Browsing by Subject "Degradation"
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Item Amine oxidation in carbon dioxide capture by aqueous scrubbing(2013-05) Voice, Alexander Karl; Rochelle, Gary T.; Sexton, Andrew J; Reible, Danny D; Willson, Carlton G; Anslyn, Eric VAmine degradation in aqueous amine scrubbing systems for capturing CO₂ from coal fired power plants is a major problem. Oxygen in the flue gas is the major cause of solvent deterioration, which increases the cost of CO₂ capture due to reduced capacity, reduced rates, increased corrosion, solvent makeup, foaming, and reclaiming. Degradation also produces environmentally hazardous materials: ammonia, amides, aldehydes, nitramines, and nitrosamines. Thus it is important to understand and mitigate amine oxidation in industrial CO₂ capture systems. A series of lab-scale experiments was conducted to better understand the causes of and solutions to amine oxidation. This work included determination of rates, products, catalysts, and inhibitors for various amines at various conditions. Special attention was paid to understanding monoethanolamine (MEA) oxidation, whereas oxidation of piperazine (PZ) and other amines was less thorough. The most important scientific contribution of this work has been to show that amine oxidation in real CO₂ capture systems is much more complex than previously believed, and cannot be explained by mass transfer or reaction kinetics in the absorber by itself, or by dissolved oxygen kinetics in the cross exchanger. An accurate representation of MEA oxidation in real systems must take into account catalysts present (especially Mn and Fe), enhanced oxygen mass transfer in the absorber as a function of various process conditions, and possibly oxygen carriers other than dissolved oxygen in the cross exchanger and stripper. Strategies for mitigating oxidative degradation at low temperature, proposed in this and previous work are less effective or ineffective with high temperature cycling, which is more representative of real systems. In order of effectiveness, these strategies are: selecting an amine resistant to oxidation, reduction of dissolved metals in the system, reduction of the stripper temperature, reduction of the absorber temperature, and addition of a chemical inhibitor to the system. Intercooling in the absorber can reduce amine oxidation and improve energy efficiency, whereas amine oxidation should be considered in choosing the optimal stripper temperature. In real systems, 2-amino-2-methyl-1-propanol (AMP) is expected to be the most resistant to oxidation, followed by PZ and PZ derivatives, then methyldiethanolamine (MDEA), and then MEA. MEA oxidation with high temperature cycling is increased 70% by raising the cycling temperature from 100 to 120 °C, the proposed operational temperature range of the stripper. PZ oxidation is increased 100% by cycling to 150 °C as opposed to 120 °C. Metals are expected to increase oxidation in MEA and PZ with high temperature cycling by 40 - 80%. Inhibitor A is not expected to be effective in real systems with MEA or with PZ. MDEA is also not effective as an inhibitor in MEA, and chelating agents diethylenetriamine penta (acetic acid) (DTPA) and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) are only mildly effective in MEA. Although MEA oxidation in real systems cannot be significantly reduced by any known additives, it can be accurately monitored on a continuous basis by measuring ammonia production from the absorber. Ammonia production was shown to account for two-thirds of nitrogen in degraded MEA at low temperature and with high temperature cycling, suggesting that it is a reliable indicator of MEA oxidation under a variety of process conditions. A proposed system, which minimizes amine oxidation while maintaining excellent rate and thermodynamic properties for CO₂ capture would involve use of 4 m AMP + 2 m PZ as a capture solvent with the stripper at 135 °C, intercooling in the absorber, and use of a corrosion inhibitor or continuous metals removal system. Reducing (anaerobic) conditions should be avoided to prevent excessive corrosion from occurring and minimize the amount of dissolved metals. This system is expected to reduce amine oxidation by 90-95% compared with the base case 7 m MEA with the stripper at 120 °C.Item Designing proteasome adaptors to deplete specific proteins from cells(2019-06-21) Bowen, Kimberly Elizabeth; Matouschek, Andreas T.; Xhemalce, Blerta; Huibregtse, Jon; Georgiou, George; Dalby, KevinCellular protein levels are governed by their rates of synthesis and degradation, and both processes are intricately regulated. One way to study the role of a protein in the cell is to artificially deplete it and observe the effects. The most common methodology for depleting proteins inhibits expression of the target through RNA interference. However, this technique acts at the protein synthesis level and cannot be used to study long-lived proteins or post-translational modifications. Thus, a complementary approach that acts on the proteins themselves would be useful. One method is to target a protein to the cell’s degradation machinery, the Ubiquitin Proteasome System (UPS). Proteins are targeted to the proteasome by the covalent attachment of ubiquitin molecules, which are recognized by the proteasome. The substrate is then translocated into the proteasome’s proteolytic core and degraded into short peptides, while the ubiquitin molecules are cleaved off and recycled. Recently, methods have been developed to deplete proteins by inducing their ubiquitination, which accelerates their degradation by the proteasome. Ubiquitin is a signaling molecule for numerous cellular pathways other than proteolysis, however, and inducing ubiquitination does not always lead to degradation. Therefore, I have developed a system to degrade specific proteins in cells using chimeric adaptors that shuttle proteins directly to the proteasome without the need for ubiquitination. I have shown that this system can be successfully applied to several proteins in vitro and that the adaptors can induce degradation of model and endogenous proteins in cells.Item The effect of nanocatalyst size on performance and degradation in the cathode of proton exchange membrane fuel cells(2011-12) Groom, Daniel Jeffrey; Ferreira, Paulo J. S. G.; Rabenberg, Llewellyn K.This thesis discusses the role of initial particle size on the mechanisms of surface area loss of carbon-supported platinum (Pt) electrocatalysts in the cathode of proton exchange membrane fuel cells. Electrocatalyst decay protocols were used to accelerate cathode performance loss for Pt catalysts. Four cathodes with mean platinum particle sizes of 2.1, 3.5, 6.7 and 11.3 nm were evaluated to elucidate the impact of particle size on initial performance and subsequent degradation, when subjected to identical potential cycles. The degradation of Pt electrochemically active surface area (ECA) was significantly greater for 2.1 and 3.5 nm initial sizes compared to 6.7 and 11.3 nm initial sizes. As expected, the ECA loss of the cathodes shows an inverse proportionality with initial particle size. However, the initial performance of the 11.3 nm initial particle size electrode was significantly lower than the three smaller sizes. Thus, an initial Pt particle size of 6.7 nm was identified to offer the ideal balance performance and durability. The current state of standardization in characterizing particle size by transmission electron microscopy (TEM) is also investigated. The result is a standardized protocol for image acquisition and analysis.Item Effects of moisture on the breakdown strength and lifetime of low permittivity dielectric for nanometer scale interconnects(2009-05) Choi, Soo Young, doctor of materials science and engineering; Ho, P. S.Advanced integrated circuit (IC) technology has implemented new materials for necessary and timely performance improvements. New materials are now required at both the front-end-of-line (FEoL) and back-end-of-line (BEoL) of the device because simple dimensional scaling with standard materials has come with performance costs that negate dimensional scaling performance improvements. At the FEoL, high-[kappa]/metal gate processes are being developed to reduce gate oxide leakage. At the BEoL, Cu-based metallization and low-[kappa] dielectric materials have been developed to reduce BEoL contribution to RC-propagation delay. Cu-based metallization has required change in integration strategy, which has led to concerns about new material reliability performance. Furthermore, continuing pressure to improve device performance requires that a new, more advanced low-[kappa] dielectric be used, which are mechanically and electrically inferior. These performance demands and greater reliability concerns must be balanced. This kind of balance requires that better understanding of the extrinsic threats to device reliability be understood and is the general area of interest for this work. In particular, this study examines the extent of degradation found in low-[kappa] dielectric when it is exposed to ambient moisture and the potential impact of this degradation on intrinsic reliability performance under electrical stress. The integration method is described for low-[kappa] dielectric processing so that potential damages during process can be explained. Local damages can allow moisture incorporation at the expense of additional dielectric performance and reliability degradation. The molecular form of moisture incorporation into low-[kappa] dielectric and potential process methods to reduce moisture incorporation are also discussed. The electrical reliability performance is shown using interdigitated structures through voltage ramped dielectric breakdown study of inter-metal dielectric (IMD). Clear evidence of dielectric degradation is found after extreme moisture incorporation. Moisture penetration impact is also examined on the long-term reliability of integrated low-[kappa] dielectric using time-dependent dielectric breakdown (TDDB). Results show a dramatic change in the observed field acceleration parameter through moisture exposure that is not easily explained in a standard way according to proposed dielectric breakdown models for low-[kappa] dielectrics. A simple modification of the thermochemical [Epsilon]-model is proposed to explain the