Macrokinetics of toluene and benzene nitration under laminar conditions

Mononitration of toluene and benzene has been carried out in a laminar jet using aqueous mixtures of nitric and sulphuric acids. With acid mixtures containing about 30 mole % H₂SO₄, the rate data obtained are in good agreement with values predicted using a model, assuming fast reaction in a zone in the aqueous phase adjacent to the interface, in conjunction with diffusivities measured under laminar conditions. At low H₂SO₄, concentrations, the rate data fit a simple kinetic model. It is shown that the model based on mass transfer with simultaneous chemical reaction can explain previously reported results for the competitive nitration of toluene and benzene in the heterogeneous liquid phase regime.     

Phase Equilibria in the Alkali Fluoride-Uranium Tetrafluoride Fused Salt Systems: II, The Systems KF-UF4 and RbF-UF4

Mixtures of alkali fluorides with uranium tetra-fluoride are of potential importance in molten-salt reactors and in the reprocessing of nuclear fuels. In this paper detailed phase diagrams are presented for the binary systems KF-UF₄ and RbF-UF₄. Data for the determination of phase boundaries were obtained in large part by quenching after equilibration. Thermal analysis and visual observation were used as supplementary methods. Phase identifications were made by X-ray powder diffraction and by optical microscopy. In the system KF-UF₄ four compounds have been identified. Two of these, 3KF.UF₄ and 7KF.6UF₄, melt congruently at 957°C. and at 789°C., respectively. The compound 2KF UF₄ melts incongruently to 3KF.UF₄ and liquid at 755° C., and the compound KF.2UF₄ melts incongruently to UF₄ and liquid at 765° C. There are three eutectic points in the system: 15.0 mole % UF₄, 735° C.; 38.5 mole % UF₄, 740° C.; and 54.5 mole % UF₄, 735° C. The compound 2KF.UF4 decomposes during cooling to 3KF.UF₄ and 7KF 6UF₄ at 608° C. Two other compounds, KF 3UF₄ and KF.6UF₄, have been described by another investigator. One of these, KF 3UF₄, was not obtained at all in the present investigation. The other, KF.6UF₄, was not obtained under equilibrium conditions and was found only in KF-UF₄ mixtures that had been exposed to the atmosphere while molten. Seven solid compounds are present in the system RbF-UF₄. All of these melt incongruently with the exception of 3RbF.UF₄ and RbF-UF₄, which melt at 995° C. and at 735° C., respectively. The incongruently melting compounds and their melting points, peritectic compositions, and melting products are: 2RbF UF₄, 818°C., 38 mole % UF₄, 3RbF -UF₄+ liquid; 7RbF.6UF₄, 693° C., 44 mole % UF₄, RbF.UF₄+ liquid; 2RbF.3UF₄, 722° C., 56.5 mole % UF₄, RbF.3UF₄+ liquid; RbF. -3UF₄, 73O°C., 57 mole % UF₄, RbF.6UF₄+ liquid; and RbF.6UF₄, 832°C., 70.5 mole % UF₄, UF₄+ liquid. The three eutectic temperatures and compositions in the system are: 10.0 mole % UF₄, 710°C.; 43.5 mole % UF₄, 675°C.; and 55.0 mole % UF₄, 714°C.     

Critical point measurements on nearly polydisperse fluids

The critical temperatures, pressures and volumes of several mixtures containing CO₂, C₂H₆, C₃H₈, and C₄H₁₀ have been measured using a heavy walled, variable volume, cylindrical glass vessel. In each mixturre the relative proportions of the three hydrocarbon solutes to one another were changed; total solute mole fraction never exceeded 0.1. A detailed study of the mixture CO₂ + C₃H₈ shows that the critical temperature exhibits a minimum at a C₃H₈ mole fraction of 0.0265. Our mixture data are analyzed using a polydisperse model of dilute solutions.     

