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Description
Solid oxide fuel cells have become a promising candidate in the development of high-density clean energy sources for the rapidly increasing demands in energy and global sustainability. In order to understand more about solid oxide fuel cells, the important step is to understand how to model heterogeneous materials. Heterogeneous materials are abundant in nature and also created in various processes. The diverse properties exhibited by these materials result from their complex microstructures, which also make it hard to model the material. Microstructure modeling and reconstruction on a meso-scale level is needed in order to produce heterogeneous models without having to shave and image every slice of the physical material, which is a destructive and irreversible process. Yeong and Torquato [1] introduced a stochastic optimization technique that enables the generation of a model of the material with the use of correlation functions. Spatial correlation functions of each of the various phases within the heterogeneous structure are collected from a two-dimensional micrograph representing a slice of a solid oxide fuel cell through computational means. The assumption is that two-dimensional images contain key structural information representative of the associated full three-dimensional microstructure. The collected spatial correlation functions, a combination of one-point and two-point correlation functions are then outputted and are representative of the material. In the reconstruction process, the characteristic two-point correlation functions is then inputted through a series of computational modeling codes and software to generate a three-dimensional visual model that is statistically similar to that of the original two-dimensional micrograph. Furthermore, parameters of temperature cooling stages and number of pixel exchanges per temperature stage are utilized and altered accordingly to observe which parameters has a higher impact on the reconstruction results. Stochastic optimization techniques to produce three-dimensional visual models from two-dimensional micrographs are therefore a statistically reliable method to understanding heterogeneous materials.
ContributorsPhan, Richard Dylan (Author) / Jiao, Yang (Thesis director) / Ren, Yi (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Within recent years, metal-organic frameworks, or MOF’s, have gained a lot of attention in the materials research community. These micro-porous materials are constructed of a metal oxide core and organic linkers, and have a wide-variety of applications due to their extensive material characteristic possibilities. The focus of this study is the MOF-5 material, specifically its chemical stability in air. The MOF-5 material has a large pore size of 8 Å, and aperture sizes of 15 and 12 Å. The pore size, pore functionality, and physically stable structure makes MOF-5 a desirable material. MOF-5 holds applications in gas/liquid separation, catalysis, and gas storage. The main problem with the MOF-5 material, however, is its instability in atmospheric air. This inherent instability is due to the water in air binding to the zinc-oxide core, effectively changing the material and its structure. Because of this material weakness, the MOF-5 material is difficult to be utilized in industrial applications. Through the research efforts proposed by this study, the stability of the MOF-5 powder and membrane were studied. MOF-5 powder and a MOF-5 membrane were synthesized and characterized using XRD analysis. In an attempt to improve the stability of MOF-5 in air, methyl groups were added to the organic linker in order to hinder the interaction of water with the Zn4O core. This was done by replacing the terepthalic acid organic linker with 2,5-dimethyl terephthalic acid in the powder and membrane synthesis steps. The methyl-modified MOF-5 powder was found to be stable after several days of exposure to air while the MOF-5 powder exhibited significant crystalline change. The methyl-modified membrane was found to be unstable when synthesized using the same procedure as the MOF-5 membrane.
ContributorsAnderson, Anthony David (Author) / Lin, Jerry Y.S. (Thesis director) / Ibrahim, Amr (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Based on theoretical calculations, a material that is highly transmissive below 3000 nm and opaque above 3000 nm is desired to replace glass covers for flat plate solar thermal systems. Additionally, a suitable replacement material needs to have a sufficiently high operating temperature in order to prevent the glazing from melting and warping in a solar system. Traditional solar thermal applications use conventional soda lime glass or low iron content glass to accomplish this; however, this project aims to investigate acrylic, polycarbonate, and FEP film as suitable alternatives for conventional solar glazings. While UV-Vis and FT-IR spectroscopy indicate that these polymer substitutes may not be ideal when used alone, when used in combination with coatings and additives, these materials may present an opportunity for a glazing replacement. A model representing a flat plate solar collector was developed to qualitatively analyze the various materials and their performance. Using gathered spectroscopy data, the model was developed for a multi-glazing system and it was found that polymer substitutes could perform better in certain system configurations. To complete the model, the model must be verified using empirical data and coatings and additives investigated for the purposes of achieving the desired materials optical specifications.
