What is the volume of LPG left in rail car?

Question

This i want for railcar cleaning. How can we calculate volume of remaining LPG and vapor of LPG

Data:

Capacity of railcar: 33475 gallon

Ammount remaining : 85 PSI

MSDS vapor pressure : 250.92 Psi

Temperature : atmospheric

Answer 1

You would normally use PV = mRT for gas.

The problem is, you need to know the composition of the LPG. LPG is typically about a 50/50 mix of butane and propane, with wide variation by supplier, time of year, and location. Also often has traces of other gases.  Butane is a liquid at room temp with about 30psi gauge, while propane is about 300 psi. So, the rail car could actually be full of liquid butane, or just propane fumes. Anyway, there won't be any liquid propane, because it will all evaporate at this pressure. Assuming you drained liquid from the bottom, since propane and butane are mutually soluable, there won't be any significant remaining liquid, other than possible isolated puddles of butane in the bottom of the tank. Most of the gas has to be propane. Unless you know it is pure propane, I would assume the vapor is butune to its vapor pressure, balance propane. Estimate should be pretty close.