Matching Items (67)
Description
The use of petroleum for liquid-transportation fuels has strained the environment and caused the global crude oil reserves to diminish. Therefore, there exists a need to replace petroleum as the primary fuel derivative. Butanol is a four-carbon alcohol that can be used to effectively replace gasoline without changing the current automotive infrastructure. Additionally, butanol offers the same environmentally friendly effects as ethanol, but possess a 23% higher energy density. Clostridium acetobutylicum is an anaerobic bacterium that can ferment renewable biomass-derived sugars into butanol. However, this fermentation becomes limited by relatively low butanol concentrations (1.3% w/v), making this process uneconomical. To economically produce butanol, the in-situ product removal (ISPR) strategy is employed to the butanol fermentation. ISPR entails the removal of butanol as it is produced, effectively avoiding the toxicity limit and allowing for increased overall butanol production. This thesis explores the application of ISPR through integration of expanded-bed adsorption (EBA) with the C. acetobutylicum butanol fermentations. The goal is to enhance volumetric productivity and to develop a semi-continuous biofuel production process. The hydrophobic polymer resin adsorbent Dowex Optipore L-493 was characterized in cell-free studies to determine the impact of adsorbent mass and circulation rate on butanol loading capacity and removal rate. Additionally, the EBA column was optimized to use a superficial velocity of 9.5 cm/min and a resin fraction of 50 g/L. When EBA was applied to a fed-batch butanol fermentation performed under optimal operating conditions, a total of 25.5 g butanol was produced in 120 h, corresponding to an average yield on glucose of 18.6%. At this level, integration of EBA for in situ butanol recovered enabled the production of 33% more butanol than the control fermentation. These results are very promising for the production of butanol as a biofuel. Future work will entail the optimization of the fed-batch process for higher glucose utilization and development of a reliable butanol recovery system from the resin.
ContributorsWiehn, Michael (Author) / Nielsen, David (Thesis advisor) / Lin, Jerry (Committee member) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2013
Description
High temperature CO2 perm-selective membranes offer potential for uses in various processes for CO2 separation. Recently, efforts are reported on fabrication of dense ceramic-carbonate dual-phase membranes. The membranes provide selective permeation to CO2 and exhibit high permeation flux at high temperature. Research on transport mechanism demonstrates that gas transport for ceramic-carbonate dual-phase membrane is rate limited by ion transport in ceramic support. Reducing membrane thickness proves effective to improve permeation flux. This dissertation reports strategy to prepare thin ceramic-carbonate dual-phase membranes to increase CO2 permeance. The work also presents characteristics and gas permeation properties of the membranes. Thin ceramic-carbonate dual-phase membrane was constructed with an asymmetric porous support consisting of a thin small-pore ionic conducting ceramic top-layer and a large pore base support. The base support must be carbonate non-wettable to ensure formation of supported dense, thin membrane. Macroporous yttria-stabilized zirconia (YSZ) layer was prepared on large pore Bi1.5Y0.3Sm0.2O3-δ (BYS) base support using suspension coating method. Thin YSZ-carbonate dual-phase membrane (d-YSZ/BYS) was prepared via direct infiltrating Li/Na/K carbonate mixtures into top YSZ layers. The thin membrane of 10 μm thick offered a CO2 flux 5-10 times higher than the thick dual-phase membranes. Ce0.8Sm0.2O1.9 (SDC) exhibited highest CO2 flux and long-term stability and was chosen as ceramic support for membrane performance improvement. Porous SDC layers were co-pressed on base supports using SDC and BYS powder mixtures which provided better sintering comparability and carbonate non-wettability. Thin SDC-carbonate dual-phase membrane (d-SDC/SDC60BYS40) of 150 μm thick was synthesized on SDC60BYS40. CO2 permeation flux for d-SDC/SDC60BYS40 exhibited increasing dependence on temperature and partial pressure gradient. The flux was higher than other SDC-based dual-phase membranes. Reducing membrane thickness proves effective to increase CO2 permeation flux for the dual-phase membrane.
