Chabazite Membranes Research Articles

High-performance 19-channel monolithic chabazite membranes for efficient separation of water/ethanol and water/isopropanol mixtures by pervaporation and vapor permeation

Pervaporation (PV) and vapor permeation (VP) using selective zeolite membranes are more energy-saving in dealing with azeotropic mixtures compared with conventional distillation for organic solvent dehydration. Herein, we developed a monolithic supported chabazite membrane and exploited its dehydration performance. The membrane was fabricated by secondary growth method on the 19-channel alumina monolithic without organic template. By finely controlling the homogeneity of nuclei growth and minimizing the intracrystalline defects through the epitaxial growth of uniformly nanosized SSZ-13 seed layer using cesium hydroxide and sodium hydroxide as cooperative hydration-mismatched inorganic structure directing agents (ISDA). The resulting monolithic chabazite membrane exhibits excellent water-perm-selectivity. The effects of feed water composition and operating temperature on the dehydration performance of the monolithic chabazite membrane were investigated through PV and VP processes. The typical membrane displayed excellent selectivities of more than 10,000 and 30,000 in 10/90 wt% water/ethanol and water/isopropanol mixtures at 393 K. The membrane exhibited excellent hydrothermal stability in a VP with a 10/90 wt% water/ethanol at 393 K for 72 h. The robust monolithic chabazite membrane with high packing density, strong mechanical strength, large membrane area and excellent water-selective performance significantly outperforms state-of-the-art membranes for dehydration in practical applications.

Synthesis and gas permeation properties of phosphorous-modified chabazite membranes

Among the numerous zeolites, chabazite (CHA) zeolites have attracted attention as a membrane material to separate CO2 with high separation performance, permeability, and stability. The phosphorus modifications improve the physicochemical properties, such as thermal and hydrothermal stability because the modified phosphorus species interacting with the framework aluminum prevents dealumination. In addition, the pore character control provided by phosphorus modifications is expected to improve the gas selectivity compared with conventional CHA membranes. Therefore, phosphorus-modified CHA zeolite (P-CHA) membranes were prepared by the secondary growth method using tetraethyl phosphonium hydroxide (TEPOH) and N,N,N-trimethyl-1-adamantammonium hydroxide as organic structure directing agents (OSDAs). The phosphonium species in P-CHA membrane affected the affinity with carbon dioxide and narrowed the pore size distribution. The effect of phosphorous-modification on the gas permeation properties was confirmed. The P-CHA membrane exhibited high permeances for H2, CO2, and N2, which are 1.5 × 10−6, 6.7 × 10−7, and 2.5 × 10−7 mol m−2s−1Pa−1, respectively. The separation performance of the P-CHA membrane for CO2/CH4 was close to the upper bound in the relationship between permeance and selectivity. For H2/CH4 and N2/CH4, separation performance of the P-CHA membrane exceeded the upper bound.

Conceptual study on extraction of formic acid from the electrolyte after electroreduction of CO2: Desalination and dehydration using a high-silica chabazite zeolite membrane

Here, we propose a two-step pervaporation system with a high-silica CHA (chabazite) membrane, which has sufficient resistance to water and acid, to demonstrate the extraction and condensation of the formic acid formed by electroreduction of CO2. The kinetic diameters of water and formic acid are similar and smaller than the pore size of CHA, while the hydrated electrolyte ions (e.g., K+ and Cl−) are larger than the pore size of CHA. Consequently, the electrolyte ions are separated from the mixture of water and formic acid in the first desalination process, and then water molecules are easily removed from the mixture in the second dehydration process. From 300 ml of an approximately 3 wt% formic acid aqueous solution containing 0.5 M KCl, 10 ml of 18.2 wt% formic acid was obtained.

Ethanol dehydration performance of three types of commercial-grade zeolite permselective membranes.

