SXI route to mesostructured materials from Fau and Beta zeolite precursors: A comparative study of their assembly behaviors in extremely acidic media

Mesoporous molecular sieves were synthesized from Beta and Fau zeolite precursors through S⁺X⁻I⁺ route under extremely acidic conditions in parallel (designated as M_Beta and M_Fau, respectively). The textural properties of M_Fau were different from its M_Beta counterpart but resembled normal MCM-41 silica from TEOS. Al content in M_Beta was almost equivalent to that in the initial Beta zeolite precursors, whereas only trace Al species was present in M_Fau from elemental analysis results. The hydrothermal stability of M_Beta after post-synthesis ammonia treatment was considerably improved compared with normal MCM-41 aluminosilicates, whereas the M_Fau after the same procedure was as unstable as normal MCM-41 silica. Thus, the assembly behaviors of Beta and Fau zeolite precursors were comparatively studied based on these results. The microstructure of Fau zeolite precursors were degraded by the extremely acidic condition, and Al species was dissolved into the synthesis mixture. However, Beta zeolite precursors survived the chemical attack of extremely acidic media and were incorporated into mesostructured framework as primary building units.     

国际互联网与沸石相关的化学化工信息资源

介绍了Internet上与沸石和天然沸石有关的化学化工信息资源,并初步讨论国际互联网和国内互联网上沸石信息量。     

Separation of p-xylene from multicomponent vapor mixtures using tubular MFI zeolite mmbranes

MFI zeolite membranes have been synthesized on tubular -alumina substrates to investigate the separation of p-xylene (PX) from m-xylene (MX) and o-xylene (OX) in binary, ternary, and simulated multicomponent mixtures in wide ranges of feed pressure and operating temperature. The results demonstrate that separation of PX from MX and OX through the MFI membranes relies primarily on shape-selectivity when the xylene sorption level in the zeolite is sufficiently low. For an eight-component mixture containing hydrogen, methane, benzene, toluene, ethylbenzene, PX, MX, and OX, a PX/(MX + OX) selectivity of 7.71 with a PX flux of 6.8 × 10⁻⁶ mol/(m² s) was obtained at 250 °C and atmospheric feed pressure. The addition of a small quantity of nonane to the multicomponent mixture caused drastic decreases in the fluxes of aromatic components and the PX separation factor because of the preferential adsorption of nonane in the zeolite channels. The nanoscale intercrystalline pores also caused serious decline in the PX separation factor. A new method of online membrane modification by carbonization of 1,3,5-triisopropylbenzene in the feed stream was found to be effective for reducing the intercrystalline pores and improving the PX separation.     

Shear-induced deformations of polyamide microcapsules

The application of microcapsules for technical, cosmetic and pharmaceutical purposes has attracted increased interest in recent years. The design of new capsule types requires a profound knowledge of their mechanical properties. Rheological studies provide interesting information on intrinsic membrane properties and this information can be used to avoid premature release of encapsulated compounds due to the action of external mechanical forces (stirring, swallowing, spreading). In this publication we report a systematic study of polyamide microcapsules. These particles were synthesized by reacting 4-aminomethyl-1,8-diaminooctane and sebacoyl dichloride at the interface between silicone oil and water. Two different experiments were performed to get information on the mechanical properties of the capsule walls. First of all, we used an optical rheometer (rheoscope) to observe the capsule deformation and orientation in shear flow. The polymerization kinetics, relaxation properties, the regime of linear-viscoelastic behavior and the shear modulus of the flat membranes were independently measured in an interfacial rheometer. Both experiments gave complementary results. It turned out that the two-dimensional elongational modulus was about 3–4 times larger than the shear modulus. This result is in fairly good agreement with a theoretical model recently proposed by Barthès-Biesel. Due to the simple synthesis and well-defined structure, polyamide microcapsules can also serve as simple model systems to understand the complicated flow properties of red blood cells. Received: 5 July 1999/Accepted in revised form: 30 August 1999     

Adsorption of polypropylene from dilute solutions on a zeolite column packing

Faujasite type zeolite CBV-780 was tested as adsorbent for isotactic polypropylene by liquid chromatography. When cyclohexane, cyclohexanol, n-decanol, n-dodecanol, diphenylmethane, or methylcyclohexane was used as mobile phase, polypropylene was fully or partially retained within the column packing. This is the first series of sorbent-solvent systems to show a pronounced retention of isotactic polypropylene. According to the hydrodynamic volumes of polypropylene in solution, macromolecules of polypropylene should be fully excluded from the pore volume of the sorbent. Sizes of polypropylene macromolecules in linear conformations, however, correlate with the pore size of the column packing used. It is presumed that the polypropylene chains partially penetrate into the pores and are retained due to the high adsorption potential in the narrow pores.     

