Solid Exchange Research Articles

Characterization of hydrotreated Cu-ZSM-5 catalyst for the selective catalytic reduction of NO by n-decane

The steam treatment of Cu-ZSM-5 prepared by solid ion exchange involves an important decrease of the NO conversion. Characterization of the solids by NO-TPD, H2-TPR, 27Al MAS NMR shows that the catalyst deactivation is mainly due to change in copper species rather than the collapse of the zeolite framework.

Determination and preconcentration of natural and radio-cesium from aqueous solution

This work reports a modified atomic emission spectrometric (AES) method to determine cesium(I), based on the measurement of emission intensity at 455.5 nm with a limit of quantitation (LOQ) of 5.5 mg/l and a linear range up to 100 mg/l. In order to increase the sensitivity and lower the detection limits, potential sorbents were investigated for preconcentrating Cs from natural waters. Among the various ion-exchange materials synthesized, potassium hexanitrocobaltate (PHNCo) yielded the highest capacity for 137Cs tagged Cs+ solutions as measured by gamma-spectrometry with a HPGe detector, showing the potential of a cesium preconcentration sorbent. As an alternative to AES determination, the PHNCo sorbent may be used for Cs+ collection from radiocesium tagged solutions and the retained activity in the dry solid exchanger be determined by gamma-spectrometry.

Bis(oxazoline)–copper complexes supported by electrostatic interactions: scope and limitations

Bis(oxazoline)–copper complexes have been supported by cation exchange in laponite and nafion-like solids. The results obtained with these catalysts in cyclopropanation reactions depend on the nature of both the chiral ligand and the support. On using the complex of 2,2′-isopropylidenebis[(4 S)-4- tert-butyl-2-oxazoline] with Cu(II), direct exchange in methanol leads to low enantioselectivities in nafion-type solids. Some improvement in enantioselectivity can be obtained by using the less coordinating nitroethane as the exchange solvent or by exchanging the support prior to use with a more soluble tetraalkylammonium cation. Another strategy consists of the exchange of copper(II) and subsequent treatment with the chiral bis(oxazoline) ligand. This system leads to slower reactions and similar enantioselectivities to those obtained by direct exchange. The best enantioselectivity obtained in the reaction between styrene and ethyl diazoacetate is around 70% ee. The recovery of the catalysts leads to a partial loss of enantioselectivity. The stability of the bis(oxazoline)–copper complex is the crucial factor for this behavior. The selectivity can be improved with the bulkier (1 R,2 S,5 R)-menthyl diazoacetate, up to 83% ee, although the reactivity in this case is much lower.

Mechanism of gas–solid exchange processes for some perovskites

Experimental data on oxygen desorption from barium cerates doped with neodymium together with data on equilibrium saturation of cerates by oxygen were used for mathematical modelling of oxygen nonstoichiometry of the oxides as a function of P O 2 . Such sorption parameters as ks 0 and Q were determined by iterative fitting of experimental with calculated data and good agreement of experimental and modelled data confirms the adequacy of proposed model. It was also fond that LaMnO 3 doped with strontium has a tendency to interact with carbon dioxide during sample annealing in air.

Recharge flux to ocean-ridge black smoker systems: a geochemical estimate from ODP Hole 504B

We use the Sr-isotopic composition of rock and anhydrite, as a monitor of fluid composition, in DSDP/ODP Hole 504B to calculate the recharge flux to the axial high-temperature hydrothermal circulation. The fluid and rock Sr-isotope profiles are well fit by a tracer transport mass-balance model that approximates fluid–solid exchange by linear kinetics. The calculated time-integrated flux of 1.7±0.2×106 kg m−2 is significantly less than the 5×106 kg m−2 calculated from thermal models that assume all magma is intruded into a high-level magma chamber at the base of the sheeted dykes. Our low flux is consistent with the observed thermal structure as recorded by secondary alteration minerals in Hole 504B and the intrusion of magma as lenses distributed through the lower oceanic crust. It leaves open the questions as to how the lower oceanic crust cools and how seawater geochemical budgets balance.

Predicting the Similar Profile Regime of Upflowing Gas–Solid Suspensions

The existence of lean and dense regimes in the fully developed upflow of gas-particle suspensions has been extensively investigated both theoretically and experimentally. Self-similar flow patterns, which have been suggested and detected within the lean regime, disappear when the solid loading is increased. The system then switches to the so-called dense regime, and the pressure drop increases more rapidly with increasing the global solid mass flow rate. The predictive capability of the model presented by Ocone et al. (1993; AICHE J 39: 1261), in relation to the features associated with these two regimes, is investigated. Since the existence of such regimes can be predicted theoretically, without making an explicit constitutive assumption on the way the solid phase exchanges momentum, the theoretical and modelling approaches are indeed independent. Consequently, from the computed results an insight can be gained into the mechanisms responsible for the observed behaviour.

