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Jiang, HuaEffect of Changes in Flow Geometry, Rotation and High Heat Flux on Fluid Dynamics, Heat Transfer and Oxidation/Deposition of Jet Fuels
Doctor of Philosophy (Ph.D.), University of Dayton, 2011, Mechanical Engineering

Jet fuel is used in high-performance military flight vehicles for cooling purposes before combustion. It is desirable to investigate the influence of the flow and heating conditions on fuel heat transfer and thermal stability to develop viable mitigation strategies. Computational fluid dynamics (CFD) simulations and experiments can provide the understanding of the fuel physical phenomena which involves the fluid dynamics, heat transfer and chemical reactions. Three distinct topics are studied: The first topic considers the effect of flow geometry on fuel oxidation and deposition. Experiments and CFD modeling were performed for fuels flowing through heated tubes which have either a sudden expansion or contraction. It was found that the peak deposition occurs near the maximum oxidation rate and excess deposition is formed near the step. This study provides information for the fuel system designer which can help minimize surface deposition due to fuel thermal oxidation.

In the second area of study, the fuel passed heated rotational test articles to investigate the effect of rotation on fuel heat transfer. The coupled effects of centrifugal forces and turbulent flow result in fuel temperatures that increase with rotational speed. This indicates that the convective heat transfer is enhanced as rotational speed increases. This work can assist the understanding of using jet fuel to cool the turbine engine.

In the third segment of research, the fuel was exposed to “rocket-like” conditions. This investigation is to explore the effect of high heat flux and high flow velocity on fuel heat transfer and oxidation/deposition. Simulations show a temperature difference over several hundred degrees in the radial direction within the very thin thermal boundary layer under rapid heating. The fuel contacting the interior wall is locally heated to a supercritical state. As a result, the heat transfer is deteriorated in the supercritical boundary layer. Both simulated and measured deposit profiles show a peak deposit near the end of the heated section. These observations may eventually have an application to the design of high speed supersonic vehicles with improved cooling capabilities.

Committee:

Jamie S. Ervin, PhD (Advisor); Steven Zabarnick, PhD (Committee Co-Chair); Timothy J. Edwards, PhD (Committee Member); Kevin P. Hallinan, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

jet fuel; heat transfer deterioration; high heat flux; temperature peak; supercritical; fuel properties; nozzle; sudden expansion/contraction in flow path; fuel deposition; turbulence models; rotation passage; recirculation flow; excess deposition

Wingert, MaxwellCarbon dioxide foaming and High-pressure rheology of polystyrene and polystyrene/organoclay nanocomposites
Doctor of Philosophy, The Ohio State University, 2007, Chemical Engineering
The polymer foam industry is slowly implementing carbon dioxide (CO2) as a low-cost, safe, and environmentally friendly blowing agent alternative to fluorocarbons and hydrocarbons. Progress is slow due to several obstacles, ranging from low blowing agent solubility to a lack of quantitative understanding of the influence of carbon dioxide on viscosity. A crucial property in foam extrusion is viscosity. Several research groups have published viscosity data of polymer melts under high pressure, using a variety of techniques. However, few studies assist in designing polymer processing equipment because most do not contain predictive scaling (e.g., WLF-analogous scaling factors) to apply to different operating conditions. A new high-pressure rotational rheometer has been applied to polystyrene and carbon dioxide at five concentrations. It provides direct measurement of the zero shear viscosity of the polymer under a high pressure diluent. The method allows many viscosity measurements to be performed on a single sample. Scaling factors are applied to the data and the WLF-Chow equation is found to describe the results when the appropriate parameter is selected. Due to an interest in using organoclay nanoparticles for foaming, the viscosity of the polystyrene-nanoclay-CO2 system is studied using the couette rheometer and an extruder slit die. At high shear rates (10 to 100 s-1), the viscosity of polystyrene-nanoclay-CO2 unexpectedly possesses a lower viscosity than polystyrene-CO2 at the same concentration. At low shear rates (10-3 to 1 s-1), this effect is not observed. It is suspected that interfacial slip is occurred at the interface at high shear rates. Polymer additives allow tuning of bubble morphology without changing operating conditions. In this study, either a second polymer or nanoparticles are studied. Poly (methyl methacrylate) (PMMA) has the ability to drastically reduce cell size of polystyrene (PS) foams. It is believed that heterogeneous nucleation occurs at the interface of PS/PMMA, but that the bubbles are able to grow out of both phases simultaneously.

Committee:

David Tomasko (Advisor)

Subjects:

Engineering, Chemical

Keywords:

nanoclay; organoclay; viscosity; carbon dioxide; co2; polystyrene; ps; couette rheometer; foaming; supercritical fluids

Vahdatzaman, MaralNovel Catalytic Etherification Reaction of Glycerol to Short-Chain Polyglycerol
Master of Science (MS), Ohio University, 2017, Chemical Engineering (Engineering and Technology)
A study that shows a novel technique to treat and enhance solid catalyst morphological properties that can be used in glycerol polymerization etherification reaction is here reported. More specifically, supercritical (SC) CO2 fluid technology and impregnation treatments have been utilized on zeolite Y sodium (ZYS) to increase available pore volume and average pore size, to maximize surface area for reaction to occur, and to enhance the material catalytic activity. SC-treatment on ZYS was performed in a bolt-closure reactor at 260C and 10.34 MPa. Impregnation treatment was performed by immersing the catalyst in solutions with different concentrations of sodium carbonate (Na2CO3). After exposing the catalyst to the Na2CO3, calcination took place. Results indicated that SC-treatment does increase the diameter pore size by an average of 46.2 Å, which leads to an increase in available pore volume. Glycerol conversion proved to be at its highest when the catalyst was impregnated; glycerol conversions surpassed 90%. The effect on di/triglycerol selectivities were also studied, and these proved to be a function of reaction time, Na2CO3 concentration, and temperature. The solid catalyst physical and performance properties were studied by accelerated surface area porosimetry (ASAP), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and also in a glycerol etherification reaction setup. The best performing catalyst was the SC-treated and impregnated, showing higher meso-to-micro pore distribution, glycerol conversion higher than 90%, and highest di/triglycerol selectivities.

