The effect of surface topography upon the adsorption of dimer molecules is analyzed by means of grand canonical ensemble Monte Carlo simulations. Heterogeneous surfaces were assumed to consist of a square lattice containing active sites with two different energies. These were distributed in three different configurations: a random distribution of isolated sites; a random distribution of grains with four high-energy sites; and a random distribution of grains with nine high-energy sites. For the random distribution of isolated sites, the results are in good agreement with the molecular simulations performed by Nitta et al. (1997). In general, the comparison with theoretical models shows that the Nitta et al. (1984) isotherm presents good predictions of dimer adsorption both on homogeneous and heterogeneous surfaces with sites having small differences in characteristic energies. The molecular simulation results also show that the energy topology of the solid surfaces plays an important role in the adsorption of dimers on solids with large differences in site energies. For these cases, the Nitta et al. model does not describe well the data on dimer adsorption on random heterogeneous surfaces (grains with one acid site), but does describe reasonably well the adsorption of dimers on more patchwise heterogeneous surfaces (grains with nine acid sites).

Molecular simulation data were used to study the performance of equations of state (EoS) and combining rules usually employed in thermodynamic property calculations. The Monte Carlo method and the Gibbs ensemble technique were used for determining composition and densities of vapor and liquid phases in equilibrium for binary mixtures of Lennard-Jones fluids. Simulation results are compared to data in the literature and to those calculated by the t-PR-LJ EoS. The use of adequate combining rules has been shown to be very important for the satisfactory representation of molecular simulation data.

A modified form of the Hicks and Young algorithm was used with the Mattedi-Tavares-Castier lattice equation of state (MTC lattice EOS) to calculate critical points of binary mixtures that exhibit several types of critical behavior. Several qualitative aspects of the critical curves, such as maxima and minima in critical pressure, and minima in critical temperature, could be predicted using the MTC lattice EOS. These results were in agreement with experimental information available in the literature, illustrating the flexibility of the functional form of the MTC lattice EOS. We observed however that the MTC lattice EOS failed to predict maxima in pressure for two of the studied systems: ethane + ethanol and methane + n-hexane. We also observed that the agreement between the calculated and experimental critical properties was at most semi-quantitative in some examples. Despite these limitations, in many ways similar to those of other EOS in common use when applied to critical point calculations, we can conclude that the MTC lattice EOS has the ability to predict several types of critical curves of complex shape.

In this work, several simulated annealing algorithms presented in the literature as solutions to different problems were compared in the scheduling of multiproduct serial batch plants. A systematic performance study of the original algorithm, based on the Boltzmann statistics, and a recently proposed algorithm, based on the Tsallis statistics, were analyzed for three different annealing schemes. It was observed that performance (defined in terms of the number of configurations) is more sensitive to the annealing scheme than to the statistics used. We also observed that the overall performance of the simulated annealing procedure is very dependent on the parameters of the algorithm and on the kind and size of the problems. For large problems, algorithms based on the Tsallis statistics converged to the global minimum more frequently than those based on the Boltzmann statistics, although they needed a larger number of configurations to obtain the results.

- A group contribution equation of state recently proposed by the authors is used to calculate the activity of solvents in polymer+solvent solutions. The model is based on the generalized van der Waals theory and combines the Staverman-Guggenheim combinatorial term with an attractive lattice gas expression. The results show that the equation correlates the properties of pure solvents and polymers accurately. Furthermore, the equation satisfactorily represents the vapor-liquid equilibrium of solutions containing polymer and solvents of different polarities.