An experimental study of micropore defects in MFI membranes

• MFI membranes were minutely examined by adsorption-branch permporometry.
• For the first time, micropore defects could be directly verified by SEM.
• The micropore defects were most likely open grain boundaries.
• The permporometry results correlated well with permeation and separation data.
• The results were also supported by nitrogen adsorption data for powders.

In the present work, two ultra-thin MFI membranes, prepared using hydroxide and fluoride ions as mineralizing agents, respectively, were carefully examined by permporometry. The amount of micropore defects, as determined by permporometry, differed significantly between the two different membranes. For the first time, it was demonstrated that the micropore defects determined by permporometry were most likely open grain boundaries. The results were verified by direct observation of the open grain boundaries by a state-of-the-art XHR-scanning electron microscopy instrument. In addition, the permporometry data were also consistent with permeation data using 1,3,5-trimethylbenzene (TMB) as a probe molecule, separation data using an equimolar mixture of n-hexane and TMB, and nitrogen adsorption data.

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