Dry Zeolite Research Articles

Hybrid silica as cues for understanding the role of water in dry zeolite synthesis

This work proposed the application of hybrid silica, with different surface hydration characteristics-behavior-properties, as silicon source in Sodalite synthesis, in order to demonstrate through experimental data that if zeolite formation is ruled by surface reactions, these may be dependent of water amount on the surface. The surfaces of the systems were investigated using of Attenuated Total Reflectance Fourier Transformed Infrared spectroscopy (FTIR-ATR) techniques, while the hydrophilic/hydrophobic behavior was studied by wettability using Static Contact Angle analyses. The influence of hydrophilic/hydrophobic properties and hydrated surface as well, on zeolite formation, was investigated through X-ray Diffraction analyses. The results agree with the proposal, showing a faster zeolite formation (24 h) when hydrophilic silica is used (SG2B), while the time of zeolite formation seems to increase according to increasing in silica hydrophobicity (24 h for SGC1B, 48 h for SGC8B and 72 h for SGC18B).

Preparation, characterization, and performance of 4A zeolite based on opal waste rock for removal of ammonium ion

In this study, 4A zeolite was prepared from opal waste rock by hydrothermal method and applied in ammonium ion adsorption. To optimize synthesis conditions, the effect of crystallization time (1–8 h), crystallization temperature (65–115°C), Na2O/SiO2 (0.6–2.0), H2O/Na2O (20–70), and SiO2/Al2O3 (1.0–3.5) was investigated. X-ray diffraction, scanning electron microscope imaging, cation exchange capacity, static water adsorption, Fourier transform infrared spectroscopy, and N2 adsorption–desorption isotherm were used for assessing properties of 4A zeolite. Adsorption experiments were performed by 1.0 g l−1 4A zeolite with NH4+ solution (5–300 mg l−1) for 4 h at room temperature. The experiment results revealed with a crystallization time of 3 h, a crystallization temperature of 85°C, Na2O/SiO2=1.0, H2O/Na2O = 40, and SiO2/Al2O3=2.0, the 4A zeolite synthesized had excellent performance with cation exchange capacity of 2.93 mmol (g dry zeolite)−1 and static water adsorption of 22.3%. The adsorption process was described by Freundlich model (R2>0.99) and the maximum adsorption capacity could reach to 53.11 mg g−1. The experimental results provided a novel approach for the utilization of opal waste rock, which is produced during the mining of opal-rich palygorskite, and for the synthesis of 4A zeolite and the removal of ammonium ion.

An insight into the comprehensive application of opal-palygorskite clay: Synthesis of 4A zeolite and uptake of Hg2+

Abstract To availably utilize opal-palygorskite clay, dry beneficiation technique was applied to separate opal and palygorskite clay. Based on separated opal from opal-palygorskite clay, 4A zeolite was successfully synthesized by using a hydrothermal method. Box-Behnken was used to optimize Na2O/SiO2, H2O/Na2O and SiO2/Al2O3 with cation exchange capacity (CEC) as the response value. The optimum parameters was determined to be Na2O/SiO2 = 1.0, H2O/Na2O = 40, and SiO2/Al2O3 = 2.0, and CEC got the maximum of 2.99 mmol/(g·dry zeolite) under the conditions. The as-obtained 4A zeolite was characterized by using X-ray diffraction (XRD), thermo gravimetric analysis (TG), acid-base titration, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and then was applied to remove Hg2+ from aqueous solution. The maximum removal capacity of Hg2+ was 41.99 mg/g and adsorption equilibrium was obtained with contact time of 2 h. Effects of pH, ionic strength, temperatures, metal cations, strippant kinds and cycle times on removal behaviors of Hg2+ onto 4A zeolite were investigated by batch experiments. The kinetics and isotherms of Hg2+ adsorption fitted well by pseudo-second kinetic and Langmuir models. When Hg2+-adsorbed 4A zeolite was desorbed using 1 mol/L NaNO3 solution, the adsorption efficiency was maintained about 70% after four cycles.

Adsorption and co-adsorption of NO and water on LaCu-ZSM5

The effect of water on NO adsorption on LaCu-ZSM5 has been studied by in-situ FTIR at 50°C identifying for which copper sites NO adsorption competes with water. The relative thermal stability of NO and H2O ad-species have been also determined by increasing the sample temperature from 50 to 400°C. Water was removed from zeolite at temperature lower than that necessary to desorb NO, as both bridged and chelating nitrates, from copper sites.A quantitative analysis of the adsorption of NO on the zeolite previously contacted with water was made by carrying out adsorption tests at temperatures far from those activating any DeNOx reaction in a lab-scale PFR reactor. The variation of the amount of adsorbed NO with the temperature of H2O desorption has been evaluated increasing the desorption temperature from 125 to 500°C after zeolite saturation with water at 125°C. The total recovery of the amount of NO adsorbed on the dry zeolite demonstrated the reversibility of water deactivation.

