Spelling suggestions: "subject:"ethoxyethanol"" "subject:"ether:ethanol""
411 |
Materials for direct methanol fuel cells: inhibition of methanol crossover using novel membrane electrode assembliesDawson, Craig January 2012 (has links)
This thesis focuses on developing an alternative system for membrane electrode assembly (MEA) formation to use with a direct methanol fuel cell (DMFC). The approach involves incorporating inorganic fillers with an industry standard Nafion polymer as part of a methanol resistant composite barrier layer at the anode/membrane interface of MEA featuring Nafion 117 membranes. This procedure is used to reduce the fuel cell losses related to the crossover of un-oxidised methanol through the membrane and prevent its subsequent reaction at the cathode. The inorganic filler used within this study was mordenite that has Si/Al ratio of 5 and by incorporating this into the barrier layer a superior DMFC performance has been achieved in comparison to a standard MEA featuring a Nafion 117 membrane. The voltage, current density and power density used as a measure of DMFC performance under a range of methanol molarities (1M-4M) and cell temperatures (40°C-70°C) have been taken for both the novel and standard MEA. Linear sweep voltammetry (LSV) and AC impedance spectroscopy (ACIS) were used to give some insight into what was occurring within the MEA with regards to methanol crossover current and the proton conductivity within the DMFC. To obtain the best possible DMFC performance a range of mordenite loadings from 0wt%1.0wt% were utilised and an optimum loading of 0.5wt% was reached. MEA which featured mordenite that had undergone ion exchange into a protonated form (from the sodium form) and had a silane functional group (glycidoxypropyltrimethoxysilane) grafted onto the surface, gave DMFC performances that were as much as 50% better than the standard. The highest power density obtained with this MEA was 43.6mW/cm-2 compared to the 35mW/cm-2 obtained using the standard. Values obtained for the methanol crossover current and proton conductivity under working DMFC operating conditions showed that this novel MEA had as much as 16% lower methanol permeability compared to the standard combined with comparable proton conductivity when using a 1M methanol feed. The durability of a novel MEA featuring the 0.5wt% functionalised H-mordenite composite barrier layer was tested in the DMFC and compared to a standard MEA at a constant current of 50mA/cm-2 over 100 hours. The cell potential fell by 0.1mV/h in comparison to a 0.23mV/h loss observed with the standard. The work reported within this study aims to show that by incorporating a thin Nafion/mordenite composite layer at the anode/membrane interface within an MEA will result in improvements in DMFC performance. The development of this technology has led to the application for a patent due to the potential for the commercial development of DMFC using this novel approach.
|
412 |
Effects of Methanol, Atrazine, and Copper on the Ultrastructure of Pseudokirchneriella Subcapitata (Selenastrum Capricornutum).Garrett, David C. 05 1900 (has links)
The toxicity of methanol, atrazine, and copper to Pseudokirchneriella subcapitata (Korshikov) Hindák historically referred to as Selenastrum capricornutum Printz were determined following 96 hrs growth in a modified Goram's growth media. Methanol and atrazine inhibited fluorescence readings in the cultures by 50% (IC50) at concentrations of 2% and 82 µg/l respectively. These toxicity values compared favorably to other published reports. The IC50 for copper was 160 µg/l which is substantially higher than reported values. This is understandable because of the high chelating capacity of Goram's media. The use of stereologically derived relative volume in the chloroplasts, mitochondria, lipid bodies, phosphate bodies, and nucleus was investigated to determine if it could be used as a sensitive endpoint in toxicity tests. The volume fractions for the chloroplasts and mitochondria were normally distributed in control cells while the nuclei, phosphate bodies, and lipid bodies were not. The chloroplasts were the most dominate organelle occupying a mean relative volume of 46% and mitochondria occupied a mean relative volume of 3%. The nucleus and phosphate bodies occupied a median relative volume of 7% and 2% respectively. The lipid bodies were rare in section profile and no meaningful median relative volume could be calculated. Up to the 82nd percentile of sectioned profiles contained no recognizable lipid bodies. The use of relative volume was not a sensitive endpoint for use in toxicity tests. No significant differences in relative volume could be detected in the nucleus or phosphate bodies following any treatment. Limited differences were detected in the mitochondria, chloroplasts, and lipid bodies. The only significant differences that appear to be biologically significant occurred in methanol treated cells where an increase in the lipid bodies' relative volume was apparently concentration dependent. Significant differences in the relative volume of mitochondria and chloroplasts do not appear to be biologically significant.
