1. Chemical Overview
IUPAC Name: 2-Methylpropene
Synonyms: Isobutene, 2-Methyl-1-propene, γ-Butylene
CAS No.: 115-11-7
Molecular Formula: C₄H₈
Structure: CH₂=C(CH₃)₂ (branched alkene)
Appearance: Colorless, flammable gas with a faint petroleum-like odor
Boiling Point: -6.9°C (19.6°F)
Melting Point: -140.3°C (-220.5°F)
Density: 0.5879 g/cm³ (lighter than air)
Flash Point: -80°C (-112°F) (extremely flammable)
Solubility: Insoluble in water, miscible with organic solvents (ethanol, ether, acetone)
2. Production Methods
Isobutylene is primarily derived from:
Steam Cracking of Naphtha or Ethane – A byproduct of ethylene production.
Fluid Catalytic Cracking (FCC) in Refineries – Extracted from C₄ hydrocarbon streams.
Dehydrogenation of Isobutane – Catalytic conversion (e.g., using Pt/Al₂O₃).
Separation from C₄ Raffinate – Via extraction or distillation (e.g., MTBE decomposition).
3. Major Applications & Industrial Uses
① Fuel & Petrochemical Industry
MTBE/ETBE Production – Gasoline octane boosters (phased out in some regions due to environmental concerns).
Alkylate Gasoline – Reacted with isobutane to produce high-octane fuel.
Isooctane & Synthetic Paraffinic Kerosene (SPK) – Jet fuel components.
② Rubber & Polymers
Butyl Rubber (IIR) – Used in tire inner liners (excellent air retention).
Polyisobutylene (PIB) – Ranges from low MW (lubricant additives) to high MW (adhesives, sealants).
Butyl Rubber Halogenation (CIIR/BIIR) – Improves heat resistance for medical stoppers.
③ Chemical Intermediates
Methyl Methacrylate (MMA) – For acrylic glass (PMMA), coatings, and adhesives.
Tert-Butyl Alcohol (TBA) – Solvent and precursor for fragrances/flavors.
Antioxidants (BHT, BHA) – Food preservatives and plastic stabilizers.
④ Specialty Applications
Cosmetics – Hydrogenated polyisobutene as a silicone alternative in skincare.
Pharmaceuticals – Intermediate for ibuprofen and other APIs.
Agrochemicals – Used in pesticide synthesis.
4. Storage & Safety Considerations
Handling: Stored as a liquefied gas under pressure (carbon steel containers).
Hazards: Highly flammable, forms explosive mixtures with air (1.8–9.6% vol).
Protection: Requires ventilation, grounding, and flame-proof equipment.
Regulations: Classified as UN1055 under international transport codes (ADR, IATA).
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