Acrylonitrile: properties, production and applications / Articles

Acrylonitrile (propenenitrile, vinyl cyanide) is the simplest representative of the class of unsaturated nitriles and one of the most important large-tonnage monomers of the modern petrochemical industry. Under normal conditions, it is a colourless or slightly yellowish, transparent, mobile liquid with a characteristic pungent odour of bitter almond. Its molecular formula is C₃H₃N, structural formula CH₂=CH–CN, and molecular mass 53.06 g/mol. The combination of a reactive double bond and a polar nitrile group gives acrylonitrile a unique ability to polymerise and copolymerise with a wide range of comonomers, making it a versatile basis for the production of synthetic fibres, engineering plastics, elastomers and carbon materials.

Chemical Nature and Physicochemical Properties

The acrylonitrile molecule contains a vinyl group, which ensures a tendency to radical and anionic polymerisation, and a nitrile group, which imparts rigidity, chemical resistance, heat resistance and gas impermeability to polymers. It is the polarity of the nitrile group that determines the unique barrier properties of acrylonitrile-based materials.

The key physical characteristics of acrylonitrile determine its industrial application:

Boiling point: 77.2–77.3 °C. The relatively low boiling point facilitates distillation but requires careful control during storage.
Melting point: minus 83.5 °C.
Density: 0.806 g/cm³ at 20 °C.
Solubility: limited solubility in water (about 7.3% at 20 °C), miscible with methanol, ethanol, acetone, benzene and other organic solvents.
Flash point: about minus 1 °C (closed cup). Acrylonitrile is classified as a flammable liquid, and its vapours form explosive mixtures with air over a wide concentration range.
Tendency to polymerise: acrylonitrile spontaneously polymerises under the action of light, heat, alkalis and peroxides. To prevent this, inhibitors (hydroquinone, hydroquinone methyl ether or ammonia) are introduced during storage, reduced temperatures are maintained, and oxygen content is controlled.

Acrylonitrile is highly toxic and belongs to hazard class 2 (highly hazardous substances) according to GOST 12.1.007-76. It penetrates the body through the respiratory tract, skin and digestive tract, causes damage to the nervous system, liver and blood, and is also classified as a suspected carcinogen. The maximum allowable concentration of acrylonitrile vapours in the working area air is 0.5 mg/m³.

Regulatory Framework and Grades

Requirements for technical acrylonitrile in Russia and CIS countries are regulated by GOST 11097-86 "Technical acrylonitrile. Specifications". The standard applies to technical acrylonitrile produced by oxidative ammoxidation of propylene, stabilised with ammonia, hydroquinone or p-methoxyphenol, and establishes requirements for the product intended for national economy needs and export.

According to the standard, acrylonitrile must meet the following indicators: appearance — transparent liquid without mechanical impurities; colour by the platinum-cobalt scale — not more than 20 units; mass fraction of acrylonitrile — not less than 99.5%; mass fraction of water — not more than 0.45%; mass fraction of aldehydes calculated as acetaldehyde — not more than 0.005%; mass fraction of hydrocyanic acid — not more than 0.001%; mass fraction of polymer — not more than 0.5%. The product must withstand the test for the absence of mechanical impurities and for storage stability.

Production Technology

Modern industrial production of acrylonitrile is almost entirely based on the heterogeneous catalytic oxidative ammoxidation of propylene (the SOHIO process). This method was developed in the early 1960s and replaced the earlier, less economical processes (acetylene, cyanohydrin), ensuring a sharp reduction in cost and growth in world production.

The ammoxidation process is carried out in a fluidised bed reactor. Propylene, ammonia and air (or oxygen) are fed into the reactor. Multi-component oxide systems based on bismuth molybdate with additives of phosphorus, iron, nickel, cobalt and other elements are used as catalysts. The reaction proceeds at a temperature of 400–500 °C and a pressure close to atmospheric. The main products are acrylonitrile (yield about 50–60%), as well as by-products — acetonitrile and hydrocyanic acid, which also find industrial application.

After the reaction, the gas mixture is cooled, washed with water to capture acrylonitrile and by-products, and then subjected to multi-stage rectification to isolate commercial high-purity acrylonitrile. Unreacted propylene and ammonia are recycled. Modern technologies are aimed at increasing catalyst selectivity, reducing the formation of by-products and reducing energy consumption.