ContributorsBessant, Justin Zachary (Author) / Friesen, Cody (Thesis director) / Lorzel, Heath (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
One of the primary bottlenecks to chemical production in biological organisms is the toxicity of the chemical. Overexpression of efflux pumps has been shown to increase tolerance to aromatic compounds such as styrene and styrene oxide. Tight control of pump expression is necessary to maximize titers and prevent excessive strain on the cells. This study aimed to identify aromatic-sensitive native promoters and heterologous biosensors for construction of closed-loop control of efflux pump expression in E. coli. Using a promoter library constructed by Zaslaver et al., activation was measured through GFP output. Promoters were evaluated for their sensitivity to the addition of one of four aromatic compounds, their "leaking" of signal, and their induction threshold. Out of 43 targeted promoters, 4 promoters (cmr, mdtG, yahN, yajR) for styrene oxide, 2 promoters (mdtG, yahN) for styrene, 0 promoters for 2-phenylethanol, and 1 promoter for phenol (pheP) were identified as ideal control elements in aromatic bioproduction. In addition, a series of three biosensors (NahR, XylS, DmpR) known to be inducible by other aromatics were screened against styrene oxide, 2-phenylethanol, and phenol. The targeted application of these biosensors is aromatic-induced activation of linked efflux pumps. All three biosensors responded strongly in the presence of styrene oxide and 2-phenylethanol, with minor activation in the presence of phenol. Bioproduction of aromatics continues to gain traction in the biotechnology industry, and the continued discovery of aromatic-inducible elements will be essential to effective pathway control.
ContributorsXu, Jimmy (Author) / Nielsen, David (Thesis director) / Wang, Xuan (Committee member) / School of Life Sciences (Contributor) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
p-Coumaric acid is used in the food, pharmaceutical, and cosmetic industries due to its versatile properties. While prevalent in nature, harvesting the compound from natural sources is inefficient, requiring large quantities of producing crops and numerous extraction and purification steps. Thus, the large-scale production of the compound is both difficult and costly. This research aims to produce p-coumarate directly from renewable and sustainable glucose using a co-culture of Yeast and E. Coli. Methods used in this study include: designing optimal media for mixed-species microbial growth, genetically engineering both strains to build the production pathway with maximum yield, and analyzing the presence of p-Coumarate and its pathway intermediates using High Performance Liquid Chromatography (HPLC). To date, the results of this project include successful integration of C4H activity into the yeast strain BY4741 ∆FDC1, yielding a strain that completely consumed trans-cinnamate (initial concentration of 50 mg/L) and produced ~56 mg/L p-coumarate, a resting cell assay of the co-culture that produced 0.23 mM p-coumarate from an initial L-Phenylalanine concentration of 1.14 mM, and toxicity tests that confirmed the toxicity of trans-cinnamate to yeast for concentrations above ~50 mg/L. The hope for this project is to create a feasible method for producing p-Coumarate sustainably.
ContributorsJohnson, Kaleigh Lynnae (Author) / Nielsen, David (Thesis director) / Thompson, Brian (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel phosphide catalysts. This work is the subject of a publication of which I am a co-author, as cited below.
Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.
Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.
This work is the subject of a publication of which I am a co-author, as cited below.
D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430
Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.
Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.
This work is the subject of a publication of which I am a co-author, as cited below.