|
413 |
Mechanistic Investigation into the Conversion of Methanol to Hydrocarbons by Zeolite CatalystsLiu, Zhaohui 10 1900 (has links)
Catalytic conversion of methanol to hydrocarbons (MTH) provides an alternative route to the production of fuels and important industrial chemicals that are currently mainly produced from the refinery of petroleum. The ability to control the product distribution of MTH according to the demands of specific applications is of crucial importance, which relies on the thorough understanding of the reaction pathways and mechanisms. Despite the significant research efforts devoted to zeolite-catalyzed MTH, it remains a challenge to establish a firm correlation between the physicochemical properties of zeolites and their catalytic activity and selectivity. In this dissertation, we designed a series of experiments to gain fundamental understanding of how the structural and compositional parameters of zeolites influence their catalytic performances in MTH. We investigated different types of zeolites, covering large-pore Beta, medium-pore ZSM-5, and small-pore DDR zeolites, and tune their crystallite size/diffusion length, hierarchical (mesoporous) structure, and Si/Al ratio (density of acid sites) by controlled synthesis or post-synthesis treatments.
The influence of mesoporosity of a zeolite catalyst on its catalytic performance for MTH, with zeolite Beta, was first investigated. The shorter diffusion length associated with the hierarchical structure results in a lower ethylene selectivity but higher selectivity towards C4-C7 aliphatics. Then we investigated the correlation between the Al content and the ethylene selectivity by ZSM-5 zeolites with similar crystal sizes but varied Si/Al ratios. We realized that ethylene selectivity is promoted with the increase of aluminum content in the framework. These two observations can be explained by the same mechanistic reason: the ethylene selectivity is associated with the propagation degree of the aromatics catalytic cycle and essentially determined by the number of the acid sites that methylbenzenes would encounter before they exit the zeolite crystallite. Last we explored how to maximize the propylene selectivity by tuning the physicochemical properties of DDR zeolites. Due to the confined pore space in DDR, the propagation of olefins-based catalytic cycle can be preferentially promoted in a tunable manner, which cannot be realized with zeolites having larger pores. Thus, the propylene selectivity increases with increasing the Si/Al ratio and decreasing the crystallite size.
|
414 |
Úskalí zastavování hydratace alkalicky aktivované strusky organickými látkami / Issues of stopping the hydration of alkali-activated slag using organic substancesChadima, Jan January 2021 (has links)
This thesis deals with the stopping of hydration of alkali activated slag by organic solvents and investigates to what extent the selected organic solvent affects the results of the analyses. The solvents used were acetone, diethyl ether, ethanol, isopropanol and methanol, and this is because these are the most commonly used organic solvents in practice. Thermogravimetric analysis along with differential thermal analysis was used to assess the degree of influence of organic solvents on the alkali activated slag and Portland cement samples. Methanol and acetone affected the samples the most and the longer the sample was stored in the solvent, the more it reacted with the organic solvent. The adverse interaction of organic solvent was greatest for the Portland cement samples. Samples that were rinsed with diethyl ether prior to analysis had lower mass losses than samples that were not rinsed. In the case of alkali activated slag, it was found that the way in which the thermogravimetric results were affected by organic solvents was highly dependent on the activator used, with the smallest effect observed for Na2CO3 activation, while the largest effect was observed for NaOH activation at temperatures below 600 °C, and for higher temperatures for water glass activation.
|
415 |
SYNTHETIC METHODS TO CONTROL ALUMINUM PROXIMITY IN CHABAZITE ZEOLITES AND CONSEQUENCES FOR ACID AND REDOX CATALYSISJohn R. Di Iorio (5929640) 16 January 2020 (has links)
<p>Zeolites
contain distinct Brønsted acid site (H<sup>+</sup>) ensembles that arise from
differences in the arrangement of framework Al atoms (Al−O(−Si−O)x−Al) between
isolated (x ≥3) and paired (x=1,2) configurations, the latter defined by their
ability to exchange certain divalent cations (e.g., Cu<sup>2+</sup>, Co<sup>2+</sup>).