Many organic solvents form difficult-to-separate mixtures with water and have an affinity for water, making drying a potential reuse prerequisite. Pervaporation (PV) and vapor permeation (VP) membrane technologies hold promise for energy-efficient solvent drying. Several water-selective membrane materials are commercially available, but performance data is limited, particularly for two recently commercialized membrane materials: chabazite (CHA) and T-type zeolites. In this work, commercial-grade samples of CHA and T-type membranes, along with a NaA zeolite membrane, were evaluated for the removal of water from ethanol. The CHA sample had the highest initial PV water permeance (6820 GPU) and water permselectivity (3430) with 5 wt% water in ethanol at 50 °C. Initial NaA membrane performance was slightly lower (6060 GPU and 3260), while the T-type membrane had the lowest initial permeance and selectivity (4260 GPU and 1090). Performance declined over time, most notably for the NaA membrane, for which water permeance fell over 50% through 39 days of testing. The T-type membrane exhibited the steadiest PV water permeance, but the most variable ethanol permeance. The PV performance of the three membranes largely overlapped the predicted range for T-type membranes. That performance generally exceeds the anticipated ethanol drying performance of non-zeolitic PV membranes but is less than that predicted for NaA and CHA membranes. The present CHA membrane results, along with other recent reports, refine earlier predictions of the ethanol dehydration performance of that type of zeolite. The changing performance with time should be understood to properly design a solvent dehydration system.

Hetero-epitaxial growth of chabazite zeolite membranes using an RHO-type seed layer

High-quality chabazite (CHA) zeolite membranes were synthesized from organotemplate-free aluminosilicate gel via epitaxial growth using RHO-type seed layer. Both zeolite RHO seeds (Si/Al = 2.4) and the synthetic gel containing cesium species led to the formation of the CHA zeolite with a high Si/Al ratio of 3.0 and a short synthesis time of 12 h. The effects of seed particles and crystallization time on membrane formation, pervaporation performance, and acid resistance were also investigated. The obtained CHA@RHO membrane prepared using commercial tubular mullite support showed a high flux of 2.3 kg m−2 h−1 and a good separation factor of 3500 for 10/90 wt% water/ethanol mixture at 348 K, which are comparable to those of homogeneous CHA membranes crystallized in organotemplate-free systems from previous reports. Moreover, these membranes were stable for the dehydration of acidic aqueous ethanol solution (with a pH value of 3.0) at 348 K for 8 d.

Green synthesis strategy of chabazite membrane and its CO2/N2 separation performance

Green synthesis strategy of chabazite membrane and its CO2/N2 separation performance

Selectivity enhancement by the presence of grain boundary in chabazite zeolite membranes investigated by non-equilibrium molecular dynamics

The effects of a sub-nanometer grain boundary in all-silica chabazite (CHA) zeolite membranes on their permeation properties were investigated by non-equilibrium molecular dynamics (NEMD). The results indicated that at the total pressure of 0.5 MPa, at 298 K, the CO2 selectivity toward CH4 drastically increased due to the presence of a grain boundary region inside the membrane. This was a consequence of the selective condensation of CO2 in the grain boundary. The calculated CO2 selectivity for the perfect crystal CHA membranes was in the range of 183–278 and depended on the surface orientation of the modeled membranes. Notably, the selectivity was comparable to the previously reported values. Two different membrane structures containing a grain boundary of approximately 0.6 nm were modeled using NEMD. In the case of the grain boundary located inside the membrane, the condensed CO2 molecules in the grain boundary region prevented permeation of CH4, resulting in significantly increased CO2 selectivity. The NEMD results suggest that compared to perfect zeolite crystal membranes, the presence of a grain boundary inside a CHA membrane increases the membrane performance, selectivity, and permeability.

