Designing a heat-exchange system upon the reconstruction and synthesis of optimal systems of distillation columns

The approach to the problem of designing optimal heat-exchange networks for the reconstruction and synthesis of distillation columns is discussed. It has been proposed to reduce the original discrete-continuous nonlinear programming problem to the modified linear programming assignment problem that takes into account a number of features of separation systems.     

Rapid fabrication of poly(ε‐caprolactone) nanofibers using needleless alternating current electrospinning

Poly(ε‐caprolactone) ( PCL) biopolymer nanofibers and micro‐fibers have been fabricated for the first time at the rates up to 14.0 g per hour using a needleless and collectorless alternating current electrospinning technique. By combining the ac‐voltage, “green” low toxicity glacial acetic acid (AA) as the solvent and sodium acetate (NaAc) as an additive, beadless PCL fibers with diameters tunable from 150 nm to 2000 nm, varying surface morphology and degree of self‐bundling are obtained. In this new approach, the addition of NaAc plays a crucial role in improving the spinnability of PCL solution and fiber morphology. NaAc reveals the concentration‐dependent effect on charge transfer and rheological properties of the PCL/AA precursor, which results in broader ranges of spinnable PCL concentrations and ac‐voltages suitable for rapid manufacturing of PCL‐based fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43232.     

Study of deformation of nonwoven fibre material during needle-punching

A dynamic model of the needle-punching process was developed in which the nonwoven material (NM) is modeled by an isotropic, deformable, continuous medium. The model allows assigning the NM elastic and plastic properties at each point of the sample. The distribution fields of the characteristics of elastic, plastic, and total deformation and stress over the entire volume of the sample were obtained as a result of modeling using the finite element method. The dependence of the characteristics of deformation on the density of the material and the damping coefficient was investigated. The model allows finding the regions and times during needle-punching when the NM is subject to the greatest stresses and strains. Modeling the process in relative units allows taking into account that the characteristics found are common to different types of NM. Translated from Khimicheskie Volokna, No. 1, pp. 33-35, January-February, 2009. Moscow State Textile University.     

Solid-state reactions upon mechanical alloying of an Fe32Al68 binary mixture

The sequence of solid-state reactions that occur upon mechanical alloying of powder mixtures of Al and Fe taken in an atomic ratio of 68: 32 has been studied by the methods of X-ray diffraction analysis, M?ssbauer spectrometry, and Auger spectrometry. Upon the formation of a nanocrystalline state (<10 nm), there takes place a mutual penetration of Al atoms into Fe and Fe atoms into Al particles. The rate of consumption of the fcc Al is substantially higher than that of the bcc Fe. The process of the mechanical alloying (MA) was found to be two-stage. At the first stage, up to 2 at % Fe is dissolved in the fcc Al, and an amorphous Fe₂₅Al₇₅ phase is formed in the interfaces, whose amount reaches 70 at % at the finish of the initial stage. In the interfaces of the ??-Fe phase, a disordered bcc phase of composition Fe₆₆Al₃₄ is formed, which contains up to 12 at % Al segregates. At the second stage, the amorphous phase crystallizes into an orthorhombic intermetallic compound Fe₂Al₅. The residual ??-Fe, bcc Fe₆₆Al₃₄, and segregated Al form a bcc phase of composition Fe₃₅Al₆₅.     

Tribochemical transformations of glycerol

The friction process is considered in this work from the viewpoint of chemical transformations, which occur in liquid lubricating medium and on the friction surface during the friction interactions. The results of tribotechnical tests of a conventional latten brass–glycerol–steel tribosystem are given and an attempt has been made to rationalize the evolution of tribotechnical characteristics of the tribosystem in the context of tribochemistry. The results of tunneling and IR spectroscopies indicate the formation of complex organic and organometallic films on the friction surface, which differ in chemical composition from the initial lubricating medium, which proves its deep triboconversion upon friction engagement. Chromato-massspectrometry studies of the products of tribotransformations of the lubricating medium enabled its identification. Based on this identification, chemical reactions, and a general scheme according to which tribochemical transformations take place in the lubricating medium have been suggested.     

