Osmotic and Activity Coefficients of {yKCl+(1−y)MgCl2}(aq) at T=298.15 K

Isopiestic vapor-pressure measurements were made at the temperature 298.15 K for aqueous KCl + MgCl₂ solutions using KCl(aq) as the reference standard. The measurements for these ternary solutions were made at KCl ionic strength fractions of y=0.0, 0.1989, 0.3996, 0.5993, 0.7925 and 1.0 (with two additional sets at y=0.0, 0.2021, 0.3998, 0.6125, 0.8209 and 1.0) for the ionic strength range from 0.4014 to 6.2790 mol?kg^?1. Our results, and those from two previous isopiestic studies, were combined and used with previously determined parameters for KCl(aq) and those determined here for MgCl₂(aq) to evaluate mixing parameters for the Clegg-Pitzer-Brimblecombe model. These combined data were also used to determine the mixing parameters of the Scatchard model. Both sets of model parameters are valid for ionic strengths of I≤12.8 mol?kg^?1, where higher-order electrostatic effects have been included in the Clegg-Pitzer-Brimblecombe mixture model. The activity coefficients for KCl and MgCl₂ were calculated from these models and the results for KCl were compared to experimental data from Emf measurements. The Scatchard model interaction parameters were used for calculation of the excess Gibbs energy as a function of the ionic strength and ionic strength fraction of KCl. The Zdanovskii-Robinson-Stokes rule of linearity for mixing of isopiestic solutions was tested.     

Experimental and kinetic study of catalytic cracking of heavy fuel oil over E-CAT/MCM-41 catalyst

The catalytic cracking of heavy fuel oil was investigated over the equilibrium fluid catalytic cracking catalyst (E-Cat) as a base component with the mesoporous MCM-41 as an additive. The catalytic performance of the E-Cat/MCM-41 system was assessed in a fixed-bed MAT unit. The reaction was performed at temperatures of 500, 530, 550 and 600°C and the product distributions in both gaseous and liquid phases were studied. The yields of products including light olefins, liquefied petroleum gas (LPG), gasoline, dry gas, coke and also the conversions obtained over different temperatures were reported and some generalities discussed. The maximum yield of propylene (17.5%) was obtained at 550°C whereas the highest conversion and gasoline yield was gained at 530°C. An eight-lump kinetic model containing 11 kinetic parameters was considered. Those parameters were estimated based on experimental data at specific temperatures by fourth order Runge–Kutta algorithm and the least square method. In addition, Arrhenius equation was used to calculate apparent activation energies. The calculated data of the product yields were in a close agreement with the experimental data.     

Estimation of the heat capacity of some uranium-rare earth mixed oxides from thermal expansion and vice versa

Estimation of the high temperature heat capacity (C _p) data from experimental high temperature thermal expansion (α _v) data and vice versa from the known values of the ratio (α_v/C _p) at low temperatures were carried out by assuming linear relationship of the ratio α _v /C _p with temperature (at T > θ _D). The assumption was examined using the known α _v and C _p values of single phase fluorite systems such as UO₂, ThO₂ and PuO₂. It was also examined using the known α _v and C _p of the mixed oxides (U_1?y La_y) O_2±x (y = 0.2, 0.4, 0.6 and 0.8). The estimated values of α _v and C _p are in good agreement with the experimental values within ±3%. Using the assumption the high temperature heat capacity data of (U_1?y Ce _y ) O₂ (y = 0.2, 0.8) and (U_1?y Gd _y ) O_2±x (y = 0.2, 0.5) were computed from the experimental high temperature α _v data.     

Organo-sulfonic acid catalyzed degradation kinetics and thermodynamic studies of nylon-6 by hydrothermal method

Nylon-6 as an engineering polymer and its starting monomer are both costly. Chemical reutilization offers some economic and environmental benefits. Depolymerization of nylon-6 was carried out by the conventional technique of hydrothermal method using various organo-sulfonic acids such as Methane sulfonic acid (MSA), para-toluene sulfonic acid (p-TSA), benzene sulfonic acid (BSA), and tetra-butyl ammonium bromide (TBAB) as a phase transfer catalyst. Various parameters such as temperature, time, normality of acids, and phase transfer catalyst concentration were varied to optimize its parameters, and characterization techniques such as amine value titrations and Fourier transform infrared spectroscopy were used for quantitative measurements. Solid-state ¹³C NMR was done for structure confirmation. A chemical kinetics interpretation shows degradation mechanism follows first-order kinetics under various catalysts. MSA has the highest reaction rate of 8.49 × 10^?2 h^?1 at 90°C; it decreases to 7.72 × 10^?2 h^?1 at 100°C. At the same time, aromatic Sulfonic acids such as p-TSA and BSA have a higher reaction rate of 8.995 × 10^?2 h^?1 and 5.582 × 10^?2 h^?1, respectively. The activation energy was lowered as the acidity of organo-sulfonic acids increased as benzene sulfonic acid has the lowest E_a. Followed by p-TSA, and MSA has the highest E_a. Free energy shows a similar kind of value. A simple theoretical model was used to calculate the activation energy. Thermodynamic parameters such as heat of enthalpy and entropy of reaction were evaluated using the Eryig–Polanyi equation. The combined catalytic effect of organo-sulfonic acids and phase-transfer catalyst provides a better environment-friendly method for depolymerizing nylon-6.     

