Molecular Sieve Materials Research Articles

Intermediate layer free PVDF evolved CMS on ceramic hollow fiber membrane for CO2 capture

The use of carbonized polymers has ushered in a new class of materials with profound implications for the gas separation industry. This study explored the transformation of polyvinylidene fluoride (PVDF) into microporous carbon structures coated onto ceramic substrates, enabling in situ growth of carbon molecular sieve (CMS) materials over hollow fibers. This material featured more robust CMS membranes than alumina and demonstrated exceptional capability in vital gas separations, particularly for CO2/CH4. This novel approach increased the selectivity for gases and exhibited remarkable aging resilience, so the material is a compelling candidate for high-performance gas separations. Furthermore, after 31 days, the weathered carbon dioxide membrane exhibited a slight permeability drift from 234.88 barrers to 195.35 barrers, while the CO2/CH4 ratio increased from 24.21 to 57.14, surpassing the Robeson 2008 upper bound. The PVDF-derived supported hollow fiber carbon membranes provide a blueprint for designing membranes for carbon capture. With the high packing density of the hollow fiber membrane and improved mechanical strength of the supported carbon membrane, this approach overcame the high fabrication costs and brittleness of other carbon membranes. In addition, the entire process for preparation of the PVDF carbon films is easily scaled up and has great potential for future practical application.

Cryogenic Testing of Molecular Sieve Materials for use in Hydrogen Liquefaction

As hydrogen continues to gain momentum as a clean fuel and energy carrier in industrial sectors, hydrogen liquefaction has emerged as an essential part of the supply chain to reduce transportation and storage costs. Hydrogen is typically produced from either electrolysis, steam-methane-reforming, or as a biproduct from chemical processing, which leads to a broad range of potential impurities in the hydrogen feed gas. Molecular sieve materials have traditionally been used to remove impurities in the hydrogen feed to prevent impurities from freezing out during liquefaction, creating blockages which disrupt operations. This work presents a new experimental system that has been developed to study cryogenic purification materials over a broad range of cryogenic temperatures and impurity levels. Results of common molecular sieve materials are presented.

Bendable and Chemically Stable Metal-Organic Hybrid Membranes for Molecular Separation.

Crystalline porous metal-organic materials are ideal building blocks for separation membranes because of their molecular-sized pores and highly ordered pore structure. However, creating ultrathin, defect-free crystalline membranes is challenging due to inevitable grain boundaries. Herein, we reported an amorphous metal-organic hybrid (MOH) membrane with controlled microporosity. The synthesis of the MOH membrane entails the use of titanium alkoxide and organic linkers containing di/multicarboxyl groups as monomers in the polymerization reaction. The resultant membranes exhibit similar microporosity to existing molecular sieve materials and high chemical stability against harsh chemical environments owing to the formation of stable Ti-O bonds between metal centers and organic linkers. An interfacial polymerization is developed to fabricate an ultrathin MOH membrane (thickness of the membrane down to 80 nm), which exhibits excellent rejections (>98% for dyes with molecular weights larger than 690 Da) and high water permeance (55 L m-2 h-1 bar-1). The membranes also demonstrate good flexibility, which greatly improves the processability of the membrane materials.

Study on Green Controllable Preparation of Coal Gangue-Based 13-X Molecular Sieves and Its CO2 Capture Application

Carbon dioxide emissions are the primary and most direct contributor to global warming, posing a significant hazard to both the environment and human health. In response to this challenge, there has been a growing interest in the development of effective carbon capture technologies. This study involved the synthesis of 13-X molecular sieve porous materials using solid waste coal gangue as a source of silicon and aluminum. The synthesis process involved the controlled utilization of an “alkali fusion-hydrothermal” reaction system. The resulting materials were characterized for their structure, morphology, and crystal composition using X-ray diffraction and field emission scanning electron microscopy. These 13-X molecular sieve materials were employed as adsorbents to capture carbon dioxide gas, and their adsorption performance was investigated. The findings indicated that the 13-X molecular sieve materials possess uniform pores and complete crystalline morphologies, and they exhibited an adsorption capacity of 1.82 mmol/g for carbon dioxide at 0 °C. Consequently, this study not only converted solid waste gangue into high-value products but also demonstrated effective atmospheric carbon dioxide capture, suggesting that gangue-based 13-X molecular sieves may serve as a potential candidate for carbon capture.

