Comparison of the catalytic properties of Al‐ZSM‐22 and Fe‐ZSM‐22 in the skeletal isomerization of 1‐butene

The catalytic activities of Al‐ZSM‐22 (Al in the framework) and Fe‐ZSM‐22 (Fe in the framework) were compared in the skeletal isomerization of 1‐butene to isobutene. The catalysts synthesized in the laboratory were characterized by means of XRD, FTIR spectroscopy, SEM and surface area measurements. The activity of the zeolites was investigated using a fixed‐bed microreactor system. Al‐ZSM‐22 demonstrated higher activity in 1‐butene transformation compared to Fe‐ZSM‐22, while the selectivity to isobutene, on the other hand, was higher over Fe‐ZSM‐22. Coke formation was monitored using a microbalance and the results showed that the weight gain of Fe‐ZSM‐22 was slightly higher compared to Al‐ZSM‐22. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cobalt‐catalyzed amination of 1,3‐cyclohexanediol and 2,4‐pentanediol in supercritical ammonia

The onestep procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixedbed reactor. Application of supercritical NH₃ as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8–10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via ,unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3propanediol.     

Non‐Isothermal Non‐Adiabatic Dehydrogenation of Cyclohexane in Catalytic Membrane Reactors

Abstract

This study focuses on modeling and analysis of the non‐isothermal, non‐adiabatic, dehydrogenation of cyclohexane in membrane catalytic reactors. The dehydrogenation reaction is endothermic with a low equilibrium conversion of 0.06 at a temperature of 473 K and pressure of 101 kPa. The membrane reactor removes hydrogen from the reaction mixture and results in increase of the reaction conversion. The analysis is made as a function of feed flow rate, feed temperature, feed composition, inert flow rate in the feed stream, flow rate of sweep gas, pressures of the tube side and shell side, permeability constant of hydrogen, and tube diameter. The analysis also includes a study of the co‐current and the counter‐current flow modes. The results show lower conversion for the counter‐current flow mode, because of the decrease in the driving force for permeation. A comparison of model predictions against previous literature studies shows good agreement.     

Quasi‐Homogeneous and Pseudospin Modes of Zirconium‐Wire Combustion in Air

A novel experimental technique is proposed for examining the transition mechanism from quasihomogeneous to heterogeneous combustion — burning of a variablepitch spring. Depending on the pitch of aircombustible zirconium springs, two combustion modes are possible. Quasihomogeneous (layerbylayer) combustion is observed in the case of smallpitch springs; as the spring pitch increases, quasihomogeneous combustion transforms into heterogeneous (pseudospin) combustion. Conditions for the occurrence of various combustion modes, depending on the spring diameter and pitch, are studied.     

Specific Features of Electric Phenomena in Self‐Propagating High‐Temperature Synthesis

Results of an experimental study of electronion emission and kinetic effects of the electric field in combustion of metallic and hybrid heterogeneous systems are presented. Nonequilibrium excitation of free electrons to an energy of 150 eV and periodic selfmodulation of the emission current during combustion are established on the basis of probing data. Under electron irradiation, the ignition temperature in the Ni–Al system decreases from 950 to 420 K, and the linear burning rate increases by a factor of 2–3 in an electric field with a frequency of 16 kHz.     

Surfactant‐Enhanced Regeneration of Polymeric Resin in a Vapor‐Phase Application

Abstract

Surfactant enhanced carbon regeneration (SECR) was employed to regenerate a polymeric resin saturated with trichloroethylene (TCE), using an aqueous solution of the anionic surfactant sodium dodecyl sulfate (SDS). More than 95% of the sorbed TCE was removed in the desorption operation with a 0.1 M SDS solution at a superficial flow rate of 1 cm/min. The desorption rate of TCE from pores of the resin is limited by the concentration of SDS in the regenerant and its flow rate. From the breakthrough curve of the subsequent adsorption cycle without a flushing step following the desorption, only 40% of the effective adsorption capacity of the virgin resin is observed for the regenerated resin. With a water flushing step following the surfactant regeneration step, the effective adsorption capacity is significantly improved to about 60% of that of the virgin resin. Thermal gravimetric analysis indicates that the reduction in the effective adsorption capacity of regenerated resin resulted from the residual SDS remaining in the pores of the resin. The regeneration step is equilibrium limited whereas the water flushing step is rate limited under the studied conditions. Despite the loss of subsequent cycle adsorption capacity, SECR may still be economical as an in‐situ, low temperature regeneration method.     

