I have been given an assignment to use a specified distillation column to separate out propene from a gas. The gas consists of propene, propane, ethane and CO2. Separating out the propane has been straight forward, but ethane and especially CO2 are giving me a hard time. To make matters worse, I am constrained to ONLY using pressure and temperature changes. No other variables can be changed, and no other components can be added. I am using UniSim, which is very similar to HYSYS, to model this column, and after a good 5-6 different case studies, I cannot for the life of me determine how to get the CO2 to condense and separate out. Researching literature from the industry shows that there is almost always a solvent, or amines used to do this, and I cannot find any examples of using just temperature and pressure. Especially not to the purity that the professor is demanding. (98.86% propene in the top product...) Can anyone tell me if this is even feasible? Surely if CO2 was that easily separated, the industry would be doing that, rather than using MDEA, amines, etc. Thanks in advance!