Understanding Cyclohexane: Properties, Applications, and Safety

Cyclohexane (CAS CAS 110-82-7) is an organic compound with the chemical formula C₆H₁₂, belonging to the group of cycloalkanes. As a colorless flammable liquid, it plays an important role in the chemical industry, both as a highly efficient solvent and as a key intermediate in the production of nylon. This article will analyze cyclohexane from the perspectives of its basic properties, industrial applications, production methods, and safety regulations.

Basic Properties and Structural Features of Cyclohexane

The molecular structure of cyclohexane consists of a closed ring of six carbon atoms, with each carbon atom connected to two hydrogen atoms by a single bond. Its most stable conformation is the chair conformation, an arrangement that minimizes intramolecular tension and energy.

Cyclohexane has a molecular weight of 84.16 g/mol, a melting point of 6.5°C, a boiling point of 80.7°C, and a density of 0.7781 g/cm³ (at 20°C). These physical properties ensure it remains liquid at room temperature, facilitating industrial transport and storage.

Analysis of Physical and Chemical Properties

Physical Properties

Cyclohexane is insoluble in water but miscible with organic solvents such as ethanol and ether. Its low viscosity and low surface tension provide excellent permeability, making it often used as a swelling agent in rubber processing.

Chemical Stability

Compared to straight-chain alkanes, cyclohexane exhibits high stability due to its cyclic structure. While not easily oxidized at room temperature and pressure, it can undergo the following reactions under certain conditions:

• Halogenation: Requires light or the presence of a catalyst to produce derivatives like chlorinated cyclohexanes.

• Dehydrogenation: High-temperature dehydrogenation (above 300°C) catalyzed by platinum or palladium to produce benzene is a typical example of aromatization.

• Oxidation reaction: Oxidation by air to form cyclohexanone and cyclohexanol is an important step in the synthesis of nylon 6 and nylon 66. The reaction formula is

Industrial Application Scenarios of Cyclohexane

Cyclohexane is a versatile compound that plays an important role in various industrial and research fields, thanks to its unique solubility and status as a key chemical intermediate.

• As a solvent:
  Cyclohexane has strong solubility for resins, coatings, and oils, making it widely used as a paint thinner, a diluent for adhesives in the rubber industry, and an extractant for oils. Due to its relatively low toxicity, cyclohexane is often used as an environmentally friendly alternative in degreasing, degreasing, and paint removal processes to replace more toxic benzene. Approximately 35% of global cyclohexane production is used for solvent production.

• A key raw material in nylon production:
  Cyclohexane is a key raw material for the production of nylon monomers, particularly indispensable in the production of nylon 66. It serves as a precursor to adipic acid and caprolactam, which are oxidised to form cyclohexanone. Cyclohexanone is further oxidised and undergoes Beckman rearrangement to ultimately produce nylon monomers. Global annual production of nylon 66 exceeds 6 million tonnes, directly dependent on a stable cyclohexane supply chain. It is also a key raw material for the production of other important organic compounds such as cyclohexanol and cyclohexanone.

• Fuel additives:
  Cyclohexane can be used as a fuel additive to effectively increase the octane rating of gasoline, thereby reducing engine knocking and improving combustion efficiency. Its application in this area complies with the ASTM D4814 standard to ensure performance and meet environmental requirements.

• Applications in research and analysis:
  In research and analysis, cyclohexane plays a crucial role, often serving as a solvent and standard substance in chromatography analysis. In organic synthesis processes, cyclohexane actively participates in the synthesis reactions of various compounds.

• Chelation Titration of Metal Ions:
  Cyclohexane can be used to detect multiple metal elements such as copper, iron, silicon, aluminium, calcium, and magnesium, particularly in chelation titration analysis.

• Precision applications in the microelectronics industry:
  In the microelectronics industry, where purity requirements are extremely high, cyclohexane is widely adopted. It serves as a solvent for photoresists and is crucial in precision cleaning processes. For the manufacturing of discrete devices and integrated circuits, different grades of cyclohexane are used for different levels of cleaning, particularly in the production of ultra-large-scale integrated circuits (ULSI), where it is indispensable.

• Essential oil extraction:
  Additionally, cyclohexane is used in essential oil extraction, demonstrating its practicality in the processing of natural products.

In summary, cyclohexane plays a pivotal role in various industrial and research fields due to its wide range of applications, high solubility, status as a key chemical raw material, and relatively low toxicity.

Production Technology and Process Flow

• Petroleum Cracking: Direct separation of cyclohexane from petroleum fractions offers low cost but limited purity, making it suitable for solvent production where high purity is not required.

• Benzene Catalytic Hydrogenation: Benzene reacts with hydrogen at 200-300°C and 1-3 MPa in the presence of a nickel-based catalyst to form cyclohexane. The reaction is:

  This method yields up to 95% and is the dominant industrial production route.

Safety Norms and Environmental Management

Cyclohexane is classified as a flammable liquid (Category 2) and a health hazard (Category 3). Care is required when handling it:

• Storage Requirements: Store away from light in explosion-proof cabinets at temperatures not exceeding 30°C and away from oxidizing agents.

• Leakage Treatment: Use activated carbon or diatomaceous earth for adsorption; direct flushing with water is strictly prohibited.

• Personal Protection: Wear nitrile gloves and a Class A gas mask to avoid skin contact or inhalation of vapors.

Market Trends and Development Prospects

With the expansion of nylon applications in automotive lightweighting and electronic components, the demand for cyclohexane is growing at an average annual rate of 4.2%. Green production processes, such as bio-based cyclohexane synthesis technology, are being developed, which will drive the industry's transition to decarbonization in the future. As a cornerstone compound of the modern chemical industry, the efficient use and safe management of cyclohexane are essential for sustainable development. Research institutes and companies need to continuously optimize production processes and reduce environmental impacts to meet growing market demands.