Synthesis, Characterizations, and Recent Applications of the Silica-based Mobil Composition of Mesoporous Material: A Review

Silica-based mesoporous materials are a class of porous materials with unique characteristics such as ordered pore structure, large surface area, and large pore volume. This review covers the different types of porous material (zeolite and mesoporous) and the physical properties of mesoporous materials that make them valuable in industry. Mesoporous materials can be divided into two groups: silica-based mesoporous materials and non-silica-based mesoporous materials. The most well-known family of silica-based mesoporous materials is the Mesoporous Molecular Sieves family, which attracts attention because of its beneficial properties. The family includes three members that are differentiated based on their pore arrangement. In this review, the major applications of the Mobil Mesoporous Molecular Sieves family, such as catalysts, adsorbents, and drug delivery agents, have been surveyed. Furthermore, the synthesis of the Mesoporous Molecular Sieves materials, the silica sources, the importance of templates, and the mechanisms of the synthesis are discussed herein. Members of this material family are characterized by many physicochemical properties that are closely related to their high silica content, crystalline structure, and pore arrangement. Commonly, the members of this family have large surface areas, high pore volumes, small pore sizes, and narrow and uniform particle size distributions. These properties enable numerous industrial applications and opportunities for scientific studies to further develop existing materials or manufacture new ones.

Advanced Metal–Organic Frameworks for Gas Separation

In the chemical process, the effective separation of small gaseous molecules with similar physical and chemical properties is of great significance. In addition, clean energy sources such as hydrogen and methane are regarded as an ideal alternative to conventional fossil fuels. However, at present, the storage technology of this kind of natural gas is not perfect. The entry of harmful substances produced by human activities into the atmosphere has become a global danger that is becoming more and more worrying. It has become an important topic for scholars and industries Development of a multi-stage channel structure with high efficiency and low energy consumption for effective separation, storage or capture of toxic and harmful substances. In order to solve this problem, we intend to study the adsorption and adsorption of MOFs in the environment aboutH2/N2, H2/CO and H2/CH4 and some other gases. Compared with molecular sieve, activated carbon and other conventional inorganic porous materials, MOFs have a broad application prospect in gas adsorption and storage with unique properties. At present, the research of metal-organic frame materials with high stability has made great progress. Through the implementation of this project, it is expected to promote its wide application in air pollution control and other aspects.

Preparation of a High-Silicon ZSM-5 Molecular Sieve Using Only Coal Gangue as the Silicon and Aluminum Sources.

The traditional preparation of ZSM-5 molecular sieves relies on chemical reagents to provide silicon and aluminum sources, which are limited as raw materials and cannot be commonly used in production practice. Using coal gangue as the raw material and using medium-temperature chlorination roasting and the pressure acid leaching process to control the silicon-aluminum ratio [n(Si/Al)] of coal gangue, a ZSM-5 molecular sieve was prepared using the alkali melting hydrothermal method. The pressure acid leaching process solved the limitation that kaolinite and mica cannot simultaneously be activated. Under optimal conditions, the n(Si/Al) of the coal gangue increased from 6.23 to 26.14 and complied with the requirements for the synthesis n(Si/Al) of a ZSM-5 molecular sieve. The effect of n(Si/Al) on the preparation of the ZSM-5 molecular sieve was studied. Finally, spherical granular ZSM-5 molecular sieve material with a microporous specific surface area of 169.6329 m2/g, an average pore diameter of 0.6285 nm, and a pore volume of 0.0988 cm3/g was prepared. Providing ideas for the high-value utilization of coal gangue, it is significant for solving the problem of coal gangue solid waste, as well as the problem of ZSM-5 molecular sieve feed stock.

