• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 4768
  • 321
  • 184
  • 122
  • 100
  • 10
  • 10
  • 6
  • 4
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 7131
  • 7131
  • 787
  • 604
  • 541
  • 535
  • 524
  • 524
  • 488
  • 461
  • 255
  • 250
  • 243
  • 222
  • 168
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Developing, implementing, and assessing coupled-tank experiments in an undergraduate chemical engineering curriculum

Inampudi, Narendra Kumar. Pinhero, Patrick J. January 2009 (has links)
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Patrick J. Pinhero. Includes bibliographical references.


Li, Hongming 01 February 2006 (has links)
The objective of this work is to advance the fundamental understanding of mixing and segregation of cohesive granular materials. Cohesion can arise from a variety of sources: van der Waals forces, electrostatic forces, liquid bridging (capillary) forces. These forces may play a significant role in the processing of fine and/or moist powders in many industries, from pharmaceuticals to materials synthesis; however, despite its prevalence, there is only limited information available in the literature on processing of cohesive materials. Instead, the vast majority of work has been directed at the study of non-cohesive (i.e., free-flowing) particles, and a wealth of information has been learned about the behavior of cohesionless materials. With growing emphasis on controlling the structure of materials at increasingly small length-scales (even tending toward the nano-scale), understanding the effects of particle interactions - which tend to dominate at smaller length-scales - on processing operations has become more important than ever. This project focuses on the effects of cohesion on mixing and segregation in simple, industrially-relevant, granular flows. In particular, the paradigm cases of a slowly rotated tumbler and the flow in a simple shear cell are examined. We take a novel approach to this problem, placing emphasis on microscopic (particle-level), discrete modeling so as to take as its staring point the well understood interaction laws governing cohesion (capillary, van der Waals, etc.), and build to the view of the macroscopic flow via experiment and Particle Dynamics Simulation. We develop and use discrete characterization tools of cohesive behavior in order to construct a simple theory regarding the mixing and segregation tendency of cohesive granular matter. This theory allows us to analytically determine a phase diagram, showing both mixed and segregated phases, and agrees both quantitatively and qualitatively with experiment. These results have implications for industrial mixing/separation processes as well as novel particle production methods (e.g., engineered agglomerates with precisely prescribed compositions).


Fan, Xin 02 June 2006 (has links)
The objectives of this work are to design, synthesize, and evaluate hydrocarbon-based or oxygenated hydrocarbon-based CO2 soluble surfactants. These surfactants would be able to form stable water-in-CO2 microemulsions with polar microenvironments capable of dissolving polar species in the bulk non-polar CO2 solvent, or to form metal precursors which can be reduced to nanoparticles in the presence of stabilizing ligands, or to generate foams in-situ for enhanced oil recovery application. Several oxygenated hydrocarbons, including acetylated sugars, poly(propylene glycol), oligo(vinyl acetate), and highly branched methylated hydrocarbons were used generate CO2-soluble ionic surfactants. Surfactants with vinyl acetate tails yielded the most promising results, exhibiting levels of CO2 solubility comparable to those associated with fluorinated ionic surfactants. For example, a sodium sulfate with single, oligomeric vinyl acetate (VAc) tails consisting of 10 VAc repeat units was 7 wt% soluble in CO2 at 25 oC and 48 MPa. Upon introduction of water to these systems, only surfactants with the oligomeric vinyl acetate tails exhibited spectroscopic evidence of a polar environment that was capable of solubilizing the methyl orange into CO2-rich phase. Silver bis(3,5,5-trimethyl-1-hexyl) sulfosuccinate, Ag-AOT-TMH, was synthesized from hydrocarbon-based ionic surfactant of sodium bis(3,5,5-trimethyl-1-hexyl) sulfosuccinate, Na-AOT-TMH through ion exchange. Ag-AOT-TMH exhibits 1.2 wt% solubility in dense CO2 at 40 oC and 52 MPa. Silver nanoparticles were produced by reducing the supercritical CO2 solution containing 0.06 wt% Ag-AOT-TMH and 0.5 wt% perfluorooctanethiol (stabilizing ligand) using a reducing agent of NaBH4. Iso-stearic acid, a short, stubby compound with branched, methylated tails, as a hydrocarbon-based nonionic surfactant, has been shown to have high solubility in carbon dioxide. The solvation of the tails by carbon dioxide has made isostearic acid sterically stabilize metallic nanoparticles as a ligand. The stability of CO2-water emulsion formed by ionic and nonionic surfactants was studied in CO2 at 22 oC and 34.5 MPa for 0.01-1.0 wt% surfactant mixed with equivalent volumes of CO2 and water. Emulsion stability was monitored by observing the rate of collapse of the white, opaque middle-phase emulsion between the transparent CO2 and water phases and the steady-state volume of the emulsion. It was found that at surfactant concentration of 0.01 wt%, oligo(vinyl acetate)10 sodium sulfate displayed the best emulsion, taking over 450 minutes to collapse.