Oxygen self-diffusion in single-crystal MgO: secondary-ion mass spectrometric analysis with comparison of results from gas–solid and solid–solid exchange

Self-diffusion coefficients for 18O in single-crystal MgO have been determined from a novel specimen comprising an epitaxial layer of high-purity Mg 18O upon a single crystal substrate of normal MgO. Heating the specimen in air produced a gas–solid exchange gradient at the sample surface as 18O in the epitaxial layer exchanged with 16O in air. A solid–solid interdiffusion gradient was produced between the substrate crystal and the 18O-enriched epitaxial layer. SIMS analysis of gas–solid exchange gradients prepared in the temperature range 1000–1650 °C provided diffusion coefficients that could be described as D/( m 2 s −1)= 1.8 −1.1 +2.9 ×10 −10 exp[−(3.24±0.13) eV/kT] . Interdiffusion gradients produced by annealing at 1100 and 1200 °C yielded the self-diffusion coefficients that were comparable to those obtained from gas–solid exchange, indicating that the surface exchange reaction is fast enough. The results are interpreted in terms of a defect model in which oxygen diffusion occurs by an interstitial type of defect as a result of suppression of anion vacancy concentration by large concentrations of extrinsic cation vacancies.

Orbital interaction analysis of cooperative Jahn–Teller distortion, orbital ordering, spin ordering, and spin exchange interactions in magnetic solids

The phenomena of cooperative Jahn–Teller distortion, orbital ordering and spin exchange in magnetic solids were examined in terms of orbital interactions between adjacent spin sites. Cooperative Jahn–Teller distortion and orbital ordering of a magnetic solid occur to minimize the two-electron two-orbital destabilizing interactions between adjacent spin sites. The magnetic structures of cubic perovskites KCuF3, LaMnO3 and YVO3 are well accounted for in terms of the spin exchange interactions associated with their ordered magnetic orbitals.

Integrated Technology for Processing Rhenium-containing Molybdenite Concentrates to Recover Molybdenum and Rhenium into Commercial Products

The paper reports on processing of molybdenite concentrate to recover molybdenum and rhenium products. The process involves roasting of molybdenite in a fluid bed. The fluid bed exhaust is passed through a cyclone, a electrostatic separator and finally subjected to wet gas scrubbing. The scrub is sent to solid ion exchange resin to produce ammonium perrhenate. The cinder from fluid bed roaster is processed to calcium molybdate and the dust from dust recovery is processed to ammonium paramolybdate.

Effect of the calcium dopant on oxide ion diffusion in yttria ceramics

Tracer oxygen diffusion coefficients, D*, in polycrystalline yttria doped with Ca have been determined by a gas–solid exchange technique and secondary ion mass spectrometry. Samples containing few pores were used to avoid their influences on diffusion profiles. The resulting profiles were assigned only to volume diffusion; no grain boundary diffusion was observed. According to the effects of Ca doping on D*, the Ca contents are divided into three regions. In a Ca content region of 0–0.17 mol%, D* changed a little with Ca doping and took a minimum experimentally at 0.02 mol%. D* increased significantly within a range of 0.17–0.54 mol% and saturated at 0.54 mol% or above because of a solubility limit. The activation energies of oxygen diffusion were estimated at 249–282 kJ/mol.

Slow-down of 13C spin diffusion in organic solids by fast MAS: a CODEX NMR Study.

One- and two-dimensional 13C exchange nuclear magnetic resonance experiments under magic-angle spinning (MAS) can provide detailed information on slow segmental reorientations and chemical exchange in organic solids, including polymers and proteins. However, observations of dynamics on the time scale of seconds or longer are hampered by the competing process of dipolar 13C spin exchange (spin diffusion). In this Communication, we show that fast MAS can significantly slow down the dipolar spin exchange effect for unprotonated carbon sites. The exchange is measured quantitatively using the centerband-only detection of exchange technique, which enables the detection of exchange at any spinning speed, even in the absence of changes of isotropic chemical shifts. For chemically equivalent unprotonated 13C sites, the dipolar spin exchange rate is found to decrease slightly less than proportionally with the sample-rotation frequency, between 8 and 28 kHz. In the same range, the dipolar spin exchange rate for a glassy polymer with an inhomogeneously broadened MAS line decreases by a factor of 10. For methylene groups, no or only a minor slow-down of the exchange rate is found.