Study on degradation of cooking fume by compound filter material and UV photodegradation.

Environmental contamination issues have steadily surfaced with the rapid development of the cooking industry. In this paper, the front end of the cooking fume exhaust was filtered by the filter material, and then, the ultraviolet photolysis technology was used for in-depth treatment. The filter material filtration performance of glass fiber, molecular sieve, and composite filter material was studied by the filter efficiency, filter resistance, and quality factor three filter performance indexes. The results show that the filter wind speed has a significant influence on the filter material fume filtration characteristics. The filtration efficiency of the pre-filter material changes the least with the increase of the wind speed when the wind speed is 18m·s-1 and the filter material tilt Angle is 60°; meanwhile, the pressure drop of the two kinds of filter material is reduced, and the quality factor is improved. Under the optimal wind speed and angle, the composite filter material of glass fiber and molecular sieve combined with UV photolysis technology was used to study the treatment of formaldehyde and acrolein, which are two volatile organic pollutants with high content in cooking fume, and the mineralization mechanism of formaldehyde and acrolein under UV light was analyzed. The results showed that the removal rates of formaldehyde and acrolein could reach 99.84% and 99.75%, respectively.

Experimental and Kinetic Modeling of n-Heptane Hydroconversion over Mesoporous Pt/MSU Catalyst. Effect of Site Activity and Residence Time

A zeolite-based mesostructured (MSU) molecular sieve material was synthesized, characterized, and used in the preparation of Pt (0.6 and 1 wt %) supported catalysts for hydroconversion of n-heptane under the experimental conditions of 300–450°C and 760 mmHg. Samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherm, and NH3-TPD (temperature-programmed deposition) techniques. The activity test shows that catalysts have good activity and selectivity for isomerization reaction. Also, increasing metal sites, selectivity tends to the production of aromatization reaction in the heterogeneous catalytic process. Based on experimental results, a kinetic model of this reaction was carried out. Based on other publications and combining the examined features, a network of the reaction was proposed. It can be claimed that the results of converging the feed from the kinetic model are in good agreement with the experimental results. Some of the superiorities of this model compared to other models are the determination of kinetics parameters, source of isomers, aromatic, and cracked products distinctly with emphasis on the effect of site activity and residence time over metal-acid sites.

Performance Assessment of Molecular Sieves for Sulfur Recovery Unit Tail Gas Treating

Due to stricter worldwide environmental mandates on SO2 emission from oil and gas industrial facilities, the modified Claus process, which is the primary tool for reducing emission of SO2 into the atmosphere in these facilities, has undergone a lot of innovative changes during the past decades. An example of such innovation is the addition of what is called tail gas treating (TGT) technologies. Currently, advanced TGT technologies ensure that gas plants and refineries emit less than 0.01% (v/v) of the sulfur species that enter into the sulfur recovery units; they commonly use absorption-based processes to separate sulfur species from the tail gas. Because of this requirement, TGT technologies are expensive. This paper reports the data that were obtained from bench-scale tests that were carried out to assess the feasibility of using commercially available adsorbents for the process that is described in the patent, Two-Stage Adsorption Process for Claus Tail Gas Treatment, US Patent No.10662061. In one of the embodiments of this process, the tail gas is treated in two steps. It is first dehydrated by 3A molecular sieves and then by 5A molecular sieves to remove H2S. The separation in the second step will ensure the presence of a rich H2S-laden stream that is ready for routing to the thermal reactor of the modified Claus process. The data collected in this study indicate the following: (1) Commercial molecular sieves can be used for cost-effective tail gas treatment of natural gas plants’ and refineries’ sulfur recovery units. (2) This cost-effectiveness of such use can be valid when molecular sieve material selection is as described in US Patent No.10662061, “Two-Stage Adsorption Process for Claus Tail Gas Treatment”. (3) Adsorption-based tail gas treatment is advantageous since it results in enabling the global oil and gas industry to virtually eliminate all SO2 emissions from its facilities.

