Study of the Heat and Kinetics of Nitration of 1,2,4‐Triazol‐5‐one (TO)

The heat effects of the nitration and dissolution processes of 1,2,4‐triazol‐5‐one (TO) in acidic environments were measured by differential reaction calorimetry. The kinetics of nitration of TO in a 200‐mL reactor were investigated by UV/Vis spectroscopy. Temperature changes were measured in a 10‐L batch reactor during the TO nitration. A model of kinetics for the synthesis of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) was proposed and it was used to simulate the phenomena occurring in the calorimeter and in the reactors. The experimental data were compared with modeling results and parameters of the Arrhenius equation for synthesis of NTO with selected nitration mixtures were determined.     

Regioselective nitration of o-xylene to 4-nitro-o-xylene using nitric acid over solid acid catalysts

The regioselective nitration of o-xylene to 4-nitro-o-xylene (4-NOX) has been studied in the liquid and vapor phase over zeolites H-beta, H-ZSM-5 and silica supported molybdenum oxide (MoO₃/SiO₂) catalysts. Zeolite H-beta showed the maximum conversion of 28% and 63% selectivity for 4-NOX in liquid phase nitration at 70 °C with 70% HNO₃. The conversion increased to 65% when the reaction was carried out in vapor phase at 150 °C using dilute 30% HNO₃. The formation of α-methylphenyl nitromethane by alkyl nitration in liquid phase was decreased in vapor phase reaction. The formation of oxidation products was also decreased in vapor phase reaction with minor amounts of dinitro and ipso-products. The influence of experimental parameters such as temperature, nitric acid concentration and WHSV on conversion and selectivity has been investigated. The use of dilute nitric acid and the selective formation of 4-NOX using dilute HNO₃ makes this process environmental friendly with a potential for commercialization.     

Preparation and characterization of cellulose nitrate-acetate mixed ester fibers

Cellulose nitrate-acetate mixed esters (CNA) were synthesized by nitration of cellulose diacetate, using HNO₃/H₂SO₄ as nitration agent. The CNA structures were confirmed and analyzed by IR and ¹H NMR. A decrease in molecular weight and an increase in nitrate group content were observed with increasing H₂SO₄ ratio and reaction time. The highest degree of nitrate substitution, 9.2%, for CNA was achieved with the reaction time of 6h in concentrated HNO₃. Increasing HNO₃ ratio in nitration media resulted in more thermally stable CNA. CNA fibers were prepared by altering the polymer concentration from 15 to 30% in an 85:15 (w/w) acetone:water solvent. The electrospun CNA fibers were characterized by SEM to investigate the influence of different NO₂% on fiber formation, diameters and architectures.     

Determination of the kinetics of chlorobenzene nitration using a homogeneously continuous microflow

The nitration of chlorobenzene with concentrated mixed acids is a fast and highly exothermic process, which suffers from considerable mass transfer resistance and poor heat transfer rates. The reaction kinetics has not been thoroughly reported before. In this work, a continuous-flow microreactor system and a homogeneous reaction condition were proposed to obtain accurate chlorobenzene nitration kinetics parameters at high mixed acid concentrations. A general model for predicting the observed reaction rate constants was established. With a new method for estimating the equilibria associated with HNO₃ in aqueous sulfuric acid, the rate constants based on nitronium ion and activation energies were obtained. Compared with batch reactors, the continuous-flow microreactor system allows for a sufficient heat transfer efficiency and accurate residence time control, making it possible to study the reaction performance more quickly and sensitively. This work may provide a reliable reference for the kinetic study of similar processes.     

