Synthetic Faujasite Research Articles

Beiträge zur kinetik der zeolith-dehydratation

The values of activation energy and order of reaction characteristics of dehydration of synthetic (A-type zeolite) and natural phillipsite and synthetic faujasite (X-type zeolite) have been determined from the derivatographic curves by the modified method of Freeman and Carroll. There is an agreement between the real and apparent reaction kinetics data and bond relation of zeolitic waters.

A 29Si n.m.r. study of the ultrastabilization process in synthetic faujasite

The removal of aluminium from the zeolite framework of the ammonium form of synthetic faujasite during calcination has been observed using solid-state 29Si n.m.r. spectroscopy.

Isomerization of cyclopropane on synthetic faujasite by pulse technique: II. Experimental study

The parameters for sorption, intercrystalline and intracrystalline diffusion, and reaction were determined for the isomerization of cyclopropane to propylene over synthetic faujasite (Li exY, NaY, and K exY). The parameters were obtained from studying the response of a continuous stirred tank reactor (CSTR) containing catalyst powder or pellets, when an impulse of cyclopropane is introduced in the reactor. The model developed for the CSTR was used successfully for the determination of the parameters for diffusion, adsorption, and chemical reaction. Both micro- and macroeffectiveness factors were obtained and the results indicated that the intracrystalline diffusion was rate limiting and that the intracrystalline diffusion coefficients were lowered by the presence of a reaction. Also it was found that K exY was inactive for the isomerization of cyclopropane over the temperature range considered.

Isomerization of cyclopropane on synthetic faujasite by pulse technique: I. Mathematical model

A mathematical model is derived to describe the transient behavior of a continuous stirred tank reactor containing catalyst particles with a bipore distribution when a stimulus is introduced. The reaction taking place inside the catalyst is assumed to be isothermal, first order, and irreversible. The expressions for the zeroth-, first-, and second-order moments of the response curve are given in terms of the adsorption equilibrium constant, the intercrystalline and intracrystalline diffusion coefficients, and the first-order reaction rate constant. A method for the determination of these parameters is presented. The same method also leads to the determination of micro- and macropore effectiveness factors.

Thiophene hydrodesulfurization over transition metal zeolites

The hydrodesulfurization (HDS) reactivities of two zeolites (a synthetic mordenite and a synthetic faujasite Y) with and without transition metal loadings were evaluated using a pulse chromotographic procedure. The initial reaction rates for thiophene HDS were determined for the following: (1) a synthetic mordenite (Zeolon 900) in the sodium and ammonium forms with the single metals nickel, iron, cobalt, manganese, chromium, tungsten, copper, rhenium, platinum, palladium, iridium, ruthenium and rhodium and with the binary metals NiMo, NiFe, NiCo, NiMn, NiCr, NiW, NiCu and NiRe present, and in the hydrogen form (Zeolon 200); (2) a synthetic faujasite Y in the ammonium and rare earth forms with and without nickel present. The initial reaction rates at 300 °C indicate that these zeolites have a dual function for HDS in which both the transition metal and the acid zeolite substrate contribute. A conventional NiMoO 3Al 2O 3 HDS catalyst was found to be superior to any of these experimental zeolites with thiophene reaction rates based on specific volume (moles of thiophene reacted per cubic centimeter of catalyst per hour). The faujasite Y catalysts, with and without nickel loading, were shown to be superior to the mordenite zeolites or the NiMoO 3Al 2O 3 catalyst with the thiophene reaction rates referred to a specific weight basis (micromoles of thiophene reacted per gram of catalyst per second). Adsorption coefficients calculated from the retention times of the thiophene pulses were an order of magnitude larger for faujasite Y compared with the mordenites, which is indicative of the more extensive surface areas characteristic of the faujasite Y zeolites. Butene-1 chemisorption at 100 °C was used as the basis for estimating the HDS reaction site population density for the determination of turnover numbers. Turnover numbers referred to the butene-1 chemisorption capacities demonstrate that the thiophene catalysts mordenite and faujasite Y, with and without nickel present, are superior to the NiMoO 3Al 2O 3 catalyst or the Ni-MoO 3 mordenite. The iron, cobalt and nickel loadings ranged from 1.7 to 3.1 wt.% with the metals present in relatively low order dispersions of 1.5–3.8% as demonstrated by hydrogen chemisorption. The noble metals were present on the zeolites in loadings ranging from 0.2 to 0.7 wt.% and demonstrated dispersions of 12–69%. A principal effect of the presence of the transition metals was to minimize coking, as evidenced by carbon analyses of the post-test catalysts. This was attributed to enhancement of hydrogenolysis reactivity. Residual sulfur determined on these post-test catalysts can be attributed in part to sulfiding of metals present but to a considerable degree it is due to a high order adsorption on the zeolite lattice surfaces.

