Manufacturing Processes

Carbon Black is produced by the thermal decomposition of hydrocarbons (liquid and gaseous hydrocarbons) under controlled conditions, most commonly through incomplete combustion of the feedstock. The most common source of feedstock for the production of Carbon Black is a heavy stream of hydrocarbon derived from coal or crude oil processing, which is referred to as Carbon Black Oil (CBO). Natural gas, distillates from coal tar (carbochemical oils) or residual oils that are created by catalytic cracking of petroleum fractions and olefins manufactured by the thermal cracking of naphtha or gasoil (petrochemical oil) are the key sources of this raw material.

Production methods differ based on the way the heat and decomposition stages are arranged. Manufacturing methods include furnace, gas, lamp and thermal black processes. More than 98% of the world's annual Carbon Black production is achieved through the furnace black process.

Furnace Black Process

The furnace black method is continuous and uses liquid and gaseous hydrocarbons as feedstock. The heated liquid feedstock is sprayed into a heat source generated by the combustion of natural gas or fuel oil and pre-heated air. Because it occurs at a very high temperature, the reaction is confined to a refractory-lined furnace. After the Carbon Black is formed, the process mixture is quenched by the injection of water. This also prevents any unwanted secondary reactions.

The Carbon Black-laden gas then passes through a heat exchanger for further cooling while simultaneously heating the required pre- heated air for process combustion. A bag filter separates the Carbon Black particles from the gas stream. The gases produced by the reaction are combustible and in most cases are burned in a boiler to generate steam and/or electricity or are alternatively flared. The Carbon Black collected by the filter has a very low bulk density and, depending on the application, is usually pelletized or further densified to facilitate onward handling.

The furnace black method offers environmental and work safety benefits. The fully enclosed installation controls and reduces the emission of process gases and dust. Besides its environmental and technological advantages, the furnace black method is flexible due to the multiple configurations and process parameters of the furnace reactor design, which allows the manufacture of a wider variety of grades of Carbon Black than any other process currently used. All raw materials and operating conditions are precisely specified. This makes it possible to produce a broad range of Carbon Black that is suitable for use in various applications without fundamentally changing the process equipment or feedstock for each product variant.

Other Processes

The other process types, although used less commonly, are of significant importance as they effectively allow for tailoring of products and solutions to customers' specific needs and typically use more highly specialized, often customized grades of Carbon Black. These processes are:

1. Gas Black.

The gas black method was developed in the mid-1930s by our predecessor company. The gas black process uses vaporized oils as a feedstock. The oil is heated and the resultant vapors are carried by hydrogen rich gas into a tube fitted with numerous burners. The individual particles impinge on the surface of a water-cooled drum. A portion of the Carbon Black generated is deposited on the roller, while the rest enters the filter system. Then the two Carbon Black streams are combined. Onward processing is similar to the furnace black process.

2. Lamp Black.

Lamp black is a specialty Carbon Black produced through the incomplete combustion of Carbon Black oil similar to the furnace black process, except that combustion occurs in a large, open, shallow vessel. Lamp black is the oldest industrial scale production process for Carbon Black still in use.

3. Thermal Black.

This method of producing Carbon Black is a semi-batch method, with natural gas as the most commonly used feedstock, although higher grade hydrocarbon oils can also be used. It involves the thermal decomposition of the feedstock in a refractory lined vessel, which decomposes the natural gas into Carbon Black and hydrogen.

After Treatment

The after treatment of the Carbon Black surface by oxidative agents (for example, ozone, nitrogen-oxides) can enhance the desired physical characteristics of the final product for certain Specialty Carbon Black grades.

Production Technologies

Chemical process

Manufacturing method

Main raw materials

Thermal-oxidative
decomposition

Furnace black process
Gas black process
Lamp black process

Aromatic oils on coal tar basis or mineral oil, natural gas
Coal tar distillates
Aromatic oils on coal tar basis or mineral oil

Thermal decomposition

Thermal black process

Natural gas (or mineral oils)

The basic raw material for producing Carbon Black consists of hydrocarbons that are split into their constituent element carbon and hydrogen by either a thermal or a thermal-oxidative (partial combustion) process. Economically the thermal-oxidative decomposition has become the predominant method with the hydrocarbons taking on a double role since they serve both as a source of heat and carbon. Every Carbon Black production method is based on those two fundamental elements, how these stages are arranged is what defines the difference between the production processes.

