CO2–CH4 permeation in high zeolite 4A loading mixed matrix membranes
Research highlights
▶ Developed procedure for formation of defect-free high loading MMMs. ▶ Substantial enhancement of mixed gas feed permeation properties with very high loading mixed matrix membranes. ▶ Proof-of-concept established: low cost, low performance membrane materials approached “upper-bound” polymer performance in aggressive mixed feeds. ▶ High performance of MMM maintained well above the plasticization pressure of the polymer.
Introduction
Dispersing filler particles in polymeric matrices is an increasingly popular method for improving pure polymeric gas transport properties [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Mixed matrix membranes (MMMs) typically consist of zeolite particles dispersed in polymers with the goal of increasing permeabilities and selectivities of desired components over those of undesired components. MMMs combine the ease of processing polymer membranes with the superior transport properties of zeolitic (and other filler) materials, ideally resulting in membranes with properties that exceed gas pair “upper-bounds” [1], [20], [21], [22]. Models predict that transport enhancements increase rapidly at high filler loadings [23], [24]. While there have been many reports of low filler loading (≤40 vol.%) MMMs showing improved transport properties over their pure polymeric matrices [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [19], [22], [25], [26], [27], only a few reports of high particle loading (≥50 vol.%) MMMs have been published [2], [3], [5], [11], [12].
Most MMM studies report only low pressure, pure gas permeation data. While low pressure, pure gas permeation experiments can be useful for characterizing new membrane materials, real feeds are complex mixtures and are often at high pressures. Mixed feed permeation properties can substantially deviate from pure gas data due to plasticization, competitive sorption, and many other complicating effects [28], [29]. Natural gas sweetening (i.e. removal of acid gases like carbon dioxide and hydrogen sulfide from methane) is among the most important target feeds for membrane separations. Moreover, economic analyses show that natural gas wells with high carbon dioxide concentrations (>20% CO2) are especially attractive targets for membrane based separations [28], [30], [31], [32], [33]. Such natural gas sources are processed at total feed pressures as high as 900 psi or more [33]. These considerations encourage testing MMMs under high pressure, simulated natural gas feeds.
In this work, high zeolite 4A loading (50 vol.%) MMMs were made using poly(vinyl acetate) (PVAc) as the matrix polymer. PVAc is well known to be a model polymer for MMM studies due to its flexibility and adhesive properties [1], [22], [34]. Also, PVAc is known to be sensitive to plasticization-induced loss in selectivity; however, stabilization of chain segments in the vicinity of solids may reduce this sensitivity. PVAc was, therefore, selected as the polymer matrix for this study. Two 50 vol.% zeolite 4A-PVAc MMMs were made from in-house synthesized zeolite 4A via solution processing. These MMMs were tested under two simulated natural gas feeds (dry CO2–CH4 at 35 °C): 1) a low case and 2) a high case. The individual component permeabilities and CO2–CH4 selectivities are reported and compared to pure PVAc values under the same conditions.
Section snippets
Gas permeability in dense membrane materials
The phenomenological definition of gas permeability, P, of a penetrant, i, in dense membranes (such as those studied in this work) is the penetrant partial pressure differential (Δpi) and membrane thickness (l) normalized flux (Ni) as given in Eq. (1):
The underlying basis for gas permeability through dense membranes is the solution-diffusion mechanism where the gases first sorb at the membrane surface from a high activity feed, then diffuse across the membrane thickness along a
Materials
PVAc (nominal MW = 500 kDa) was purchased from Sigma–Aldrich (Milwaukee, WI). Anhydrous toluene was also purchased from Sigma–Aldrich (Milwaukee, WI) and used without further purification. Zeolite 4A, 0.5–1.5 μm average size was synthesized by our group. The high quality of the zeolite 4A was confirmed by XRD, elemental analysis, cryogenic N2 physisorption, and pressure decay gas sorption at 35 °C.
Dense film preparation
Pure PVAc dense film membranes were made from PVAc-toluene solutions. First, ∼7 g PVAc beads were dried
Pure zeolite 4A
Calcined zeolite 4A crystals were prepared using a hydrothermal method that utilized tetramethyl ammonium hydroxide as a structure directing agent. The details of synthesis are omitted for brevity, but a variety of characterization experiments were used to confirm successful zeolite 4A preparation.
