Application Of Molecular Sieves Research Articles

Scalable, Interfacially Synthesized, Covalent-Organic Framework (COF)-Based Thin-Film Composite (TFC) Hollow Fiber Membranes for Organic Solvent Nanofiltration (OSN).

Covalent organic frameworks have great potential for energy-efficient molecular sieving-based separation. However, it remains challenging to implement COFs as an alternative membrane material due to the lack of a scalable and cost-effective fabrication mechanism. This work depicts a new method for fabricating a scalable in situ COF hollow fiber (HF) membrane by an interfacial polymerization (IP) approach at room temperature. The 2D COF film was constructed on a polyacrylonitrile HF substrate using aldehyde (1,3,5-trimethylphloroglucinol, Tp) and amine (4,4'-azodianiline (Azo) and 4,4',4″-(1,3,5-triazine- 2,4,6-triyl) trianiline (Tta)) as precursors. The COF membrane on the PAN substrate showed 99% rejection of Direct red-80 with remarkable solvent permeance. The rejection analysis revealed that the structural aspects of the solute molecule play a major role in rejection rather than the molecular weight. We further optimized the precursor concentrations to improve the permeation performance of the resulting membrane. The durability study reveals excellent stability of the membrane toward organic solvents. This study also demonstrated the easy scalability of the membrane fabrication approach. The approach was further extrapolated to fabricate a cation-based COF membrane. These charged membranes exhibited an enhanced rejection performance. Finally, this approach can facilitate industrially challenging molecular sieving applications using COF-based membranes.

Inhibitability of soil loss and runoff during interrill erosion due to the application of molecular sieve produced through the gas refining process

Inhibitability of soil loss and runoff during interrill erosion due to the application of molecular sieve produced through the gas refining process

Precisely tailored graphene oxide membranes on glass fiber supports for efficient hydrogen separation

Graphene oxide (GO)-based membranes have been widely studied for various separation applications, but it is highly desirable to tailor their structure for the separation of small molecules such as hydrogen. Herein, we demonstrate the fabrication of a thin GO membrane by using a low-cost and highly gas permeable glass fiber (GF) filter as a porous substrate. By partial thermal reduction of GO, the interlayer channel size of the GF-supported GO membrane is precisely tailored for molecular sieving, leading to extraordinarily enhanced hydrogen separation performance. With the synergistic effect of retained functional-group interactions, the quasi-reduced GO (q-rGO) membrane displays a H2 permeance of 783 ± 50 gas permeance units (GPU) and an impressive H2/CO2 separation factor as high as 3636 ± 312, which is the highest selectivity for H2/CO2 reported thus far. In addition, the q-rGO membrane exhibits excellent durability with no performance degradation during a 120-h test. Our results represent a key step toward GO membrane-based molecular sieving applications.

Lipase-catalyzed synthesis of fructosyl myristic acid esters as biosurfactants in a low solvent media: Optimization of the bioconversion

Lipase-catalyzed synthesis of fructosyl myristic acid esters as natural food biosurfactants in low solvent reaction media was investigated. The effect of chain length of fructose-based glycosides as acyl acceptors was found to be inversely proportional to the bioconversion yield. The application of molecular sieves proved unsuccessful in low-solvent media due to their saturation and mass transfer limitations. The substitution of low-solvent myristic acid reaction media with 5% oleic acid led to similar bioconversion yield than that achieved without oleic acid, while no solidification of the reaction media was observed. Response surface methodology using a 3-factor and 5-level central composite design was used to achieve a compromise between mass transfer limitations and catalytic activity of lipase in low-solvent myristic acid reaction media enriched with oleic acid. Modeling found reduced quadratic models accurately described the yield and productivity of the reaction. Maximum bioconversion yield (22%) was achieved using 0.2 mol/L of fructose and 5% (w/v) of Lipozyme® RM IM in a reaction media composed of 80% myristic acid and 10% oleic acid. Lipozyme® RM IM catalyzed successfully 5 consecutive reactions before showing reduction of its synthetic activity at the 6th cycle. The end-product profile analysis confirmed the selectivity of Lipozyme® RM IM towards saturated fatty acids over unsaturated one and the formation of fructosyl monoester and diester of myristic acids. This study lays the ground of a sustainable approach for the acylation of myristic or longer saturated fatty acids with carbohydrates for a great potential as functional ingredients.

