Energy and Cost Evaluation for the Concentration and Dehydration Process of Bioethanol by Zeolite Membranes

The pressure swing adsorption method (PSA) is one of the energy-saving technologies and adopted for dehydration of bioethanol, however further progress in cost-saving is unlikely because the PSA method has some restrictions in its process. On the other hand, the zeolite membranes have the potentiality to improve energy consumption and the acid-resistant zeolite has been developing to overcome the weak property of materials. In the present study, the required membrane performances and process applications were studied through the process simulations for the distillation and dehydration of bioethanol to achieve the economical advantages over the conventional processes. Increase of the water flux is effective in reducing energy because it enables to operate in the low-energy mode without a vacuum pump. However, the reduction ratio is relatively a little because the distillation energy is majority in total energy. The equipment cost can be reduced due to the decrease of membrane modules. Fluctuations of separation factor have little effect on the energy consumption and cost, but the separation factor of about 10,000 is thought to be necessary for controlling ethanol leakage through the membrane. Reducing the ethanol concentration at the outlet of the distillation tower in order to lower the load of distillation can decrease the energy consumption significantly and also decrease the cost. Additionally, the cost reduction of 6 JPY kg-EtOH(-1) can be achieved if the membrane which has flux of 36 kg . m(-2) . h(-1) and separation factor of 10,000 is applied for the concentrating process substituted for distillation. The comparable cost reduction of 6 JPY kg-EtOH(-1) is realized for the hydrous ethanol production in the similar process of replacing distillation to membrane separation. These calculated cost reductions are enough for stimulating the progress of membrane separation for bioethanol enrichment.