ICP mass spectrometry was done by Columbia Analytical Services (Tucson, AZ) to determine the silicon, aluminum, and sodium content of the zeolite 4A. Oxygen content was determined by EDS. Table 1
Conclusions
Poly(vinyl acetate) was used as the polymer matrix to form high zeolite 4A loading MMMs. Mixed CO2–CH4 feeds were permeated through these MMMs at 35 °C to assess the viability of these materials for natural gas purification. Although PVAc and zeolite 4A were primarily chosen as inexpensive, well studied model materials, the resulting transport enhancements were quite significant. Plotting the 2 mixed feed cases’ permeation properties on Robeson's most current CO2–CH4 upper-bound illustrates that
Acknowledgements
NSF-STC (CERSP) under agreement CHE-9876674 and Award no. KUS-I1-011-21 made by the King Abdullah University of Science and Technology (KAUST) for this research.
References (50)
- et al.
Tailoring mixed matrix composite membranes for gas separations
Journal of Membrane Science
(1997) - et al.
Zeolite-filled silicone-rubber membranes .1. Membrane preparation and pervaporation results
Journal of Membrane Science
(1987) - et al.
Mixed matrix membranes (MMMs) comprising organic polymers with dispersed inorganic fillers for gas separation
Progress in Polymer Science
(2007) - et al.
Filler–polymer combination: a route to modify gas transport properties of a polymeric membrane
Polymer
(2004) - et al.
The effects of polymer chain rigidification, zeolite pore size and pore blockage on polyethersulfone (pes)-zeolite a mixed matrix membranes
Journal of Membrane Science
(2005) - et al.
Crosslinked mixed matrix membranes for the purification of natural gas: effects of sieve surface modification
Journal of Membrane Science
(2008) - et al.
Mixed matrix hollow fiber membranes made with modified hssz-13 zeolite in polyetherimide polymer matrix for gas separation
Journal of Membrane Science
(2007) - et al.
Zeolite-filled polyimide membrane containing 2,4,6-triaminopyrimidine
Journal of Membrane Science
(2001) - et al.
Adsorbent filled membranes for gas separation. 1. Improvement of the gas separation properties of polymeric membranes by incorporation of microporous adsorbents
Journal of Membrane Science
(1993) - et al.
Effect of zeolite particle size on the performance of polymer–zeolite mixed matrix membranes
Journal of Membrane Science
(2000)
Gas permeation characteristics of polymer–zeolite mixed matrix membranes
Journal of Membrane Science
Hydrogen separation and purification using polysulfone acrylate–zeolite mixed matrix membranes
Journal of Membrane Science
Theoretical analysis of diffusional movement through heterogeneous barriers
Journal of the American Pharmaceutical Association
The upper bound revisited
Journal of Membrane Science
Metal organic framework mixed matrix membranes for gas separations
Microporous and Mesoporous Materials
Permeation models for mixed matrix membranes
Journal of Colloid and Interface Science
Membrane-based gas separation
Journal of Membrane Science
Membrane processes for the removal of acid gases from natural-gas . 1. Process configurations and optimization of operating-conditions
Journal of Membrane Science
Membrane processes for the removal of acid gases from natural-gas . 2. Effects of operating-conditions, economic-parameters, and membrane-properties
Journal of Membrane Science
Non-ideal effects in organic–inorganic materials for gas separation membranes
Journal of Molecular Structure
Diffusivities in glassy-polymers for the dual mode sorption model
Journal of Membrane Science
Characterization of low permeability gas separation membranes and barrier materials; design and operation considerations
Journal of Membrane Science
Effect of titania pigment on the residual strain, glass-transition and mechanical-properties of a pmma coating
Polymer
Molecular-sieving effect of the zeolite-filled silicone-rubber membranes in gas permeation
Journal of Membrane Science
Hybrid membrane materials comprising organic polymers with rigid dispersed phases
AICHE Journal
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