Browsing by Subject "membranes"
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Item Catalytic Membrane Reactor for Extraction of Hydrogen from Bioethanol Reforming(2013-11-26) Kuncharam, Bhanu VardhanThis research explores a novel application of catalytic membrane reactors for high- purity hydrogen extraction from bioethanol reforming. Conventional membrane systems employ hydrogen permselective materials such as palladium, polymer membranes, which present several material challenges including embrittlement, thermal degradation and poisoning by hydrocarbons when used for high-temperature hydrocarbon reforming. Thus, the present work is motivated by an interest in employing reactor design concepts to alleviate our reliance upon permselective materials. Catalytic membrane reactor with segregated reactant(s) is employed to demonstrate the hypothesis that high-purity hydrogen with competitive hydrogen recoveries can be achieved by manipulating the reaction and diffusion phenomena, and corresponding thermal gradients inside the catalytic membrane, in the absence of any permselective materials. The hypothesis is demonstrated in two designs: (1) a single functional layer design for water-gas-shift catalytic membrane reactor, and (2) a multi-layer design for bioethanol reforming. A two-dimensional model is developed to describe reaction and diffusion in the catalytic membrane coupled with plug-flow equations in the retentate and permeate volumes using shell and tube architecture. Simulation results for a typical diesel reformate mixture (9 mol% CO, 3 mol% CO2, 28 mol% H2 and 15 mol% H2O) demonstrate that H2:CO permselectivities of 90:1 to > 200:1 with permeate hydrogen recoveries of 20% to 40% can be achieved through appropriate catalytic membrane design. This single reaction simulation results are used to establish a clear rubric of design rules that are then used as a base for designing catalytic membrane reactor for extraction of hydrogen from bioethanol (16 mol% ethanol). The two-dimensional catalytic membrane reactor for bioethanol reforming is simulated, using a network of ethanol reforming reactions and a composite iicatalyst with unique catalytic layers active for one or more reactions. The isothermal simulation results show that an apparent H2:CO permselectivity of 100:1 with hydrogen recovery of 15% can be achieved at appropriate design and flow configuration. This model is extended to a non-isothermal design, which predicted a decrease in membrane performance owing to endothermic reforming reaction. An autothermal design with an additional combustion catalyst layer to counteract the endothermic thermal gradients enhanced the non-isothermal membrane performance. Experiments were conducted to validate the water-gas-shift catalytic membrane reactor model using a gas permeation system; results qualitatively agree with the modeling results and quantitively with an error.Item Synthesis and Characterization of Films and Membranes of Metal-Organic Framework (MOF) for Gas Separation Applications(2012-12-12) Shah, Miral Naresh 1987-Metal-Organic Frameworks (MOFs) are nanoporous framework materials with tunable pore size and functionality, and hence attractive for gas separation membrane applications. Zeolitic Imidazolate Frameworks (ZIFs), a subclass of MOFs, are known for their high thermal and chemical stability. ZIF-8 has demonstrated potential to kinetically separate propane/propene in powder and membrane form. ZIF-8 membranes propane-propene separation performance is superior in comparison to polymer, mixed matrix and carbon membranes. The overarching theme of my research is to address challenges that hinder fabrication of MOF membranes on a commercial scale and in a reproducible and scalable manner. 1. Current approaches, are specific to a given ZIF, a general synthesis route is not available. Use of multiple steps for surface modification or seeding causes reproducibility and scalability issues. 2. Conventional fabrication techniques are batch processes, thereby limiting their commercialization. Here we demonstrate two new approaches that can potentially address these challenges. First, we report one step in situ synthesis of ZIF-8 membranes on more commonly used porous ?-alumina supports. By incorporating sodium formate in the in situ growth solution, well intergrown ZIF-8 membranes were synthesized on unmodified supports. The mechanism by which sodium formate promotes heterogeneous nucleation was investigated. Sodium formate reacts with zinc source to form zinc oxide layer, which in turn promotes heterogeneous nucleation. Sodium formate promotes heterogeneous nucleation in other ZIF systems as well, leading to ZIF-7, Zn(Im)2 (ZIF-61 analogue), ZIF-90, and SIM-1 films. Thus one step in situ growth using sodium formate provides a simplified, reproducible and potentially general route for ZIF film fabrication. One step in situ route, although advantageous; is still conventional in nature and batch process with long synthesis time. This limits commercialization, due to scalability and manufacturing cost issues. Taking advantage of coordination chemistry of MOFs and using temperature as driving force, continuous well-intergrown membranes of HKUST-1 and ZIF-8 in relatively short time (15 min) using Rapid Thermal Deposition (RTD). With minimum precursor consumption and simplified synthesis protocol, RTD provides potential for a continuous, scalable, reproducible and commercializable route for MOF membrane fabrication. RTD-prepared MOF membranes show improved separation performances, indicating improved microstructure.