ContributorsLu, Bo (Author) / Lin, Yuesheng (Thesis advisor) / Crozier, Peter (Committee member) / Herrmann, Macus (Committee member) / Forzani, Erica (Committee member) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2014
Description
Organic optoelectronic devices have remained a research topic of great interest over the past two decades, particularly in the development of efficient organic photovoltaics (OPV) and organic light emitting diodes (OLED). In order to improve the efficiency, stability, and materials variety for organic optoelectronic devices a number of emitting materials, absorbing materials, and charge transport materials were developed and employed in a device setting. Optical, electrical, and photophysical studies of the organic materials and their corresponding devices were thoroughly carried out. Two major approaches were taken to enhance the efficiency of small molecule based OPVs: developing material with higher open circuit voltages or improved device structures which increased short circuit current. To explore the factors affecting the open circuit voltage (VOC) in OPVs, molecular structures were modified to bring VOC closer to the effective bandgap, ∆EDA, which allowed the achievement of 1V VOC for a heterojunction of a select Ir complex with estimated exciton energy of only 1.55eV. Furthermore, the development of anode interfacial layer for exciton blocking and molecular templating provide a general approach for enhancing the short circuit current. Ultimately, a 5.8% PCE was achieved in a single heterojunction of C60 and a ZnPc material prepared in a simple, one step, solvent free, synthesis. OLEDs employing newly developed deep blue emitters based on cyclometalated complexes were demonstrated. Ultimately, a peak EQE of 24.8% and nearly perfect blue emission of (0.148,0.079) was achieved from PtON7dtb, which approaches the maximum attainable performance from a blue OLED. Furthermore, utilizing the excimer formation properties of square-planar Pt complexes, highly efficient and stable white devices employing a single emissive material were demonstrated. A peak EQE of over 20% for pure white color (0.33,0.33) and 80 CRI was achieved with the tridentate Pt complex, Pt-16. Furthermore, the development of a series of tetradentate Pt complexes yielded highly efficient and stable single doped white devices due to their halogen free tetradentate design. In addition to these benchmark achievements, the systematic molecular modification of both emissive and absorbing materials provides valuable structure-property relationship information that should help guide further developments in the field.
ContributorsFleetham, Tyler Blain (Author) / Li, Jian (Thesis advisor) / Alford, Terry (Committee member) / Adams, James (Committee member) / Arizona State University (Publisher)
Created2014
Description
Organic light emitting diodes (OLEDs) are a promising approach for display and solid state lighting applications. However, further work is needed in establishing the availability of efficient and stable materials for OLEDs with high external quantum efficiency's (EQE) and high operational lifetimes. Recently, significant improvements in the internal quantum efficiency or ratio of generated photons to injected electrons have been achieved with the advent of phosphorescent complexes with the ability to harvest both singlet and triplet excitons. Since then, a variety of phosphorescent complexes containing heavy metal centers including Os, Ni, Ir, Pd, and Pt have been developed. Thus far, the majority of the work in the field has focused on iridium based complexes. Platinum based complexes, however, have received considerably less attention despite demonstrating efficiency's equal to or better than their iridium analogs. In this study, a series of OLEDs implementing newly developed platinum based complexes were demonstrated with efficiency's or operational lifetimes equal to or better than their iridium analogs for select cases.
In addition to demonstrating excellent device performance in OLEDs, platinum based complexes exhibit unique photophysical properties including the ability to form excimer emission capable of generating broad white light emission from a single emitter and the ability to form narrow band emission from a rigid, tetradentate molecular structure for select cases. These unique photophysical properties were exploited and their optical and electrical properties in a device setting were elucidated.
Utilizing the unique properties of a tridentate Pt complex, Pt-16, a highly efficient white device employing a single emissive layer exhibited a peak EQE of over 20% and high color quality with a CRI of 80 and color coordinates CIE(x=0.33, y=0.33). Furthermore, by employing a rigid, tetradentate platinum complex, PtN1N, with a narrow band emission into a microcavity organic light emitting diode (MOLED), significant enhancement in the external quantum efficiency was achieved. The optimized MOLED structure achieved a light out-coupling enhancement of 1.35 compared to the non-cavity structure with a peak EQE of 34.2%. In addition to demonstrating a high light out-coupling enhancement, the microcavity effect of a narrow band emitter in a MOLED was elucidated.
