Issues

Experimental  results on solubility of the styrene, phenol, methylphenylcarbinol,  acetophenone, ethylbenzene, propylene glycol and molybdenum as a complex with  Trilon B in supercritical СO₂ obtained using a dynamic (flow) method are  presented. The obtained data are described in the framework of Peng — Robinson  equation. The results of experiments on the extraction of organic components  from the waste formed in the olefin epoxidation process at Nizhnekamskneftekhim  Inc., on the analysis of extract composition, and on the testing of the extract  as an epoxidation catalyst are presented.

A subcritical water  extraction method for production of vegetable extracts possessing an  antiradical activity is suggested. The major advantages of the method are (a)  the possibility of extraction of up to 38 % of active substances of various  chemical nature, including phenolic compounds, and (b) the absence of toxic  organic solvents. The method is tested by producing extracts from Crataegus sanquinea Pall., Tilia cordata Mill.,  Helichrysum arenarium L., Matricaria recutita L. and Hypericum perforatum L. It is demonstrated that water- and  ethanol-soluble fractions of obtained extracts have comparable antiradical activity  measured in the reaction with diphenilpicrylhydrazyl radical.

A direct carboxylation  of benzene and its derivatives PhX (X = Me, Br, Ph, OPh, OMe) and of  mesitilene, durene and ferrocene in the presence of various Lewis acids (AlCl₃, FeCl₃, ZrCl₄,  ZnCl₂) in supercritical CO₂ medium is studied. In  all the cases secondary transformations proceed faster compared to the primary  reaction of carboxylic acid formation. For the system AlCl₃/CO₂/toluene  studied in detail the optimal conditions of <em>p</em>-toluic  acid formation are found. Quantum-chemical (DFT) calculations of carboxylation  in AlCl₃/CO₂/benzene system using  PRIRODA code allows one to trace a more energetically feasible reaction path.

The  effect of conditions of polyester fibrous material processing in supercritical  carbon dioxide (SC-CO₂) onto the localization of cyclic oligomers of  ethylene terephthalate on the fiber surface is investigated. It is shown that  the cyclic oligomers are deposited on the surface of polyester fibrous  materials in the form of large associates. The mechanism of oligomer migration  from the inner areas of polyester fiber plasticized in SC-CO₂ is  considered. Recommendations for the minimization of amount of oligomers  localized on the surface of polyester fibrous materials during their dyeing in  the SC-CO₂ medium are suggested. It is shown that the deposition of  oligomers on the surface of polyester fabrics does not negatively affect the  quality of their hydrophobization by superdispersed polytetrafluoroethylene in  SC-CO₂ medium.

Exact  analytical expressions for large-scale finite local fluctuations in  hydrodynamic velocity and temperature of dense non-ideal fluid are obtained.  Two simple models are proposed for probability distribution of density and  temperature finite fluctuations. It is shown that the fluctuating fluid can be  considered as two random fractions, one being more rarefied and the other being  more dense than the averaged fluid. The distinctive features of these random  fractions make them play different roles in physical and chemical behavior of  the fluid. It is stated that large-scale finite local fluctuations are common  for wide range of fluid states, not only for the neighborhood of gas— liquid  critical point.

The  studies aimed at the environmentally benign destruction of hazardous organic  substances (OS) and wastes via their oxidation in supercritical water (SCW) are  reviewed. The advantage of SCW application is the capability of complete and  rapid oxidation of OS in closed systems. The rate of oxidation is determined by  temperature, OS to SCW and oxidant ratios, bond strengths in molecules of OS,  their solubility in SCW and decreased in a sequence of aliphatic > aromatic,  heterocyclic > polycyclic aromatic substances. The main products of  oxidation are CO₂, H₂O and N₂; sulfur,  phosphorus and halogens are converted into corresponding mineral acids. Still,  there are several difficulties in practical implementation of particular  processes on industrial scale and related to the achievement of acceptable  endurance, sustained and accident- free operation of SCW oxidation units.  Heterogeneous processes on reactor walls result in negative phenomena, such as  corrosion of constructional materials, precipitation and deposition of salts,  and, as consequence, in the varied with time on stream kinetics of the main and  conjugated reactions.

The sensitivity of IR and Raman spectra to the hydrogen bonding in methanol is quantitatively characterized using the factor of comparative sensitivity K, which can be expressed as a ratio of the values of intensities (I_b/I_nb)_IR/(I_b/I_nb)_RS for IR absorption and Raman scattering (b and nb indexes are attributed to H-bonded and non-bonded components, respectively). It was found that the value of K ≈20 for methanol is equal to the one calculated for n-butanol, although the change in the degree of hydrogen bonding in both cases was obtained using different approaches. It is shown that in some cases Raman spectra can be transformed into IR absorption spectra, and vise versa. It is important for the understanding of the difference in the shape of OH-valence vibration bands obtained using these two techniques.

