Self-defect-healing of silicalite-1 membrane in alkaline aqueous solution with surfactant

Alkaline treatment with surfactant was applied to silicalite-1 membrane for defect healing. By immersion of silicalite-1 membrane into an aqueous solution of sodium hydroxide and cetyltrimethylammonium bromide (CTAB), defects among crystals were sealed, with amorphous silica leached from the membrane itself. During the treatment, the zeolite pores in the membrane were protected by CTAB from excess alkaline etching. As a result, the separation performance of silicalite-1 membrane was successfully improved by this post-treatment without a decrease in permeability due to the collaborative effect of NaOH and CTAB. The separation factor for n-hexane/2,3-dimethylbutane mixture increased from 86.5 to 559 after only a 15 min treatment. In addition, the separation performances of other zeolite membranes (Na-∗BEA, Na-ZSM-5, and Na-MOR) were also improved by the treatment. This novel defect-healing technique breaks the trade-off line of permeation and separation performance observed with previous post-treatments.