LPG Components C3 & C4 estimation from its RVP

LPG Components C3 & C4 estimation from its RVP

When LPG consist of n-Propane and n-Butane mainly with traces of ethane and pentane plus as impurities, LPG Vapour Pressure  kPa at 37.8 C can be used for estimation of C3 & C4 in it.  Depending upon the ambient temperature, there requires different percentages of C3 and C4 in LPG for proper efficient use in applications. Thus, following information empowers users more knowledge of C3 and C4 from LPG Vapour Pressure  kPa at 37.8 C.

The LPG derived from natural gas consists mainly Propane and Butane with minor impurities of Ethane and pentane.

Similar Apps on Petroleum Calculations developed by RJ Patel- see here.

Following table data taken from ASTM D 2598 can be used for estimation of LPG Composition.

Constants of vapour pressure given above are empirical values for calculation purpose.

A trendline from above data, with assumption of approximate 1 % (Ethane + C5 & above) is derived as

%  C3 = Propane %V = 0.1058*LPG VP - 31.172.      VP= Vapour Pressure  kPa at 37.8 C.

%  C4 =  99 - % C3.

% C2 + C5 = 1 % …..(Assumption)

Above equation is best suitable for LPG derived from Natural Gas.

Following table represents the data from above equation and from GC determination.

Sr.N.	LPG Vapour Pressure	% V from Equation		% V from GC
	kPA @37.8C	C3	C4	C3	C4
1	384	9.5	89.5	10.2	88.8
2	499	21.6	77.4	22.5	76.5
3	612	33.6	65.4	32.4	66.6
4	705	43.4	55.6	43.9	55.1
5	832	56.9	42.1	58.2	40.8
6	945	68.8	30.2	68.1	30.9
7	1018	76.5	22.5	78.3	20.7
8	1129	88.3	10.7	87.5	11.5
9	1212	97.1	1.9	95.8	3.2

Conclusion: The above equation estimates the C3 and C4 Vol percentage satisfactorily in LPG.

An App giving LPG Vapour pressure at 37.8 C and estimation of Propane and Butane Volume % as C3 and C4 can be found in authors App collection.

LPG Components C3 & C4 estimation from its Density is given here.

Keywords:   LPG, Propane, Butane, Vapor Pressure