Optimal Synthesis of Distillation Systems for Bioethanol Separation. Part 2. Extractive Distillation with Complex Columns

In the first part of the work the dehydration of bioethanol by extractive distillation was considered to define the best simple column sequence. It was proved that among all the simple configurations generated, two sequences with three columns are able to consistently reduce the energy demand and the capital costs compare to the four-column sequence used as a reference. Then, starting from the selected simple column configurations different complex sequences were predicted. It was evidenced that thermally coupled configurations realized only a limited saving in the capital costs. The two column configuration with a vapor side stream is able to reduce the capital costs, but not all the solvent can be recovered. Its convenience is related to the trade-off between the solvent cost and the savings in the capital costs achieved. The two-column configurations with a divided wall column represent an excellent alternative for bioethanol production because their performances are not limited by the solvent recovery.