Reforming of methanol and glycerol in supercritical water

Reforming of pure glycerol, crude glycerin, and methanol (pure and in the presence of Na₂CO₃) in supercritical water was investigated. Continuous experiments were carried out at temperatures between 450 and 650 °C, residence times between 6 and 173 s, and feed concentrations of 3-20 wt%. For methanol the gas products are mainly H₂, CO₂, and CO. The carbon-to-gas efficiency and the observed activation energy for pure methanol are higher than for methanol with Na₂CO₃. This can be explained by assuming different decomposition mechanisms for pure methanol and methanol with Na₂CO₃. For glycerol, H₂, CO, CO₂, CH₄, and higher hydrocarbons are produced. The carbon-to-gas efficiencies of crude glycerin and pure glycerol are comparable. Overall, 2 of the 3 carbon atoms present in glycerol end up in carbon oxides, while 1 carbon atom becomes C_xH_y. The overall mechanism of glycerol decomposition involves the dehydration of 1 mole of H₂O/mole glycerol. For both, methanol and glycerol at carbon-to-gas efficiencies below 70%, the gas yields (mole/mole feed) and carbon-to-gas efficiency correlate well.     

Development of composite powders of the Ti-Al-N system produced from Ti-Al intermetallic compounds

The kinetics of nitrating intermetallic compounds Ti₃Al, TiAl, and TiAl₃ in the range of 1200–1400°C is studied; the compositions of the reaction products and the process mechanisms are identified. It is established that nitration of Ti₃Al and TiAl is intense at 1200°C and complete nitration is achieved at 1400°C with 3 h exposure. Nitration of TiAl₃ differs significantly from nitration of Ti₃Al and TiAl; the process has several stages, is slow, and complete nitration is achieved only after 6 h exposure at 1400°C. __________ Translated from Novye Ogneupory, No. 8, pp. 52–54, August, 2006.     

Polymerization of methyl methacrylate in water in presence of the metal oxides TiO2 and Cu2O

Rates of sodium bisulfite-initiated polymerization of methyl methacrylate in water were determined in absence and in presence of the metal oxides TiO₂ and Cu₂O at 30°, 40°, 50°, and 60°C. Cuprous oxide and titanium dioxide enhanced the rate of polymerization and reduced the molecular weight as compared with the figures obtained in absence of oxide, the effect of the former being more pronounced than the latter. With TiO₂, the rate was increased from 2.3 to 3.2 × 10^?5, while with Cu₂O, it was increased to 8.6 × 10^?5 mole/l./sec, both at concentrations of 9 g/l. water. The apparent energy of activation for the polymerization of methyl methacrylate between 40°C and 50°C was found to be 15.6 kcal/mole in absence of the metal oxides, and 7.6 kcal/mole and 2.8 kcal/mole in presence of titanium dioxide and cuprous oxide, respectively. The number-average molecular weight was found to decrease slightly with the addition of TiO₂ but to decrease greatly when Cu₂O was added.     

Experimental study of the structure of laminar premixed flames of ethanol/methane/oxygen/argon

The structures of three laminar premixed stoichiometric flames at low pressure (6.7 kPa): a pure methane flame, a pure ethanol flame, and a methane flame doped by 30% of ethanol, have been investigated and compared. The results consist of mole fraction profiles of CH₄, C₂H₅OH, O₂, Ar, CO, CO₂, H₂O, H₂, C₂H₆, C₂H₄, C₂H₂, C₃H₈, C₃H₆, CH₃-C CH (propyne), CH₂ C CH₂ (allene), CH₂O, and CH₃HCO, measured as a function of the height above the burner by probe sampling followed by on-line gas chromatography analyses. Flame temperature profiles have been also obtained by using a PtRh thermocouple. The similarities and differences between the three flames have been analyzed. The results show that, in these three flames, the mole fraction of the intermediates with two carbon atoms is much larger than that of the species with three carbon atoms. In general, the mole fraction of all intermediate species in the pure ethanol flame is the largest, followed by the doped flame, and finally the pure methane flame.     

Simultaneous Absorption of Carbon Dioxide and Sulfur Dioxide into Aqueous 2-Amino-2-Methy-1-Propanol

Abstract

Carbon dioxide and sulfur dioxide were simultaneously absorbed into aqueous 2-amino-2-methyl-1-propanol (AMP) in a stirred semi-batch tank with a planar gas-liquid interface within a range of 0–4.0 kmol/m³ of AMP, 0.03–0.3 mole fraction of CO₂, 0.005–2 mole fraction of SO₂, and 298–318 K. Absorption data of each gas in the CO₂-AMP and SO₂-AMP systems are obtained to verify their reaction regimes, based on film theory, respectively, which are used to analyze the simultaneous absorption mechanisms of CO₂ and SO₂ in the CO₂-SO₂-AMP systems. The measured absorption rates of CO₂ and SO₂ are compared to those formulated by an approximate solution of the mass balances with simultaneous reactions.     

