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Ethylene - Thermophysical Properties

Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.

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Ethylene, C2H4, is a highly flammable, colorless and noncorrosive gas with a sweet odor. It is easily ignited and a flame can easily flash back to the source of the leak. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. Can cause explosion. Vapors arising from the boiling liquid are lighter than air. Ethylene is not toxic, but is a simple asphyxiant.

Ethylene is used as an anesthetic, a refrigerant, and to make other chemicals as polymers and plastics.

Ethylene is produced in petrochemical processes, as steam cracking  where hydrocarbons and steam are heated to 750–950 °C. This process converts large hydrocarbons into smaller ones and introduces unsaturated products.

The phase diagram of ethylene is shown below the table.

Chemical, physical and thermal properties of ethylene:
Values are given for gas phase at 25oC /77oF / 298 K and 1 bara, if not other phase, temperature or pressure given.

Property Value Unit Value Unit Value Unit Value Unit
Autoignition temperature 723 K 450 °C 842 °F
Boiling Point 169 K -104 °C -155 °F
Critical density 7.63 mol/dm3 214 kg/m3 0.415 slug/ft3 13.4 lb/ft3
Critical pressure 5.06 MPa=MN/m2 50.6 bar 49.9 atm 734 psi=lbf/in2
Critical temperature 282.4 K 9.2 °C 48.6 °F
Critical volume 131 cm3/mol 0.00467 m3/kg 2.41 ft3/slug 0.0748 ft3/lb
Density 40.6 mol/m3 1.138 kg/m3 0.00221 slug/ft3 0.07104 lb/ft3
Density (liquid) at -104 °C/-155°F 20567 mol/m3 577 kg/m3 1.12 slug/ft3 36.0 lb/ft3
Flammable, gas and liquid yes highly
Flash point 137 K -136 °C -213 °F
Gas constant, individual, R 296.4 J/kg K 0.0823 Wh/(kg K) 1772 [ft lbf/slug °R] 55.08 [ft lbf/lb °R]
Gibbs free energy of formation (gas) 68 kJ/mol 2424 kJ/kg 1042 Btu/lb
Heat (enthalpy) of combustion (gas) -1411 kJ/mol -50303 kJ/kg -21.6 Btu/lb
Heat (enthalpy) of formation (gas) 52.4 kJ/mol 1868 kJ/kg 803 Btu/lb
Heat (enthalpy) of evaporation at -104°C/-155°F 13.6 kJ/mol 483 kJ/kg 207.7 Btu/lb
Heat capacity, Cp (gas) 42.9 J/mol K 1.53 kJ/kg K 0.365 Btu/lb°F or cal/g K
Heat capacity, Cp (liquid) at -104°C/-155°F 67.4 J/mol K 2.40 kJ/kg K 0.574 Btu/lb°F or cal/g K
Heat capacity, Cv (gas) 34.6 J/mol K 1.24 kJ/kg K 0.295 Btu/lb°F or cal/g K
Heat capacity, Cv (liquid) at -104°C/-155°F 38.7 J/mol K 1.38 kJ/kg K 0.330 Btu/lb°F or cal/g K
Ionization potential 10.5 eV
log KOW (Octanol/Water Partition Coefficient) 1.13
Melting point 104.15 K -169.0 °C -272.2 °F
Molecular Weight 28.054 g/mol 0.06185 lb/mol
Solubility in water, at 25°C 0.131 mg/ml
Sound velocity 330 m/s 1082 ft/s 739 mi/h
Specific Gravity (gas) (relativ to air) 0.978
Specific Heat Ratio (gas) - CP/CV 1.24
Specific Heat Ratio (liquid) - CP/CV 1.74
Specific Volume 0.0247 m3/mol 0.879 m3/kg 453 ft3/slug 14.1 ft3/lb
Standard molar entropy, S° (gas) 219.32 J/mol K 7.82 kJ/kg K 1.87 Btu/lb °F
Standard molar entropy, S° (liquid) 117.8 J/mol K 4.20 kJ/kg K 1.00 Btu/lb °F
Surface tension at -104°C/-155°F 16.00 dynes/cm 0.016 N/m
Thermal Conductivity 0.020 W/m°C 0.0118 Btu/hr ft °F
Triple point pressure 0.000122 MPa=MN/m2 0.00122 bar 0.00120 atm 0.0177 psi=lbf/in2
Triple point temperature 104.0 K -169.16 °C -272.49 °F
Vapor (saturation) pressure 6.9449 MPa=MN/m2 5.21E+04 mm Hg 68.543 atm 1007.30 psi=lbf/in2
Viscosity, dynamic (absolute) 0.0103 cP 6.9 [lbm /ft s*10-6] 0.22 [lbf s/ft2 *10-6]
Viscosity, kinematic 9.05 cSt 97.4 [ft2/s*10-6]

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Follow the links below to get values for the listed properties of ethylene at varying pressure and temperature:

See also more about atmospheric pressure, and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure,
as well as Thermophysical properties of:
Acetone, Acetylene, Air, Ammonia, Argon, Benzene, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Helium, Hydrogen, Hydrogen sulfide, Methane, Methanol, Nitrogen, Oxygen, Pentane, Propane, Toluene, Water and Heavy water, D2O.

Ethylene is a gas at standard conditions. However, at low temperature and/or high pressures the gas becomes a liquid or a solid.

The ethylene phase diagram shows the phase behavior with changes in temperature and pressure. The curve between the critical point and the triple point shows the ethylene boiling point with changes in pressure. It also shows the saturation pressure with changes in temperature.

Ethylene phase diagram

At the critical point there is no change of state when pressure is increased or if heat is added.

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

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