Investigation Of Membrane Degradation Mechanism In The Fermentation/Pervaporation Process

In recently years, the dwindling fossil fuel and the environmental issues caused by the conbustion of fossil fuels have been araised people’s attention. As a green renewable energy, bioethanol has been become a hotspot of research which produced by fermentation process.However,yeast growth will be influenced by serious product inhibition during fermentation process which lead to the decline of ethanol productivity.Ethanol could be removed from fermentation broth by ISPR(in situ product recovery) during the fermentation process.Then we could decrease the concentration of ethanol in the fermentation broth and overcame the product inhibition. Pervaporation is a viable and promising separation technique which could be integrated with fermentation.Nevertheless,the phenomenon of membrane degradation appeared during the PV/fermentation integrated process.Not only the productivity of ethanol is affacted directly,but also the membrane have to be replaced frequently during the ethanol production process as the degradation of the pervaporation membrane which add the assistant time and then increase the material cost and operation cost.The issue limits the industrial application of the PV/fermentation integrated technique.For the membrane degradation in PV/fermentation process,the main materials and mechanism are discussed.Firstly,the degree of membrane degradation is understood preliminarily through the PV/fermentation experiment.Secondly,the changes of membrane performance as adding glucose,glycerol and succinic to the ethanol water solution are investigated.And then ascertain the main materials that affact the membrane performance. Finally,the mechanisms of membrane degradation are inverstigated according to the three possible reasons including membrane fouling concentration polyrization and changes of vapor-liquid equilibrium.It could provide us a powerful basis to discovery the reasonable methods to solve this issue.Firstly, the total flux dropped from 303.9g·m-2·h-1 reduction is about 41.1%.Nevetheless,the water flux have no significant change.Secondly,the concentration of glucose,glycerol,succinic are relatively high in the fermentation broth.Effect of these components on the membrane performance are investigated.As the control experiment,the performance of PDMS membrane for ethanol water solution.Then,a pervaporation experiment were conducted after lwt% glucose,glycerol and succinic added to the feed.The results showed that the total flux decreased from 531.5 to 505.1,flux reduction is about 41.1%.The memrbane performance had a relatively obvious change. Glycerol maybe one of the main materials that caused the membrane degradation.Nevertheless,the membrane performance keeped consistent basically after adding glucose and succinic.Overall,these constituents coundn’t lead to membrane degradation at the concentration of 1 wt%.Finally,the machenisms of membrane degradation were investigated.The increase of ethanol flux and the reduction of water flux were caused by the change of vapor-liquid equilibrium when the concentration of glucose and salt added to the feed is higher than 1mol·L-1.The total flux incerased 11.4% when the concentration of glycerol reached 0.5mol·L-1,while the ethanol flux remain unchanged.However,only when the concentration of these constituents were at a high leval, did it have a great influence on the vapor-liquid equilibrium.And membrane degradation coundn’t occur at the same concentration of fermentation broth.The concentration polarization in pervaporation process could decrease the flux and separation factor. However,the changes of membrane performance because of the concentration polarization when using the fermentation broth are at the same leval compared with ethanol water solution. The components of fermentation broth coundn’t aggravate the degree of concentration polarization.Pervaporation experiments of ethanol water solution contains glucos,glycerol and succinic were conducted.It indicated that PDMS membrane have a Before and after these tests, membrane performance keep consistent.It indicated that the PDMS membrene have strong antifouling ability.Above all,the effect of membrane fouling,concentration polarization and the change of vapor-liquid equilibrium on membrane performance are very little theoretically.The membrane degradation may be caused by the decrease of the ethanol concentration in the fermentation broth.