Committee:

Sunggyu Lee (Advisor); Monica Burdick (Committee Member); Douglas Goetz (Committee Member); Jixin Chen (Committee Member)

Subjects:

Chemical Engineering

Keywords:

supercritical fluid technology; zeolite; etherification reaction; short-chain polyglycerol

Gao, WeihongAdsorption of supercritical carbon dioxide on microporous adsorbents: experiment and simulation
Doctor of Philosophy, The Ohio State University, 2005, Chemical Engineering
Supercritical carbon dioxide is an efficient solvent for adsorption separations because it can potentially be used as both the carrier solvent for adsorption and the desorbent for regeneration. Recent results have demonstrated an anomalous peak or “hump” in the adsorption isotherm near the bulk critical point when adsorption isotherm is plotted as a function of bulk density. This work presents new data for adsorption and desorption of carbon dioxide on NaY zeolite over a wide range of pressures (vaccum-2800psia) at temperatures near the critical point of carbon dioxide (32.0 to 50.0°C). The results indicate a strong affinity for CO2 as well as a significant “hump” near the critical point. The lattice model previously developed by Aranovich and Donohue is applied to correlate adsorption isotherms. The model successfully predicted the adsorption isotherms at the whole pressure range but failed to predict the adsorption “hump” near the critical point with physically meaningful parameters. To investigate this behavior in more detail, molecular simulation is executed to explore adsorption of CO2 on activated carbon and Na Y zeolite at 32.0°C. We checked the effect of pore width on the adsorption, and compared simulation with experiment data. The excess adsorption by simulation is larger than experiment data, and simulation did not catch adsorption “hump” near the critical point.

Committee:

David Tomasko (Advisor)

Keywords:

zeolite; SUPERCRITICAL; excess adsorption; pore; adsorption of CO2

Baskaya, Fadime SuhanPhase equilibrium at supercritical (SC) conditions: solubility analysis of curcumin in supercritical carbon dioxide and co-solvent mixtures, and phase equilibrium analysis of cis-1,4-(poly)isoprene in propane and co-solvent mixtures
Master of Science, University of Akron, 2005, Chemical Engineering
Although the existence of supercritical fluids has been known for over a century, relatively little attention was given to them until recently. After the significant rise of energy costs, and increased governmental regulations due to environmental concerns, their application has attracted more attention. In this thesis, the study of high-pressure phase behavior was extended to a highly polar component, and a polymeric substance in the binary and ternary systems of curcumin-supercritical CO2, curcumin-supercritical CO2/acetone, cis-1,4-(poly)isoprene-propane, and cis-1,4-(poly)isoprene-propane/supercritical CO2. The equipment used in the study had a view cell, for accurate visual observation of the high-pressure phase behavior, and syringe pumps to supply necessary fluids to the system. Supercritical CO2 and propane were used as solvents to investigate the curcumin. Curcumin has been known for a very long time, and used in Ayurvedic and Chinese medicine for centuries. Recently curcumin attracted researchers’ attention due to its effect on Alzheimer, AIDS, cancer, and various diseases. Natural rubber, present in Russian dandelion and guayule plants, has the potential to be a valuable chemical commodity produced by sustainable biotechnology. Cis-1,4-(poly)isoprene is the main compound in natural rubber. The Elliott-Suresh-Donohue (ESD) and Peng Robinson (PR) equation of states were used to correlate the experimental data in the literature. The ESD equation of state is a semi empirical equation of state that was developed especially for associated and non-spherical mixtures. The model is cubic for non-associating molecules, and has only three real roots for associating fluids. For the systems involved with self-associating fluids, hydrogen bonding between similar molecules, model needs a single interaction parameter (kij) for each component pairs. The ESD equation of state was also used to correlate experimental data obtained from phase equilibrium analyzer. In an effort to place the thermodynamic modeling on a firmer theoretica basis, the Step Potential Equilibrium and Dynamics (SPEAD) model was studied. The model was extended to new chemical families in the study. Furthermore, its application to variable polymer structure was demonstrated by evaluating the asymptotic trend of the perturbation terms to the infinite chain limit and showing the similarities and differences to n-alkane (polyethylene) chains. This research will enlighten the understanding of phase behavior of highly polar material in supercritical conditions, and cis-1,4-(poly)isoprene in supercritical conditions. It will also guide further possible applications, such as producing fine particles using supercritical antisolvent method, or cis-1,4-(poly)isoprene extraction from a plant origin.

Committee:

J. Elliott (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Supercritical fluids; High pressure behavior; ESD equation of state; SPEAD Model

Johnson, Thomas G.Heat Transfer in Brine Solutions at Supercritical Pressure
Master of Science (MS), Ohio University, 2015, Mechanical Engineering (Engineering and Technology)
Heat transfer and differential pressure in a heat exchanger system at supercritical pressure were investigated. A single dimensional heat transfer model was developed to predict heat transfer rates and temperature profiles in a heat exchanger flowing water near the critical point. A series to trials were performed using test fluids representing produced water over a pH range of 4.0 to 9.0. The temperature profile and differential pressure were measured as the test fluids were heated from 150 °C to 350 °C at 3450 psi (23.8 Mpa) while flowing through the tube side of an experimental concentric tube counterflow heat exchanger. The flow conditions were in the transition region with Reynolds numbers ranging from 4,000-6,000. The test fluid was heated by supercritical de-ionized water flowing through the shell section of the heat exchanger. Seven trials were performed with a duration of 7.5 hours each reporting an average heat flux of 34.22 ± .64 kW/m2. Results showed little to no decrease in heat flux due to fouling. No measureable increase in differential pressure across the heat exchanger was observed during any of the trials.

Committee:

Jason Trembly, Dr. (Advisor)

Subjects:

Energy; Engineering

Keywords:

Supercritical Water; Heat Transfer; Flowback and Produced Water

Ellis, Jeffrey LeClairDense Carbon Dioxide Assisted Polymer Processing at the Nanoscale
Doctor of Philosophy, The Ohio State University, 2009, Chemical Engineering
Nanotechnology is continually becoming more integrated into consumer products used by the general public on a daily basis. Consumers reap the benefits of enhanced properties for these commercial products, and yet they are still affordable. For biomedical products, that include nanofeatures, this is not yet a reality. The materials and methods used to fabricate these products are still far too expensive. There are many inexpensive and commercially available polymers that have potential to be used in these advanced biomedical products, but the fabrication techniques still lack the simplicity required to create an inexpensive end product.Supercritical CO2 has been used to overcome the polymeric nanofabrication barriers for high throughput production of biomedical devices. Novel CO2-assisted low temperature polymer nanoprocessing fabrication techniques have been implemented for use in biomedical product creation. Polymer nanofabrication techniques such as bonding, imprinting, and active biomolecule immobilization were demenonstrated. Due to being CO2-assisted techniques, these processes are intrinsically inexpensive and environmentally benign. In order to thoroughly investigate these nanofabrication techniques the interactions between CO2 and the polymer were examined on a thermodynamic level. Thermodynamic modeling results of high pressure CO2/polystyrene systems were used along with experimental bonding, imprinting, and immobilization results. It was found that the solubility of CO2 in a polymer matrix and the resulting reduction of the polymer glass transition temperature (Tg) largely dictate the polymer chain mobility and therefore the polymer's processability. For instance, it was shown that the polymer bond strength of polystyrene, bonded via a CO2-assisted technique, depended largely on the proximity of the processing conditions to the reduced Tg curve. It was also found that low aspect ratio nanofeatures could be patterned by CO2-assisted nanoimprint lithography in polystyrene at conditions near the reduced Tg curve. These CO2-assisted low temperature polymer processing techniques are now better understood in terms of the CO2/polymer thermodynamic properties, thus making these, and other similar, techniques easier to control. This fundamental information can be applied to scaling-up these technologies so that inexpensive polymer biomedical products with nanofeatures can soon be commercially produced, thus benefiting the health of society.