Manipulation of the synthesis conditions used to prepare MFI zeolites has been
proposed to influence the proximity of framework Al atoms, but in a manner that
is neither determined randomly nor by any simple predictive rules. Moreover, the
effects of proton proximity have been studied for hydrocarbon catalysis in MFI
zeolites, but interpretations of catalytic phenomena are convoluted by effects
of the distribution of framework Al atoms among different crystallographic
tetrahedral sites (T-sites) and diverse pore environments (i.e., confining
environments) present in MFI. This work instead focuses on the chabazite (CHA)
framework, which contains a single crystallographically-distinct lattice
tetrahedral site (T-site) that allows clarifying how synthesis conditions
influence Al proximity, and in turn, how H<sup>+</sup> site proximity
influences catalysis independent of T-site location. </p>
<p> Selective quantification of the
number and type of H<sup>+</sup> site ensembles present in a given zeolite
allows for more rigorous normalization of reaction rates by the number of active
sites, but also for probing the number and identity of active sites on
bifunctional catalysts that contain mixtures of Brønsted and Lewis acid sites. Gaseous
NH<sub>3</sub> titrations can be used to count the total number of protons on small-pore
CHA zeolites, which are inaccessible to larger amine titrants (e.g., pyridine,
alkylamines), and can be used to quantify the exchange stoichiometry of extraframework
metal cations (e.g., Cu<sup>2+</sup>, [CuOH]<sup>+</sup>) that are stabilized at
different framework Al arrangements. Additionally, paired Al sites in CHA zeolites
can be titrated selectively by divalent Co<sup>2+</sup> cations, whose sole
presence is validated by measuring UV-Visible spectra, counting residual
protons after Co<sup>2+</sup> exchange, and titration of paired Al with other
divalent cations (e.g., Cu<sup>2+</sup>). These different titration procedures
enabled reliable and reproducible quantification of different Al arrangements,
and recognition of the effects of different synthetic methods on the resulting arrangement
of framework Al atoms in CHA zeolites. </p>
<p>Upon
the advent of this suite of characterization and titration tools, different
synthetic methods were developed to crystallize CHA zeolites at constant
composition (e.g., Si/Al = 15) but with systematic variation in their paired Al
content. The substitution of N,N,N-trimethyl-1-adamantylammonium (TMAda<sup>+</sup>)
cations for Na<sup>+</sup> in the synthesis media (Na<sup>+</sup>/TMAda<sup>+</sup><2),
while holding all other synthetic variables constant, resulted in CHA zeolites
of similar composition (Si/Al = 15) and organic content (ca. 1 TMAda<sup>+</sup>
per cage), but with percentages of paired Al (0-44%) that increased with the
total amount of sodium retained on the zeolite product. This result suggests
that sodium atoms are occluded near the ammonium group of TMAda<sup>+</sup> leading
to the formation of a paired Al site. Replacement of Na<sup>+</sup> by other
alkali cations in the synthesis media allowed for the crystallization of CHA (Si/Al
= 15) at higher ratios of alkali to TMAda<sup>+ </sup>than accessible by Na<sup>+</sup>,
likely due to the ability of different alkali cations to favor (or inhibit)
crystallization of other zeolite phases. Incorporation of different alkali
cations during CHA crystallization influences the formation of paired Al sites
in different ways, likely reflecting the nature of different alkali to
preferentially occupy different positions within the CHA framework. <i>Ab initio</i> molecular dynamics simulations
were used to assess the stability of various Al-Al arrangements in the presence
of combinations of alkali and TMAda<sup>+</sup> cations, and provide
thermodynamic insight into electrostatic interactions between cationic
structure-directing agents that stabilize paired Al sites in CHA. </p>
<p> Using these synthetic procedures to
prepare CHA zeolites of similar composition, but with varied arrangements of
framework Al, the catalytic consequences of framework Al arrangement were
investigated using acid and redox catalysis. The low-temperature (473 K) selective
catalytic reduction of NOx with NH<sub>3</sub> (NH<sub>3</sub>-SCR) was
investigated over Cu-exchanged CHA zeolites containing various Al arrangements.