Thermal-Oxidative Processes

a) Furnace Black Process

The Furnace Black Process is the most common production method of Carbon Black. It is continuous and uses liquid and gaseous hydrocarbons as feedstock and as heat source. The liquid feedstock is sprayed into a heat source generated by the combustion of natural gas and pre-heated air. The reaction is confined to a refractory-lined furnace. After the Carbon Black is formed, the process mixture is quenched by the injection of water. This prevents secondary reactions. The Carbon Black loaded gas passes through a heat exchanger for cooling, while heating up the required process air. A bag filter system separates the Carbon Black particles from the gas stream. The Carbon Black collected has a very low bulk density and is usually pelletized or densified for further handling.

The wet-pelletizing process uses water and a binding agent in a mixer which transforms the Carbon Black into spherical pellets which are dehydrated in rotary dryers. The binding agent ensures that the product is resistant to attrition and easy to transport.

Specialty Carbon Blacks produced are loosely densified and packed as powder blacks or are transformed into pellets. Oil-pelletized blacks are an additional variant utilizing mineral oils in the pelletization process. Due to the light oil coating these Carbon Blacks are easier to disperse and apt for dust-free handling.

The Furnace Black method is environmentally, economically and technically leading. It offers great flexibility in production of many different grades and produces a broad range of Carbon Blacks for various applications without having to change the process. Particle aggregation can be controlled by adding small quantities of alkaline metal salt. The Furnace Black process delivers particles in the range of 10-80 nm.

b) Gas Black Process

The Gas Black process is based on coal tar distillates as feedstock. The oil is heated in a vaporizer and the resultant vapors are carried by a hydrogen-rich gas into a gas tube fitted with multiple burners. The flames impinge on the surface of a water-cooled drum. A portion of the Carbon Black generated is deposited on the roller while the rest enters the filter system. In the next step the two Carbon Black streams are combined. The processing is similar to the Furnace Black process.

The Gas Black method allows to produce primary particle sizes with a range of 10-30nm. The trade off is less flexible in defining the structure. The Gas Blacks are almost exclusively used in pigment applications, where the fine-particles are essential. Due to contact with oxygen at high temperature acidic oxides form on the surface of the particles. In contrast to Furnace Black, Gas Blacks therefore show an acidic reaction when suspended in water.

Oxidative post-treatment also makes it possible to further increase acidic surface. The resulting Carbon Blacks are used in Coating and Printing Ink.

c) Lamp Black Process

The Lamp Black process is the oldest Carbon Black production method. The lamp black apparatus consists of a cast-iron pan that holds the liquid feedstock. This is surmounted by a fire-proof flue hood, lined with refractory bricks.

The air gap between the pan and the hood, as well as the vacuum in the system, regulate the air supply. Radiant heat from the hood causes raw material to vaporize and partially combust, most of it is converted into Carbon Black.

After the cooling stage the Carbon Blacks are passed through a filter. The processing is similar to the Furnace Black method.

Nowadays the Lamp Black process only produces one type of Specialty Carbon Black and one type of Rubber Black. These are characterized by a broad particle size of 60- over 200nm and can be widely used in a number of Special Applications.

Thermal Decomposition

a) Thermal Black Process

The Thermal Black manufacturing process is a non-continuous or cyclic process with natural gas as feedstock.

A Thermal Black plant delivers maximum efficiency when operated in tandem mode: two reactors operating alternately in cycle between 5-8 minutes. One is heated with natural gas/ oil/air mixture, the other is fed with pure feedstock which undergoes thermal decomposition. The actual Carbon Black formation occurs in the absence of oxygen at decreasing temperatures.

This results in Thermal Blacks which form slowly and in high particle sizes from 300-500nm.