Synthesis and Gas Permeation Properties of STT-type Zeolite Membranes

Abstract

Zeolite membranes can be used for separation and purification of natural gas. Natural gas contains mainly methane and carbon dioxide, but also contains acidic gases, such as hydrogen sulfide, and water. The application of conventional zeolite membranes containing aluminum to these separation processes is difficult because of poor acid durability and reduced flux in the presence of water. Pure silica zeolite membranes have high acid stability and are hydrophobic. In this study, STT-type zeolite was chosen as a membrane material for the relatively high pore volume and pure silica STT-type zeolite can be prepared. STT-type zeolite was milled in a ball mill for 8 h, and then coated on a porous alumina substrate. STT-type zeolite membranes were prepared by the secondary growth method. Times for synthesis of the STT-type zeolite particles and ball milling were optimized. The effects on permeance of synthesis time, and of the structure-directing agent/SiO₂ and H₂O/SiO₂ ratios for secondary growth were investigated. STT-type zeolite membrane prepared from gel with a mole ratio of 1.0 SiO₂ : 0.25 N,N,N-trimethyl-1-adamantane ammonium hydroxide : 54 H₂O with hydrothermal synthesis for 8 days at 150 °C had high permeance ratio (169) for hydrogen to sulfur hexafluoride (SF₆).