MULTIRESPONSE MODELING OF THE OXIDATION OF NAPHTHALENE OVER A VANADIA CATALYST

The oxidation of naphthalene was studied over an industrial vanadium pentoxide (V₂O₅) catalyst which was promoted by potassium sulphate. Multi-response data were obtained at 335, 350, 365 and 380°C for oxygen to naphthalene mole ratios from 47:1 to 3:1. The data were fitted to the two-step Redox and Steady State Adsorption (SSAM) Models using multiple-response non-linear regression techniques.

In this, the first reported study of the application of multi-response techniques to modeling of naphthalene oxidation, certain inadequacies in the two-step models have been found. In particular, negative activation energies were obtained for the oxidation of naphthalene and 1,4-naphthoquinone in the formation of phthalic anhydride. An activation energy of 146 kJ.mol^-1 was obtained for the rate of oxidation of the catalyst. The overall process of naphthalene oxidation was highly temperature-sensitive over the range of temperatures investigated as evidenced by an effective activation energy of 125 kJ.mol^-1.     

OPTIMISATION OF THE PREPARATION OF RANEY COPPER-ZINC CATALYSTS FOR METHANOL SYNTHESIS

The large number of variables involved in the preparation of Raney copper-zinc catalysts for methanol synthesis were screened by statistical methods using a Plackett-Burman screening design. Three important variables, leach reaction temperature, leach digestion temperature and leach digestion time were further investigated using a central composite design. It was found that active Raney copper-zinc catalysts were produced using high (348-358?K) extraction temperature, low (298-318?K.) digestion temperature and long (70-80 min) digestion time     

Creep-Sintering and Microstructure Development of Heterogeneous MgO Compacts

Simultaneous creep and densification and the microstructure development of magnesium oxide powder compacts were studied at 125°C and for applied stresses of up to 0.25 MPa. Die-pressing the powder into compacts with a relative green density of ∼0.40 led to an approximately bimodal distribution of pores, with one fraction having sizes of the order of 10 times the (initial) particle size and the other fraction having pore sizes of the order of the particle size. The presence of the large pores in turn gave rise to rather unusual sintering effects. After first decreasing with relative density (ρ), the densification rate (dρ/dt) and the creep rate (dɛ/dt) then increased dramatically for 0.6 < ρ < 0.75. This range of ρ corresponded to the stage of microstructure development when grain growth and coalescence of the smaller pores have created a more uniform pore distribution. Above ρ∼ 0.75, both dρ/dt and dɛ/dt again decreased with ρ. These trends in the densification behavior are discussed in terms of material parameters such as the equilibrium dihedral angle and the pore coordination number.     

Derivation of a Revised Model for Activity Calculation in Multisilicate Melts

Hollitt's model for prediction of thermodynamic properties in multicomponent silicate melts has been revised to better reflect network modifier depolymerization effectiveness as a function of basicity and melt composition. This model is based on the free energy changes in a melt caused by the breaking of silicate polyions by the addition of basic oxides; these free energy changes are in turn related to the change in the concentration of various oxyanion molarities caused by such additions. Application of the revised model to actual systems shows good agreement with experimental data; possible model improvements are discussed.     

Investigation of the Heat Transfer Characteristics

In the present study a numerical investigation of the heat transfer in an annular combustion chamber of a typical industrial gas turbine was done using a Galerkin-based finite-element solution of the problem. Results were obtained for three basic cases: constant flux incident on the entire combustion segment, constant flux in three quadrants of the chamber and a different magnitude constant flux in the other quadrant, and different magnitude fluxes on the upstream and downstream portions of the chamber. The chamber Biot numbers, dimensionless heat flux, and dimensionless structural wall and thermal barrier coating thicknesses were found to have a crucial effect on the chamber temperature distribution. It was shown that changing the magnitude of the heat flux in a single quadrant prominently alters the temperatures throughout the wall in this area, leading to exceedingly steep temperature gradients. It was also found that any step decrease in downstream incident flux leads to a sharp drop in temperatures at the interface of the thermal barrier coating and the combustion gases.     

COOPERATIVE NAVIGATION AND THE FACULTY OF LANGUAGE

This paper presents an approach to simulating the evolution of language in which communication is viewed as an emerging phenomenon with both genetic and social components. A model is presented in which a population of agents is able to evolve a shared grammatical language from a purely lexical one, with critical elements of the faculty of language developed as a result of the need to navigate in and exchange information about the environment.