Committee:

David Tomasko (Advisor); L. James Lee (Committee Member); James Rathman (Committee Member); Sherwin Singer (Committee Member)

Subjects:

Chemical Engineering

Keywords:

polymer processing; polystyrene; supercritical CO2; nanotechnology; polymer bonding

Viggiano, Rocco PInvestigations into High Surface Area and Hierarchical Phase Segregated Network Structures
Doctor of Philosophy, Case Western Reserve University, 2015, Macromolecular Science and Engineering
Aerogels are an interesting class of materials that possess many exotic and extreme properties. These properties are developed as the gel network is produced from solution. As the gel develops, it builds a hierarchical structure, possessing architectures at different size scales through molecular and macro-scale interactions. Once the solvent is removed, and the resultant aerogel is produced, the hierarchical nature of the material produces many desirable properties including: extremely high porosities (greater than 90% pore volume)[1], extremely low thermal conductivities (10-30 mW/m-k)[1], very low densities (as low as 0.002 g/cm3)[2], low refractive indices (as low as 1.01),[3] low dielectric constants (between 1.0 and 1.5),[4] high surface areas,[5,6] and the slowest speed of sound through a solid material. The first chapter of this thesis deals with the structure/property relationships of polymer/clay aerogels interfused with uniformly distributed air bubbles were examined. Through the incorporation of a polyelectrolyte in a montmorillonite (MMT) clay solution, the viscosity was systematically changed by the addition of ions with different charges. The bubbles were achieved via high speed mixing and were stabilized through the use of the surfactant sodium dodecyl sulfate (SDS). As the charge of the ion increased from +1 (Na+ ions) to +2 (Ca2+ ions) to finally +3 (Al3+ ions), the modulus of the resultant aerogels increased. The foamed polymer/clay aerogels showed a reduction in thermal conductivity while retaining similar mechanical properties to unfoamed polymer/clay aerogels. The most promising composition was one which contained 5% MMT clay/5% poly(vinyl alcohol)/0.5% xanthum gum/0.5% SDS/0.2% Al2(SO4)3·6(H2O) possessing a density of 0.083 g/cm3, an average modulus of 3.0 MPa, and a thermal conductivity of 41 mW/m·K. The second project investigated the feasibility of incorporating ground recycled polyurethane (PU) foam into clay/polymer aerogels. This was demonstrated and a range of compositions were prepared and characterized to determine the effect of variation in the formulations on density and mechanical properties of the resulting materials. The study followed a modified combinatorial approach. Initially, experiments were performed in water using either sodium exchanged montmorillonite or laponite clay, poly(vinyl alcohol) (PVOH) solution as the polymer binder, and the recycled PU foam. Freezing and freeze-drying the aqueous gels produced aerogels, which were characterized through density and mechanical testing, scanning electron microscopy, and thermal gravimetric analysis. The study was expanded by exploring alternative binder chemistries, including the use of an alginate polymer in place of the PVOH, or adding a polyisocyanate as across-linking agent for PVOH. The effect of recycled PU foam content, clay type and level, and binder type and level on mechanical properties of the aerogels were determined. The goal of the third project was to determine if lignin could be converted into foam-like aerogels using a well-established and environmentally benign freeze drying process. Interest in lignin as a bio-resource has been gaining popularity in recent years, as it is currently viewed by most industries as a waste product that in most cases is simply burned as a fuel source. The use of lignin in a polymer/clay aerogel offers the potential for a high value-added foam-like material potentially usurping the use of traditional petroleum derived foams in some applications. The present work demonstrates that lignin/clay and lignin/alginate aerogel samples can possess compressive moduli as high as 36.0 MPa. The final project addresses a fundamental material property concern associated with polyimide aerogels. Polyimide aerogels possess low dielectric constants, low thermal conductivities, high porosity, flexibility and low densities with outstanding mechanical properties. However, polyimide aerogels will undergo thermally induced shrinkage at temperatures far below their glass transition temperatures (Tg) or their onset of decomposition temperatures. Attempts to minimize thermal shrinkage were successful when a rigid filler, such as cellulose nanocrystals (CNCs), were introduced into the polyimide backbone. As an alternative to using rigid fillers, it was proposed that the incorporation of bulky, space filling moieties into the polymer backbone would also provide an effective route to reduce thermal shrinkage. An array of 20 polyimide aerogels were synthesized from 3,3’4,4’-biphenyltetracarboxylic dianhydride (BPDA) and 4,4’-oxydianiline (ODA) and in some cases BPDA and a combination of ODA and 9,9’-bis(4-aminophenyl) fluorene (BAPF). The aerogels were cross-linked with 1,3,5-benzenetricarbonyl trichloride (BTC). The polymer concentration, n-value and molar concentration of ODA and BAPF were varied. The resultant aerogels were fully characterized and were subjected to isothermal heating at 150 °C and 200 °C for up to 500 hours. It was observed that the samples containing BAPF possessed the lowest thermal shrinkages. Reductions in thermal shrinkage of around 20% were observed in samples containing the highest molar concentrations of BAPF.

Committee:

David Schiraldi, Ph.D. (Advisor); Mary Ann Meador, Ph.D. (Advisor); Gary Wnek, Ph.D. (Committee Member); Eric Baer, Ph.D. (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Chemistry; Engineering; Experiments; Inorganic Chemistry; Materials Science; Organic Chemistry; Polymer Chemistry; Polymers

Keywords:

Aerogel, High Surface Area, Low Thermal Conductivity, Montmorillonite Clay, Polyvinyl alcohol, Polyurethane Foam, Lignin, Polyimide, Gel, Network, Cross-Linking, Ice Templating, Freeze-Drying, Lyophilization, Supercritical Fluid Extraction

JADHAV, ABHIJIT VILASSYNTHESIS OF POLYSTYRENE PARTICLES IN SUPERCRITICAL CARBON DIOXIDE USING NOVEL SURFACTANTS
MS, University of Cincinnati, 2004, Engineering : Materials Science
Supercritical carbondioxide (SCCO2) can be advantageously used as a “green solvent” for various processes over the traditional organic and aqueous solvents. We report here the free radical dispersion polymerization of styrene in SCCO2. The process used novel surfactants, polysiloxane-polystyrene diblock copolymers for stabilizing the monomer dispersion in the SCCO2. AIBN was the initiator for the process. This investigation studies the use of polystyrene-b-poly(dimethylsiloxane) (PS-b-PDMS) and polystyrene-b-poly(methylphenylsiloxane) (PS-b-PMPS) as surfactants and their effect on properties of the product such as particle morphology, size, size distribution and molecular weight distribution. The chemical conversion of styrene to polystyrene was observed from Nuclear Magnetic Resonance (NMR) Spectroscopy and Infrared (IR) Spectroscopy. Typical Number Average Molecular Weight, Mn obtained for the polystyrene from Gel Permeation Chromatography (GPC) was ~ 7000 g/mol and the polydispersity index was ~ 2.0. The Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) behavior confirmed that polystyrene synthesized here was similar in properties to a polystyrene standard of similar molecular weight. The Environmental Scanning Electron Microscopy (ESEM) revealed that the polystyrene particles were spherical in shape and their size ranged between 5-10 microns.

