Integrated thermodynamic and kinetic model of homogeneous catalytic N-oxidation processes

The homogeneous phosphotungstic acid catalyzed N-oxidation of alkylpyridines by hydrogen peroxide has important applications in pharmaceutical and fine chemical industries. Current industry practice is to employ a semibatch reactor with gradual dosing of hydrogen peroxide into an alkylpyridine/catalyst solution under isothermal conditions. However, due to lack of understanding of reaction mechanism and thermodynamic behavior, this system is subject to significant risk of flammability, fires and explosions due to hydrogen peroxide decomposition. In this study, we conducted semibatch N-oxidation process in an isothermal reaction calorimeter (RC1) over a wide range of temperature, catalyst amount and oxidizer dosing rates. Reactor pressure, reaction heat generation rate and in situ FTIR spectra of liquid phase species were recorded in real-time during experiments, and final product was quantified using HPLC and GC–MS analytical tools. We developed an integrated thermodynamic and kinetics model of homogeneous N-oxidation reaction based on experimental results and past literature findings. More specifically, Wilson excess Gibbs model was employed to estimate activity coefficients of highly nonideal liquid mixture. We found ideal gas law was satisfactory in calculating incondensable oxygen pressure. First principle reaction mechanism and kinetics parameters of (a) catalytic N-oxidation reaction; (b) catalytic hydrogen peroxide decomposition reaction; (c) noncatalytic N-oxidation reaction; (d) noncatalytic hydrogen peroxide decomposition reaction was derived based on experimental findings of this study and past literature. The proposed integrated thermodynamic model and kinetics model successfully predicted highly nonlinear reactor pressure, species concentration and reaction enthalpy generation rate profile of homogenous catalytic N-oxidation and H₂O₂ decomposition reaction. The optimal reactions conditions with maximum N-oxide product yield and minimum reactor pressure and catalyst usage was theoretically identified and further verified by experiments. The obtained model can be used for inherently safer reactor design and applied to other homogeneous tungstic acid catalytic hydrogen peroxide oxidation processes.     

Steady-State Detonation Wave Parameters in a FEFO/Nitrobenzene Solution

This paper gives the results of experimental studies of the reaction zone structure during steady detonation in bis-(2-fluoro-2,2-dinitroethyl)-formal (FEFO, C₅H₆N₄O₁₀F₂) and its mixtures with nitrobenzene (NB). For pure FEFO, the pressure and particle velocity at the Chapman—Jouguet point and the characteristic reaction time were measured. For FEFO/NB, the dependence of the detonation parameters of the mixture on the NB concentration was determined, and the detonation front was shown to be unstable in pure and in mixtures containing more than 30% NB.     

A Thermal Decomposition Model of Aminoguanidium 5,5′‐Azobis‐1H‐Tetrazolate and the Effect of Pressure and Particle Size on the Rate of Decomposition

The temperature histories of aminoguanidinium 5,5′‐azobis‐1H‐tetrazolate (C₄H₁₄N₁₈, AGAT) were measured in order to construct a thermal decomposition model of the compound. The effects of chamber pressure and AGAT particle size were also examined. The results of the study suggest that the thermal decomposition of AGAT occurs in three phases: solid phase, condensed phase, and residue. It was found that the condensed phase consists of decomposition zone I where dramatic temperature rise occurs, decomposition zone II where gradual temperature rise occurs, and the cooling zone where decomposition and temperature stop rising. It was also suggested that the temperature of the decomposition surface which is the interface of the solid phase and the condensed phase was ∼500 K, and that N₂ and NH₃ were suggested to occur in the vicinity of the decomposition surface of decomposition zone I. In addition, it was suggested that the thickness of the decomposition zones I and II decreases and that the maximum‐temperature‐reached increases with an increase in atmospheric pressure. The rate of decomposition of AGAT was found to follow Vieille's equation and the rate of decomposition increases with an increase in pressure. The rate of decomposition increased slightly with an increase in particle size.     