Study on Specific Heat of Water Adsorbed in Zeolite Using DSC

In this study, the specific heat of water included in an adsorbent was analyzed by a differential scanning calorimeter in the temperature range from −50 °C to 50 °C. Zeolites with pore sizes of 3 A and 9 A were employed as adsorbents, and the measurement was performed with various water mass fractions in zeolites. In this article, the water was defined as being composed of adsorbed water and free water that is not adsorbed in zeolite. As a result, the specific heat of the dry zeolite increased with temperature. The specific heat of the adsorbed water was measured by a special experimental procedure to establish the experimental accuracy. It was found that the specific heat of the adsorbed water had values in the range from (3 to 5) J · g−1 · K−1.

Removal of sulfonamide antibiotics from water: Evidence of adsorption into an organophilic zeolite Y by its structural modifications

Sulfonamide antibiotics are persistent pollutants of aquatic bodies, known to induce high levels of bacterial resistance. We investigated the adsorption of sulfadiazine, sulfamethazine, and sulfachloropyridazine sulfonamides into a highly dealuminated faujasite zeolite (Y) with cage window sizes comparable to sulfonamide dimensions. At maximal solubility the antibiotics were almost completely (>90%) and quickly (t<1min) removed from the water by zeolite. The maximal amount of sulfonamides adsorbed was 18-26% DW of dry zeolite weight, as evidenced by thermogravimetric analyses and accounted for about one antibiotic molecule per zeolitic cage. The presence of this organic inside the cage was revealed by unit cell parameter variations and structural deformations obtained by X-ray structure analyses carried out using the Rietveld method on exhausted zeolite. The most evident deformation effects were the lowering of the Fd-3m real symmetry in the parent zeolite to Fd-3 and the remarkable deformations which occurred in the 12-membered ring cage window after sulfadiazine or sulfachloropyridazine adsorption. After sulfamethazine adsorption, zeolite deformation caused a lowering in symmetry up to the monoclinic P2/m space group. The effective and irreversible adsorption of sulfonamides into organophylic Y zeolite makes this cheap and environmentally friendly material a suitable candidate for removing sulfonamides from water.

Microwave regeneration of zeolites in a 1 meter column

AbstractAlthough sorption is a common method of removing volatile organic compounds (VOC's) from processes, the adsorbent must be regenerated to repeat the process. The use of microwaves to regenerate the bed of adsorbent can be more efficient than conventional heating methods. Desorption of methanol from a silicalite zeolite was studied by the use of microwaves in cylindrical column. Temperature probes at five axial and three radial positions monitored the temperature profile in time. A significant amount of microwave energy passed through the dry zeolite bed, whereas a strong attenuation occurs if methanol is adsorbed. The radial temperature distribution conforms to theoretical predictions; however, microwave reflections cause a distortion of the predictions in the axial direction. Irregularities during the saturation of the bed indicated a chemical reaction during the irradiation with microwaves. A fraction of the methanol reacted under microwave irradiation to form dimethylether and water, and to methoxylate the zeolite surface. © 2009 American Institute of Chemical Engineers AIChE J, 2009

The nucleophilic chemical reactions of NaX Faujasite zeolite with diisopropyl phosphorofluoridate (diisopropyl fluorophosphate, DFP)

Diisopropyl phosphorofluoridate (commonly known as diisopropyl fluorophosphate and commonly abbreviated DFP) was adsorbed in dry NaX zeolite with and without adsorption of a stoichiometric amount of water. The chemical products from the reaction of zeolite and water with DFP, in relation to residual DFP, were identified and quantified from the quantitative NMR chemical shift values and intensities of solid-state 13C and 31P NMR and solution 13C, 31P, 17O and 1H NMR. In dry zeolite, DFP undergoes an elimination reaction to form propene and a framework bound isopropyl phosphorofluoridate ion. In NaX loaded with a stoichiometric amount of water, DFP undergoes hydrolysis to form isopropanol and isopropyl hydrogen phosphate. Upon addition of water to the DFP exposed zeolite, residual DFP undergoes hydrolysis to form isopropanol and isopropyl hydrogen phosphorofluoridate. Evidently upon addition of water to the dry DFP exposed NaX, the previously formed framework bound isopropyl phosphorofluoridate ion is also hydrolyzed to isopropyl hydrogen phosphate. Addition of water to the zeolite after DFP adsorption increased the hydrolysis reaction from 6.5% to 44.5%. Unlike other reported catalyzed hydrolyses, where hydrolysis of DFP involves water attack on the phosphorous, in NaX zeolite the ester carbon is attacked.

