For xylene separation, hierarchy is not all bad


The three xylenea isomers are each employed in numerous growth market applications (polymers, plastifiers and resins). It is thus vital to improve the efficiency of the separation processes for these isomers, the most widely used process being liquid phase adsorption on zeolite materials. For the competitiveness of the process, these materials must be optimized while maintaining a subtle balance between their adsorption capacity, their selectivity with respect to the different isomers and the accessibility of the latter to selective regions. These properties are directly linked to the texture and topology of the zeolite support, made up of agglomerated crystallites.

Recourse to zeolites with a network of auxiliary pores makes it possible to improve liquid phase accessibility to the selective regions located in the microporosity. However, during the synthesis of these supports, the introduction of the secondary porous network must be carried out while minimizing its impact on the selective regions due to a modification to the microporosity access surface.

To achieve this, a range of characterization methodsb was used to relate the adsorptive behavior of the different isomers to the textural and surface properties (figure) of the zeolites(1). This exhaustive characterization makes it possible to rationalize the impact of the secondary pore network and paves the way for optimization of the “hierarchical” zeolite synthesis process for xylene separation.

Morphological textural and surface characterization
Morphological, textural and surface characterization of different zeolites with hierarchized porosity used for 
xylene separation.

Combining these experimental results with atomistic models will lead to a better understanding of the impact of surface chemistry on adsorbent selectivity with respect to the different isomers.

a - Ortho, meta and paraxylene.
b - Comprising XRD, microscopy, nitrogen physisorption, mercury intrusion, IR, NMR, xylene adsorption by gas phase thermogravimetry and liquid phase batch

(1) I. Medeiros-Costa, C. Laroche, J. Pérez-Pellitero, B. Coasne, Microporous & Mesoporous Materials (2019), Special Issue “ Patarin (1985-2019)”

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