A SIMPLE METHOD FOR STUDYING THE KINETICS OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR

A methodology for studying the kinetics of gas-solid reactions in a fluidized bed reactor is presented. This procedure is based on the analysis of the response of the system (flue gases) when batches of solids of different weight are added to the reactor. The method has been applied to the study of limestone particle calcination. The calcination rate constants obtained are in good agreement with those found in the literature. The method offers the advantage of simplicity and avoids the use of model assumptions or empirical correlations.     

Kinetics of the decomposition of total aliphatic waxes in olive oil during deodorization

Changes in the content of aliphatic waxes during industrial deodorization and/or physical refining of bleached olive oil were studied in an experimental discontinuous pilot plant of 250 kg deodorizer using nitrogen as stripping gas in place of steam. The kinetic constants for the decomposition of waxes during the deodorization process were determined. The reaction orders studied are zero (or can be considered zero) within the working interval. The values of rate constants, activation energy, frequency factor, increment of activation Gibbs free energy, activation enthalpy, and activation entropy are established.     

Methodology to resolve the transport equation with the discrete ordinates code TORT into the IPEN/MB-01 reactor

Resolution of the steady-state Neutron Transport Equation in a nuclear pool reactor is usually achieved by means of two different numerical methods: Monte Carlo (stochastic) and Discrete Ordinates (deterministic). The Discrete Ordinates method solves the Neutron Transport Equation for a set of selected directions, obtaining a set of directional equations and solutions for each equation which are the angular flux. In order to deal with the energy dependence, an energy multi-group approximation is commonly performed, obtaining a set of equations depending on the number of energy groups. In addition, spatial discretization is also required and the problem is solved by sweeping the geometry mesh. However, special cross-sections are required due to the energy and directional discretization, thus a methodology based on NJOY99 code capabilities has been used. Finally, in order to demonstrate the capability of this method, the 3D discrete ordinates code TORT has been applied to resolve the IPEN/MB-01 reactor.     

Enantiospecific synthesis of (R)-1,7-dioxaspiro [5.5]undecane [major component of olive fruit fly (Dacus Oleae) sex pheromone] from d-Fructose

The synthesis of the title compound13 has been carried out through the preparation of its precursor, (3R,4R,5S,6R)-3,4,5-trihydroxy-1,7-dioxaspiro[5.5]undecane (6), obtained fromd-fructose using Wittig's methodology, reduction, and spiroketalation. Compound6 was transformed into13 by a Barton deoxygenation at C-5 followed by a Corey dideoxygenation at C-3,4 of the appropriately protected derivatives.Enantiospecific synthesis of spiroacetals. Part II. For Part I, see Izquierdo and Plaza (1990).     

Homogeneous Catalyzed Ozone Decomposition in the Presence of Co(II).

The homogeneous decomposition of ozone in the presence of a Co(II) catalyst has been investigated in aqueous solution. Under the conditions investigated (Co(II) concentration: 0.0 – 2.0?ppm, pH: 1.6- 8.4, O₃ concentration: 5 10^?5 – 2.0 10⁴?M) the process can be assumed to follow pseudo first order kinetics with respect to ozone. Cobalt concentration dependency also obeys first order kinetics although it may be considered to reach a steady state concentration. pH exerts a positive influence on the decomposition rate from 1.6 to 7.1, the process leveling off at pH 8.4. An Arrhenius analysis of the temperature effect gave a moderate activation energy of the global reaction (E=10917?cal mol^?1). A more detailed radical mechanism than a simple pseudo first order reaction can be postulated for simulation purposes. By numerical optimization of some unknown kinetic constants the influence of several operating variables can be adequately predicted.     

A computational fluid dynamic analysis of gas and particle flow in flame spraying

The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate. The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations compared fairly well with experimental results obtained with the optical DPV2000 system.     

Influence of Reinforcement Content and Matrix Composition on the Oxidation Resistance of Aluminum-Matrix Composites (A3xx.x/SiCp)

A study was made on the influence of the SiCp proportion and the matrix concentration of four composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) on their oxidation behavior. Gravimetric tests were used in a kinetics study of the corrosion process at different temperatures (350, 400, 450, and 500°C). The influence of corrosion on mechanical properties was evaluated by hardness measurements. The nature of corrosion products and the influence of the microstructure on the morphology and growth of the oxidation layer were analyzed by SEM and low-angle XRD. The extent of the damage due to oxidation for Al/SiCp composites increases with the SiCp concentration due to the increase of nucleation sites. One of these nucleation sites is in the interface region between the matrix and the particles. Oxidation was influenced more by the percentage of alloy elements in the matrix than by the proportion of SiCp reinforcement. The presence of Cu and Ni in the matrix favors the oxidation process through the formation of different intermetallic compounds.     

Photoacoustic technique for simultaneous measurements of thermal effusivity and absorptivity of pigments in liquid solution

A photoacoustic (PA) methodology, in the transmission configuration, for simultaneous measurements of thermal effusivity and molar absorption coefficient (absorptivity) for pigments in liquid solution is introduced. The analytical treatment involves a self-normalization procedure for the PA signal, as a function of the modulation frequency, for a strong absorbing material in the thermally thin regime, when the light travels across the sample under study. Two fitted parameters are obtained from the analysis of the self-normalized PA amplitude and phase, one of them proportional to the sample's optical absorption coefficient and from which, taking it for a series of samples at different concentrations, the pigment's absorptivity in liquid solution can be measured, the other one yields the sample's thermal effusivity. Methylene blue's absorptivity in distilled water was measured with this methodology at 658 nm, finding good agreement with the corresponding one reported in the literature.