Committee:

Dr. Stephen Clarson (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Supercritical Carbon Dioxide; Polystyrene; Poly(dimethylsiloxane); Poly(methylphenylsiloxane)

Brisbin, Judith AnnEXTRACTION TECHNIQUES FOR TRACE ELEMENT DETERMINATIONS OF BIOLOGICAL AND ENVIRONMENTAL SAMPLES INCLUDING ELEMENTAL SPECIATION OF LOBSTER USING INDUCTIVELY COUPLED PLASMA - MASS SPECTROMETRY
PhD, University of Cincinnati, 2001, Arts and Sciences : Chemistry
Adequate identification and quantification of elemental species in the environment are necessary to completely assess their potential toxicity. Inductively coupled plasma - mass spectrometry (ICP - MS) coupled to chromatographic separation is a widely used, highly sensitive detector. For samples to be analyzed by ICP - MS, they must first be extracted into a solution capable of being nebulized into the ICP. A variety of extraction procedures were evaluated for the extraction of arsenic and other analytes from lobster tissue samples using ICP - MS detection. Room temperature mixing, sonication, soxhlet, microwave assisted, supercritical carbon dioxide and subcritical water extractions were evaluated for a variety of solvent systems and optimum conditions determined using a partially defatted Lobster Hepatopancreas marine reference material (TORT-2, National Research Council of Canada). Microwave assisted extraction (MAE) yielded comparable or improved recoveries for all of the analytes monitored and proved to be the mildest, fastest, least complicated and most reproducible extraction technique. MAE at 75 °C for 2 minutes exposure time yielded quantitative recovery of arsenic from TORT-2 and lobster tissue samples purchased from a local restaurant A novel gradient anion exchange chromatographic technique was developed that allows the speciation of arsenobetaine (AB), arsenocholine (AC), arsenite (As III), arsenate (As V), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) in ~ 27 minutes using ammonium carbonate buffer. Low detection limits, excellent long-term stability and baseline resolution of all of the arsenic species evaluated were achieved when the ratio of AC:AB was less than ~ 12.5:50. This technique was successfully applied to TORT-2 and lobster tissue samples. AB was the major arsenic species identified. AC, DMAA, AS V and unknown peaks, possibly arsenosugars, were also found. Methanol and isopropanol were evaluated as extraction solvents for a variety of analytes and samples using microwave assisted extraction and found to be relatively equivalent. Increased exposure time and temperature typically resulted in higher recoveries. The use of ammonium pyrrolidine dithiocarbamate and ethylenediamine tetraacetic acid as chelating agents also improved the extraction efficiency of some analytes. Recoveries were found to generally show some dependence upon the analyte of interest and the sample matrix.

Committee:

Joseph Caruso (Advisor)

Subjects:

Chemistry, Analytical

Keywords:

INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY; ARSENIC SPECIATION; MICROWAVE ASSISTED EXTRACTION; LOBSTER TISSUE; SUBCRITAL AND SUPERCRITICAL FLUID EXTRACTION

Ramirez, Carmen HernandezEnhancement of the rate of solution of relatively insoluble drugs from solid-solid systems prepared by supercritical fluid technology
Doctor of Philosophy, The Ohio State University, 2007, Pharmacy
Supercritical fluid technology, specifically the method of rapid expansion of supercritical solutions (RESS), has been used to prepare small particles consisting of solid solutions of a relatively insoluble drug and a water-soluble excipient. With an increasing number of relatively insoluble compounds being discovered, a general process for enhancing drug dissolution rates would assist formulation of these compounds for therapeutic use. Solid solutions could serve as a means for enhancing drug dissolution rates, since the drug is dispersed in a solid solvent in its smallest form, i.e., a molecule, prior to entering into solution. Therefore, solid solutions consisting of the relatively insoluble model drugs lidocaine or probucol and a water-soluble surfactant, poloxamers 407, 188, or 403 were prepared by RESS processing. Dissolution studies of these systems were performed and evaluated for their ability to enhance drug release rates. Furthermore, the mechanism by which solid solutions form in these systems was determined using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) was also used to study the surface characteristics of these particulate systems. Dissolution studies of these particles showed an enhanced rate of release of drug in the presence of poloxamer. This enhancement was due to the apparent formation of solid solutions. DSC of these particulate systems also indicated the formation of solid solutions of drug and poloxamer with increasing proportion of poloxamer. With the formation of solid solutions, hydrogen bonding occurred between the drug and poloxamer. This bonding was dependent on the polyoxyethylene chain length of the three poloxamers, i.e., where hydrogen bonding primarily occurs. Solid solutions formed for systems consisting of drug and poloxamers 407 or 188, which have similar polyoxyethylene lengths and hence similar amounts of available sites for bonding. Solid solutions however did not form for systems consisting of drug and poloxamer 403 since poloxamer 403 has approximately half the polyoxyethylene length of poloxamers 407 and 188. Lastly, SEM shows the formation of small particles that vary in appearance as functions of poloxamer concentration.

Committee:

Sylvan Frank (Advisor)

Keywords:

Drug delivery; supercritical fluids; solid dispersions; solid solutions

Tung, David C.Welding Metallurgy of Nickel-Based Superalloys for Power Plant Construction
Doctor of Philosophy, The Ohio State University, 2015, Welding Engineering
Abstract Increasing the steam temperature and pressure in coal-fired power plants is a perpetual goal driven by the pursuit of increasing thermal cycle efficiency and reducing fuel consumption and emissions. The next target steam operating conditions, which are 760°C (1400°F) and 35 MPa (5000 psi) are known as Advanced Ultra Supercritical (AUSC), and can reduce CO2 emissions up to 13% but this cannot be achieved with traditional power plant construction materials. The use of precipitation-strengthened Nickel-based alloys (superalloys) is required for components which will experience the highest operating temperatures. The leading candidate superalloys for power plant construction are alloys 740H, 282, and 617. Superalloys have excellent elevated temperature properties due to careful microstructural design which is achieved through very specific heat treatments, often requiring solution annealing or homogenization at temperatures of 1100 °C or higher. A series of postweld heat treatments was investigated and it was found that homogenization steps before aging had no noticeable effect on weld metal microhardness, however; there were clear improvements in weld metal homogeneity. The full abstract can be viewed in the document itself.