Composite Powders with the Pseudoeutectic Structure in the Al2O3 – TiN System

The processes occurring in the synthesis of composite powders in Al₂O₃ – TiN system are considered for two variants: the first variant is the reaction of carbothermic reduction of TiO₂ mixed with Al₂O₃ with simultaneous nitration, and the second one is direct nitration of metallic titanium dispersed in aluminum oxide under high-frequency heating in a “cold” crucible. The synthesis produces submicron composite powders, which are promising for application in construction ceramics.     

Simultaneous Absorption of Carbon Dioxide and Sulfur Dioxide into Aqueous 1,8-Diamino-p-menthane

Abstract

Carbon dioxide and sulfur dioxide were simultaneously absorbed into aqueous 1,8-diamino-p-menthane (DAM) in a stirred semi-batch tank with a planar gas-liquid interface within a range of 0–2.0 kmol/m³ of DAM, 0.01–0.12 mole fraction of CO₂, 0.001–0.012 mole fraction of SO₂, and 298-318 K. Absorption data of each gas in the CO₂-DAM and SO₂-DAM systems are obtained to verify their reaction regimes, based on film theory, respectively, which are used to analyze the simultaneous absorption mechanisms of CO₂ and SO₂ in the CO₂-SO₂- DAM systems. In the simultaneous absorption rate of CO₂ and SO₂ into DAM solution, the absorption of CO₂ belongs to the second-order reaction of finite rate and the absorption of SO₂ belongs to the instantaneous reaction regime.     

Thermal Decomposition of Energetic Materials 57. Products of some self-igniting fuel-HNO3 Systems

Exothermic reactions of some self igniting fuel-HNO₃ systems have been examined by the rapid-scan FIR/thermal profiling technique. A sudden rise in temperature is observed when the liquid oxidizer is dropped onto the solid fuel. Simultaneous monitoring of the gas products of the reaction occurring between p-phenylenediamine and HNO₃ reveals the formation of Co₂, NO₂ and HONO. Immediate evolution of NO₂ is observed in the synergistically igniting systems comprised of substituted anilines, Mg and HNO₃. Thiocarbohydrazide and its acetone and benzaldehyde monoderivatives on reacting with HNO₃ produce SO₂, NO₂ and, possibly, OCS. The results are explained in terms of the oxidation and nitration reactions occurring in these systems.     

Nitration of phenol over silica supported H4PW11VO40 catalyst

Vanadium incorporated tungstophosphoric acid (TPAV₁) supported on silica was synthesized and characterized by BET-surface area, Fourier transform infrared spectroscopy, X-ray diffraction and Laser Raman techniques. Nitration of phenol was studied at room temperature (25 °C) using HNO₃ in the presence of 0–20 wt.% TPAV₁/SiO₂ catalysts taking 1, 2-dichloroethane as solvent. The effects of various parameters such as phenol/HNO₃ mole ratio, reaction time, catalyst weight, and stirring speed on the catalyst activity were studied. 8 wt.% TPAV₁/SiO₂ has shown the best activity, regioselectivity and reusability in the nitration of phenol, with a conversion of 92.6% and o-nitrophenol selectivity of 97.9%.     