The Application of Composite Energy Methods to n-butyl Radical β-scission Reaction Kinetic Estimations

Hydrocarbon cracking reactions are key steps in petroleum refinery processes and understanding reaction kinetics has very important applications in the petroleum industry. In this work, G3 and complete basis set (CBS) composite energy methods were applied to investigate butyl radical β-scission reaction kinetics and energetics. Experimental thermodynamic and kinetic data were employed to evaluate the accuracy of these calculations. The CBS compound model proved to have excellent agreement with the experimental data, indicating that it is a reliable method for studying other large hydrocarbon cracking reactions. Furthermore, a reaction kinetic model with pressure and temperature effects was proposed. For P ≤ P ₀, k = 2.04 × 10⁹ × P ^0.51 × e^(-9745.70/T); for P > P ₀, k = 9.43 × 10¹³ × e^{(-15135.70/T)}, where k is the reaction rate constant in units of s⁻¹; P is pressure in units of kPa, T is temperature in units of Kelvin, and the switching pressure is P ₀ = 1.53 × 10⁹ × e^{(-10610.24/T)}. This model can be easily applied to different reaction conditions without performing additional expensive and complicated calculations.     

Synthesis and electrochemical performances of Li1+ y Mn2− y O4 powders of well-defined morphology

The spinel phases Li_{1+ y} Mn_{2− y} O₄ have been synthesized by a novel synthesis method that presents advantages compared to the classical ceramic method, namely, in terms of preparation time, costs and electrochemical performances of the resulting products. This consists of a two-stage process. First, two precursor phases (Li-EG and Mn-EG) are synthesized by reacting powdered lithium hydroxide and electrolytic manganese dioxide (EMD) in ethylene glycol (EG) under reflux, respectively. Secondly, the precursor products are mixed and heat treated under air, following various heating sequences, to produce electrochemically active Li_{1+ y} Mn_{2− y} O₄ powders of well-defined morphology. Once the synthesis parameters involved in these two steps are controlled, the obtained Li_{1+ y} Mn_{2- y} O₄ powders exhibit electrochemical performances that compare favorably with those observed in the case of the high-temperature (HT) Li_{1+ y} Mn_{2− y} O₄ made by the ceramic route, both in terms of reversible/irreversible capacities and cycling behavior at 25 °C and 55 °C. Received: 12 August 1997 / Accepted: 20 October 1997     

New process for low temperature preparation of LiNi1−xCoxO2 Cathode material for lithium cells

LiNi_1−yCo_yO₂ has been prepared at a temperature as low as 400 °C by molten ion exchange using a βNi_1−yCO_yOOH and either LiNO₃ or LiOH. The mechanism of these reactions was clarified using DTA and TG analyses. The material prepared using the LiNO₃ is well crystallized because the reaction takes place in viscous state since LiNO₃ melts and then reacts with the oxyhydroxide. However, in the case of using LiOH, a solid-solid diffusion reaction takes place and leads to a material with broad XRD peaks. The electrochemical characteristics of these materials were evaluated and compared with those prepared by the usual processes at high temperature.     

Prompt NO: Theoretical prediction of the high-temperature rate coefficient for CH + N2 → HCN + N

With potential-energy-surface parameters provided by Walch's calculations of the reaction path, we have calculated the thermal rate coefficient for the reaction, The theory employed assumes that the change in the reaction of the electron spin has little or no effect on the rate coefficient. The resulting expression for k₁, in the temperature range, 1000 K ≤ T ≤ 4000 K, is in remarkably good agreement with the limited amount of experimental data available, suggesting that the assumption is valid. The origins of the “prompt-NO” phenomenon, our analysis of reaction (RI), and comparison of the results with experiment are all discussed in detail. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 253–259, 1997.     