A hybrid MP2/planewave-DFT scheme for large chemical systems: proton jumps in zeolites

We present an embedding scheme to introduce local corrections at post Hartree–Fock level to density functional theory (DFT) calculations. As a first application we study proton jump reactions in the zeolite HSSZ-13 and show that energy barriers and rate constants are significantly changed by second-order Møller–Plesset perturbation theory (MP2) corrections to plane wave based DFT calculations. Electronic energy barriers increase from 68 to 81 kJ/mol (dry zeolite), and from 22 to 30 kJ/mol (hydrated zeolite). The predicted heats of adsorption of one water molecule onto the Brønsted acidic sites O 1 and O 2 are 73 and 69 kJ/mol, respectively.

First direct observation of reactive carbenes in the cavities of cation-exchanged Y zeolites.

[reaction: see text] Herein we report the first direct observation of reactive carbenes within the cavities of cation-exchanged Y zeolites. Chloro(phenyl)- and bromo(phenyl)carbenes were generated upon laser photolysis of 3-halo-3-phenyldiazirines incorporated within dry zeolites and the absolute reactivity of the carbenes was investigated as a function of counterbalancing cation and coincorporated quenchers in order to elucidate the behavior of these intermediates within zeolites. Product analysis performed upon thermolysis of the diazirine in Y zeolites yielded products that were identified as those derived from the carbene.

Understanding competitive adsorption of water and trichloroethylene in a high-silica Y zeolite

In this study, the adsorption of trichloroethylene (TCE) and water was investigated on a hydrophobic Y zeolite with an Si to Al ratio of 80. Single adsorbate isotherms for water or TCE, and TCE isotherms under conditions of 100% relative humidity (RH) were measured over the temperature range from 5 to 47 °C. Water adsorption isotherms were well described by the Freundlich isotherm model with isotherm exponents of 1.5. Isosteric heats for water adsorption were less exothermic than the enthalpy for water condensation, and ranged from −34 to −39 kJ/mol. Entropy changes associated with water adsorption were less negative than those for condensation of bulk water, indicating that the adsorbed phase had less structure than bulk water. Type V isotherms were observed for TCE adsorption under conditions of 0% RH. Isosteric heats for TCE adsorption on the dry zeolite ranged from −40 to −56 kJ/mol, and showed regions where the heats of adsorption both increased and decreased with increasing TCE loading. The Henry’s law asymptote for TCE adsorption on the dry zeolite was not experimentally accessible at the lowest vapor concentrations investigated. Type V isotherms with a linear region were observed for TCE adsorption under conditions of 100% RH. The isosteric heats for TCE adsorption on the wet zeolite depended strongly on the adsorbed phase concentration, and ranged from −35 to −64 kJ/mol. At adsorbed phase TCE concentrations below 0.01 g/g, the presence of water increased TCE uptake by the zeolite. However, at all other TCE loadings the presence of water decreased TCE adsorption by up to 83%.

Preparation and properties of ZSM-5 zeolite membrane obtained by low-temperature chemical vapor deposition

A zeolite membrane was obtained by in situ crystallization of silicalite-1 from a layer of silica species prepared by the novel method of low-temperature chemical vapor deposition (LTCVD) on a porous cordierite support. The XRD and SEM analyses showed a three-layer membrane: a 3–5 μm-thick compact layer, a 45 μm-thick zeolite-in-pore layer and the support. The pure gas permeation data indicate that the synthesized zeolite layer is dense and pinhole-free. In water-alcohol mixture pervaporation, the membrane exhibited a behavior of hydrophilic materials, with a high selectivity to water and a fair flux. This behavior can be explained by the presence of Al in the framework due to Al migration from the support. The membrane flux and selectivity decreased fairly slowly with time in the transient regime of water—ethanol pervaporation with the dry membrane, suggesting slow sorption equilibria of water and ethanol with the dry zeolite.

