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Research and Production Status of Oil-based Needle Coke

2020-11-12

Abstract: Needle coke is a kind of porous solid with silver gray appearance, obvious fiber texture trend, high crystallinity, high strength, high graphitization, low thermal expansion, low ablation, etc. It is used to make graphite electrodes, battery anode materials and High-quality raw materials for high-end carbon products. With the rapid development of the graphite electrode industry, oil-based needle coke with environmental protection characteristics has once again become a research hotspot.


1 Introduction 


Needle coke is a kind of porous solid with silver-gray appearance and obvious fiber texture. It has the characteristics of high crystallinity, high strength, high graphitization, low thermal expansion, low ablation, etc. It has special applications in national defense and civil industries. And importantly, it is a high-quality raw material for manufacturing graphite electrodes, battery anode materials and high-end carbon products [1].


According to the different production materials used, needle coke can be divided into two types: oil-based and coal-based: needle coke produced from petroleum refining products is called oil-based needle coke, and coal tar pitch and its fractions Needle coke produced from oil is called coal-based needle coke. The production of needle coke from petroleum products has obvious advantages in environmental protection, is less difficult to implement, and has low production costs, which has attracted increasing attention.


Oil-based needle coke can be divided into green coke and cooked coke (calcined coke). The green coke is used to produce various battery anode materials, and the cooked coke is used to produce high-power graphite electrodes. In recent years, with the increasingly severe environmental protection situation, the rapid development of new energy vehicles has driven the demand for battery anode materials; at the same time, the backward converters of iron and steel enterprises have been replaced by electric furnaces. Under the dual role, the market demand for needle coke has increased substantially. At present, the world's oil-based needle coke production is dominated by American companies. Only a few companies in my country have achieved stable production, such as Jinzhou Petrochemical, Jingyang Petrochemical and Yida New Materials. High-end needle coke products mainly rely on imports. Not only is a lot of money wasted, but it is also easily contained. It is of great strategic significance to accelerate the research on the production process of needle coke and realize the advancement with production as soon as possible.


2 The development history of oil-based needle coke


As early as the 1950s, the American Great Lakes Carbon Company produced needle coke through the delayed coking process; in 1960, the American Continental Oil Company (Conoco, later merged with Phillips) applied for a patent for the production of needle coke; in 1969, the standard Standard Oil's first needle coke industrial production facility was put into production in Los Angeles. Since then, American companies represented by Great Lakes Carbon have monopolized 80% of the oil-based needle coke market worldwide.


my country’s needle coke research began in the 1970s. The Sinopec Research Institute of Petroleum and Chemical Industry (hereinafter referred to as the Chinese Academy of Petrochemical Sciences) passed laboratory and pilot tests, using thermally cracked residual oil and FCC clarified oil as raw materials, successively in Fushun The Second Petroleum Plant, Daqing Petrochemical Plant, and Anqing Petrochemical Plant have all succeeded in industrialization tests, but they have failed to achieve continuous industrial production due to various reasons such as raw materials, market, and technology. In 1995, the 0.1Mt/a needle coke device constructed by Jinzhou Petrochemical applied the technology of the Chinese Academy of Petroleum Sciences to start up successfully, filling the gap in the domestic oil-based needle coke. After technological transformation, Jinzhou Petrochemical became the first domestic company capable of stably producing oil-based coke. Needle coke enterprise. In a sense, the Chinese Academy of Sciences and Jinzhou Petrochemical have contributed to the development of needle coke in China. In addition to the Petroleum Institute of Petroleum, China University of Petroleum has also explored the mechanism of thermal reaction and coking reaction and has also made certain achievements.


In recent years, with the rapid development of society and economy, the domestic demand for needle coke has increased significantly. As a petroleum product with high added value, needle coke has once again become one of the hot spots in the petrochemical field. Not only are existing manufacturers competing to pass Technological transformation to expand production capacity, traditional petrochemical companies such as Shanghai Petrochemical, Maoming Petrochemical, and Jinling Petrochemical also intend to enter the needle coke market. Shanghai Petrochemical uses catalytic oil slurry as raw material[2]. In 2015, it used "distillation cutting-hydrorefining" and other processes for raw material pretreatment, and conducted industrial tests on a 1.0Mt/a delayed coking unit to obtain high-power graphite electrodes. High-quality needle coke products required by the index.


3 Production of oil-based needle coke


At this stage, the domestic oil-based needle coke production is based on delayed coking technology. The production process mainly includes three stages: raw material pretreatment, delayed coking, and calcination.

3.1 Raw material selection and pretreatment


Raw materials are a key factor affecting the quality of needle coke. Suitable raw materials can greatly reduce the difficulty of generating mesophase pitch and eliminate subsequent unstable factors. The raw materials for producing needle coke should have the following characteristics:


① The content of aromatic hydrocarbons is high, especially the content of the linearly arranged 3 and 4-ring short side chain aromatic hydrocarbons is 40%-50%. In this way, the aromatic hydrocarbon molecules condense with each other to form larger planar aromatic molecules during carbonization. The bond electron clouds overlap each other to form a relatively complete graphite-like structure lattice [3].