Cu cations exchange as both divalent Cu<sup>2+</sup> and monovalent [CuOH]<sup>+</sup>
complexes, which exchange at paired and isolated Al sites, respectively, and
turnover with similar SCR rates (473 K). <i>In
situ</i> and <i>operando</i> X-ray
absorption spectroscopy (XAS) were used to monitor the oxidation state and
coordination environment of Cu as a function of time and environmental
conditions. Rationalization of these experimental observations by first-principles
thermodynamics and <i>ab initio</i>
molecular dynamics simulations revealed that both Cu<sup>2+</sup> and [CuOH]<sup>+</sup>
complexes are solvated by NH<sub>3</sub> and undergo reduction to Cu<sup>+</sup>
upon oxidation of NO with NH<sub>3</sub>. Cu<sup>+</sup> cations become mobilized
by coordination with NH<sub>3</sub> under reaction conditions (473 K,
equimolar NO and NH<sub>3</sub> feed), and activate O<sub>2</sub> through a
dicopper complex formed dynamically during reaction. These results implicate
the spatial density of nominally site-isolated Cu cations and, in turn, the
arrangement of anionic framework Al atoms that anchor such cationic Cu
complexes, influence the kinetics of O<sub>2</sub> activation in selective
oxidation reactions, manifested as SCR rates (per 1000 A<sup>3</sup>) that
depend quadratically on Cu density (per 1000 A<sup>3</sup>) and become
rate-limiting processes in practice at low temperatures.</p>
<p>Furthermore,
first-order and zero-order rate constants (415 K, per H<sup>+</sup>) of
methanol dehydration, a probe reaction of acid strength and confinement effects
in solid Brønsted acids, are nearly one order of magnitude larger on paired
than on isolated protons in CHA zeolites, reflecting differences in prevalent
mechanisms and apparent enthalpic and entropic barriers at these different
active site ensembles. Yet, these differences in rate constants and activation
parameters at isolated and paired protons do not persist within larger pore
zeolites (e.g., MFI). <i>In situ </i>IR
spectra measured during steady-state methanol dehydration catalysis (415 K,
0.05-22 kPa CH<sub>3</sub>OH) reveal that surface methoxy species are present
in CHA zeolites containing paired protons, but not in CHA zeolites containing
only isolated protons or MFI zeolites, providing evidence that sequential dehydration
pathways via methoxy intermediates become accessible on paired protons in CHA.
Density functional theory is used to provide atomistic detail of confined
intermediates and transition states at isolated and paired protons in CHA and
MFI zeolites, indicating that paired protons in CHA preferentially stabilize
dehydration transition states that are partially-confined within the 8-membered
ring (8-MR) of CHA. These findings provide evidence that catalytic diversity
for the same stoichiometric reaction among zeolites of fixed structure and
composition, even for frameworks containing a single T-site, can be introduced
deliberately through synthetic control of the atomic arrangement of matter. </p>
|
416 |
Vliv volby léčebného postupu na výsledek léčby, náklady na hospitalizaci, posthospitalizační péči a kvalitu života pacientů přeživších akutní otravu metanolem. / Role of therapeutic approach in the treatment outcome, hospital costs, one-year post-hospital medical costs and quality of life in the patients who survived acute methanol poisoning.Rulíšek, Jan January 2021 (has links)
(English) Background: Methanol poisoning is severe medical condition with a need of urgent intensive treatment. Mass poisoning outbreak took place in the Czech Republic in 2012-2013. Costs of hospital treatment of methanol poisoning present significant financial burden to healthcare systems. The effect of treatment modality choice on clinical outcome and healthcare costs is not known, as well as its impact on the quality of life of methanol poisoning survivors after hospital discharge. Aim: To compare different therapeutic methods, choice of antidote (fomepizole versus ethanol) and extracorporeal elimination method (intermittent vs. continuous dialysis) for optimizing clinical outcome, cost-effectiveness, hospital costs, post-discharge costs, and the quality of life in survivors. Methods: For prospective cohort study, all patients hospitalized with acute methanol poisoning were included (n=106); for hospital and one-year healthcare costs study, all survivors of acute methanol poisoning (n=83) were included. For longitudinal quality of life study all survivors with informed consent (n=54) and control group of chronic alcohol abusers, age- and gender-balanced, without history of methanol poisoning (n=23), were included. Results: Comparative data of clinical effectiveness of elimination techniques...
