Influence of reaction products on the selective oxidation of ethene

The kinetics of the selective oxidation of ethene in air over an industrial silver on ¿-alumina catalyst were studied. Special attention was paid to the influence of the reaction products on the reaction rates of epoxidation and complete combustion. Kinetic data were obtained in two different types of internal recycle reactor and in a cooled tubular reactor, and were fitted separately to several reaction rate expressions based on different kinetic models. A Langmuir-Hinshelwood mechanism, in which adsorbed ethene reacts with adsorbed molecular oxygen, was chosen as the best kinetic model. The reaction products compete for adsorption on the active sites and reduce the rates of both reactions. Carbon dioxide enhances the selectivity towards ethene oxide, whereas water has almost no influence on the selectivity. The fitting of the three individual data sets obtained in the three reactors results in accurate, but different, reaction rate expressions, whereas the fitting of the three data sets simultaneously results in less accurate reaction rate expressions. The systematic deviations found may be explained, to some extent, by differences in the operating regimes in each reactor. The main reason for the deviations is probably the different catalyst activities in the three reactors caused by poisoning. The effect of the addition of products to the feed on the behaviour of the cooled tubular reactor can be described reasonably well by a mathematical model in which the kinetic equations obtained in the laboratory reactors are incorporated. The results of these simulations are sensitive to the kinetics used

A novel reactor for determination of kinetics for solid catalyzed gas reactions

A novel perfectly mixed laboratory reactor for determining kinetics of heterogeneously catalyzed gas-phase reactions has been developed. Perfect mixing is achieved by circulating the gas in the reactor using an axial flow impeller in a well streamlined enclosure. Pellets are fixed in a rectangular opening in the blades of the impeller. They rotate with the impeller, thus realizing high particle velocities in the reactor. Interparticle mass transfer was studied experimentally by vaporization of naphthalene pellets. The mass-transfer coefficient in the novel reactor was found to depend on the velocity of a particle in the reactor. Mass-transfer coefficients in an internal recycle reactor at equal impeller tip speeds are 4-6 times lower than those in the novel reactor, and conditions can be chosen easily where at higher rotational speeds the mass- and heat-transfer rates are 8-10 times higher than in classical recycle reactors. The recycle flow rate in a recycle reactor was found to depend strongly on the resistance to flow caused by the catalyst bed itself. The novel reactor was tested under reacting conditions using the hydrogenation of ethene

Determination of the kinetics of ethene epoxidation

Several problems and pitfalls in the use of laboratory reactors for the determination of the kinetics of ethene epoxidation over industrial silver on α-alumina catalyst are discussed. Also, commonly used methodologies for kinetic studies are dealt with because of the general nature of some problems. Some advice is given in choosing and using the appropriate reactor type. Further, a method is discussed to determine kinetics in a cooled tubular reactor without having to use heat transport relations.\ud \ud The activation and deactivation of the silver catalyst have been studied in a Berty-type reactor, in a novel internal recycle reactor and in a cooled tubular reactor. It was found necessary to activate the silver catalyst for approximately 170 reaction hours under reaction conditions to obtain a stable and reproducible catalyst activity. Thermal sintering was probably of importance in experiments at the maximum temperature of 543 K. Deliberate addition of small amounts of 1,2-dichloroethane resulted in rapid deactivation of the catalyst. The activity could be restored by addition of small amounts of ethane to the feed. Also, fluorine and silica have been shown to poison the catalyst. Differences in the behaviour of the catalyst in the three reactors may be attributed to the sensitivity of the catalyst towards tiny amounts of poisons present in the reactors and feed mixtures used

Symplectic reduction of quasi-morphisms and quasi-states

We prove that quasi-morphisms and quasi-states on a closed integral symplectic manifold descend under symplectic reduction to symplectic hyperplane sections. Along the way we show that quasi-morphisms that arise from spectral invariants are the Calabi homomorphism when restricted to Hamiltonians supported on stably displaceable sets.Comment: 20 pages; v2: added remarks and updated references, to appear in Journal of Symplectic Geometr

Medical geography and its contribution to the aetiology of rare systemic connective tissue diseases : a thesis presented in partial fulfilment of the requirements for the degree of Master of Arts in Geography at Massey University

This thesis is in two interrelated parts. Part One traced the historical development of medical geography since the idea of applying a geographical perspective to medical problems was first mooted in 4 B.C. The main trends in the evolving philosophy and methodology of this field were noted, and a distinction was made between the Western and Soviet interpretations of the nature and scope of medical geography. The methods available to medical geographers for cartographically portraying medical data were discussed. Part Two represented the application cf geographical principles to the study of rare systemic connective tissue diseases. The inherent problems of collection. and of verification of the medical data used in this study were detailed. Using cartographic and statistical techniques the diseases under study were spatially and temporally defined. It was found that scleroderma had a statistically significantly high incidence in the Taieri Geographic County, and it was this disease and this area which wore the principal contributory factors to the statistically significantly high incidence of all connective tissue diseases at the larger scales of areal units in the Otago region. The structures of the populations affected by these diseases were also studied, with the findings generally confirming the results obtained in overseas surveys. No association was found between the incidence of systemic lupus erythematosus, and high sunshine hours, while the disease subsets did not exhibit a rural or urban bias in their incidence. Paucity of cases precluded a study of the possible racial predilection of the diseases or any association of incidence with a patient's occupation. Suggested avenues for possible aetiological research accruing from this analysis were detailed

Displacing Lagrangian toric fibers by extended probes

In this paper we introduce a new way of displacing Lagrangian fibers in toric symplectic manifolds, a generalization of McDuff's original method of probes. Extended probes are formed by deflecting one probe by another auxiliary probe. Using them, we are able to displace all fibers in Hirzebruch surfaces except those already known to be nondisplaceable, and can also displace an open dense set of fibers in the weighted projective space P(1,3,5) after resolving the singularities. We also investigate the displaceability question in sectors and their resolutions. There are still many cases in which there is an open set of fibers whose displaceability status is unknown.Comment: 53 pages, 26 figures; v3: minor corrections and updated references. To appear in Algebraic & Geometric Topolog