Study On Preparation And Application Of ZIFs Membranes In The Gasoline Vapor Recovery

The release of volatile organic compounds (VOCs), from the process ofoil extaction, transportation, and applications, will endanger human health,therefore the recovery of gasoline vapor will be still a major challenge in thepetrochemical industry. ZIFs are a class of metal-organic hybrid crystallinematerial and have unque properties, such as structural diversity, construct ortailor frameworks with desired property. In this work, several ZIFsmembranes were prepared and the membrane performances were evaluatedby the applications in gasoline vapor recovery.The ZIF-8/ZrO2membranes were synthesized by a seeded growthmethod with the molar composition of Zn(NO3)2·6H2O:2-MeIM: DMF=1:1:282, and characterized by X-raydiffraction (XRD) and scanning electronmicroscopic (SEM) technologies, a rod-like ZIF-8crystal structure wasclearly observed and the active layer had a thickness of approximately25μm;Thermal gravimetry analysis (TGA) was conducted to evaluate the thermalstability of the activated ZIF-8samples, and the results indicated the absenceof guest molecules and preventing collapse of the ZIF-8frameworks. Thecrystallization time and crystallization temperature on membrane formationconditions were also studied, the uniform and defect-free ZIF-8membraneswere synthesized at130°C for24h. The effects of operating pressure,operating temperature, feed concentration, stage cut and different alkanecomponents on the separation performances of ZIF-8membranes weresystematically investigated. At130°C, the ZIF-8membrane showed anoptimum permeance of7.16×10-8mol/(m2·s·Pa) with the correspondingseparation factor of2.46for the N2/n-C6H14model mixtures at a operatingpressure of0.05MPa, a stage cut of0.293and a n-hexane volume fraction of30vol%, the separation performances of ZIF-8/ZrO2membranes in nitrogen/single alkane (C5/C6/C7) model mixtures and nitrogen/three alkanes(C5+C6+C7) model mixtures followed: p(n-C5H12)> p(n-C6H14)>p(n-C7H16)，(n-C7H16)>(n-C6H14)>(n-C5H12).The ZIF-78/ZnO membranes were synthesized by reactive seeding synthesis method with the molar composition of Zn(NO3)2·6H2O: nIm:nbIm: DMF=1:1.25:1.25:1000, and characterized by XRD and SEMtechnologies, the pure ZIF-78membranes were observed with a hexagonalprism structure and a thickness of about20μm; TGA was conducted toevaluate the thermal stability of the activated ZIF-78samples, and the resultsindicated the absence of guest molecules and preventing collapse of theZIF-78frameworks. The effects of crystallization time and temperature on theZIF-78membranes were investigated. Compact and continuous ZIF-78membranes were synthesized successfully at120°C for24h. Moreover, thegasoline vapor recovery performances of ZIF-78mebranes were characterizedwith n-C6H14/N2model mixtures. At20°C, the separation factor of themembrane for n-C6H14/N2is2.27, with the corresponding permeance of6.2210-8mol/(m2·s·Pa) at a operating pressure of0.06MP, n-hexane volumefraction of30vol%and a stage cut of0.2. Three kinds of single alkane(C5/C6/C7) and nitrogen system: p(n-C5H12)> p(n-C6H14)> p(n-C7H16)，(n-C5H12)>(n-C6H14)>(n-C7H16).The ZIF-69membranes were synthesized by a seeded growth method onthe-Al2O3support and activated. The ZIF-69memranes and powder werecharacterized by XRD, SEM and TGA technologies, the pure ZIF-69membranes were observed and the guest molecules were removed from themembrane channels. The effects of some parameters including the ratio ofraw materials, crystallization time and temperature on the ZIF-69membraneswere investigated. Complete and defect-free ZIF-69membranes weresynthesized under the conditions that included the molar composition ofZn(NO3)2·6H2O: nIm: cbIm: DMF=0.5:1:1:260,100°C and72h. Toassess the integrity of the ZIF-69membrane, single gas N2permeationmeasurements were performed on the ZIF-69membranes under differenttrans-membrane pressure drops. In order to investigate the operationconditions with ZIF-69membrane for separating N2/n-C6H14model mixtures,the effects of operating pressure, operating temperature, feed conditions andstage cut on the separation performance were investigated. The resultsshowed that the total permeance of N2/n-C6H14model mixtures was5.02×10-8mol/(m2·s·Pa) and the separation factor was2.60at a operating temperature30°C, operating pressure of0.08MP, n-hexane volume fraction of20vol% and a stage cut of0.2. Three types of gasoline vapor systems (N2/n-C5H12，N2/n-C6H14，N2/n-C7H16): p(n-C5H12)> p(n-C6H14)> p(n-C7H16)，(n-C7H16)>(n-C6H14)>(n-C5H12).