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Propane Butane Mixture - Evaporation Pressure

Evaporation pressure of propane butane mixture vs. temperature.

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 -44 oF (-42 oC) at atmospheric pressure. Butane evaporates at 33 oF (0.6 oC) at atmospheric pressure.

Vapor pressures for mixtures of the two products relative to atmospheric pressure (gauge pressure) are indicated below.

Propane Butane Mixture - Evaporation Pressure
Liquid MixtureVapor Pressure (psig)
Propane
(C3H8)
(%)
1007050300
Butane
(C4H10)
(%)
0305070100
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) = 6894.8 Pa (N/m2) = 6.895×10-3 N/mm2 = 6.895×10-2 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 - metric units -  bar

Butane Vapor Pressure (abs)

Butan Vapor Pressure
Temperature
(oC)
Vapor Pressure
(bar abs)
-101.5 0.0013
-77.8 0.013
-59.1 0.053
-44.2 0.13
-16.3 0.53
-0.5 1.01
18.8 2.03
50.0 5.07
79.5 10.1
116 20.3
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