The System Bi2O,—B2O3

The phase diagram for the system Bi₂O₃-B₂O₃ has been determined experimentally. The melting point of Bi₂O₃ has been redetermined as 825° C with an estimated overall uncertainty of about ±3°C, and the molal heat of fusion of Bi₂O₃, calculated from the slope of the liquidus curve, is 2050 cal per mole. The system contains a body-centered cubic phase of approximate composition 12Bi₂O₃·B₂O₃, which melts incongruently at 632°C. Four congruently melting compounds exist in the system: 2Bi₂O₃· B₂O₃·5B₂O₃, Bi₂O₃·3B₂O₃, and Bi₂O₃·4B₂O₃, with melting points, respectively, of 675°, 722°, 708°, and 715°C. The Bi₂O₃·4B₂O₃ compound exhibits a sluggish transformation at 696°C. Compositions containing up to 97.5 wt% (85 mole %) Bi₂O₃ can be partly or totally quenched to glass. Indices of the quenched glasses are greater than 1.74. A region of liquid immiscibility extends at 709°C from almost pure B₂O₃ to 19.0 mole % Bi₂O₃. The extent of immiscibility theoretically calculated agrees with the experimentally determined value when 1.20 A is used for the ionic radius of Bi³⁺.     

Condensed Phase Relations in the Systems ZrO2-WO2-WO3 and HfO2-WO2-WO3

Phase relations for the systems ZrO₂–WO₂–WO₃ and HfO₂–WO₂–WO₃ from 1000° to 1700° C were determined by the quenching technique using sealed sample containers. In the system ZrO₂–WO₃, 1:2 compound, ZrW₂O₈ forms, having a cubic structure with a= 9.159 A. The ZrW₂O₈ melts incongruently at 1257°± 3°C to ZrO₂ and liquid and has a lower limit of stability at 1105°C, below which ZrO₂ and WO₃ coexist in equilibrium. One eutectic and one peritectic were established: at 1231°± 3°C and 74 mole % WO₃, and at 1257°± 3°C and 71 mole % WO₃, respectively. Along the join ZrO₂–WO₂, no compound formed. Two invariant points were determined: ZrO₂, WO₂, W, and liquid are in equilibrium at 1430°± 5°C and 76 mole % WO₂, whereas WO₂, W₁₈O₄₉, W, and liquid coexist at 1530°± 5°C and 89 mole % WO₂- Equilibrium relations in the system ZrO₂–WO₂–WO₃ were investigated at four temperatures. At 1200°C, a cubic phase with composition near W₂₀O₅₈ was found; it exists in equilibrium with ZrO₂, W₁₈O₄₉, W₂₀O₅₈, and WO₃. As the temperature increases, the liquid formed along the ZrO₂–WO₃ join extends into the ternary system, crosses the join ZrO₂–W₂₀O₅₈ at 1300°C, and crosses the join ZrO₂–W₁₈O₄₉ at 1400°C. The cubic phase can take more zirconium into its solid solution at 1300° than at 1200°C. At 1500°C, the system can no longer be treated as a simple ternary oxide system because of the presence of metallic tungsten, and equilibrium relations are presented on the basis of the system ZrO₂–W–WO₃. Phase equilibrium relations in the systems HfO₂–WO₃, HfO₂–WO₂, and HfO₂–WO₂–WO₃ in the temperature ranges studied are much like those in the corresponding zirconium system.     

Investigation of the Correlations Between Nitro Group Charges and Some Properties of Nitro Organic Compounds

The so‐called nitro group charge method (NGCM) is successfully established to investigate some properties of nitro compounds including the molecular stability measured by total energy (only for isomers), the bond lengths, bond dissociation energies (BDE), and the nitrating activities, in that the method considers the molecular structure. These properties are intrinsically and especially thermodynamically consistent with each other and can be well related qualitatively and even quantitatively with nitro group charges (Q_Nitro). The correlations between Q_Nitro and the properties are: (1) for nitro isomers, the more negative the average Q_Nitro, the lower the total energy and the more stable is the isomer; (2) for any separate group of nitro compounds, the more negative Q_Nitro, the shorter the R‐nitro bond length; (3) for the bond dissociation energy, more negative Q_Nitro corresponds to a higher BDE of the R‐nitro bond; (4) by NGCM, the conditions, the reaction rates and the occurrence ratios of products of some nitration can be predicted and compared: the more negative Q_Nitro of the product, the easier and faster the nitration, and the higher the occurrence ratio of the corresponding product.     