Evaluating isotherm models for the prediction of flue gas adsorption equilibrium and dynamics

We evaluated isotherm models for the precise prediction of adsorption equilibrium and breakthrough dynamics. Adsorption experiments were performed using pure N₂, CO₂ and their binary mixture with an activated carbon (AC) material as an adsorbent. Both BET and breakthrough measurements were conducted at various conditions of temperature and pressure. The corresponding uptake amount of pure component adsorption was experimentally determined, and parameters of the four different isotherm models, Langmuir, Langmuir-Freundlich, Sips, and Toth, were calculated from the experimental data. The predictive capability of each isotherm model was also evaluated with the binary experimental results of binary N₂/CO₂ mixtures, by means of sum of square errors (SSE). As a result, the Toth model was the most precise isotherm model in describing CO₂ adsorption equilibrium on the AC. Based on the breakthrough experimental result from the binary mixture adsorption, non-isothermal modeling for the adsorption bed was performed. The breakthrough results with all of the isotherm models were examined by rigorous dynamic simulations, and the Toth model was also the most accurate model for describing the dynamics.     

Experiments on the effect of the pressure on the mineral transformation of coal ash under the different reaction atmosphere

This paper investigated the effect of the pressures, reaction atmospheres and coal ash species on the ash fusibility with high-pressure thermogravimetric analysis (PTGA) apparatus and X-ray diffraction (XRD) analysis. Each specimen analyzed by XRD was observed for the mineral conversion and formation of new minerals with the pressures under different atmospheres. These results indicate that the pressure restrains the transformation and decomposition of minerals. Many low-temperature minerals are still present under the elevated pressure. The different reaction atmospheres have different effects on the formation of coal ash minerals. Under the N₂ atmosphere, the present microcline may decrease the melting temperature of coal ash. And later, it transforms into sanidine at high pressure; thus, the melting temperature of coal ash may increase. Under the CO₂ atmosphere, the minerals such as microcline, lomonitite, geothite and illite are still present with the increase in pressure; this may reduce the melting temperature. While under the H₂O atmosphere, there are magnetite and anorthoclase, which may produce the low-temperature eutectics decreasing the melting temperature. The coal ash abundance in basic oxides or higher SiO₂, Fe₂O₃, K₂O and Na₂O has lower melting temperature. While the ash sample with more SiO₂ and Al₂O₃ and less Fe₂O₃ and basic oxides may lead to higher melting temperature.     

Modeling the Reactions Between Ammonia and Dinitrogen Pentoxide to Synthesize Ammonium Dinitramide (ADN)

Only three references about the reactions of ammonia (NH₃) with dinitrogen pentoxide (N₂O₅) have been published in the course of the last 150 years. None of them describes the reactions referring to the products in dependence on the reaction conditions. In this report the experimental results due to the reaction of NH₃ and N₂O₅ lead to three equations. One of these, the formation of dinitrogen oxide (N₂O) in addition to ammonium nitrate (NH₄NO₃; AN) was not mentioned before in the references available. The other reactions are known as the formation of ammonium dinitramide (NH₄N(NO₂)₂; ADN) and AN beside the formation and decomposition of nitramide (NH₂NO₂; NA) into water and dinitrogen oxide. Summarizing the known reactions of NH₃ with N₂O₅ and those of the intermediate products in a reaction scheme a model was established for the selectivity of ammonium dinitramide (ADN) and for the dependence on the reaction conditions. The model is in good accordance with the experimental results.     

Kinetic analysis and modelling of thermal degradation of perspex (PMMA) and perspex blend plastic waste

The thermal decomposition of pure perspex and a mixture of 50% perspex and 50% poly(ethylene terephthalate; PET) was carried out between 295 and 325°C using a thermogravimetric analyser (TGA) in air and nitrogen (N₂) atmosphere. The weight losses of decomposition products were measured during these experiments. The thermal degradation process is slower in inert atmosphere than air, where oxidation reaction expedites the decomposition process. Kinetic rate constants (k), pre‐exponential factor (A) and activation energy (E) for both pure prespex and a blend of perspex/PET were calculated for both air and N₂ conditions. The thermal degradation process followed a third‐order reaction in air and second‐order in N₂. A second‐order (n = 2) model for the pyrolytic process based on simultaneous reactions was developed using experimental data for pure and blend. The pyrolytic products are gases, liquids, waxes, aromatics and char, which can be ultimately used as raw material and fuel in various applications. It is important to note that the addition of PET to perspex was found to suppress/inhibit the decomposition of perspex compared with pure perspex. Pre‐exponential factor (A) and activation energy (E) values support such an observation. © 2012 Canadian Society for Chemical Engineering     

