Simultaneous ethanol production and separation using integrated fermentation and evaporation system under vacuum condition

• Main Author: Nguyen, Viet D.
• Format: text
• Language: English
• Published: Animo Repository 2010
• Subjects: Ethanol; Fermentation; Manufacturing processes; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/291; https://animorepository.dlsu.edu.ph/context/etd_doctoral/article/1290/viewcontent/CDTG004759_P.pdf
• Institution: De La Salle University

An integrated fermentation and separation process operated under vacuum condition for ethanol production was investigated in this study using Sacchamromyces cerevisiae as fermentation inoculum and glucose as sugar source. In recent years, very high sugar concentration fermentation has been continuously suggested in the industry to produce high ethanol concentration. For the fermentation process, the growth and production ability of cells are inhibited by high ethanol and sugar concentrations. The limitation of conventional processes can be solved by the integration of fermentation with separation. When ethanol is removed from the fermentation broth, its inhibition effect on growth rate of cells is diminished. Fermentation under vacuum pressure is known as an effective method for continuous ethanol removal since at this condition ethanol-water solution will boil at the fermentation temperature. In this study, new ideas for the integration of fermentation and separation process operating under vacuum pressure was investigated in order to find a suitable method, which did not only prevent product and/or substrate inhibitions but also improved the productivity and yield of the fermentation process. The experiments started with batch fermentation to find out the suitable temperature condition. Based on the preliminary batch fermentation experiments, it was decided that all succeeding experiments were carried out at approximately 33 0C. Then, a kinetic model for batch fermentation was developed to investigate the effects of high initial glucose and ethanol concentrations on the growth rate and production rate of yeast cells. It was found that the parameters used in the model that could describe kinetic behavior in the wide range of initial glucose concentrations were independent of the initial substrate concentration. In order to evaluate the survival and activation ability of the yeast cells under vacuum pressure, batch fermentation experiments at pressures in the range of 760 47 mm Hg were performed. The results indicated that the yeast cells could survive and convert glucose to ethanol without oxygen or air supply and the vacuum system could be maintained without running the vacuum pump continuously. The advantage i of fermentation under vacuum also came from high ethanol concentration collected in the cold-trap. This ethanol concentration reached approximately 50% by weight at the end of the fermentation. A kinetic model for the ethanol fermentation under vacuum was developed to investigate the effect of vacuum pressure on the growth rate and production rate of the yeast. A process modification of integrated fermentation and separation operated under vacuum condition was investigated. At atmospheric condition, the dry biomass remained at low concentration of 2.4 g L-1; only 30% glucose was utilized. On the other hand, at vacuum condition, 52% of glucose was converted and the cell dry-mass concentration remained at a higher concentration of 4.2 g L-1. The productivity of ethanol at vacuum condition when compared to atmospheric condition showed an increase of approximately 1.6 times. A kinetic model was developed and used to predict the dynamic behavior of the integrated process. The simulation results showed almost 90% agreement between experimental and estimated data. The validation of the kinetic model of the integrated process indicated that the model could be used to predict the behavior of the integrated fermentation and separation system at different conditions. The kinetic model was applied to the integrated fermentation and separation process, the kinetic parameters were determined. For further application, the kinetic model and parameters could be used to predict kinetic behavior and concentration profiles of residual substrate, product and biomass of the integrated process. These kinetic parameters and the concentration profiles could provide the basis for the design of the scale-up integrated fermentation and separation. Potential applications of the kinetic model and parameters include process control in terms of high productivity, total amount of product and process optimization.