Study on Influencing Factors of Molecular Sieve Oxygen-Production System

Molecular sieve oxygen-production technology, as a kind of air separation–oxygen production, is receiving more and more attention from every oxygen industry. The two-bed molecular sieve oxygen-production system studied in this paper can generally produce enriched gas with an oxygen concentration of more than 90%, which has the characteristics of strong applicability, high reliability, low cost and high efficiency. However, the gas oxygen concentration of a production system is greatly affected by internal and external factors such as the molecular sieve materials, atmospheric pressure and temperature environment. Through the continuous research of the molecular sieve oxygen-production system, it has been found that the oxygen cycle of the molecular sieve bed and the diameter of the washing and sizing hole also have an effect on the gas oxygen concentration of the production system. Therefore, in this paper, the two-bed molecular sieve oxygen-production device is the research object, with different oxygen-production cycles (including pressure time) and different washing and sizing hole diameter simulation experiments used to explore the molecular sieve oxygen-production system’s optimal oxygen-production cycle (including pressure time) and the rinsing sizing hole’s optimal aperture, to find the structure of the oxygen-production system and the control parameters for the oxygen-production efficiency of the law. The results show that the optimal oxygen-production cycle of the molecular sieve system is 8.0 s (pressure equalization time is 1.3 s), and the optimal diameter of the washing and sizing hole is 0.8 mm.

Morphology evolution of zeolite MFI nanosheet fragments during secondary growths

Two-dimensional zeolite materials (nanosheets) offer facile ways to fabricate highly selective separation membranes; however, synthetic methods for non-aggregated zeolite nanosheets are still limited. For MFI-type zeolite materials, their nanosheets can be directly synthesized by the seeded growth with diammonium-cation structure-directing agents (SDA). In this study, we further investigated the secondary growth of zeolite MFI nanosheet fragments using diammonium-cation SDAs, to expand our knowledge on the self-regulated growth of zeolite MFI crystals. Owing to the absence of rotational intergrowth, nanosheet-fragment seeds yield zeolite MFI nanosheets with improved uniformity in thickness and shape, facilitating the investigation of their morphological variation under extensive synthesis conditions. This revealed that two distinct nanosheet morphologies, with strongly coupled shapes and predominant thicknesses, can be acquired depending on the synthesis temperature. Particularly, the growth along the c-axis is facilitated with the increasing synthesis temperature, thereby yielding flat zeolite MFI nanosheets with slight thickening. The isolated ad-layers on these nanosheets confirm that the thickening of nanosheets evolves with 2-nm step growth, which is identical to the nanosheet formation from cylindrical nanocrystal seeds. Finally, fractions of rhombus-shaped and rectangular nanosheets vary with the type of fragment seeds, indicating that the transition between those two nanosheets is kinetically hindered. The growth of zeolite MFI nanosheets using the diammonium-cation SDAs provides valuable insights on zeolite crystal growths, which will promote advanced synthesis techniques for the morphology control of zeolites and, probably, other molecular sieve materials.

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

Facile temperature-controlled preparation of nanowire OMS-2 and its high performance in peroxymonosulfate-activated catalytic degradation of organic pollutants

Currently, nanowires present a type of unique one-dimensional materials showing promising prospects in many fields. The octahedron molecular sieve (OMS-2, with chemical compositions of K[Formula: see text][Formula: see text]Mn8O16) materials are utilized extensively as efficient catalysts for numerous critical reactions. In this work, it was found that the evolution from [Formula: see text]-MnOOH microrod to OMS-2 nanowire can be induced facilely by altering the temperature of hydrothermal treatment. The obtained OMS-2 nanowire exhibited high catalytic activity and high durability in peroxymonosulfate (PMS) activated degradation of rhodamine B (RhB) or methylene blue (MB). Under optimum conditions (OMS-2 catalyst: 0.1 g⋅L[Formula: see text]; RhB or MB: 8 mg⋅L[Formula: see text], 100 mL), the degradation can be completed within 10 min. The possible reason for OMS-2 nanowire’s high performance was also proposed.

