Time-Dependent Permeance of Gas Mixtures through Zeolite Membranes

Abstract

The time-dependent permeation behavior of binary gas mixtures through a ZSM-5 zeolite membrane was studied. Although steady-state permeation rates were indistinguishable for CO(2) and N(2) or for cis- and trans-2-butene in binary mixtures, differences in the rate of approach to steady state allowed component distinction. In "normal" systems, one component is initially enriched in the permeate following application of a pulse of analyte gas to the membrane, and then disappears more quickly upon termination of the pulse. Mixtures of cis- and trans-2-butene exhibit qualitatively different behavior; the permeate is enriched in cis-2-butene during both the leading and trailing edges of a sample pulse (though not at steady state). These differences in permeation behavior reflect different balances among multiple transport mechanisms through the zeolite membrane, thought to reflect a combination of selective component sorption and intracrystalline diffusion; in the case of cis- and trans-2-butene, these two factors oppose one another. It is known that this mechanistic complexity can engender synergistic effects, wherein the presence of one component can affect the permeation of another. These may limit applicability to true "unknowns", but resulting complications should be less problematic in well-defined process applications.

Predicting Single-Component Permeance through Macroscopic Zeolite Membranes from Atomistic Simulations

“…There are obviously situations in which transient behaviors are important. 62 It is straightforward to extend the methods developed here to the modeling of transient results.…”

“…Finally, we note that only steady-state situations have been examined in this paper. There are obviously situations in which transient behaviors are important …”

Membrane introduction Mass Spectrometry: Trends and applications

“…Tandem MS greatly facilitates mixture analysis by MIMS Creaser & Stygall, 1995), but at a cost in terms of the complexity of the instrumentation and experiment. Other alternatives for mixture analysis include the use of chemically selective af®nity (Xu et al, 1995) and zeolite (Bennett & Cook, 1998;Bennett et al, 1999) membranes, data treatment using multivariant techniques and sample modulation (``dynamic MIMS''). The problem has been alleviated by these methods, as now discussed.…”

Direct coupling of a carbon nanotube membrane to a mass spectrometer: Contrasting nanotube and capillary tube introduction systems

“…Introduction of volatile analytes to the mass spectrometer (MS) has been commonly accomplished by capillary tubes, and other orifices, or by the use of thin polymer films, such as polydimethylsiloxane (PDMS) membranes, using the technique called membrane inlet (or introduction) mass spectrometry (MIMS) [2][3][4]. Since its development in 1963 [5], MIMS has been tested using new membrane materials and technologies, such as zeolite membranes [6] and microporous hollow fibers [7], or using alternative polymer membranes [4]. The MIMS technique has employed a variety of membrane modules, where a gas or liquid sample flows through the membrane inlet system and analytes diffuse through the membrane material or pores into the MS.…”