I must admit I had not heard of the term Cohobation so I looked into it.  I found this: “Cohobation,” a word in alchemy and pharmaceutical chemistry that means “continuous distillation to extract the very essence of a compound substance.”
From this and other various sites I visited, I concluded that a cohobation column is the same as a rectification column mostly on a laboratory scale and that the columns are not very sophisticated.  I’m not really able to determine exactly the column internals, but they appeared to be packed. However, one called a Vigreux column could be packed or not packed.  For more information, visit:
http://en.wikipedia.org/wiki/Condenser_(laboratory)  and http://www.kgw-isotherm.com/produkte/kolonne.html

I think the inquirer would be well served if he spoke with one of the vendors or contact someone in the pharmaceutical or essential oil industries.