Improvement of the refinement process for bioethanol

Abstract

Biomass is a carbon neutral material, and the development of processes for the use of the bioethanol is accelerating worldwide as the demand for its use as an alternate transportation fuel increases. Bioethanol has already been put to practical use in Brazil and United States. Today, sugarcane and corn are two of the materials used as the raw material in biomasses; however it is necessary to develop technology that uses lignocellulosic biomass as a raw material that can be used in large quantities at low prices because of the need to reduce the production costs. Thus, it is necessary to rationalize the process involving the resolution of biomass, the saccharification and co-fermentation of the cellulose and the process for refining the ethanol generated. In this report, we examined rationalization of the ethanol refinement process. The pressure swing adsorption (PSA) and membrane methods were examined as rationalization processes. With the membrane method the driving force for the dehydration becomes small in the high purity region, for example at more than 99wt%, and so an excessive membrane area is required. With the PSA method it is necessary to recycle the adsorbed water to the distillation column because of the need to recover the dissolved ethanol in the adsorbed water. A Hybrid process is proposed in which water is roughly removed until the level of 99wt% of the ethanol by the membrane method, and the ethanol is then dehydrated to a high purity afterwards by a small-scale PSA method. This Hybrid process is most advantageous from the viewpoint of energy and the equipment expense. When the content of the acetic acid in the bioethanol goes to 50 mg/kg, distillated ethanol of 85wt% may be supplied to the Hybrid process from a viewpoint of saving energy and equipment costs.