Alkaline-treatment with pore-filling agent for defect-healing of zeolite membrane

Defects in silicalite-1 membrane is readily healed by an alkaline-treatment in aqueous solutions of NaOH and organic additives such as cetyltrimethylammonium bromide (CTAB) and tetramethylammonium bromide (TMABr). In this study, we investigated the role of organic additive in the course of alkaline-treatment. From the evaluation of weight and micropore volume of silicalite-1, it was shown that 3.6 and 3.1 molecules per unit cell of CTA⁺ and TMA⁺ entered the micropore of silicalite-1 during the treatment. CTA⁺ or TMA⁺ locating in the micropore inhibited the diffusion of NaOH into the micropore of zeolite and suppressed the dissolution from the inside of crystal. In contrast, the defect in silicalite-1 membrane was not healed by using an aqueous solution of NaOH and tetrabutylammonium bromide (TMABr), which was not able to enter the micropore of silicalite-1. We concluded that the use of organic additives, which can enter the micropore, was important for the defect-healing of siliclaite-1 membrane by the alkaline-treatment.