THE FORMATION MECHANISM OF THE VITRIFIED SLAG IN A PLASMA ARC REACTOR FOR HAZARDOUS WASTE TREATMENT

Various hazardous wastes with additives have been vitrified to investigate the formation mechanism of the glassy slag by a 30 kW DC plasma-arc reactor developed by the Institute of Mechanics, Chinese Academy of Sciences. The average temperature in the reaction area is controlled at 1500°C. The chemical compositions of three sorts of fly ashes are analyzed by XRF (X-Ray Fluorescence). Fly ashes with vitrifying additives can be vitrified to form glassy slag, which show that the ratio of the whole oxygen ions to the whole network former ions in glass (R) is appropriate in the range of 2~3 to form durable vitrified slag. In this experiment, the arc power is controlled below 5 kW to inhibit waste evaporation. To enhance the effects of heat transfer to wastes, ferrous powder has been added into the graphite crucible, which aggregates as ingot below the molten silicate after vitrification. The slag fails to form glass if the quenching rate is less than 1 K/min. Therefore, the slag will break into small chips due to the sharp quenching rate, which is more than 100 K/sec.

The photochemistry of dioxorhenium(V)

The excited-state properties of trans-ReO₂(py)₄⁺ (ReO₂⁺) in acetonitrile solution have been investigated. The excited-state absorption spectrum of ReO₂⁺ is dominated by bleaching of the ground state MLCT and d-d systems. The reduction potential of ReO₂^2+/+* is estimated from emission and electrochemical data to be -0.7 V (SSCE). The ReO₂⁺ excited state efficiently reduces methylviologen and other pyridinium and olefin acceptors. The resulting Re(VI) species oxidizes secondary alcohols and silanes. Acetophenone is the product of sec-phenethyl alcohol oxidation.

The emission properties of ReO₂⁺ in aqueous solutions of anionic and nonionic surfactants have been investigated. The emission and absorption maxima of ReO₂⁺ are dependent on the water content of its environment. Emission lifetimes vary over four orders of magnitude upon shifting from aqueous to nonaqueous environments. The emission lifetime has a large (8.6) isotope effect (k(H₂O)/k(D₂O)) that reflects its sensitivity towards the environment. These properties have been used to develop a model for the interactions of ReO₂⁺ with sodium dodecyl sulfate (SDS). A hydrophobic ReO₂⁺ derivative, ReO₂(3-Ph-py)₄⁺, has been used to probe micelles of nonionic surfactants, and these results are consistent with those obtained with SDS.

The emission properties of ReO₂⁺ in Nafion perfluorosulfonated membranes have been investigated. Absorption and emission spectroscopy indicate that the interior of the membrane is quite polar, similar to ethylene glycol. Two well-resolved emission components show different lifetimes and different isotope effects, indicative of varying degrees of solvent accessibility. These components are taken as evidence for chemically distinct regions in the polymer film, assigned as the interfacial region and the ion cluster region.

The unsubstituted pyridine complex shows monophasic, τ = 1.7 µs, emission decay when bound to calf thymus DNA. Switching to the 3-Ph-py complex yields a biphasic emission decay (τ₁ = 2.4 µs, τ₂ = 10 µs) indicative of an additional, solvent-inaccessible binding mode. Photoinduced electron transfer to methylviologen leads to oxidative cleavage of the DNA as detected by gel electrophoresis. Electrochemical and spectrophotometric techniques used with organic substrates also can be used to monitor the oxidation of DNA. Abstraction of the ribose 4' hydrogen by ReO₂²⁺ is a possible mechanism.

Studies in nuclear reactor dynamics : I. The accuracy of point kinetics. II. The effect of delayed neutrons on the spectrum of the group-diffusion operator

This thesis is a theoretical work on the space-time dynamic behavior of a nuclear reactor without feedback. Diffusion theory with G-energy groups is used.

In the first part the accuracy of the point kinetics (lumped-parameter description) model is examined. The fundamental approximation of this model is the splitting of the neutron density into a product of a known function of space and an unknown function of time; then the properties of the system can be averaged in space through the use of appropriate weighting functions; as a result a set of ordinary differential equations is obtained for the description of time behavior. It is clear that changes of the shape of the neutron-density distribution due to space-dependent perturbations are neglected. This results to an error in the eigenvalues and it is to this error that bounds are derived. This is done by using the method of weighted residuals to reduce the original eigenvalue problem to that of a real asymmetric matrix. Then Gershgorin-type theorems .are used to find discs in the complex plane in which the eigenvalues are contained. The radii of the discs depend on the perturbation in a simple manner.

