Stationary operating regimes of chemical reactors

We investigate the existence and also the number of possible stationary operating regimes of continuous reactors of finite length with a fixed fine-grained catalyzer layer. It is assumed that the effective chemical reaction rate is expressed by a single-valued function of very general form of the temperature and concentration of the primary component in the stream. It is shown in section 1 that in an adiabatic reactor the solution of the direct and inverse problems of finding the stationary regimes always exists and for the inverse problem the solution is unique. In section 2 we establish some sufficient conditions for the uniqueness of the direct problem for the case in which the effective thermal conduction and diffusion coefficients are equal. In section 3 we examine a very simple diffusion model of a reactor with heat removal. An attempt is made to determine the region of variation of the parameters (characterizing the temperature of the supplied mixture, its input rate, heat removal and reactor length) in which the various stationary regimes exist, in particular the low and high temperature regimes and also both of these regimes together.     

Enthalpies of formation of acetyl radicals

The database on the enthalpies of formation (Δ_f H ^○) of aliphatic acetyl radicals of the RC·(O) type is analyzed and extended. Δ_f H ^○ values are estimated for the first time for three compounds on the basis of experimental data. The data were analyzed using the additive group approach with the determination and correction of parameters. Good correspondence between the Δ_f H ^○(RC·(O)) values calculated according to parameters with experimental data is observed.     

A statistical comparison of non-isothermal methods of kinetic investigation

A statistical analysis of some non-isothermal kinetic techniques is given. Comparison of the kinetic parameter values obtained by different techniques has shown them to be statistically non-equivalent. Hypotheses of significance or non-significance of discrepancies in the kinetic parameter values should therefore be tested using two-dimensional normal distributions. Comparisons of the results obtained by various techniques using activation energy values only lead to erroneous conclusions.     

Effect of Surfactant Hydrophobicity on the Physicochemical Properties of Alkylpyridinium Alkylsulfates and Electroanalytical Characteristics of Membranes Based on These Compounds

Reasoning from the regularities of the variation of electrochemical properties of sensors based on alkylpyridinium alkylsulfates (n = 10–15), we demonstrated that detection limits for surfactants are related to the solubility of ionophores. The slopes of electrode functions, selectivity, apparent extraction and dissociation constants of ionophores are governed by the hydrophobicity of the active components of membranes.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 5, 2005, pp. 514–519.Original Russian Text Copyright © 2005 by Kulapin, Chernova, Kulapina.     

The Kinetic Aspects of the Interaction of Nitrite Ions with Sulfanilic Acid and 1-Naphthylamine in Aqueous and Micellar Media

The kinetics of the reaction of nitrite ions with sulfanilic acid and 1-naphthylamine in aqueous and micellar (sodium dodecyl sulfate) media was studied step-by-step. The diazotization of sulfanilic acid with the nitrite ion was found to occur virtually instantaneously. Anionic surfactant micelles did not influence the rate of this reaction. The calculated effective rate constants and activation energies of the azo coupling reaction between synthesized sulfophenyldiazonium and 1-naphthylamine showed that the passage from water into the micellar medium decelerated the reaction. It was found that sodium dodecyl sulfate micelles played the role of a reagent separator.     

Supramolecular systems based on the melamine salt of bis(hydroxymethyl)phosphinic acid (melafen) dihydrate and surfactants

Bis(hydroxymethyl)phosphinic acid and melamine were shown by FTIR and UV spectroscopy to form the salt (melafen), whose cations and anions involving water molecules can be joined into supramolecular structures due to electrostatic interactions and hydrogen bonds. The conductometry, dielcometric titration, and dynamic light scattering methods showed that melafen in water and chloroform in a concentration range of 10⁻¹⁰–10⁻⁴ mol L⁻¹ involving the solvent structures exist as supramolecular polymeric nanostructures, whose size and properties change nonlinearly depending on the melafen concentration. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1207–1214, June, 2008.