Fermentation-Pervaporation Coupled Process For Ethanol Production In A SRMB System And Unit Design For Rectification Of Downstream Product

For the development of ethanol fermentation production technology in a rubber membrane bioreactor system, the coupling process of fermentation and pervaporation was experimentally studied in a silicone rubber membrane bioreactor with the volume of 4L and the effective membrane area of 0.08m2. A rectification process was proposed to condense the product downstream and corresponding unit was designed. At the same time, the energy-consumptions for two rectification processes were analyzed.The experiment was conducted at 35℃. The microorganism was alcohol instant active dry yeast and the carbon source substrate was glucose of technical grade. The variations of composition in broth and condensate and the performances of PDMS were measured. Commonly, fermentation tends to suspend when accumulated ethanol concentration in fermentor reaches to 68g/L because of product inhibition. However, with pervaporation coupled in the process, ethanol concentration decreased quickly below the inhibition concentration, so that the fermentation could proceed continuously. Ethanol productivity of 4.02g/(L·h) was achieved after SMBR reached a steady state. Ethanol concentration in fermentation broth changed from 63~20g/L, and total flux and selectivity of the PDMS membrane were 800~1220 g/(m2·h) and 5~9.2, respectively. Compared with the results for traditional fermentation and model solution under similar experimental conditions, the coupling of fermentation and pervaporation makes the process enhanced and the system operate steadily.For advancing the concentration of product, downstream collecting system was improved. Two rectification proposals were put forward, and the corresponding processes and devices were designed and calculated. Proposal A: a vacuum rectifier was introduced to the existing system. Proposal B: the ethanol steam is transported by a vacuum pump to a rectifier operated in normal atmospheric pressure. Comparatively, proposal A consumes more energy, but has higher productivity and lower facility cost. Proposal B is energy-saving, but has lower productivity and higher facility-cost.This study has referenced value and instructional significance, for optimizing processes of ethanol production in SMBR, economy analysis and design of industrialized system.