Committee:

John Lippold (Advisor); Boian Alexandrov (Committee Member); Antonio Ramirez (Committee Member)

Subjects:

Materials Science; Metallurgy

Keywords:

Welding Metallurgy; Stress Relaxation Cracking; Stress Relief Cracking; 740; 282; 617; AUSC; Advanced Ultra Supercritical; PWHT; Stress Relaxation Testing; Stress Relief Testing; Compact Tension Samples; Residual Stress; Pre-Compression; Superalloy;

De Silva, Chamara L.Removal of Phenol from Oil/Gas Wastewater by Catalytic Supercritical Water Treatment
Master of Science (MS), Ohio University, 2016, Chemical Engineering (Engineering and Technology)
The U.S. oil/gas industry generates over 21 billion barrels of produced water annually. This wastewater stream contains a host of components including suspended solids, dissolved solids, and hydrocarbons. This waste stream represents a significant beneficial resource if reused to offset other water consumption demands. However, many beneficial reuse applications have strict hydrocarbon limits. Oxidation of hydrocarbons in supercritical water media provides an effective removal technique allowing wastewater reuse. In order to quickly and effectively remove hydrocarbons in supercritical water a heterogeneous catalyst is needed. In this study, an MnO2 catalyst on a TiO2 support was synthesized and evaluated for removal of phenol in supercritical water. Synthesized catalysts were characterized using temperature programmed reduction, pulse chemisorptions and X-ray powder diffraction. Catalyst activity for phenol conversion was evaluated in a continuous packed bed reactor at supercritical water conditions, while analyzing vapor and liquid products. Evaluated process variables included free O2 concentration and the catalyst Mn loading. Both variables had positive effects on phenol conversion. The process reached complete destruction of phenol at an O2 level of 500% of the stoichiometric O2 for complete oxidation. Increase in catalyst Mn loading increased its active sites concentration enhancing the contribution of heterogeneous reaction kinetics for phenol supercritical water oxidation (SCWO); however a saturation limit appeared to be reached as Mn loading is further increased. A part of the Mn composition appeared to be unable to create active sites on the catalyst due to interactions with TiO2. A phenol conversion of 70% was reached at 12% (w/w) Mn in the catalyst with 100% excess O2.

Committee:

Jason Trembly, PhD (Advisor); David Young, PhD (Committee Member); Marc Singer, PhD (Committee Member); Natalie Kruse, PhD (Committee Member)

Subjects:

Chemical Engineering; Energy; Engineering; Environmental Engineering

Keywords:

Supercritical; produced water; catalyst; MnO2; TiO2; phenol

Schroder, Andrew UA Study of Power Cycles Using Supercritical Carbon Dioxide as the Working Fluid
PhD, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
A real fluid heat engine power cycle analysis code has been developed for analyzing the zero dimensional performance of a general recuperated, recompression, precompression supercritical carbon dioxide power cycle with reheat and a unique shaft configuration. With the proposed shaft configuration, several smaller compressor-turbine pairs could be placed inside of a pressure vessel in order to avoid high speed, high pressure rotating seals. The small compressor-turbine pairs would share some resemblance with a turbocharger assembly. Variation in fluid properties within the heat exchangers is taken into account by discretizing zero dimensional heat exchangers. The cycle analysis code allows for multiple reheat stages, as well as an option for the main compressor to be powered by a dedicated turbine or an electrical motor. Variation in performance with respect to design heat exchanger pressure drops and minimum temperature differences, precompressor pressure ratio, main compressor pressure ratio, recompression mass fraction, main compressor inlet pressure, and low temperature recuperator mass fraction have been explored throughout a range of each design parameter. Turbomachinery isentropic efficiencies are implemented and the sensitivity of the cycle performance and the optimal design parameters is explored. Sensitivity of the cycle performance and optimal design parameters is studied with respect to the minimum heat rejection temperature and the maximum heat addition temperature. A hybrid stochastic and gradient based optimization technique has been used to optimize critical design parameters for maximum engine thermal efficiency. A parallel design exploration mode was also developed in order to rapidly conduct the parameter sweeps in this design space exploration. A cycle thermal efficiency of 49.6% is predicted with a 320K [47°C] minimum temperature and 923K [650°C] maximum temperature. The real fluid heat engine power cycle analysis code was expanded to study a theoretical recuperated Lenoir cycle using supercritical carbon dioxide as the working fluid. The real fluid cycle analysis code was also enhanced to study a combined cycle engine cascade. Two engine cascade configurations were studied. The first consisted of a traditional open loop gas turbine, coupled with a series of recuperated, recompression, precompression supercritical carbon dioxide power cycles, with a predicted combined cycle thermal efficiency of 65.0% using a peak temperature of 1,890K [1,617°C]. The second configuration consisted of a hybrid natural gas powered solid oxide fuel cell and gas turbine, coupled with a series of recuperated, recompression, precompression supercritical carbon dioxide power cycles, with a predicted combined cycle thermal efficiency of 73.1%. Both configurations had a minimum temperature of 306K [33°C]. The hybrid stochastic and gradient based optimization technique was used to optimize all engine design parameters for each engine in the cascade such that the entire engine cascade achieved the maximum thermal efficiency. The parallel design exploration mode was also utilized in order to understand the impact of different design parameters on the overall engine cascade thermal efficiency. Two dimensional conjugate heat transfer (CHT) numerical simulations of a straight, equal height channel heat exchanger using supercritical carbon dioxide were conducted at various Reynolds numbers and channel lengths.

Committee:

Mark Turner, Sc.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Milind Jog, Ph.D. (Committee Member)

Subjects:

Energy

Keywords:

supercritical carbon dioxide;power cycle;engine;thermodynamics;fluid properties;heat exchangers

Talreja, ManishTowards Understanding Interfacial Phenomena in Polymer-CO2 Systems
Doctor of Philosophy, The Ohio State University, 2010, Chemical Engineering

Supercritical (high pressure) CO2, owing to its ability to make polymers pliable at temperatures much lower than the glass transition temperature (Tg), has been established as a very promising solvent for numerous macro scale polymer processing applications. In this work, we have tried to expand the scope of supercritical CO2 assisted polymer processing to nano length scales with particular focus on manufacturing biomedical devices from polymer thin films. At such small length scales, however, the properties of the polymer become size dependent since the interfacial effects start dominating the bulk effects. As a result, adapting the macro and micro level fabrication technologies to nano level is not straightforward and requires integration of both theoretical and experimental tools.

We have used CO2 assisted Nano-Imprint Lithography (CO2-NIL) for fabricating nanochannels on polystyrene thin films. CO2-NIL is a novel technique in which the features from a rigid mold are transferred on to a CO2 pressurized polymer thin film by application of compressive force. We have explored efficiency of pattern transfer, resolution, and effects of molecular weight on transferability of patterns, and have thus established CO2-NIL as a highly efficient and cost effective fabrication technique capable of transferring patterns as small as 20 nm in step height.

