Home – Home – Jornals – Chemistry for Sustainable Development 2010 number 6

Different classes of compounds exhibiting the properties of inhibitors for NO synthases are considered in the review. Literature data on natural and synthetic agents published between the years 2003 and 2009 are analyzed and systematized.

We consider the absorption and catalytic conversion of a single-stage method of obtaining high yield of pure hydrogen. This process involves simultaneous catalytic conversion of hydrocarbons into hydrogen and sorption removal of by-product - carbon dioxide. Different aspects of absorption and catalytic conversion are analyzed, including its technical implementation in flow reactors with fluidized and fixed bed, as well as high-temperature CO₂ absorbents and catalysts necessary for the process. It is shown that the preferred scheme for production of hydrogen from methane is that with two or more fixed bed reactors, loaded with a mixture of a conventional nickel containing catalysts of steam conversion and a high temperature reversible absorbent. The analysis of the perspective high-regenerated absorbent of CO₂: individual and deposited oxides of alkaline-earth metals, mixed lithium salts, promoted hydrotalcite. It is shown that the absorbents based on CaO have sufficient stationary dynamic capacity, stable under conditions of absorption and catalytic conversion, and optimal thermodynamic properties.

A technique was developed to remove and immobilize the cadmium ions from simulated industrial effluents. The cadmium ions were removed from industrial effluents by applying most economical method of sorption under certain physicochemical conditions. Removal of cadmium ions from industrial effluents using silica sand (originated from Ravi River) was studied to optimize the physicochemical conditions for maximum removal. The range of pH and temperature was optimized to get maximum removal of metal ions. Maximum removal (94-98 %) of cadmium was achieved with pH 10 and at temperature 25 ^oC. Under optimized conditions with temperature range of 298-318 K, ΔH, ΔS and ΔG₂₉₈ for 200 mg/L solution were -71.10±3.8 kJ/mol, -220.2±11.5 J/(mol · K) and -6.70±0.4 kJ/mol, respectively, and for 250 mg/L solution thermodynamic entities were ΔH = -108.7±5.7 kJ/mol, ΔS = -335.7±17.5 J/(mol · K) and ΔG₂₉₈ = -9.64±0.4 kJ/mol. This removal required certain physicochemical conditions; therefore, there were chances of desorption of the adsorbed metal ions under changed physicochemical conditions in final disposal. It was necessary to stabilize/immobilize sorbed metals ions by converting this "secondary waste" in a stable vitreous material having high resistance to leachibility. Such stabilization/immobilization of sorbed metal ions was obtained by converting the silica sand along with the sorbed cadmium ions into the glass matrix to prevent leaching/mobilization in final disposal under natural conditions. Stability of sorbed metals ions in final matrix was tested by desorption attempts in acidic and basic media and in ground water as well.

Data on the determination of petroleum products in surface and near-bottom water of Lake Baikal and its tributaries by means of express method (fluorometry, 168 samples) on board the research vessel are presented, as well as the data on n-alkanes and polycyclic aromatic hydrocarbons (PAH) obtained under laboratory conditions by means of gas chromatography/mass spectrometry. It was established that the oil product content of surface waters at the deep-sea stations of reference section does not exceed 10 μg/dm³, in water depth and in the near-bottom layer 5-7 μg/dm³, including n-alkanes - 0.15 μg/dm³, PAH (priority pollutants) - 0.012 μg/dm³; the concentration of benzo[a]pyrene is up to 10 times below MPC for drinking water (0.005 μg/dm³), total content of six PAH compounds under control in drinking water of EEC is up to 50 times lower than MPC_EEC (0.2 μg/dm³). Increased background of oil products reaching 50 μg/dm³ (MPC for fishery) was detected at limited regions of intense navigable waterways. Extremal concentrations of oil products (up to 1.3 · 10⁴ μg/dm³), n-alkanes (up to 500 μg/dm³), PAH (up to 20 μg/dm³) were discovered in the samples taken from the water surface of the lake in the regions of natural oil shows. With an increase in the distance from oil show boundaries (oil spots on water surface) the concentrations of oil products decrease sharply but exceed the average value for the water area of the lake almost by a factor of two (11 μg/dm³).

Comparative investigation of obtaining conditions and the "stability" of water-soluble intermolecular complexes of low-soluble pharmaceutical substances and different polysaccharides with β-cyclodextrin was carried out. Substantial improvement of the pharmacological characteristics of resulting complexes in comparison with initial pharmaceutical substances was demonstrated.