In addition to demonstrating excellent device performance in OLEDs, platinum based complexes exhibit unique photophysical properties including the ability to form excimer emission capable of generating broad white light emission from a single emitter and the ability to form narrow band emission from a rigid, tetradentate molecular structure for select cases. These unique photophysical properties were exploited and their optical and electrical properties in a device setting were elucidated.
Utilizing the unique properties of a tridentate Pt complex, Pt-16, a highly efficient white device employing a single emissive layer exhibited a peak EQE of over 20% and high color quality with a CRI of 80 and color coordinates CIE(x=0.33, y=0.33). Furthermore, by employing a rigid, tetradentate platinum complex, PtN1N, with a narrow band emission into a microcavity organic light emitting diode (MOLED), significant enhancement in the external quantum efficiency was achieved. The optimized MOLED structure achieved a light out-coupling enhancement of 1.35 compared to the non-cavity structure with a peak EQE of 34.2%. In addition to demonstrating a high light out-coupling enhancement, the microcavity effect of a narrow band emitter in a MOLED was elucidated.
ContributorsEcton, Jeremy David (Author) / Li, Jian (Thesis advisor) / Adams, James (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2014
Description
Organic light emitting diodes (OLEDs) is a rapidly emerging technology based on organic thin film semiconductors. Recently, there has been substantial investment in their use in displays. In less than a decade, OLEDs have grown from a promising academic curiosity into a multi-billion dollar global industry. At the heart of an OLED are emissive molecules that generate light in response to electrical stimulation. Ideal emitters are efficient, compatible with existing materials, long lived, and produce light predominantly at useful wavelengths. Developing an understanding of the photophysical processes that dictate the luminescent properties of emissive materials is vital to their continued development. Chapter 1 and Chapter 2 provide an introduction to the topics presented and the laboratory methods used to explore them. Chapter 3 discusses a series of tridentate platinum complexes. A synthetic method utilizing microwave irradiation was explored, as well as a study of the effects ligand structure had on the excited state properties. Results and techniques developed in this endeavor were used as a foundation for the work undertaken in later chapters. Chapter 4 introduces a series of tetradentate platinum complexes that share a phenoxy-pyridyl (popy) motif. The new molecular design improved efficiency through increased rigidity and modification of the excited state properties. This class of platinum complexes were markedly more efficient than those presented in Chapter 3, and devices employing a green emitting complex of the series achieved nearly 100% electron-to-photon conversion efficiency in an OLED device. Chapter 5 adapts the ligand structure developed in Chapter 4 to palladium. The resulting complexes exceed reported efficiencies of palladium complexes by an order of magnitude. This chapter also provides the first report of a palladium complex as an emitter in an OLED device. Chapter 6 discusses the continuation of development efforts to include carbazolyl components in the ligand. These complexes possess interesting luminescent properties including ultra-narrow emission and metal assisted delayed fluorescence (MADF) emission.
ContributorsTurner, Eric (Author) / Li, Jian (Thesis advisor) / Adams, James (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2014
Description
The absorption spectra of metal-centered phthalocyanines (MPc's) have been investigated since the early 1960's. With improved experimental techniques to characterize this class of molecules the band assignments have advanced. The characterization remains difficult with historic disagreements. A new push for characterization came with a wave of interest in using these molecules for absorption/donor molecules in organic photovoltaics. The use of zinc phthalocyanine (ZnPc) became of particular interest, in addition to novel research being done for azaporphyrin analogs of ZnPc.
A theoretical approach is taken to research the excited states of these molecules using time-dependent density functional theory (TDDFT). Most theoretical results for the first excited state in ZnPc are in only limited agreement with experiment (errors near 0.1 eV or higher). This research investigates ZnPc and 10 additional porphyrin analogs. Excited-state properties are predicted for 8 of these molecules using ab initio computational methods and symmetry breaking for accurate time- dependent self-consistent optimization. Franck-Condon analysis is used to predict the Q-band absorption spectra for all 8 of these molecules. This is the first time that Franck-Condon analysis has been reported in absolute units for any of these molecules. The first excited-state energy for ZnPc is found to be the closest to experiment thus far using a range-separated meta-GGA hybrid functional. The theoretical results are used to find a trend in the novel design of new porphyrin analog molecules.
