Combined Vapor Permeation and Continuous Solid-State Distillation for Energy-Efficient Bioethanol Production

Abstract

Extracting ethanol by steam directly from fermented solid-state bagasse is an emerging technology of energy-efficient bioethanol production. With continuous solid-state distillation (CSSD) approach, the vapor with more than 25 wt% ethanol flows out of the column. Conventionally, the vapor was concentrated to azeotrope by rectification column, which contributes most of the energy consumption in ethanol production. As an alternative, a process integrating CSSD and vapor permeation (VP) membrane separation was tested. In light of existing industrial application of NaA zeolite hydrophilic membrane for dehydration, the prospect of replacing rectification operation with hydrophobic membrane for ethanol enriching was mainly analyzed in this paper. The separation performance of a commercial PDMS/PVDF membrane in a wide range of ethanol–water-vapor binary mixture was evaluated in the experiment. The correlation of the separation factor and permeate flux at different transmembrane driving force was measured. The mass and energy flow sheet of proposed VP case and rectification case were estimated respectively with process simulation software based on experimental data. Techno-economic analysis on both cases was performed. The results demonstrated that the additional VP membrane cost was higher than the rectification column, but a lower utilities cost was required for VP. The discount payback period of supplementary cost for VP case was determined as 1.81 years compared with the membrane service lifetime of 3 years, indicating that the hybrid CSSD-VP process was more cost effective and energy efficient.

Feasibility Study on Bioethanol Production by One Phase Transition Separation Based on Advanced Solid-State Fermentation

“…An Excel spreadsheet linked to the built-in workbook in the simulator was used to calculate membrane modules. Membrane performance parameters including total flux and separation factor were obtained from reference [24].…”

“…In addition, the costs of zeolite membrane are much higher than organic membrane, which is unacceptable for a cost-effective ethanol production process. The feasibility of replacing rectification with a commercial PDMS and PVDF composite hydrophobic membrane to enrich the CSSD outlet vapor to more than 70 wt% ethanol concentration has been verified [24].…”

“…Figure 2 displays the processing diagram of bioethanol production with OPTS technology integrating ASSF, CSSD and dual VP operations [12,18,24]. Fermentable sugars kept in solid substrate are converted into ethanol in an ASSF bioreactor and extracted by steam in the CSSD column.…”

“…VP can not only utilize the energy of the CSSD column outlet vapor, but also greatly reduce the required membrane area compared with liquid fermentation. Moreover, the reasonable layout could enable the vapor to keep its phase state until reaching product concentration [24].…”

Cellulose Nanofiber Preparation Combined with Bioethanol Production from Fermented Sweet Sorghum Bagasse

“…When the alkali dosage in FSSB rises to 30% (w/dry w), the corresponding condensate alkalinity is up to 12.94 mg/L. In practical production, the vapor overhead the continuous solid-state distillation column will be fed into a rectification column or vapor permeation module . The alkali in the vapor can be completely removed by the rectifying operation and dissolved into column kettle liquid, which would not affect the fuel ethanol grade.…”