Formation of Phases upon the Mechanosynthesis and Subsequent Annealing of Samples of Cementite Composition Alloyed with Chromium and Nickel

Using X-ray, Mössbauer, and magnetic measurements, the formation of phases has been investigated upon mechanosynthesis in a ball planetary mill and upon the subsequent annealing of samples of the cementite composition (Fe_0.95–уСr_0.05Ni _y )₇₅C₂₅, where у = 0–0.20, which contains two alloying elements (chromium and nickel). It has been shown that, in the mechanosynthesis process, cementite alloyed with chromium and a small amount of nickel and an amorphous phase alloyed with chromium and nickel have been formed. Upon heating above 300°С, the amorphous phase is crystallized into nickel-enriched cementite. In the process of annealing at higher temperatures, the most nickel-rich cementite decomposes with the formation of austenite. As a consequence, after annealing at medium temperatures, the composition of the alloys contains cementite alloyed mainly with chromium and some amount of alloyed austenite, which can be found in ferromagnetic or paramagnetic states depending on the Ni content. Annealing at 800°С bring about the complete or partial decomposition of cementite contained in the alloys. The intensity of the decomposition has been determined by the nickel content in the samples.     

Electrocatalytic Processes on PbO<Subscript>2</Subscript> Electrodes at High Anodic Potentials

The determination of the electrocatalytic activity and selectivity of electrodes with respect to the target process is considered to be of interest both in the theoretical aspect for the development of electrocatalysis theory and in application for efficient electrocatalysts which can be used in electrochemical systems for wastewater treatment. The purpose of the given work was to identify the relationship between the chemical and phase composition of materials based on lead dioxide, their physicochemical properties, and their electrocatalytic activity. The main research methods were quasi-stationary polarization and impedance spectroscopy, photocolorimetry, fluorescent and spectrophotometry in the UV and visible regions, atomic absorption spectroscopy, and high performance liquid chromatography (analysis of the solutions). It was shown that the modification of lead dioxide by ionic additives results in significant changes in the electrocatalytic activity of the system in respect to the oxygen evolution reaction and electrochemical oxidation reactions of organic compounds. It was found that, at low polarizations, the oxygen evolution reaction is limited by the electrochemical desorption step (the second electron transfer), and its overpotential at PbO₂-modified electrodes increases in the order that coincides with the dependence in which the number of oxygen-containing particles strongly bound to the electrode surface increases. It was found that the rate of oxidation of organic substances on the anode materials involved is directly proportional to the amount of oxygen-containing radicals formed on the electrode during the water oxidation.     

Thermal transitions of resveratrol on a carbon black surface

Methods of thermogravimetric analysis, differential scanning calorimetry, and thermal desorption mass-spectrometry are used to study the processes of thermolysis of resveratrol on the surface of graphitized thermal carbon black (GTCB). The results obtained in thermolysis of pure resveratrol and resveratrol adsorbed on GTCB from diethyl ether are compared. The regions of maximum evolution of thermolysis products are determined; their compositions are identified; an increase in thermal stability of resveratrol supported on the surface of graphitized thermal carbon black is observed.     

Anti-Kasha Behavior of 3-Hydroxyflavone and Its Derivatives

Excited state intramolecular proton transfer (ESIPT) in 3-hydroxyflavone (3HF) has been known for its dependence on excitation wavelength. Such a behavior violates Kasha’s rule, which states that the emission and photochemistry of a compound would only take place from its lowest excited state. The photochemistry of 3HF was studied using femtosecond transient absorption spectroscopy at a shorter wavelength excitation (266 nm), and these new experimental findings were interpreted with the aid of computational studies. These new results were compared with those from previous studies that were obtained with a longer wavelength excitation and show that there exists a pathway of proton transfer that bypasses the normal first excited state from the higher excited state to the tautomer from first excited state. The experimental data correlate with the electron density difference calculations such that the proton transfer process is faster on the longer excitation wavelength than compared to the shorter excitation wavelength.     

Kinetic aspects of the effect of CO pressure and methanol concentration on cyclohexene hydrocarbomethoxylation in the presence of the Pd(PPh3)2Cl2-PPh3-p-toluenesulfonic acid catalytic system

The dependence of the rate of the cyclohexene hydrocarbomethoxylation reaction catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid system on the CO pressure and methanol concentration at temperatures varied in the range of 358–388 K has been investigated. The data are interpreted in terms of the previously proposed mechanism involving as intermediates ion pairs containing cationic hydride, alkyl, and acyl palladium complexes. By the least squares technique, apparent constants relating to the effect of CO pressure and methanol concentration have been estimated for the rate equation derived earlier. The apparent activation energies have been determined for these constants, and the following stability series of palladium complexes has been proposed on their basis: $$ Pd(PPh_3 )_2 (CO)_2 > Pd(PPh_3 )_4 > Pd(PPh_3 )_2 (CH3OH)_2 > H\mathop {Sol}\limits^ \oplus [Pd(PPh_3 )_2 (Cl)(Sol)]^ \ominus . $$