Tomonori Takahashi

p-Xylene separation with MFI-type zeolite membrane

Abstract Several authors reported the separation of xylene isomers through MFI-type zeolite membrane, however, the results were inconsistent. They used the alumina support and the defects can be induced in the zeolite membrane during the calcination due to the thermal expansion mismatch between alumina support and zeolite membrane. In this study, the self-supporting MFI-type zeolite membrane was used to avoid the defect formation. The self-supporting MFI-type zeolite was fabricated on Teflon plate in an autoclave at 353 K for 24–96 h. The vapor permeation were carried out by Wicke–Kallenbach method in the nitrogen gas flow to examine the p -xylene separation from the ternary mixture of xylene isomers as a function of time up to 72 h, temperature between 303 and 673 K, feed partial pressure between 0.3 and 5.l kPa and membrane thickness between 60 and 130 μm. The permeation flux of p -xylene showed the maximum at 473 K in the p -xylene partial pressure of 0.3 kPa. This could be described by the competitive effects between the amount of equilibrium adsorption and the diffusivity. The permeation of m - and o -xylene were small values and almost constant between 473 and 673 K. As a result, the separation factors of p - to m -xylenes and p - to o -xylenes showed the maximum value of 250 at 473 K. From 473 to 673 K, the permeation flux was proportional to the partial pressure both in the single component feed and the ternary mixture of xylene isomers. The permeation flux of p -xylene depended little on the apparent membrane thickness from 130 to 60 μm. It is suggested from the microstructure of the membrane that the dense layer may not be the entire thickness but part of the thickness. We concluded that the MFI-type zeolite membrane can separate the p -xylene selectively from the ternary mixture of xylene isomers above 473 K.

Improvement of oxidation resistance of Silicon Nitride sintered body by CVD Si3N4 coating

CVD(Chemical Vapor deposition) Si3N4 coating on the silicon nitride sintered body was developed to improve the oxidation resistance of the substrate. The silicon nitride sintered body coated with CVD Si3N4 showed excellent oxidation and corrosion resistance compared with silicon nitride sintered body substrate in both the static oxidation atmosphere and the hot oxidation gas stream.