Solids motion in rolling mode rotating drums operated at low to medium rotational speeds

The industrial-scale rotating drums are usually operated in the rolling or slumping mode. For the rolling mode, the granular material bed can be divided into two regions, namely, a ‘passive’ region where particles are carried up by the drum wall, and an ‘active’ region where particles cascade down. As solids mixing mainly occurs in the active region, solids motion in this region and solids exchange between the active and passive regions are of prime importance for the overall performance of the drum. This paper reports some observations on particle motion in the transverse plane of a three-dimensional rotating drum operated at low and medium rotational speeds. The non-invasive PEPT (positron emission particle tracking) technique is used to follow particle trajectory and velocity. A mathematical model based on the thin-layer approximation is proposed to describe solids motion in the active layer. Reasonable agreement between the model predictions and experiments is obtained. A new parameter termed the ‘solids exchange coefficient’ is proposed to characterise particle exchange between the passive and active regions. A theoretical expression for this parameter is also derived. This expression, upon application of the thin-layer approximation, is reduced to give an explicit relationship between the solids exchange coefficient and drum operating parameters such as rotational speed and fill percentage, as well as the bed material rheological properties. The solids exchange coefficient is also shown to give a possible scale-up rule for rotating drums operated in a rolling mode.

Integrated Technology for Processing Rhenium-containing Molybdenite Concentrates to Recover Molybdenum and Rhenium into Commercial Products

The paper reports on processing of molybdenite concentrate to recover molybdenum and rhenium products. The process involves roasting of molybdenite in a fluid bed. The fluid bed exhaust is passed through a cyclone, a electrostatic separator and finally subjected to wet gas scrubbing. The scrub is sent to solid ion exchange resin to produce ammonium perrhenate. The cinder from fluid bed roaster is processed to calcium molybdate and the dust from dust recovery is processed to ammonium paramolybdate.

Ion Exchange of Zeolite Na-Pc with Pb2+, Zn2+, and Ni2+ Ions

AbstractThis paper examines the ion-exchange properties of synthetic zeolite Na-Pc, which was produced from perlite-waste fines and has a SiO2:Al2O3 ratio of 4.45:1 and a cation-exchange capacity (CEC) of 3.95 meq g−1. Although equilibrium is attained rapidly for all three metals, exchange is incomplete, with Ac(max) (maximum equilibrium fraction of the metal in the zeolite) being 0.95 for Pb, 0.76 for Zn, and 0.27 for Ni. In both Na → ½Pb and Na → ½Zn exchange, the normalized selectivity coefficient is virtually constant for NAC (normalized equilibrium fraction of the metal in the zeolite) values of ≤0.6, suggesting a pronounced homogeneity of the available exchange sites. The Gibbs standard free energy, ΔG°, of the Na → ½Pb exchange calculated from the normalized selectivity coefficient is −3.11 kJ eq−1 and, for the Na → ½Zn exchange, it is 2.75 kJ eq−1.Examination of the solid exchange products with X-ray diffraction (XRD) revealed a possible decrease in crystallinity of zeolite Pb-Pc as suggested by the significant broadening and disappearance of diffraction lines. This decrease is associated with a reduction of pore opening, as indicated from Fourier-transform infrared analysis (FTIR), which in turn results in a decrease of the amount of zeolitic water. Thermogra-vimetric-differential thermogravimetric (TG-DTG) analysis showed that water loss occurs in three steps, the relative significance of which depends on the type of exchangeable cation and subsequently on the type of complex formed with the cation and/or the zeolite channels. Zeolite Na-Pc might be utilized in environmental applications, such as the treatment of acid-mine drainage and electroplating effluents.

Suppression of sidebands in two-dimensional exchange and MQMAS spectroscopies in solids by variable-speed magic-angle sample spinning

The variable-speed magic-angle sample spinning (VSMAS) technique has been extended to two-dimensional spectroscopy in solids yielding two-dimensional spectra free of spinning sidebands.

Cation Exchange Resin Supported Oxidation of Alkylbenzenes and Olefins using Potassium Permanganate†

Rapid and efficient oxidation of alkylbenzene side chains at the benzylic positions as well as oxidative cleavage of olefins with potassium permanganate in presence of solid polymeric cation exchange resins in good yields is reported.

Improved estimation of zeolite diffusion coefficients from zero–length column experiments

Zero-length column (ZLC) diffusion experiments have been performed on dilute systems of benzene and ethylbenzene in silicalite in the temperature range of 325–485K. The linear gas–solid exchange model with ideal vapor mixing in the sorption zone and Henry adsorption and Fick diffusion with concentration–independent coefficients was able to fit the full-time response curves. Systematic effects were accounted for in the fitted models, especially for crystal shape, size distribution, and apparatus. The effect of the surface barrier hypothesis at zeolite pore mouths is analyzed. It is shown that accounting for systematic effects and a thorough execution of the parameter estimation process lead to substantially better fits and affect parameter values. The newly established intracrystalline diffusivities are up to one order of magnitude higher than those in the literature. The transient ZLC adsorption coefficients are consistent with values determined independently under equilibrium conditions.

