Propane Butane Mixures - Evaporation Pressures

Evaporation pressures of propane butane mixtures

It is common to distribute a mixture of propane (C3H8) and butane (C4H10) (LPG) for combustion purposes.

Propane is more suited to colder environments since it evaporates at -44oF (-42oC) at atmospheric pressure. Butane evaporates at 33oF (0.6 oC) at atmospheric pressure.

The vapor pressures for mixtures of the two products:

Vapor Pressure (psig)
Mixture Propane (C3H8)
(%)
100 70 50 30 0
Butane (C4H10)
(%)
0 30 50 70 100
Temperature
(oF)
-44 0 0 0 0 0
-30 6.8 0 0 0 0
-20 11.5 4.7 0 0 0
-10 17.5 9 3.5 0 0
0 24.5 15 7.6 2.3 0
10 34 20.5 12.3 5.9 0
20 42 28 17.8 10.2 0
30 53 36.5 24.5 15.4 0
40 65 46 32.4 21.5 3.1
50 78 56 41 28.5 6.9
60 93 68 50 36.5 11.5
70 110 82 61 45 17
80 128 96 74 54 23
90 150 114 88 66 30
100 177 134 104 79 38
110 204 158 122 93 47
  • 1 psi (lb/in2) = 144 psf (lbf/ft2) = 6,894.8 Pa (N/m2) = 6.895x10-3 N/mm2 = 6.895x10-2 bar

Note that the evaporation temperature is not the only parameter that influences on evaporation of the propane butane mixture. Evaporation requires heat and if the heat transferred to the liquid gas is limited - the liquid cools down and the evaporation is  reduced.

  • Larger consumers requires heat exchangers fueled with hot water, electric heater or combustion of the propane butane mix itself to supply the evaporation heat.
  • Smaller consumers requires propane butane mix containers with efficient heat transfer from the surroundings. By example - composite containers provides less heat transfer compared to steel containers and may cause problems at lower surroundings temperatures.  

Propane Butane Mix Vapor Diagram - psig

propane butane mix vapor diagram - imperial units - psig

Propane Butane Mix Vapor Diagram - bar

propane butane mix vapor diagram - imperial units - bar

Related Topics

  • Combustion - Boiler house topics - fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency
  • Gases and Compressed Air - Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves
  • Material Properties - Material properties for gases, fluids and solids - densities, specific heats, viscosities and more

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