Browsing by Subject "Inhibitor"

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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 V
Amine 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.
Persistence in the superintendency : Latina superintendents’ perspectives
(2019-06-19) Olivarez, Adelaida; Reyes, Pedro, 1954-; Pringle , Patrick G.; Sharpe, Edwin R.; Olivarez, Ruben D.
The role of superintendent is complex and evolving. The pool of viable superintendent candidates may be facing an impending shortage over the next several years. This paper examines the most viable motivators and inhibitors that superintendents report for persisting in the role and conversely, for considering exiting the field. Motivators consist of altruistic reasons for serving including the desire to make a difference, building a leadership team, the ability to affect communities, be an agent of change, and to transform school organizations. The inhibitors highlight superintendents’ concerns with school finance models, increased stressors and time commitment for the job, the politics of conflict with their school boards, and a lack of minority representation. The literature provides recommendations for mitigating inhibitors, including increased training and communication to support healthy superintendent-board relations, diversifying the pool of candidates, and raising awareness in leadership preparation programs for the management of job stressors. These measures are critical to the vitality of the superintendency, especially in light of a shrinking pool of viable, diversified candidates. A study was conducted to identify the inhibitors, motivators, and strategies for three Latina superintendents serving in the superintendent role in Texas. The study design was a qualitative multiple-case study of the phenomenon of the Latina superintendents within their contextual environments. Data for the study were analyzed using grounded theory methodology. The study findings reveal recommendations for leveraging motivators, alleviating inhibitors, and removing access barriers for Latina aspirants to the role
Targeting multifunctional human ALDOA in cancer signaling
(2018-08-16) Stancu, Bogdan Gabriel; Dalby, Kevin N.; Fast, Walter; Mills, Edward; Ren, Pengyu; Tiziani, Stefano
Human fructose-bisphosphate aldolase A (ALDOA) is a key enzyme in glycolysis that catalyzes the conversion of fructose 1,6-bisphosphate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. ALDOA has also been shown to play key moonlighting roles associated with cellular structure, motility and proliferation. This aldolase isoenzyme is significantly overexpressed in a number of human tumors and has been shown to have oncogenic potential. We have demonstrated that ALDOA overexpression has further inference through cycling of hypoxia inducible transcription factor-1 (HIF-1) regulation. This feed-forward loop mediated through AMPK is a new target to consider in the irregular hypoxic environment of solid tumors. The body of work that follows presents five different methods of targeting and inhibiting ALDOA function. Using small molecule probes, the function and regulation of these iterations is characterized, towards better understanding of the role of ALDOA in cells and in cancer