No description available.

Olefin/Paraffin separation, traditionally carried out by cryogenic distillation, is difficult to achieve due to the similar size and volatility of the components. Recently, many studies have explored membrane separation methods that utilize a metal ion to facilitate preferential olefin transport across the membrane. However, much of this work focuses on smaller molecules, C2-C3, which are gaseous at room temperature, while little work has been done studying separation of larger molecules, C5 and greater, which are generally liquid at room temperature. The processes developed to separate small molecules are not necessarily directly applicable to separate larger molecules. A polymer electrolyte membrane consisting of an active layer of polyethylene oxide (PEO) and silver tetrafluoroborate (AgBF4) has shown high selectivity for separating gaseous olefin/paraffin mixtures. The current project investigates the feasibility of applying this membrane to the separation of pentene and pentane (liquid C5 olefin and paraffin). Process variables investigated are the: pure component permeability ratio, equilibrium sorption uptakes, pure component diffusivities, and stable membrane lifetime. Permeation tests on individual species (n-pentane and 1-pentene) were performed in two operating modes with membranes of varying silver concentrations: direct liquid contact to the membrane, and vapour contact to the membrane. The vapour contact mode showed improved membrane stability in comparison to the liquid contact mode. The olefin/paraffin permeability ratio increases with increasing silver content in the membrane, however, the membrane selectivity is much lower than that achieved with smaller olefin/paraffin pairs. Selective chemical interactions between pentene and the membrane were observed, as the pentene sorption uptake is higher than that of pentane. In addition, a residual fraction is observed – a fraction of the pentene does not desorb from the membrane at ambient conditions – indicating a permanent or semi-permanent interaction. Desorption of pentane is determined to follow a Fickian diffusion model, while desorption of pentene appears to be governed by pseudo-second order kinetics.

Membrane separations provide a potentially attractive technology over conventional processes due to their advantages, such as low capital cost and energy consumption. The goal of this thesis is to design hybrid membranes that facilitate specific gas separations, especially olefin/paraffin separations. This thesis focuses on the designing dendrimer-based hybrid membranes on mesoporous alumina for reverse-selective separations, synthesizing Cu(I)-dendrimer hybrid membrane to facilitate olefin/paraffin separations, particularly ethylene/methane separation, and investigating the influence of solvent, stabilizing ligands on facilitated transport membrane. Reverse-selective gas separations have attracted considerable attention in removing the heavier/larger molecules from gas mixtures. In this study, dendrimer-based chemistry was proved to be an effective method by altering dendrimer structures and generations. G6-PIP, G4-AMP and G3-XDA are capable to fill the alumina mesopores and slight selectivity are observed. Facilitated transport membranes were made to increase the olefin/paraffin selectivity based on their chemical interaction with olefin molecules. Two approaches were explored, the first was to combine facilitator Cu(I) with dendrimer hybrid membrane to increase olefin permeance and olefin/paraffin selectivity simultaneously, and second was to facilitate transport membrane functionality by altering solvents and stabilizing ligands. Promising results were found by these two approaches, which were: 1) olefin/paraffin selectivity slightly increased by introducing facilitator Cu(I), 2) the interaction between Cu(I) and dendrimer functional groups are better known.

