Blocking defects in SAPO-34 membranes with cyclodextrin

Abstract: The CO2/CH4 separation selectivity of SAPO-34 membranes increased by 20–150% after soaking them in 1–2% aqueous β-cyclodextrin (CD) solution and drying them at 473K. The percentage increase was higher at higher pressures, and the selectivities increased more for membranes with more defects. The CD decreased the CO2 fluxes at high pressures by about 10–20%, whereas CH4 fluxes decreased by 30–60%. The flux of CF4, which is too large to enter the SAPO-34 pores and thus only permeates through defects, decreased 80% for one membrane (5.7MPa feed pressure) after CD deposition; this confirmed that defects were effectively blocked. Even before CD exposure, the CF4 permeance at 2.8MPa was only 0.25% of the CO2 mixture permeance for that membrane. Permporometry also showed that CD blocked defects; the maximum defect size decreased from greater than 30nm to less than 20nm. About 91% of the overall defect area in the original membrane was from defects smaller than 8nm, whereas 99% was for defects smaller than 2nm after CD deposition. The membrane separation performance did not change during 3 days of continuous measurements, nor did it change after long term storage at 473K in air. [Copyright &y& Elsevier]