Growth of a faujasite-type zeolite membrane and its application in the separation of saturated/unsaturated hydrocarbon mixtures

High-Performance FAU Zeolite Membranes Derived from Nano-Seeds for Gas Separation

In this study, high-performance FAU (NaY type) zeolite membranes were successfully synthesized using small-sized seeds of 50 nm, and their gas separation performance was systematically evaluated. Employing nano-sized NaY seeds and an ultra-dilute reaction solution with a molar composition of 80 Na2O: 1Al2O3: 19 SiO2: 5000H2O, the effects of synthesis temperature, crystallization time, and porous support (α-Al2O3 or mullite) on the formation of FAU membranes were investigated. The results illustrated that further extending the crystallization time or increasing the synthesis temperature led to the formation of a NaP impurity phase on the FAU membrane layer. The most promising FAU membrane with a thickness of 2.7 µm was synthesized on an α-Al2O3 support at 368 K for 8 h and had good reproducibility. The H2 permeance of the membrane was as high as 5.34 × 10-7 mol/(m2 s Pa), and the H2/C3H8 and H2/i-C4H10 selectivities were 183 and 315, respectively. The C3H6/C3H8 selectivity of the membrane was as high as 46, with a remarkably high C3H6 permeance of 1.35 × 10-7 mol/(m2 s Pa). The excellent separation performance of the membrane is mainly attributed to the thin, defect-free membrane layer and the relatively wide pore size (0.74 nm).

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.

Membranes for olefin-paraffin separation: An industrial perspective

In the next decade, separation science will be an important research topic in addressing complex challenges like reducing carbon footprint, lowering energy cost, and making industrial processes simpler. In industrial chemical processes, particularly in petrochemical operations, separation and product refining steps are responsible for up to 30% of energy use and 30% of the capital cost. Membranes and adsorption technologies are being actively studied as alternative and partial replacement opportunities for the state-of-the-art cryogenic distillation systems. This paper provides an industrial perspective on the application of membranes in industrial petrochemical cracker operations. A gas separation performance figure of merit for propylene/propane separation for different classes of materials ranging from inorganic, carbon, polymeric, and facilitated transport membranes is also reported. An in-house-developed model provided insights into the importance of operational parameters on the overall membrane design.

Recent Progress in a Membrane-Based Technique for Propylene/Propane Separation

The similar physico-chemical properties of propylene and propane molecules have made the separation process of propylene/propane challenging. Membrane separation techniques show substantial prospects in propylene/propane separation due to their low energy consumption and investment costs, and they have been proposed to replace or to be combined with the conventional cryogenic distillation process. Over the past decade, organosilica membranes have attracted considerable attention due to their significant features, such as their good molecular sieving properties and high hydrothermal stability. In the present review, holistic insight is provided to summarize the recent progress in propylene/propane separation using polymeric, inorganic, and hybrid membranes, and a particular inspection of organosilica membranes is conducted. The importance of the pore subnano-environment of organosilica membranes is highlighted, and future directions and perspectives for propylene/propane separation are also provided.

Membrane-Based Olefin/Paraffin Separations

Efficient olefin/paraffin separation is a grand challenge because of their similar molecular sizes and physical properties, and is also a priority in the modern chemical industry. Membrane separation technology has been demonstrated as a promising technology owing to its low energy consumption, mild operation conditions, tunability of membrane materials, as well as the integration of physical and chemical mechanisms. In this work, inspired by the physical mechanism of mass transport in channel proteins and the chemical mechanism of mass transport in carrier proteins, recent progress in channel-based and carrier-based membranes toward olefin/paraffin separations is summarized. Further, channel-based membranes are categorized into membranes with network structures and with framework structures according to the morphology of channels. The separation mechanisms, separation performance, and membrane stability in channel-based and carrier-based membranes are elaborated. Future perspectives toward membrane-based olefin/paraffin separation are proposed.

Synthesis of FAU-Type Zeolite Membranes with Antimicrobial Activity

In this study, a layer of a pure and dense phase of FAU-type zeolite was synthesized directly on the surface of α-Al₂O₃ plane macroporous support. Before hydrothermal synthesis, a step of cleaning of the support by an anionic detergent was performed, a roughness surface is created, allowing the anchoring of the zeolite nuclei and then their growth, favoring in this sense the formation of a homogeneous zeolite layer. The obtained membranes were fully characterized using X-ray diffraction analysis (XRD), nitrogen sorption, scanning electron microscopy (SEM), and mercury porosimetry. After 24 h of thermal treatment at 75 °C, a homogeneous zeolite layer composed of bipyramidal crystals of FAU-type zeolite is obtained with a thickness of about 2.5 µm. No obvious defects or cracks can be observed. It was found that the increase in heating temperature could lead to the appearance of an impurity phase, GIS-type zeolite. Then the ideal zeolite membrane was exchanged with Ag⁺ or Zn²⁺ cations to studies their antimicrobial properties. Zeolites membranes exchanged with Ag⁺ showed an agar-diffusive bactericidal activity against gram negative Escherichia coli (E. coli) bacteria. Zn²⁺ exchanged zeolite membrane presented a bacteriostatic activity that is less diffusive in agar. As expected, non-exchanged zeolite membrane (in its Na⁺ form) have no effect on bacterial activity. This process is particularly interesting for the synthesis of a good quality FAU-type zeolite membranes with antimicrobial properties.