② Asphaltenes and gums that exist in the molecular structure of fused-ring large aromatic hydrocarbons are low in content. These substances have strong molecular polarity and high reactivity. During carbonization, they are easily condensed to form coke precursors, and there is no opportunity for mutual alignment. , Generally require less than 2% of heptane insoluble matter.


③ The sulfur content is not more than 0.6%, and the nitrogen content is not more than 1%. Sulfur and nitrogen are easy to escape due to high temperature during the production of electrodes, resulting in swelling, causing cracks in the electrodes.


④ The ash content is less than 0.05%, and there are no mechanical impurities such as catalyst powder, which will cause the reaction to proceed too fast during carbonization, increase the difficulty of mesophase sphere formation, and affect the properties of coke.


⑤ The content of heavy metals such as vanadium and nickel is less than 100ppm, because the compounds composed of these metals have catalytic effect, which will accelerate the nucleation of mesophase pellets, and the pellets are difficult to fully grow. At the same time, these metal impurities left in the product will also cause voids, Problems such as cracks cause the strength of the product to decrease.


⑥ Quinoline insoluble matter (QI) is zero, QI will adhere to the mesophase, hindering the growth and fusion of spherical crystals, and the needle coke structure with good fiber structure cannot be obtained after coking.


⑦ The density is greater than 1.0g/cm3 to ensure sufficient coke yield.


In fact, feedstock oils that meet the above requirements are relatively rare. From the perspective of components, FCC slurry, furfural extraction oil, and ethylene tar with high aromatic content are ideal raw materials for needle coke production. Catalytic cracking oil slurry is one of the by-products of the catalytic device. It is usually delivered as a cheap fuel oil. Because of its high aromatic content, it is a high-quality raw material for the production of needle coke in terms of composition. In fact, it is worldwide Most needle coke products are prepared with catalytic cracking oil slurry as raw materials.


Wang Bin [4] analyzed the effects of different components in FCC slurry on mesophase transformation, and discussed their influence on the formation of needle coke. A higher content of aromatic components and a certain content of saturated components are needed to produce higher quality needle coke.


Zhang Debao[5] and Liu Chuan[6] investigated the effects of different types of FCC slurry on the properties of needle coke. They believed that the different fractions of raw materials had different effects on the mesophase structure, which further verified the preparation of FCC slurry. The feasibility of needle coke.


Furfural extracted oil is another product in the oil refining process. It is based on the principle of "similar compatibility", using furfural solvent to extract the sideline oil of atmospheric and vacuum distillation to obtain a by-product rich in aromatics[7,8 ]. China National Offshore Oil Corporation and China University of Petroleum used furfural extracted oil from heavy residues such as naphthenic crude oil vacuum distillate as raw materials to prepare mesophase pitch and finally high-quality needle coke. However, only a small number of lubricating oil refineries have furfural extracted oil products, and it is more difficult to obtain raw materials than catalytic cracking oil slurry, so the furfural extracted oil to prepare needle coke has not been applied on a large scale.


Ethylene tar is a by-product of the production of ethylene by the cracking of hydrocarbons. It contains more polycyclic aromatic components such as indene and methylindene. In 1978, Shell used ethylene tar as a raw material to produce needle coke products on an industrial plant for the first time, but the technology was strictly kept secret. The Chinese Academy of Sciences [9] put forward the raw material pretreatment method and suitable process operating conditions for producing needle coke from ethylene tar, and verified the coking experiment, and obtained needle coke products with low thermal expansion coefficient.


XianglinCheng [10] et al. co-carbonized ethylene tar pitch and waste polystyrene to prepare needle coke. The results showed that after adding waste polystyrene to ethylene tar pitch, the optical structure of the coke changed from rough mosaic texture to high Uniaxially oriented flow area. At the same time, the low viscosity of mesophase pitch is conducive to the development of mesophase and high uniaxial alignment. The increase in alkyl content greatly improves the characteristics of needle coke. Judging from the current situation, the production of needle coke with ethylene tar as a raw material has not been industrialized in China.


Under the existing oil refining process conditions, no matter what kind of oil is used, it cannot be used as a raw material to directly produce needle coke and must be pretreated. In principle, the pretreatment methods can be divided into distillation, extraction, hydrogenation and other methods: the distillation method uses the difference in the distillation range distribution of different components to enrich the ideal components and undesirable components through distillation The extraction method uses the different solubility of aromatic components and asphaltenes and gums in organic solvents such as furfural. The separation is carried out by extraction-separation. Shandong Yida adopts the supercritical system developed in cooperation with China University of Petroleum. Continuous separation technology; hydrogenation method aims to remove undesirable components such as sulfur and nitrogen through high temperature and high pressure hydrogenation reaction. In most cases, one method does not meet the demand, and it is often necessary to use a combination of two methods.