Separation of noble gases using CHA-type zeolite membrane: insights from molecular dynamics simulation

Separation of krypton/xenon is an important issue in some industrial applications. This study evaluates the performance of chabazite (CHA) zeolite membrane for krypton/xenon separation using molecular dynamics simulations. The permeation process was investigated at different temperatures (298, 323, 348, and 373 K) and applied pressures up to 25 MPa. The obtained results demonstrated high selectivity for Kr atoms; thus, only Kr atoms can permeate through the CHA membrane by applying external pressure. Permeation of Kr increased by increasing the temperature, but there was an optimum point for applied pressure. The best permeation (6.93 × 10−5 mol/(m2 s Pa)) was obtained at P = 3 MPa and T = 373 K. However, some simulations were performed at high temperature (700 K) and found higher permeation. The potential of mean force (PMF) of Kr and Xe atoms was also calculated to study the capability of CHA membrane for the separation of Kr/Xe gas mixtures. The results of PMF indicated that the driving force is needed for the permeation of Kr or Xe through the CHA membrane. Xenon atom could not easily pass through the membrane in comparison with Kr atom, which was also confirmed by simulation results.

Chabazite-Type Zeolite Membranes for Effective CO2 Separation: The Role of Hydrophobicity and Defect Structure.

Chabazite (CHA)-type zeolites are promising for the separation of CO2 from larger molecules, such as N2 (relevant to postcombustion carbon capture) and CH4 (relevant to natural gas/biogas upgrading). In particular, the pore size of CHA zeolites (0.37 × 0.42 nm2) can recognize slight molecular size differences between CO2 (0.33 nm) and the larger N2 (0.364 nm) or CH4 (0.38 nm) molecules, thus allowing separation in favor of CO2 through CHA membranes. Furthermore, the siliceous constituents in the CHA zeolite can reduce the adsorption capacity toward the smaller H2O molecule (0.265 nm) and, thus, the H2O permeation rate. This is highly desirable for securing good molecular sieving ability with CO2 permselectivity in the presence of H2O vapor. Indeed, a siliceous CHA film obtained with a nominal Si/Al ratio of 100 (CHA_100) showed high CO2/N2 and CO2/CH4 separation performance, especially in the presence of H2O vapor; ∼13.4 CO2/N2 and ∼37 CO2/CH4 separation factors (SFs) at 30 °C. These SFs were higher than the corresponding values (∼5.2 CO2/CH4 SFs and ∼31 CO2/CH4 SFs) under dry conditions; such improvement could be ascribed to defect blocking by physisorbed water molecules. Finally, the contribution of molecular transport through zeolitic and nonzeolitic parts was quantitatively analyzed by combining information extracted from image processing of fluorescence confocal optical microscopy images with a one-dimensional permeation model. It appears that ∼19 and ∼20% of the total CO2 permeance for CHA_100 were reduced due to transport inhibition by the physisorbed water molecules on the membrane surface and defect, respectively.

Preparation of CHA zeolite (chabazite) crystals and membranes without organic structural directing agents for CO2 separation

CHA zeolite (chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of cesium and fluoride salts on the crystallization of chabazite crystals and membranes were investigated. Highly crystalline chabazite and uniform chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/N2 and CO2/CH4 binary mixtures through chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO2/N2 and CO2/CH4 separation selectivities as high as 16 and 46 together with CO2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO2/N2 and CO2/CH4 binary mixtures, respectively. The CO2/N2 and CO2/CH4 selectivities lost only 11% and 15%, and CO2 permeances lost only 18% and 20% in equimolar wet CO2/N2 and CO2/CH4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K.

Organic template-free synthesis of high-quality CHA type zeolite membranes for carbon dioxide separation

