Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Koros William; Committee Member: Hess Dennis; Committee Member: Jones Christopher; Committee Member: Meredith Carson; Committee Member: Wong CP. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The aim of this thesis was to research the new synthesis methodology of ionothermal synthesis, used for the synthesis of zeolite type materials, mainly aluminophosphates. An ionic liquid or eutectic mixture is to act as both the organic template and the solvent, hence eliminating the space filling effects in the reaction from the water. Initial reactions were carried out using the ionic liquid 1-ethyl-3-methylimidazolium bromide which acted as the solvent and template in the production of four three-dimensional structures and one layered structure. The addition of cobalt into the aluminophosphate framework was investigated and resulted in three different cobalt-aluminophosphates being synthesised, including one new zeolite framework. Experiments were carried out into the effect of altering the imidazolium cation alkyl chain. It appears likely that in the presence of fluoride, some of the imidazolium cations undergo a metathesis reaction forming 1,3-dimethylimidazolium which acts as a template in the formation of an aluminophosphate. Preliminary investigations have also been started into the effects of changing the ionic liquid anion from bromide to phosphorus hexafluoride and bis((trifluoromethyl)sulfonyl)amide. The use of these anions resulted in the production of several different one and two-dimensional structures. The use of eutectic mixtures as solvent and template was also investigated as a cheaper, more easily synthesised solvent than the ionic liquids. The results show a new methodology of eutectic mixtures acting as template delivery agents through the slow, in situ decomposition of the urea derivative of the eutectic mixture. This synthesis method resulted in the formation of nine one and two-dimensional aluminophosphates.

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Die CFD-Modellierung des Fasertransports wurde auf der Basis des Euler/Euler-Ansatzes untersucht. Die Nachbildung des Transportverhaltens der Partikel erfordert die korrekte Beschreibung des Impulsaustausches. Hierfür liefert die Auswertung der Sinkgeschwindigkeiten aus den Experimenten am Versuchsstand "Säule" die notwendigen Informationen. Über die Vorgabe von Partikeldichte und Partikeldurchmesser kann die Sinkgeschwindigkeit nachgebildet und der Partikeltransport adäquat modelliert werden. Beispielsimulationen einer partikelbeladenen Strömung im Versuchsstand "Ringkanal" lieferten plausible Resultate. Das Anlagerungs- bzw. Abtragungsverhalten der Partikel an Hindernissen (z. B. Wehren) wurde über die Modellierung einer vom Feststoffanteil abhängigen Viskosität simuliert. Dieser Zusammenhang wurde an die Ergebnisse der Experimente im Ringkanal angepasst. Erste Demonstrationsrechnungen zur Beschreibung des Partikeltransportes an Hindernissen ergaben plausible Resultate. In anderen Beispielen zeigte die Parametervariation einer feststoffabhängigen Viskosität jedoch einen zu geringen Einfluss auf die berechneten Ablagerungsmengen, um die experimentellen Befunde zu reproduzieren. Es wurde ein Modell des Differenzdruckaufbaus aus den Kompaktierungseigenschaften der auf dem Sieb abgelagerten Fasern entwickelt und an Experimenten justiert. Damit steht neben den in der Literatur veröffentlichten Korrelationen ein weiteres Verfahren zur Berechnung des Differenzdrucks zur Verfügung. In einer Machbarkeitsstudie wurde die Wirkung eines Siebes auf das Strömungsfeld unter Nutzung des Modellansatzes des porösen Körpers in CFX-4.4 implementiert. Das implementierte Modell liefert qualitativ plausible Resultate.

