Propane Butane Mix Evaporation Pressure

The evaporation pressure of a Propane Butane mixture

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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 (-0.5 ^oC) at atmospheric pressure.

The vapor pressure of a mixture of the two products can be found in the table below:

Vapor Pressure (psig)
Mixture	Propane (C₃H₈) (%)	100	70	50	30	0
Mixture	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

Note that the evaporation temperature is not the only parameter that influence on the evaporation of the propane butane mixture. The evaporation requires heat and if the heat transfer to the liquid gas is limited the liquid will be under cooled and the evaporation reduced. Larger consumes requires in general heat exchangers fueled with hot water, electric heater or combustion of the propane butane mix itself. Smaller amounts of consumption requires containers with efficient heat transfer. By example composite container provides less heat transfer compared with steel containers.