Kazachkin, Dmitry V. 02 June 2006 (has links)
The present study is of great importance both from industrial application side and from fundamental point of view. The work considers ecologically significant industrial processe - utilization of chlorinated hydrocarbons. Particularly, 1,2-dichloroethane utilization is chosen as a model reaction to study the kinetics of hydrogenation process in fixed batch flow reactor over Pt-Cu silica supported bimetallic catalysts. The fundamental part of the study includes correlation search between kinetics performance and electronic-structural properties of Pt-Cu bimetallic catalyst. Establishing correlation between electronic-structural properties and performance in chemical reactions are of prime significance for understanding of chemical nature of particular chemical systems. The understanding means the ability to govern the process that is of huge interest for industrial applications. The kinetic performance is determined directly by testing the selected catalyst in fixed bed reactor. The main characteristics derived from kinetics testing that are interesting for current study - selectivity and activity. The product of interest for presented process is ethylene, C2H4. The electronic-structural properties were derived mainly from the infrared-red (FTIR) study of carbon monoxide (CO) test molecule. The correlation between electronic-structural properties and kinetics performance are related to freshly pretreated catalyst. It was established that the selectivity toward C2H4 is a strong function of Cu/Pt atomic ratio that depends on the size of Pt ensembles: the smaller the size of Pt ensembles the higher selectivity toward C2H4. Activity slightly decreases as Cu/Pt ratio is increasing. The observed kinetics performance is rationalized based on knowledge derived from FTIR study and knowledge from previously published works. Structural sensitivity of C-Cl bond cleavage reaction is established for 1,2-dichloroethane hydrodechlorination. Elementary step of C-Cl bond cleavage is require 2-6 platinum atoms. Besides, the role of Cu as a main component responsible for C2H4 formation is shown experimentally. The structural dependence is rationalized in terms of ensemble size effect. The mechanism of 1,2-dichloroethane hydrodechlorination reaction for highly selective catalysts is explained in terms of independent role of Pt and Cu.


Jiang, Canping 02 June 2006 (has links)
Herpes simplex virus type 1 (HSV-1) is a promising vector for gene therapy applications. To be used as therapeutic agents, HSV-1 vectors must meet the stringent criteria of high titer and purity. Thu, development of scalable, efficient HSV-1 vector purification strategies is essential to advance HSV-1 vectors into clinic. In this dissertation, a novel, efficient HSV-1 vector purification method, based on immobilized metal affinity chromatography (IMAC), was developed. I first evaluated the feasibility of using various transition metal ions (Cu2+, Zn2+, Ni2+, and Co2+) for the purification of HSV-1 vectors. Results show that none of the metals investigated provided a means of separating the virus from impurities. However, of interest is the finding that neither the virus nor the impurities bound to immobilized Co2+, suggesting that this metal could be useful for HSV-1 vector purification if the vector could be endowed with the affinity toward cobalt. Accordingly, I constructed an HSV-1 recombinant bearing a cobalt affinity tag (HAT) in the heparan sulfate binding domain of the virion envelope glycoprotein B (gB). It was found that the productivity and infectivity of the tagged HSV-1 mutant (KgBHAT) was not adversely affected by the mutation; while the binding and elution of KgBHAT on cobalt charged iminodiacetate (IDA-Co2+) columns confirmed that efficient purification was possible. By reducing cobalt ion leakage and optimizing the loading conditions, flow rate, and chromatographic substrate, efficient purification of KgBHAT from crude supernatant was achieved with over 70% virus infectivity recovery and over 95% reduction in protein and DNA impurities. Finally, I found that purification of KgBHAT on IDA-Co2+ columns using crude supernatant as starting material resulted in significant loss in virus infectivity. Electron spinning resonance revealed that the virus inactivation was caused by hydroxyl free radicals generated from the interaction between cobalt ions and components in crude virus supernatant. Appropriate amounts of free radical scavenger, a free radical scavenger, or imidazole in the loading material was able to protect HSV-1 from inactivation, and led to high virus infectivity recovery from IMAC purification. This finding is the first report of free radical mediated biological inactivation in an actual IMAC purification.

