Non-isothermal two-membrane reactors for reversible gas phase reactions

The performance of a non-isothermal two-membrane reactor for reversible chemical reactions in gas phase has been analyzed by numerical simulation. The analyzed reactions were of the form: aA = bB + cC. Two membranes, that are permeable to all the components of the reaction mixture, are supposed to be the most permeable to one of the two reaction products, satisfying the condition of reverse products permselectivities. The reactant is taken to be the slowest permeating component. A negative temperature influence on the permeabilities of components has been assumed. Co-current plug flow pattern has been accepted. It has been shown that it is possible to enhance reactant conversion above that of a conventional reactor for both endothermic and exothermic reversible reactions, including adiabatic and non-adiabatic case. By using a two-membrane reactor, considerable lowering of feed temperatures is enabled for an endothermic reaction. For endothermic reactions, there is the optimum feed temperature, whereas for exothermic reactions, the higher the temperature, the lower is the attained conversion. In reactor design, the optimal external heat exchange for both endothermic and exothermic reactions can be determinated.     

Numerical solution of nonlinear and non-isothermal general rate model of reactive liquid chromatography

Abstract

A nonlinear general rate model (GRM) of liquid chromatography is formulated to analyze the influence of temperature variations on the dynamics of multi-component mixtures in a thermally insulated liquid chromatographic reactor. The mathematical model is formed by a system of nonlinear convection–diffusion reaction partial differential equations (PDEs) coupled with nonlinear algebraic equations for reactions and isotherms. The model equations are solved numerically by applying a semi-discrete high-resolution finite volume scheme (HR-FVS). Several numerical case studies are conducted for two different types of reactions to demonstrate the influence of heat transfer on the retention time, separation, and reaction. It was found that the enthalpies of adsorption and reaction significantly influence the reactor performance. The ratio of density time heat capacity of solid and liquid phases significantly influences the magnitude and velocity of concentration and thermal waves. The results obtained could be very helpful for further developments in non-isothermal reactive chromatography and provide a deeper insight into the sensitivity of chromatographic reactor operating under non-isothermal conditions.     

Complex heterogeneous catalytic reactions. Some aspects of simulation

Heterogeneous catalytic reactions take place by stage mechanisms. The existence of reactants and products (at reactor input and output) and intermediates (not included in final equations of reactions) enables to derive a series of linear algebraic equations observed in stationary conditions in each point of reactor and in each point of catalyst grain. This “theory of stationary complex reactions” was developed first in the works of J. Horiuti and M.I. Temkin. Accounting some relationships of this theory enables to derive the first integrals for the set of the differential equations describing the zero-gradient reactors, flow reactors, and fluidized-bed reactors. Their consideration in the internal diffusion processes results in the relationships of diffusion stoichiometry and similar relationships for the grain surface concentrations and temperature. All the said relationships should be taken into account for calculation of the relevant reactors. Accounting the given relationships provides the correct solution of the relevant problem and reduces the order of the set of the differential equations to be solved. Some calculation features and restrictions in solution of inverse kinetic problems arise also if the mechanism of reactions involves reversible and equilibrium routes. This study systematizes the aforesaid issues and indicates to applicability and importance of the features of complex heterogeneous catalytic reactions for simulation of catalytic processes.     

Chromatographic study of the adsorption kinetics of albumin on monoclonal and polyclonal immunoadsorbents

Summary High-performance liquid chromatography (HPLC) has been used to study the adsorption kinetics of proteins on immunoadsorbents. The adsorption rate constant of human serum albumin (HSA) on monoclonal and polyclonal anti-HSA antibodies immobilized on a silica HPLC support was determined by saturating the column with repeated pulse injections. Studies on polyclonal immunodsorbents of different capacities enable evaluation of the contribution of transport to the binding sites. The adsorption properties of two different monoclonal anti-HSA antibodies immobilized on a chromatographic support were characterized by different approaches. The location of the epitope on the HSA molecule was determined by enzyme-linked immunoassay (ELISA) with albumin fragments. The chromatographic method was used to determine the column capacity and the adsorption rate constant of HSA on the immunoadsorbent. To compare the affinity of the antibodies for the antigen, an indirect ELISA method was used to determine the equilibrium constant of antigen-antibody association in solution Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th september, 1996.     

