Synthesis, structural order and magnetic behavior of self-assembled epsilon-Co nanocrystal arrays

The synthesis of magnetic nanoparticles with monodispere size distributions, their self assembly into ordered arrays and their magnetic behavior as a function of structural order (ferrofluids and 2D assemblies) are presented. Magnetic colloids of monodispersed, passivated, cobalt nanocrystals were produced by the rapid pyrolysis of cobalt carbonyl in solution. The size, size distribution (std. dev.< 5%) and the shape of the nanocrystals were controlled by varying the surfactant, its concentration, the reaction rate and the reaction temperature. The Co particles are defect-free single crystals with a complex cubic structure related to the beta phase of manganese (epsilon-Co). In the 2D assembly, a collective behavior was observed in the low-field susceptibility measurements where the magnetization of the zero field cooled process increases steadily and the magnetization of the field cooling process is independent the temperature. This was different from the observed behavior in a sample comprised of disordered interacting particles. A strong paramagnetic contribution appears at very low temperatures where the magnetization increases drastically after field cooling the sample. This has been attributed to the Co surfactant-particle interface since no magnetic atomic impurities are present in these samples.

Three-dimensional model of bubbling fluidized bed combustion

 Diplomityön tarkoituksena on kehittää kolmiulotteinen malli kerrosleijupoltolle. Työn kirjallisuusosa sisältää seuraavat perusteet kerrosleijupolton tekniikasta: yleistiedot, leijutus- ja palamisilmiöt, kiinteän aineen ja kaasun sekoittuminen, päästöt ja lämmönsiirto. Lisäksi palamissysteemin mallinnuksen perusteet ja ratkaisumenetelmät ovat esitelty. Työn mallinnusosassa kehitetty koodi on ohjelmoitu Fortran-ohjelmointikielellä. Kehitetty malli perustuu olemassa olevaan malliin kiertoleijupoltosta. Yhtälö kiintoainekonsentraatioprofiilille on vaihdettu ja kiertovirta on poistettu koodista. Mallilla on tehty herkkyystarkasteluja polttoaineen ja kaasun sekoittumisen sekä reaktiokertoimen vaikutukselle. Visualisointi on tehty ohjelmassa Tecplot 360 ja mallinnustuloksia on vertailtu mitattuihin tuloksiin. Mallin laskemattulokset vastaavat hyvin mittaustuloksia ja kokemusperäisiä tietoja; monissa tapauksissa malli pystyy kvantitatiivisesti kuvaamaan parametrien variointia ja kaikissa tapauksissa malli antaa ainakin kvalitatiivisesti oikeita tuloksia. Työhön liittyvän kehityksen ja mallinnuskokemuksen perusteella on tehty ehdotukset mallin tulevaa kehitystä ja mittauksia varten.

Implementation of population balances in simulation of gas-liquid reactors using a CFD-PBM coupled approach

In bubbly flow simulations, bubble size distribution is an important factor in determination of hydrodynamics. Beside hydrodynamics, it is crucial in the prediction of interfacial area available for mass transfer and in the prediction of reaction rate in gas-liquid reactors such as bubble columns. Solution of population balance equations is a method which can help to model the size distribution by considering continuous bubble coalescence and breakage. Therefore, in Computational Fluid Dynamic simulations it is necessary to couple CFD and Population Balance Model (CFD-PBM) to get reliable distribution. In the current work a CFD-PBM coupled model is implemented as FORTRAN subroutines in ANSYS CFX 10 and it has been tested for bubbly flow. This model uses the idea of Multi Phase Multi Size Group approach which was previously presented by Sha et al. (2006) [18]. The current CFD-PBM coupled method considers inhomogeneous flow field for different bubble size groups in the Eulerian multi-dispersed phase systems. Considering different velocity field for bubbles can give the advantageof more accurate solution of hydrodynamics. It is also an improved method for prediction of bubble size distribution in multiphase flow compared to available commercial packages.