Control-Relevant System Identification using Nonlinear Volterra and Volterra-Laguerre Models

Soni, Abhishek 02 June 2006 (has links)
One of the key impediments to the wide-spread use of nonlinear control in industry is the availability of suitable nonlinear models. Empirical models, which are obtained from only the process input-output data, present a convenient alternative to the more involved fundamental models. An important advantage of the empirical models is that their structure can be chosen so as to facilitate the controller design problem. Many of the widely used empirical model structures are linear, and in some cases this basic model formulation may not be able to adequately capture the nonlinear process dynamics. One of the commonly used nonlinear dynamic empirical model structures is the Volterra model, and this work develops a systematic approach to the identification of third-order Volterra and Volterra-Laguerre models from process input-output data. First, plant-friendly input sequences are designed that exploit the Volterra model structure and use the prediction error variance (PEV) expression as a metric of model fidelity. Second, explicit estimator equations are derived for the linear, nonlinear diagonal, and higher-order sub-diagonal kernels using the tailored input sequences. Improvements in the sequence design are also presented which lead to a significant reduction in the amount of data required for identification. Finally, the third-order off-diagonal kernels are estimated using a cross-correlation approach. As an application of this technique, an isothermal polymerization reactor case study is considered. In order to overcome the noise sensitivity and highly parameterized nature of Volterra models, they are projected onto an orthonormal Laguerre basis. Two important variables that need to be selected for the projection are the Laguerre pole and the number of Laguerre filters. The Akaike Information Criterion (AIC) is used as a criterion to determine projected model quality. AIC includes contributions from both model size and model quality, with the latter characterized by the sum-squared error between the Volterra and the Volterra-Laguerre model outputs. Reduced Volterra-Laguerre models were also identified, and the control-relevance of identified Volterra-Laguerre models was evaluated in closed-loop using the model predictive control framework. Thus, this work presents a complete treatment of the problem of identifying nonlinear control-relevant Volterra and Volterra-Laguerre models from input-output data.


Hong, Lei 02 June 2006 (has links)
Over the past two decades the use of near-/super-critical carbon dioxide has received much attention as a green alternative to organic solvents for chemical reactions, separations, and extractions because of its pressure-tunable physicochemical properties and economic advantages. However the advantages are diminished because of a relative narrow range of CO2-soluble materials. The goal of this work is to identify, design and synthesize oxygenated hydrocarbon-based CO2-soluble polymers that are able to serve as construction blocks for copolymers, dispersants, surfactants, thickeners, and chelating agents. Without concerning on the cost and the environmental persistence like fluorinated materials, the inexpensive, environmentally benign materials would significantly enhance the viability of near-/super-critical carbon dioxide-based technology. Based on both experimental heuristics and ab initio simulation results of molecular modeling (performed by Dr. Johnsons group), we proposed specific new polymer structures: poly(3-acetoxy oxetane) (PAO), poly(vinyl methoxymethyl ether) (PVMME), poly(vinyl 1-methoxyethyl ether) (PVMEE), and cellulose triacetate (CTA) oligomers. Phase behavior studies were also performed with novel CO2-philic compounds containing vinyl acetate, propylene glycol, or multiple tert-butyl groups. PAO, PVMME and PVMME were soluble in CO2, but not as soluble as poly(vinyl acetate). Oligomers of cellulose triacetate with as many as four repeat units solubilized into dense CO2 less than 14 MPa in the concentration range of 1-5 wt%. Phase behaviors of more than thirty compounds in dense CO2 were studied in this project. A new type of phase behavior for solid (at ambient temperature) CO2-philes that melt and dissolve in CO2 was detailed using a model binary mixture of β-D-maltose octaacetate and CO2. Copolymers of tetrafluoroethylene (TFE) and vinyl acetate (VAc) exhibited lower miscibility pressures than either of the homopolymers, probably due to quadradentate binding configurations with CO2. Phase behavior investigation of poly(propylene glycol) (PPG) monobutyl ether in CO2 demonstrated ether-CO2 interactions should receive as much attention as carbonyl-CO2 interactions when designing CO2-philic functional groups. 1,3,5-tri-tert-butylbenzene and tri-tert-butyl-phenol were both extraordinarily soluble in CO2, and are excellent candidates for CO2-soluble sand binders. In summary, although a new CO2 thickener was not identified, new non-fluorous CO2-soluble materials were identified that were, in general, acetate-rich with flexible chains, weak self-interactions, and multidentate interaction between CO2 and solute functional groups.