Advances in the application of molecular sieves as catalysts for lignin depolymerization—HZSM‐5 as an example

AbstractAt present, mankind faces the problem of increasingly serious global environmental crisis and growing shortage of petrochemical resources, making it more and more necessary to seek renewable substitute for petroleum. Biomass resources, which have received widespread attention and worldwide research, are the most common source of renewable carbon. Moreover, they are considered to be the major source of renewable green carbon today. Biomass resources contain three main aggregates, which are cellulose, hemicellulose, and lignin, as well as small amounts of other additional materials. Notably, the aromatic ring ethers linkage inside lignin molecules enables it to serve as a renewable and suitable feedstock for the production of aromatic chemicals and fuels. However, the recognition that lignin is the most difficult lignocellulosic biomass to degrade makes it much less valuable for practical applications. Therefore, in order to achieve high‐value conversion and utilization of lignin and replace non‐renewable fossil resources, the targeted conversion of lignin into chemicals and materials has become one of the major hot research areas. To this end, this article reviews research results on the use of molecular sieves (HZSM‐5) as catalysts for lignin degradation and conversion, providing an outlook on future research directions.

Application of Molecular Sieves for Drying Transformers Insulated with Mineral Oil, Natural Ester, or Synthetic Ester

A high level of moisture in the insulation system of power transformers is often the cause of their failure. This can be prevented by drying a transformer in its place of installation. In the article the application of molecular sieves (MS) in the drying process of the transformer insulation system was analyzed. The water sorption isotherms of 3A MS in mineral oil, natural ester, and synthetic ester at 35 °C were determined, which was not described in the literature before. An evaluation of the influence of temperature on the drying dynamics of electro-insulating liquids using MS was also carried out. The drying dynamics were tested at three temperatures, i.e., 35 °C, 50 °C, and 65 °C, which allowed to analyze the effect of temperature on a short-term or continuous drying process. The tests showed that 3A MS’s ability to adsorb water varied depending on the type of electro-insulating liquid. The determined water sorption isotherms, described by means of Langmuir adsorption model, make it possible to calculate the amount of MS needed for drying transformers with different liquid insulation. The research and analyses show the MS’s great potential for the drying of transformer insulation systems.

Discussion on Water Dew Point and Hydrocarbon Dew Point of Natural Gas

During natural gas processing and gathering and transportation, water dew point and hydrocarbon dew point as two of control parameters in natural gas because of safety, economy and efficiency etc. In the field chilled mirror manual visual method always be taken to measure water and hydrocarbon dew point due to online instrument test under a differential condition from the pipeline. For hydrocarbon dew point, there’re some assays have implied that heavier components in natural gas have an important effect on hydrocarbon dew point, at the same time hydrocarbon dew point gained under the pressure between 2MPa~4MPa is equal to the max condensation temperature which has a practical meaning. On the other hand, the retrograde condensation cannot be ignored; for water dew point, application of molecular sieve would make dew point measurement easier, while application of dehydrating agents such as methanol; glycols and glycerol could cause interference, instruments &operators differences are exist, but the changing process is consistent when chilled down temperature. In this case, Attention should be given to a white fog which might appear on the center of the surface of the chilled mirror one or more times while temperature dropping down. At last some suggestions are given from two aspects of processing and measurement of water and hydrocarbon dew point.