Microporous chabazite (CHA) zeolite is very promising for CO2 capture because of its appropriate pores with molecular dimensions for the preferential adsorption of CO2 molecules. Herein, CHA type zeolite particles and membranes were prepared by using a seeded growth method in the absence of an organic structure directing agent (OSDA) or template. After substantial effort to find appropriate and reliable conditions for obtaining continuous CHA type zeolite membranes, it was recognized that the formation of these membranes is a highly sensitive function of the Si/Al ratio in the synthetic precursor. Using the appropriate Si/Al ratio of ~50, OSDA-free CHA type zeolite membranes were manufactured with high reproducibility. The resulting OSDA-free CHA type zeolite membranes showed maximum CO2/N2 and CO2/CH4 separation factors of ~12.5 ± 3.8 and ~28.8 ± 6.9, respectively, with a moderate CO2 permeance of ~1 × 10−7molm−2s−1Pa−1. Notably, under more realistic wet conditions (i.e., in the presence of H2O vapor), the separation performance at temperatures above 75°C was comparable to that obtained under dry conditions, although permeation was hindered below 50°C, apparently due to the strong adsorption of H2O vapor.

Influence of the Synthesis Parameters on the Morphology and Dehydration Performance of High-Silica Chabazite Membranes

Influence of the Synthesis Parameters on the Morphology and Dehydration Performance of High-Silica Chabazite Membranes

Synthesis of chabazite/polymer composite membrane for CO2/N2 separation

There is considerable interest in using zeolite membranes for gas separations. For CO2 and N2 separation, much research has focused on faujasitic (FAU) membranes. Simulations suggest that chabazite (CHA) membranes can also be good at CO2 and N2 separation. In this study, we have focused on CHA membranes grown on porous polymeric polyethersulfone (PES) supports. Recently, we have reported on a dehydration rehydration hydrothermal (DRHT) process for FAU membrane growth on PES supports, which results in rapid crystallization. It is well known that FAU can be converted to CHA by an interzeolite conversion method, and is our choice for CHA synthesis in this study. A synthesis method for isolated CHA nanocrystals with size of 50–100 nm is reported. Rapid DRHT-based CHA powder synthesis and CHA/PES membrane growth are also being reported, all made by the interzeolite conversion of FAU. The CHA/PES membranes of ∼4 μm thickness were coated with polydimethylsiloxane (PDMS), and at 25 °C, CO2 permeance of 1243 GPU with CO2/N2 selectivity of 19 was observed. The porosity of the PES support was critical to enhancing the formation and stability of the CHA membrane, since the CHA membrane on the PES surface was bonded to interconnected CHA crystals that grew within the PES from the seed crystals.

Microwave synthesis of zeolite CHA (chabazite) membranes with high pervaporation performance in absence of organic structure directing agents

Thin and compact zeolite chabazite membranes were prepared by microwave heating using symmetric stainless steel tubular supports. The microstructures (crystal size and membrane thickness) and separation performances of supported chabazite layers were strongly affected by heating method, synthesis time and synthesis temperature. The best membrane prepared by microwave heating under optimized conditions showed fluxes of 7.3 and 9.1 kg/(m2 h) and separation factors of 2000 and 2500 for 90 wt.% ethanol and isopropanol aqueous solutions at 348 K, respectively. These fluxes were twice as high as those of the chabazite membranes prepared by conventional heating due to the thinner zeolite layers and lower resistance of the support layer in the microwave heating system. The membrane prepared on the 3-time-reused stainless steel support showed comparable separation performance with the membrane on the fresh support, suggesting that the stainless steel supports had a good reuse prospect for chabazite membrane preparation. Synthesis reproducibility and hydrothermal stability of chabazite membranes by microwave heating were also investigated.

Fluoride-mediated synthesis of high-flux chabazite membranes for pervaporation of ethanol using reusable macroporous stainless steel tubes

Pure and intergrown chabazite layers were synthesized on symmetric stainless steel supports using fluoride route. The location of fluoride specie in membrane crystals and the effect of fluoride precursor on the crystallization of supported chabazite layers were demonstrated. Membrane morphologies and qualities were strongly influenced by fluoride concentration, synthesis time, aging time and gel composition. The best membrane synthesized in fluoride media displayed a high flux of 6.0kg/(m2h) (water permeance of 16,000GPU) and separation factor of 2000 (selectivity of 2300) for a 90wt% ethanol aqueous solution at 348K, whose flux was ~60% higher than our pervious fluoride-free membrane. The stainless steel substrates can be repeatedly utilized for the growth of chabazite membrane with high performance after a simple clean process, which reduces membrane cost to a large extent. Fluoride-mediated synthesis of chabazite membrane was reproducible and the resulted membranes showed high hydrothermal, long-term test and acid stabilities.

