote oil, and 40% for PC. The annual production volume of PC is estimated to be approximately 900 000 t.
Production sites and production process of PC are given in Table 6.1.3.1. An actual output of PC (estimated in 2009) in each region is estimated to be from 400 000 to 500 000 t/year in China, 280 000 t/year in Japan, 110 000 t/year in South Africa, and 50 000–100 000 t/year in Eastern Europe. Production of PC is particularly grown in China as the center where extensive economic development is under way.
6.1.3.3.1 Production Process
The production process is roughly divided into two types, the delayed coker and calciner process and the chamber coking process. A main production process is the delayed coker and calciner process, and the chamber coking process is used mainly in Eastern Europe and in China. (See the Section 6.1.3.1)
Table 6.1.3.1 Production of pitch coke.
| Region | Company | Production process | Grade | Capacity | Quantity |
|---|---|---|---|---|---|
|
Europe
|