A theoretical approach is taken to research the excited states of these molecules using time-dependent density functional theory (TDDFT). Most theoretical results for the first excited state in ZnPc are in only limited agreement with experiment (errors near 0.1 eV or higher). This research investigates ZnPc and 10 additional porphyrin analogs. Excited-state properties are predicted for 8 of these molecules using ab initio computational methods and symmetry breaking for accurate time- dependent self-consistent optimization. Franck-Condon analysis is used to predict the Q-band absorption spectra for all 8 of these molecules. This is the first time that Franck-Condon analysis has been reported in absolute units for any of these molecules. The first excited-state energy for ZnPc is found to be the closest to experiment thus far using a range-separated meta-GGA hybrid functional. The theoretical results are used to find a trend in the novel design of new porphyrin analog molecules.
ContributorsTheisen, Rebekah (Author) / Adams, James B (Thesis advisor) / Li, Jian (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2014
Description
Pervaporation is a membrane separation technology that has had industrial application and which is the subject of ongoing research. Two major factors are important in judging the quality of a membrane: selectivity and permeation flux. Although many types of materials can be used for the separation layer, zeolites will be the material considered in this thesis. A simple mathematical model has been developed to demonstrate the inter-relationships between relative permeation flux, reduced selectivity, and the relative resistance to mass transfer of the support to the zeolite layer. The model was applied to several membranes from our laboratory and to two examples from the literature. The model offers a useful way of conceptualizing membrane performance and facilitates the comparison of different membrane performances. The model predicts the effect of different supports on zeolite supported membrane performance.
ContributorsMann, Stewart (Author) / Lin, Jerry (Thesis advisor) / Lind, Mary Laura (Committee member) / Nielsen, David (Committee member) / Arizona State University (Publisher)
Created2014
Description
The production of nanomaterials has been increasing and so are their applications in various products, while the environmental impacts and human impacts of these nanomaterials are still in the process of being explored. In this thesis, a process for
producing nano-titanium dioxide (nano-TiO2) is studied and a case-study has been conducted on comparative Life Cycle Assessment (LCA) of the application of these nano-TiO2 particles in the sunscreen lotion as a UV-blocker with the conventional organic chemical sunscreen lotion using GaBi software. Nano-TiO2 particles were identified in the sunscreen lotion using Transmission Electron Microscope suggesting the use of these particles in the lotion.
The LCA modeling includes the comparison of the environmental impacts of producing nano-TiO2 particles with that of conventional organic chemical UV-blockers (octocrylene and avobenzone). It also compares the environmental life cycle impacts of the two sunscreen lotions studied. TRACI 2.1 was used for the assessment of the impacts which were then normalized and weighted for the ranking of the impact categories.
Results indicate that nano-TiO2 had higher impacts on the environment than the conventional organic chemical UV-blockers (octocrylene and avobenzone). For the two sunscreen lotions studied, nano-TiO2 sunscreen variant had lower environmental life cycle impacts than its counterpart because of the other chemicals used in the formulation. In the organic chemical sunscreen variant the major impacts came from production of glycerine, ethanol, and avobenzone but in the nano-TiO2 sunscreen variant the major impacts came from the production of nano-TiO2 particles.
Analysis further signifies the trade-offs between few environmental impact categories, for example, the human toxicity impacts were more in the nano-TiO2 sunscreen variant, but the other environmental impact categories viz. fossil fuel depletion, global warming potential, eutrophication were less compared to the organic chemical sunscreen variant.
producing nano-titanium dioxide (nano-TiO2) is studied and a case-study has been conducted on comparative Life Cycle Assessment (LCA) of the application of these nano-TiO2 particles in the sunscreen lotion as a UV-blocker with the conventional organic chemical sunscreen lotion using GaBi software. Nano-TiO2 particles were identified in the sunscreen lotion using Transmission Electron Microscope suggesting the use of these particles in the lotion.
The LCA modeling includes the comparison of the environmental impacts of producing nano-TiO2 particles with that of conventional organic chemical UV-blockers (octocrylene and avobenzone). It also compares the environmental life cycle impacts of the two sunscreen lotions studied. TRACI 2.1 was used for the assessment of the impacts which were then normalized and weighted for the ranking of the impact categories.