Nitration of nitrobenzene at high‐concentrations of sulfuric acid: Mass transfer and kinetic aspects

This article reports studies on mass transfer and kinetics of nitration of nitrobenzene at high concentrations of sulfuric acid in a batch reactor at different temperatures. The effects of concentration of sulfuric acid, speed of stirring, and temperature on mass transfer coefficient were investigated. The kinetics of nitration under homogenized conditions was studied at different sulfuric acid concentrations at these temperatures. The reaction rate constants were determined. The variation of rate constant with sulfuric acid concentration was explained by the M_c function. The activation energies of the reactions were determined from the Arrhenius plots. The regimes of the reactions were determined using the values of the mass transfer coefficients and the reaction rate constants. A model was developed for simultaneous mass transfer and chemical reaction in the aqueous phase. The yields of the three isomers of dinitrobenzene were determined, and the variation of isomer distribution with sulfuric acid concentration and temperature was analyzed. This work demonstrates that more than 90% conversion of nitrobenzene is possible at high‐sulfuric acid concentrations resulting in high yield of the product even at moderate temperatures and at low speeds of stirring. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Chemical Kinetics of the Thermal Decomposition of NTO

The kinetics of thermal decomposition of 3‐nitro‐2,4‐dihydro‐3H‐1,2,4‐triazol‐5‐one (NTO) in the temperature interval from 200 °C to 260 °C was investigated using a glass Bourdon gauge. The overall decomposition reaction includes two distinct stages: the fast first‐order decomposition and the subsequent autocatalytic reaction. The importance of the first stage increases with increasing decomposition temperature and decreasing loading density of the Bourdon gauge (m/V). A period of preliminary heating, at a lower temperature, strongly influences the autocatalytic stage when the decomposition is carried out at a higher temperature. In the temperature domain 200–220 °C, the Arrhenius constants of the decomposition reaction are found to be close to the values usually observed for nitrocompounds: E=173 kJ/mol and log₁₀ k≈12.5 (s⁻¹). It is shown that a simple model of NTO decomposition based on an autocatalytic reaction of the m‐th order can describe the course of the decomposition at high temperature but the m number appears to be excessively high, up to 4. A new model of the decomposition is developed, including an initial monomolecular reaction, decomposition of the crystalline substance, and an autocatalytic reaction of NTO dissolved in liquid decomposition products. This model gives the common order of autocatalysis, m=1.     

The role of polyaniline salts in the removal of direct blue 78 from aqueous solution: A kinetic study

Three polyaniline salts (PANI–H₂SO₄, PANI–H₃PO₄, and PANI–HNO₃) have been synthesized by chemical oxidative polymerization of aniline. They have been tested as adsorbents for the removal of the textile dye direct blue 78 (DB78) from aqueous solution. The interaction followed pseudo-second-order kinetics whether the rate of interaction was measured from the depletion of dye concentration in solution or the increase in the amount of dye adsorbed on the PANI surface. The removal rate was a function of the activity of the polymer as well as the reaction parameters of the polymer/dye system. The activity of the PANI depended on the polymerization conditions. These conditions involve the concentration of aniline, ammonium peroxydisulfate as oxidant, and sodium dodecylsulfate (SDS), the type of dopant acid (H₂SO₄, H₃PO₄, HNO₃), and the polymerization time. Higher removal rate was observed at oxidant/aniline mole ratio equals 1. The rate of removal was in the order PANI–H₃PO₄ > PANI–H₂SO₄ > PANI–HNO₃. The rate decreased with increasing the concentration of DB78 and pH. It increased with increasing the load of PANI. Pseudo-second-order kinetics, external surface adsorption, and intraparticle diffusion models were concurrently operating in the removal of DB78 with PANI.     

Combustion synthesis of mullite–titanium boride composite

Mullite/TiB₂ composite has been prepared successfully by combustion synthesis from blends of fine TiO₂–B₂O₃–Al–SiO₂ powders. Despite the dilution effect due to silica addition and the endothermic character of mullite formation reaction, thermodynamic calculation shows that the overall reaction between the reactants is still highly exothermic. Depending on the silica grain size and the preheating temperature, partial to full conversion of reactants into products can be achieved during the process. At 550 °C preheating temperature, complete conversion of the reactants to mullite/TiB₂ was achieved. Adiabatic combustion temperature and mullite molten fraction are calculated as a function of preheating temperature.     

