Home – Home – Jornals – Chemistry for Sustainable Development 2004 number 6

The kinetics of ethyl radical generation during the pyrolysis of n-undecane on barium chloride (accelerating the heterogeneous constituent of the process) and on defect-bearing magnesium oxides (accelerating the homogeneous constituent of the process) was investigated by means of freezing out in the cavity of the EPR spectrometer. It was shown that the activation energy of radical generation on barium chloride (E = 192 kJ/mol) is lower than the activation energy of thermal pyrolysis (E = 322 kJ/mol). The phenomenon of ignition of the surface is observed with the catalysts that accelerate the homogeneous constituent of the process and create the «catalysis sphere.» Below the critical temperature, in spite of the presence of catalysts, ordinary thermal pyrolysis goes on between the catalyst granules. At a higher temperature, the catalyst generates radicals with the activation energy characteristic of the radical reactions (E = 4 kJ/mol). The possibility to increase the productivity and to control the selectivity of pyrolysis of hydrocarbons by including non-conventional heterogeneous catalysts into the process is demonstrated.

The problem of reliable prediction of the safety of burial of the spent nuclear fuel in the environmental components is connected with the reliability of quantitative models describing solubility/precipitation of uranium dioxide UO₂(s) as the major component, depending on a number of physicochemical parameters, such as temperature, E_h-pH, salt composition and concentration of electrolyte solutions. In the present paper we report on the free Gibbs' energy of formation of this phase and the accompanying complexes in the solutions of different composition. The reported values of Gibbs' energy allow reliable model reproduction of the experimental results on solubility and the concentrations of dissolved uranium observed in nature. In addition, the reasons that may cause local non-equilibrium fluctuations of the concentrations of this element under the conditions conjugated with the radioactive decay of short- and medium-lived isotopes are discussed.

Oxidation of the 0.2 M solutions of H_7+mP(V^IV)_m(V^V)_4-mMo₈O₄₀ (H_mHPA-4) by oxygen at temperatures from 373 to 433 K under O₂ pressure up to 8 atm (810 kPa) is investigated. The maximal reaction rate is observed at 433 K. At a higher temperature, partially oxidized 0.2 M solutions of H_mHPA-4 are thermally unstable. With an increase in the extent of oxidation of H_mHPA-4 solutions, the apparent activation energy increases.

A rapid method to analyze the whole blood and its fractions for zinc content involving stripping voltammetery with the use of the modified thick-film carbon-containing electrodes is proposed. The method allows one to make the analysis free from metal mercury and its soluble salts, preliminary deproteinization of samples, and also to decrease the sample necessary for analysis to 5-50 ml. The measurable range of zinc concentration in blood and in its fractions is 100-20 000 mg/l.

Results concerning the development of the new polymeric composite materials and coatings based on PTFE are presented. Experimental results obtained testify that application of such composites allows one to enhance operating performance and reliability of machines and mechanisms.

An investigation of the oxidized and modified carbon materials and sorbents around them has been carried out by physicochemical methods (electron microscopy, thermoanalysis, X-ray diffraction, and IR spectroscopy). The processes of mercury sorption to the new modified carbon sorbents under static and dynamic conditions are studied with model solutions and processing media. It has been found that adsorption capacity for mercury depends on oxidation state of the carbon surface and on the properties of the introduced modifier.

The approach based on the use of sulphur dioxide from metallurgical off-gases as a reagent in the technologies of processing of the crude ore is considered, which allows, in specific cases, a sulphur closed cycle to be set up. The expedients are demonstrated, which enable one to reduce the body of sulphur ingress to processing with a feed stock, and to enhance the efficiency of sulphur productions now in operation.

Regularities in catalytic oxidation of "Acid chrome dark blue" dye in water solutions are studied under the effect of Fe-montmorillonite catalyst obtained by intercalation of iron polyhydroxocomplexes into the montmorillonite clay from Mukhortalinskoye deposit (Buryatia). An impact of the initial concentrations of reagents, temperatures, and ðÍ on the reaction rate is studied. The outcomes of organic dyes oxidation bear witness to the possibility of practical application of Fe-montmorillonite catalyst in the processes of sewage decontamination from dyes.

Thermal transformations of sapromixite from the Barzas deposit are investigated under the conditions of pyrolysis processes in an inert atmosphere, hydropyrolysis in the atmosphere of hydrogen, thermal dissolution in the residue from oil refining and catalytic hydrogenation. It is shown that sapromixite can be transformed with a high yield into liquid hydrocarbon products. The main products of this transformation is the fraction of liquid hydrocarbons with boiling point above 180 ^oC; its yield from sapromixite is substantially (up to 7.7 times during pyrolysis) higher than the corresponding value for brown coal. The highest degree of sapromixite conversion into liquid and gaseous products was achieved for its pyrolysis in the atmosphere of hydrogen and for hydrogenation in the presence of mechanically activated iron-ore catalyst. For hydrogenation, maximal conversion of sapromixite reaches 94-97mass % at a temperature within 400-430^oC. For hydropyrolysis of sapromixite, the degree of conversion increases with an increase in the process temperature and reaches 78-80mass % at 430-460^oC. Further temperature rise causes a sharp increase in the amount of gas formed and a decrease in the yield of liquid products. The application of iron-ore catalyst during hydrogenation allows one to increase the sapromixite conversion degree by 21-23% and to achieve total yield of liquid products of hydropyrolysis up to 58 mass % with rather low gas formation.

Ecological and economic aspects of the use of sorption heat facilities (refrigerators and thermal pumps) under the conditions existing in Russia are considered, along with their competitiveness in comparison with traditional systems. It is shown that sorption refrigerators are preferable in comparison with compression ones if waste heat (or solar energy) is used. If regeneration is carried out by burning natural gas, sorption devices can be more ecologically pure only in exclusive cases, so, in order to decrease emissions of greenhouse gases, is it reasonable to develop compression devices with high coefficient of performance (COP ³ 4). Sorption heat pumps with the coefficient of amplification COA>1 are ecologically safer and economically more efficient that gas heaters. In the case of COA_abs=1.7, consumption of natural gas decreases by 41 %; for COA_abs=1.5 - by 33%, which means substantial practical interest. Analysis may be useful either for the determination of the promising character of various sorption devices followed by elaboration of the corresponding technical policy or for choosing the economic parameters affecting the competitiveness of technologies, including those for separate regions of Russia.

The generalized approach and methodology of formulating and solving a series of direct problems of chemical equilibrium aimed at estimating the real state of substances in aqueous solutions as subsystems of natural and technological water is presented. A minimal set of the key terms is outlined in brief (locality and partial character of equilibrium, physicochemical decomposition, initial system, system under investigation and so on); these terms are necessary to master the approach and the procedure, and also to use correctly the corresponding results in solving the complex problems connected with the description of the state of water systems. Examples of two implementations (estimation of the consumption and evolution of carbon dioxide during photosynthesis, breathing of hydrobionts, oxidative destruction of organic matter in surface water, partial analysis of the local states of mercury in the environment) illustrate the technology of applying this approach and the procedures, and also their self-descriptiveness. Specific results obtained within these examples are of independent interest.