Early intervention for conversion disorder: neurologists and psychiatrists working together

It has been shown that for the reaction catalyzed by "biodegradative" L-threonine dehydratase from E. coli strains K-12 and 980 in 0.5 M phosphate-carbonate buffer, pH 8.4 and pH 9.5, the plots of initial reaction rate (v) versus the initial substrate concentration ([S]0 are characterized by several inflection points, i. e. an intermediate plateau. The plot of v versus the allosteric activator (AMP) concentration have very complicated shapes: there are several inflection points, and also the maximum at L-threonine concentration equal to 3-10(2) and 5-10(-2) M. High AMP concentrations inhibit the enzyme at high substrate concentrations. The reduced glutathion dose not influence the enzyme and does not alter the activating effect of AMP. On the basis of the data obtained it is proposed that the substrate and AMP shift the equilibrium between multiple oligomeric enzyme forms differing in catalytic activity and kinetic manifestations of allosteric interactions between the active and allosteric AMP-binding sites towards polymerization. Thus, the functioning the enzyme under study is discussed in the frames of the model of dissociating regulatory enzymes with multiple intermediate oligomeric forms.

Ion-exchange resins as stationary phase in reactive chromatography

Dynamic behavior of bothisothermal and non-isothermal single-column chromatographic reactors with an ion-exchange resin as the stationary phase was investigated. The reactor performance was interpreted by using results obtained when studying the effect of the resin properties on the equilibrium and kinetic phenomena occurring simultaneously in the reactor. Mathematical models were derived for each phenomenon and combined to simulate the chromatographic reactor. The phenomena studied includes phase equilibria in multicomponent liquid mixture¿ion-exchange resin systems, chemicalequilibrium in the presence of a resin catalyst, diffusion of liquids in gel-type and macroporous resins, and chemical reaction kinetics. Above all, attention was paid to the swelling behavior of the resins and how it affects the kinetic phenomena. Several poly(styrene-co-divinylbenzene) resins with different cross-link densities and internal porosities were used. Esterification of acetic acid with ethanol to produce ethyl acetate and water was used as a model reaction system. Choosing an ion-exchange resin with a low cross-link density is beneficial inthe case of the present reaction system: the amount of ethyl acetate as well the ethyl acetate to water mole ratio in the effluent stream increase with decreasing cross-link density. The enhanced performance of the reactor is mainly attributed to increasing reaction rate, which in turn originates from the phase equilibrium behavior of the system. Also mass transfer considerations favor the use ofresins with low cross-link density. The diffusion coefficients of liquids in the gel-type ion-exchange resins were found to fall rapidly when the extent of swelling became low. Glass transition of the polymer was not found to significantlyretard the diffusion in sulfonated PS¿DVB ion-exchange resins. It was also shown that non-isothermal operation of a chromatographic reactor could be used to significantly enhance the reactor performance. In the case of the exothermic modelreaction system and a near-adiabatic column, a positive thermal wave (higher temperature than in the initial state) was found to travel together with the reactive front. This further increased the conversion of the reactants. Diffusion-induced volume changes of the ion-exchange resins were studied in a flow-through cell. It was shown that describing the swelling and shrinking kinetics of the particles calls for a mass transfer model that explicitly includes the limited expansibility of the polymer network. A good description of the process was obtained by combining the generalized Maxwell-Stefan approach and an activity model that was derived from the thermodynamics of polymer solutions and gels. The swelling pressure in the resin phase was evaluated by using a non-Gaussian expression forthe polymer chain length distribution. Dimensional changes of the resin particles necessitate the use of non-standard mathematical tools for dynamic simulations. A transformed coordinate system, where the mass of the polymer was used as a spatial variable, was applied when simulating the chromatographic reactor columns as well as the swelling and shrinking kinetics of the resin particles. Shrinking of the particles in a column leads to formation of dead volume on top of the resin bed. In ordinary Eulerian coordinates, this results in a moving discontinuity that in turn causes numerical difficulties in the solution of the PDE system. The motion of the discontinuity was eliminated by spanning two calculation grids in the column that overlapped at the top of the resin bed. The reactive and non-reactive phase equilibrium data were correlated with a model derived from thethermodynamics of polymer solution and gels. The thermodynamic approach used inthis work is best suited at high degrees of swelling because the polymer matrixmay be in the glassy state when the extent of swelling is low.

Pitkäketjuisten keteenien valmistusreaktiot ja kinetiikka.