Dissolution of Fissile Materials Containing Plutonium and Beryllium Metals

Abstract

Scrap materials containing plutonium (Pu) metal were dissolved at the Savannah River Site (SRS) as part of a program to disposition nuclear materials during the deactivation of the FB‐Line facility. Some of these items contained both Pu and beryllium (Be) metal as a composite material. The Pu and Be metals were physically separated to minimize the amount of Be associated with the Pu; however, a dissolution flowsheet was required to dissolve small amounts of Be combined with the Pu metal using a dissolving solution containing nitric acid (HNO₃) and potassium fluoride (KF). Since the dissolution of Pu metal in HNO₃/fluoride (F^?) solutions was well understood, the primary focus of the flowsheet development was the dissolution of Be metal.

Initially, small‐scale experiments were used to measure the dissolution rate of Be metal foils using conditions effective for the dissolution of Pu metal. The experiments demonstrated that the dissolution rate was nearly independent of the HNO₃ concentration over the limited range of investigation and only a moderate to weak function of the F^? concentration. The effect of temperature was more pronounced, significantly increasing the dissolution rate between 40 and 105°C. The offgas analysis from three Be metal foil dissolutions demonstrated that the production of hydrogen (H₂) was sensitive to the HNO₃ concentration, decreasing by a factor of approximately two when the concentration was increased from 4 to 8 M. In subsequent experiments, complete dissolution of Be samples from a Pu/Be composite material was achieved in a 4 M HNO₃ solution containing 0.1–0.2 M KF. Gas samples collected during each experiment showed that the maximum H₂ generation rate occurred at temperatures below 70–80°C.

A Pu metal dissolution experiment was performed using a 4 M HNO₃/0.1 M KF solution at 80°C to demonstrate flowsheet conditions developed for the dissolution of Be metal. As the reaction progressed, the rate of dissolution slowed. The decrease in rate was attributed to the complexation of F^? by the dissolved Pu. The F^? became unavailable to catalyze the dissolution of plutonium oxide (PuO₂) formed on the surface of the metal which inhibited the dissolution rate. To compensate for the complexation of F^?, an increase in the concentration to 0.15–0.2 M was recommended. Dissolution of the PuO₂ was addressed by recommending an 8–10 h dissolution time with an increase in the dissolving temperature (to near boiling) during the final 4–6 h to facilitate the digestion of the solids. Dilution of the H₂ concentration below 25% of the lower flammability limit by purging the dissolver with air was also necessary to eliminate the flammability concern.     

Intensification of nitrous acid oxidation

An alternative solution to the reduction of a discharge of residual nitric oxide and nitrogen dioxide into atmosphere has been proposed. Instead of using methane or ammonia for SCR or gas absorption into alkali solutions, which are the most popular treatment methods of tail gases, now the use of powerful oxidant—ozone capable of transforming nitrous acid and nitric oxides into nitrogen of the highest oxidation level—could be employed for this purpose. As the intensive oxidation and ozonation of nitrous acid is the heterogeneous gas-liquid process, the solubility of oxygen and ozone in HNO₂/HNO₃ aqueous solution was necessary to be determined. Variations of reaction rates depending on temperature, ozone dose and nitrous and nitric acid concentrations were studied experimentally. The kinetic model of the reactions, 2HNO₂+O₂→2HNO₃ and HNO₂+O₃→O₂+HNO₃, were proposed and the kinetic parameters (rate constants and activation energies) were estimated on the basis of experimental data in semi-batch laboratory gas-liquid contactor with the liquid phase drawn from an absorption column in the nitric acid plant. The determined kinetic parameters were then used in designing and modeling of the oxidation of nitrous acid using ozone-oxygen mixture in a continuous bubble column. The model consists of mass transfer kinetic equations and material balance equations for the gas and liquid phases. The co-current flow of gas and liquid phases and the complex kinetics of chemical reaction in the liquid phase were taken into account. The variation of the following process conditions, flow rate, compositions of the gas and liquid phases, temperature, and pressure in the bubble column of different diameters and heights, were studied in numerical solutions of the proposed model.     