To understand the surface characteristics and the molecular level effects of CO2 on polymer thin films, which are essential for optimizing the nanoscale experiments, we have used Polymer Density Functional Theory (PDFT) as our primary tool since it provides an adequate balance between the amount of details extracted and the computational costs involved. PDFT is a statistical mechanics based approach in which we express the free energy of the system as a functional of spatially varying density distributions of CO2 and polymer segments. Equilibrium density distributions, free energy at equilibrium, and hence the equilibrium properties are then obtained by minimizing this functional. We have studied CO2 solubility in polymer, surface adsorption of CO2 on polymer surface, interfacial tension, and interfacial width for both polyethylene and polystyrene thin films. In addition, we have shown how the molecular level structural changes induced by CO2 facilitate the nanoscale polymer processing, and that the causal mechanism of these changes is the enthalpic interactions between the polymeric segments and the CO2 molecules. This work is the first instance of application of PDFT to polymer films pressurized by CO2. We have also significantly enhanced the capability of PDFT by handling polymer chains much longer than previously reported using this theory, similar to the ones used commercially.

PDFT is a very powerful tool that can be used to study the thermodynamic behavior in several important technologies, especially the ones dominated by the surface phenomena. In addition to the nanoscale processing of polymer thin films, we have applied this theory to study the scaling approach to bubble nucleation in CO2 based polymer foams and the surface tension in ‘petroleum hydrocarbon-CO2 mixtures’ at the reservoir conditions. The data from the latter are significant for CO2 assisted enhanced oil recovery applications.

Committee:

Isamu Kusaka, PhD (Advisor); David L. Tomasko, PhD (Committee Member); L. James Lee, PhD (Committee Member); Susan Olesik, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

PDFT; CO2-NIL; Supercritical CO2; polymer thin films; alkane-CO2 surface tensions for EOR scaling in Bubble Nucleation

GABELMAN, ALANMASS TRANSFER IN DENSE GAS EXTRACTION USING A HOLLOW FIBER MEMBRANE CONTACTOR
PhD, University of Cincinnati, 2003, Engineering : Chemical Engineering
Hollow fiber membrane contactors offer a number of advantages over dispersed phase contactors for extraction of aqueous feeds. In addition, dense gases provide benefits that traditional extraction solvents do not. A mathematical model of a membrane contactor was developed that predicts the steady state fluid velocities and solute concentrations by solving the applicable conservation equations, with the gravitational force term included. Model predictions were compared to experimental data obtained in our laboratory for the extraction of isopropanol or acetone into dense CO 2 , and to data reported by others for extraction of various solutes into dense CO 2 or propane. Generally, predicted mass transfer coefficients and yields were in reasonable agreement with experimental values, except for data obtained using a module that was particularly susceptible to flow maldistribution and the resulting loss of efficiency. The model predicted that the portion of the mass transfer resistance attributable to the aqueous phase decreased with decreasing solute partition coefficient as expected. Mass transfer coefficients and yields were higher for solutes with higher partition coefficients. A theoretical study of acetone extraction from aqueous solution into supercritical CO 2 was performed, with tube side CO 2 flow with or against gravity. Buoyancy-induced flow was important for large (1.8 mm inside diameter) but not small (0.6 mm ID) fibers, consistent with our expectation that such flow is more difficult to achieve when the characteristic length is small. The importance of buoyancy-induced flow decreased with increasing imposed fluid velocity, as forced convection masked the effects of free convection. For the range of conditions studied, the mass transfer coefficient obtained with flow in the direction of gravity was as much as 33% higher than for flow opposing gravity. Ethanol and isopropanol extractions performed by others using spray, sieve tray or packed columns were run on a simulated membrane contactor, and the resulting values for the height of an equivalent theoretical stage (HETS) were compared to the reported values for the conventional contactors. In most instances the simulated membrane contactor offered a significantly (in some cases, substantially) lower HETS than the corresponding traditional column, indicating that the membrane contactor was more efficient.

Committee:

Dr. Sun-Tak Hwang (Advisor)

Subjects:

Engineering, Chemical

Keywords:

membrane contactor; finite element method; supercritical fluid; dense gas; mass transfer

Srinivasan, NarayananPretreatment of Guayule Biomass Using Supercritical CO2-based Method for Use as Fermentation Feedstock
Doctor of Philosophy, University of Akron, 2010, Chemical Engineering
Guayule is a commercial desert shrub grown in the dry regions of Arizona and California. Its resin and latex products are non-allergenic to most people unlike the products made from the rubber from Hevea brasiliensis. Latex and resins, however, make up only about 20% of biomass. Converting the waste bagasse to biorefinery feedstock makes good economic sense. A supercritical CO2-based process had been developed for pre-treating the guayule. Our approach used supercritical CO2 and moisture for mild hydrolysis and subsequent explosion, created by sudden pressure release. The pretreatment involved: adding water to the bagasse, raising system temperature, pressurizing using supercritical CO2, holding the system for a period of time, and exploding the bagasse. The different pretreatments were compared based on the sugar yield from the enzyme hydrolysis and our method was more effective than other techniques such as acid hydrolysis and delignification. No inhibitory/toxic effects were apparent in terms of growth of Trichoderma reesei Rut C-30. A factorial design was performed to find the optimum working conditions for maximum sugar yields from the supercritical CO2 pretreatment of the guayule. The optimum yields of glucose and pentose were 55% and 60% from enzyme hydrolysis at a temperature of 170 °C, 3800 psi, 57% moisture and 32 minutes of holding time. Additional solvents like acetone and ethanol were tried in place of water as solvents. Although acetone and ethanol gave yields 50% and 54% which are comparable with that of water, only in case of acetone the working conditions were milder (60 °C). A study involving the removal of lignin from the biomass was performed using the supercritical CO2 method. A Supercritical carbon dioxide-ethanol- water system was studied to extract the lignin present in the bagasse. The extraction process was not efficient and removed very little lignin (30%). Guayule has a lot of hemicelluloses and so micro-organisms that can metabolize xylose efficiently in addition to glucose were chosen and were tested for their ethanol tolerance and ability to withstand the hydrolyzate toxicity. Three yeast species were found to consume xylose and have high ethanol tolerance. But the highest yield of ethanol was from the simultaneous saccharification fermentation of the pretreated bagasse with the K.marxianus yeast, 0.36 g ethanol/ g of hydrolysable sugars. The process as a whole aims at using a non food crop as a source of fermentation feedstock. There is no competing use as a food crop and hence no increase in food prices. The supercritical pretreatment process preserves all kinds of sugars including the hemicelluloses. The process does not destroy any sugars compared to the widely used dilute acid pretreatment. The fermentation process involves the use of yeasts that can metabolize hemi-cellulosic sugars in addition to the six carbon sugars and produce ethanol. The thermotolerant K.marxianus yeast gave a high ethanol yield compared to the others. Its ability to grow at higher temperatures enabled the use of SSF process at 42 °C where the enzyme activity is high enough for faster sugar release. The yield of the whole process is 8% (0.08 g ethanol/ g bagasse).