Nitrous oxide decomposition and reduction over copper catalysts supported on various types of carbonaceous materials

Copper supported on three different allotropic forms of carbon materials have been prepared and evaluated as catalysts for the N₂O decomposition and reduction reactions. It was found that all the catalysts underwent severe deactivation during the N₂O decomposition reaction due to the gasification of carbon substrates. This behavior was particularly evident when activated carbon was used as the support medium. The chemical identity of the active entity involved in the carbon gasification process is believed to consist of a mixture of Cu⁺ and Cu²⁺ species and, according to the well established mechanism, the reaction proceeds in such a manner so that the surface of the catalyst undergoes a redox cycle at the gas/solid carbon interface. The introduction of CO into the system was shown to result not only in an enhancement in the activity of the desired N₂O decomposition reaction, but also served to inhibit the deleterious carbon gasification process. In addition, this procedure stabilized the copper particles in the metallic state, which is the active species responsible for the dissociation of N₂O. Copper dispersed on a diamond substrate appeared to attain the highest activity for the N₂O reduction reaction, a feature that is associated with the ability of the metal to undergo a wetting and spreading action on the support surface, possibly resulting in an epitaxial relationship between the two components.     

Detonation spraying of TiO2-2.5 vol.% Ag powders in a reducing atmosphere

In the present work, rutile powders containing additions of metallic silver (2.5 vol.%) were detonation sprayed in a reducing atmosphere formed by gaseous detonation products of the C₂H₂ + 1.05O₂ mixture. The initial volume of the C₂H₂ + 1.05O₂ mixture - explosive charge - used for a detonation pulse was computer-controlled as the fraction of the barrel volume filled with the mixture. Using a previously developed model of the detonation process, the particle temperatures and velocities were calculated to explain the observed phase and microstructure development in the coatings. With increasing explosive charge, the temperature of the sprayed particles increased and rutile was partially reduced to oxygen-deficient TiO_2−x and then to Ti₃O₅. When the melting temperature of rutile was not reached, the coatings were porous; semi-molten particles formed denser coatings obtained with higher spraying efficiency. Silver inclusions in the titanium oxide matrix experienced melting and substantial overheating, but remained well preserved in the coatings.     

A selective and convenient synthesis of gemini surfactants over heterogeneous basic catalyst

Tri-ethanolamine (C₆H₁₅O₃N) and fatty acid (C₁₀H₂₀O₂, C₁₂H₂₄O₂, C₁₄H₂₈O₂ and C₁₆H₃₂O₂) using MgO–ZrO₂ selectively gave the corresponding 2-(bis(2-hydroxyethyl)amino)ethyl alkanoate in good yield. Further the reaction of 2-(bis(2-hydroxyethyl)amino)ethyl alkanoate with epichlorohydrin or 1,2-dichloroethane (in the presence of the 2-(alkanoyloxy)-N,N-bis(2-hydroxyethyl)ethanaminium chloride) over same heterogeneous catalysis to afford novel N,N-bis(2-(alkanoyloxy)ethyl)-N,N,N,N-tetrakis(2-hydroxyethyl) propane-1,3-diaminium or N,N-bis(2-(alkanoyloxy)ethyl)-N,N,N,N-tetrakis(2-hydroxyethyl)ethane-1,2- diaminium (gemini surfactants), respectively. The ease of the diaminium reaction was found to be due to the neighboring-group participation (NGP) in the quaternization step. Results of esterification and diaminium reactions, reported herein were optimized for several catalytic effects to understand the probable mechanism. The catalysts can be easily separated from reaction and showed good recyclability.     

Transport of Small Molecules through Polyphenylene Oxide Membranes Modified by Fullerene

Abstract

Homogeneous membranes based on fullerene‐polyphenylene oxide compositions containing up to 2 wt% fullerene C₆₀ were prepared. The effect of fullerene addition on PPO transport properties was studied in gas separation and pervaporation processes. Permeability coefficients of H₂, O₂, N₂, CH₄, and CO₂ were measured; a correlation between gas transport properties and membrane free volume was established. Pervaporation properties were studied for the system with ethyl acetate synthesis reaction: quaternary system ethanol—acetic acid—water—ethyl acetate and some constituent binary and ternary mixtures. Pervaporation in binary systems, ethanol–water and ethyl acetate–water was considered with the use of the data on sorption capacities and interaction parameters. In pervaporation of a quaternary reacting mixture, the permeate containing essentially ethyl acetate was obtained. Results show that membranes with fullerene additives exhibit improved transport properties.     

