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

• Solvent Sector: Cyclohexane possesses a strong solvency capacity for resins, coatings, and greases, making it widely used in paint thinners and the rubber industry. Approximately 35% of the world's cyclohexane is used in solvent production.

• Nylon Production: As a precursor for adipic acid and caprolactam, cyclohexane is oxidized to produce cyclohexanone, which is then further oxidized and undergoes Beckman rearrangement to create nylon monomers. The global production of nylon 66, exceeding 6 million tonnes per year, is directly dependent on the cyclohexane supply chain.

• Fuel Additive: Cyclohexane improves gasoline octane and reduces engine knock. Its application adheres to ASTM D4814 to ensure combustion efficiency and environmental compliance.

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.