Coal tar is a byproduct derived from the carbonization of coal, a process that involves heating coal in the absence of air to produce coke, coal gas, and coal tar. This complex mixture of hydrocarbons has a wide range of applications, from medicinal uses to industrial applications. Understanding how coal tar is derived and its various applications can provide insights into its significance in different sectors.

Derivation of Coal Tar

The derivation of coal tar begins with the process of coal carbonization, which is typically carried out in coke ovens. During this process, coal is heated to temperatures between 900°C and 1100°C in the absence of air. This high-temperature treatment causes the coal to decompose into several byproducts, including coke, coal gas, and coal tar.

Carbonization Process

The carbonization process can be divided into several stages:

• Drying: The initial stage involves the removal of moisture from the coal. As the temperature rises, the water content evaporates.
• Devolatilization: At higher temperatures, volatile compounds are released from the coal. These compounds include gases such as methane, hydrogen, and carbon monoxide, as well as tar and other organic compounds.
• Solid Residue Formation: The remaining solid material, known as coke, is primarily composed of carbon and is used in various industrial processes, particularly in the production of steel.

During the devolatilization stage, coal tar is collected as a liquid byproduct. It is then subjected to further processing to separate it into different fractions based on their boiling points. This separation is typically achieved through a process known as fractional distillation.

Fractional Distillation

Fractional distillation is a crucial step in the derivation of coal tar. It involves heating the coal tar to different temperatures to separate it into various components. The main fractions obtained from coal tar distillation include:

• Light Oils: These are the first fractions to be distilled and include compounds such as benzene, toluene, and xylene. These light oils are used as solvents and in the production of chemicals.
• Middle Oils: This fraction includes naphthalene and phenol, which are used in the production of plastics, resins, and other chemicals.
• Heavy Oils: These oils contain compounds such as creosote and anthracene. They are used in wood preservation, as well as in the production of dyes and pigments.
• Pitch: The final residue left after distillation is known as pitch. It is a solid material used in the production of roofing materials, road construction, and as a binder in various industrial processes.

Applications of Coal Tar

Coal tar has a wide range of applications across various industries due to its complex composition and unique properties. Some of the key applications include:

Medicinal Uses

Coal tar has been used for centuries in the treatment of skin conditions such as psoriasis, eczema, and dandruff. Its anti-inflammatory and antipruritic properties make it effective in reducing itching and inflammation associated with these conditions. Coal tar is available in various forms, including ointments, creams, shampoos, and soaps.

Industrial Applications

Coal tar is widely used in industrial applications due to its chemical composition and properties. Some of the key industrial uses include:

• Wood Preservation: Creosote, a fraction of coal tar, is used as a wood preservative to protect against rot, fungi, and insects. It is commonly used in the treatment of railway ties, utility poles, and marine pilings.
• Road Construction: Coal tar pitch is used in the production of asphalt and bitumen for road construction. It provides durability and resistance to weathering, making it an essential component in the construction of roads and highways.
• Electrodes: Coal tar pitch is used as a binder in the production of carbon electrodes for the aluminum and steel industries. These electrodes are essential for the electrolysis process in aluminum production and for electric arc furnaces in steelmaking.
• Dyes and Pigments: Coal tar derivatives, such as anthracene and naphthalene, are used in the production of dyes and pigments. These compounds are essential in the textile, paint, and printing industries.

Chemical Production

Coal tar is a valuable source of various chemicals used in the production of plastics, resins, and synthetic fibers. Some of the key chemicals derived from coal tar include:

• Benzene: Used as a starting material in the production of plastics, resins, and synthetic fibers.
• Toluene: Used as a solvent and in the production of explosives, dyes, and pharmaceuticals.
• Phenol: Used in the production of plastics, resins, and as a disinfectant.
• Naphthalene: Used in the production of mothballs, dyes, and as a precursor for other chemicals.

Environmental and Safety Considerations

While coal tar has numerous applications, it is important to consider the environmental and safety implications associated with its use. Coal tar contains several polycyclic aromatic hydrocarbons (PAHs), which are known to be carcinogenic and harmful to human health and the environment.

Health Risks

Exposure to coal tar and its derivatives can pose significant health risks. Prolonged or repeated exposure to coal tar can lead to skin irritation, respiratory issues, and an increased risk of cancer. It is essential to use protective equipment and follow safety guidelines when handling coal tar and its products.

Environmental Impact

The production and use of coal tar can have adverse effects on the environment. PAHs present in coal tar can contaminate soil and water, posing a risk to aquatic life and ecosystems. Proper disposal and management of coal tar waste are crucial to minimize its environmental impact.

Conclusion

Coal tar is a versatile byproduct derived from the carbonization of coal, with a wide range of applications in medicinal, industrial, and chemical sectors. Its unique properties make it valuable in various industries, from wood preservation to road construction and chemical production. However, it is essential to consider the health and environmental risks associated with coal tar and take appropriate measures to ensure safe handling and disposal. Understanding the derivation and applications of coal tar can help in making informed decisions about its use and management.