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      Isobutene
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      Isobutene
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      C4H8
      Isobutene

      Physical Properties

      Under solid (grey), liquid (blue) and vapor states (white) along the equilibrium curves

      • General properties
      • Solid phase
      • Liquid Phase
      • Gas Phase
      (P)
      log(P)
      Download
      • Molecular weight
        56.106
        g/mol
      • Content in air
        /

      Critical Point

      • Temperature
        144.94
        °C
         292.892 °F 418.09 K
      • Pressure
        40.098
        bar
         4.0098E6 pa 581.5721 lbf/in2 39.5736 Atm 4009.8 Kpa 3.0076E4 mmHg
      • Density
        233.963
        kg/m³
         14.6058 lb/ft³

      Triple Point

      • Temperature
        - 140.75
        °C
         - 221.35 °F 132.4 K
      • Pressure
        6.449E-6
        bar
         6.449E-1 pa 9.3535E-5 lbf/in2 6.3647E-6 Atm 6.449E-4 Kpa 4.8372E-3 mmHg
      Pressure 1.013 bar
      • Melting point
        - 140.34
        °C
         - 220.612 °F 132.81 K
      • Latent heat of fusion (at melting point)
        105.714
        kJ/kg
         45.4793 Btu/lb 25.2663 kcal/kg
      • Solid density
        /
      Pressure 1.013 bar
      • Liquid density
        626.479
        kg/m³
         39.1097 lb/ft³
      • Boiling point
        - 7
        °C
         19.4 °F 266.15 K
      • Latent heat of vaporization (at boiling point)
        391.634
        kJ/kg
         168.4853 Btu/lb 93.6028 kcal/kg
      Pressure1.013barTemperature
      • Compressibility factor Z
        9.6136E-1
        9.6845E-1
        9.7217E-1
      • Cp/Cv ratio γ
        1.1329
        1.1226
        1.117
      • Dynamic viscosity
        7.364E-5
        Po
         7.364 µPa.s 7.364E-6 PA.S 4.9484E-6 lb/ft/s
        7.7972E-5
        Po
         7.7972 µPa.s 7.7972E-6 PA.S 5.2395E-6 lb/ft/s
        8.0842E-5
        Po
         8.0842 µPa.s 8.0842E-6 PA.S 5.4323E-6 lb/ft/s
      • Gas density at boiling point
        2.684
        kg/m³
         1.6756E-1 lb/ft³
        2.684
        kg/m³
         1.6756E-1 lb/ft³
        2.684
        kg/m³
         1.6756E-1 lb/ft³
      • Gas density
        2.6032
        kg/m³
         1.6251E-1 lb/ft³
        2.4496
        kg/m³
         1.5292E-1 lb/ft³
        2.3584
        kg/m³
         1.4723E-1 lb/ft³
      • Heat capacity at constant pressure Cp
        1.556
        kJ/(kg.K)
         3.7189E-1 BTU/lb∙°F 1556 J/kg∙K 3.7189E-1 kcal/kg∙K
        1.5978
        kJ/(kg.K)
         3.8188E-1 BTU/lb∙°F 1597.8 J/kg∙K 3.8188E-1 kcal/kg∙K
        1.629
        kJ/(kg.K)
         3.8934E-1 BTU/lb∙°F 1629 J/kg∙K 3.8934E-1 kcal/kg∙K
      • Heat capacity at constant volume Cv
        1.3735
        kJ/(kg.K)
         3.2827E-1 BTU/lb∙°F 1373.5 J/kg∙K 3.2827E-1 kcal/kg∙K
        1.4233
        kJ/(kg.K)
         3.4018E-1 BTU/lb∙°F 1423.3 J/kg∙K 3.4018E-1 kcal/kg∙K
        1.4584
        kJ/(kg.K)
         3.4857E-1 BTU/lb∙°F 1458.4 J/kg∙K 3.4857E-1 kcal/kg∙K
      • Liquid (at boiling point)/gas equivalent
        240.66
        mol/mol
        255.75
        mol/mol
        265.64
        mol/mol
      • Solubility in water
        /
        /
        /
      • Specific gravity
        1.93
        1.93
        1.93
      • Specific volume
        3.842E-1
        m³/kg
         6.1543 ft³/lb
        4.082E-1
        m³/kg
         6.5387 ft³/lb
        4.24E-1
        m³/kg
         6.7918 ft³/lb
      • Thermal conductivity
        14.988
        mW/m∙K
         8.6657E-3 Btu/ft/h/°F 1.2896E-1 cal/hour∙cm∙°C 3.5822E-5 cal/s∙cm∙°C 1.4988E-2 W/(m∙K)
        16.469
        mW/m∙K
         9.522E-3 Btu/ft/h/°F 1.417E-1 cal/hour∙cm∙°C 3.9362E-5 cal/s∙cm∙°C 1.6469E-2 W/(m∙K)
        17.494
        mW/m∙K
         1.0115E-2 Btu/ft/h/°F 1.5052E-1 cal/hour∙cm∙°C 4.1812E-5 cal/s∙cm∙°C 1.7494E-2 W/(m∙K)
      • Vapor pressure
        1.324
        bar
         1.324E5 pa 19.203 lbf/in2 1.3067 Atm 132.4 Kpa 993.0844 mmHg
        2.221
        bar
         2.221E5 pa 32.2129 lbf/in2 2.192 Atm 222.1 Kpa 1665.8916 mmHg
        3.035
        bar
         3.035E5 pa 44.0189 lbf/in2 2.9953 Atm 303.5 Kpa 2276.4435 mmHg
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      C4H8
      Isobutene