In this dissertation, I have investigated applying the laser ablation of microparticle aerosol (LAMA) process to the production of nanocomposite polymer membranes for olefin/paraffin separation. Experimental results for three major thrusts are presented: 1) an investigation into the scalability of the LAMA process, 2) a new laser ablation technique for nanoparticle production from aqueous feedstocks, and 3) characterization of olefin-selective polymer nanocomposite membranes produced using LAMA. The propensity for Ag nanoparticles to form agglomerates in LAMA is investigated. Nanoparticle samples were collected on TEM grids at several feedstock aerosol densities. As the density increased, the particle morphology shifted from single nanoparticles 5 nm in diameter to chained agglomerates of 20 nm diameter primary particles. The results are in agreement with a numerical model of Brownian agglomeration and diffusion. Factors influencing nanoparticle morphology, such as temperature, initial nanoparticle charge, and feedstock aerosol density are discussed. It is shown that agglomeration occurs on a much longer timescale than the other processes, and can be treated independently. A new nanoparticle synthesis technique is presented: laser ablation of aqueous aerosols. A Collison nebulizer is used to generate a mist of ~10 [mu]m diameter water droplets containing dissolved transition metal salts. Water from the droplets quickly evaporates, leaving solid particles which are ablated by an excimer laser. Ablation results in plasma breakdown and photothermal decomposition of the feedstock material. For AgNO₃ ablated in He gas, metallic Ag nanoparticles were produced. For Cu(NO₃)₂ ablated in He gas, crystalline Cu₂O nanoparticles were produced. For Ni(NO₃)₂ ablated in He gas, crystalline NiO nanoparticles were produced. A combination of AgNO₃ and Cu(NO₃)₂ ablated in a reducing atmosphere of 10%H₂/He yielded nonequilibrium Ag-Cu alloy nanoparticles. Membranes composed of poly(ethylene glycol diacrylate) (PEGDA) and Ag nanoparticles were produced by the LAMA process. Permeation and sorption measurements for the light olefins and paraffins were conducted for these membranes. The membranes showed very little improvement in olefin/paraffin selectivity compared with neat PEGDA membranes. Using the LAMA implementation described here, it was impossible to produce membranes with high Ag loading. Whether membranes containing more Ag would exhibit improved selectivity remains an open question. / text

Olefin/Paraffin separation, traditionally carried out by cryogenic distillation, is difficult to achieve due to the similar size and volatility of the components. Recently, many studies have explored membrane separation methods that utilize a metal ion to facilitate preferential olefin transport across the membrane. However, much of this work focuses on smaller molecules, C2-C3, which are gaseous at room temperature, while little work has been done studying separation of larger molecules, C5 and greater, which are generally liquid at room temperature. The processes developed to separate small molecules are not necessarily directly applicable to separate larger molecules. A polymer electrolyte membrane consisting of an active layer of polyethylene oxide (PEO) and silver tetrafluoroborate (AgBF4) has shown high selectivity for separating gaseous olefin/paraffin mixtures. The current project investigates the feasibility of applying this membrane to the separation of pentene and pentane (liquid C5 olefin and paraffin). Process variables investigated are the: pure component permeability ratio, equilibrium sorption uptakes, pure component diffusivities, and stable membrane lifetime. Permeation tests on individual species (n-pentane and 1-pentene) were performed in two operating modes with membranes of varying silver concentrations: direct liquid contact to the membrane, and vapour contact to the membrane. The vapour contact mode showed improved membrane stability in comparison to the liquid contact mode. The olefin/paraffin permeability ratio increases with increasing silver content in the membrane, however, the membrane selectivity is much lower than that achieved with smaller olefin/paraffin pairs. Selective chemical interactions between pentene and the membrane were observed, as the pentene sorption uptake is higher than that of pentane. In addition, a residual fraction is observed – a fraction of the pentene does not desorb from the membrane at ambient conditions – indicating a permanent or semi-permanent interaction. Desorption of pentane is determined to follow a Fickian diffusion model, while desorption of pentene appears to be governed by pseudo-second order kinetics.

No description available.