Molecular simulation study of adsorption, diffusion and dissociation

Chen, liang 27 September 2006 (has links)
There are two main objectives in my research work. The first objective is to investigate the adsorption behavior of various gases on single walled carbon nanotubes. This is accomplished by using the classical molecular simulation methods. Our simulation work has provided molecular level interpretation of some interesting phenomena observed experimentally by our collaborators. The second objective is to study the catalytic properties of metal/metal carbide surfaces and interfacial phenomena by using ab initio density functional theory. We have studied the adsorption of various gases on carbon nanotubes by using classical molecular simulation and optimization techniques. We specifically have investigated the displacement of adsorption on different adsorption sites. The systems investigated include CO2 on SWNT, Xe/CF4 on SWNT and CO2/Xe on SWNT. Our simulations indicate that CO2 is easily replaced from the endohedral and interstitial sites of SWNT bundles by Xe, while the groove/external surface sites loose much less CO2. These calculations agree very well with the experimental observations. We have also observed unique one dimensional behavior of gases adsorbed on carbon nanotubes by using optimization and parallel tempering Monte Carlo. The results show that CO2 molecules adsorbed in the groove sites of single walled carbon nanotubes display behavior that is quasi-1-dimensional. At finite coverages of CO2 in grooves clusters containing only odd numbers of molecules are formed at low temperatures. Even numbers of molecules form two clusters, each containing an odd number of molecules. We have carried out density functional theory studies on the catalytic properties of metal surfaces. We investigated adsorption of CO on the Ag(110) surface and CO adsorption, diffusion and dissociation on the W(111) surface. The CO molecule is found to non-dissociatively adsorb in end-on configurations (alpha states) and dissociatively absorb in inclined configurations (beta states). The dissociation of beta state CO is found to have an activation energy of about 0.8 eV, which is lower than the energy required to desorb CO molecularly from the surface. We have also studied the tungsten difussion mechanisms in cobalt. Our calculations indicate that the diffusion is vacancy mediated. Therefore, we proposed the triangle and quadrangle mechanims, and examined the full diffusion pathways.

Molecular Modeling Applied to CO2-Soluble Molecules and Confined Fluids

Wang, Yang 31 January 2007 (has links)
CO2 is known to be an environmentally benign solvent. However, its feeble solvent power inhibits its wide use in industrial applications. The ultimate goal of this research is to design and optimize polymers that are highly soluble in CO2. Molecular modeling methods have been used to analyze the results from experiments and make predictions. We have employed ab initio quantum mechanical methods to investigate interactions between CO2 molecules and polymers. This is done by computing the interactions between CO2 and polymer moieties and important functional groups. These functional groups include ether oxygens, carbonyl oxygens, and fluorines. We have identified several factors that believed to be responsible for CO2-philicity. These factors include multiple site bindings, acidic hydrogens, and geometric considerations. We have designed three possible CO2-soluble molecules based on our calculation results. Our experimental colleagues have synthesized and tested the corresponding polymers to compare with our predictions. Single wall carbon nanotubes have attracted significant scientific interest as adsorption media since their discovery. Fluids confined in nanotubes have significantly different behavior from bulk fluids. We have performed simulations for alkanes adsorbed in the internal and external sites of carbon nanotubes. The simulation results qualitively match the experimental data from temperature programmed desorption. The diffusion coefficients in bulk and confined phases have been calculated. We have also studied the structure and infrared spectra of water adsorbed in nanotubes over a wide range of temperatures. Our simulation studies have identified the essential physics responsible for a distinctive infrared band observed in recent experiments.

The Influence of H2S on Palladium and Palladium-Copper Alloy Membranes

Morreale, Bryan David 31 January 2007 (has links)
Dense metal membranes have been identified as a promising technology for post-gasifier forward water-gas shift membrane reactors. Unfortunately, the impurities present in the gasifier effluent streams, such as H2S, can have adverse effects on the mechanical and chemical stability of potential metal membranes in the form of corrosion or catalyst deactivation, respectively. Thus, this study has focused on the identification and characterization of dense metal membranes that can tolerate the harsh environments encountered in the gasification process without significant detrimental effects on permeability. Pd-Cu alloys have been of interest in recent years due to its catalytic activity for hydrogen dissociation, high permeability relative to Pd, suppression of the hydride-phase transition and limited reports of stability in the presence of H2S. Initially, the permeability of pure palladium, pure copper and palladium-copper alloys containing 80wt%, 60wt% and 53wt% Pd was evaluated with hydrogen retentate streams at temperatures and pressures ranging from 350 to 900oC and 0.1 to 2.86 MPa, respectively. Results indicate that crystalline phase plays a significant role in membrane performance, with the B2, 60wt%Pd-Cu alloy exhibiting the highest permeability of the alloys tested at temperatures below approximately 500oC. However, at temperatures corresponding to an fcc crystalline temperature for all of the alloys, membrane performance increased with increasing palladium content of the alloy. Additionally, the permeability the above mentioned alloys, along with pure palladium, have been evaluated in a H2S containing retentate gas mixture at temperatures of 350, 450 and 635oC. Permeability measurements coupled with SEM and XRD analysis of post tested membranes indicate that the mechanisms influencing performance is strongly dependent on operating temperature, alloy composition, crystalline structure, and exposure time. Gravimetric analysis of the growth rate of the metals sulfides observed on the palladium-copper alloys and pure palladium during the transient period of flux measurements was conducted. A model of hydrogen transport through a composite membrane with a Pd base and a growing palladium tetra-sulfide film was then developed and fit to the transient flux results and sulfide growth rate. The optimization of the model resulted in the first reported values of the permeability of palladium tetra-sulfide.

Page generated in 0.0831 seconds