Simulated moving bed reactor for p-xylene production: Optimal particle size

Abstract

In a previous work, a hybrid unit combining separation and isomerization within a Simulated Moving Bed Reactor unit (based on an existing Simulated Moving Bed) for the production of p-xylene was analyzed with the currently-used particle diameter of 0.62mm. The unit is part of a proposed aromatics complex where lower p-xylene purities allow the use of a homogeneous mixture of adsorbents and catalysts within the columns. In this work a similar study is carried out with four particle diameters: 0.5, 0.7, 0.8, and 0.9mm, maintaining the extract and raffinate purity at 0.70 and 0.95 respectively, and a mass ratio of 0.9g adsorbent per g of adsorbent-plus-catalyst. After performing simulations using the true moving bed approach, it is verified that the high amount of desorbent is mainly caused by the reverse reaction in the isomerization of xylenes. Furthermore, the highest productivity is offered by the 2-6-14-2 configuration for every particle size studied. The system is then analyzed with that arrangement of columns under the maximum pressure drop of the existing Simulated Moving Bed unit (685kPa). The optimal particle diameter is 0.62mm, exhibiting the highest productivity (267.40kg/m3·h), and a desorbent consumption of 0.06 m3/kg. The results also show that a single study with a small particle size is sufficient to accurately determine the best configuration for the system. (c) 2015 Canadian Society for Chemical Engineering.