Preparation and characterization of alumina‐supported metal‐carbonyl‐derived model catalytic systems in UHV conditions

Active catalysts for metathesis of alkenes, hydrodesulfurization, and hydrogenation can be prepared by exposing a high‐surface‐area alumina support to molybdenum hexacarbonyl at room temperature. This strategy is mimicked in ultrahigh vacuum by adsorbing molybdenum hexacarbonyl onto an ultrathin hydroxylated alumina film grown onto a Mo(100) substrate. In contrast to results found on high surface area, no Mo(CO)₆ is found to adsorb on alumina at 300 K, and significant molybdenum deposition is only found by heating the sample to above 670 K. Alternatively, molybdenum hexacarbonyl adsorbs on alumina when cooled to 80 K. In this case the majority of the carbonyl desorbs intact and temperature‐programmed desorption and X‐ray photoelectron spectroscopy indicate that ∼2% of a monolayer of the carbonyls undergoes decarbonylation. Auger and X‐ray photoelectron spectroscopy measurements reveal that molybdenum carbide (MoC) is deposited onto the alumina surface heated to 700 K forming a monolayer after an exposure of ∼50 L. This layer is reduced to the metal by heating to ∼1500 K by reaction with the alumina substrate to evolve CO and form metallic molybdenum. The carbide can be reformed by heating the metal‐covered alumina sample in ethylene at 900 K, and the carbide can once again be reduced to the metal by heating to 1500 K. This process can be repeated so that the carbide can be regrown by reaction with ethylene and reduced by annealing in vacuo to 1500 K. Subcarbonyl species are detected after adsorbing Mo(CO)₆ on hydroxylated alumina at 80 K as the sample is heated to ∼200 K. At higher temperatures, the molybdenum is oxidized to an approximately 4+ oxidation state and deposits primarily oxalate species on the surface. The adsorbed oxalates thermally decompose at ∼300 K to evolve CO to form surface formates. These are stable to ∼560 K and react to evolve CO at this temperature. It is also found that the extent of decarbonylation depends on the degree of alumina hydroxylation so that heating hydroxylated alumina to 900 K, which removes ∼50% of the surface hydroxyls, decreases the both CO desorption yield and the oxalate coverage by 50%. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Striking Effect of Ionic‐Liquid Anions in the Extraction of Sr2+ and Cs+ by Dicyclohexano‐18‐Crown‐6

Abstract

The nature of the ionic‐liquid (IL) anion has been found to have a remarkable effect on the solvent extraction of Sr²⁺ and Cs⁺ by dicyclohexano‐18‐crown‐6 dissolved in ionic liquids. In particular, the extraction efficiency increases with the hydrophobicity of the IL anion as reflected by the solubility in water of ILs having a common cation. Since a cation‐exchange mechanism is operating in these systems, the influence of the IL anion is in large part attributable to an expected Le Chatelier effect in which a greater aqueous concentration of IL cation, obtained when using an IL anion of lower hydrophobicity, opposes cation exchange. This dependence is opposite to that found for IL cations, indicating a significant advantage of using ILs with hydrophobic anions for cation extraction. Furthermore, the extraction selectivity for Sr²⁺ over Na⁺, K⁺, and Cs⁺ can be significantly improved through the use of hydrophobic anions for the ILs containing 1‐ethyl‐3‐methylimidazolium or 1‐butyl‐3‐methylimidazolium cations.     