Committee:

Lu-Kwand Ju, Dr. (Advisor); Richard Elliott, PhD (Committee Member); Lingyun Liu, PhD (Committee Member); Teresa Cutright, PhD (Committee Member); Donald Ott, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

bagasse; PRETREATMENT; lignin; GUAYULE; SUPERCRITICAL; hydrolysis; sugar

Fields, Patrice R.Methods for the Characterization of Electrostatic Interactions on Surface-Confined Ionic Liquid Stationary Phases for High Pressure Liquid Chromatography
PhD, University of Cincinnati, 2011, Arts and Sciences: Chemistry
This body of work is a continuation of work previously completed in our group that examines the retention properties of surface confined ionic liquid (SCIL) stationary phases under reversed-phase and supercritical fluid chromatographic conditions. SCIL’s have been shown to be useful for separating a variety of both organic and inorganic compounds. However, there has been little work done to elucidate the different retention mechanisms and properties that allow for the wide range of retention modes observed. The first chapter provides a brief history and survey of the properties of ionic liquids. The first chapter also includes an overview of the linear solvation free energy relationship (LSER), which is used to characterize the retention of solute sets containing both neutral and ionizable compounds in under reversed-phase and supercritical conditions. This chapter also provides insight into the evolution and development of molecular solute descriptors. The second chapter discusses several methods that can be employed to modify the LSER model to account for electrostatic interactions between the SCIL stationary ohases and ionizable solutes in reversed-phase chromatography. The P, D and J solute descriptors are evaluated based on their ability to fit the retention of ionizable solutes to the LSER model and to produce coefficient values that are consistent with the underlying molecular interactions and what has been previously reported in reversed-phase studies. The third chapter investigates the use of the LSER model to characterize the retention mechanism of two SCIL stationary phases under supercritical conditions. The LSER coefficients generated via the multiple linear regression of chromatographic retention data are compared and analyzed for statistical difference from one another. The two SCIL phases are further compared to a 2-ethylpyridine (EP) stationary phase, which is more commonly used in chromatography with compressible fluids. This chapter further examines the viability of the P and J solute descriptors to describe the electrostatic interactions between the SCIL stationary phases and ionizable solutes under supercritical conditions. The fourth chapter examines the ion exchange properties of several SCIL stationary phases. A series of small inorganic ions in acetonitrile-water mixtures are used to probe mechanistic differences in the stationary phases due to the substituents attached to the exchange moiety after correcting for loading differences between the phases. Connections have been made between the observed retention properties and the solvation of both the anion analytes and the stationary phase. The fifth chapter summarizes the findings of the previous chapters and offers suggestions for the future directions for this project while the appendix describes a method for estimating the viscosity of binary and ternary supercritical fluids. The estimates are based on a form of Darcy’s law and relates the effect of temperature, pressure and flow rate on the estimates.

Committee:

Apryll Stalcup, PhD (Committee Chair); James Mack, PhD (Committee Member); Thomas Ridgway, PhD (Committee Member)

Subjects:

Chemistry

Keywords:

Surface-confined ionic liquid;LSER;Ionization;Electrostatic interactions;Reversed-phase chromatography;Supercritical fluid chromatography

Narayana Swamy, NaveenSupercritical Carbon Dioxide Pretreatment of Various Lignocellulosic Biomasses
Master of Science (MS), Ohio University, 2010, Chemical Engineering (Engineering and Technology)
In the production of cellulosic ethanol, the pretreatment of biomass step is considered the most expensive and difficult part of the process. In Supercritical CO2 (SC-CO2) pretreatment method, CO2, which is considered a green solvent is used to treat the biomass. In this work corn stover, switchgrass and rye straw were pretreated using the SC-CO2 at various temperatures and pressures and subsequently enzyme hydrolyzed using the cellulase enzyme. The samples were analyzed for the presence of glucose. A typical CO2 to biomass ratio of 5/50 (g/g) was used in tests. Biomass samples were wetted with water prior to the SC-CO2 treatment. CO2 pressure was released as quickly as possible by opening a quick release value. For all pretreatments glucose yields from corn stover was higher than untreated samples (12mg/100mg biomass) and the maximum glucose yield (30mg/100mg biomass) was found at 3500psi and 150°C. These conditions were chosen for the pretreatment of various other biomasses. The maximum glucose yield for untreated switchgrass and rye straw were found to be 12mg/100mg biomass and 7.6mg/100mg biomass, respectively. The pretreated switchgrass (14mg/100mg of biomass) showed no improvement in the glucose yield as compared to an untreated sample. However, the pretreated corn stover (30mg/100mg biomass) and rye straw (13.5mg/100mg biomass) showed threefold and twofold increase, respectively. The SC-CO2 pretreatment with addition of catalysts such as H2SO4 and HCl was studied on rye straw. The addition of H2SO4 and HCl to the SC-CO2 pretreatment both improved the glucose yield as compared with the SC-CO2 pretreatment. The X-Ray diffraction result showed that there was no change in crystallinity of the SC-CO2 treated corn stover when compared to the untreated. SEM results showed the changes in surface morphology of the SC-CO2 treated corn stover when compared with untreated corn stover. This shows that the increase in glucose yield from enzyme hydrolysis for the SC-CO2 treated corn stover is due to increase in surface area. Carbonic acid (a weak acid) from dissolved CO2 in water phase may also contribute.

Committee:

Tingyue Gu, PhD (Advisor); Douglas Goetz, PhD (Committee Co-Chair); Ahmed Faik, PhD (Committee Member); Ben Stuart, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

Supercritical; Carbon Dioxide; Pretreatment; Lignocellulosic; Biomass; Biofuels

Kleman, Angela MAsymmetric Hydroformylation of Styrene in Supercritical Carbon Dioxide
Master of Science in Chemical Engineering, University of Toledo, 2005, Chemical Engineering
Hydroformylation reactions in supercritical carbon dioxide provide an environmentally conscious method of producing aldehydes for fine chemical and pharmaceutical products. Asymmetric ligands, such as (R)-BINAP, may be used to provide an enantioselective product. The benefits of producing a selective product include an overall reduction in costs, including those costs associated with separation and disposal of undesired and potentially harmful products. When these reactions are performed in environmentally benign solvents, such as supercritical carbon dioxide (scCO2), additional environmental benefits are derived, such as ease of recycling of the solvent and unconverted reactants and elimination of the need for organic solvents. In this study, rhodium based catalysts were prepared in supercritical carbon dioxide and evaluated for the hydroformylation of styrene to produce 2-phenylpropionaldheyde. Triphenylphosphine and (R)-BINAP were examined as ligands and their effects on the reaction were examined. The experiments showed that a catalyst is produced that promotes hydroformylation of styrene in supercritical carbon dioxide and that enantiomeric selectivity could be obtained using (R)-BINAP ligands.