Preliminary study of molecular sieve materials to alleviate problems faced by tropical peatland

Zeolites are crystalline aluminosilicates usable for numerous applications, including in the separation or purification gas processes, catalysts, ion exchanger and adsorbent. These benefits are due to their molecular sieve property. One of the appropriate technologies for the peat management related to C sequestration and potential peat fire suppressor is molecular sieve material, i.e., zeolite-clinoptilolites and other gas adsorbent material taken from empty fruit bunches of oil palm (EFBOP) obtained through the pyrolysis process (biochar). This study assessed the physicochemical and morphological characterization of natural zeolite-clinoptilolite type, originated from Bayah, Banten, Indonesia, and biochar as gas adsorbent to minimize greenhouse gas emissions and C sequestration. Physicochemical characteristics of 60-80;80-100, 100-150 particles mesh size of zeolite and biochar were measured according to standard analytical procedures based on Kepmentan 261/KPTS/SR.310/M/4/2019. Mineralogical characteristics and the capacity to absorb greenhouse gasses (CO2 and N2) were determined using SEM-EDS and Brunauer-Emmet-Teller analysis, respectively. The result indicated that 100- 150 mesh zeolite had a higher CEC value (126.45 cmol(+) kg−1), CO2 (1.0586 mmol g−1) and N2 adsorption capacity (75.6 cm3 g−1), compared to biochar originated from EFBOP 26.9 cmol(+) kg−1; 0.071 mmol g−1; and 1.66 cm3 g−1, respectively. Biochar observed in this research yielded a higher pH and organic carbon content, with larger pore space. Combining zeolite and biochar provided an optimal result to deplete greenhouse gas emission i.e., 0.3662 mmol g−1, and improved water retention as indicated by water holding capacity percentage.

Co-transport of water and p-xylene through carbon molecular sieve membranes

Carbon molecular sieve (CMS) materials are a potential candidate for scalable and high-performance reverse osmosis membranes due to their impressive chemical and thermal stabilities. Moreover, they have the potential to enable impressive rejections of small neutral solutes from water based on their known ability to separate small organic molecules. CMS has been extensively examined for gas and organic solvent separations, but the transport of organic and aqueous mixtures through CMS microstructures is poorly understood. In this work, we investigated the sorption, diffusion, and permeation behavior of organic compounds and water in poly(vinylidene fluoride)(PVDF)-derived CMS (PVDF-CMS). Experimental observations of diffusion, sorption, and permeation shows how the properties of penetrants such as polarity and molecular size affect the transport rates and selectivity. These basic transport and sorption parameters are utilized in sorption-diffusion models to permeation rates of water-organic mixtures in CMS membranes. The transport of water and p-xylene in CMS was experimentally confirmed to follow the sorption-diffusion mechanism. The sorption-diffusion model ideal permselectivity indicates that the CMS is p-xylene selective over water. Water/p-xylene mixture permeation experiments revealed an increased selectivity of p-xylene over water, thus providing tentative evidence for a competitive sorption-selective separation mechanism. This work suggests that CMS membranes exhibit organic-permeable separation properties in water/organic separations. The results presented here highlight the potential for the removal of dilute organics in water via CMS pervaporation membranes.

From Al-SBA-15 to Ga-SBA-15: Morphology and acidity evolution in the acid-free synthesis

Tuning the morphological and acidic properties of mesoporous molecular sieve materials is highly valuable for catalyst design towards the reactions involving large molecules. In this work, a series of Ga-containing SBA-15 ordered mesoporous materials (OMMs) were synthesized following the acid-free strategy. Ga-SBA-15 exhibits an acid amount of 0.48 mmol/g, comparable to the Al-SBA-15 (0.45 mmol/g). In addition, it is found that the straight short stick particles of Al-SBA-15 integrally bended upon a replacement of Al with Ga and the tendency continuous with the incremental addition of gallium, until fully transforms into the highly dispersed isolated bending particles of Ga-SBA-15. Owing to the improved interparticle-type mesoporosity derived from the dispersed bending particles, the active sites on external surface are highly accessible for large molecules. As for the acidic property, the Brönsted-type acidic property of Al-SBA-15 changed to the Lewis-type acidity with the replacement of gallium. In the Ga-SBA-15 case, more than 93% of strong acid sites were confirmed as Lewis characteristic. On the other hand, Low Density Polyethylene (LDPE) exhibits a faster decomposition rate over Ga-SBA-15 than Al-SBA-15 and Al–Ga bimetallic doped SBA-15 (galloaluminosilicate) catalysts. • Ga-containing SBA-15 mesoporous materials were synthesized following the acid-free strategy. • Replacement of Al with Ga induces a morphological evolution from the straight short stick to a bending shape. • Ga-SBA-15 exhibits strong Lewis acidity and hierarchical pore structure solely composed of interparticle-type mesopores.

