Study Of Situ Ethanol/Water Separation Through External-Vapor Permeation Using A PDMS Composite Membrane

The fuel ethanol as the clean substitution energy of unregenerate energies has attracted a lot of attentions, it can largely release the crisis of energies at the moment. Besides, it is green, environmentally friendly, no pollution, so it can ease the atmospheric contamination and gradually replace the traditional fossil fuel.As we all know, the process of fuel ethanol fermentation is a typical product inhibition process, namely, the gradual increase of product fuel ethanol can in turn restrain the total fermentation process in the process of fermentation process. The result is that the process of fermentation process becomes slower and slower, and the productivity rate also drops. So we need find one method which can timely separate the product fuel ethanol on-line, and decrease the inhibition effect of the product. At the process of ethanol fermentation, The most common method is to separate the product ethanol timely. Although the vapor permeation technology has many similarities with the traditional pervaporation technology, now the present study results can indicate that it has many particular superiorities relative to the process of pervaporation technology. For example, in the process, the vapor can directly contact the membrane surface which can largely decrease the membrane pollution and realize the long-time cyclic utilization, so this technology may realize the mass production in the industrial range. So many scientists and researchers start to attach importance to the vapor permeation technology and attempt to couple this particular technology with fuel ethanol fermentation process. Besides, this technology can realize to separate the product ethanol in-situ in the process of fermentation, so ti can ease the inhibiting effect of the product ethanol playing in the whole fermentation process.In our present study, we study the split type gas cycle vapor permeation technology. At the first, we study the traditional pervaporation technology for the separation of low concentration ethanol/water solution with the self-made PDMS membrane. But, we gradually find that the pervaporation flux is rather lower because of the thick membrane. Also, it cannot resolve the series of traditional problems of pervaporation technology, for example, the reduction of pervaporation flux because of the serious membrane pollution. Besides, We study the vapour permeation of the commercial PDMS membrane used for low concentration ethanol/water solution. We study a series of influence factors of the process, including the solution concentration, the solution temperature, the membrane contactor temperature, the vapour temperature, the different membrane materials, the vacuum degree behind the membrane module, the different vapour volume flux, the different condensing temperature behind the membrane module, the different V/A (fermentation broth liquid volume/membrane area), all the experiments are conducted with air distributor. All these experiment results can provide many references for the following scholars, they can also provide valuable references for its possible industry application.The results indicate that with the self-made PDMS membrane to separate the low concentration ethanol/water solution, the separation factor can reach about10, but the permeation flux is always rather lower, about300-500g/(m2·h). Besides, we study the vapor permeation properties of the commercial PDMS membrane. With the rising of solution concentration, both the permeation flux and selectivity rise with a great degree. With the rising of solution temperature and membrane contactor temperature, both the permeation flux and selectivity rise with a little degree. But with the rising of vapor temperature and vapour volume flux, both the permeation flux and selectivity rise with a great degree. But with the rising of the vacuum degree behind the membrane module, the permeation flux increases slowly but the selectivity decreases with a great degree. With the rising of the vacuum degree behind the membrane module, the permeation flux increases slowly but the selectivity decreases with a great degree. With the reducing of condensing temperature behind the membrane module, both the permeation flux and the selectivity increase with a great degree. Besides, comparing the commercial PDMS membrane with other modified PVTES membranes, the results indicate that though the permeation flux of the commercial PDMS membrane is rather lower than other modified PVTES membranes, the selectivity has rather a slight advantage. Finally, we study the commercial PDMS membrane used for different food solution systems, the results are that the commercial PDMS membrane is not only suitable for the low concentration ethanol/water solution, but also is appropriate for the low concentration n-butyl alcohol/water solution. So these results can provide certain value for the commercial PDMS membrane used for other separation process.