Results indicate that nano-TiO2 had higher impacts on the environment than the conventional organic chemical UV-blockers (octocrylene and avobenzone). For the two sunscreen lotions studied, nano-TiO2 sunscreen variant had lower environmental life cycle impacts than its counterpart because of the other chemicals used in the formulation. In the organic chemical sunscreen variant the major impacts came from production of glycerine, ethanol, and avobenzone but in the nano-TiO2 sunscreen variant the major impacts came from the production of nano-TiO2 particles.
Analysis further signifies the trade-offs between few environmental impact categories, for example, the human toxicity impacts were more in the nano-TiO2 sunscreen variant, but the other environmental impact categories viz. fossil fuel depletion, global warming potential, eutrophication were less compared to the organic chemical sunscreen variant.
ContributorsThakur, Ankita (Author) / Dooley, Kevin (Thesis advisor) / Dai, Lenore (Committee member) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2014
Description
This dissertation presents a systematic study of the sorption mechanisms of hydrophobic silica aerogel (Cabot Nanogel®) granules for oil and volatile organic compounds (VOCs) in different phases. The performance of Nanogel for removing oil from laboratory synthetic oil-in-water emulsions and real oily wastewater, and VOCs from their aqueous solution, in both packed bed (PB) and inverse fluidized bed (IFB) modes was also investigated. The sorption mechanisms of VOCs in the vapor, pure liquid, and aqueous solution phases, free oil, emulsified oil, and oil from real wastewater on Nanogel were systematically studied via batch kinetics and equilibrium experiments. The VOC results show that the adsorption of vapor is very slow due to the extremely low thermal conductivity of Nanogel. The faster adsorption rates in the liquid and solution phases are controlled by the mass transport, either by capillary flow or by vapor diffusion/adsorption. The oil results show that Nanogel has a very high capacity for adsorption of pure oils. However, the rate for adsorption of oil from an oil-water emulsion on the Nanogel is 5-10 times slower than that for adsorption of pure oils or organics from their aqueous solutions. For an oil-water emulsion, the oil adsorption capacity decreases with an increasing proportion of the surfactant added. An even lower sorption capacity and a slower sorption rate were observed for a real oily wastewater sample due to the high stability and very small droplet size of the wastewater. The performance of Nanogel granules for removing emulsified oil, oil from real oily wastewater, and toluene at low concentrations in both PB and IFB modes was systematically investigated. The hydrodynamics characteristics of the Nanogel granules in an IFB were studied by measuring the pressure drop and bed expansion with superficial water velocity. The density of the Nanogel granules was calculated from the plateau pressure drop of the IFB. The oil/toluene removal efficiency and the capacity of the Nanogel granules in the PB or IFB were also measured experimentally and predicted by two models based on equilibrium and kinetic batch measurements of the Nanogel granules.
ContributorsWang, Ding (Author) / Lin, Jerry Y.S. (Thesis advisor) / Pfeffer, Robert (Thesis advisor) / Westerhoff, Paul (Committee member) / Nielsen, David (Committee member) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2011
Description
Advanced composites are being widely used in aerospace applications due to their high stiffness, strength and energy absorption capabilities. However, the assurance of structural reliability is a critical issue because a damage event will compromise the integrity of composite structures and lead to ultimate failure. In this dissertation a novel homogenization based multiscale modeling framework using semi-analytical micromechanics is presented to simulate the response of textile composites. The novelty of this approach lies in the three scale homogenization/localization framework bridging between the constituent (micro), the fiber tow scale (meso), weave scale (macro), and the global response. The multiscale framework, named Multiscale Generalized Method of Cells (MSGMC), continuously bridges between the micro to the global scale as opposed to approaches that are top-down and bottom-up. This framework is fully generalized and capable of modeling several different weave and braids without reformulation. Particular emphasis in this dissertation is placed on modeling the nonlinearity and failure of both polymer matrix and ceramic matrix composites.
ContributorsLiu, Guang (Author) / Chattopadhyay, Aditi (Thesis advisor) / Mignolet, Marc (Committee member) / Jiang, Hanqing (Committee member) / Li, Jian (Committee member) / Rajadas, John (Committee member) / Arizona State University (Publisher)
Created2011