Desorption of isoamylene from loaded acid liquors

The desorption of 2-methyl-2-butene (isoamylene) from loaded sulphuric acid solutions, having an acid strength of about 60 per cent (w/w) and loading upto 0·45 g mole of isoamylene per g mole of H₂SO₄, was found to be preceded by a fast reaction, which occurred in the film adjacent to the interface. The specific rates of desorption of isoamylene into inert hydrocarbons—n-heptane and toluene and an inert gas—nitrogen, were found to be proportional to the isoamylene concentration j, expressed as g mole of isoamylene per g mole of H₂SO₄, and agreed among themselves at the same value of j.The technique of desorption preceded by a fast reaction was employed for the measurement of effective interfacial area in liquid—liquid and gas—liquid agitated contactors. The absorption of isobutylene into fresh and loaded solutions of sulphuric acid was also used for the measurement of effective interfacial area in gas—liquid agitated contactors for comparative purposes. The values of effective interfacial area for the gas—liquid system obtained by the desorption technique were found to be comparable with those obtained from the absorption of isobutylene in fresh and loaded solutions of sulphuric acid, under otherwise comparable conditions.     

Influence of stoichiometry and alkalinity on barium hexaferrite formation via the supercritical water crystallization method

Fine particles of barium hexaferrite were prepared from aqueous solutions of iron nitrate, barium nitrate and potassium hydroxide by utilizing a continuous flow type supercritical water crystallization method. The influence of stoichiometry (Fe/Ba mole ratio) and alkalinity (R) on the product composition and morphology was studied under fixed temperature, pressure and residence time. Experiments were performed with varying Fe/Ba mole ratios and alkali mole ratio (R). Within mole ratio ranges of 0.5< Fe/Ba< 5, BaO-6Fe₂O₃ single phase was produced; and as the Fe/Ba mole ratio increased, α-Fe₂O₃ was also formed and its quantity increased with increasing mole ratio. At an Fe/Ba ratio of 12, stoichiometric mole ratio of BaO-6Fe₂O₃, the only product formed was α-Fe₂O₃ fine particles. In the case of the influence of alkalinity, single phase α-Fe₂O₃ was detected at R of 0.5 and if R exceeded 2, a single phase BaO-6Fe₂O₃ was detected. According to the results of the experiment and the study of reaction mechanisms, the formation of BaO-6Fe₂O₃ proceeds via a non-stoichiometric reaction and the product composition and morphology can be controlled by adjusting the reaction parameters to obtain optimum conditions for Ba(OH)₂ precipitate formation.     

On the nature of the burning rate-controlling reaction of energetic materials for the gas-phase model

For model systems with known kinetics of elementary reactions (CH₃NO₂ and HN₃), temperature ranges are established in which the rate-controlling reactions are the initial endothermic decomposition of the starting material or the subsequent secondary reactions. Heat release in reactions of NO₂, NO, and N₂O with various fuels, such as CH₂O, CO, H₂, and HCN, is modeled to establish the kinetic parameters and nature of the rate-controlling reactions in gas flames of nitro compounds. It is shown that the activation energy of the heat-release reaction due to the interaction of NO₂ with a hydrocarbon fuel (which is characteristic of the first flame of nitro compounds) is in the range of 29–33 kcal/mole, depending on the type of fuel. According to the calculations performed, the activation energy of the rate-controlling heat-releasing process due to the deoxidation of NO and N₂O (which is typical of the second flame of nitro compounds) is 43–58 kcal/mole. In the range of high pressures, where the flames merge, the kinetic parameters of heat release are determined by the reactions of the most reactive nitrogen oxide NO₂. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 59–71, May–June, 2007.     

Regioselective and green synthesis of nitro aromatic compounds using polymer‐supported sodium nitrite/KHSO4

Polymer supported reagents have become the subject of considerable and increasing interest as insoluble materials in the organic synthesis. Use of polymeric reagents simplifies routine nitration of aromatic compounds because it eliminates traditional purification. In this article, the use of readily available cross‐linked poly(4‐vinylpyridine) supported sodium nitrite, [P₄‐Me] NO₂, as an efficient polymeric nitrating agent in the presence of KHSO₄ is described. A good range of available aromatic compounds were also subjected to nitration in the presence of [P₄‐Me] NO₂/KHSO₄. This reagent is regioselective and chemoselective nitrating polymeric reagent for activated aromatic rings. In this procedure, the work‐up is easy, and the spent polymeric reagent is easily regenerated and reused. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011