Needle coke – The main raw material for graphite electrodes
Needle coke is a high-quality variety vigorously developed in carbon materials, and its appearance is a porous solid with a silver-gray and metallic luster.
Its structure has an obvious flowing texture, with large and few pores and a slightly elliptical shape. The particles have a large aspect ratio, and some have fibrous or needle-like textures. It has a lubricating texture when touched by hand.
Classification of needle coke
According to different raw materials, needle coke can be divided into oil-based needle coke and coal-based needle coke.
The United States takes petroleum residue as raw material and produces needle coke as oil-based needle coke. Japan is the representative of coal tar pitch and its fractions as raw materials, and the needle coke produced is coal-based needle coke.
The use of needle coke
Needle coke is the raw material for the production of high-end carbon products such as ultra-high power electrodes, special carbon materials, carbon fibers, and composite materials.
It is a high-quality material for manufacturing high-power graphite electrode and ultra-high-power graphite electrodes. Graphite electrodes made of needle coke have the advantages of strong thermal shock resistance, high mechanical strength, good oxidation performance, low electrode consumption and large allowable current density.
Needle coke price trend
Due to the increase in demand for Electrode, Silicon metals & ferroalloys, Carbon block, Rubber compounds, and Others, the demand for needle coke in the global market has greatly increased.
In 2020, the global needle coke market size will be 1,209.52 kilotons, and it is expected that during the forecast period (2021-2026), the compound annual growth rate will be approximately 12%.
Therefore, the price of needle coke will show an upward trend, and there will be a long duration.
Needle coke production process
There are four main types of coal-based needle coke production technology as follows.
In 1971, the American LCI company first proposed the vacuum separation method to separate needle coke from coal tar pitch and applied for a US patent. The core technology is to cut raw materials suitable for the production of needle coke through vacuum distillation. The process is relatively simple and needle-shaped. The yield of coke is low.
In 1981, LCI applied for a US patent for the method of removing quinoline insoluble (QI) in asphalt by solvent treatment. That is, the QI is aggregated with the co-polymerization agent liquid first, and the aggregate is separated in the gravity settler. The processing technology is similar to the industrial equipment of Japan’s Shindai Chemical Co., Ltd. to produce needle coke with coal tar pitch. The needle coke obtained by solvent treatment technology has a high yield and good quality, but the process is more complicated and the investment is also high.
In 1985, LCI Company and Mardzen Petrochemical Company of Japan applied for a U.S. patent for the ML process. This process combines a special raw material pretreatment technology with a unique two-stage delayed coke system. It is the first set of coal tar pitches as raw material. Needle coke production equipment. The produced needle coke has the best quality, but it also has the problems of low yield, complicated process, and high investment.
In 1985, Anshan Coking Research Institute, Anshan University of Iron and Steel, and Shijiazhuang Coking Plant jointly developed the flash-polycondensation process and applied for a Chinese patent. The method is to send the mixed raw oil to a specific flash tower, flash out the flash oil at a certain temperature and vacuum, and the flash oil enters the polycondensation kettle for polymerization to obtain polycondensation pitch. The process yield is moderate and the process is simple. The domestic Anshan coastal chemical fertilizer plant has been put into industrialization trials, but because the technology is not perfect, it has stopped. Domestically, the main quality indicators of coal-based needle coke are based on the standards of Japan’s Shindai Ka. That is, true specific gravity ≥ 2.13, ash content ≤ 0.1%, volatile content ≤ 0.5%, sulfur content ≤ 0.5%, thermal expansion coefficient CTE 1×10-6/℃, and moisture content ≤ 0.2%.