Pro-oxidant activity of nickel (II) pyridoxal complexes. Synthesis,characterization and peroxidase activity assays

The synthesis of Ni (II) complexes with pro-oxidant applications has demonstrated many advantages, such as accelerated reactions, solution stability and with high selectivity reactions. In this work we describe the synthesis, characterization and structural analysis of nickel ([(Ni)(C₃₀H₂₈N₄O₄S₂)]);([(Ni)(C₃₁H₃₀N₄O₄S₂)]) and ([(Ni)(C₃₃H₃₇N₄O₄S₂)]·DMF — complex 3) complexes with ligands obtained from the condensation of pyridoxal and aryl-thiol amines and their application as a pro-oxidant in the reaction of the phenol-aminoantipyrine adduct. The complexes show variation in carbon spacers between pyridoxal molecules: ethane, propane and butane. It was found that the spacer two carbons containing the most significant as the pro-oxidant activity.     

Adsorbate-assisted NO decomposition in NO reduction by C3H6 over Pt/Al2O3 catalysts under lean-burn conditions

The rates and product selectivities of the C₃H₆-NO-O₂ and NO-H₂ reactions over a Pt/Al₂O₃ catalyst, and of the straight, NO decomposition reaction over the reduced catalyst have been compared at 240C. The rate of NO decomposition over the reduced catalyst is seven times greater than the rate of NO decomposition in the C₃H₆-NO-O₂ reaction. This is consistent with a mechanism in which NO decomposition occurs on Pt sites reduced by the hydrocarbon, provided only that at steady state in the lean NO _x reaction about 14% of the Pt sites are in the reduced form. However, the (extrapolated) rate of the NO-H₂ reaction at 240C is about 10⁴ times faster than the rate of the NO decomposition reaction thus raising the possibility that NO decomposition in the former reaction is assisted by H_ads. It is suggested that adsorbate-assisted NO decomposition in the C₃H₆-NO-O₂ reaction could be very important. This would mean that the proportion of reduced Pt sites required in the steady state would be extremely small. The NO decomposition and the NO-H₂ reactions produce no N₂O, unlike the C₃H₆-NO-O₂ reaction, suggesting that adsorbed NO is completely dissociated in the first two cases, but only partially dissociated in the latter case. It is possible that some of the associatively adsorbed NO present during the C₃H₆-NO-O₂ reaction may be adsorbed on oxidised Pt sites.     

A study of nitrous oxide decomposition over calcium oxide in combustion condition

A study of N₂O decomposition reaction over a bed of CaO particles in a fixed bed reactor has been conducted. Effects of parameters such as concentration of inlet N₂O, reaction temperature and effects of CO, CO₂, O₂, and NO gas presented in the combustion gas environment have been investigated. The experiment showed that the N₂O decomposition reaction was accelerated by the increase of reaction temperature, and the existence of CO, while the reaction was hindered by the existence of CO₂, NO. O₂ also affected the N₂O decomposition. Heterogeneous gas-solid reaction kinetics were proposed for the reaction conditions and compared with homogeneous reaction kinetics.     

Thermal Analysis of Ammonium Dinitramide Decomposition

The new energetic material ammonium dinitramide (ADN), NH₄N(NO₂)₂, has been investigated with regard to its thermal properties and decomposition behavior. Thermal decomposition of ADN is observed after complete melting at 91.5 °C. The main decomposition pathway is based on the formation of NH₄NO₃ and N₂O followed by the thermal decomposition of NH₄NO₃ to N₂O and H₂O at higher temperatures. Side reactions forming NO₂, NO, NH₃, N₂ and O₂ are described and a mechanism for the acid-catalized decomposition of hydrogen dinitramide, dissociation product of ADN, is proposed.     