Propylene is one of the most important feedstocks of the petrochemical industry with an estimated 2015 worldwide demand of 100 million tons. Retrofitting conventional C3 splitters is highly desirable due to the huge amount of thermal energy required to separate propylene from propane. Membrane separation is among the alternatives that both academia and industry have actively studied during the past decades, however; many challenges remain to advance membrane separation as a scalable technology for energy-efficient propylene/propane separations. The overarching goal of this research is to provide a framework for development of scalable ZIF-based mixed-matrix membrane that is able to deliver attractive transport properties for advanced gas separations. Zeolitic imidazolate frameworks (ZIFs) were pursued instead of conventional molecular sieves (zeolites and carbon molecular sieves) to form mixed-matrix membrane due to their intrinsic compatibility with high Tg glassy polymers. A systematic study of adsorption and diffusion in zeolitic imidazolate framework-8 (ZIF-8) suggests that this material is remarkably kinetically selective for C3 and C4 hydrocarbons and therefore promising for membrane-based gas separation and adsorptive separation. As a result, ZIF-8 was used to form mixed-matrix dense film membranes with polyimide 6FDA-DAM at varied particle loadings and it was found that ZIF-8 significantly enhanced propylene/propane separation performance beyond the “permeability-selectivity” trade-off curve for polymeric materials. Eventually, this research advanced ZIF-based mixed-matrix membrane into a scalable technology by successfully forming high-loading dual-layer ZIF-8/6FDA-DAM asymmetric mixed-matrix hollow fiber membranes with attractive propylene/propane selectivity.

To date there exists a great deal of energetic and economic inefficiency in the separation of olefins from paraffins because the principal means of achieving industrial purity requirements is accomplished with very energy intensive cryogenic distillation. Mitigation of the severe energy intensity of the propylene/propane separation has been identified as one of seven chemical separations which can change the landscape of global energy use, and membranes have been targeted as an emerging technology because they offer scalability and lower capital and operating costs. The focus of this work was to evaluate a new direction of material development for the very industrially relevant propylene/propane separation using membranes. The objective was to develop a rational design approach for generating highly selective membranes using a relatively new platform of materials known as polyimides of intrinsic microporosity (PIM-PIs), the prospects of which have never been examined for the propylene/propane separation. Structurally, PIMs comprise relatively inflexible macromolecular architectures integrating contortion sites that help disrupt packing and trap microporous free volume elements (< 20 Å). To date most of the work reported in the literature on this separation is based on conventional low free volume 6FDA-based polyimides which in the best case show moderate C3H6/C3H8 selectivities (<20) with C3H6 permeabilities too low to garner industrial interest. Due to propylene and propane’s relatively large molecular size, we hypothesized that the use of more open structures can provide greater accessibility to the pores necessary to enhance membrane sieving and flux. It has been shown for numerous key gas separations that introduction of microporosity into a polymer structure can defy the notorious permeability/selectivity tradeoff curve and induce simultaneous boosts in both permeability and selectivity. The cornerstone approach to designing state of the art high performance PIM-PI membranes for the light gas separations involving maximizing the intra-segmental rigidity of the polymer chain was applied to the C3H6/C3H8 separation. A study regarding a stepwise maximization of intra-molecular rigidity and its effects on C3H6/C3H8 permeation was evaluated by conducting systematic structural modifications to high performance PIM-PIs. State of the art increases in performance were observed in pure-gas measurements as there were significant increases in C3H6/C3H8 selectivity and C3H6 permeability upon doing so. However, mixed-gas measurements showed that there were 65% losses in selectivity due to competitive sorption and mainly plasticization. Based on the conclusions drawn, a fundamental departure from conventional PIM design principles was used, instead emphasizing enhancing inter-chain interactions by introduction of a flexible diamine and functionalization with hydroxyl groups to attempt to immobilize the polymer chains. In doing so, the polymer chains may be able to pack more efficiently and upon sub-Tg annealing cause a microstructural reorganization to form a coplanarized configuration due to the combination of inter-chain charge transfer complexes (CTC) and hydrogen bonding networks. This approach successfully mitigated plasticization, but more importantly resulted in a tightening of the microstructure, especially in the ultra-microporous range (<7 Å) thereby yielding significant boosts in C3H6/C3H8 selectivity. Based on the PIM platform and novel polymer design approach thereof, the C3H6/C3H8 upper bound was thrust to new limits and led to the generation of the most selective solution processable polymers reported for the C3H6/C3H8 separation. Although the PIM platform has redefined the polymer upper bound, the permeability/selectivity tradeoff still endures, as the C3H6 permeabilities were on the order of 1 to 3.5 Barrer for the most selective polymers. To bridge that gap in permeability, several different approaches were taken. For the first time attempted for C3H6/C3H8 separation, high temperature heating of a PIM-PI to form thermally-rearranged and carbon molecular sieve membranes was employed. The TR membrane showed increased C3H6 permeability and about 50% losses in C3H6/C3H8 selectivity, while the CMS membrane formed at 600 oC showed modest gains in C3H6/C3H8 selectivity with significant improvements in C3H6 permeability. Finally, hybrid nanocomposite membranes incorporating a metal-organic framework structure into a PIM-PI matrix was used. ZIF-8, which has demonstrated high diffusive selectivities for C3H6/C3H8, was dispersed within the polymer, since previous work by the Koros group indicated that its incorporation into polyimide matrices can facilitate major improvements in both C3H6/C3H8 selectivity and C3H6 permeability compared to the respective neat polymer. Focus was directed towards attempting to improve polymer/nanoparticle adhesion by enhancing the interactions between the polymer and filler particles to mitigate the interfacial defects notorious in mixed-matrix membranes (MMM). To do so, ZIF-8 was dispersed into one of the best performing hydroxyl functionalized PIM-PI for the C3H6/C3H8 separation. The highest loaded mixed-matrix membrane in a glassy polymer to date of 65% (w/w) was achieved. The membranes showed pure-gas selectivities ranging from 34 with 10 Barrer at 30% loading to 43 with 38 Barrer at 65% loading. Strong performance and plasticization resistance were sustained in mixed-gas experiments even to feed pressures approaching the vapor pressure of the C3H6/C3H8 mixture, as selectivities well over 20 were achieved with high permeabilities, thereby demonstrating the potential commercial viability. Based on the work reported in this dissertation, we hope to help lay a framework to be able to tailor membrane performance and future membrane design to meet the demands of the different applications of the propylene/propane separation and hence show that there can be a marketplace for membranes in the separation. These include the debottlenecking of cryogenic distillation towers for production of polymer-grade propylene (99.5%) to reduce the associated extensive energy load, production of chemical-grade propylene (92-95% propylene), or for the recovery and recycling of olefins from reactor purges of petrochemical processes.