results.Item Found, fucked up, fixed(2019-05-09) Kovitya, Mark Thongchai; Williams, Jeff, M.F.A.; Hauft, Amy, 1957-Found, Fucked Up, Fixed is an overview of my sculptural work engaging with the arbitrary distinctions created between opposing sites and how those distinctions are used to alienate subjects in pursuit of maintaining order and in turn, a sense of stability. Boundaries are porous and permeable membranes through which shared meaning slips; they are a third space that is neither a site of complete inclusion nor total exclusion. Considering the boundary traversing the ideal and the failure of the ideal reveals seemingly distinct oppositions that are not at all distinct, but the same. The following report examines my artistic production within the context of other artists, critics, philosophers, and literary theorists who have observed the ambiguity inherent in boundary regions. Also considered here are the conceptual foundations for the use of abstracted and exaggerated anatomical fragments as a strategy for questioning boundaries, the application of entropic processes, the degradation of form and content, and the use of “filthy” materialsItem Leveraging selective peptoid degradation for biosensing applications(2022-08-12) McKenzie, Hattie Christine (Schunk); Rosales, Adrianne M.; Suggs, Laura J.Development of multi-functional materials and biosensors that can achieve an in-situ response designed by the user is a current need in the biomaterials field, especially in complex biological environments, such as inflammation, where multiple enzymatic and oxidative signals are present. In the past decade, there has been extensive research and development of materials chemistries for detecting and monitoring enzymatic activity, as well as for releasing therapeutic and diagnostic agents in regions undergoing oxidative stress. However, there has been limited development of materials in the context of enzymatic and oxidative triggers together, despite their closely tied and overlapping mechanisms. One major fundamental design challenge to integrating multiple sensing elements in tandem is instability and uncontrolled cross-reactivity. Thus, to successfully detect biomarkers in synergy, there is need for innovative strategies in controlling biostability while maintaining well-defined bioactivity. We aim to address this challenge using synthetic, sequence-defined peptoids. Due to their N-substitution, peptoids are generally regarded as resistant to biological degradation, such as enzymatic and hydrolytic mechanisms. This stability is an especially attractive feature for therapeutic development and is a selling point of many previous biological studies. However, oxidative degradation of peptoids mediated by reactive oxygen and nitrogen species (ROS/RNS) is key mode of degradation that remains to be fully explored. ROS and RNS are biologically relevant in numerous contexts where biomaterials may be present, thus, improving understanding of peptoid oxidative susceptibility is crucial to exploit their full potential in the biomaterials field. Toward this end, we demonstrate a fundamental characterization of sequence-defined peptoid chains in the presence of chemically generated ROS, as compared to ROS-susceptible peptides such as proline and lysine oligomers. These results expand understanding of peptoid degradation to oxidative and enzymatic mechanisms, and demonstrate the potential for peptoid incorporation into materials where selectivity towards oxidative degradation is necessary, or directed enzymatic susceptibility is desired. By considering the materials chemistry of enzymatically and oxidatively triggered biomaterials in tandem, we hope to encourage synthesis of new biosensors that capitalize on their synergistic roles and overlapping mechanisms in inflammatory environments for future applications in disease diagnosis and monitoring.Item Oxidation and thermal degradation of methyldithanolamine/piperazine in CO₂ capture(2011-12) Closmann, Frederick Bynum; Rochelle, Gary T.; Bedell, Stephen; Lawler, Desmond F.; Ekerdt, John G.; Willson, Carlton G.The solvent 7 molal (m) methyldiethanolamine (MDEA)/2 m piperazine (PZ) presents an attractive option to industry standard solvents including monoethanolamine (MEA) for carbon dioxide (CO₂) capture in coal-fired power plant flue gas scrubbing applications. The solvent was tested under thermal and oxidizing conditions, including temperature cycling in the Integrated Solvent Degradation Apparatus (ISDA), to measure rates of degradation for comparison to other solvents. Unloaded 7 m MDEA/2 m PZ was generally thermally stable up to 150 °C, exhibiting very low loss rates. However, at a loading of 0.25 mol CO2/mol alkalinity, loss rates of 0.17 ± 0.21 and 0.24 ± 0.06 mM/hr, respectively, for MDEA and PZ were measured. No amine loss was observed in the unloaded blend. Thermal degradation was modeled as first-order in [MDEAH⁺], and a universal Ea for amine loss was estimated at 104 kJ/mol. An oxidative degradation model for 7 m MDEA was developed based on the ISDA data. From the model, the rate of amine loss in 7 m MDEA/2 m PZ was estimated at 1.3 X 10⁵ kg/yr, based on a 500 MW power plant and 