In the second part the effect of delayed neutrons on the eigenvalues of the group-diffusion operator is examined. The delayed neutrons cause a shifting of the prompt-neutron eigenvalue s and the appearance of the delayed eigenvalues. Using a simple perturbation method this shifting is calculated and the delayed eigenvalues are predicted with good accuracy.

Hydrogen-Atom Transfer Photochemistry of Tetrakis(µ-pyrophosphito)diplatinate(II)

In many senses, the hydrogen-atom transfer reactions observed with the triplet excited state of pyrophosphito-bridged platinum(II) dimers resemble the reactions of organic ketone nπ* states. The first two chapters describe our attempts to understand the reactivity differences between these two chromophores. Reactivity of the metal dimers is strongly regulated by the detailed nature of the ligands that ring the axial site, the hydrogen-abstraction center. A hydrogen-bonded network linking the ligands facilitates H-atom transfer quenching with alcohols through the formation of a hydrogen-bonded complex between the alcohol and a dimer. For substrates of equal C-H bond strength that lack a hydroxyl group (e.g., benzyl hydrocarbons), the quenching rate is several orders of magnitude slower.

The shape and size of the axial site, as determined by the ligands, also discriminate among quenchers by their steric characteristics. Very small quenchers quench slowly because of high entropies of activation, while very large ones have large enthalpic barriers. The two effects find a balance with quenchers of "just the right size."

The third chapter discusses the design of a mass spectrometer that uses positron annihilation to ionize neutral molecules. The mass spectrometer creates positron-molecule adducts whose annihilation produces fragmentation products that may yield information on the bonding of positrons in such complexes.

Mechanism and applications of the photochemistry of Bis(η^5-cyclopentadienyl)titanacyclobutanes

The photochemically induced reductive elimination of cyclopropanes from bis(η⁵-cyclopentadienyl)titanacyclobutanes has been examined. Stereochemical labelling studies indicate that the cyclopropane is initially formed in a 6±1:1, ratio favoring retention of stereochemistry. The starting titanacyclobutane is isomerized during the course of the reaction. The isomerization of the starting material results from metal-carbon bond homolysis to yield a 1,4-biradical, which can either close to give the starting material or generate cyclopropane. The 1,4-biradical can be observed through a cyclopropyl carbinyl rearrangement employing 2-bis(η⁵- cyclopentadienyl)titana-5,5-dimethylbicyclo[2.1.0]pentane, to give the titanium alkylidene, 1-bis(η⁵-cyclopentadienyl)titana-3,3-dimethyl-1,4- pentadiene, which can be observed directly by NMR at low temperature.

The oxidation of titanacyclobutanes by chemical and electrochemical methods also yields cyclopropanes. Reduction of the metal center does not yield cyclopropanes. Depending on the oxidant, stereochemically labelled titanacyclobutanes yield cyclopropanes that are between 7:1 and 100:1 retention:isomerization. The fragmentation reaction resembles the photochemically induced reductive elimination. Both result from formal oxidation of a metal-carbon bond, which then results in very rapid formation of cyclopropane.

The titanocene generated photochemically reacts with a variety of substrates even at low temperature. Titanocene can be generated in a glass at 77 K. The titanocene can be trapped in noncoordinating solvents in high yield with bulky internal acetylenes to give monoacetylene adducts of titanocene. Less bulky acetylenes give the titanacyclopentadienes. The titanocene can be trapped with olefins to give less stable adducts, which appear by NMR analysis to be intermediate in structure between a titanacyclopropane and an η² olefin adduct of titanocene. Reaction of titanocene with butadiene gives a stable product, which appears to be the s-trans butadiene adduct of titanocene. It does not isomerize on heating. Titanocene reacts with epoxides to give titanocene-µ-oxo polymer and olefin. Stereochemically labelled epoxides and episulfides yield isomerized olefin upon deoxygenation by titanocene. The observations are rationalized as a result of a 1,4-biradical formed by stepwise insertion of titanocene into a carbon-oxygen bond.

I. Nuclear magnetic resonance analysis of ferrocenylcarbonium ion. II. Ferrocene catalyzed photochemistry

I. Nuclear magnetic resonance spectra of appropriately substituted ferrocenylcarbonium ions reveal the α-protons of the substituted ring to be more shielded than β-protons. The observation is discussed in terms of various models proposed for the ferrocenylcarbonium ion and is found to support a model in which the iron is bonded to all six carbona of the substituted ring.