Highly solvent-durable thin-film molecular sieve membranes with insoluble polyimide nanofibrous substrate

Permselective thin-film composite membranes are gaining a significant role in solvent-based molecular sieving applications. Nevertheless, the lack of desirable substrate materials, which combines high flux, solvent resistance as well as a straightforward fabrication process, is still the biggest bottleneck for large-scale commercial implementation. For the first time, we propose to fabricate an insoluble polyimide nanofibrous substrate by a sequential strategy involving electrospinning polyamic acid followed by a thermal imidization. The water-absent electrospinning process leads to 1-fold enhanced mechanical strength and higher solvent-resistance of substrate compared to the conventional phase inversion process. The resultant thin-film nanofibrous composite (TFNC) membranes exhibit exceptional potential for nanofiltration by showing high permeability, rejection, and stability in water as well as polar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran compared to state-of-art membranes. The strategy of using electrospun insoluble polyimide as the substrate establishes a scalable approach to design high-performance TFNC membranes for a wide range of challenging molecular sieving applications.

Quantitative structural descriptors of sodalite materials

Topological characterization of 3D molecular structures is an emerging research area in the fields of theoretical and computational chemistry. Such a characterization of the underlying connectivity and molecular structure yields quantitative structural descriptors, also called topological indices (TIs) that aim to predict chemical properties and biological activities. Sodalite is a complex three dimensional crystalline structure consisting of a network of interconnected tunnels and cages. Due to the shape selective properties, sodalite structures are grasped in molecular sieving applications for sequestering molecules on the basis of size, shape and polarity. We have derived the exact analytical expressions of various topological descriptors for the sodalite structures by employing graph-theoretical cut method techniques that reduce the complex structures with tunnels and cages into simpler graphs.

A solution-processable and ultra-permeable conjugated microporous thermoset for selective hydrogen separation

The synthesis of a polymer that combines the processability of plastics with the extreme rigidity of cross-linked organic networks is highly attractive for molecular sieving applications. However, cross-linked networks are typically insoluble or infusible, preventing them from being processed as plastics. Here, we report a solution-processable conjugated microporous thermoset with permanent pores of ~0.4 nm, prepared by a simple heating process. When employed as a two-dimensional molecular sieving membrane for hydrogen separation, the membrane exhibits ultrahigh permeability with good selectivity for H2 over CO2, O2, N2, CH4, C3H6 and C3H8. The combined processability, structural rigidity and easy feasibility make this polymeric membrane promising for large-scale hydrogen separations of commercial and environmental relevance.

Minimizing Non-selective Nanowrinkles of Reduced Graphene Oxide Laminar Membranes for Enhanced NaCl Rejection

Reduced graphene oxide membranes (rGOMs) have been intensively studied for desalination and molecular sieving applications, benefiting from their selective and stable two-dimensional (2D) nanochann...

Growth of ZnO self-converted 2D nanosheet zeolitic imidazolate framework membranes by an ammonia-assisted strategy

Shaping crystalline porous materials such as metal organic frameworks (MOFs) and zeolites into two-dimensional (2D) nanosheet forms is highly desirable for developing high-performance molecular sieving membranes. However, conventional exfoliation–deposition is complex and challenging for the large-scale fabrication of nanosheet MOF tubular membranes. Here, for the first time, we report a direct growth technique by ZnO self-conversion and ammonia assistance to fabricate zeolitic imidazolate framework (ZIF) membranes consisting of 2D nanosheets on porous hollow fiber substrates; the membranes are suitable for large-scale industrial gas separation processes. The proposed fabrication process for ZIF nanosheet membranes is based on the localized self-conversion of a pre-deposited thin layer of ZnO in a ligand solution containing ammonium hydroxide as a modulator. The resulting ZIF 2D nanosheet tubular membrane is highly oriented and only 50 nm in thickness. It exhibits excellent molecular sieving performance, with high H2 permeance and selectivity for H2/CO2 separation. This technique shows great promise in MOF nanosheet membrane fabrication for large-scale molecular sieving applications.

Ammonia Released by Streptomyces aburaviensis Induces Droplet Formation in Streptomyces violaceoruber.

