Avaliação de regras de combinação na predição da adsorção de hidrocarbonetos utilizando o método Monte Carlo

Abstract

The adsorption of hydrocarbons has been systematically investigated because of its diversity applications in separation processes in the petrochemical industry and in catalytic processes. The experimental determination of adsorption isotherms for both pure components and their mixtures, usually requires a lot of time and financial resources. Thus, molecular simulation appears as an attractive tool to estimate the properties of adsorption and evaluate new materials. However, there is no systematic way of obtaining the force field parameters between different atoms. In general, these parameters are adjusted to better describe the adsorption properties, such as adsorption capacity, isosteric heat and Henry coefficients. This approach limits the predictive capacity of molecular simulation. In this work, was proposed a new combination rule for the Lennard-Jones (LJ) potential with the objective of improving the predictive capacity of molecular simulation that will be based only on the force field for pure species (adsorbent and adsorbate). Linear alkanes adsorption studies were performed in the 1-6 carbon atoms range using Monte Carlo simulations (GCMC) for three different temperatures in MFI type zeolite. The alkanes were described according to the TraPPE force field which shows a good representation for the alkanes behavior in the fluid phase. The Grand Canonical ensemble (GCMC), implemented in the open source Cassandra V2.2 was used to simulate the adsorption. The new combination rule and the classic Lorentz-Berthelot rule were tested. The results were compared with previous experimental data and molecular simulation results reported in the literature. The results indicated that the use of combination rules satisfactorily describes most of the systems investigated, being sometimes superior to the simulations using adjusted parameters, thus confirming the possibility of using this tool in the predictive form to evaluate the adsorption in zeolites. In order to reinforce this evaluation, new simulations involving mixtures of methane-ethane in zeolite type 5A and 2-methyl-pentane and n-hexane in silicalite were carried out. The new results reinforce the previous conclusion.