Prediction of the Elution Profile of Aromatic Compounds in RP‐HPLC

Abstract

An efficient prediction method for the elution profile was used to separate aromatic compounds such as benzene, toluene, chlorobenzene, o‐xylene, and 1,2‐dichlorobenzene by RP‐HPLC. The retention factor and bandwidth were predicted under linear‐gradient condition with the three retention models. The elution profiles were calculated based on the linear and quadratic equations of retention factor, lnk=lnk _w +S?, lnk=L+M?+N?², k=A+B/?, where ? was the vol.% of methanol. The elution profiles were calculated by the Gaussian distribution with obtained retention factor and bandwidth. Two kinds of experiments were performed; one is the isocratic runs to estimate the coefficients of three retention models, and the other is the linear gradient runs that were carried out with same initial mobile phase composition (water/methanol=96/4, vol.%), two final mobile phase compositions (water/methanol=24/76 and 40/60, vol.%), and three gradient times (20, 40, and 60 min). The predicted elution profiles by the three retention models and new prediction method have good agreement with experimental data in the employed gradient conditions. The minimum average errors of calculated and experimental results of aromatic compounds were lower than 3.5% by Bi‐poly equation.     

Location of Mn in MnAPO‐11: influence of synthesis from aqueous and non‐aqueous media

MnAPO11 samples were synthesized from aqueous (MnAPO11(A)) and ethylene glycol (MnAPO11(NA)) media. The crystallinity of the samples was more when the synthesis was carried out in ethylene glycol. Chemical and thermogravimetric analyses reveal greater incorporation of Mn in the framework of MnAPO11(NA) than in MnAPO11(A). At least five different types of Mn(II) species are detected in the samples by ESR. The studies suggest that Mn is more homogeneously distributed in MnAPO11(NA) than in MnAPO11(A).     

Redox and photo‐redox properties of isolated Mo5+ ions in MoH‐ZSM‐5 and MoH‐beta zeolites: in situ ESR study

Redox and photo‐redox properties of isolated Mo⁵⁺ ions stabilized in H‐ZSM‐5 and H‐beta zeolites are studied by in situ ESR in flowing O₂, NO, H₂, and C₃H₆. Upon oxidation of pre‐reduced samples at 20 °C, NO demonstrates a higher oxidative ability, as compared with O₂. Interaction of Mo⁵⁺ ions with propene at 20 °C results in formation of a chemisorption complex with enhanced reactivity of Mo(V) toward NO. Illumination of the Mo⁵⁺/HZSM‐5 sample with UV‐visible light causes measurable acceleration of Mo(V) oxidation by NO at 20 °C. Therefore, photochemical activation of the oxidation step could be realized, in principle, for Mo/zeolite catalysts. At 500 °C in the reaction mixture NO + H₂, the step of the catalytic site reduction is fast, and the dynamic equilibrium of the redox reaction Mo(VI) ↔ Mo(V) for MoH‐ZSM‐5 and MoH‐beta seems to be strongly shifted to Mo⁵⁺. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some Features of Gas‐Flame Propagation in Narrow Tubes

The dependence of the flamefront curvature on the composition of the mixture in tubes of various diameters is considered. The combustionwave velocities are measured for different fractions of fuel in the mixture. It is shown that the dependence of the burning velocity on the composition of the mixture has two maximums, one of them being related to the transition of the laminar combustion mode to turbulent combustion. Combustion turbulization is caused by flame instability to acoustic oscillations. Variations of the combustionwave shape due to acoustic oscillations are observed.     

Comparison of Hydrometallurgical Parameters of N,N‐Dialkylamides and of Tri‐n‐Butylphosphate