ESR studies on hydroxyl radical reactions with glycine

Radicals H₂N? ?H? COOH and H₂N? ?H? COO^? which have different ESR. spectra are observed during the reaction of hydroxyl radicals with glycine in aqueous solution. Rapid and reversible exchange between the different dissociated radicals is induced by addition of phosphoric acid. The pH dependence of the ESR. spectra yields the pK value and rate constants for proton transfer reactions between the radicals and phosphoric acid.     

Identification of phenyl-substituted polycyclic aromatic compounds in ring furnace gases using GC-MS and GC-AED

Summary The ring furnace baking process is an intermediate step in the production of graphite electrodes. In this process coal tar pitch is pyrolized to form amorphous carbon and volatile aromatic and polycyclic aromatic compounds (PACs). These gaseous ring furnace emissions were analysed by GC-MS and GC-AED. As a result of the pyrolytic reactions taking place, several phenyl-substituted PACs are generated, which were identified by their chromatographic retention indices and mass spectra. Pure reference compounds were analysed for verification if available. A number of phenyl-PACs are reported to be present in coal tar-related material, including phenylpyridines and phenyldibenzofurans previously unreported. A formation scheme for phenyl-dibenzofurans on the basis of a radical mechanism is proposed. Dedicated to Prof. Dr. Wolfgang Meyer zu Reckendorf, Münster, on the occasion of his 65th birthday. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

A systematic study of the desorption of different ion-pairing reagents on reversed phase thin-layers

Summary The absolute concentrations and the concentration distribution of different cationic ion-pairing reagents, such as tetramethylammonium bromide, tetrabutylammonium bromide, cetyltrimethylammonium bromide and trioctylmethylammonium chloride were studied after chromatographic development on physically and chemically bonded reversed-phase layers. The combination of the chromatographic conditions involved three variations. Untreated layers were chromatographed with mobile phases containing the ion-pairing reagent. Several layers were treated with the ion-pairing reagent prior to the chromatographic run, and methanol-water mixtures were used as mobile phase. In a third set of experiments both the layer and the mobile phase contained the ion-pairing reagent. The chromatographic behaviour of acid, neutral and basic model compounds were also studied. For the determination of different reagents remaining on the layer after the chromatographic run, spectrophotometric, potentiometric methods and capillary electrophoresis were used. The performance of the analytical methods was evaluated. Results obtained for the absolute concentrations and distribution of the reagents and the retention data were compared to those obtained on silica gel layers. A discussion of the retention mechanism is given. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Numerical approximation of a nonisothermal two-dimensional general rate model of reactive liquid chromatography

A nonlinear and nonisothermal two-dimensional general rate model is formulated and approximated numerically to allow quantitatively analyzing the effects of temperature variations on the separations and reactions in liquid chromatographic reactors of cylindrical geometry. The model equations form a nonlinear system of convection-diffusion-reaction partial differential equations coupled with algebraic equations for isotherms and reactions. A semidiscrete high-resolution finite volume method is modified to approximate the system of partial differential equations. The coupling between the thermal waves and concentration fronts is demonstrated through numerical simulations, and important parameters are pointed out that influence the reactor performance. To evaluate the precision of the model predictions, consistency checks are successfully carried out proving the accuracy of the predictions. The results allow to quantify the influence of thermal effects on the performance of the fixed beds for different typical values of enthalpies of adsorption and reaction and axial and radial Peclet numbers for mass and heat transfer. Furthermore, they provide useful insight into the sensitivity of nonisothermal chromatographic reactor operation.     

Inverse-electron-demanddiels-alder reactions of condensed pyridazines VI: Ring transformations of pyrido[2,3-d]pyridazine intog-fused quinolines

Summary A series ofg-annelated quinolines was synthesized, employing pyrido[2,3-d]pyridazine as an azadiene in inverse-electron-demandDiels-Alder reactions with electron-rich dienophiles (enamines and a ketene-N,S-acetal). In cases where isomer mixtures were obtained, NOE difference spectroscopy was used for structural assignment.Dedicated with best wishes to Prof. Dr. F. Sauter on the occasion of his 65^th birthday     