Tämän diplomityön tarkoituksena oli tutkia pitkäketjuisten rasvahappokloridien ja alkyyliketeenidimeerien (AKD) valmistusreaktioiden kinetiikkaa. Työn tavoitteena oli saada mittaustuloksia, joiden perusteella voitaisiin kehittää reaktioille kineettinen kineettinen malli ja suorittaa valmistusprosessien alustava optimointi. Teoreettisessa osassa on selvitetty rasvahappokloridien ja alkyyliketeenidimeerien (AKD) eri valmistustapoja. Lisäksi on perehdytty tarkemmin rasvahappokloridien dehydrohalogenointireaktioiden reaktiomekanismeihin ja valmistusprosessin problematiikkaan. Kokeellisessa osassa tutkittiin rasvahappokloridien valmistusta klooraamalla öljyhappoa 30 mol-% fosforitrikloridiylimäärällä lämpötiloissa 45, 50 ja 55OC. Alkyyliketeenidimeerien valmistusta tutkittiin dehydrohalogenoimalla palmitiini- ja öljyhappokloridia 0-30 mol-% trietyyliamiiniylimäärällä inertissä liuottimessa, lämpötiloissa 45 ja 50OC. Reaktiot toteutettiin puolipanosreaktiona, joissa reaktioastiassa olevaan reagenssin ja liuottimen seokseen lisättiin lähtöaine tasaisena massavirtana. Reaktioiden etenemistä seurattiin FT-IR- ja GC-analyysien avulla. Kalorimetrisilla kokeilla tutkittiin öljyhappokloridin dimeroitumisreaktion reaktiolämmön muodostumista ja UV-VIS-analyyseillä seurattiin öljyhappokloridin vanhenemista. Öljyhappokloridin valmistusreaktiolle saatiin hyvä kineettinen malli. Kineettisen mallin puutteena voidaan pitää sitä, ettei kokeissa saatu tietoa mahdollisten sivutuotteiden muodostumisesta. Sovitusohjelmalla saatiin sovitettua estimaatit reaktionopeusvakioille lämpötiloissa 45, 50 ja 55OC. Happokloridien dimeroitumisreaktioiden kineettisen mallin sopivuudelle saatiin suhteellisen hyvä kuva Kuten öljyhappokloridin tapauksessa, myöskään AKD:n valmistusreaktioissa syntynyt sivutuotteita, joten niiden osuutta oletettuun kineettiseen malliin ei tunneta. Sovitusohjelmalla saatiin sovitettua estimaatit reaktionopeusvakioille lämpötiloissa 45 ja 50OC.

Jätevesilaitosten mallinnus

TäTässä työssä tarkastellaan jäteveden biologiseen puhdistukseen käytettävän aktiiviliete-prosessin kuvaamista matemaattisen mallintamisen avulla. Jäteveden puhdistus on jo vanha keksintö ja aktiivilieteprosessikin on otettu ensimmäisen kerran pilot- käyttöön vuonna 1914. Myös jätevesilaitosten matemaattinen mallintaminen on ollut pitkään tunnettu tekniikka ja ensimmäiset dynaamiset mallit kehitettiin 1950–luvulla. Työn alkuosassa on tarkasteltu jätevesilaitosten matemaattista mallintamista kirjallisuus-lähteiden pohjalta. Tarkastelun painopiste on suunnattu erilaisiin matemaattisiin malleihin ja mallintamisen kehitykseen. Mallintamisen ohessa on kiinnitetty huomiota aktiiviliete-prosessiin ja siihen vaikuttaviin tekijöihin. Mallintamiseen vaikuttavista tekijöistä erityistä huomiota on kiinnitetty ilmastukseen, bakteerien kasvuun ja selkeytykseen sekä niiden vaikutuksiin prosessin kannalta. Matemaattisen mallintamisen tarkastelun jälkeen työssä on pohdittu CFD–mallintamisen hyödyntämismahdollisuuksia aktiivilieteprosessien kuvaamisessa. Mallintamisosiossa on tarkasteltu Activated Sludge Model No. 3 (ASM 3) mallin rakennetta ja sisältöä sekä sen eri tekijöiden vaikutuksia malliin. Työn tässä osassa on tarkasteltu myös hapensiirtoa ilmastuksessa ilmakuplista veteen ja selkeytystä osana aktiivilieteprosessia. Tässä osiossa on käyty läpi myös kaikki prosessin kannalta oleelliset yhtälöt, esimerkiksi reaktionopeus- ja massataseyhtälöt.