|
417 |
Studium oxidace CO a metanolu za vysokého tlaku na katalyzátorech ve formě nanoprášků oxidů kovů vzácných zemin a tenkých vrstev na bázi platiny / High pressure CO and methanol oxidation study over nanopowders Rare Earth Oxides and platinum thin film catalystsRednyk, Andrii January 2016 (has links)
Title: High pressure CO and methanol oxidation study over nanopowder Rare Earth Oxides and platinum thin film catalysts Author: Mgr. Andrii Rednyk Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Vladimír Matolín, DrSc. matolin@mbox.troja.mff.cuni.cz Abstract: This doctoral thesis focuses on reactivity study of nanopowder rare earth oxides (REOs) and platinum based thin film catalysts using microreactor with high pressure reaction cell. REOs nanoparticles were prepared by new approach based on sol-gel chemistry. Magnetron sputtering technique was used for preparation of thin film samples. In the first part of the thesis CO oxidation on REOs and on Pt, PtOx thin films were performed. Among prepared REOs catalyst better activity exhibited alumina stabilized ceria, due to higher surface area. Both Pt and PtOx deposited on silicon substrate exhibited similar activity. When carbon (G-foil or C interlayer) is used as support, activity of Pt thin film decreases while PtOx preserves high activity. In the second part of the thesis steam reforming of methanol (SRM) and partial oxidation of methanol (POM) were performed on Pt thin films. It was shown that PtOx thin film exhibited superior activity compared to other samples with the same thickness. It is due to the reduction of platinum...
|
418 |
Studium interakce systémů oxid ceru-kov s plyny - oxidace oxidu uhelnatého a dekompozice metanolu / Study of cerium oxide-metal interaction with gases - carbon monoxide oxidation and methanol decompositionKolářová, Tatiana January 2016 (has links)
Title: Study of cerium oxide-metal intraction with gases - carbon monoxide oxidation and methanol decomposition Author: Tatiana Kolářová Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Václav Nehasil, Dr., Department of Surface and Plasma Science Abstract: Dissertation thesis is focused on the study of two catalytic systems on the basis of cerium oxide-metal. The systems were characterized by various methods of surface analysis. The first part of the work concerns influence of the preparation parameters on the character of gold nanoparticles deposited onto the sputtered cerium oxide layers from a solution. Catalytic activity of prepared Au/CeOx/(C)/Si systems, containing particles with the mean sizes of 4- 10 nm, was tested toward CO oxidation at atmospheric pressure. The results show that with increasing amount of gold present on the samples, also the productivity of CO2 during the reactions grows. The work is further focused on the preparation of an inverse model CeOx/Pt(111) system. On this system, adsorption of methanol at low temeperatures and its decomposition during a heating was studied. It is apparent from presented results that the decomposition of methanol on the inverse CeOx/Pt(111) systems behaves in a different way than on a clean platinum sample or a thick...
|
419 |
Studium tenkovrstvových katalyzátorů pro redukci kyslíku na katodách palivových článků s polymerní membránou / Study of thin film catalysts for oxygen reduction reaction on proton exchange membrane fule cell cathodeKomárková, Zuzana January 2017 (has links)
In this thesis, we present the investigation of influence of methanol crossover, which significantly decreases the performance of DMFC (Direct Methanol Fuel Cell). Additionally the poisoning effect occurs on the cathode side. The durability of cathode catalyst exposed by methanol vapor is studied. Moreover, the regene- rative behavior after exposition has been found. The comparison of commercial catalyst with our own sputtered Pt and PtCo and PtRu thin layers as cata- lyst is presented. Obtained results have shown that PtCo is reasonable compro- mise between pure Pt, which has high performance, and PtRu, which is tolerant to methanol poisoning. Future research should further evaluate the advantages of PtCo cathode catalyst prepared by standard procedures and its market poten- tial in comparison with PtRu. 1
|
420 |
Visualization of cavitation and investigation of cavitation erosion in a valveKrahl, Dominik, Weber, Jürgen, Fuchs, Maik January 2016 (has links)
Avoiding cavitation and especially cavitation erosion are tasks, which have to be considered when working with hydraulics. State of the art is the assessment of the risk of erosion by component testing or to completely avoid cavitation by means of CFD. Another reliable method to assess the risk of cavitation erosion is until now not available. This paper deals with this problem and delivers comparative values for a later method development. In a first step the cavitation of a poppet valve, which controls a methanol flow, is visualized. The resulting three cavitation appearances are deeply examined. After that the results of long-term tests at different operation conditions are presented. A poppet surface analysis following each experiment has shown different types of surface attacks. As a result of this work it is shown that both cavitation appearance and surface attack are strongly influenced by the temperature dependent air solubility of the liquid.
|
Page generated in 0.0495 seconds