Deactivated iron catalyst in the fischer-tropsch synthesis

The selectivity for higher hydrocarbons (C₁₁–C₁₇) has been studied in the Fischer-Tropsch synthesis using fresh and used fused iron catalysts under different reaction conditions. On increasing the temperature higher hydrocarbon products were formed in the C₁₁–C₁₇ range. The deactivated fused iron catalyst is less active but selective to heavier hydrocarbon chain molecules. The product distribution is shifted towards heavier hydrocarbons due to the effects of the pore volume, presence of potassium and site densities at the surface.     

Influence of rice husk ash and wollastonite on plasticizer migration in polyvinyl chloride system

The influence of rice hull ash and wollastonite on the migration problem of plasticizer EDOS from polyvinyl chloride (PVC) has been studied. The methods of optical interferometry, IR spectroscopy, viscometry, SEM and EDX were used to study the mutual solubility and diffusion mobility in the PVC-EDOS system in the presence fillers and without them, as well as the phase structure of plasticized filled systems. It is shown that in a fully compatible PVC-EDOS system, a diffusion mixing mechanism is observed, and the interdiffusion coefficients increase from 10⁻⁸ to 10⁻⁶ (cm²/s) with increasing plasticizer concentration. The introduction of a dispersed filler somewhat reduces the interdiffusion coefficients. The sorption of the plasticizer on the surface of the dispersed filler has been established, which leads to a decrease in the migration of EDOS from the composition. It was found that the introduction of wollastonite leads to a smaller increase in viscosity and an improvement in the technological properties of the system. And the introduction of environmentally neutral rice husk ash reduces the migration of the plasticizer and improves the stability of the composition during operation, which also has a positive effect on the environmental friendliness of this system.     

Regulation of calf renal 25-hydroxyvitamin D-hydroxylase activities by calcium-regulating hormones

Parathyroid hormone and 1,25-dihydroxyvitamin D3 had opposite effects on calf renal 25-hydroxyvitamin D3 24-, 23-, and 1 alpha-hydroxylase activities. Parathyroid hormone administration increased renal 25-hydroxyvitamin D3-1 alpha-hydroxylase activity 7-fold while 25-hydroxyvitamin D3-23- and 24-hydroxylase activities were essentially the same as controls. Administration of 1,25-dihydroxyvitamin D3 increased 25-hydroxyvitamin D3-23-hydroxylase and 24-hydroxylase activities 4-fold and decreased 25-hydroxyvitamin D3-1 alpha-hydroxylase activity to undetectable concentrations. Vitamin D deficiency increased 25-hydroxyvitamin D3-1 alpha -hydroxylase activity 13-fold, and 25-hydroxyvitamin D3-23-hydroxylase and 24-hydroxylase activities were undetectable. These results confirm previous reports with regard to control of renal 25-hydroxyvitamin D3-24-hydroxylase and 1 alpha -hydroxylase in other species and represent new findings relative to the control of 25-hydroxyvitamin D3-23-hydroxylase. Plasma P was lower and 1,25-dihydroxyvitamin D3 higher in calves treated with parathyroid hormone, and Ca and 1,25-dihydroxyvitamin D3 were lower in the vitamin D-deficient calves. 1,25-Dihydroxyvitamin D3-treated calves had higher plasma P and lower Mg than controls. Further studies using this calf model should lead to better understanding of Ca-regulating hormones control of vitamin D metabolism.     

Hydrothermal transformations of organic matter of low permeability rocks from domanic formation of the romashkino oil field

Abstract

The oil generating potential of Domanic rocks from Dankov–Lebedyan horizon of the Zelenogorsk area of Romashkino oil field was evaluated by Rock-Eval pyrolysis technique. The result of given method depends on the content, composition, and thermal stability of organic matter in rocks. During hydrothermal processes, the distinctive conversion behavior of organic matter at temperatures of 200°С, 250°С, 300°С, and 350°С in CO₂ environment was revealed. The yield of obtained aquathermolysis products and their quality were evaluated. The results of the studies suggest that low-permeability carbonate rocks of the Dankov–Lebedyan horizon contain productive beds with content of C_org 1.89–3.03%, which when developed using thermal methods, can become an additional source of liquid hydrocarbons.     

Decomposition of Fe5C2 catalyst particles in carbon nanofibers during TEM observation

The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe₃C). However, for Hägg carbide nanoparticles (χ-Fe₅C₂), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.     

Numerical study of mixed-mode fracture in concrete

In the present paper, a finite element code based on the microplane model for concrete is used for the analysis of typical mixed-mode geometries: a Single-Edge-Notched beam, a Double-Edge-Notched specimen and a Dowel-Disk specimen. A local smeared fracture finite element analysis is carried out. As a regularization procedure, the crack band method is used. The principal objective of the study was to investigate whether the smeared fracture finite element code is able to predict mixed-mode fracture of concrete with no optimisation of the material model parameters. Comparison between experimental and numerical results shows that the used code predicts structural response and crack patterns realistically for all cases investigated. Moreover, it is shown that for most of the studied geometries a mixed-mode fracture mechanism dominates at crack initiation, however, with increase of the crack length mode-I fracture becomes dominant and the specimens finally failed in mode-I fracture.