Adsorption isotherms and diffusion coefficients for n-C4 and i-C4 in the transport pathways through tubular ZSM-5 zeolite membranes were determined for a range of temperatures by using 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 indicated that butanes diffused mainly through zeolite pores. The Maxwell-Stefan diffusion coefficients for n-C4 and i-C4 in the ZSM-5 membranes were similar to those measured using other macroscopic techniques for zeolite crystals and membranes. The diffusion coefficients increased with increasing feed partial pressure for a high-quality membrane (table 61).

Adsorption and Diffusion Properties of Butanes in ZSM-5 Zeolite Membranes. T.Q.Gardner, J.B.Lee, R.D.Noble, J.L.Falconer: Industrial and Engineering Chemistry Research, 2002, 41[16], 4094–105

Table 62

Diffusion of Isobutane in ZSM-5