Molecular Dynamics Studies of Hydrofluorocarbons in Faujasite-type Zeolites: Modeling Guest-Induced Cation Migration in Dry Zeolites

We have developed and applied a new force field for simultaneously modeling the dynamics of hydrofluorocarbons (HFCs) and exchangeable Na cations in faujasite-type zeolites. Our aim is to account for (i) the zeolite’s capacity of separating HFC isomers, (ii) the experimentally observed unusual cation migration in Na-Y from the ‚-cages into the supercages upon the adsorption of HFCs, and (iii) the abnormal trans/ gauche ratio in these systems. Energy minimizations and molecular dynamics simulations performed with this force field give excellent agreement with experimental data on heats of adsorption, guest -host distances, infrared spectra, and conformer ratios for different coverages of HFC-134 (CF2H-CF2H) and HFC-134a (CH2F-CF3 )i n Na-X (Si:Al ) 1.2) and Na-Y (Si:Al ) 2.4). The force field also accounts partially for the observed cation migration at intermediate loadings and fully at high loadings. The extent of migration is found to be influenced by the competition among Na-O, Na-F, and Na-Na interactions. The Na-O interaction disfavors migration because Na(I′) sites are found to be energetically more favorable than Na(III′) sites; the Na-F attraction obviously favors migration; and surprisingly, the Na -Na repulsion also favors migration because moving Na cations into supercages leads to better cation dispersion. This migration occurs

Absolute Reactivity of the 4-Methoxycumyl Cation in Non-Acid Zeolites

The reactivity of the 4-methoxycumyl cation in a series of alkali metal cation-exchanged zeolites (LiY, NaY, KY, RbY CsY, NaX, NaMor, and Naβ) in the absence and presence of coadsorbed alcohols and water is examined using nanosecond laser flash photolysis. In dry zeolites, the absolute reactivity of the carbocation is found to be strongly dependent on the nature of the alkali counterion, the Si/Al ratio, and the framework morphology, with the lifetime of the carbocation in Naβ being almost 10000-fold longer than in CsY. The results suggest a mechanism for carbocation decay involving direct participation of the zeolite framework as a nucleophile, leading to the generation of a framework-bound alkoxy species. Intrazeolite addition reactions of alcohols and water to the 4-methoxycumyl cation can be described in terms of both dynamic and static quenching involving molecular diffusion through the heterogeneous topology and rapid coupling between the alcohol and the carbocation encapsulated within the same cavity. The dynamics of the quenching reactions are different from similar reactions in homogeneous solution due to both the passive and active influences of the zeolite environment. In a passive sense, the zeolite decreases the reactivity of the nucleophilic quencher by hindering molecular diffusion. However, the zeolite actively promotes the efficiency of intracavity coupling by enhancing the deprotonation of the oxonium ion intermediate, allowing the reaction to go to completion.

Volatilization of Fission Products from Metallic Melts in the Melt-Dilute Treatment Technology Development for Al-Based DOE Spent Nuclear Fuels

The melt-dilute treatment technology is being developed to facilitate the ultimate disposition of highly enriched Al-Base DOE spent nuclear fuels in a geologic repository such as that proposed for Yucca Mountain. Currently, approximately 28 MTHM is expected to be returned to the Savannah River Site from domestic and foreign research reactors. The melt-dilute treatment technology will melt the fuel assemblies to reduce their volume and alloys them with depleted uranium to isotopically dilute the 235U concentration and reduce the potential for criticality and proliferation concerns. A critical technology element in the development of the melt-dilute process is the development of an offgas system. Experimental tests using both cesium surrogates and radioactive cesium have shown that zeolite 4A is an effective gaseous cesium trap and as a result a preliminary offgas system concept has been developed employing dry zeolite 4A absorber beds as the primary cesium trapping medium. Final, validation of this offgas concept will occur during pilot-scale irradiated testing.

Absolute Rate Constants for SN1-like Ionization Reactions in Zeolites: Determination of Zeolite Ionizing Power

A kinetic probe molecule has been developed to investigate the absolute ionizing power of cation-exchanged (LiY, NaY, KY, RbY, and CsY) Y-zeolites. The probe, the 2-chloro-1-(4-methoxyphenyl)ethyl radical, was generated within the supercages of MY upon laser photolysis of 2-chloro-1-(4-methoxyphenyl)ethyl acetate under both dry and hydrated conditions. The ionizing power of the cation-exchanged Y-zeolites depends on the nature of the counterion and increases upon going from CsY to LiY. In addition, the ionizing powers of the dry zeolites are weaker than that of neat water and are more similar to water/methanol mixtures containing from 30% to 70% water. A significant reduction in the absolute ionizing ability of the zeolite was found when the zeolite was hydrated by the coadsorption of water.