Applications

Production of polyacrylonitrile (PAN) fibres. This is the largest consumption area for acrylonitrile, accounting for a significant share of global demand. Polyacrylonitrile fibres (acrylic, nitron) possess high strength, resistance to light and weathering, softness and the ability to retain shape. They are widely used in the production of clothing, knitwear, carpets, home textiles and technical fabrics. Thanks to the polar nitrile group, PAN fibres dye well and have a pleasant tactile texture.

Production of ABS plastics and SAN. Acrylonitrile is a key comonomer in the production of high-impact ABS plastics (acrylonitrile-butadiene-styrene) and styrene-acrylonitrile copolymers (SAN). ABS plastics combine high impact strength, hardness, chemical resistance and good processability. They are used in the automotive industry (interior parts, mirror housings, grilles), production of household appliances, electronics housings, toys and pipes. SAN is used for transparent products, tableware and battery cases.

Production of nitrile rubbers (NBR). Copolymerisation of acrylonitrile with butadiene yields nitrile rubbers, which possess exceptional resistance to oils, fuels and fats. Nitrile rubbers are used in the production of oil-resistant hoses, seals, gaskets, oil seals and gloves. It is on the basis of NBR that nitrile gloves, widely used in medicine and industry, are made.

Production of carbon fibres. Polyacrylonitrile fibres are the main precursor for producing high-strength carbon fibres. Controlled pyrolysis of PAN fibres forms a structure that provides exceptional strength and stiffness at low weight. Carbon fibres find application in the aerospace industry, production of sports equipment, wind energy, automotive industry and construction.

Chemical synthesis and other applications. Acrylonitrile is used to produce acrylamide, acrylic acid and its esters, adiponitrile (a nylon feedstock), as well as in cyanoethylation reactions for modifying polymers, starch and cellulose. It is used in the production of ion-exchange resins, flocculants for water treatment, oil additives, adhesives, dyes and pharmaceuticals. In small volumes, acrylonitrile is used as a fumigant and in analytical chemistry.

Safety and Storage

Acrylonitrile belongs to highly hazardous substances (hazard class 2). It is toxic by inhalation, ingestion and skin contact, and has general toxic, irritating and carcinogenic effects. Acute poisoning can lead to damage to the central nervous system, impaired respiration and cardiac activity. When working with acrylonitrile, personal protective equipment must be used: filtering gas masks, rubber gloves, safety goggles and protective clothing. All operations must be carried out in sealed equipment with effective ventilation.

Acrylonitrile is highly flammable, and its vapours form explosive mixtures with air. Combustion releases toxic gases, including nitrogen oxides and hydrogen cyanide. Storage is carried out in hermetic containers made of stainless steel or with an internal coating, in a cool, light-protected place, away from ignition sources, oxidisers, alkalis and peroxides. Addition of a polymerisation inhibitor and temperature control are mandatory. During transportation, acrylonitrile is classified as dangerous goods and requires compliance with special transport rules.

Market and Trends

The global acrylonitrile market demonstrates steady growth, driven by demand for acrylic fibres, ABS plastics, nitrile rubbers and carbon fibres. The Asia-Pacific region is the largest producer and consumer of acrylonitrile, due to large-scale production of textiles, plastics and composite materials. Key industry trends include the development of more efficient and selective ammoxidation catalysts, reduction of energy consumption and carbon footprint of production, and the development of bio-based technologies for producing acrylonitrile from renewable feedstock (e.g., from glycerol). Requirements for production safety and reducing emissions of volatile organic compounds are tightening. Organising supplies of acrylonitrile, including grade selection, quality confirmation and logistics taking into account dangerous goods requirements, requires an individual approach and a reliable partner.

Conclusion

Acrylonitrile remains one of the key monomers of the global petrochemical industry, providing for the production of acrylic fibres, ABS plastics, nitrile rubbers, carbon fibres and many other products. Its unique properties — the ability to polymerise and copolymerise, the polarity of the nitrile group and the availability of feedstock — make it indispensable in modern industry. Organising supplies of acrylonitrile, including grade selection, quality confirmation and logistics, requires an individual approach that takes into account specific technological requirements and operating conditions.