Coal tar

Coal Tar and Its Distillation Products

Coal Tar is a thick, dark, viscous liquid obtained during the dry distillation of bituminous coal. It is a complex mixture of hundreds of organic compounds, primarily aromatic hydrocarbons, phenols, and heterocyclic compounds. Coal tar is a valuable resource in the chemical industry, as it can be further distilled to yield various aromatic compounds used in a wide range of applications, from medical treatments to the synthesis of chemicals and materials.

Production

Diagram illustrating the distillation of coal tar

The production of coal tar is a by-product of the coke-making process used in steel production. Bituminous coal is heated in the absence of air in a coke oven, resulting in the breakdown of the coal into coke, volatile organic compounds, and coal tar. The coal tar is collected and later subjected to fractional distillation to isolate its components.

Composition

Coal tar is composed of a vast number of compounds. The major groups of compounds in coal tar include:

• Aromatic hydrocarbons, such as benzene, toluene, and xylene (BTX)
• Phenols, including phenol itself and cresols
• Heterocyclic compounds, such as pyridine and quinoline
• High molecular weight polymers and asphaltenes

Distillation Products

The fractional distillation of coal tar yields several important chemical products:

• Light Oils, containing benzene, toluene, and xylene, used as solvents and chemical feedstocks.
• Middle Oils, rich in naphthalene and phenols, used in the production of dyes, plastics, and pharmaceuticals.
• Heavy Oils, from which anthracene, creosote, and other heavy aromatics are derived, used in the production of insecticides, fungicides, and preservatives.
• Tar Pitch, the residue from the distillation process, used in road construction and as a binding agent in briquettes.

Applications

Coal tar and its distillation products have a wide range of applications:

• Pharmaceuticals: Coal tar is used in the treatment of psoriasis and eczema.
• Chemical Production: Aromatic compounds derived from coal tar are used to manufacture dyes, plastics, pharmaceuticals, and synthetic fibers.
• Materials: Tar pitch is utilized in roofing, road construction, and as a binder in the aluminum industry.

Environmental and Health Concerns

Coal tar and some of its components have been identified as carcinogenic. Handling and use of coal tar products are regulated to minimize exposure and environmental impact.

See Also

• Coke (fuel)
• Aromatic hydrocarbons
• Phenols
• Environmental impact of the coal industry

References

• "The Chemistry and Technology of Coal" by James G. Speight provides an in-depth look at coal tar production and its applications.
• The International Agency for Research on Cancer reports on the carcinogenicity of coal tar and coal-tar pitches.

External Links

• Environmental Protection Agency (EPA) - Information on regulations and health concerns related to coal tar and its by-products.
• Chemical Safety Facts - Details on the safe use and handling of chemical products derived from coal tar.