Fixed-Bed Adsorption Separation Of Xylene Isomers over SiO2/Silicallite-1 Core-Shell Adsorbents

Abstract

Abstract:SiO 2 /Silicalite-1 core-shell material has been demonstrated as potential shape selective adsorbent in gas phase separation of p-xylene from a mixture of p/o-xylene isomers. The core-shell composite comprised of large silica core and thin polycrystalline silicalite-1 shell which was synthesized via a self-assembly of silicalite-1 nanocrystals on core silica surface followed by a secondary seeded growth method. The core materials, SiO 2 used in this study has mesoporosity with an average pore diameter of 60Å and hence offers no shape selectivity for xylene isomers. However, the shell, silicalite-1 contains rigid pore structures and preferentially adsorbs p-xylene from their isomers mixtures. A series of adsorption fixed bed breakthrough adsorption/desorption experiment was performed to obtain the equilibrium isotherms and adsorption isotherm parameters of xylene isomers. The equilibrium isotherms of xylene isomers follow the Langmuir's model. A chromatographic adsorption model has been used to describe the fixed-bed breakthrough profiles of xylene isomers. The model has successfully predicted the responses of the binary mixtures of p/o-xylene isomers. The SiO 2 /silicalite-1 core-shell adsorbents have shown para-selectivity as high as 15.

Separation of Xylene Isomers: A Review of Recent Advances in Materials

“…Binary breakthrough experiments at 423 K showed a high selectivity of 15 for PX/OX. Further research concluded that PX/OX selectivity arose solely from a molecular sieving effect of the silicalite-1 shell, while the core possessed no selectivity . A ZSM-11/silicalite-2 core–shell molecular sieve with a compact silicalite-2 shell also proved effective for the separation of xylenes…”

Synthesis of Engineered Zeolitic Materials: From Classical Zeolites to Hierarchical Core–Shell Materials

“…Matching with theoretical expectations, the smaller hydrocarbons were efficiently separated from the large ones by the shape‐selective silicalite‐1 shell (Figure d). Following this, core@shell and hollow zeolites were successfully used for several gas or liquid phase adsorptive separation processes, as listed in Tables . The importance of the film quality and thickness, i.e., fewer defects, pinholes, and cracks, as well as the orientation of the crystals to determine the separation performances of zeolitic membranes was also discussed extensively .…”

Synthesis of microporous/mesoporous core–shell materials with crystalline zeolitic shell and supported metal oxide silica core

“…The desirable final products, non-aggregated core@shell microspheres, should meet a set of quality criteria including the preserved core mesoporosity during the shell formation process, complete shell coverage, pore network connectivity between constituents of the composite, and the absence of free zeolite crystals in the bulk. Although there are few examples of core@zeolite that can be produced by using a onepot hydrothermal crystallization process [22][23][24][25][26] , the synthesis of a great number of zeolitic core@shell materials is only viable through a multi-step synthesis route 3,4,9,11,12,15,21,[27][28][29][30][31][32][33] . The multistep synthesis route usually involves preliminary adsorption of zeolite nanocrystals onto large core particles followed by growing these nanocrystals in an appropriate synthesis gel mixture 34,35 (Scheme 1).…”

“…In particular, high surface area, high pore volume mesoporous silica spheres with the ability of hosting various functional groups (e.g., metals, metal oxides, etc.) when finely covered with a zeolitic shell may hold considerable promise in a variety of applications [11][12][13][14][15][16][17][18][19][20] .…”

“…), when finely covered with a zeolitic shell may hold considerable promise in a variety of applications. [11][12][13][14][15][16][17][18][19][20] The outstanding properties of a zeolitic core@shell are tightly related to the complete shell coverage as well as the proper communication between micro/mesopore networks of the constituents. The importance of shell integrity on the selective adsorption of small molecules from a hydrocarbon mixture containing butane, toluene, and 1,3,5trimethylbenzene was demonstrated in the pioneering work of Bouizi et al, 21 by using a β-zeolite@silicalite-1 material with maximum shell coverage, i.e., a triple-shell composite.…”