Streptomyces violaceoruber grown in co-culture with Streptomyces aburaviensis produces an about 17-fold higher volume of droplets on its aerial mycelium than in single-culture. Physical separation of the Streptomyces strains by either a plastic barrier or by a dialysis membrane, which allowed communication only by the exchange of volatile compounds or diffusible compounds in the medium, respectively, still resulted in enhanced droplet formation. The application of molecular sieves to bioassays resulted in the attenuation of the droplet-inducing effect of S. aburaviensis indicating the absorption of the compound. 1H-NMR analysis of molecular-sieve extracts and the selective indophenol-blue reaction revealed that the volatile droplet-inducing compound is ammonia. The external supply of ammonia in biologically relevant concentrations of ≥8mM enhanced droplet formation in S. violaceoruber in a similar way to S. aburaviensis. Ammonia appears to trigger droplet production in many Streptomyces strains because four out of six Streptomyces strains exposed to ammonia exhibited induced droplet production.

Application of Molecular Sieves in Transformations of Biomass and Biomass-Derived Feedstocks

Molecular sieves (zeolites, mesoporous materials, hierarchic systems, two-dimensional zeolites) are important acid catalysts for transformations of biomass into required products. This article covers the upgrading potential of different types of biomass based on their source and discusses the reaction pathways of their transformations emphasizing the role of molecular sieve catalysts. As typical examples, catalytic pyrolysis, deoxygenation, transesterification, dehydration, isomerization, and condensation reactions were chosen. Properties and chemical/textural characteristics of the most important molecular sieve catalysts are briefly discussed and related to their catalytic behavior in biomass transformations. Finally, potential of novel molecular sieve catalysts towards biomass upgrading is highlighted and some examples of novel zeolitic materials are addressed.

New Routes Study for Synthesis of Molecular Sieves Type Al-MCM-41 and Al-SBA-15

The areas of research, synthesis and catalytic application of zeolites as molecular sieves are a field of great development and prominence in recent decades. Needs of the industries of petrochemical and fine chemicals have been encouraging specific studies for the application of molecular sieves looking for technological, commercial, and more recently sustainable developments. In this work molecular sieves type Al-MCM-41 and Al-SBA-15 has been synthesized using new synthesis routes by replacing the silica source conventionally used by rice husk. The molecular sieves obtained were confirmed by X-ray diffraction. Through the thermograms the decomposition of the driver at different temperatures was noticed. According to SEM micrographs can be observed that the material shows an aggregate of relatively uniform short particles.

The Role of Catalysis in Determining Men’s Quality of Life

Modern civilization, whose spectacular development took place in the second half of XX century as the result of scientific and information revolution has six characteristic features: (1) it is a mass civilization, (2) it is mobile, (3) it is global, (4) it is free of the spectre of famine, (5) it is built on informatics, (6) human lifespan is steadily prolonged. In order to achieve these goals it was necessary to invent thousands new materials and to find out methods of their fast and cheap production in large quantities. The unique possibility of the fast and selective production of the desired chemical molecules, required to obtain a material with defined properties, is offered by catalysis. Catalysis comprises technological processes of the largest scale, such as catalytic cracking of billions tons of crude oil per year and smallest scale enzymatic reactions with micrograms of product formed with 100% chemo-, regio- and stereoselectivity. With the rapidly growing earth’s population increasingly important becomes not only the production of materials needed in our modern society, but also the destruction of undesired by-products of its activities, making the application of catalysis to pollution control one of important tasks. The progress of catalysis, both science and technology, was in the last 50 years driven by the development in five fields: (1) new materials, particularly those based on the principle of molecular imprinting (use of templates), (2) application of new surface science techniques to identify active sites and surface reaction intermediates, (3) quantum chemical modeling of elementary steps of catalytic reactions, (4) design of new reactors, (5) development of computational catalysis, (6) development of new ways for carrying catalytic reactions, (7) biocatalysis using enzymes, modified by mutagenesis and recombination techniques to make them selective and active in conditions of the desired technological process. Application of molecular sieves, catalytic antibodies, metallocene catalysts, asymmetric catalysis, fuel cells, control of automotive exhaust are described and pending change of the paradigm of catalysis is discussed.

