Fabrication Of PDMS/ZIF-8 Mixed Matrix Membrane And Its Application In Pervaporation

As a kind of renewable energy,biobutanol has a promising application prospect.However,product derived from fermentation is often low concentration aqueous solution of butanol.The crux is to separation butanol from its aqueous solution effectively.Pervaporation(PV)is a green and efficient membrane separation technique for separating liquid mixture.It is very suitable for the separation process of butanol/water system.To realize this process,the core is the fabrication of PV membrane.Compared with the traditional organic membrane and inorganic membrane,the mixed matrix membrane(MMM)can combine their strengths simultaneously.PDMS(polydimethylsiloxane)exhibits high hydrophobicity and excellent membrane forming properties.While ZIF-8,one kind of MOF materials,has high specific surface area,strong surface hydrophobicity and high adsorption selectivity for butanol/water system.Therefore,this research use ZIF-8 as filling particle to fabricate PDMS/ZIF-8 mixed matrix membrane(MMM)to further improve the pervaporation performance of PDMS membrane.Firstly,ZIF-8 was successfully synthesized in ammonia solution,and the characterization of FTIR,XRD and BET reflected the correct molecular structure,crystal structure and pore characteristics of ZIF-8,respectively.After that,serial MMMs were prepared in different loading by the solution blending method.The hydrophobicity of the MMMs was improved,and the contact angle was raised from 108.18° to 114.36° at the loading of 9wt%.To test pervaporation performance of these MMMs,1.5wt%butanol/water solution was used as feed at 55 ?.At the loading of 1wt%,a highest separation factor of 51.60 and a flux of 808.85 was obtained.However,ZIF-8 was aggregated seriously when the loading is high,resulting in dramatically decay of MMM's pervaporation performance.To solve this problem,this research regulated the particle size of ZIF-8.The void between large particles is larger compared with the small ones,so that the polymer is more likely to seal these void.Based on this assumption,this research synthesized micro-sized ZIF-8(mZIF-8)to fabricate MMMs.By introducing the auxiliary ligand 1-methymidazole,it was determined that the optimal mixture ratio of the reaction system was zinc:2-methimidazole:1-methymidazole:methanol=1:4:2:1000,and the maximum size of mZIF-8 was 1.21?m.After incorporating mZIF-8 into PDMS,the flux of MMMs were significantly promoted,and the negative influence of aggregation was relieved in some extent.At the loading of 3wt%,a maximum flux of 1009.90 g/m2h was obtained,and the separation factor is 44.21.Finally,in order to modify ZIF-8 and improve its compatibility with PDMS,this research used poly dopamine to coat ZIF-8 and conducted hydrophobic modification by grafting silane coupling agent on the surface of poly dopamine coated ZIF-8.According to results of XRD and FTIR,structure of ZIF-8 was not influenced after modification and alkyl chain was grafted on the surface of ZIF-8 succesfully.The optimal performance was obtained when mZIF-8 was modified with octyltrimethoxysilane.At the loading of 3wt%,and the maximum flux and separation factor was 1125.35 g/m2 h,44.22,respectively.Compared with pristine PDMS membrane,trade-off of the membrane was overcomed,and the flux and separation factor was improved by 50%,33%,respectively.