Electron beam-assisted cracking of synthetic paraffins

The electron beam-initiated cracking of a mixture of C₁₇–C₁₂₀ paraffins at 350–370°C has been studied. The cracking regime implied simultaneous feedstock irradiation and rapid distillation of fragmentation products from the irradiation zone. The distillate was a mixture of 61.5 wt % alkanes and 38.5 wt % alkenes. The product molecule contained on average 13 carbon atoms. The gasoline fraction in the condensate was 32.3 wt %. It was demonstrated that the product composition can be changed depending on the geometric parameters of reaction equipment and temperature distribution at the reactor outlet.     

Quantum scattering calculation for reaction Br + H2 on two potential energy surfaces

Three‐dimensional time‐dependent quantum wave packet calculations have been carried out for Br + H₂ on a new global ab initio and a semi‐empirical extended London–Eyring–Polanyi–Sato potential energy surface. It is shown that on the ab initio surface, the threshold energy is much lower, and the reaction probabilities, cross sections, and rate constants are much larger. The effects of the initial rovibrational excitation have also been studied. Comparison of rate constants with experimental measurement implies that the ab initio surface is more suitable for quantum dynamic calculation. The possible reasons and mechanism for the dynamical difference on the two PES are analyzed and discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The relationship between properties of fluorinated graphite intercalates and matrix composition

Inclusion compounds (intercalates) of fluorinated graphite matrix with butanone (C₂F_xBr_z·yCH₃COC₂H₅, x = 0.49, 0.69, 0.87, 0.92, z ≈ 0.01) were prepared by guest substitution from acetonitrile to butanone. The kinetics of the thermal decomposition (the 1st stage of filling → the 2nd stage of filling) was studied under isothermal conditions at 294–313 K. The relationship of the host matrices structure with inclusion compounds’ thermal properties and kinetic parameters is discussed.     

Determination of the sequence distribution and stereoregularity of ethyl α-benzoyloxymethylacrylate–methyl methacrylate copolymers by means of proton and carbon-13 NMR

Proton and Carbon-13 NMR spectra of ethyl α-benzoyloxymethylacrylate (E)–methyl methacrylate (M) copolymers were analyzed in terms of sequence distribution and stereoregularity of monomer units. The copolymers were prepared by free radical polymerization in benzene at 50°C. The methoxy region of the M proton signal resonance was found to be sensitive to the copolymer composition for M-centred sequences. The carbon-13 NMR spectra of the EM copolymers, in particular the carbonyl signal resonances of carbomethoxy and carboethoxy groups, are discussed in terms of M- and E-centred configurational sequences. The experimental values were in excellent agreement with those calculated taken into account the terminal copolymerization model and Bernoullian distribution of stereoregularity with the statistical parameters determined from reactivity ratios r_E = 0.32 and r_M = 1.34 and the coisotacticity parameters σ_MM = 0.22, σ_EE = 0.70, and σ_ME = σ_EM = σ = 0.30. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3483–3493, 1997     

Carboxyl terminated polyamide 12 chain extension using a dioxazoline coupling agent

High molar mass Polyester Amide was obtained by coupling reaction of Carboxyl-Terminated Polyamide 12 (CTPA) with a dioxazoline (OO). The analysis of the experimental condition effects on the reaction conversion and the structure of the polymer obtained did not show any particular side reaction. A kinetic study comparing the reactivity of the dioxazoline used with CTPA and decanoic acid (DA) as model reactants showed the equireactivity of the two oxazoline functions and of the acid functions of the CTPA and DA. A kinetic model was proposed. The reaction rate at different temperatures and the activation energy were calculated. The evolution of the different reactant concentrations were modeled and compared with experimental data. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3697–3705, 1997     

Brownian dynamics simulations of the reactions of hydrated electrons with components of DNAs and a DNA double-helix

As a first step toward developing simulation models for studying the indirect mechanism of radiation damage to DNAs, we have carried out Brownian dynamics simulations to study the reactions of hydrated electrons with a 12-base-pair B-DNA, (dA)₁₂(dT)₁₂, and with bases, monodeoxynucleotides, and polydeoxynucleotides. We first studied in detail the sensitivity of diffusion reaction rate constants to different model and simulation parameters. Based on the sensitivity studies, a set of model and simulation parameters was obtained for the final production runs. The use of this set of parameters reduced the computational costs but delivered reasonably reliable results. The calculated reaction rate constants were in qualitative agreement with experiments. For the DNA double-helix, (dA)₁₂(dT)₁₂, the simulations demonstrated that hydrated electrons preferred to attack the two ends of the double-helix. Electrostatic interactions between the DNA and the hydrated electrons make the T strand more susceptible to attack than the A strand. The increased reactivity of the T strand due to electrostatic interactions results from the increased reactivity of the C6 sites of the thymine bases, at the expense of the reactivity of the C8 sites of the adenine bases. The reactivity of the relatively buried reactive sites of the adenine and thymine bases are less affected by electrostatic interactions. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 888–901, 1997     

