Ethanol Continuous Fermentation In A Silicone Rubber Membrane Bioreactor And Energy-consuming Analysis

Technology of ethanol continuous fermentation with a silicone rubber membrane bioreactor has great importance in developing economized agricultural product processing, new petroleum-replaced clean energy production and low cost manufacture of chemical raw materials, etc. Operating functions of silicone rubber membrane bioreactor system are studied in this thesis. A silicone rubber membrane bioreactor system, including raw material treatment, product recovering and operating factors controlling, is assembled in the experiment, in which the reactor's volume is 4L and the effective membrane area is 0.024m². Through testing variations of broth and condensate under different operating conditions and calculating heat-transfer and energy-consuming in the condensation system, the suitable operating factors for ethanol continuous fermentation are found, and application potential of silicone rubber membrane bioreactor in industry is testified.Both temperature and glucose concentration in substrate have influence on fermentation process. At higher temperature (40℃), growth periods of yeast cells become shorter, while at lower temperature (25℃), metabolism of yeast cells become slower; the highest cell concentration is achieved at 35℃ which comes up to 16g/l and the accompanying ethanol concentration in broth is over 130g/l. Yeast cell growth will be inhibited when the glucose concentration in substrate is either too high or too low, but because the cells can survive longer in higher glucose concentration environment, increasing glucose concentration in broth properly will benefit to ethanol continuous fermentation process.The continuous fermentation experiment which last 350 hours shows that the pervaporation character of silicone rubber membrane can eliminate the inhibition effect of production ethanol effectively. Cell concentration in broth keeps at 14g/l around during the long period, over 3 times more than those in conventional fermentation processes. Ethanol solution of 45.2w% can be obtained from 8w% broth directly, which means large amount of energy will be saved for subsequent distillation operations. The silicone rubber membrane in this bioreactor systempossesses excellent separation property. It has a flux of over 1500g/m²-h and a selectivity between 9.5 to 10 when evaporating the 5w% ethanol-water solution at 40 ℃., showing a good potential economy benefit.Through analysis of the condensation system, which based on a simple but accurate thermodynamics model, the relationship between temperature and product concentration is developed. The analysis and experiment show that appointed-concentration products can be obtained simply by controlling condensers' set-temperatures. This result has an important significance not only for the simplification of drinking ethanol process and the improvement of product quality, but also for the equipment design and process control.