Template-free synthesis of MFI-type zeolite membranes: Permeation characteristics and thermal stability improvement of membrane structure

MFI-type zeolite membranes have shown promise for molecular sieving applications that require high chemical and thermal stability. In this work, MFI-type zeolite membranes were prepared by template-free seeded growth method in order to minimize defects and/or intercrystalline gaps that form during the calcination step required for template removal. Membranes were synthesized on two types of supporting materials, alumina and zirconia coated alumina. Synthesized membranes were characterized by molecular probing techniques including pervaporation of xylene isomers and TIPB as well as permeation of He and SF 6. It was found that in order to obtain a high quality MFI-type zeolite film, the initial seed layer is an important factor. The quality of silicalite seed layer could be controlled by dip coating times with silicalite suspension; it was found that ideal selectivity for p/ o-xylene of up to 20 could be obtained. Results also indicated that a high quality MFI-type zeolite film could be formed on zirconia intermediate layer as well. MFI-type zeolite membranes with zirconia intermediate layer prepared by annealing method showed relatively large He permeance above 10 −7 mol m −2 s −1 Pa −1 with selectivity of around 50 (He/SF 6) at 25 °C. These membranes showed high thermal stability at 500 °C, however, the stability was largely affected by heating/cooling rate of membrane.

Application of molecular sieves in the fractionation of lemongrass oil from high-pressure carbon dioxide extraction

The aim of this work was to study the feasibility of simultaneous process of high-pressure extraction and fractionation of lemongrass essential oil using molecular sieves. For this purpose, a high-pressure laboratory-scale extraction unit coupled with a column with four different stationary phases for fractionation: ZSM5 zeolite, MCM-41 mesoporous material, alumina and silica was employed. Additionally, the effect of carbon dioxide extraction variables on the global yield and chemical composition of the essential oil was also studied in a temperature range of 293 to 313 K and a pressure range of 100 to 200 bar. The volatile organic compounds of the extracts were identified by a gas chromatograph coupled with a mass spectrometer detector (GC/MS). The results indicated that the extraction process variables and the stationary phase exerted an effect on both the extraction yield and the chemical composition of the extracts.

Concentration Profiling of a Molecular Sieve Membrane by Step-Scan Photoacoustic Spectroscopy

We report the quantitative, nondestructive determination of the concentration profile of an organic molecule in a nanoporous polycrystalline zeolite molecular sieve membrane by step-scan IR photoacoustic experiments and analysis. A heterogeneous zeolite membrane model system was constructed by growing a zeolite MFI layer on a macroporous α-alumina substrate, followed by calcination to remove the organic tetrapropylammonium (TPA) structure-directing agent, and finally the growth of a second TPA-containing layer over the first. Step-scan photoacoustic spectroscopy is then used with a large range (10−500 Hz) of incident signal modulation frequencies to obtain a series of depth-dependent IR spectra. Deconvolution of these spectra and analysis of band intensities by the theory of photoacoustic signal generation allows for the determination of the TPA concentration profile. We briefly discuss the implications of this technique for understanding structure−property relationships in materials deposited as membranes for molecular sieving applications.

Application of mesoporous MCM-48 and SBA-15 materials for the separation of biochemicals dissolved in aqueous solution

The application of molecular sieves for the separation and purification of biological molecules has been limited because of their available pore size (>1.3 nm). With the development of synthetic mesoporous materials, the available pore size range (1.5-10 nm) has been extended. They have pores large enough to allow access for a number of biological molecules. This work investigated the use of two mesoporous materials (MCM-48 and SBA-15) with different pore sizes and structures for adsorption of cephalosporin C as a model compound of biological molecules in terms of ethanol concentration, solution pH, and temperature. It was found that these materials have the potential for the separation and purification processes of biochemicals including antibiotics, amino acids, and proteins.