The utilized feedstocks range widely from gases over renewable sources to high aromatic oils like coal tar distillates or bottoms of the cracking processes of naphtha or vacuum oils. These feedstocks are used in five different carbon black production processes. A continuous quality control and characterization of the feedstock is the basis for constant high-quality products.
Gas black production is an open process with a constant air flow. It allows the production of carbon black with the primary particle sizes ranging from 10 to 30 nm. Gas blacks are characterized by their loose structure and exceptional dispersibility. As a result of contact with oxygen at high temperatures, acidic oxides form on the surface of the carbon black particle. In contrast to furnace blacks, gas blacks undergo an acidic reaction when suspended in water.
The Furnace Black method has become the most common in large scale carbon black manufacturing. The technology is continuous and uses liquid and gaseous hydrocarbons as feedstock and as a heat source retrospectively. The liquid feedstock is sprayed into a heat source that is generated by the combustion of the natural gas and pre-heated air. As it occurs at a very high temperature, the reaction is confined to a refractory-lined furnace, hence the name. After the carbon black is formed, the process mixture is quenched by injecting water. The carbon black loaded gas then passes through a heat exchanger for further cooling, while simultaneously heating up the required process air. A bag filter system separates the carbon black particles from the gas stream. The carbon black collected by the filter has a very low bulk density. Because of the light oil coating, these carbon black are characterized by an easy dispersion and virtually dust-free handling. Besides its environmental, economic and technical advantages it allows greater flexibility as the manufacturing of different grades is easier than in any other process currently being used. This makes it possible to produce a broad range of carbon black without fundamentally changing the process for each product variant.
Acetylene is the feedstock to produce acetylene black. It is exothermally decomposed in a closed system, whereby the carbon black and elemental hydrogen is generated. In contrast to the furnace black there is no pre-combustion chamber and no water quenching involved in the process. A further distinctive point is the use of multiple small reactors in parallel. The acetylene black and the process gas are cooled from far above 2000°C reaction temperature to ambient temperatures by heat exchangers. After separating the hydrogen from the acetylene black, it is pneumatically conveyed to a multi stage densification process.
The properties of acetylene black are unique. Due to the morphology it exhibits superior thermal conductivity and the very clean feedstock provides excellent purity and high absorption capacity for liquids. The high reaction temperatures result in a “more graphitic” product compared to other types of CB, which results in excellent electrical conductivity. Acetylene black is very hydrophobic and has therefore a very low moisture absorption.
This method of producing carbon black is a noncontinuous or cyclic process, with natural gas as the most commonly used feedstock. A thermal black plant delivers maximum efficiency when operated in a tandem mode. It consists of two reactors operating alternately in cycles lasting five to eight minutes. One of which is heated with a natural gas or oil/air mixture while the other is fed with pure feedstock which undergoes thermal decomposition. The actual carbon black formation occurs in the absence of oxygen and at decreasing temperature. This leads to carbon black properties that are markedly different from those achieved by thermal-oxidative processes. Thermal black do form relatively slowly, resulting in coarse primary particle sizes ranging from 300 to 500 nm.
The lamp black process is the oldest commercial carbon black production process. It consists of a cast-iron pan that holds the liquid feedstock. It is surmounted by a fire-proof flue hood that is lined with refractory bricks. The air gap between the pan and the hood, as well as the vacuum present in the system, help regulate the air supply and thus enable the manufacturer to fine tune the carbon black’s ultimate properties. Although the radiated heat from the hood causes the raw material to vaporize and partially combust, most of it is converted to carbon black. In order to separate the solids, process gases containing carbon black are passed through a filter after the cooling stage. These carbon black are characterized by a broad primary particle size distribution ranging from approximately 60 to over 200 nm in particle size.
In the after-treatment process the produced carbon black gets further processed with agents. Thereby the polarity of the surface area gets enhanced and fosters the interactions between carbon black and other chemical substances. This could be polar polymers, binding agents in coatings or paint formulas. As a result, a better dispersibility and wettability is achieved creating a smoother surface in the end application. In batteries the after-treated carbon black reduce the water loss to a minimum and improve the batteries performance.