A standard practice in refineries is to use a holding tank in order to mix the light naphtha output of the refinery for quality control. During the first six hours of operation of the refinery, the stream feeding the holding tank at 200 kg/min had 30% by weight of n-pentane, 40% by weight of n-hexane, 30% by weight of n-heptane. During the next 12 hours of operation the mass flow rate of the feed stream was 210 

Chapter 4

kg/min and the composition changed to 40% by weight of n-pentane, 40% by weight of n-hexane, and 20%

by weight of n-heptane. Determine the following:

The average density of the feed streams
The concentration of the feed streams in mol/m3.

After 12 hours of operation, and assuming the tank was empty at the beginning, determine:

The volume of liquid in the tank in m3.
The concentration of the liquid in the tank, in mol/m3. The partial density of the species in the tank.