Thermal black process

Some special processes for producing carbon black are based on the thermal decomposition of lower gaseous hydrocarbons in the absence of air. Natural gas and acetylene are commonly used as raw materials. 

The thermal black process, which was developed in the 1930s, is still used for the production of coarse carbon blacks (nonreinforcing carbon blacks) for special applications in the rubber industry. Contrary to the above-described processes, energy generation and the pyrolysis reaction are not carried out simultaneously. Natural gas eventually blended with vaporized oil is used as both a feedstock and a fuel. 

A thermal black plant consists of two furnaces, which are used in alternate heating and production periods of ca. 5-min duration (Fig. 57). Each of the cylindrical furnaces (4 m in diameter and 6 m high) contains a network of heat-resistant bricks. They are heated with natural gas and air. At a temperature of ca. 1400 °C, the air is switched off and only natural gas is introduced for pyrolysis. Since this reaction is endothermic, the temperature falls. At about 900 °C, a new heating period is necessary. 

The products leaving the furnace, carbon black and nearly pure hydrogen, are cooled by injecting water into an ascending channel. The carbon black is separated in the collecting system. 

Carbon blacks of lower particle size can be produced by diluting natural gas with recycled hydrogen. Fine thermal blacks (FT blacks) with mean primary particle sizes of 120-200 nm are manufactured in this way. Medium thermal blacks (MT blacks) with mean particle sizes of 300-500 nm are still produced and are obtained by using undiluted feed stock. The yield of MT blacks is about 40% with respect to the amount of feedstock and fuel used. 

One could also include the thermal black method in the group of thermal-oxidative processes, with the distinction that energy generation and decomposition reaction are not simultaneous. However, the fact that the actual carbon black formation takes place in the absence of oxygen and at decreasing temperatures results in carbon black properties that are markedly different from those achieved with thermal-oxidative processes. 

Thermal blacks are formed relatively slowly, resulting in coarse particles in sizes ranging from 300 to 500 nm, referred to as medium thermal. However, formerly, when using natural gas only as feedstock, it was possible to dilute it with inert gases and produce a thermal black consisting of particles in the range of 120 to 200 nm. This was referred to as fine thermal although it has virtually disappeared from the market. 

Thermal blacks are used for mechanical rubber goods with high filler contents. Cheaper products (clays, milled coals, and cokes), however, have gained increasing 

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Thermal cracking thermal black process natural gas... 

Figure 57. Thermal black process a) Thermal black reactor b) Cooler c) Filler bricks d) Inlet for the feedstock e) Inlet for the fuel f) Outlet for the burned fuel g) Outlet for the pyrolysis products h) Carbon black outlet i) Blower...

In the thermal black process, natural gas is cracked to carbon black and hydrogen at 1100 to 1650°C in a refractory-lined furnace in a two-cycle (heating and making, or decomposition) operation. The reaction is... 

The gas furnace process, is similar to the oil furnace process but, like the thermal black process, uses natural gas as feedstock. 

Thermal decomposition Thermal black process Acetylene black process Natural gas or mineral oils Acetylene... 

S.7.6.2.3 Pyrolysis Processes in the Absence of Oxygen Thermal Black Process... 

The thermal black process operates discontinuously and generally utilizes natural gas as a feedstock. A production unit consists of two cylindrical furnaces connected to one another, in which refractory bricks are piled one on top of another for heat storage with a large cavity in between. The two furnaces are operated alternately while the first furnace is being heated to the reaction temperature (ca. 1300 to 1500°C) with a stoichiometric mixture of air and combustible gas (mainly natural gas), natural gas is fed into the second already heated furnace and is thermally pyrolyzed. Since the reaction is endothermic, the furnace cools and the gas flows are switched when a critical minimum temperature is reached and the first furnace utilized, while the second is heated up again. The cycle time is about 5 minutes. 

Carbon black was produced even in pre-industrial times, from oils and resins, for the manufacture of pigments. At the beginning of the 19 th century, the lamp black and thermal black processes were introduced, which used mainly aliphatic hydrocarbons (natural gas) as raw material. 

The properties of the carbon black are particularly dependent on the reaction conditions of the pyrolysis. The distribution of particle sizes from furnace carbon black extends from around 10 nm to 100 nm. (Smaller particles can be produced by the gas black method, larger particles by the thermal black process.) Small carbon black particles are obtained with high reaction temperatures and reaction times of around 10 sec., whereas the manufacture of carbon black with a particle diameter of 35 to 65 nm requires lower temperatures and reaction limes of 1 to 2 sec. 

The Thermal Black Process. Thermal black is a large particle size, low structure carbon black made by the thermal decomposition of natural gas, coke... 

Several modem processes for the production of carbon-based blacks (flame carbons . v.) are based on the thermal decomposition of lower gaseous hydrocarbons in the absence of air. Developed in the 1930s, the thermal black process is still used for the production of pigments. In distinction from other carbon black processes, the method is discontinuous the reaction furnace is heated to about 1400°C with a mixture of natural gas and air, then the air is switched off. The gas is decomposed, an andothermic process which cools the furnace. This cycle is then repeated. Fine thermal blacks of particle size 120-200 nm and medium thermal blacks of 300-500mn are typically produced (Buxbaum, 1998). 

This process is conducted at about 1300 °C. Commonly the hydrogen gas byproduct is used for other furnaces. The thermal black process has a theoretical yield of about 45 to 60% of available carbon. Also, thermal blacks are quite different from the furnace blacks in that the thermal blacks have significantly larger particle size and much lower structure. 

The two major commercial processes for manufacturing carbon black are the thermal black process which uses natural gas as the hydrocarbon feed stock, and the furnace black process which petroleum oil as the feedstock. The thermal process produces the largest particle size (0.1 to 0.5 xm) and lowest structure blacks. The furnace process accounts for over 95% of the total carbon black produced and can be controlled to produce both small and large particle size grades in the range of 0.01 to 0.10pm. 

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