      Liquid / Gas Volumes

      Calculate a liquid or gas volume or a mass

      Liquid Phase

      At boiling point at 1.013 bar

      m3(Volume)
      kg(Mass)

      Gas Phase

      at 1.013 bar and boiling point

      m3(Volume)
      kg(Mass)
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      C4H8
      Isobutene

      Applications

      Examples of uses of this molecule in Industry and Healthcare

      Chemicals

      Isobutylene (or isobutene) is the feedstock for production of polybutene (butyl rubber). Isobutene is an intermediate in the manufacturing of methyl terbuthyl ether (MTBE).

      Chemicals
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      C4H8
      Isobutene

      Safety

      Information to safely use this molecule

      • Major hazards
      • Material compatibility
      Safety
      • GHS02
        Flammable

      Autoignition Temperature in Air at Patm and Flammability Limits in Air at Patm and 293.15 K (except if the temperature is indicated)

      • Europe (according to EN1839 for Limits and EN 14522 for autoignition temperature)

        • Auto-ignition temperature
          465
          °C
           869 °F 738.15 K
        • Flash point
          /
        • Lower flammability limit
          1.6
          vol/%
           1.6E4 ppm 1.6E4 ppm 1.6E-2 vol/vol
        • Upper flammability limit
          10
          vol/%
           10.E4 ppm 10.E4 ppm 0.1 vol/vol

      • US (according to NFPA for Limits and ASTM E659 for autoignition temperature)

        • Auto-ignition temperature
          465
          °C
           869 °F 738.15 K
        • Flash point
          /
        • Lower flammability limit
          1.8
          vol/%
           1.8E4 ppm 1.8E4 ppm 1.8E-2 vol/vol
        • Upper flammability limit
          9.6
          vol/%
           9.6E4 ppm 9.6E4 ppm 9.6E-2 vol/vol

      Odor

      Sweet

      Metals

      • Aluminium
        Satisfactory
      • Brass
        Satisfactory
      • Monel
        Satisfactory
      • Copper
        Satisfactory
      • Ferritic Steel
        Satisfactory
      • Stainless steel
        Satisfactory
      • Zinc
        no data
      • Titanium
        no data

      Plastics

      • Polytetrafluoroethylene
        Satisfactory
      • Polychlorotrifluoroethylene
        Satisfactory
      • Polyvinylidene fluoride
        Satisfactory
      • Polyvinyl chloride
        Satisfactory
      • Ethylene tetrafluoroethylene
        Satisfactory
      • Polycarbonate
        no data
      • Polyamide
        Satisfactory
      • Polypropylene
        Satisfactory

      Elastomers

      • Buthyl (isobutene- isoprene) rubber
        Not recommended
        significant swelling
      • Nitrile rubber
        Satisfactory
      • Chloroprene
        Not recommended
        significant swelling
      • Chlorofluorocarbons
        Satisfactory
      • Silicon
        Not recommended
        significant swelling and modification of the properties of the material
      • Perfluoroelastomers
        Satisfactory
      • Fluoroelastomers
        Satisfactory
      • Nitrile rubber
        Satisfactory
      • Neoprene
        Satisfactory
      • Polyurethane
        no data
      • Ethylene-Propylene
        Not recommended
        significant swelling and modification of the properties of the material

      Lubricants

      • Hydrocarbon based lubricant
        Not recommended
        significant loss of mass
      • Fluorocarbon based lubricant
        Satisfactory

      Materials compatibility

      Recommendations : Air Liquide has gathered data on the compatibility of gases with materials to assist you in evaluating which materials to use for a gas system. Although the information has been compiled from what Air Liquide believes are reliable sources (International Standards: Compatibility of cylinder and valve materials with gas content; Part 1- Metallic materials: ISO11114-1 (March 2012), Part 2 - Non-metallic materials: ISO11114-2 (April 2013), it must be used with extreme caution and engineering judgement. No raw data such as these can cover all conditions of concentration, temperature, humidity, impurities and aeration. It is therefore recommended that this table is only used to identify possible materials for applications at high pressure and ambient temperature. Extensive investigation and testing under the specific conditions of use need to be carried out to validate a material selection for a given application. Contact the regional Air Liquide team for expertise service.

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      C4H8
      Isobutene

      Learn More

      General information

      More information

      Isobutylene or 2-methylpropene is a hydrocarbon of industrial significance. Polymer and chemical grade isobutylene is typically obtained by dehydrating tertiary butyl alcohol or catalytic dehydrogenation of isobutane. Isobutylene is used as an intermediate in the production of a variety of products. It is also used in the production of oxygenated fuel. It is a colorless flammable gas.

      C4H8

      Isobutene