THE KINETICS OF COBALT(II) EXTRACTION WITH EHEHPA IN HEPTANE FROM ACETATE SYSTEM USING AN IMPROVED LEWIS CELL TECHNIQUE†

ABSTRACT

The cobalt(II) extraction kinetics and mechanism with EHEHPA (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) were investigated by an improved constant interfacial area stirred cell. The effects of the buffer species, stirring rate, temperature, specific interfacial area and surfactants on the extraction rate showed that the extraction regime was dependent on the extraction conditions and the most probable reaction zone was at the liquid-liquid interface. This extraction process was reaction controlled at lower concentration of the reactants, while it was mixed chemical reaction-diffusion or diffusion controlled only for higher concentration of the reactants. An interfacial extraction reaction model with diffusion was derived. The kinetics of the extraction process was simulated with this model.     

Simulation of DME synthesis from coal syngas by kinetics model

DME (Dimethyl Ether) has emerged as a clean alternative fuel for diesel. There are largely two methods for DME synthesis. A direct method of DME synthesis has been recently developed that has a more compact process than the indirect method. However, the direct method of DME synthesis has not yet been optimized at the face of its performance: yield and production rate of DME. In this study it is developed a simulation model through a kinetics model of the ASPEN plus simulator, performed to detect operating characteristics of DME direct synthesis. An overall DME synthesis process is referenced by experimental data of 3 ton/day (TPD) coal gasification pilot plant located at IAE in Korea. Supplying condition of DME synthesis model is equivalently set to 80 N/m³ of syngas which is derived from a coal gasification plant. In the simulation it is assumed that the overall DME synthesis process proceeds with steadystate, vapor-solid reaction with DME catalyst. The physical properties of reactants are governed by Soave-Redlich-Kwong (SRK) EOS in this model. A reaction model of DME synthesis is considered that is applied with the LHHW (Langmuir-Hinshelwood Hougen Watson) equation as an adsorption-desorption model on the surface of the DME catalyst. After adjusting the kinetics of the DME synthesis reaction among reactants with experimental data, the kinetics of the governing reactions inner DME reactor are modified and coupled with the entire DME synthesis reaction. For validating simulation results of the DME synthesis model, the obtained simulation results are compared with experimental results: conversion ratio, DME yield and DME production rate. Then, a sensitivity analysis is performed by effects of operating variables such as pressure, temperature of the reactor, void fraction of catalyst and H₂/CO ratio of supplied syngas with modified model. According to simulation results, optimum operating conditions of DME reactor are obtained in the range of 265–275 °C and 60 kg/cm². And DME production rate has a maximum value in the range of 1–1.5 of H₂/CO ratio in the syngas composition.     

Particle Size Control of Nanocrystalline Anatase TiO2 Synthesized by Hydrolysis of Titanyl Organic Compounds

The global nanocrystalline anatase TiO₂ particle can be obtained by hydrolysis of titanyl organic compounds. Its particle size is mostly influenced by the titanyl organic compounds' concentration, nitric acid (HNO₃) concentration, reaction time and temperature, and especially the HNO₃ concentration. The formation of nanocrystalline TiO₂ with bigger size can be accelerated by a higher temperature, thick solution of reactant (titanyl organic compounds), and HNO₃. Vice versa, in order to gain smaller particles, such as 6 nm, the reaction conditions should be set at a thin reactant solution, low temperature, and low HNO₃ concentration. The reason lies in the hydrolyzing mechanism of titanyl organic compounds, which is strongly influenced by the temperature and pH.     

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%.     