D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430
ContributorsTata, Bharath (Author) / Deng, Shuguang (Thesis director) / Muhich, Christopher (Committee member) / Chemical Engineering Program (Contributor, Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Escherichia coli is a bacterium that is used widely in metabolic engineering due to its ability to grow at a fast rate and to be cultured easily. E. coli can be engineered to produce many valuable chemicals, including biofuels and L-Phenylalanine—a precursor to many pharmaceuticals. Significant cell growth occurs in parallel to the biosynthesis of the desired biofuel or biochemical product, and limits product concentrations and yields. Stopping cell growth can improve chemical production since more resources will go toward chemical production than toward biomass. The goal of the project is to test different methods of controlling microbial uptake of nutrients, specifically phosphate, to dynamically limit cell growth and improve biochemical production of E. coli, and the research has the potential to promote public health, sustainability, and environment. This can be achieved by targeting phosphate transporter genes using CRISPRi and CRISPR, and they will limit the uptake of phosphate by targeting the phosphate transporter genes in DNA, which will stop transcriptions of the genes. In the experiment, NST74∆crr∆pykAF, a L-Phe overproducer, was used as the base strain, and the pitA phosphate transporter gene was targeted in the CRISPRi and CRISPR systems with the strain with other phosphate transporters knocked out. The tested CRISPRi and CRISPR mechanisms did not stop cell growth or improved L-Phe production. Further research will be conducted to determine the problem of the system. In addition, the CRISPRi and CRISPR systems that target multiple phosphate transporter genes will be tested in the future as well as the other method of stopping transcriptions of the phosphate transporter genes, which is called a tunable toggle switch mechanism.
ContributorsPark, Min Su (Author) / Nielsen, David (Thesis director) / Machas, Michael (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The problem of catastrophic damage purveys in any material application, and minimizing its occurrence is paramount for general health and safety. We have successfully synthesized, characterized, and applied dimeric 9-anthracene carboxylic acid (Di-AC)-based mechanophores particles to form stress sensing epoxy matrix composites. As Di-AC had never been previously applied as a mechanophore and thermosets are rarely studied in mechanochemistry, this created an alternative avenue for study in the field. Under an applied stress, the cyclooctane-rings in the Di-AC particles reverted back to their fluorescent anthracene form, which linearly enhanced the overall fluorescence of the composite in response to the applied strain. The fluorescent signal further allowed for stress sensing in the elastic region of the stress\u2014strain curve, which is considered to be a form of damage precursor detection. Overall, the incorporation of Di-AC to the epoxy matrix added much desired stress sensing and damage precursor detection capabilities with good retention of the material properties.
ContributorsWickham, Jason Alexander (Co-author) / Nofen, Elizabeth (Co-author, Committee member) / Koo, Bonsung (Co-author) / Chattopadhyay, Aditi (Co-author) / Dai, Lenore (Co-author, Thesis director) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Lignin is a naturally abundant source of aromatic carbon but is largely underutilized in industry because it is difficult to decompose. Under the current study we engineered Corynebacterium glutamicum for the depolymerization of lignin with the goal of using it as raw feed for the sustainable production of valuable chemicals. C. glutamicum is a standout candidate for the depolymerization and assimilation of lignin because of its performance as an industrial producer of amino acids, resistance to aromatic compounds in lignin, and low extracellular protease activity. Three different foreign and native ligninolytic enzymes were tested in combination with three signal peptides to assess lignin degradation efficacy. At this stage, six of the nine plasmid constructs have been constructed.
ContributorsEllis, Dylan Scott (Author) / Varman, Arul Mozhy (Thesis director) / Nannenga, Brent (Committee member) / Nowroozi, Farnaz (Committee member) / Chemical Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Due to the wide range of health properties flavonoids possess, flavonoids are sold in health supplements to the general public. Flavonoids are also utilized in research but have a high cost due to current production techniques. This project focuses on engineering two DNA recombinants to develop new strains of Corynebacterium glutamicum that can produce flavonoids pinocembrin and naringenin. After culturing Escherichia coli colonies containing genes of interest, the genes were collected and purified by PCR reactions. The recombinant plasmid was assembled using CPEC and successfully transformed into Escherichia coli, with plans to transform Corynebacterium glutamicum to experiment and determine which recombinant can produce more pinocembrin and naringenin. Design work for other DNA recombinants, which were not the focus of this project, was also completed.
ContributorsWong, Adam (Co-author, Co-author) / Varman, Arul Mozhy (Thesis director) / Nielsen, David (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05