Committee:

Martin Abraham (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Enantioselectivity; Supercritical Carbon Dioxide; BINAP; Rhodium Complexes; Catalysis; Asymmetric Hydroformylation; Styrene; Triphenylphosphine; Ligands

Wang, RuoleiApplications of Unconventional Processes in Polymer Synthesis – Supercritical Fluids and Sonochemistry
Doctor of Philosophy, University of Akron, 2005, Engineering
The polymer industry has become one of the fastest growing areas in the materials industry for several decades, and would be continue to do so in the foreseeable future. However, due to growing environmental and health concern, the polymer manufacturers have faced increasing pressure to apply environmentally benign technologies in order to accommodate tightened environmental regulations. In the process of searching for clean and low emission polymerization techniques, supercritical fluid technology and sonochemistry have attracted more and more interest because of their unique advantages over conventional techniques. The present study is to expand our knowledge of polymer synthesis processes involving supercritical fluid, sonochemistry and microemulsion technologies. This study included three affiliated projects as supercritical dispersion polymerization, ultrasonically initiated polymerization in near-critical environment and ultrasound assisted microemulsion polymerization in aqueous solution. The success of projects will significantly broaden the application potential for these advanced chemical processes in both conventional and unconventional systems. In the study of dispersion polymerization in scCO2, a new PDMS macromonomer has been successfully applied as surfactant to stabilize the polymerization process. The polymerization results indicated that the conversion is increasing with the increasing of stabilizer concentration, and the particle morphology become more uniform at the same time. In the study of ultrasound irradiation in high-pressure medium, it has been confirmed that sonication alone could initiate the polymerization process. The monomer: CO2 ratio and ultrasound irradiation time appeared to have impact on the molecular weight and its distribution of the polymeric products. Discrete morphology from SEM image suggested that the polymer particles could be stabilized without surfactant during the polymerization process. In the study of ultrasound assisted microemulsion polymerization, ultrasound irradiation has been proved crucial to achieve a stable microemulsion polymerization. The kinetics study suggested that sonication could facilitate the polymerization dramatically. The ultrasound irradiation has also been proved to be an effective approach to control the particle size and its distribution of resultant polymer solution.

Committee:

Henry Cheung (Advisor)

Subjects:

Engineering, Chemical

Keywords:

polymerization; POLYMER; ultrasound; microemulsion; SUPERCRITICAL; ultrasound irradiation; MMA

Mohammed Nor, AzmiThe Effect of Turbulent Flow on Corrosion of Mild Steel in High Partial CO2 Environments
Doctor of Philosophy (PhD), Ohio University, 2013, Chemical Engineering (Engineering and Technology)
The need to develop natural gas hydrocarbon gas fields that have high concentrations of CO2 necessitates technical evaluation of the feasibility of using carbon steels as infrastructure material particularly as its use would positively impact the economic viability of such development projects. This requires a suitable CO2 corrosion prediction model. However, the upper pressure limit of existing CO2 corrosion prediction models is 20 bar, well below the encountered subcritical and supercritical pressures (73.4 bar). Employing existing models for the design of the production assets would lead to over prediction, resulting in over design and high costs. A further requirement for the development of a suitable corrosion model for high CO2 partial pressure environments was the inclusion of the effect of flow. Therefore, this study focused on three parameters that might affect the flow-sensitivity of CO2 corrosion: CO2 partial pressure, pH, and temperature. To accomplish the objectives, two types of flow geometries were used to study flow-sensitive corrosion at elevated CO2 partial pressure and high temperature environment: rotating cylinder electrode (RCE) and thin-channel flow cell (TCFC). Since TCFC was a new flow apparatus, the mass transfer behavior of TCFC was characterized using limiting current density technique. In the experiment, the limiting current density of API 5L X-65 carbon steel was measured at various velocities in 1 wt% NaCl electrolyte at pH 3.0 for each of the test temperatures of 30o C and 50o C. The data showed good correlation with the mass transfer correlation of Sleicher and Rouse for a smooth pipeline. This established TCFC as being suitable for study of flow-sensitive corrosion. In RCE experiments, the effect of pH (pH 3.0 to pH 5.0) was studied at CO2 partial pressure of 10 bar and temperature of 25o C and 50o C in 1 wt% NaCl electrolyte. The findings indicated that the increase in pH led to the decrease in corrosion rate. Most importantly, the findings revealed that the effect of pH on flow-sensitivity as compared against a mass transfer correlation was not considerable even when the concentration of hydrogen ions was relatively high. This was attributed to the dominant effect of flow-insensitive chemical-reaction controlled hydration of dissolved CO2 that precedes the direct reduction of carbonic acid. The effect of temperature (25o C, 50o C, and 80o C) at CO2 partial pressure of 10 and 80 bar and at pH 3.0 and pH4.0 showed that the increase in temperature considerably accelerated CO2 corrosion rates. However, the increase in temperature even at 80o C did not seem to significantly enhance the flow-sensitivity of CO2 corrosion. This again may be attributed to the dominance of direct reduction of carbonic acid that was limited by the slow hydration of aqueous CO2. The effect of increasing CO2 partial pressure (10, 40, and 80 bar) as carried out at pH 3.0 and 50o C was to enhance CO2 corrosion rate due to the increase in the direct reduction of carbonic acid as its concentration increased. However, the increase was not linear and became relatively smaller as the CO2 partial pressure increased further probably due to the saturation of adsorbed carbonic acid on the steel surface. In fact, in the RCE experiments, the corrosion rate decreased at high CO2 partial pressure and temperature (80 bar and 80o C). However, this was more due to the formation of protective iron carbonate layers, resulting from the change in water chemistry. Nevertheless, the TCFC experiments with a larger volume of test solution produced more realistic results with no iron carbonate layer formation at 80 bar and 80o C test conditions. Even in the absence of iron carbonate layers in the TCFC, the flow-sensitivity of CO2 corrosion at elevated CO2 partial pressure was still relatively low due to the dominance of flow-insensitive hydration of aqueous CO2. Notwithstanding this, the fact that the corrosion rates at low temperature (25o C) in the RCE and TCFC with similar mass transfer coefficients correlated well indicated that CO2 corrosion was geometry-independent.

Committee:

Srdjan Nesic, Prof. (Advisor); Howard Dewald, Prof. (Committee Member); Jeffrey Rack, Prof. (Committee Member); Dusan Sormaz, Assoc. Prof. (Committee Member); David Young, Dr (Committee Member)

Subjects:

Chemical Engineering

Keywords:

Supercritical CO2; thin-channel flow cell; rotating-cylinder electrode; high CO2 corrosion; modeling; mass-transfer characterization