chemical condenser questions

[stoicism2025]

I'm working at a small chemical plant here. we use a THF, which evaporates easily. To reuse it, we boil it off (10,000 pounds per hour, like a big pot of really volatile water) and then do distillation.

we have two cooling units, like two different refrigerators. The first one cools the hot THF "steam" down to 100 degrees Fahrenheit.

We know that at this temperature, if any THF is still a gas, it will only exert a pressure of 5.2 psia.

Then, we send whatever "steam" is left into a second, much colder cooler, bringing it down to 32 degrees Fahrenheit. At this freezing point, any remaining THF gas will have a very low pressure of just 0.9 psia.

My question is tht after the first chemical condenser, how much THF is still floating around as a gas?

And then, after the second chemical condenser, how much THF is still a gas?

We need to figure out those vapor flow rates at each step to design the system properly and know how much liquid THF we're recovering.

We're assuming no other gases are mixed in with the THF vapor.

 

[pouchbearer]

the theoretical calculation is to divide the vapour pressure at 100 degrees with the system pressure and then do the same at 32 degrees.

 

[lena.nitro11]

That sounds like a very interesting setup at work! I have to agree with @pouchbearer for the theoretical calculation. But if you really want to nail down those vapor flow rates, you'll likely need to use the ideal gas law (PV = nRT) or a more sophisticated equation of state, along with the total pressure in your system at each cooling stage.

 

[gab.riels]

If you're working with pure THF vapor and know the total pressure, you can use the vapor pressure at each temperature to estimate how much THF remains as gas. At 100°F, with a vapor pressure of 5.2 psia, the fraction of THF vapor is basically the ratio of that vapor pressure to the system pressure, same idea at 32°F with 0.9 psia so after the first condenser, roughly (5.2 / total system pressure) of the THF stays gaseous, and after the second, it's (0.9 / total system pressure).