基于液相色谱信息的西青果化学成分抑制α-葡萄糖苷酶活性数学模型的构建

中药提取物是一个组成复杂、机理不明晰的混合物体系,其对靶标的作用是其中所有化合物的综合影响,如何表征和评价其生物活性值得深入研究。本文采用羟丙基葡聚糖凝胶色谱柱分离西青果乙醇提取物,得到29组成分连续变化的样品,采集样品的色谱信息(254 nm波长下)与活性信息,运用逐步回归法建立成分的峰面积(Vi,自变量)与活性(以对酶的抑制率(W)表示,因变量)之间的数学方程,确定对活性影响显著的成分。结果表明,29组样品包含55个峰,这些峰对应成分的峰面积(Vi,i=1,2,…,55)与W之间存在数学关系:W=V7×(-0.034±0.013)+V18×(-0.155±0.051)+V29×(-0.142±0.028)+V4×(0.079±0.020)+V11×(0.074±0.028)+V36×(-0.117±0.053)+85.669±4.476,复相关系数R=0.854,显著度=0.037,稳健性良好,对活性影响最显著的物质为第18、29、36、4、11和7号峰对应的化合物。该方法同样适用于不同中药资源的成分与多种不同活性等方面的研究,对于中药的研发具有重要意义。     

Electroreduction of bromate anion on inactive RDE under steady-state conditions: Numerical study of ion transport processes and comproportionation reaction

The study is devoted to analyzing the electroreduction of bromate anion BrO ₃^- on catalytically inactive (e.g., carbon) electrodes by numerical methods. This process is realized due to the combination of the reversible mediator pair Br₂/Br^- and the process of comproportionation (reaction of bromate and bromide anions) in solution phase. These reactions increase the concentration of bromine and bromide near the electrode surface; hence, this process is autocatalytic (EC″ mechanism). Within the framework of this study, a numerical algorithm which allows the system of diffusion-kinetic equations to be solved for this system is proposed for one-dimensional transport and the process under steady-state conditions. The results are compared with the conclusions of the approximate analytical theory published in Electrochim. Acta, 2015, vol. 173, p. 779, which allows inferring that both approaches are correct. The deviation between the latter is observed only in the cases of violation of approximations lying in the basis of the corresponding analytical relationships. Thus, the predictions of the analytical theory of practical interest can be considered as reliably confirmed by numerical calculations, particularly, the prediction on the nonmonotonous dependence of the maximum current on the diffusion layer thickness (or the RDE rotation rate) including the anomalous region of this dependence in which the current increases with the increase in the diffusion layer thickness.     

Analysis of two-dimensional models for liquid chromatographic reactors of cylindrical geometry

This work presents the analytical solutions of two-dimensional isothermal reactive general rate models for liquid chromatographic reactors of cylindrical geometry. Both irreversible and reversible reactions are considered. The model equations form a linear system of convection-diffusion-reaction partial differential equations coupled with algebraic equations for isotherms. Analytical solutions are derived by integrated implementation of finite Hankel transform, Laplace transform, eigen-decomposition technique, and conventional ordinary differential equations solution technique. To verify the analytical results, a high-resolution finite volume scheme is also applied to numerically approximate the model equations. The current results can be very useful to optimize and upgrade the liquid chromatographic reactors.     

Contribution to the kinetics of ozone-olefin reactions

Kinetics of the reaction of O₃ with single olefins and olefin-pairs have been investigated. The reactions were carried out by passing O₃ into a solution of the olefin(s). Most relative rate data gave the best fit to a zero order rate law, especially in cases where olefin consumption was extensive. The results are interpreted in terms of a reversible complex.     

Heterogeneous exchange reactions of unstable simple systems

The analysis of less than 10⁻⁹ g of the isotope²⁰⁴Pb in lunar samples was carried out by an (n, 2n) activation using high energy (>8. 8 MeV) neutrons. A procedure of using the neutrons produced by bombardment of a specially designed Be sample holder with deuterons in a cyclotron was developed and compared to irradiation carried out in the core of a nuclear reactor, Radiochemical separations and X ray-γ ray coincidence counting techniques are necessary to achieve the required sensitivity. Although the flux of neutrons of sufficient energy from the cyclotron procedure is somewhat lower can be obtained in the best reactor irradiations, the high radioactivity due to other elements produced by the (n, γ) reactions in the reactor is eliminated. Radiochemical procedures for the analysis of Bi, Tl, Zn in the same samples are also described.     