Olefin/paraffin separation is a large potential market for membrane applications. Carbon molecular sieve membranes (CMS) are promising for this application due to the intrinsically high separation performance and the viability for practical scale-up. Intrinsically high separation performance of CMS membranes for olefin/paraffin separations was demonstrated. The translation of intrinsic CMS transport properties into the hollow fiber configuration is considered in detail. Substructure collapse of asymmetric hollow fibers was found during Matrimidﾮ CMS hollow fiber formation. To overcome the permeance loss due to the increased separation layer thickness, 6FDA-DAM and 6FDA/BPDA-DAM polyimides with higher rigidity were employed as alternative precursors, and significant improvement has been achieved. Besides the macroscopic morphology control of asymmetric hollow fibers, the micro-structure was tuned by optimizing pyrolysis temperature protocol and pyrolysis atmosphere. In addition, unexpected physical aging was observed in CMS membranes, which is analogous to the aging phenomenon in glassy polymers. For performance evaluation, multiple "proof-of-concept" tests validated the viability of CMS membranes under realistic conditions. The scope of this work was expanded from binary ethylene/ethane and propylene/propane separations for the debottlenecking purpose to mixed carbon number hydrocarbon processing. CMS membranes were found to be olefins-selective over corresponding paraffins; moreover, CMS membranes are able to effectively fractionate the complex cracked gas stream in a preferable way. Reconfiguration of the hydrocarbon processing in ethylene plants is possible based on the unique CMS membranes.