Sinkkirikasteen liuotusprosessin kineettinen mallinnus

Työssä on tehty kineettinen simulointimalli sinkkirikasteen liuotusprosessista. Prosessi on pieni osa Kokkolan sinkinvalmistusprosessia, jonka muita osia ovat: pasutus, neutraaliliuotus, konversio, liuospuhdistus ja elektrolyysi. Rikasteen liuotukseen tulee konversioprosessin liuos ja liuotuksesta lähtevä neste menee takaisin neutraaliliuotukseen. Saostunut jarosiitti läjitetään. Kokkolan liuotusprosessi koostuu liettoreaktorista ja kahdesta neljän liuotusreaktorin sarjasta. Liuotukseen syötetään paluuhappoa liettoreaktoriin ja liuotuspiirien ensimmäisiin liuotusreaktoreihin. Happea syötetään kaikkiin liuotusreaktoreihin. Prosessin mallintamiseen käytettiin Aspen Plus-simulointiohjelmaa, johon pystyttiin syöttämään kineettisiä yhtälöitä. Reaktionopeusyhtälöitä käytettiin raudan hapetuksen, sulfidien liuotuksen ja jarosiitiin saostumisen mallintamiseen, eli kaikkiin liuotusreaktoreissa tapahtuviin reaktioihin. Kineettiset yhtälöt etsittiin kirjallisuudesta. Liettoreaktori puolestaan mallinnettiin syöttämällä ohjelmaan reaktioyhtälöt ja antamalla niille etenemisasteet. Jarosiitin liukenemisesta työssä on tehty laboratoriokokeita, koska aiheesta ei kirjallisuudesta löytynyt kineettistä tietoa. Liuotuskokeissa käytetyn kiintoaineen kuitenkin todettiin sisältävän liikaa götiittiä, että tuloksista olisi voitu laskea kinetiikkaa jarosiitin liukenemiselle. Simulointimallilla laskettiin yksi tapaus vertailukohdaksi, johon malliin tehtyjä muutoksia verrattiin. Mallilla tutkittiin konversiosta tulevan jarosiitin määrän vaikutusta, reaktorikoon merkitystä ja rikasteen liuotuksen sekä jarosiitin saostuksen reaktionopeuksien muutoksen vaikutuksia. Käytetyillä kineettisillä yhtälöillä reaktioiden todettiin tarvitsevan vain ¾ käytetystä reaktiotilavuudesta, rikasteen liuotusnopeuden kohtalaisen pienellä hidastamisen todettiin vähentävän sinkin saantoa ja jarosiitin saostuksen reaktionopeuden kasvulla todettiin myös olevan negatiivinen vaikutus sinkin saantoon. Simulointimallissa käytettyjen reaktionopeusyhtälöiden varmentaminen kokeilla todettiin tarpeelliseksi, sillä jo kohtalaisen pienillä muutoksilla havaittiin olevan merkitystä prosessin toimivuuteen. Lisäksi todettiin jarosiitin liukenemisen huomioimisen olevan tarpeen.

Ozonólise das ligninas organossolve e kraft eucalipto. Parte II: cinética nos meios ácido e básico

Organosolv and kraft lignins were treated with ozone both in basic and acid media and the reaction was studied kinetically. In contrast to reported studies, ozone was more efective in basic medium. Kraft lignin was degraded faster than organosolv lignin in both media but in the basic medium the rate of reaction was very much faster than in the acid one: for kraft lignin, the observed degradation was 93% for 2 min of reaction in the basic medium and 56% for 10 min of reaction in the acid medium; for organosolv lignin, 47% and 25%, respectively, in the same times. Higher phenolic hydroxyl groups contents increase the reaction rate.

Essential factors for control of the equilibrium in the reversible rearrangement of M3N@Ih-C80 fulleropyrrolidines: Exohedral functional groups versus endohedral metal clusters

The effects of exohedral moieties and endohedral metal clusters on the isomerization of M3N@Ih-C80 products from the Prato reaction through [1,5]-sigmatropic rearrangement were systematically investigated by using three types of fulleropyrrolidine derivatives and four different endohedral metal clusters. As a result, all types of derivatives provided the same ratios of the isomers for a given trimetallic nitride template (TNT) as the thermodynamic products, thus indicating that the size of the endohedral metal clusters inside C80 was the single essential factor in determining the equilibrium between the [6,6]-isomer (kinetic product) and the [5,6]-isomer. In all the derivatives, the [6,6]- and [5,6]-Prato adducts with larger metal clusters, such as Y3N and Gd3N, were equally stable, which is in good agreement with DFT calculations. The reaction rate of the rearrangement was dependent on both the substituent of exohedral functional groups and the endohedral metal-cluster size. Further DFT calculations and 13C NMR spectroscopic studies were employed to rationalize the equilibrium in the rearrangement between the [6,6]- and [5,6]-fulleropyrrolidines

