The thermal cracking method is a discontinuous carbon black manufacturing method, and each production line is equipped with two reaction furnaces lined with refractory materials. During production, first feed natural gas and air into a reaction furnace and burn it, and stop feeding air after the reaction furnace reaches a certain temperature, so that the natural gas will be pyrolyzed to generate carbon black under the condition of isolating the air. When the reaction furnace is carrying out the cracking reaction, another reaction furnace starts to burn natural gas to preheat. Each reaction furnace is burned and heated after the cracking reaction is completed and the temperature drops to a certain level, so that the cycle is produced. The produced carbon black and flue gas mixture is cooled by spraying water, and then the collected carbon black is granulated. Using natural gas, coke oven gas or heavy liquid hydrocarbons as raw materials, in the absence of oxygen and flames, carbon black is produced by high-temperature pyrolysis, which is called thermal black. It is the category with the lowest specific surface area in the carbon black variety pedigree, with a nitrogen adsorption specific surface area of 6-14m2/g and a particle size of 130-470nm. Its oxygen content and structure are very low. This type of carbon black has practically no structure. Basically exists as a single spherical particle.
There are three main varieties of thermal black: medium thermal black, non-polluting medium thermal black and fine thermal black. The nitrogen adsorption specific surface area of medium thermal black is 6-10m2/g, and that of fine thermal black is 10-14m2/g.
Thermal black is the carbon black with the largest particle size and lowest structure. The rubber compound filled with thermal carbon black has low tensile properties, but has high elasticity, low hardness and heat generation, and low electrical conductivity, and the filling amount of thermal carbon black is large. It is suitable for sleeper pads that require high elasticity, Rubber products with low heat generation and good insulation properties. In addition, thermal carbon black has large carbon content and high purity, which can be used in the production of cemented carbide and carbon products.
Natural gas pyrolysis carbon black is produced by pyrolysis of natural gas isolated from air and heated to 1300°C. It is composed of a large number of spherical and elliptical carbons and a small amount of welded particles. It has large particle size, small specific surface area, low structure, easy dispersion, and good fluidity. High filling capacity and other characteristics. Because of its low surface activity, it is also called non-reinforcing carbon black. It is one of the widely used carbon black varieties in tire inner liners, rubber hoses, tapes, oil seals, and fluorine rubber products.
According to the specific surface area, thermal cracking carbon black is divided into N800 or N900 series carbon black, while furnace carbon black is from N100 to N700 series. Thermal cracking carbon black has the largest particle size (average diameter of 240-320NM) in carbon black, and its specific surface area is the lowest, only 7-11m2/G. Relatively speaking, the particle size of furnace carbon black is three to twenty times smaller than that of thermal cracking carbon black (the average diameter is 15-80NM), and its specific surface area is 27-145m2/G.
Thermal cracking carbon black dibutyl phthalate (DBPA) absorption value is the smallest among all kinds of carbon black, the value is between 32-47ml/100G, which shows that the particle aggregation degree is very small or the structure very low. Thermal cracking carbon black appears as many individual spherical carbon black particles on the electron micrograph, with a small degree of aggregation, consisting of a small number of fused particles.
The reaction time for the production of thermal cracking carbon black is longer than that of furnace carbon black, coupled with the high temperature (1300°C) required for thermal cracking of natural gas, the graphite layer plane of thermal cracking carbon black becomes very orderly, so that Only the surface of the layer plane is exposed on the particle surface. The unsaturated carbon bonds at the edge of the layer plane are not exposed, so thermal carbon black has no reaction sites to react with elastomers, and unlike furnace carbon black, it does not contain organic functional groups that increase surface activity.
Pyrolytic carbon black manufacturers all over the world include CANCARB LIMITED in Canada, EVONIC in the United States and GAZPROM in Russia. The largest of them is Canada's Kencarber Company, which has a production capacity of 45,000 tons per year, stable quality, and advanced technology. The total global market share of THERMAX FLOFORM N990 and other ultra-pure thermal cracking carbon blacks exceeds 80%.
At present, the technology of producing medium particle pyrolysis carbon black (MT) in our country is not yet mature. Some manufacturers of rubber products that do not require high performance mostly use imported or domestic natural gas semi-reinforcing carbon black or spray carbon black for filling, but due to the particle size and structure, the application effect is quite different from that of MT carbon black. Therefore, in the fields of sealing, fluid transportation and shock absorption that have strict requirements on compression set performance, anti-permeation performance, fuel and chemical medium resistance, and dynamic performance, the world's rubber industry usually uses medium-particle thermal cracking carbon black (MT) to Make fill application.