Propane Butane Mixtures - Evaporation Pressures - Boiling Points
It is common practice to use a mixture of propane (C3H8) and butane (C4H10) in essential oil hydrocarbon extraction practices.
Propane is more suited to colder environments since it boils at -44oF (-42oC) at atmospheric pressure. Butane boils at 33oF (0.6 oC) at atmospheric pressure. Adding propane will increase the pressure inside the system relative to butane under the similar conditions.
Vapor pressures for mixtures of the two products relative to atmospheric pressure are indicated below.
| Vapor Pressure (psig) | ||||||
|---|---|---|---|---|---|---|
| Mix | Propane (C3H8) (%) |
100 | 70 | 50 | 30 | 0 |
| Butane (C4H10) (%) |
0 | 30 | 50 | 70 | 100 | |
| Temp (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 | |
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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 boiling temperature is not the only parameter that influences on boiling of the propane butane mixture. Boiling requires heat and if the heat transferred to the liquid gas is limited - the liquid cools down and the evaporation is reduced unless the pressure is also reduced. This process is called adiabatic cooling.
Propane Butane Mix Vapor Diagram - psig
