Matching Items (5)
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- All Subjects: Membranes (Technology)
- All Subjects: MOF
- Creators: Mu, Bin
- Creators: Shan, Bohan
- Status: Published
Description
Membranes are a key part of pervaporation processes, which is generally a more
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.
ContributorsYin, Huidan (Author) / Lind, Mary Laura (Thesis advisor) / Mu, Bin (Committee member) / Nielsen, David (Committee member) / Seo, Don (Committee member) / Lin, Jerry (Committee member) / Arizona State University (Publisher)
Created2017
Description
The large-scale anthropogenic emission of carbon dioxide into the atmosphere leads to many unintended consequences, from rising sea levels to ocean acidification. While a clean energy infrastructure is growing, mid-term strategies that are compatible with the current infrastructure should be developed. Carbon capture and storage in fossil-fuel power plants is one way to avoid our current gigaton-scale emission of carbon dioxide into the atmosphere. However, for this to be possible, separation techniques are necessary to remove the nitrogen from air before combustion or from the flue gas after combustion. Metal-organic frameworks (MOFs) are a relatively new class of porous material that show great promise for adsorptive separation processes. Here, potential mechanisms of O2/N2 separation and CO2/N2 separation are explored.
First, a logical categorization of potential adsorptive separation mechanisms in MOFs is outlined by comparing existing data with previously studied materials. Size-selective adsorptive separation is investigated for both gas systems using molecular simulations. A correlation between size-selective equilibrium adsorptive separation capabilities and pore diameter is established in materials with complex pore distributions. A method of generating mobile extra-framework cations which drastically increase adsorptive selectivity toward nitrogen over oxygen via electrostatic interactions is explored through experiments and simulations. Finally, deposition of redox-active ferrocene molecules into systematically generated defects is shown to be an effective method of increasing selectivity towards oxygen.
First, a logical categorization of potential adsorptive separation mechanisms in MOFs is outlined by comparing existing data with previously studied materials. Size-selective adsorptive separation is investigated for both gas systems using molecular simulations. A correlation between size-selective equilibrium adsorptive separation capabilities and pore diameter is established in materials with complex pore distributions. A method of generating mobile extra-framework cations which drastically increase adsorptive selectivity toward nitrogen over oxygen via electrostatic interactions is explored through experiments and simulations. Finally, deposition of redox-active ferrocene molecules into systematically generated defects is shown to be an effective method of increasing selectivity towards oxygen.
ContributorsMcIntyre, Sean (Author) / Mu, Bin (Thesis advisor) / Green, Matthew (Committee member) / Lind, Marylaura (Committee member) / Arizona State University (Publisher)
Created2019
Description
Among the alternative processes for the traditional distillation, adsorption and membrane separations are the two most promising candidates and metal-organic frameworks (MOFs) are the new material candidate as adsorbent or membrane due to their high surface area, various pore sizes, and highly tunable framework functionality. This dissertation presents an investigation of the formation process of MOF membrane, framework defects, and two-dimensional (2D) MOFs, aiming to explore the answers for three critical questions: (1) how to obtain a continuous MOF membrane, (2) how defects form in MOF framework, and (3) how to obtain isolated 2D MOFs. To solve the first problem, the accumulated protons in the MOF synthesis solution is proposed to be the key factor preventing the continuous growth among Universitetet I Oslo-(UiO)-66 crystals. The hypothesis is verified by the growth reactivation under the addition of deprotonating agent. As long as the protons were sufficiently coordinated by the deprotonating agent, the continuous growth of UiO-66 is guaranteed. Moreover, the modulation effect can impact the coordination equilibrium so that an oriented growth of UiO-66 film was achieved in membrane structures. To find the answer for the second problem, the defect formation mechanism in UiO-66 was investigated and the formation of missing-cluster (MC) defects is attributed to the partially-deprotonated ligands. Experimental results show the number of MC defects is sensitive to the addition of deprotonating agent, synthesis temperature, and reactant concentration. Pore size distribution allows an accurate and convenient characterization of the defects. Results show that these defects can cause significant deviations of its pore size distribution from the perfect crystal. The study of the third questions is based on the established bi-phase synthesis method, a facile synthesis method is adopted for the production of high quality 2D MOFs in large scale. Here, pyridine is used as capping reagent to prevent the interplanar hydrogen bond formation. Meanwhile, formic acid and triethylamine as modulator and deprotonating agent to balance the anisotropic growth, crystallinity, and yield in the 2D MOF synthesis. As a result, high quality 2D zinc-terephthalic acid (ZnBDC) and copper-terephthalic acid (CuBDC) with extraordinary aspect ratio samples were successfully synthesized.
ContributorsShan, Bohan (Author) / Mu, Bin (Thesis advisor) / Forzani, Erica (Committee member) / Dai, Lenore (Committee member) / Lin, Jerry (Committee member) / Liu, Jingyue (Committee member) / Arizona State University (Publisher)
Created2019
Description
Metal-organic frameworks (MOFs) are a new set of porous materials comprised of metals or metal clusters bonded together in a coordination system by organic linkers. They are becoming popular for gas separations due to their abilities to be tailored toward specific applications. Zirconium MOFs in particular are known for their high stability under standard temperature and pressure due to the strength of the Zirconium-Oxygen coordination bond. However, the acid modulator needed to ensure long range order of the product also prevents complete linker deprotonation. This leads to a powder product that cannot easily be incorporated into continuous MOF membranes. This study therefore implemented a new bi-phase synthesis technique with a deprotonating agent to achieve intergrowth in UiO-66 membranes. Crystal intergrowth will allow for effective gas separations and future permeation testing. During experimentation, successful intergrown UiO-66 membranes were synthesized and characterized. The degree of intergrowth and crystal orientations varied with changing deprotonating agent concentration, modulator concentration, and ligand:modulator ratios. Further studies will focus on achieving the same results on porous substrates.
ContributorsClose, Emily Charlotte (Author) / Mu, Bin (Thesis director) / Shan, Bohan (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
While the solution diffusion model and pore flow model dominate pervaporation transport mechanism modeling, a new model combining the solution diffusion and viscous flow models is validated using membranes with large scale defects exceeding 2 nm in diameter. A range of membranes was characterized using scanning electron microscopy and x-ray diffraction (XRD) to determine quality and phase characteristics. MFI zeolite membranes of He/SF6 pure gas permeation ideal selectivities of 25, 15, and 3 for good, medium, and poor quality membranes were subjected to liquid pervaporations with a 5% ethanol in water feed, by weight. Feed pressure was increased from 1 to 5 atm, to validate existence of viscous flow in the defects. Component molar flux is modeled using the solution diffusion model and the viscous flow model, via J_i=F_i (γ_i x_i P_i^sat )+(ρ )/M_W ∅/μ_ij x_i P_h. A negative coefficient of thermal expansion is observed as permeances drop as a function of temperature in all three membranes, where ϕ=((ϵr_p^2)/τ∆x). Experimental parameter ϕ increased as a function of temperature, and increased with decreasing membrane quality. This further proves that zeolitic pores are shrinking in one direction, and pulling intercrystalline voids larger, increasing the (ϵ/τ) ratio. Permiabilities of the bad, medium, and good quality membrane also decreased over time for both ethanol and water, meaning that fundamental membrane characteristics changed as a function of temperature. To conclude, the model reasonably fits empirical data reasonably well.
ContributorsWilliams, Suzanne Jean (Author) / Lin, Jerry Y.S. (Thesis advisor) / Emady, Heather (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2016