Assessment of micropore accessibility for hydrocarbon oxidation in manganese oxide sieves

Octahedral molecular sieve (OMS) materials classified by their different tunnel sizes are defined by edge-sharing MnO6 octahedra. Four different OMS materials (OMS-1, OMS-2, OMS-5, and OMS-6) are benchmarked for ethane (C2H6) and cyclohexane (C6H12) oxidative dehydrogenation (ODH) and compared with commercial MnO2, M1 phase MoVTeNb oxide, and vanadium oxide (V2O5). The accessibility of the quadrilateral tunnels of the OMS materials to C2H6 and C6H12 were further evaluated using density functional theory (DFT). C2H6 and C6H12 ODH rates for the four OMS materials were higher than those measured for commercial MnO2, MoVTeNbO, and V2O5. The C2H6/C6H12 rate ratios on the four OMS oxides are larger than V2O5. Rate relations for selective accessibility for C2H6 in small pores, accessibility to both molecules in large pores, and the presence of tunnel defects are discussed. Product selectivities show slightly higher ethylene selectivity in smaller pores suggesting possible connections between pore confinement and selectivity.

Influence of hydrothermal time on the formation of SAPO-56 structure and its catalytic activity of removal NOx by NH3-SCR with Cu/SAPO-56

The SAPO-56 molecular sieve material was prepared under hydrothermal conditions at 200 °C with different hydrothermal times using precursors including Al(OH)3, LUDOX AS-30, H3PO4, and TMHD (N,N,N′,N′-tetramethyl-hexane-1,6-diamine) as an organic structure-directing agent. The samples were characterized by X-ray diffraction, field emission scanning electron microscopes, Energy-dispersive X-ray spectroscopy, NH3 temperature - programmed desorption, N2 adsorption-desorption, and UV-Vis Diffuse Reflectance Spectroscopy methods. Electron paramagnetic resonance technique was applied to determine isolated Cu2+ ions in the framework. Although materials shared the same AFX framework structure, they owned different physicochemical properties, especially in terms of crystal size, surface area, and acidity. Next, the catalytic activity of removal NOx of Cu/SAPO-56 and Cu/ZSM-5 using commercial ZSM-5 as support with the loading of 3 wt%Cu synthesized by aqueous ion-exchange method was assessed in the selective catalytic reduction with NH3.

In-situ generation of polymer molecular sieves in polymer membranes for highly selective gas separation

Molecular sieve materials (MSMs) are regarded as ideal fillers for the fabrication of mixed matrix membranes (MMMs). However, the preparation of MSMs-based MMMs usually involves physical mixing of insoluble filler and polymer matrix, which inevitably leads to filler agglomeration and two-phase incompatibility especially for high filler loading. Herein, we report a new strategy to construct MMMs through generating polymer molecular sieve (PMS) fillers in-situ in a thermally stable polymer matrix by post heating treatment. The in-situ generated PMS-based MMMs (i-PMS MMMs) possess greatly improved interfacial compatibility between matrix and filler and the effective loading content of PMS filler can reach as high as 70 wt%. The molecular sieving property of PMS endows the i-PMS MMMs with high gas selectivity of 183.0 for H2/CH4 and 128.9 for H2/N2, approaching or exceeding the state-of-the-art 2015 upper bound.