Incorrect quantitative analysis of cracking catalysts through use of copper radiation

An error can occur in the measurement of synthetic faujasite content of a catalyst by comparing a synthetic faujasite's diffracted intensity to that of a reference standard. The error is due to the failure of all diffracted X rays to emerge from the catalyst particle prior to passage to the powdered sample's surface. The error is not avoided by use of an internal standard. Absorption calculations estimate the synthetic faujasite content of 44 μm-size catalyst particles will be low by 17% if Cu K α is used. Use of more penetrating Mo K α indicates the Cu K α analysis is actually low by 26%.

Effect of aluminosilicate composition on acid and catalytic properties of dealuminized zeolites

1. When various samples of synthetic faujasite are dealuminated by (ethylenediamino)tetraacetic acid to the same Si/Al ratio the number of aluminum atoms in the unit cell differs and depends on the aluminosilicate composition of the starting sample. 2. At a constant Si/Al ratio the samples with a smaller number of aluminum atoms in the unit cell have a greater adsorption capacity toward ammonia and a higher catalytic activity. 3. The properties of zeolites with a faujasite structure depend not only on the Si/Al ratio, but also on the absolute number of aluminum atoms in the unit cell.

Low silica synthetic faujasite X and synthetic zeolite A formation from sodium-aluminosilicate gels

Synthetic zeolites A and X were prepared from sodium-aluminosilicate gels by crystallization under hydrothermal conditions and at water bath temperature. The process of crystallization and physico-chemical studies on the synthetic zeolites and amorphous aluminosilicate hydrates, from which formed, have been examined by X-ray diffraction measurements, chemical analyses and differential analyses. The structures of synthetic zeolites A and X have been determined in their hydrated form. Zeolite A is represented by the oxide formula : Na2O. Al2O3 . 2 SiO2 . 0.16 NaAlO2 . 4.30 H2O. and the zeolite has the composition (unit cell composition) Na12 [12 AlO2 . 12 SlO2] . NaAlO2 . 29 H2O. The synthetic zeolite X is represented by the oxide formula Na2O . Al2O3 . 2.1 SiO2 (5.63 7.02 ) H2O and the simple zeolite has the composition (unit cell composition) Na94 [94 AlO2 . 94 SiO2] . (260 264) H2O.

Diffusion in synthetic faujasite powder and pellets

AbstractTransient sorption rates of allene and methylacetylene in synthetic faujasite (Linde 13X) powder and self‐bonded pellets are studied in a constant‐volume, constant‐pressure system at three temperatures. The intracrystalline diffusion coefficients are found to be in the order of 10−11 cm2/s and the activation energy for diffusion is 4.0 kcal/g‐mole.A simple bipore distribution model for transient diffusion in macropores and micropores is presented. It agrees well with the experimental data and quantitatively predicts the macropore diffusion coefficients. The flow in the macropores is found to be in the Knudsen flow regime.

Synthetic Faujasite Type Zeolite Formed from Allophane

The process of formation of faujasite type zeolite from allophane was studied by X-ray di-ffractiometry. The mixtures having various SiO2/A1203 molar ratios were prepared by adding silica gel to allophane, and these mixtures were heated with NaOH solution under atomospheric pressure. Then, a few kinds of zeolite were prepared. With the increase of the treating time, the A type zeolite was transformed into hydroxy sodalite either through the reaction Ior through the reactionII-III. With the increase of the SiO2/A1303 mo1ar ratio.the reactionII IIItoo: k place instead of the reaction I. Faujasite type zeolite also was transformed into phillipesite type zeolite through the reaction process N with the increase of the SiO2/A120s molar ratio. When the SiO2/A120s molar ratip ef starting mixtures was low, A type zeolite or phillipsite or type zeolite were resulted. But urider the condition that the SiO2/A120s molar ratio was low, the A type zeolite formed was transformed into faujasite type zeolite with the increase of the treating time. The process of the formation of zeolites from allophane could be summarized as follow:

Properties and reactivity of growing polymer radicals of n-butyl methacrylate prepared on the surface of synthetic faujasite

The kinetics of formation of n-butyl methacrylate growing polymer radicals have been studied. Radicals have been prepared by parallel adsorption of benzoyl peroxide and the monomer on a synthetic zeolite in the temperature range 80–100°. The rate constants for their formation are related to the kinetics of the benzoyl peroxide decomposition. The differences between the ESR spectra of the growing polymer radicals of n-butyl, allyl, ethyl, methyl methacrylates and methacrylic acid have been observed. The reactions of these radicals with oxygen and the reactivities of the resulting peroxy radicals have been examined also. The peroxy radicals are much less stable than the alkyl radicals. To account for this fact, we have considered possibilities of intramolecular transfer reactions of the radical along the polymer chains.

Chemiluminescence in the decomposition of benzoyl peroxide on the synthetic faujasite Na X

It was found that benzoyl peroxide on the surface of synthetic faujasite Na X in the presence of benzene emits in inert atmosphere a considerably more intense chemiluminescence than benzoyl peroxide in benzene solution (benzoyl peroxide concentration in solution was in both cases 6.5 g/l). This may well be accounted for by the catalytic influence of the zeolite on the accelerated decomposition of benzoyl peroxide. From this point of view the kinetics of the chemiluminescence process followed were investigated and identification of the excited species was attempted.