The Reaction X + Cl2→XCl + Cl (X = Mu,H, D). II. Comparison of experimental data with theoretical results derived from a new potential energy surface

We consider experimental implications for the Mu + Cl₂, H + Cl₂, and D + Cl₂ reactions of the extended London—Eyring—Polanyi—Sato (LEPS) potential energy surface derived from experimental data in paper I. In the present calculations, it is necessary to make additional implicit and explicit assumptions concerning the three-dimensional (3D) nature of the potential surface, since the inversion procedure of paper I yields information only on the collinear (1D) part of the surface. We have performed accurate 1D quantum calculations of reaction probabilities, which are then transformed into 3D by an information theoretic 1D → 3D transformation incorporating a constraint to allow for angular momentum transfer effects in light+heavy—heavy atom reactions. This procedure implicitly accounts for the 3D nature of the potential surface. The calculated vibrational and vibrotational product distributions are in good agreement with those determined in thermal chemiluminescence experiments. The Sato parameters for the 1D surface also define a full 3D surface. This is used as an approximation to the true surface, and its properties are explored in 3D quasiclassical trajectory calculations. Comparison is made for the H and D reactions with available chemiluminescence, molecular beam and kinetic experimental data for differential and total reaction cross sections, energy disposal, rate coefficients and Arrhenius parameters. Some kinetic isotope effects in the Mu, H, and D reactions are discussed using vibrationally adiabatic theory. Comparison is also made with results from other calculations in the literature for the H + Cl₂ and D + Cl₂ reactions.     

Interpretation of Isotope Exchange Data “without Time”: Nonisothermal Exchange of Dioxygen with Oxides1

As a result of transformation of isotope-exchange rate equations (isotope-kinetic equations), a relationship was derived that does not contain time and universally relates the variables of isotope composition (an isotope-mechanistic equation). With the use of this relationship, mechanistic parameters that characterize atomic rearrangements can be determined from experimental data even in cases when the rate of exchange varied in the course of a process, for example, under nonisothermal conditions. The use of the proposed approach for the treatment of the results of dynamic thermal isotope exchange in the O₂–YBa₂Cu₃O _y and O₂–Pt/CeZrO systems demonstrated that the experimental data were excellently described by the theoretical equation derived in this work     

The relationship between properties of fluorinated graphite intercalates and matrix composition 7

Inclusion compounds (intercalates) of fluorinated graphite matrix with ethyl acetate (C₂F_xBr_z·yCH₃COOC₂H₅, x = 0.49, 0.69, 0.87, 0.92, z = 0.01) were prepared by guest substitution from acetonitrile to ethyl acetate. The kinetics of the thermal decomposition (the first stage of filling → the second stage of filling) was studied under isothermal conditions at 291–307 K. The relationship of the host matrices’ structure with inclusion compounds’ thermal properties and kinetic parameters is discussed.     

Experimental Design for Modeling and Multi‐response Optimization of Catalytic Cyclohexene Epoxidation over Polyoxometalates

An experimental design methodology was applied to optimize cyclohexene epoxidation with hydrogen peroxide in the presence of acid‐activated montmorillonite clay supported on 11‐molybdovanado‐phosphoric acid, with the Keggin structure H₄[PVMo₁₁O₄₀] · 13H₂O (PVMo) as catalyst. The statistical study of the process was achieved through a two‐level, full‐factorial experimental design with five process parameters. The significant input variables (key factors) that influenced the performance of cyclohexene oxidation are the catalyst weight, catalyst loading, temperature, H₂O₂ concentration, and the reaction time. The effect of the individual parameters and their interaction effects on the cyclohexene conversion, as well as the selectivity of cyclohexane‐1,2‐diol, was determined, and a statistical model of the process was developed. The process was optimized by considering the two responses simultaneously, which allows defining the optimal regions for the significant process variables. The optimal conditions were obtained for the catalyst weight of 0.05 g, temperature of 70°C, and reaction time of 9 h, with 20% PVMo as the active phase and hydrogen peroxide as oxidant.