Synthesis of mono- and bi-layer zeolite films on alumina substrates

Bilayer zeolite films ZSM-5/ZSM-5, ZSM-5/EMC-1 and NaY/ZSM-5 were synthesized on α-alumina plates. The bottom ZSM-5 or faujasite Y (NaY) zeolite layers were obtained by direct hydrothermal synthesis or by using a seeding step followed by a secondary growth method, respectively, while the secondary growth method was used for the synthesis of all the top zeolite layers. A complete characterization of the obtained materials is proposed using various techniques, such as X-ray diffraction, scanning electron microscopy, X-ray fluorescence and nitrogen sorption measurements. Continuous and highly crystallized bi-layer zeolite films with thicknesses around 11–18 μm were obtained.     

Size effect of complexing microcapsules on copper ion extraction

In a previous work [J. Microencapsulation, in press], polyamide microcapsules containing a poly(acrylic acid) gel as a macromolecular ligand (PAA-CAPS) with a mean diameter of 210 μm were prepared using an original two-step polymerization process combining interfacial polycondensation and radical polymerization in a water in oil inverse emulsion system. Extractions of many divalent cations were examined. In this work, we proposed to synthesise by the same process, smaller microcapsules with a mean diameter of 10 μm (PAA-μCAPS). Reference polyamide microcapsules, i.e. without ligand were also synthesized (μCAPS) and (CAPS) [J. Microencapsulation, in press]. Microcapsule wall thickness was evaluated by SEM and TEM observations of microcapsule cross-section cuts, microcapsule water content was determined by thermogravimetric experiments. Specific surface area and total volume of the pore of microcapsules were determined by BET method based on N₂ adsorption/desorption. The comparison of the extractabilities and the stripping of Cu(II) into the various kind of microcapsules were examined.     

Investigation and development of environmentally friendly processes on zeolite catalysts

The synthesis of alkylphenols, alkylanilines and nitro-aromatic compounds with different substituents in the aromatic ring on highly active and selective zeolite catalysts has been studied with regard to zeolite acidity and structure. These studies open the way for solid, environmentally friendly catalysts instead of liquid ones producing harmful liquid wastes in huge amounts.     

Ab initio quantum chemical study on the zeolite catalyzed transformations of para-xylene

Unimolecular 1,2-methyl shift reaction and disproportionation of para-xylene is investigated by means of ab initio quantum chemical calculations. Isolated gas-phase models are used to estimate the optimum volume of the reaction complex. Space filling of the computed models is examined in zeolite Y, Beta and ZSM-5. It is suggested that the shape selectivity effect of zeolite molecular sieves on the disporportionation reaction can be associated with the steric conditions of the intrinsic rearrangement of the reaction complex in the course of the chemical transformation.     

Influence of residence time and catalyst regeneration on the pyrolysis–zeolite catalysis of oil shale

Oil shale from the Kark region of Pakistan has been pyrolysed in a fixed bed batch reactor and the properties of the derived shale oil determined. The reactor system was then modified to incorporate a second reactor where the derived vapours from oil shale pyrolysis were passed directly to the second reactor containing zeolite ZSM-5 catalyst. The influence of the process parameters of vapour residence time (VRT) over the catalyst and the regeneration of the catalyst were examined. The yield and composition of the derived gases before and after catalysis were determined. In addition, the yield and composition of the derived oil in terms of total nitrogen and sulphur content and the content of aromatic hydrocarbons in the oils was investigated. The results showed that the yield of oil after catalysis was reduced with a consequent higher yield of gases and formation of coke on the catalyst. The main gases from the pyrolysis of oil shales were CO₂, CO, H₂, CH₄, C₂H₄, C₂H₆ and C₃H₆, C₃H₈ and minor concentrations of other hydrocarbon gases. The main role of catalysis was to convert the long chain alkanes and alkenes in the oil to lower molecular weight, short chain, alkyl substituted and iso species and high concentrations of aromatic hydrocarbons. Total nitrogen and sulphur contents in the oils were markedly reduced after catalysis. This reduction was reflected in the reduced concentration of nitrogen and sulphur containing aromatic hydrocarbons. The influence of longer VRTs was to increase the formation of aromatic hydrocarbons, reduce the nitrogen, and sulphur compounds in the oils. The influence of catalyst regeneration, involving five regenerations was not significant on the yield and composition of the derived catalytically upgraded oils.     