II. Ferrocene catalyzes the photoisomerization of the piperylenes and the photodimerization of isoprene. Our results suggest a mechanism in which a complex of ferrocene and diene is excited to its second singlet state which dissociates to a triplet-state ferrocene molecule and a triplet-state diene molecule. The triplet-state diene, then, proceeds to isomerize or attack ground-state diene to form dimers.

Estimation of catalyst activity profiles and deactivation parameters from reactor operating data with applications to naphtha reforming

Techniques are developed for estimating activity profiles in fixed bed reactors and catalyst deactivation parameters from operating reactor data. These techniques are applicable, in general, to most industrial catalytic processes. The catalytic reforming of naphthas is taken as a broad example to illustrate the estimation schemes and to signify the physical meaning of the kinetic parameters of the estimation equations. The work is described in two parts. Part I deals with the modeling of kinetic rate expressions and the derivation of the working equations for estimation. Part II concentrates on developing various estimation techniques.

Part I: The reactions used to describe naphtha reforming are dehydrogenation and dehydroisomerization of cycloparaffins; isomerization, dehydrocyclization and hydrocracking of paraffins; and the catalyst deactivation reactions, namely coking on alumina sites and sintering of platinum crystallites. The rate expressions for the above reactions are formulated, and the effects of transport limitations on the overall reaction rates are discussed in the appendices. Moreover, various types of interaction between the metallic and acidic active centers of reforming catalysts are discussed as characterizing the different types of reforming reactions.

Part II: In catalytic reactor operation, the activity distribution along the reactor determines the kinetics of the main reaction and is needed for predicting the effect of changes in the feed state and the operating conditions on the reactor output. In the case of a monofunctional catalyst and of bifunctional catalysts in limiting conditions, the cumulative activity is sufficient for predicting steady reactor output. The estimation of this cumulative activity can be carried out easily from measurements at the reactor exit. For a general bifunctional catalytic system, the detailed activity distribution is needed for describing the reactor operation, and some approximation must be made to obtain practicable estimation schemes. This is accomplished by parametrization techniques using measurements at a few points along the reactor. Such parametrization techniques are illustrated numerically with a simplified model of naphtha reforming.

To determine long term catalyst utilization and regeneration policies, it is necessary to estimate catalyst deactivation parameters from the the current operating data. For a first order deactivation model with a monofunctional catalyst or with a bifunctional catalyst in special limiting circumstances, analytical techniques are presented to transform the partial differential equations to ordinary differential equations which admit more feasible estimation schemes. Numerical examples include the catalytic oxidation of butene to butadiene and a simplified model of naphtha reforming. For a general bifunctional system or in the case of a monofunctional catalyst subject to general power law deactivation, the estimation can only be accomplished approximately. The basic feature of an appropriate estimation scheme involves approximating the activity profile by certain polynomials and then estimating the deactivation parameters from the integrated form of the deactivation equation by regression techniques. Different bifunctional systems must be treated by different estimation algorithms, which are illustrated by several cases of naphtha reforming with different feed or catalyst composition.

Evaluación de dosis de radiación producida por una pérdida de refrigerante en reactor nuclear.

EN]This is a document done to try to see the effect of a nuclear power plant accident. In particular, it studies what would be the radiation doses delivered to the people in the close areas around the power plant of Garoña, if it had suffered from a loss of coolant accident during its normal functioning.

Research on operating conditions at the catalytic reactor for the combined removal of NOx and PCDD/PCDFs from MWI plants

The management of municipal solid waste (MSW), particularly the role of incineration, is currently a subject of public debate. Incineration shows to be a good alternative of reducing the volume of waste and eliminating certain infectious components. Moreover, Municipal Waste Incinerators (MWI), are reported to be highly hygienic and apart from that MWIs are immediately effective in terms of transport (incinerators can be built close to the waste sources) and incineration's nature. Nevertheless, the emissions of many hazardous substances make the Municipal Waste Incineration (MWI) plants to be unpopular. Metals (especially lead, manganese, cadmium, chromium and mercury) are concentrated in fly and bottom ashes. Furthermore, incomplete combustion produces a wide variety of potentially hazardous organic compounds, such as aldehydes, polycyclic aromatic hydrocarbons (PAH), chlorinated hydrocarbons including polychlorinated dibenzodioxins (PCDD) and dibenzofurans (PCDF), and even acid gases, including NOx. Many of these hazardous substances are carcinogenic and some have direct systemic toxicity.