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 -44oF (-42oC) at atmospheric pressure. Butane evaporates at 33oF (0.6 oC) at atmospheric pressure.
Vapor pressures for mixtures of the two products relative to atmospheric pressure (gauge pressure) are indicated below.
| Liquid Mixture | Vapor Pressure (psig) | |||||
|---|---|---|---|---|---|---|
| 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) = 6894.8 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 - bar
Butane Vapor Pressure (abs)
| 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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