Estimation of xylenes adsorption selectivities: Impact on the p-xylene Simulated Moving Bed separation process

The majority of xylenes dedicated to petrochemicals use are used to produce PX which is, among the different isomers of the mixed xylenes, the most produced one to be consumed in the polyester chain, mainly in the production of fiber. In the scope of the p-xylene separation by Simulated Moving Bed Technology (SMB) it is important to improve the existing tools to study the different aspects that will affect its overall performance in order to achieve a better understanding of the process. This work intended to study the impact of a new thermodynamic model for the xylenes adsorption on the SMB process. For that, was developed a new methodology based on an iteration scheme between the laboratory (using experimental data regression) and simulation work to be able of describing the real xylenes selectivities variation along the separation column for two types of adsorbents ( FAU1 and FAU2). Those models are only valid for the specific solids studied and in the concentrations range of the SMB process. For the data regression was used an auxiliary software ( DESIGN EXPERT) that gave as an output a series of coefficients associated to the xylenes concentration and to be used in the different selectivities equations. To validate the models, a comparison between the SMB simulator and the pilot plant concentration profiles was established and a good prediction of the process behavior was observed. However, the results have shown that significant model improvements can be made based on the choice of the different selectivities that are directly calculated by solving the model.