Time-property least-squares spectral method for population balance equations

In multiphase chemical reactor analysis the dispersed phase distribution plays a major role in obtaining reliable predictions. The population balance equation is a well established equation for describing the evolution of the dispersed phase. However, the numerical solution of this type of equations is computationally intensive. In this work, a time-property least squares spectral method is presented for solving the population balance equation including breakage and coalescence processes. In this problem, both property and time are coupled in the least squares minimization procedure. Spectral convergence of the L ² least squares functional and L ² error norms in time-property is verified using a smooth solution to the population balance equation.     

Gas-phase reactions in plasmas of SF6 with O2: Reactions of F with SOF2 and SO2 and reactions of O with SOF2

The plasma chemistry of SF₆/O₂ mixtures is particularly complicated because of the large number of possible reactions. Over a wide range of conditions, products including SF₄, SOF₄, SOF₂, and SO₂F₂ can be formed but thre is considerable uncertainty about the major reactions which contribute to the formation of these species. In this work reactions of oxygen atoms with SOF₂ and fluorine atoms with SOF₂ and SO₂ have been studied in order to determine the principal sources of SO₂F₂ in these plasmas. Reactions were studied at 295 K in a gas flow reactor sampled by a mass spectrometer. No reaction could be detected between oxygen atoms and SOF₂, which for the conditions employed, means that the upper limit for the reaction rate coefficient is 1×10^–14 cm³ sec^–1. The reaction of fluorine atoms with SOF₂ was studied with the helium bath gas number density ranging from 3.1×10¹⁶ to 2.0×10¹⁷ cm^–3. Within this range the rate coefficient increased with increasing [He] from (4.1 to 10.8)×10^–14 cm³ sec^–1. SO₂ was found to react with fluorine atoms with a rate coefficient which appeared to be independent of the helium bath gas number density over the range given above. The possibility that this reaction occurred entirely on the walls of the reactor is discussed.     

Solvent effects in gold-catalysed A-coupling reactions

Gold-catalysed A³-reactions proceed efficiently when conducted in 2,2,2-trifluoroethanol as solvent. The rates of these reactions are accelerated considerably when conducted in a microwave reactor.     

Standard enthalpies of formation in the gas phase and relative stability of tautomers of C-nitro-1,2,4-triazole and isomers of N-alkyl-C-nitro-1,2,4-triazole: quantum-chemical studies

Quantum-chemical calculations of the standard enthalpies of formation in the gas phase of C-nitro-1,2,4-triazole and isomers of N-alkyl-C-nitro-1,2,4-triazoles (Alk = Me, Et, i-Pr, t-Bu) were carried out by the B3LYP method using equations for the isodesmic reactions and isomerization reactions. The relative Gibbs free energies of tautomers and isomers in aqueous solution were calculated. For the tautomers of C-nitro-1,2,4-triazole the structural indexes of aromaticity were estimated and the electron population density of the Natural Bond Orbital was analyzed. The relative stabilities of the described tautomers and isomers in the gas phase and in solutions were discussed on the basis of the results of the calculations. Dedicated to Academician B. A. Trofimov in his 70^th jubilee. Translated from Khimiya Geterosiklicheskikh Soedinenii, No. 1, 83-94, January, 2009.     

Simulation of nonisothermal reactive liquid chromatography using two-dimensional lumped kinetic model

A nonisothermal two-dimensional lumped kinetic model of reactive liquid chromatography is formulated and applied to simulate the separation of multicomponent mixtures in a fixed-bed cylindrical column operating under nonisothermal condition. The axial and radial variations of concentration and temperature as well as reversibility of the chemical reactions are incorporated in the model equations. The model comprises a system of convection-diffusion-reaction partial differential equations coupled with algebraic and differential equations. Due to the nonlinearity of adsorption and reaction kinetics, it is required to apply an accurate numerical scheme for solving the model equations. In this study, an efficient and accurate high-resolution flux-limiting finite-volume scheme is proposed to solve the model equations. A number of stoichiometrical reactions are numerically simulated to determine the level of coupling between the temperature and concentration profiles. Moreover, the effects of various critical parameters on the process performance are examined. The results obtained are beneficial for understanding reaction and separation processes inside a liquid chromatographic reactor and to improve its performance.