Effect of oxygen plasma treatment on the release behaviors of poly(epsilon-caprolactone) microcapsules containing tocopherol

The biodegradable poly(epsilon-caprolactone) microcapsules (PCL) containing tocopherol (TC) were prepared by emulsion solvent evaporation method, and microcapsules were treated by oxygen plasma to enhance the hydrophilic microcapsules. The morphologies and thermal properties of the microcapsules were determined by SEM and DSC measurements. The microcapsules studied were characterized by surface free energy or work of adhesion through contact angle measurement. As a result, the features of the microcapsules could be adjusted by manufacturing condition, such as surfactant and core ratio. The surface free energy or work of adhesion of the microcapsules was increased with increasing the time of plasma treatment, which could be attributed to the increased hydrophilic groups during oxygen plasma treatment. The release profile of the microcapsules was determined by UV-vis spectroscopy and the microcapsules containing tocopherol showed the rapid release rate, as compared with untreated ones.     

Adsorption of polyethylene from thermodynamically good solvents on a zeolite stationary phase

Adsorption of linear polyethylene and isotactic polypropylene on columns packed with zeolites ZSM‐5, Y, and silicalite was studied using high‐temperature liquid phase chromatography. Linear polyethylene was fully retained on a column packed with ZSM‐5 zeolite from non‐polar solvents, such as 1,1,2,2‐tetrachloroethane and 1,3,5‐trimethylbenzene at a temperature of 140°C. Partial adsorption on ZSM‐5 zeolite was found for polyethylene in 1,2,4‐trichlorobenzene and on silicalite from 1,2,4‐trichlorobenzene and 1,3,5‐trimethylbenzene. On the other hand, adsorption of polyethylene was not found from polar liquids, such as 2‐ethylhexyl acetate, cyclohexyl acetate, and cyclohexanone. Isotactic polypropylene was not adsorbed on any tested sorbent.     

Dielectric observations on polystyrene microcapsules and the theoretical analysis with reference to interfacial polarization

Dielectric measurements were carried out for polystyrene microcapsules which were prepared by means of an interfacial polymer deposition technique. The microcapsules showed a couple of dielectric relaxations termedP for lower andQ for higher frequencies. The frequency profiles were characteristic of the structure that shelled spheres were dispersed in a continuous medium. Gelatin aqueous solutions, cationic polyelectrolyte solutions and distilled water were loaded in the capsule interior to examine the effect of conductivities of the constituent aqueous phases on the dielectric properties. Relaxation frequencies of the relaxationsP andQ observed were directly proportional to the conductivities of the continuous medium and of the capsule interior, respectively. A dielectric theory was proposed for a suspension of shelled spheres in a continuous phase in order to analyze the relaxation data observed for the microcapsules. Volume fraction of the capsules, relative permittivity and conductivity of the capsule interior and thickness of the capsule wall are evaluated from the dielectric observations by use of the theoretical formulas derived. The dielectric behavior observed for the polystyrene microcapsules are interpreted quantitatively in terms of the dielectric theory proposed.     

Preparation and mechanical properties of thermal energy storage microcapsules

A series of heat energy storage microcapsules was prepared using melamine-formaldehyde resin as the shell material and the mechanical properties of the shell were investigated. A phase change material whose melting point was 24 °C was used as core and the quantity of heat involved in phase transition was 225.5 J/g. Average diameter of the microcapsules varied from 5 to 10 μm, and the globular surface was smooth and compact. The mechanical properties of the shell were evaluated by observing the surface morphological structure change after application of pressure by means of scanning electron microscopy. When the mass ratio of the core and shell material is 3:1, a yield point of about 1.1×10⁵ Pa was found and when the compression was increased beyond this point the microcapsules showed plastic behavior. This has been attributed to the cross-link density and to the high degree of reaction of the shell material. Different yield points subsequently reflected differences in the mechanical behavior. It was also found that the mechanical intensity of double-shell microcapsules was better than that of single shelled ones.     

A novel urea conductometric biosensor based on zeolite immobilized urease

A new approach was developed for urea determination where a thin film of silicalite and zeolite Beta deposited onto gold electrodes of a conductometric biosensor was used to immobilize the enzyme. Biosensor responses, operational and storage stabilities were compared with results obtained from the standard membrane methods for the same measurements. For this purpose, different surface modification techniques, which are simply named as Zeolite Membrane Transducers (ZMTs) and Zeolite Coated Transducers (ZCTs) were compared with Standard Membrane Transducers (SMTs). Silicalite and zeolite Beta with Si/Al ratios 40, 50 and 60 were used to modify the conductometric electrodes and to study the biosensor responses as a function of changing zeolitic parameters. During the measurements using ZCT electrodes, there was no need for any cross-linker to immobilize urease, which allowed the direct evaluation of the effect of changing Si/Al ratio for the same type of zeolite on the biosensor responses for the first time. It was seen that silicalite and zeolite Beta added electrodes in all cases lead to increased responses with respect to SMTs. The responses obtained from ZCTs were always higher than ZMTs as well. The responses obtained from zeolite Beta modified ZMTs and ZCTs increased as a function of increasing Si/Al ratio, which might be due to the increased hydrophobicity and/or the acid strength of the medium.     

