Лако-красочные материалы — производство

The preferred feedstocks for most carbon black production processes, especially the furnace process, are heavy oils, which are composed mainly of aromatic hydrocar­bons. The aromatic form of carbon gives the highest carbon to hydrogen ratio, thus maximizing the available carbon, and is the most efficient one in terms of carbon black yields. In theory, the greater the aromaticity the more efficient is the process. Unfortunately as the number of combined rings increases, the substances move from viscous liquids to solid pitches. Therefore, in reality, the most suitable oils are those in which the majority of the carbon is in the form of substances comprising three or four-membered rings.

Distillates from coal tar (carbochemical oils), or residual oils that are created by catalytic cracking of mineral oil fractions and olefin manufacture by the thermal cracking of naphtha or gas-oil (petrochemical oil) can also be used as a source of raw material. Quality is the main criteria to favor a specific feedstock. Here a variety

of properties are important: density, distillate residue, viscosity, carbon/ hydrogen ratio, asphaltene content, specified impurities, etc. All these play a role for the desired feedstock specifications. The BMCI (Bureau of Mines Correlation Index) provides a measure of aromaticity based on either density and average boiling point or viscosity and API gravity [4.7]. Economically a suitable feedstock should have an index above 120.

However, the BMCI is really only applicable to feedstocks derived from petroleum. In the case of carbochemical oils, the BMCI may not reflect the true aromaticity of the product. For this reason, the carbon/hydrogen ratio is more favored for carbo­chemical products. However, as this measurement is also superior to BMCI, even for petrochemical products, the carbon/hydrogen ratio or the carbon content are becoming the preferred criteria for all carbon black feedstocks.

Additional quality requirements involve impurities from foreign matter. Alkaline metals, for instance, are important because they have a direct effect on a specific carbon black property. The sulfur content of the oil can also play a significant role in production operations since, in many countries, producing sites have to meet rigorous environmental standards. Sulfur emissions from combustion processes are restricted by law. Furthermore, carbon blacks having high sulfur contents might be prohibitive for certain applications. When describing the various production methods we will also address the different raw materials that can be used to produce carbon black.

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