Triggering the generation of an iron(IV)-oxo compound and its reactivity toward sulfides by RuII photocatalysis

The preparation of [FeIV(O)(MePy2tacn)]2+ (2, MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) by reaction of [FeII(MePy2tacn)(solvent)]2+ (1) and PhIO in CH3CN and its full characterization are described. This compound can also be prepared photochemically from its iron(II) precursor by irradiation at 447 nm in the presence of catalytic amounts of [Ru II(bpy)3]2+ as photosensitizer and a sacrificial electron acceptor (Na2S2O8). Remarkably, the rate of the reaction of the photochemically prepared compound 2 toward sulfides increases 150-fold under irradiation, and 2 is partially regenerated after the sulfide has been consumed; hence, the process can be repeated several times. The origin of this rate enhancement has been established by studying the reaction of chemically generated compound 2 with sulfides under different conditions, which demonstrated that both light and [Ru II(bpy)3]2+ are necessary for the observed increase in the reaction rate. A combination of nanosecond time-resolved absorption spectroscopy with laser pulse excitation and other mechanistic studies has led to the conclusion that an electron transfer mechanism is the most plausible explanation for the observed rate enhancement. According to this mechanism, the in-situ-generated [RuIII(bpy)3] 3+ oxidizes the sulfide to form the corresponding radical cation, which is eventually oxidized by 2 to the corresponding sulfoxide

Cinética de redução do catalisador CuO/ZnO/Al2O3

The reduction kinetics of a CuO/ZnO/Al2O3 catalyst by hydrogen was investigated isothermally and by temperature programmed reduction (TPR). Two reducible Cu2+ species were detected; the first one was identified as CuO bulk and the other as Cu2+ strongly interacting with alumina, possibly in the form of copper aluminate. The activation energies for the reduction of these two species were 60 and 90 kJ mol-1, respectively, and the reaction order with respect to hydrogen was one. The isothermal reduction data showed that the isotropic growth model is the most appropriate to describe the reaction rate data for both Cu2+ species.

Degradação fotocatalítica do fungicida tebuconazole em solução aquosa

The tebuconazole photocatalytic degradation kinetics was studied in a batch reactor using TiO2 (P25-Degussa) as catalyst and a high pressure mercury lamp. The photolysis, adsorption and irradiation effects in the reaction rate were evaluated. Afterward, the suspension catalyst concentration and initial pH to the maximum reaction rate was determined. It was observed that the reaction rate can be approached by a pseudo-first order, with a maximum kinetics constant at 260 mg L-1catalyst concentration and pH 7.7.

Effect of temperature on the electro-oxidation of ethanol on platinum

We present in this work an experimental investigation of the effect of temperature (from 25 to 180 ºC) in the electro-oxidation of ethanol on platinum in two different phosphoric acid concentrations. We observed that the onset potential for ethanol electro-oxidation shifts to lower values and the reaction rates increase as temperature is increased for both electrolytes. The results were rationalized in terms of the effect of temperature on the adsorption of reaction intermediates, poisons, and anions. The formation of oxygenated species at high potentials, mainly in the more diluted electrolyte, also contributes to increase the electro-oxidation reaction rate.

Determinação de parâmetros cinéticos em fluxo com câmara de gradiente e deteção espectrofotométrica: aplicação à reação entre o violeta de cristal e o ião hidróxido

A didactic experiment is proposed aimed to extend the Flow Injection Analysis (FIA) based methodology to the area of physical chemistry/chemical reactors for undergraduate labs. Our prime objective was to describe the use of a gradient chamber for determination of the rate constant for the reaction between crystal violet and the hydroxide ion. The study was complemented by determining the effect of temperature on the rate constant. The kinetic parameters, activation energy and reaction rate constant are determined based on an assumption of rate orders. The main didactic advantages of the proposed experimental set-up are the use of less reagents, contributing to a more environmental friendly experiment. The experiment illustrates also the reduction of associated errors and time by using automated analysis owing to decreased operator manipulation.