Chemical vapor deposition on chabazite (CHA) zeolite membranes for effective post-combustion CO2 capture.

Chabazite (CHA) zeolites with a pore size of 0.37 × 0.42 nm(2) are expected to separate CO2 (0.33 nm) from larger N2 (0.364 nm) in postcombustion flue gases by recognizing their minute size differences. Furthermore, the hydrophobic siliceous constituent in CHA membranes can allow for maintaining the CO2/N2 separation performance in the presence of H2O in contrast with the CO2 affinity-based membranes. In an attempt to increase the molecular sieving ability, the pore mouth size of all silica CHA (Si-CHA) particles was reduced via the chemical vapor deposition (CVD) of a silica precursor (tetraethyl orthosilicate). Accordingly, an increase of the CVD treatment duration decreased the penetration rate of CO2 into the CVD-treated Si-CHA particles. Furthermore, the CVD process was applied to siliceous CHA membranes in order to improve their CO2/N2 separation performance. Compared to the intact CHA membranes, the CO2/N2 maximum separation factor (max SF) for CVD-treated CHA membranes was increased by ∼ 2 fold under dry conditions. More desirably, the CO2/N2 max SF was increased by ∼ 3 fold under wet conditions at ∼ 50 °C, a representative temperature of the flue gas stream. In fact, the presence of H2O in the feed disfavored the permeation of N2 more than that of CO2 through CVD-modified CHA membranes and thus, contributed to the increased CO2/N2 separation factor.

Potential Separation of SF6 from Air Using Chabazite Zeolite Membranes

AbstractChabazite zeolite membranes were synthesized by the secondary growth method. Chabazite powders were obtained by decomposition of zeolite Y and subsequent ion exchange to produce a fully exchanged potassium chabazite. The synthesized powders were used as seeds for membrane synthesis. Chabazite membranes were prepared via hydrothermal synthesis on porous α‐alumina disks as supports. The effects of synthesis parameters including synthesis temperature and synthesis time on the chabazite zeolite membranes were investigated. The synthesized powders and membranes were characterized and the separation performance of the synthesized membranes were evaluated by separation of N2/SF6 and O2/SF6 gas mixtures. Gas permeation results are discussed in terms of optimum synthesis temperature and time.

Preparation of chabazite membranes by secondary growth using zeolite-T-directed chabazite seeds

Chabazite crystals were directly prepared from template-free aluminosilicate gel with the addition of nano-sized zeolite T (∼100nm). This new route requires only one thirtieth seeds amount for a certain product, and one twentieth synthesis time compared with the classic one by the conversion of zeolite Y crystals. A pure and dense chabazite membrane was prepared on macroporous supports by secondary growth. The membrane synthesis parameters such as seeds, supports and synthesis time on membrane formation and pervaporation performance were also studied. Eight chabazite membranes prepared on macroporous stainless-steel supports showed a high average flux of 3.4kgm−2h−1 and high average selectivity of 2100 with low deviations on the flux and selectivity for a water/ethanol (10/90wt%) mixture at 75°C, indicating membrane synthesis using stainless-steel supports had a good reproducibility. The as-synthesized chabazite membranes also showed good hydrothermal stability under pervaporation test in a water-rich ethanol aqueous solution.

Synthesis of a mordenite/ZSM-5/chabazite hydrophilic membrane on a tubular support. Application to the separation of a water-propanol mixture.

A selectivity of 71 is achieved in the separation of a gas phase water-propanol mixture, using a mordenite/ZSM-5/chabazite membrane that is hydrothermally synthesized onto the inner surface of a porous α-alumina tubular support.