Scale-up of SAPO-34 Membranes for CO2/CH4 Separation

SAPO-34 membranes have pores with a diameter of approximately 0.38 nm and have the potential to be used for large scale removal of CO₂ impurities from natural gas. Tubular SAPO-34 membranes have been shown previously to have high permeances and selectivities at high pressures, so that CO₂ can be removed while maintaining CH₄ at high pressures. Here we show that the SAPO-34 membrane preparation can be scaled up and simplified. The membranes were prepared on 7-channel monolith alumina supports to increase the membrane surface area per volume.

The SAPO-34 separation layers were grown on both single-channel and monolith supports using seeded synthesis where the SAPO-34 seeds were deposited on the supports either by dip-coating, rub-coating, or a newly developed seeding technique. The membranes prepared on monolith supports had average CO₂ permeances of 6.3 x 10^-7 +/- 0.9 mol/(m²sPa) and average selectivities of 56 +/- 4 for 50/50 CO₂/CH₄ mixtures at 46 bar feed pressure. These permeances and selectivities were probably limited by concentration polarization because the available mass flow controllers limited the maximum feed rate and resulted in high stage cuts when the seven-channel monoliths were used. Analysis of the monolith membranes by SEM indicate that the SAPO-34 layers were a few µm thick, and they were slightly thinner than SAPO-34 membranes prepared on single channel tubes.