Characterization of SAPO-34 membranes by water adsorption

The effects of humidity on gas permeation were studied for five SAPO-34 mem branes with different fractions of permeation through non-SAPO pores. Membr anes with high CO2/CH4 separation selectivities (>20) were stable in humidi fied gases, but degradation was seen for some membranes after months of exp osure to the laboratory atmosphere. Once the membranes started to degrade, the rate of degradation appeared to accelerate, The degradation created non -SAPO pores that were larger than the SAPO-34 pores, as indicated by i-C4H1 0 permeance, CO2/CH4 selectivity, and CO2 flux dependence on pressure. The effect of humidity on gas permeance correlated with these indicators of non -SAPO pores. Adsorbed water appeared to completely block the SAPO pores, bu t permeation through non-SAPO pores increased with humidity. Therefore, wat er adsorption can be used to determine membrane quality and the fraction of transport through non-SAPO pores. (C) 2001 Elsevier Science B.V. All right s reserved.