Isobutylene: properties, production, applications
Isobutylene (isobutene, 2-methylpropene) is one of the most important olefin hydrocarbons and a key monomer in the modern petrochemical industry. Its chemical formula is C₄H₈ (CH₂=C(CH₃)₂), with a molar mass of 56.11 g/mol and CAS registry number 115-11-7. Isobutylene is one of the four isomers of butylene and is a branched alkene with a double bond between the first and second carbon atoms.
Physicochemical Properties
Isobutylene is a colourless gas with a faint petroleum-like or coal gas odour. At ambient temperature and pressure, it exists as a gas but is easily liquefied under pressure. Its melting point is –140.4 °C, and its boiling point is –6.9 °C. The density at boiling point is 0.5879–0.6266 g/cm³. The refractive index nD-25 is 1.3814. The vapour pressure at 37.7 °C is 3278 mm Hg. The flash point is below –20 °C.
Isobutylene is practically insoluble in water (0.03 g/100 ml at 20 °C) but readily soluble in ethanol, ether, benzene and other organic solvents. In terms of chemical properties, isobutylene exhibits all the characteristic reactions of olefins with a double bond. It can undergo polymerisation, copolymerisation, alkylation, hydration and other reactions. Due to its high reactivity, isobutylene is widely used as a chemical building block for the synthesis of various products.
Production Methods
Several main methods for isobutylene production are used in industry:
1. Catalytic dehydrogenation of isobutane — the most widely adopted industrial method. The process is carried out on oxide catalysts (e.g., chromium or aluminium oxides) at temperatures of 500–600 °C. The reaction involves the abstraction of hydrogen from isobutane. A characteristic feature is the limitation of conversion by equilibrium conditions; the degree of conversion increases with temperature rise and pressure reduction.
2. Extraction from C₄ fractions — isobutylene is present in hydrocarbon C₄ fractions generated during petroleum product pyrolysis and cracking. Extractive distillation or concentration via intermediate product formation is used for separation. One common method involves converting isobutylene to methyl tert-butyl ether (MTBE) followed by decomposition.
3. Dehydration of isobutyl alcohol — a less common method involving catalytic dehydration of isobutyl alcohol with water elimination.
4. Metathesis of ethylene and 2-butene — a modern method used to produce high-purity isobutylene.
Isobutylene is available in various purity grades: chemical grade (typically ≥95%) and high-purity (≥99.5–99.99%) for polymerisation applications. Butyl rubber production requires a purity of at least 99.5%.
Applications
Isobutylene is one of the key monomers in the petrochemical industry and finds wide application in various sectors:
Synthetic Rubber Production. This is the main application of isobutylene. Butyl rubber — a copolymer of isobutylene with isoprene — possesses unique properties: low gas and vapour permeability, high heat and light resistance, and excellent chemical resistance. Butyl rubber is widely used in automotive tyre production (especially inner tubes and inner liners for tubeless tyres), as well as in rubber technical products, conveyor belts, gaskets and seals.
Polyisobutylene (PIB). Polymerisation of isobutylene yields polyisobutylene — a polymer with unique properties used for anti-corrosion coatings of chemical equipment and pipelines, electrical insulation materials, adhesives, sealants, and as additives to oils and fuels.
Methyl Methacrylate (MMA). Isobutylene serves as a feedstock for methyl methacrylate production — the monomer for polymethyl methacrylate (acrylic glass).
High-Octane Fuel. Isobutylene is used for alkylation of aromatic compounds and isobutane to produce isooctane — a component of high-octane aviation gasoline. Butylene-based alkylate achieves up to 98 RON.
MTBE and Other Additives. Isobutylene is a feedstock for methyl tert-butyl ether (MTBE) production — a high-octane gasoline additive.
Medical Materials. SIBS (styrene-isobutylene-styrene) thermoplastic elastomers based on isobutylene are used in the production of stents, catheters and other medical devices due to their biocompatibility and mechanical properties.
Production of antioxidants, fragrances and gas odorisation agents.
Global Market
The global isobutylene market shows steady growth. In 2025, the market was valued at USD 29.41 billion. It is projected to reach USD 37.15 billion by 2031 at a CAGR of 3.98%. According to other estimates, the market was USD 32.04 billion in 2025 with a projected growth to USD 43.29 billion by 2032 (CAGR 4.39%). In the industrial isobutylene segment, the market was valued at USD 3.94 billion in 2024 with a projected growth to USD 5.33 billion by 2031 (CAGR 4.5%).
Key players in the global market include INEOS, TPC Group, ExxonMobil Chemical, LyondellBasell, Evonik, Honeywell, Maruzen Petroleum, Idemitsu Kosan, Sumitomo Chemical, Songwon, as well as Chinese producers — Shunda Chemical, Qixiang Petrochemical, Beijing Yanshan Petrochemical, Zibo JinLin Chemical, Wanhua and others.
The main market growth driver is the expansion of automotive production and the growing demand for high-performance tyres. The development of electric vehicles creates additional opportunities for butyl rubber applications due to its high gas impermeability and resistance.