Evaluation of a method for micro-defect sealing in ZSM-5 zeolite membranes by chemical vapor deposition of carbon

This work presents a systematic study on closing micro-defects in zeolite membranes using chemical vapor deposition of carbon. For chemical vapor deposition (CVD), different carbon sources, dwell times and temperatures were applied. The zeolite membranes used in this study were fabricated by hydrothermal syntheses on the inner surface of porous ceramic substrates in single channel geometry. The quality of the membranes was characterized by permporometry, single gas permeation measurements and microstructural techniques (e.g. electronmicroscopy). For proof of concept, g-Al2O3 ultrafiltration membranes with 2 nm pore diameter without any zeolite layer were coated with carbon by CVD using n-hexaneand ethyne. Especially a treatment with ethyne lead to a narrowing of the pore size of the ultrafiltration membrane and reduced the number of micro defects. Subsequently, the method was applied to close intercrystalline defects in zeoliteZSM-5 membranes. Compared to pure ZSM-5 membranes, CVD treated membranes exhibited lower permeances and enhanced ideal permselectivity for H2/SF6 and He/SF6. Though the method has to be further improved, those first results emphasize the potential of this general method for closing defects in different zeolite membranes.