Spectroscopic Studies of Electron and Hole Trapping in Zeolites: Formation of Hydrated Electrons and Hydroxyl Radicals

The trapping of electrons by water clusters and the reaction of positively charged holes in pulsed electron radiolysis of hydrated zeolites X and Y were studied using time-resolved transient absorption spectroscopy. The fully hydrated zeolites, under 12 mbar of water vapor, exhibit a short-lived structureless absorption band centered at 620 nm. This is attributed to hydrated electrons confined to the 13 Å supercages of the zeolites. The band is blue-shifted by 0.28 eV relative to that of the hydrated electrons in bulk liquid water. With the gradual removal of water molecules from the zeolite cavities, a continuous red shift of the transient absorption spectra is observed in both zeolites X and Y. The similarity of the spectral features of hydrated electrons in zeolites to those of water cluster anions in the gas phase suggests that water exists in the form of clusters in the zeolite supercages. The spectral shift with decreasing size of the water clusters presumably demonstrates that the confinement of water by the zeolite cages on the nanometer dimension affects solvation and electronic structures of the excess electrons. It is shown that water clusters trap electrons more weakly as their sizes become smaller and that cation cluster trapping sites are gradually formed during dehydration. Electron transfer from the water cluster trapping sites to the cation cluster trapping sites is clearly observed when the water content is decreased to ∼32 water molecules per pseudocell (a supercage plus a sodalite cage) in zeolites X with a Si/Al ratio of 1.0. A high radiolytic yield of Ge = 5.8 is measured for the water cluster trapped electrons in fully hydrated NaY. The unique transport of hydrated electrons in zeolite cages is understood in terms of an adiabatic model. The reactivity of positively charged holes generated by the ionizing radiation as geminate pairs with excess electrons is examined in both hydrated and dry zeolites. Trapping and reactions of the positive holes with aromatic molecules and water leads to the formation of organic radical cations and hydroxyl radicals, respectively. Essentially the same high yield of hydroxyl radicals as that of water cluster solvated electrons is measured in zeolite Y at the highest water content, GOH• = 6.0. The addition reactions of OH• with aromatic molecules included in zeolites is found to be limited by the slow diffusion of OH• through the zeolite supercages.

Electrochemistry of Oxygen, Isopropanol Vapor, and Uranyl, Cobalt(II), Nickel(II), and Copper(II) Ions in Dry Zeolites at Elevated Temperatures

not Available.

Investigation of the hydration of zeolite NaA by two-dimensional sodium-23 nutation NMR

A 2-dimensional nutation NMR expt. is used to observe the change of quadrupole parameters of Na+ ions in zeolite NaA when the zeolite is loaded in steps with H2O. Two Na sites were obsd. in the dry zeolite, at, resp., 6-rings and 8-rings, and the H2O absorption was monitored at these sites. When the amt. of absorbed H2O is increased in steps, the quadrupole interaction of Na at the 6-rings at first decreases; with more absorbed H2O the quadrupole interaction of the Na+ ions at the 8-rings becomes small. Relaxation effects in the rotating frame, studied by combining rotary echoes with nutation NMR, indicate a mobility of Na+ ions or H2O mols.

Polymerization of N-Vinylcarbazole by SK-500 Molecular Sieve

Abstract The polymerization of N-vinylearbazole (NVC) by SK-500 molecular sieve obeys the relation, rate of polymerization (R) = [NVC]1,0 (weight of SK-500)°−7Oat 30°C. Stirring increases the rate but the reaction order does not change. The highest catalytic activity, observed at 500°C precalculation temperature, does not correspond to the highest solid acidity of the sieve, realized at 200°C precalculation temperature. Pyridine and n-butylamine (⋍10−3 M) inhibit and hydrogen chloride (⋍10−3 M) and phosphoryl chloride (⋍10−4 M) cocatalyze the polymerization. Both R and the degree of polymerization (F) increase up to a maximum at −9 −10% uptake of water (g/g of dry zeolite) and thereafter fall. Alumina and silica increase .Rp Pn decreases with an increasing alumina content and rises initially at low silica content, falling at a high concentration of the latter. Nitrobenzene retards the polymerization. P is independent of [NVC], percentage conversion, and weight of SK-500. It appears that the polymerization...