dungnt,
HYSYS is mostly used for hydrocarbon processing i.e. once you are trying to simulate packages/units with crude oil (or its cuts) as the feed. HYSYS is very good in this but maybe it is not the best for simulating chemical reactions, especially if there are tons of complicated reactions of various types of hydrocarbons. PRO/II is older than HYSYS and more expensive I believe! The reason that it may be used in more plants could be its popularity before HYSYS being released (but that is only my guess which might be wrong).
There are many other differences between this two software packages. If you want to get some idea, you can search "Mass transfer rate based" term and you will find that HYSYS is not simulating a separation equipment e.g. towers on a mass transfer based rate, but I believe other software like ProMax does. It means that the simulation in "Mass transfer rate based" is not based on equilibrium stages and tray efficiency but is based on the mass transfer rate on each tray which gives you the option to specify how far the separation is from ideality for each two of the components...
On top of the information above, the numerical solution in each software is unique and I have found HYSYS faster in this aspect so far...
Hope this helps...
Best,
Milad
Edited by ahmadikh, 24 November 2014 - 04:52 PM.