by jasper » 03 March 2013, 16:50
If it is a Chemsep distillation column you are calculating (which you did not mention, but this is what I am guessing from the message about the diffusion volume): this is a unit operation that is unable to deal with solids. It will not succeed if a solid phase results from a flash calculation. Which is not surprising for a distillation column, they typically do not contain solids.
If indeed this is the Chemsep column, you can read the full reason for the solution failure in its calculation report.
But the long and the short of it is, make sure that no solids are entering the distillation column. You can use for example a solids separator before the feed of the distillation column to remove the solids from the feed.