90% CO₂ capture. In terms of amine loss, the solvent can be ranked with other cycled solvents from greatest to least as follows: 7 m MDEA>7 m MDEA/2 m PZ>8 m PZ. Thermal degradation pathways and mechanisms for 7 m MDEA/2 m PZ include SN2 substitution reactions to form diethanolamine (DEA), methylaminoethanol (MAE), 1-methylpiperazine (1-MPZ), and 1,4-dimethylpiperazine (1,4-DMPZ). The formation of the amino acids bicine and hydroxyethyl sarcosine (HES) has been directly tied to the formation of DEA and MAE, respectively, through oxidation. As a result of the construction and operation of the ISDA for cycling of solvents from an oxidative reactor to a thermal reactor, several practical findings related to solvent degradation were made. The ISDA results demonstrated that increasing dissolved oxygen in solvents leaving the absorber will increase the rate of oxidation. A simple N2 gas stripping method was tested and resulted in a reduction to 1/5th the high temperature oxidation rate associated with dissolved oxygen present in the higher temperature regions of an absorber/stripper system. The ISDA experiments also demonstrated the need to minimize entrained gas bubbles in absorber/stripper systems to control oxidation. When the ISDA was modified to intercept entrained gas bubbles, the oxidation rate was reduced 2 to 3X.Item Pathways to the proteasome in yeast(2023-12) Spaller, B. Logan; Matouschek, Andreas T.; Cambronne, Lulu; Huibregtse, Jon; Paull, Tanya; Barrick, JeffreyThe proteasome is a highly selective and precisely regulated protease that degrades proteins essential for cellular homeostasis. This dissertation explores the molecular mechanisms by which the proteasome selects its substrates from a diverse protein pool First, the interplay between different pathways to the proteasome was investigated, revealing a hierarchy in degradation whereby substrates delivered by ubiquitin-like (UBL) domains may have priority access to the proteasome. Next, the role of spacing between the ubiquitin tag and disordered initiation region in degradation was investigated. The findings reveal another layer to substrate selection by the proteasome, and provide important considerations when determining whether a given protein may be degraded by the proteasome. Overall, this research provides new insights into how the proteasome selects its substrates in a diverse protein pool.Item Process-induced chemical and physical transformations during twin-screw processing(2021-08-13) Liu, Tongzhou; Zhang, Feng, Ph. D.; Williams III, Robert O.; Ghosh, Debadyuti; Lynd, Nathaniel; Bi, Vivian (Yunxia)Application of twin-screw processing in pharmaceutical industry has gained increasingly favor in last two decades. Twin-screw processing is solvent-free and easy to be integrated to continuous manufacturing to achieve many advantages, such as consistent product quality, easier scale-up, better in-process quality control. Two major applications of twin-screw processing are twin-screw melt granulation (TSMG) and twin-screw melt extrusion (TSE). TSMG relies on efficient heating and intensive mixing to facilitate binder coating on drug crystal and enable supreme tabletability of granules. TSE applied thermal and mechanical energy to change drug to the amorphous state which improves drug bioavailability. However, the thermal and mechanical stress in twin-screw processing may cause chemical and physical transformations of APIs. Unwanted chemical and physical transformations will jeopardize drug product quality. In Chapter 1, mechanism of TSMG was reviewed. The impact of processing parameters and drug-binder interactions on granule properties was discussed. The location and origin of the thermal and mechanical stress were also discussed. In Chapter 2, a miscible drug-binder system was used to study effect of the binder (HPC) level on granule properties and drug (acetaminophen) physicochemical change. The binder level was critical on granule properties, as insufficient binder caused high amount of ungranulated powder and excessive binder caused overgranulation. The amorphization of drug occurred at high binder level and was restricted to granule surface where the binder was enriched. In Chapter 3, the degradation of a thermal labile drug (gliclazide) was investigated when a miscible binder (HPC) was used in TSMG. TSMG process involved in a quick heating section and a slow cooling section. 60% of drug degradation occurred in the cooling and was correlated to granule temperature. Drug degradation and physicochemical change in the heating section was associated with specific mechanical energy input. The nature of drug physicochemical change was crystal defect other than amorphization. In Chapter 4, the drug degradation in TSE was modeled to predict degradation. Drug (ritonavir) degradation in TSE was found in an oxygen deprived condition and affected by the chemical environment of polymer (copovidone). A first-order kinetics model in combination with Arrhenius equation was validated to predict degradation when we used the measured processing temperature and residence time.Item The thermodynamics of degradation(2017-05) Osara, Jude Asuelimen; Bryant, Michael