Abstract: In this work, carbon molecular sieve (CMS) membranes were prepared based on a polymer of intrinsic microporosity, named PIM-6FDA-OH. The goal of this work was to examine the effect of the fabrication parameters of the CMS membranes on the gas separation performance of the final CMS membranes produced. Furthermore, the performance changes are reported for membranes physically aged over 7, 30, 60, and 90 days. The membranes prepared consisted of thin-film (about 3 !m thick) CMS selective layers supported by a stainless-steel tube. The experiments were split into four projects. The first project aimed to determine the effect the layer thickness had on the final performance of the produced CMS membranes. Five pairs of membranes were prepared using different coating solution concentrations, and different number of layers. The concentrations used were 5 (1 layer), 7.5 (1 layer), and 9 wt% (1, 2, and 3 layers) polymer in THF. The membranes had the same soak time of 15 minutes and pyrolysis temperature of 650 °C. The results showed that the increase in number of layers did not provide any benefits and was unnecessary. Moreover, the decrease in concentration produced membranes with higher permeances but with a greater loss in selectivity. Therefore, the 9 wt% concentration solution with one layer was chosen for the remaining experiments. The second project examined the effect of the pyrolysis temperature on the performance of the final membranes produced. All membranes were made with the 9 wt% solution and the soak time was held constant at 15 minutes. The soak temperatures tested were: 700, 750, 850, and 950. °C. The membranes pyrolyzed at temperatures above 650 °C were severely defective. This suggests that either the precursor polymer could not form defect-free thin membranes using high soak temperatures, or another potential reason is related to interfacial defect formation between the CMS layer and the porous stainless-steel support. Further experiments are required to fully understand the soak temperature effect on the formation of thin CMS films on porous supports. The third project examined the effect of the soak time (i.e. time the membranes are held isothermally at the pyrolysis temperature) on the final performance of the membranes. The same 9 wt% solution was used, and the pyrolysis temperature was 650 °C. The pyrolysis soak times were 15 minutes, 1 hour, 3 hours, and 10 hours, respectively. The results showed that as the soak time increased the membranes became denser and provided higher selectivities and lower permeances. Furthermore, the membranes with longer soak times became more size-sieving earlier during physical aging than the membranes made with shorter soak times. Physical aging was accelerated with an increase in soak time, i.e., membranes made by soaking over 10 hours reached stable permeance over time starting at day 7. The fourth project aimed to investigate the preparation process, as well as to test the performance of the membranes under different environments. Two types of polyimide precursor membranes were made, one set with the pristine polyimide and the other one with a PDMS top coating. The results showed that the membranes with PDMS had similar selectivities but far slower permeances than the CMS membranes, the membranes made without PDMS coating had much lower selectivities and permeances. CMS membranes soaked for 15 minutes and 3 hours, respectively, were tested to check the permeances of all the five gases (H2, O2, N2, CH4, and CO2) under pressure cycles from 2 to 8 bar. The membranes passed the tests and their permeances were not affected by exposing them to high pressures and back, except for the membranes soaked for 3 hours when tested with CO2.

<p> Rate of adsorption data for gases on molecular sieve·s and coals have been interpreted using equations for unsteady state diffusion derived from Fick's law for spheres usually, ignoring the amount adsorbed and the shape of the adsorption isotherm. These inappropriate equations result in calculated diffusivities that are too low and activation energies that are too large. </p> <p> Numerical. solutions of Fick's law were made for diffusion and adsorption in a porous sphere of radius R by finite difference methods for the following conditions: a. Diffusion is the rate-controlling step, and the diffusivity, D, is constant. b. Within an increment of the particle the total amount of adsorbate per unit volume, T is related to the "effective" concentration, c, by a Langmuir-like isotherm T = abC/(1 + bC). c. At zero tine the particle containing no adsomate is