(329n) Multi-Scale Simulation Starting at the Molecular Level for N-Hexane Chromatographic Process

Chromatographic adsorption has been used as one of industrial operations for high purity separation. Traditionally, the adsorption process development has been based on heuristic knowledge and expertise, which is time-consuming and costly. Model-based simulation and optimization may help to accelerate the adsorption process development and effectively search optimum operation conditions. This study presents a multi-scale simulation approach starting at the molecular level for the n-hexane chromatographic adsorption process. With the explosive growth of computational power in recent year, molecular simulation has flourished in order to predict the molecular structure of a material and its physical properties. The molecular simulation is performed in Materials Studio v.4.0 (Accerlys Software Inc., USA) with the Forcite and the Sorption modules. The molecular structure of the activated carbon is constructed with periodic boundaries to fit physical properties measured (porosity, specific surface area and density) and is optimized, using the COMPASS (Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies) force field including bonding and non-bonding interaction potentials of atoms. A Grand Canonical Monte Carlo (GCMC) method is used for the prediction of adsorption isotherms of n-hexane on the activated carbon structure constructed by utilizing COMPASS. In GCMC simulation, the temperature, volume and chemical potential, which can be directly related to pressure and temperature using the bulk gas equation of state, are specified, while the number of particles and associated configurational energy are allowed to fluctuate. The adsorption isotherms obtained from the molecular simulation are exploited as a model parameter needed for the adsorption process simulation. The process simulation is performed in FAST-Chrom/SMB (Fast and Accurate Simulation Tools for Chromatography and SMB), which developed by our own laboratory. The simulation results are in a good agreement with the experimental results of n-hexane on the activated carbon.

Keywords: Multi-scale simulation, Molecular simulation, Process simulation, Chromatographic adsorption, Activated carbon, COMPASS, Grand canonical Monte Carlo (GCMC) method, Adsorption isotherms.