Fractional extraction of the sum of lichens of Cladonia genus was carried out. The effect of presowing treatment of the spring wheat seeds with the preparation obtained from the ethanol extraction of lichens on the development of root rot agents was considered. Rather high efficiency in suppression of root rod was confirmed. The stimulating effect of the preparation on growth processes and increase in wheat productivity was revealed.

The process of dissolution of asphalt-tar-paraffin deposits of paraffinaceous type in the gas condensate of alkane basis and a mixture of hexane with benzene at a temperature of 10 and 25 °С was investigated. The kinetic description of the process was made with the help of Erofeev-Kolmogorov equation. Kinetic parameters were calculated: rate constants, activation energies and orders of the reactions of dissolution of asphalt-tar-paraffin deposits in the solvents under investigation.

Single-phase membrane materials having the composition SrCo_{0.8 - x}Nb_xFe_0.2O_{3 - z} were obtained. The effect of doping with niobium on thermal stability and transport characteristics of the obtained compounds was studied. It was shown that the isomorphous substitution of cobalt ions with highly charged Nb⁵⁺ cations causes an increase in thermal stability of the compounds under investigation in the reductive atmosphere and suppression of the phase transition perovskite - brownmillerite, which is accompanied by acceptable decrease in oxygen permeability.

A process was studied concerning the combustion of municipal wastewater sediments from sludge fields of the Gorvodocanal Co. (Novosibirsk), in the fluidized bed of a catalyst. It was found that at the process temperature of 700 °C, the burnout level of the sediment amounted up to 98 %. In this case, the content of toxic substances (Hg, HCl, SO₃, P₂O₅, СО, NO_x meets the sanitary standards. It was demonstrated that the combustion of sediments is possible after its preliminary drying up to obtaining the moisture level equal to 54 %.

Potentialities were studied concerning the obtaining of hydrated antimony pentoxide (HAP) via much simpler methods than the method of SbCl₅ hydrolysis described in the literature. A sorption capacity was tested for the HAP obtained with respect to Cs⁺and Sr²⁺, whose, radionuclides are of environmental hazard when released into water basins. The oxides obtained were studied by means of powder X-ray diffraction method. It is established that the treatment of Sb powder by 16 M HNO₃ solution and the subsequent drying at 150 °C results in obtaining antimony tetroxide rather than pentoxide. Evaporation of antimony solution in nitrohydrochloric acid (aqua regia) and drying at the same temperature results in the formation of HAP, whose composition is close to Sb₂O₅ · 5H₂O. Adding HNO₃ to the solutions in the course of evaporation results in decreasing the hydration level. It was revealed that when HNO₃/HCl molar ratio in aqua regia is equal to 5 : 1 the HAP composition approaches to Sb₂O₅ · 3H₂O (H₃SbO₄), whereas with HNO₃/HCl = 9 : 1 therein the hydrate composition approaches to Sb₂O₅ · 2H₂O (H₄Sb₂O₇).

An effect was studied concerning the preliminary heating of activated carbon at the temperature of 250 °C on the porosity parameters of the adsorbent and the state of its surface. A comparative analysis was performed for the adsorption extraction of aniline and phenol from aqueous solutions by initial and pre-heated samples of the adsorbent. It was demonstrated that the thermal treatment of activated carbon causes an increase in the adsorption level of aniline and exerts almost no effect on the adsorption of phenol.

Results are presented concerning the optimization of composition and conditions for obtaining titanium-containing zeolite, a catalyst for allyl alcohol liquid-phase epoxidation by an aqueous solution of hydrogen peroxide in the methanol environment. The composition and conditions for catalyst preparation were revealed to provide a maximum yield of glycidol.

Five- and seven-membered cyclic ketals of 3-phenylsulphanylbutane-1,2,4-triol were obtained via thiolysis of 3,5,8-trioxaspiro[bicyclo[5.1.0]octane-4,1′-cyclohexane] thiophenol, followed by isomerisation. The syntheses were carried out using the methods of green chemistry (reactions in water without the use of organic solvents). The thiolysis in basic medium proceeds in a selective manner resulting in the formation of ketal from 1,3-dioxepane series only. In hot water, by the contrast, a mixture of isomeric spiroacetals is formed. The obtained β-hydroxysulphides and their acetates were oxidized to yield corresponding sulphones. The structure of the isomeric products was confirmed by the method of 1D and 2D NMR spectroscopy and
X-ray diffraction analysis.