| N-butanol as a new emerging energy fuel can be produced by biomass fermentation process;however,it is usually obtained in the fermentation production process as a mixture with ethanol and acetone,subsequently leading to its lower energy efficiency.Therefore,it will play a decisive role whether n-butanol can be effectively produced through biomass fermentation and can be purified and separated from fermentation broth.At present,polymer/metal-organic framework(MOFs)mixed matrix membranes(MMMs)have showed excellent practical application prospects in the research of alcohol-water separation.Polyvinyl alcohol(PVA)is one of the most studied polymer materials and it has become an excellent water removal membrane material.However,PVA membrane is often limited by high swelling and poor thermal stability,so it is necessary to modify PVA properly to improve its properties.Among many MOFs materials available,UiO-66 is outstanding in water resistance stability and its skeleton structure does not collapse at extremely high temperatures,and thus it has shown great development potential in water-removing pervaporation separation.In this Master's Thesis,a series of PVA/UiO-66 MMMs with UiO-66 content of 5-30wt.%have been prepared by the liquid casting method,along with fumaric acid as the cross-linking agent and self-made UiO-66 as the modification filler.Subsequently,the physical properties of these MMMs are comprehensively investigated,and the membrane surface properties are highlighted by analyzing the contact angle measurements.Finally,these MMMs are used in alcohol/water separation from two aspects of alcohol/water adsorption and alcohol/water pervaporation.The main research contents and some meaningful conclusions of the Master's Thesis can be described as follows:1)Firstly,From the analysis results of XRD and FTIR of PVA/UiO-66 MMMs,it can be concluded that the filled modified PVA composite film has shifted the X-ray diffraction peaks and shifted the infrared absorption peaks of the two groups-OH and-C=O,indicating that there is a strong interaction between UiO-66 and PVA.SEM results show that there are no obvious defects between the two materials,but with the increase of UiO-66,the interface bonding will be affected.The light transmittance/haze results show that with the increase of UiO-66 loading,the light transmittance appears to decline while the opposite is applied to the haze index.The tensile results show that PVA membrane after crosslinked with fumaric acid has the highest tensile strength and it is 109 MPa.After adding UiO-66,the tensile strength of MMMs is seen to gradually decrease with the increase of the filler content.The swelling results show that the unfilled PVA and filled membranes have exbihited rather similar swelling tendcy in three liquid solvents but the swelling is gradually reduced in all solvents upon increasing the UiO-66 content.The swelling degree values for all the membranes considered are decreasing in the order of pure water>alcohol/water solution>pure alcohol.2)Secondly,using the measured contact angle data,the membrane surface energy values are calculated with the Owens-Wendt method.The calculations show that the surface characteristic of PVA membrane have changed considerably after embedded with UiO-66,and the surface energy is decreased with the increase in the UiO-66 content and it is 55.73×10-3N m-1for the unfilled PVA but dropped to 31.35×10-3N m-1for the 30 wt.%UiO-66 MMM.3)Thirdly,the effects of temperature and UiO-66 content on the membrane adsorption separation of 10 wt.%ethanol aqueous solution have been considered.As we can see,with the increase in UiO-66 content,the amount of ethanol adsorbed in the PVA membrane increases while the amount of water adsorption decreases.In the meanwhile,the ethanol/water adsorption separation factor increases whereas the total adsorption amount decreases.Moreover,ethanol/water adsorption separation factor and total adsorption amount are both seen to increase as temperature increases.These results turn to show that PVA MMMs are preferential to adsorb ethanol than water,leading to very large ethanol/water adsorption separation factor.4)Finally,the water removal performances of the PVA/UiO-66 MMMs for ethanol/water,n-butanol/water,and n-butanol/ethanol/aqueous solutions have been investigated through pervaporation.The results show that(1)with UiO-66 increased,the water/n-butanol separation factor has been affected heavily and as the content of UiO-66 is20 wt.%,the separation factor reaches the maximum of 2266,and is 164%higher than that of pure PVA membrane.On the contrary,the membrane permeation fluxes and permeances of both water and n-butanol are decreased after adding the UiO-66 filler.(2)As the feed water content increases,dehydration separation factor and selectivity are both decreased while the flux or permeance increases.When the feed water concentration is 10 wt.%,the pervaporation separation index(PSI)is the highest of 2561 kg/m2·h.(3)As the feed temperature increases,the dewatering separation factor for ethanol/water or n-butanol/water solution decreases while the flux increases significantly and the permeate water concentration also decreases.At 70°C,after 15 wt.%UiO-66 MMM pervaporation,the water concentration in n-butanol has increased from 10 wt.%in the feed to 99.57 wt.%in the permeate while for the ethanol/water solution the water concentration has increased from 10 wt.%to 95.02 wt.%.In the meanwhile,such memrbanre has resulted in a dehydration separation factor of 2998 for 90/10 wt.%n-butanol/water system at 40°C,and it is the best dehydration separation effect achieved in our work,but for 90/10 wt.%ethanol/water system the dehydration separation factor is just 256.These results indicate that such MMM is more effective for n-butanol dehydration than for ethanol dehydration.(4)For the 80/10/10 wt.%n-butanol/ethanol/water ternary solution by adding ethanol,the dewatering separation factor for the 15 wt.%UiO-66 MMM has substantially deceased.At40°C it is the highest of 1162 over the feed termepature range considered here but greatly reduced by 61.2%as compared to that achieved for(90/10 wt.%)n-butanol/water binary solution,indicating that the presence of the third component of ethanol has a significant side effect on the dehydration separation of n-butanol aqueous solution by pervaporation. |
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