David; Matthews, Ronald D.; Fahrenthold, Eric; Khonsari, Michael; Kyriakedes, SteliosMaterial degradation occurs as a result of irreversible dissipative processes and forces. Various forms of degradation mechanisms exist such as friction, chemical reactions, plasticity, dislocation movements and corrosion all irreversibly leading to failure of a particular system or component. The first and second laws of thermodynamics describe states of a system from the perspective of energy content and exchanges. The first law prescribes energy conservation while the second law introduces the concept of irreversibility in systems as thermodynamic energies decrease, also known as entropy. It has been shown severally that entropy generation accompanies all degradation mechanisms simply by the irreversible nature of the dissipative processes involved. Hence, predicting and quantifying the effect of these processes based on accurate estimate of entropy produced led to the formulation of the Degradation-Entropy Generation (DEG) Theorem by Michael Bryant, Michael Khonsari and Frederick Ling (2008). The DEG theorem also establishes that if a critical value of degradation measure exists, at which failure occurs, there must also exist critical values of accumulated irreversible entropies, and the relationship between them has also been formulated in an independent study in Russia. A close look at 2 classical theories: Holm’s wear equation, w = kNx/H (subsequently modified to the more commonly used Archard’s equation) and Coulomb friction law, F = μN, shows a direct proportionality between wear and energy dissipated by friction, w ∝ Fx. Application of the DEG theorem to a similar sliding friction between two surfaces and the resulting wear characterized by the accompanying entropy generated (or energy dissipated) is shown to define an equivalent wear coefficient k as the Holm-Archard equation. Currently, this study focuses on further development and validation of the DEG theorem primarily in the area of its application to friction wear, grease degradation, battery ageing and fatigue analysis. A consistent thermodynamic approach for evaluating entropy generation accumulation is proposed. An investigation into the dissipative processes relevant to the degradation mechanisms is carried out for correlation to entropy generation. In addition to mathematical formulations, this work includes theorem verification using empirical fatigue data from previously published studies as well as seminal work - new battery and grease experiments to measure DEG parameters.Item Thermal degradation and oxidation of aqueous piperazine for carbon dioxide capture(2011-05) Freeman, Stephanie Anne; Rochelle, Gary T.; Maynard, Jennifer A.; Reible, Danny D.; Katz, Lynn E.; Critchfield, JamesAbsorption-stripping with aqueous, concentrated piperazine (PZ) is a viable retrofit technology for post-combustion CO2 capture from coal-fired power plants. The rate of thermal degradation and oxidation of PZ was investigated over a range of temperature, CO2 loading, and PZ concentration. At 135 to 175 °C, degradation is first order in PZ with an activation energy of 183.5 kJ/mole. At 150 °C, the first order rate constant, k1, for thermal degradation of 8 m PZ with 0.3 mol CO2/mol alkalinity is 6.12 × 10-9 s-1. After 20 weeks of degradation at 165 °C, 74% and 63%, respectively, of the nitrogen and carbon lost in the form of PZ and CO2 was recovered in quantifiable degradation products. N-formylpiperazine, ammonium, and N-(2-aminoethyl) piperazine account for 57% and 45% of nitrogen and carbon lost, respectively. Thermal degradation of PZ likely proceeds through SN2 substitution reactions. In the suspected first step of the mechanism, 1-[2-[(2-aminoethyl) amino]ethyl] PZ is formed from a ring opening SN2 reaction of PZ with H+PZ. Formate was found to be generated during thermal degradation from CO2 or CO2-containing molecules. An analysis of k1 values was applied to a variety of amines screened for thermal stability in order to predict a maximum recommended stripper temperature. Morpholine, piperidine, PZ, and PZ derivatives were found to be the most stable with an allowable stripper temperature above 160 °C. Long-chain alkyl amines or alkanolamines such as N-(2-hydroxyethyl)ethylenediamine and diethanolamine were found to be the most unstable with an allowable stripper temperature below 120 °C. Iron (Fe2+) and stainless steel metals (Fe2+, Ni2+, and Cr3+) were found to be only weak catalysts for oxidation of PZ, while oxidation was rapidly catalyzed by copper (Cu2+). In a system with Fe2+ or SSM, 5 kPa O2 in the inlet flue gas, a 55 °C absorber, and one-third residence time with O2, the maximum loss rate of PZ is expected to 0.23 mol PZ/kg solvent in one year of operation. Under the same conditions but with Cu2+ present, the loss rate of PZ is predicted to be 1.23 mole PZ/kg solvent in one year of operation. Inhibitor A was found to be effective at decreasing PZ loss catalyzed by Cu2+. Ethylenediamine, carboxylate ions, and amides were the only identified oxidation products. Total organic carbon analysis and overall mass balances indicate a large concentration of unidentified oxidation products.