TY - JOUR
T1 - A microscope FTIR mapping study on diffusion of hydrocarbons in single silicalite crystal particles
AU - Lin, Y. S.
AU - Yamamoto, N.
AU - Choi, Y.
AU - Yamaguchi, T.
AU - Okubo, T.
AU - Nakao, S. I.
N1 - Funding Information:
Y.S. Lin is grateful to the Japan Society for Promotion of Science and the US National Science Foundation for supporting his visit to the University of Tokyo.
PY - 2000/8
Y1 - 2000/8
N2 - A simple microscope FTIR mapping method is illustrated for studying anisotropic diffusion in zeolite. This method is based on measurements of evolution of the adsorbate concentration (IR absorbance) profiles in two principal directions of a single zeolite crystal particle of a few ten microns in sizes. A mathematical model is presented and a comparison of its numerical solution with experimental data allows the determination of the diffusivity in each direction in zeolite crystals. Diffusion rates during desorption of n-hexane, n-octane and p-xylene in silicalite particles of 130 x 50 x 50 μm were experimentally studied with the microscope FTIR line mapping. Negligible changes in adsorbate concentration profiles were observed after the silicalite particle saturated with one of the three hydrocarbons was exposed to air for about 15-44 h at room temperature. Under vacuum conditions and at higher temperatures, the hexane concentration profiles developed within about 0.5 h, from which the averaged diffusivity of hexane in the a and b channels of silicalite was found 1.1 x 10-10 cm2/s (at 80°C), significantly higher than that for the c direction. Due to the intergrown microstructure of the single silicalite particles studied in this work, unusual adsorbate concentration profiles were observed in some cases. These results suggest that the adsorbate may diffuse in or out of the single crystal particle through the intercrystallite gaps connected with the straight b channels of silicalite. (C) 2000 Elsevier Science B.V. All rights reserved.
AB - A simple microscope FTIR mapping method is illustrated for studying anisotropic diffusion in zeolite. This method is based on measurements of evolution of the adsorbate concentration (IR absorbance) profiles in two principal directions of a single zeolite crystal particle of a few ten microns in sizes. A mathematical model is presented and a comparison of its numerical solution with experimental data allows the determination of the diffusivity in each direction in zeolite crystals. Diffusion rates during desorption of n-hexane, n-octane and p-xylene in silicalite particles of 130 x 50 x 50 μm were experimentally studied with the microscope FTIR line mapping. Negligible changes in adsorbate concentration profiles were observed after the silicalite particle saturated with one of the three hydrocarbons was exposed to air for about 15-44 h at room temperature. Under vacuum conditions and at higher temperatures, the hexane concentration profiles developed within about 0.5 h, from which the averaged diffusivity of hexane in the a and b channels of silicalite was found 1.1 x 10-10 cm2/s (at 80°C), significantly higher than that for the c direction. Due to the intergrown microstructure of the single silicalite particles studied in this work, unusual adsorbate concentration profiles were observed in some cases. These results suggest that the adsorbate may diffuse in or out of the single crystal particle through the intercrystallite gaps connected with the straight b channels of silicalite. (C) 2000 Elsevier Science B.V. All rights reserved.
KW - Anisotropic diffusion
KW - Infrared spectrometer
KW - Zeolite
KW - Zeolite membrane
KW - Zeolite microstructure
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U2 - 10.1016/S1387-1811(00)00141-4
DO - 10.1016/S1387-1811(00)00141-4
M3 - Article
AN - SCOPUS:0034238169
SN - 1387-1811
VL - 38
SP - 207
EP - 220
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
IS - 2-3
ER -