INFLUENCE OF OSMOTIC DEHYDRATION ON TEXTURE AND PECTIC COMPOSITION OF KIWIFRUIT SLICES

ABSTRACT In order to optimize the osmotic dehydration process as a pre-treatment to freezing, chemical and structural characteristics of the raw fruit have to be studied together with their influence on the solid liquid exchanges and on the quality of the end products Textural properties of fruits are intimately associated with the cellular structure and pectic composition. So the influence of osmodehydration on the modification of texture and water-soluble, oxalate-soluble and residual protopectin in kiwifruit slices was studied. To determine the optimum firmness level of the raw kiwifruit, the fruits were processed at three instrumentically measured texture levels: firm, medium and soft. Chemical and physical analyses showed that the biggest difference among the three groups of fresh kiwifruit was the protopectin content which was correlated directly with texture. No relationships were found between texture changes and pectic composition during osmodehydration, the slight firmness increase probably being produced by the soluble solids concentration.

Mineralogical controls on the oxygen isotopic compositions of UOCs

We report the results of oxygen isotopic analyses made on mineral separates prepared from chondrules and whole meteorites (UOCs). Feldspar/glass (mainly chondrule mesostasis) is more 16O-poor than the olivine/low Ca pyroxene from which it was separated. This relationship is true both for chondrules and whole meteorites from the three UOC groups. Feldspar and glass have exchanged to a higher degree with 16O-poor gases than ferromagnesian minerals because of the susceptibility of framework silicates and glass to gas–solid diffusion. Olivine and low Ca pyroxene have preserved primitive isotopic compositions. In this way, mineralogy is the dominant control on the oxygen isotopic compositions of UOCs. The similarity of chondrule and whole meteorite isotope compositions suggests that for many UOCs, matrix and chondrules have undergone exchange with the same isotope reservoirs. This exchange postdates chondrule formation and is believed to have occurred after consolidation with the surrounding chondrite matrix in a parent body regolith. After this gas–solid exchange, some isotopic equilibration took place between feldspar and the other relatively 16O-rich solids, as a result of metamorphism. A progressive decrease in the values of δ 18O feldspar/glass–δ 18O olivine/pyroxene for bulk meteorites occurs with increasing petrologic subtype, from 8 0 00 for a type 3.2 to 2.5% for a type 3.9. A chemical origin for the initial 16O-poor gas reservoirs in the H, L, and LL parent bodies by processes of mass independent fractionation is considered more likely than nucleosynthesis. Feldspar/glass separated from Adrar 003 (L/LL3.2) may be in, or close to having, isotopic equilibrium with the 16O-poor gases for L or LL chondrites. On this basis and assuming that the gas was dominated by H 2O and its isotopic composition lay along a line of slope 1 (corresponding to what has been called the equilibrated chondrite line), a tentative upper limit for gas–solid isotopic exchange in UOCs can be calculated, which gives 370°C.

Effect of particle size on solids mixing in bubbling fluidized beds

Abstract Experimental and theoretical studies of both vertical and lateral mixing of solids in a two-dimensional bubbling fluidized bed (1300 X 920 X 60 mm ? ) are conducted by using heated particles as the tracer. The effect of particle size on solids mixing is studied. Fluctuations in the concentration responses along both vertical and lateral directions have been observed experimentally. These fluctuations become increasingly more prominent as the bed particle size increases. The convection-diffusion model of solids mixing [L. Shen, M. Zhang, Y. Xu, Powder Technol. 84 (1995) 207–212] is used to analyze the experimental data. The dynamics of solid exchange between the bubble wake and the emulsion phase in bubbling fluidized beds is investigated, and a new model for exchange coefficient is proposed. In the model, particle sized d p , particle density ρ p , gas viscosity μ ? , gas density ρ ? minimum fluidization velocity U ml and bubble size D B , etc., are taken into account: where A = 1.0 × 10 7 . The exchange coefficient K W values for the model do not compare favorably with the predictions of two available theoretical models in the literature [K. Yoshida, D. Kunii, J. Chem. Eng. Jpn. 1 (1968) 11–16: T. Chiba, H. Kobayashi, J. Chem. Eng. Jpn. 10 (1977) 206–210]. These models predict that the wake exchange coefficient should increase with increase in minimum fluidization velocity U mt (i.e. particle size d p ). However, our model shows that the wake exchange coefficient K w decreases with minimum fluidization velocity U m . With the model of wake exchange coefficient, the convection-diffusion model of solids mixing is found to predict the experimental trends reasonably well. The model for solids exchange between the bubble wake and the emulsion phase in a gas fluidized bed is needed in modeling solids mixing and segregation patterns.