| Biomass energy is a clean,low-carbon and environment-friendly energy.Due to its renewable nature,it is considered to be the best alternative to traditional fossil energy.One of the important applications of biomass energy is to use microorganisms to ferment ethanol from biomass,but the ethanol generated in the fermentation process will in turn inhibit the activity of microorganisms and reduce the subsequent ethanol production rate.One of the ways to improve the productivity of ethanol fermentation is to continuously remove ethanol from the fermentation liquid when ethanol is produced from the fermentation liquid,so as to reduce the ethanol concentration and the inhibition of microorganisms.Pervaporation(PV)is a new membrane separation technology.Due to its advantages of high efficiency,simple equipment,low cost,low pollution and low energy consumption,it is widely used in the separation and purification of biofuels.The combination of hydrophobic pervaporation membrane and fermentation tank can not only achieve continuous production of biomass ethanol,but also reduce energy,economic and environmental costs.Polydimethylsiloxane(PDMS)is one of the common pervaporation membrane materials.Silica repeating units and methyl substituents endow PDMS with high hydrophobicity.Ethanol has a high diffusion rate and excellent selectivity in PDMS membranes.Therefore,PDMS is considered to be the most representative alcohol pervaporation selective membrane material for removing alcohol from aqueous solution at low alcohol concentration.However,PDMS pervaporation membrane has the following problems:the preparation process takes too long;The controllability of the thermal curing process is insufficient,which is easy to produce defects;Continuous preparation cannot be realized;PDMS membranes lack efficient permeation channels,and the passage of bio alcohol takes a lot of time,which limits the transmission efficiency of PDMS membranes.In addition,the mechanical strength of PDMS membrane needs to be improved,which limits the application of PDMS pervaporation membrane.In this paper,polyamide 6(PA6)hollow fiber membrane was prepared by melt spinning.PA6has a large number of amide bonds(NH-CO)on the molecular chain.These amide bonds can easily combine with each other to form hydrogen bonds,which makes PA6 base film have excellent tensile strength and flexibility.The membrane surface was modified and grafted with PDMS to realize pervaporation.It is expected to provide a new idea for the development and application of polyamide 6 hollow fiber membrane.The specific research contents are as follows:(1)PA6 hollow fiber membrane was prepared by blending PA6 with porous agent PLA by melt drawing;PA6 membrane surface was modified and grafted with PDMS for pervaporation.At600 mm Hg,the permeation flux of the prepared membrane to ethanol solution is 114.22 g/(m~2·h),and the separation factor is 5.7;The permeation flux of 1.5 wt%acetic acid solution is 894.2g/(m~2·h),and the separation factor is 4.1.(2)PA6 hollow fiber membrane was prepared by melt blending of ethylene vinyl alcohol copolymer(EVOH)as a porogen with PA6.It was observed by electron microscope that there were 200 to 300 nm micropores on the surface.The maximum retention rate of carbon ink(300nm)could reach 80%,and the flux could reach 522.4 L/(m~2·h)while effectively retaining carbon ink.Then the membrane surface was modified and grafted with PDMS.The PDMS layer generated on the membrane surface blocked the original membrane pore.The prepared membrane had a maximum permeation flux of 844.2 g/(m~2·h)for ethanol solution at 0.008 MPa,a maximum separation factor of 8.67,a maximum permeation flux of 1834.4 g/(m~2·h)for acetic acid at 0.008MPa,and a separation factor of 6.55.The mechanical properties of the film were improved obviously,the elongation at break was 28.8%,and the maximum tensile strength was 12.4 MPa. |
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