An approach to analysis of pigment release from microcapsules with size distribution

We have studied the release curve for microcapsules with size distribution. On the basis of an analogy to the relaxation phenomena with multiple characteristic times, we propose a stretched exponential release curve for the system with size distribution and relate the release curve to the size distribution function of the microcapsule. This method was successfully applied to the transfer of azo-pigments from inner medium of dioctyl phthalate to dispersing medium of methanol through poly(ureaurethane) microcapsule membrane.     

Effect of oxyfluorination on electromagnetic interference shielding behavior of MWCNT/PVA/PAAc composite microcapsules

Composite microcapsules of poly(vinyl alcohol)/poly(acrylic acid)/multi-walled carbon nanotubes were prepared and the electromagnetic interference shielding behavior was evaluated for the composite microcapsules. The dispersion and adhesion of multi-walled carbon nanotubes in microcapsules were improved by the surface modification through direct oxyfluorination which introduced polar groups on the multi-walled carbon nanotubes. The composite microcapsules containing the oxyfluorinated multi-walled carbon nanotubes showed significant increases in permittivity, permeability, and electromagnetic interference shielding efficiency. The electromagnetic interference shielding efficiency of composite microcapsule increased up to 51 dB mainly base on the absorption mechanism.     

Micromechanical assessment of PMMA microcapsules containing epoxy and mercaptan as self-healing agents

Mechanical properties of microcapsule shell have great influence on microcapsule suitability as a mechanical trigger in a self-healing composite. The elastic modulus and hardness of polymethyl methacrylate (PMMA) microcapsules containing epoxy prepolymer (EC 157) and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) as healing agents were investigated using nanoindentation technique. The influence of the PMMA average molecular weight (M_W), the kind of core material, and the mechanical mixing rate on the mechanical properties of the microcapsule shell were studied using the Taguchi experimental design approach. The results indicated that the most important factors which affect the elastic modulus and the hardness of microcapsules shell are the Mw of PMMA and the kind of core material. The average elastic modulus of PMMA shell of epoxy and mercaptan-loaded microcapsules was found between 2.386 and 3.495 GPa. The hardness of PMMA shell of healing agent microcapsules was obtained in the range of 0.064–0.219 GPa. This constitutes essential knowledge in order to design capsules with tailored properties for self-healing materials.     

Effect of gas phase modification of analcime zeolite composite membrane on separation of surfactant by ultrafiltration

Ceramic–analcime zeolite composite membranes have been synthesized by hydrothermal crystallization of zeolite over clay supports. The zeolite layer is characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and pore size distribution determined using the bubble point technique. The XRD pattern of the zeolite is found to match with JCPDS file #19-1180 which is an analcime-o zeolite of molecular formula NaAlSi₂O₆·H₂O having orthorhombic crystal structure with lattice parameters: a=13.72 Å, b=13.714 Å and c=13.714 Å. In this paper, we report a gas phase nitration scheme, in which we show through the elemental analysis that the modification of entire matrix (and not limited to pores and channels) occurs. The nitrated zeolite was reduced to aminated zeolite membrane by reacting it hydrazine hydrate.

Separation of surfactant (CPC) was performed using these three types (unmodified, nitrated and aminated) of membranes and it showed about 300% increase in the retention of the surfactant after its modification. Its hydrophilic nature also increases as shown by the increase in the permeate flux. In order to find the reason for this enhanced performance, structural analysis of the modified membranes was carried out. The XRD patterns of these were found to be identical and they did not match with those of any of the compounds given in the JCPDS files. The patterns were therefore indexed, using first principle, to find their crystal structure and it was found that the structure changed from orthorhombic for unmodified to tetragonal geometry for the modified zeolites. This also caused about 10% increase in the unit cell volume of the modified zeolites. Anion exchange capacity and the elemental analysis showed that the nitration occurred over the entire zeolite matrix (not restricted to the pores and channels) and on an average about one amine group was present in every second formula unit of the zeolite. This extensive presence of nitrate or amine group in the zeolite matrix makes the modified zeolite membrane highly hydrophilic and may be responsible for the increase in the retention of the surfactant and permeate flux for the modified membranes.