In this study, inorganic membrane that can be used under high temperature, high pressure difference for hydrogen separation was prepared by three consecutive steps ; namely, sol-gel technique, in-situ hydrolysis of TEOS, and soaking and vapor deposition(SVD).
First, we apply sol-gel technique onto the $α-Al_2O_3$ support that has an asymmetric structure and pore size of 80 nm. In this step, $\gamma-Al_2O_3$ sol mixed with Pd precursor is coated onto the support by dip-coating method followed by calcination at 500℃. After repeating the sol-gel precedure several times, support pores were further modified by in-situ hydrolysis of TEOS and $H_2O$ in the cylindrical pores of the membrane. In this step, TEOS vapor flows into the outside of the membrane and water vapor flows into the inside of the membrane. The two vapors react in the middle of the support and forms a layer of $SiO_2$. This method is very effective in narrowing the pores of the membrane and the membrane prepared by this method is very effective especially when the transmembrane pressure is relatively high. To enhance the hydrogen selectivity of the membrane, the membrane was further modified by Soaking and Vapor Deposition (SVD) method onto the membrane. In the SVD step, the metal source, palladium(Ⅱ) acetate, was decomposed in pores in nitrogen atmosphere. During SVD, temperature is gradually increased from room temperature to 180℃ under reduced pressure. We formed an intermediate layer of palladium in the vicinity of the interface between the two layers of the support.
The membrane prepared by this multistep method shows a good hydrogen selectivity at high temperature and at high transmembrane pressure(?P). The separation factor of hydrogen and nitrogen is above the Knudsen limit(3.74) up to $\Delta$P = 35psi.