Ion exchange in synthetic zeolites. Part 2.—Thermodynamic formalism for incomplete exchange

In zeolites, ion-exchange phenomena can be limited by steric or ion-sieve effects. A thermodynamic study of the ion-exchange in these systems, using the Gaines and Thomas equation, requires the application of adequate normalization and correction procedures to the experimental exchange isotherms. Such a procedure is developed, and a practical demonstration is given for the exchange of sodium ions by n-alkylammonium ions in synthetic faujasite. The correctness of the method is substantiated by a thermodynamic development, in which the formulae are derived starting from the Gibbs-Duhem equation.

Fe3+ Ions in crystalline aluminosilicate frameworks: electron spin resonance, phosphorescence, and thermal studies

E.s.r., phosphorescence, and thermal studies of the synthetic zeolites mordenite and faujasite indicate that the Fe3+ impurity ions occupy tetrahedral Si4+ or Al3+ positions in the framework.

Thermal behavior of synthetic faujasite

Data are presented to show that the thermal stability of synthetic faujasite is dependent on the level of sodium present. A simple relationship has been found between the sodium content of ammonium-exchanged faujasite and the temperature at which breakdown of the zeolite structure occurs. This relationship extends to sodium contents below 0.1%, and demonstrates the existence of a continuum of properties for variously exchanged faujasite samples. Regardless of the degree of sodium removal or the method of exchange employed, X-ray diffraction analysis shows that the faujasite structure is retained to just below the breakdown temperature, that material heated just beyond the breakdown temperature is amorphous, and that material heated further, to beyond the mullitization temperature, contains crystalline mullite. The data obtained support the hypothesis that thermally induced migration of cations is an important part of the mechanism for facilitation of exchange, and for structure degradation as well.

Selective exchange of cation sites in zeolites observed by electron spin resonance of Mn 2+—II. Linde y

The technique of using electron spin resonance to monitor the location of Mn 2+ ions has enabled a rapid, self-consistent assessment to be made of the way in which the cation distribution in synthetic faujasite depends on the nature of the cations present and on the heat treatment. The distribution is determined not only by the ionic charge and radius but also by the degree of covalent character of the cation bonding. During dehydration, the bi- and tervalent ions concentrate in sites within the sodalite cages due to the retention of fragments of water molecules in this region. Evidence for this comes from the existence of Mn 2+ centres with higher than usual covalency and from the relationship of the E.S.R. data with recent i.r. and structural data.

A study of surface diffusion by NMR: Sulfur hexafluoride adsorbed on synthetic faujasite

Spin-lattice relaxation times have been measured as a function of temperature for the fluorine nuclei in sulfur hexafluoride adsorbed on synthetic faujasite for various compositions ranging from 0.83 to 6.62 molecules SF 6 per cage. The data were interpreted according to the BPP theory to obtain the activation enthalpy ΔH for translational diffusion, which varied from 2.45 kcal/mole at 0.83 molecules per cage to 4.00 kcal/mole at 6.62 molecles per cage. There is a steep jump in ΔH when the number of molecules per cage reaches approximately four. Calculated values for room temperature diffusion coefficients ( ca. 10 −6 cm 2/sec) are also given.

NMR Relaxation in Adsorbed Molecules. V. SF6 on Faujasite: Dipolar Coupling of Fluorine Nuclei to Ferric-Ion Impurities

The spin—lattice and spin—spin relaxation times for fluorine nuclei of SF6 adsorbed to maximum capacity on dehydrated synthetic faujasite have been measured as functions of temperature from 77° to 300°K. These have been interpreted according to the theory of Torrey as arising from diffusion of SF6 molecules in the magnetic field of paramagnetic iron impurities in the faujasite. The mean time between diffusional jumps is well represented as τ=1.14×10−12 exp(4000/RT) sec.

Vapour phase adsorption measurements of c6 hydrocarbon mixtures on synthetic faujasite

AbstractA new apparatus is described for measuring pure component isotherms of condensable vapours at temperatures of 25°–150° and pressures up to 600 mm. Facilities are also incorporated into the unit to permit the study of multicomponent adsorption. Without disturbing the adsorption equilibrium, the gas phase can be separated from the adsorbed phase for subsequent analysis by independent methods. With n‐hexane, hexene‐1, 1,5‐hexadiene and benzene on synthetic faujasite at 97°, the pure component isotherms follow the Langmuir equation and the amount adsorbed at saturation has a nearly constant value of 0.23 liq. ml/g. In the adsorption of binary mixtures of benzene and n‐hexane at 97°, the separation factor varies strongly with composition and ranges in value from 13 to 52. A maximum factor is observed at intermediate compositions. Hexene‐1‐n‐hexane mixtures under the same conditions give a lower separation factor of 2–3 which is more nearly constant with composition. Data on multicomponent adsorption of other mixtures are also presented.

The Ion-Exchange Properties of Zeolites. I. Univalent Ion Exchange in Synthetic Faujasite

The Ion-Exchange Properties of Zeolites. I. Univalent Ion Exchange in Synthetic Faujasite