Caprolactam (CPL): properties, production and applications

Caprolactam (CPL, ε-caprolactam, hexahydro-2H-azepin-2-one) is a cyclic amide of ε-aminocaproic acid and one of the most important products of the modern chemical industry. Its molecular formula is C₆H₁₁NO, with a molecular mass of 113.16 g/mol. Under normal conditions, it is a colourless crystalline solid or a colourless liquid (at temperatures above 70 °C) with a faint characteristic odour. Caprolactam is readily soluble in water, ethanol, ether and other organic solvents. The primary use of caprolactam is the production of polyamide-6 (nylon-6), which accounts for the overwhelming share of global consumption.

Physicochemical Properties

Caprolactam has the following key characteristics: density — 1.01 g/cm³, melting point — 69.2 °C (according to other data, about 70 °C), boiling point — 262.5 °C. The crystallisation temperature for the highest grade is not lower than 68.8 °C. Caprolactam is a combustible substance: flash point — not more than 135 °C, autoignition temperature — not more than 400 °C. The lower explosive limit in air is 43 g/m³.

Regulatory Framework and Grades

Requirements for caprolactam in Russia and CIS countries are regulated by GOST 7850-2013 "Caprolactam. Specifications". The standard applies to caprolactam (lactam of ε-aminocaproic acid) produced synthetically from benzene, aniline, phenol and toluene, and establishes requirements for the product manufactured for national economy needs and export. Caprolactam is produced in grades A and B in solid crystalline and liquid form.

Key quality indicators for the highest grade include: permanganate index — not more than 4 units, colour of aqueous solution (50%) — not more than 3.0 Hazen units, content of volatile bases — not more than 0.4 mmol/kg, mass fraction of iron — not more than 0.00002%, mass fraction of oxime — not more than 0.002%, mass fraction of water — not more than 0.07%. Caprolactam is intended for the production of chemical fibres and yarns and polyamide resins.

Production Technology

Industrial caprolactam production is based on several main technological routes. Historically, the first and most widespread process includes the following stages: hydrogenation of benzene to cyclohexane, oxidation of cyclohexane to cyclohexanone, oximation of cyclohexanone to produce cyclohexanone oxime, and subsequent Beckmann rearrangement into caprolactam. Various methods are used for oximation: the HPO process (hydroxylamine phosphate), the HAO process (ammoximation) and others. Ammoximation (HAO) is considered the most modern and environmentally friendly, featuring a short process cycle, few by-products and low energy consumption. There is also the toluene method (SNIA), based on the oxidation of toluene followed by hydrogenation of the resulting benzoic acid.

In Russia, caprolactam is produced synthetically from benzene in solid (crystalline) and liquid form.

Applications

Polyamide-6 (nylon-6) production. This is the dominant consumption area for caprolactam — it accounts for about 95% of global use. Polyamide-6 is produced by hydrolytic polymerisation of caprolactam with ring opening, or by anionic polymerisation. In turn, polyamide-6 is processed into three main product groups: polyamide fibres (textile and technical yarns, tire cord), engineering plastics and films.

Polyamide fibres. About 54% of caprolactam is used for nylon fibres, and about 43% for nylon resins and films. Fibres are used in the textile, carpet and industrial sectors (tire cord, technical fabrics).

Engineering plastics. Polyamide-6 based on caprolactam is used in the automotive industry (under-the-hood parts, fuel system components, fasteners), electrical and electronics (connectors, housings), as well as for food packaging films and cable insulation.

Other applications. Caprolactam is used for the synthesis of lysine (an essential amino acid), in the production of pharmaceuticals (e.g., ε-aminocaproic acid), as a solvent in some chemical processes, and for producing polyamide adhesives and coatings.

Global Market

Estimates of the global caprolactam market volume vary depending on the methodology. According to The Business Research Company, the market was valued at USD 17.19 billion in 2025, projected to reach USD 18.49 billion in 2026 at a CAGR of 7.6%. According to Straits Research, the market was valued at USD 17.38 billion in 2025, USD 18.04 billion in 2026, and is projected to reach USD 24.31 billion by 2034 at a CAGR of 3.8%. According to Research and Markets, the market was valued at USD 18.1 billion in 2025 with a projected growth to USD 25.3 billion by 2034 at a CAGR of 3.76%. In physical terms, according to Expert Market Research, the global market volume was about 7.21 million tonnes in 2025.

Global caprolactam production capacity in 2024 was estimated at 10.78 million tonnes per year. China is the largest producer and consumer of caprolactam, controlling about 70% of the global market. China's caprolactam production capacity grew from 1.47 million tonnes in 2013 to 7.4 million tonnes in 2025. The largest global producers are Chinese companies, as well as enterprises from Germany and the USA, which together account for more than 60% of global exports. Key market growth drivers are increasing demand for polyamide-6 in the automotive industry (replacing metals with plastics), the development of textile production and the expansion of engineering plastics applications.

Production in Russia and the CIS

Russia is one of the significant producers of caprolactam. In 2025, caprolactam output in Russia decreased by 20.3% year-on-year to 129,200 tonnes. The decline was driven by low export demand, a shortage of liquid sulfur (essential for production), and reduced domestic demand for technical and tire cord yarns.

The key caprolactam producer in Russia is PJSC KuibyshevAzot (Tolyatti), which holds a leading position in Russia, the CIS and Eastern Europe. In 2025, the company's share of total Russian output was 53%. Notably, only 3.9% of the company's caprolactam sales went to the Russian market — the bulk of production was exported. The structure of caprolactam consumption in Russia is dominated by producers of polyamide fibres and yarns, including tire cord fabric for the tire industry.

Safety and Storage

By the degree of impact on the body, caprolactam belongs to moderately hazardous substances (hazard class 3 according to GOST 12.1.007). The maximum allowable concentration (MAC) of caprolactam aerosol in the working area air is 10 mg/m³. On contact with skin, it causes dermatitis; when ingested, it causes convulsions, changes in internal organs and nervous system disorders. Burns from the heated product are possible when working with liquid caprolactam.

Caprolactam is a combustible substance. When burning, it releases nitrogen oxide, ammonia and carbon monoxide. Fire extinguishing agents are finely sprayed water and chemical foam. When working with liquid caprolactam, a filtering gas mask with grade A or BKF cartridge, protective clothing and rubber gloves are used; with crystalline caprolactam — a respirator, protective clothing and rubber gloves.

Crystalline caprolactam is packaged in five-layer paper bags with polyethylene liners or in polyethylene bags. Liquid caprolactam is transported in specially equipped tank cars and stored in tanks under a nitrogen blanket. The guaranteed shelf life for crystalline caprolactam is 2 months (according to some data, 6 months), and for liquid caprolactam — 15 days from the date of manufacture.

Conclusion

Caprolactam remains one of the key products of the global chemical industry, providing for the production of polyamide-6, textile and technical fibres, engineering plastics and films. Growing demand for polyamide-6 in the automotive industry, textile production and packaging, as well as the development of chemical recycling technologies, create sustained long-term demand for this essential monomer. China, Germany and the USA remain the leading players in the global caprolactam market, and Russia, possessing significant production capacities and export potential, maintains its position as one of the key suppliers of the product to the international market.