Overall kinetics of hydrogen peroxide formation by direct combination of H2 and O2 in a microreactor

Direct combination (DC) of hydrogen and oxygen over a heterogeneous catalyst in a microreactor is a novel method of producing hydrogen peroxide with significant economic advantages over the currently dominant anthraquinone autoxidation method. A kinetic rate expression for this reaction is required for design and modeling of a microreactor for the DC process. Since the formation of H₂O₂ by the DC process involves four simultaneous reactions (synthesis of H₂O₂, synthesis of water, reduction of H₂O₂ by H₂ and decomposition of H₂O₂), the overall rate expression must take into account each of these reactions. In this work, we describe a reactor model that involves the four component reactions as well as mass transfer effects. The model is verified by comparing the predicted reactor performance with experimental data. In addition to providing a tool for reactor design, the model also confirms important assumptions regarding the mechanism of DC reaction.     

Quantitative studies by differential scanning calorimetry of the reaction between hydrogen peroxide and lignocellulose

Heat of reaction and kinetic parameters were determined by differential scanning calorimetry for decomposition of hydrogen peroxide, reaction of hydrogen peroxide with lignocellulosic materials, glucose and pinitol, and for the reaction of the same materials with produced or introduced oxygen. The heat of decomposition of hydrogen peroxide obtained in N₂ (720 cal/g H₂O₂) was in fair agreement with literature data, considering the different temperature and pressure conditions. The heats of reaction of hydrogen peroxide and lignocelluloses were higher when determined in N₂ (1670–2500 cal/g H₂O₂) than in O₂ (1450–2020 cal/g H₂O₂) atmosphere. The activation energy for decomposition of hydrogen peroxide amounted to 20.3 kcal/mol in N₂ and 15.9 kcal/mol in O₂ with frequency factors of 5.7 × 10⁹ and 3.7 × 10⁷ min^?1, respectively. The activation energies for the reaction of hydrogen peroxide and lignocellulosic materials tested were similar and not influenced by the atmospheric composition, ranging overall between 19.7 and 22.4 kcal/mol. The corresponding frequency factors ranged between 2.77 × 10⁹ and 2.23 × 10¹¹.     

Formation of BN from BCNO and the development of ordered BN structure: I. Synthesis of BCNO with various chemistries and degrees of crystallinity and reaction mechanism on BN formation

We synthesized BCNO compounds and investigated how the synthesis conditions impact i) BCNO formation, their chemistry and degree of crystallinity, and ii) BN formation from BCNO and its structural ordering. Heating boric acid (H₃BO₃) and melamine (C₃H₆N₆) mixture yields intermediate amorphous BCNO compound. Increasing the synthesis temperature, and H₃BO₃ to C₃H₆N₆ ratio promote BN formation and its structural ordering. We propose a possible reaction mechanism for BN formation from H₃BO₃ and C₃H₆N₆ mixture and we explain the observations based on thermodynamic and kinetic considerations. An increase in synthesis temperature promotes BN formation since the reactions are endothermic. An increase in H₃BO₃ to C₃H₆N₆ ratio promotes BN formation since theoretical BN formation temperature decreases with the above ratio. Furthermore, it enhances material transfer and mobility of the BN layer by forming B₂O₃ phase. We also propose a processing-structure correlation map that can help determining experimental conditions for single-phase amorphous BCNO synthesis.     

Reactions of normal alcohols in the presence of a dehydrogenating iron catalyst

A oxidizing condensation of normal alcohols C₄ to C₁₂ in the gas phase over Fe₃O₄ catalyst containing Cr, Si and K oxides was studied. The reactions were carried out in a continuous process at atmospheric pressure. Initially the alcohols undergo dehydrogenation to aldehydes and esters, and at higher temperatures symmetric ketones containing 2n - 1 atoms of carbon in a molecule are formed. A mechanism for the reaction is proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the role of C<Subscript>2</Subscript>O radicals in the prompt-NO mechanism

The measurements of NO concentrations in the post-flame zone of different hydrocarbon + O₂ + N₂ flames at standard temperature and atmospheric pressure available in the literature are compared with predictions of the original Konnov reaction mechanism and with the same mechanism extended by the reaction of C₂O with N₂. The goal was to investigate the possible role of this reaction proposed by Williams and Fleming [Proc. Combust. Inst., Vol. 31 (2007), pp. 1109–1117]. This new reaction of C₂O with N₂ seems to be a reasonable explanation of the deficiencies in the prompt-NO route. Direct comparisons of the experimental measurements performed in different flames with the modeling strongly suggests that the upper limit of this reaction rate constant is k = 7 · 10¹¹ exp(−17,000/RT) [cm³/(mole · sec)]. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 3–7, September–October, 2008.