Straight‐chain N,N‐dihexyloctanamide (DHOA) and branched‐chain N,N‐di(2‐ethylhexyl)isobutyramide (D2EHIBA) have been identified as promising alternatives to tri‐n‐butylphosphate (TBP) for the reprocessing of spent uranium based fuels, and selective extraction of ²³³U from irradiated thorium fuels, respectively. The present work deals with the effects of different hydrodynamic parameters such as viscosity, density, and interfacial tension (IFT) on the phase‐separation time (PST) under uranium and thorium loading conditions. The IFT values have been determined under varying experimental conditions such as the aqueous nitric acid concentration, n‐dodecane purity, ligand concentration, and thorium/uranium loading conditions. These studies have suggested that the quality of n‐dodecane affects the IFT values of different solutions. The IFT values of D2EHIBA changed marginally (23.3 ± 0.9 mNm^?1) against THOREX feed solution for the wide range of D2EHIBA concentration (0.1–1.0 M). However, IFT, viscosity, and PST values increased with uranium loading of 1.1 M DHOA. These studies suggested that a lower phase‐disengagement rate with increased uranium loading was mainly due to the increased viscosity of the loaded 1.1 M DHOA solution.     

On‐line addition of catalyst in high‐temperature reactors: high selectivity to olefins

By adding solutions containing catalyst salts to hot monolith catalysts during partial oxidation processes, the salt decomposes instantly and is deposited selectively near the front face. We have used this technique to deposit extremely small amounts of Pt on α-Al₂O₃ monoliths during ethane oxidation to olefins. We find that on this catalyst with H₂ addition, the selectivity to ethylene rises from ∼ to over 80% at an ethane conversion of ∼60% and at complete O₂ conversion. We also examine the addition of promoters including Sn, which gives improved performance compared to the Pt catalyst alone. This appears to be a general effect that could be useful in preparing catalysts with different loadings and distributions in high‐temperature processes. It can also be used for rapid and accurate diagnosis of catalysts and additives and to modify catalysts on‐line in situations where deactivation or catalyst loss occurs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combustion Modes and Mechanisms of High‐Temperature Oxidation of Magnesium in Oxygen

Oxidation and combustion of single magnesium particles in an oxygen–argon mixture is experimentally studied. A diagram of hightemperature oxidation of magnesium is constructed, and a relation between the structural features of the oxide film and macrokinetics of hightemperature oxidation and mechanisms of transition between different oxidation regimes is established.     

Effect of Channel Geometry and Mixture Temperature on Detonation‐to‐Deflagration Transition in Gases

Results from theoretical and experimental studies of deflagrationtodetonation transition in hydrocarbon–air mixtures are reported. The effects of internal geometry, turbulence transition of the flow, and the temperature and fuel concentration in the unburned mixture on detonation initiation are considered.     

Performance of metal‐oxide‐promoted LiCl/sulfated‐zirconia catalysts in the ethane oxidative dehydrogenation into ethene

The effects of some transition‐ and lanthanide‐metal oxides in LiCl/sulfated‐zirconia (SZ) catalysts on catalytic behavior in the oxidative dehydrogenation of ethane were investigated. It is found that modification of LiCl/SZ by metal oxides significantly improves the catalytic activity and ethene yield. Among those additives, Ni and Nd oxides show the best promoting effect in terms of ethane conversion and ethene yield. 93% ethane conversion with 83% selectivity to ethene has been achieved over the Nd₂O₃–LiCl/SZ catalyst at 650°C. In addition, those oxide‐promoted LiCl/SZ catalysts are also found to exhibit a longer stability in catalytic performance. Metal‐oxide additives change the chemical structure and surface redox properties, which accounts for the enhancement of activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Shock‐Wave Initiation of Detonation of Double‐Base Propellants

In the known experimental system active charge–target–HE charge to be tested, critical pressures of shock waves initiating detonation of doublebase propellant charges are determined. TNT charges of various density were used as active HE, and copper plates 5 mm thick were used as targets. The pressure of the shock wave acting on the propellant versus the TNT density was constructed; this dependence being known the critical pressure can be readily determined with only the density of the active charge available. It was found that doublebase propellants are close to liquid HE in terms of sensitivity to shock waves; the critical pressure is 6.0–9.0 GPa for a charge diameter of 40 mm and decreases with increasing diameter. By an example of the NDT2 propellant, it is shown that the use of factorypacked propellants in line charges may lead to failure in transfer of detonation from one propellant charge to another.