A facile coating to intact SAPO-34 membranes for wet CO₂/CH₄ mixture separation

The excellent performance of SAPO-34 membranes for CO₂/CH₄ separation is detracted by the water interaction, resulting in membrane instability and low durability. Herein, a new facile coating strategy using α, ω-dihydroxypolydimethylsiloxane (PDMS) has been developed for surface protection of SAPO-34 membranes by dip-coating. The fabrication of coating layer was optimized by finely tailoring the coating solution parameters, such as the viscosity and PDMS concentration. The developed membranes were evaluated under dry and wet CO₂/CH₄ mixture systems with effect of temperature and pressure. PDMS/SAPO-34 membrane could provide high separation performance in both systems. The separation selectivity of 68 and CO₂ permeance of 1.41 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ was achieved for wet mixture of CO₂/CH₄ at 80 °C during 120 h continuous operation. Furthermore, the PDMS/SAPO-34 membrane showed a wonderful performance after half a year storage, with 5–8% changes of CO₂ permeance and selectivity for the dry CO₂/CH₄ mixtures, while for un-modified SAPO-34 membrane, a decline of 71% in CO₂ permeance and 85% in CO₂/CH₄ separation selectivity was observed. The results demonstrated that the PDMS-coated SAPO-34 membrane could be a promising candidate for natural gas purification.