Experimental Study and Mathematical Modeling of Metals Dissolution from LCD Boards in Na2S2O8 Environment

The current article aims to study the influence of pH, temperature, and oxidant concentrations on the dissolution process of metals from liquid crystal display (LCD) boards in a Na₂S₂O₈ environment. The dissolution rate of metals is enhanced by the decrease of pH and increase of temperature and Na₂S₂O₈ concentration. Based on the obtained results, a reaction mechanism was proposed and the reaction rate parameters (pre-exponential factor and activation energy) were determined. Kinetic analysis of the leaching process was performed in accordance with a shrinking core model. The activation energy was found to be 29,924, 11,871, 22,434, and 38,401 J/mol for Cu, Sn, Ni, and Pt, respectively, in a temperature range of 30°C–75°C, which was also an indication of the combined transport–chemical control. The experimental results were in good agreement with the simulated data and revealed that persulfate solutions are suitable reactants for metals leaching from LCD boards.     

Kinetics of hydantoin formation

The reaction of lignite in a slagging gasifier produces reactants which in turn form 5,5-dimethylhydantoin (DMH) as a major constituent in the condensate water. Variations in plant operating conditions made it impossible to accurately study the kinetics of formation of DMH in the actual gasifier water, and thus a model system was chosen. The reaction of acetone cyanohydrin in the presence of excess ammonium carbonate at concentrations approaching those obtained in the condensate water were studied at 50,70, and 90 °C. Secondorder kinetics were obeyed, and the pseudo second-order rate constants at the respective temperatures were 1.86, 3.6, and 4.62 dm³ mol^{? 1} h^{? 1}. Independent variation of the concentration of either acetone, cyanide, ammonia or carbonate gave results consistent with the interpretation that the formation of DMH is first order in all reactants: rate of formation of DMH = k[acetone][HCN][NH₃][CO₂]. The pseudo second-order rate constant is a complex rate constant including several rapid equilibria. A mechanism consistent with the kinetic data is presented.     

Chemical control on the size and properties of nano NiFe2O4 synthesized by sol–gel autocombustion method

Nickel ferrite nanoparticles have been synthesized by sol–gel auto combustion route. The significant role played by nitric acid added to the precursor solution in controlling the reaction rate phase purity, crystallinity, crystallite size, thermal and magnetic properties of nanoparticles was explored and reported. Also, the influence of annealing on the properties were studied. Samples of average crystallite size ranging from 10 nm to 40 nm have been obtained by controlling the HNO₃ concentration and by increasing the annealing temperature. The size-dependent structural, thermal and magnetic properties were investigated and reported. The Hopkinson peak was observed for all the crystalline samples near the Curie temperature. The highest value 47.3 emu/g of saturation magnetization was obtained for the sample prepared with higher concentration (6 mol/L) of HNO₃.     

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.     

Preparation and characterisation of BaTiO3 nanopowder by microwave assisted microemulsion method

Through the microwave assisted reverse microemulsion method, BaTiO₃ nanopowders are prepared in 10 min by selecting water/OP-10/hexanol/cyclohexane reverse microemulsion system, Ba(NO₃)₂ and tetrabutyl titanate as reactants. The effect of reaction temperature, reaction time, concentration of reactants and molar ratio of water and surfactant on the reaction was studied, and the prepared powders were characterised by X-ray diffraction, TEM and X-ray fluorescence analysis. The results show that cubic phase BaTiO₃ powders of particle size about 50–80 nm with uniform distribution and good dispersion were prepared under atmospheric pressure in 10 min at 65°C. The method has characteristics of lower reaction temperature, shorter reaction time, smaller particle size, narrow particle size distribution and good particle dispersion.     

2‐Acetyl‐4,6,8,10,12‐Pentanitro‐Hexaazaisowurtzitane (PNAIW) Preparation and Properties

2‐Acetyl‐4,6,8,10,12‐pentanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (PNAIW) is formed in the last step of nitration of acetyl isowurtzitane derivatives. The amount of the PNAIW formed depends on the conditions of the nitration reaction (temperature, time, and nitrating mixture used) and on the type of the starting acetyl intermediate. The highest PNAIW yields (30 %) were obtained by nitrating 2,6,8,12‐tetraacetylhexaazaisowurtzitane (TAIW) at 60 °C for half an hour using HNO₃/H₂SO₄ nitrating mixture. HPLC, NMR, FTIR, and DSC measurements were used in the study and their results are reported.