TECHNICAL AND ECONOMICAL COMPARISON OF DISTILLATION/DEHYDRATION CONCEPTS FOR BIOALCOHOL – WATER MIXTURES

摘要

In the state-of-art production of bioalcohol the distillation/dehydration step is the most energy intensive unit operation and in the respect to the cost breakdown of the overall costs the second highest after the raw materials. Therefore any attempts to reduce the production costs of ‘bioethanol’ and biobutanol have to consider the distillation/dehydration step. The state-of-art process of today is distillation of the fermentation broth to a concentration close to the azeotrope in one or several columns followed by dehydration by molecular sieve adsorption or by entrainer distillation. During the last three decades membrane based processes like pervaporation or vapour permeation have become more and more important of solvents. For the dehydration of bioalcohols these technologies are use today only in a few cases, however, membranes can reduce the energy consumption considerably. The paper will evaluate the pros and cons of various distillation/dehydration concepts and the required energy input. It will be shown that distillation combined with pervaporation or vapour permeation and vapour recompression has the lowest energy requirements and can reduce specific cost to the range of 0.05 ?/l EtOH (99.8 wt %) for EU Market conditions in 2010. The optimal combination largely depends on local conditions and costs for thermal and electrical energy.