SAPO-34 membranes on stainless steel, tubular supports separated CO 2 from CH 4 at feed pressures up to 3.1 MPa. The highest CO 2 permeance was 2.4 × 10 -7 mol/(m 2 s Pa) for a 50/50 feed mixture at a pressure drop of 0.14 MPa. For a pressure drop of 3 MPa, the CO 2 /CH 4 separation selectivities at 253 K were 140-150; at lower pressure drops, the highest selectivity was 270. The highest CO 2 flux was 21 kg/(m 2 h) at 295 K and a pressure drop of 3 MPa. Separation selectivity decreased as temperature increased because separation was partly based on competitive adsorption. As transmembrane pressure drop increased, both CO 2 flux and CO 2 permeate concentration increased for a 50/50 mixture. The flux pressure dependence was modeled by Maxwell-Stefan diffusion for mixtures. Methane decreased the CO 2 diffusion rate and, thus, decreased the CO 2 flux. The CH 4 flux was also lower in a mixture because CO 2 inhibits CH 4 adsorption.

No abstract

No abstract

Adsorption isotherms and diffusion coefficients for n-C 4 and i-C 4 in the transport pathways through tubular ZSM-5 zeolite membranes were determined over a range of temperatures by a transient permeation method. The permeate response to step changes in the feed were measured, and the transport was modeled as Maxwell-Stefan diffusion with single site Langmuir adsorption in the zeolite. The heats of adsorption and the Langmuir parameters were comparable to values reported for MFI powders. The similarity of the membrane and powder isotherms indicates that butanes diffuse mainly through zeolite pores. Maxwell-Stefan diffusion coefficients for n-C 4 and i-C 4 in the ZSM-5 membranes were similar to those measured by other macroscopic techniques for zeolite crystals and membranes, and diffusion coefficients increased with increasing feed partial pressure for a high-quality membrane. The effective membrane thickness was also estimated from these transient measurements.

Butane isomer adsorption isotherms and diffusivities in the transport pathways through Al-ZSM-11 (MEL), Al-ZSM-5 (MFI), and B-ZSM-5 zeolite membranes were measured by