Efficient Removal of Volatile Organic Compounds by FAU-Type Zeolite Coatings

Silicone and pure organic binders were used to develop FAU-type zeolite coatings applied on pre-treated aluminum substrates by using a spraying method and then cured under specific conditions. The influence of the amount of binder on adhesion properties of zeolite coatings was first investigated to determine the optimum ratio between zeolite and binder. Zeolite coatings were then elaborated with a high zeolite content (between 70 and 80 wt.%) to ensure high adsorption capacities. The amount of binders involved in different zeolite coatings was sufficient to achieve interesting adhesion and cohesion properties. The accessibility of zeolite microporosity was studied by nitrogen adsorption-desorption measurements, which revealed a very small or no loss of the micropore volume for the optimized coatings. Volatile Organic Compounds (VOCs) adsorption measurements were carried out using n-hexane as probe molecule. FAU-type zeolite in powder form adsorbs 180 mg/g_{anhydrous zeolite}, whereas the amounts of n-hexane adsorbed by zeolite coatings ranged from 131 to 175 mg/g_{anhydrous zeolite}.

Synthesis of fly ash-based self-supported zeolites foam geopolymer via saturated steam treatment

It is reported the synthesis of self-supported zeolite foam geopolymers (ZFG) from fly ash (FA) using saturated steam. These materials could be used as porous bulk-type solid adsorbents. Characterization analyses show that the alkaline activator (AA) modulus affects the structural unit distribution in foam geopolymer (FG), which ultimately provides different chemical compositions for the nucleation of zeolites resulting in different types of zeolites. Furthermore, the pore structure of ZFGs range from micro- to the macro-range and combine the functional micro-porosity of the zeolites, the meso-porosity and the macro-porosity of the foam geopolymer. ZFGs exhibit low apparent density (approximately 355 Kg/m³) and higher compressive strength (ranging from 1.03 MPa to 2.96 MPa). The possibility of using these innovative materials as heavy metal (Pb²⁺) adsorbents was then evaluated. The results show that they have a great capacity for the removal of the Pb²⁺ (as high as 123.2 mg g^-1) and high adsorption efficiency (equilibration time as fast as 60 min). The lightweight bulk-type ZFGs could be used in packed beds as membranes for easy collection, unlike granular adsorbents. Moreover, their production contributes to the elimination of polluting FA solid wastes, mitigating the environmental impact associated with this waste disposal, while decreasing production costs.

Effect of host framework on the diffusion process in microporous material: a molecular dynamics simulation investigation

One of the central assumptions when a particle moves through a window in microporous materials is that interaction of the diffusing particle with the silicon (Si) and aluminum (Al) atoms of the framework can be neglected, as the presence of bulkier oxygen in the host structure is thought to hinder close proximity of the diffusing particle to Si and Al. We examine this assumption, exploring the diffusion path and cross-checking the bottleneck associated with the diffusion process. Our study reveals that short-range interactions between the diffusing species and Si/Al of the host have a significant effect on the diffusion process. Guest-host interaction energy increases significantly if interaction between Si and Al atoms with the diffusing species is considered. The self-diffusion coefficient (D) decreases significantly in the linear regime, whereas in the anomalous regime, surprisingly, D increases. The increase in D is due to a decrease in the activation energy in the anomalous regime, whereas in the linear regime, activation energy increases, thus D decreases. Graphical abstract a Interaction energies (E _a) for different LJ potential for guest-guest interactions (σ_gg) along the diffusion path; b correspondingdiffusivity values.

Mercaptoundecanoic acid capped palladium nanoparticles in a SAPO 34 membrane: a solution for enhancement of H₂/CO₂ separation efficiency

In this work, the high quality Pd/SAPO 34 membranes were grown on the support using a secondary (seeded) growth hydrothermal technique followed by insertion of 11-mercaptoundecanoic acid capped palladium (MUA-Pd) nanoparticles (NPs) to the membrane surface. For this, first, the indigenous low cost clay-alumina support was treated with poly diallyldimethylammonium chloride (PolyDADMAC) polymer, and subsequently, a seed layer of SAPO 34 crystals was deposited homogeneously in a regular orientation. Since PolyDADMAC is a high charge density cationic polymer, it assisted in reversing the charge of the support surface and produced an attractive electrostatic interaction between the support and zeolite crystals. This may facilitate the zeolite grain orientation in the synthesized membrane layer. Here, the Pd NPs were deposited in the membrane matrix by a simple dip-coating method. After thermal treatment of the Pd/SAPO 34 membrane, the defects were formed because of the removal of the structure-directing agent (SDA) from the zeolite pores but the presence of Pd NPs, which were entrapped inside the nonzeolitic pores and clogged the defects of the membrane. Field emission scanning electron microscopy (FESEM) and elemental mapping of the membrane cross-section confirmed that most of the Pd NPs were deposited at the interface of the membrane and the support layer which may increase the membrane efficiency, i.e., separation factor, as well as permeability of H2 through the membrane. As the membrane structure was associated with the oriented crystal, the pores were more aligned and permeation adequacy of H2 through the membrane enhanced. These membranes have a relative hydrogen permeance of 14.8 × 10(-7) mol·m(-2)·s(-1)·Pa(-1). The selectivity of H2/CO2 based on single gas permeation was 10.6, but for the mixture gas (H2/CO2 55:45), the H2/CO2 mixture separation factor increased up to 20.8 at room temperature. It is anticipated that this technique may be useful for making a defect free membrane and also a hydrogen selective Pd loaded membrane with lower cost (as the quantity of Pd is low) which can be utilized for a "clean energy" related application.

Mussel-inspired polydopamine modification of supports for the facile synthesis of zeolite LTA molecular sieve membranes

Inspired by bio-adhesive ability of marine mussel, a versatile and effective synthesis strategy was developed to prepare dense zeolite LTA membranes.

Stepwise synthesis of sandwich-structured composite zeolite membranes with enhanced separation selectivity

Sandwich-structured composite zeolite membranes with enhanced hydrogen selectivity were prepared on porous α-Al(2)O(3) supports by using 3-aminopropyltriethoxysilane as an interlayer.