surrounded by adsozbate of concentration, Co, which remains constant throughout the rate process, and d. Equilibrium is established immediately at the periphery of the sphere. </p> <p> The solutions are obtained in terms of Z = Q/Q and T=(DCo/QR^2) t = kt, where t is time, k is a constant equal to the term within the brackets, and Q and Q are the amounts adsorbed per unit volume at time t and at equilibrium. The quantity within brackets is also a valid expression for linear and Freundlich-like adsorption isotherms and probably holds for other isotherms. Plots of z as a function of T shift systematically as the parameter B = bCo increased from 0, corresponding to a linear adsorption isotherm, to large values; the value of Z at a given T increasing with increasing values of B. For B = 0 the numerical solution is identical with analytical solution for the linear adsorption isotherm which for values of z <0.87 is given by kt = (2/π) { (-1 - πZ/6) - (1 ~πZ/3) ^1/2 } where k = DCo/R^2Q. For large values of B the numerical solutions approach as a limit the parabolic law kt = (1/2) {(1- 2Z/3) - (1- Z) } The value of (1/k~) o.zidt~ at short times increases fran 3.385 for B = 0 to 4 .. 243 for very large values of B.. From experimental data the value of k derived using the equation for B = 0 is 1.56 larger than for the parabolic equation. Hence the values of D obtained from the initial linear portions of t.he rate curve change by only a factor of 1.56 when the type of isotherm is changed from linear to rectangular. </p> <p> Rates of adsorption and the adsorption isotherm were determined for N2 , CH4, co2 , and C2H6 on samples of Linde 4A molecular sieve at several temperatures from -78° to +50°C in a manostatic volumetric aborption apparatus. The Langmuir equation satisfactorily approximatedthe isotherms and the values of B were moderately large at the lower temperatures of each series of experiments, eg., for N2 at -78°C, 10.6; for CH4 at -78°C, 7.3; for co2 at 0°C, 64; for Ci!6 at 0° and 30°C, 37 and 10.3. </p> <p> The rate data plotted as Z against t^1/2 were not linear at short times but curved upward initially before becoming linear. The initial (, nonlinear portion persisted significantly longer than the brief uncertain period at the beginning of the experiment. This phenomena could result from the equilibration at the periphecy of the particles requiring a finite time rather than being instantaneous. </p> <p> An equation based on the parabolic law model and a first order equilibration process was derived, which fits. the experimental data for 0.05 < Z < 0.95. This equation is appropriate only to data with a large value of B, but is probably a reasonable approximation for other rate data. </p> <p> The rates of adsorption for different molecules were co2 > N2 > CH4 > c2H6 · The activation energies for the diffusivity were found to be 4.1 and 6.0 kcal./nole for methane and ethane. The _heats of adsorption were found to be 7.2 and 8.3 kcal/mole for methane and ethane. </p> / Thesis / Master of Engineering (MEngr)

A vapor phase impregnation technique with Pt(acac)₂ has been developed and used to load Pt into aluminosilicate (KL, BaKL, KBaKL, NaY, CsNaY, FAU, EMT, ZSM-12 and SSZ-24) and aluminophosphate (AIP0₄-5 and VPI-5) molecular sieves. ¹³C MAS NMR, TEM and H₂ chemisorption measurements reveal that Pt can be loaded into the micropores of molecular sieves with both charged and neutral frameworks. Pt containing molecular sieves were tested as catalysts for the aromatization of n-hexane at 460 - 510°C and atmospheric total pressure in order to study the influence of Pt cluster size and support acidity/basicity, microstructure and chemical composition on activity and selectivity. High selectivity to benzene over most of the zeolite samples demonstrates that support acidity/basicity and microstructure do not contribute directly to the aromatization selectivity over Pt catalysts. A clear trend of increasing benzene selectivity with decreasing Pt cluster size is found. These observations suggest that the exceptional reactivity of Pt/KL for the aromatization of n-hexane results from the lack of any acidity in the support and the ability of zeolite L to stabilize the formation of extremely small Pt clusters. Pt/AIP0₄-5 and Pt/VPI-5 show high selectivity to n-hexane with little formation of benzene while opposite is observed for Pt/SSZ-24. The differences in catalytic behavior are attributed to variations in the environment of Pt clusters which are situated in either an aluminophosphate or silicate micropore. See document for rest of abstract. / Ph. D.

Meta-diisopropylbenzene is reacted with propylene over the acid form of the molecular sieves SAPO-5, mordenite, offretite, beta, hexagonal and cubic faujasite (hex and FAU), L, SAPO-37, and an amorphous silica-alumina at temperatures around 463 K in a flow-type fixed-bed reactor. A small amount of cracking is observed. The main reactions of meta-diisopropylbenzene are isomerization and alkylation. This alkylation is proposed as a new test reaction to characterize the effective size of the voids in larger pore (12 T-atom rings or above) molecular sieves by measuring the amount ratio of formed 1,3,5- to 1,2,4-triisopropylbenzene. In most cases, this ratio increases with the increasing effective void size of the molecular sieves in the order: SAPO-5 < mordenite < offretite < beta < hex ≈ FAU < L < SAPO-37 < amorphous silica-alumina. Since samples with the FAU topology show lower selectivities to 1,3,5-triisopropylbenzene than the mesoporous, amorphous silica-alumina, pore curvature has an influence on alkylation selectivity even for voids of 13 A size. / Ph. D.

The aim of this thesis was to synthesise CoAPO-34 and FeAPO-34 using ionothermal synthesis in the presence of organic amines. Using this method provides an alternative route to prepare such materials under low pressure instead of the higher pressure associated with hydrothermal or solvothermal synthesis. Both materials have chabazite (CHA) topology and they are known to act as catalysts. CoAPO-34 was ionothermally prepared using 1-ethyl-3-methylimidazolium bromide (EMIMBr) in presence of 1, 6-hexadiamine (HDA). This study has found that when the synthesis was carried out without HDA, AlPO-11 was preferentially obtained instead of CoAPO-34. Broad line signals which appear between 2000 to 5000 ppm in both spin-echo ³¹P NMR spectra of as-synthesised and calcined CoAPO-34 confirm that the Co²⁺ ions have been successfully incorporated within the framework of the material. FeAPO-34 was synthesised under ionothermal conditions using 1-ethyl-3-methylimidazolium chloride in the presence of ethylenediamine (EDA). In the absence of EDA, the synthesis has produced AlPO-34 instead of FeAPO-34. Broad line signals that appear between 1000 to 14000 ppm in spin-echo ³¹P NMR spectra of both as-synthesised and calcined FeAPO-34 are direct evidence of isomorphous substitution of framework aluminum by Fe(II) or Fe(III). Another aim of this study was to explore the ionothermal synthesis of copper containing aluminophoshate of DNL-1 (Cu/DNL-1). This material was attractive to explore because it contains 20 ring extra-large pores and Cu(I) species in the channels of the framework, potentially giving material the ability to simultaneous store NO and to generate NO from NO₂⁻ anions. Cu/DNL-1 was successfully prepared under ionothermal conditions using EMIMBr and HDA. Without HDA in the synthesis, AlPO-11 was obtained. In this material, copper ions were not incorporated in the Cu/DNL-1 skeleton framework. This was confirmed by absence of broadline signal at >500 ppm in spin-echo ³¹P NMR spectrum of the sample. The copper ions are expected to be present as extra-framework cations. Extra-framework Cu(I) species that were formed by high temperature calcination of Cu/DNL-1 are active to produce NO from NO₂⁻. Therefore, the calcined Cu/DNL-1 can be used to simultaneously store and produce NO from nitrite. This has the potential to significantly extend the lifetime of gas delivery in the material to prevent thrombus formation.

Structure direction in the synthesis of phosphate-based materials (aluminophosphates, AlPOs; magnesiumaluminophosphates, MgAPOs; silicoaluminophosphates, SAPOs; magnesiumsilicoaluminophosphates, MgAPSOs), has been investigated through co-templating synthesis studies supported by molecular modelling. These solids have been characterised by diffraction and solid-state NMR, and their properties in gas adsorption and catalysis have been measured. The parameters in the hydrothermal synthesis of SAPO STA-7, St Andrews porous solid number 7, (SAV), in which the macrocycle 1,4,7,11- tetraazacyclotetradecane (cyclam) and tetraethylammonium (TEA) cations are used as co-templates, were investigated in detail. A new route involving a reversal of the mixing order of reagents leads to the formation of single crystals up to 50 μm with perfect tetragonal prismatic morphology that was not achieved via previous synthetic routes. For the first time in SAPO STA-7, X-ray diffraction locates the tetraethylammonium cation (TEA) in tg.tg. conformation. The synthesis and full characterisation of a novel aluminophosphate structure designated STA-14 (KFI) represents the first example of a designed synthesis of a zeotype. The synthesis route is based on a co-templating approach supported by molecular modelling to design the specific template for one of the two types of cages within the structure. The first, a larger type of cage, also present in AlPO-42 (LTA), is templated by the azaoxacryptand 4,7,13,16,21,41-diaza-1,10-bicyclo[8,8,8]- hexocosane (‘Kryptofix 222’, hereafter K222). The modelled co-template configuration, in this case TEA in the tt.tt configuration, was experimentally observed by X-ray diffraction. Modifying the gel chemistry leads to SAPO and MgAPSO STA-14, which display high pore volumes for N₂ adsorption, similar to those of STA-7 and SAPO-34 (CHA). Furthermore, during these synthetic studies, a novel fully tetrahedrally- coordinated magnesiumaluminophosphate layer phase has been prepared, with a structure of relevance to hypothetical VPI-5 (VFI) type extended structures. Molecular modelling was also applied in another aluminophosphate-based material, that of STA-2 (SAT), to predict a template that could be prepared from inexpensive reagents. Existing routes required the use of expensive quinuclidine as a precursor to the template 1,4-bisquinuclidinium butane. The template suggested by modelling, 1,4-diazabicyclo (2,2,2)octane butane (NC₆H₁₂N⁺-C₄H₈-⁺NC₆H₁₂N), labelled DABCO_C4, templated AlPO STA-2 successfully. Structure characterisation of the as- prepared form of AlPO STA-2 using X-ray synchrotron data suggest the formation of Al- OH-Al units to accommodate the positively-charged template within the neutral framework and a combination of ¹³C, ¹⁴N and ¹⁵N NMR studies have been used to give further details of the template environment in the cages. The gas adsorption behaviour of the stable materials STA-7, STA-14 and STA-2 was evaluated for CO₂. High pressure adsorption (0 to 40 bars) on STA-7 and STA-14 shows similar behaviour due to their structural and chemical similarities. The total uptake of CO₂ for SAPO STA-7 is less than for the zeolite NaX (FAU) (3.4 and 5.2 mmolg -1 respectively at 373 K and 12 bars) but the usable capacity for pressure swing adsorption technology (PSA) between 1 to 20 bar for STA-7 is twice the value for NaX. The affinity of adsorption towards CO₂ and its low uptake at 1 bar made SAPO STA-7 a desirable sorbent for PSA. The zeotype affinity of adsorption for different probe gases is different, CO₂ >> CH₄ > CO, to that for zeolite NaX CO₂ >> CO > CH₄. Low pressure CO₂ adsorption (0 to 1 bar) in STA-7, STA-14 and STA-2 at temperatures between 273 and 303 K demonstrates that the topology and therefore the total free pore volume accessible to the gas molecules is the most important factor in determining the uptake in these solids, but that the composition and distribution of the silicon cations within the framework also has an important effect. For example at 273 K and 1 bar, the uptake of the STA-2 framework in the SAPO form is ca. 2wt% higher than in the AlPO form, but compared with SAPO STA-7, the uptake due to pore volume limitations is 10wt% lower under same conditions. In addition, the high quality of the SAPO STA-7 crystals obtained by the new route made them suitable in collaborations for the direct observation of diffusion of methanol by interference microscopy (IFM) and the study of their crystal growth by combined atomic force microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The catalytic applications of the STA-7 and STA-14 for the methanol-to-olefins reaction (MTO) and the argon adsorption at 87 K were also performed collaboratively. The results are reported and discussed here in the light of their structure and composition.