Peculiar properties of fluid mixtures in the vicinity of the critical point of the pure solvent are commonly used in supercritical-fluid technologies, such as fluid extraction, enhanced oil recovery, supercritical chromatography, and micronization. These properties are linked to critical-point anomalies, in particular, very large compressibility and very low interfacial tension. Water, near its vapor-liquid critical point, as a supercritical solvent, is well studied, in contrast to supercooled water. However, more recently, many scientists have started to believe that deep in super-cooled region, not directly accessible to bulk-water experiments, there exists a critical point of liquid—liquid separation («liquid water polyamorphism»). If the water liquid — liquid critical point exists, the addition of a solute will generate critical lines emanating from the pure- water critical point. The phenomenon would be conceptually similar to what is known near the vapor-liquid critical point and what is commonly exploited in supercritical-fluid science and technology. This new idea has not yet been elaborated. The investigation of aqueous systems below the freezing temperature of pure water would not only shed light on the nature of plausible water polyamorphism, but also could open the way for utilizing cold water as a novel and unusual supercritical-fluid solvent.

The application of a combined approach to the analysis of strongly coupled spectral bands is demonstrated. An OD-bond stretching vibration, v(OD), band shape in HDO molecule in the mixture [D₂O] : [H₂O] = 1 : 60 as a function of temperature under the conditions of isobaric heating is taken as an example. The following approaches are used for the analysis of spectral changes: (i) spectral band asymmetry and spectral band derivative analysis, (ii) difference spectroscopy, (iii) 2D-cross-correlation analysis, and (iv) Principal Component Analysis. The obtained results may be used as initial data in the procedure of spectral band fitting. This fact is important for tasks related to interpretation of poorly resolved or strongly overlapped spectral bands.

Numerical simulation techniques are used to study transformations of hydrogen-bonded water clusters at the transition to the supercritical state. It is demonstrated that the destruction of the infinite hydrogen-bonded cluster, i.e. passing the percolation threshold, is taking place in the subcritical region. At critical temperature structural fluctuations become so significant that the fluid behaves as a system with two types of ordering. The existence of tetrahedral clusters in supercritical water is confirmed at high pressure only.

The topology and energetic characteristics of H-bonded clusters in methanol and methanol—heptane mixtures in a wide range of state temperatures are studied by means of IR-spectroscopy. Average numbers of H-bonds per one molecule of methanol are calculated. Conclusion about the structural transformation occurring in the mixture under study is drawn based on the analysis of changes in spectral parameters of intermolecular  —O...H bonds at rising temperature.

The pressure dependence of the main spectral lines in Raman spectra of antracene and of 1 M water solutions of NaClO₄ and Na₂WO₄ was measured by optic cell with sapphire windows at pressures up to 140 MPa. The obtained values of spectral shifts (from 0.6 to 1.1 cm^-1 per 100 MPa) correspond to those described in literature for 1 M water solution of sodium sulfate.

A synthesis of novel carborane-containing phosphites is carried out. Their efficiency as ligands in rhodium-catalyzed hydroformylation of alkenes in supercritical carbon dioxide (SC-CO₂) is tested. It is demonstrated that in the presence of newly synthesized carboranylamidophosphites a high alkene conversion at low catalyst loading can be achieved. An improved regioselectivity is obtained in SC-CO₂ medium compared to toluene.

An experimental study of supercritical fluid extraction with carbon dioxide from carbonaceous rocks demonstrate the possibility of selective extraction of hydrocarbons, preferentially alkanes and naphthenes, independently of the facial-genetic type of initial material. The determined composition of supercritical extracts makes them suitable for the production of lubricating oils.

The extraction of <em>Juniperus oblonga M. Bieb.</em> fruits,growing in Dagestan (Russia) in a height of 1750 m above sea level, was obtained by means of supercritical CO₂ extraction. The extraction was carried out at constant temperature 311 K and pressures 8, 10, 15, 20, 25, and 30 MPa. Using the gas chromatography/mass spectrometry analysis, 43 compounds in the extract obtained at 10 MPa are identified. Among them the major components are: α-pinene (7,11 %), sabinene (19,47 %), β-myrcene (11,97 %), limonene (2,64 %),  β-elemene (2,31 %), germacrene-D (20,66 %), germacrene-D-4-ol (4,90 %), bisabolol (2,78 %), linoleic acid (5,28 %).

Combined models describing thermodynamic properties <em>F</em> related to the coexistence curve (including densities of liquid and gaseous phase, <em>ρ</em>_l and <em>ρ</em>_g, an order parameter, <em>f</em>_s, a coexistence curve diameter, <em>f</em>_d, a pressure of saturation, <em>P</em>_s, are discussed. They are presented in the form of equations <em>F = f (τ, D, С)</em> those follow the scaling theory of critical phenomena and include critical characteristics <em>D = (α, β, T_c, ρ_c, P_c, ...)</em> and fitting coefficients <em>C</em>. Models are based on a statistical treatment of experimental data and elaborated for a series of substances (CH₄, NH₃, SF₆, water, methanol, ethanol, diethyl ether and fluorinated alkanes R134a, R143a, R236ea). The input data sets cover a wide temperature interval, that includes the critical point area. Some applied calculations are performed using the combined models; among them are values of the first and the second derivatives of the saturation pressure.
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Thermodynamic aspects of innovative binary mixture (BM) technology for increasing of productivity of oil-bearing beds that provides with a substantial cut of oil well watering (compared to the conventional steam heating) are discussed. The inorganic and organic ammonium nitrates (NH₄NO₃
       and HOCH₂CH₂NH₃⁺NO₃^-, respectively) are comparatively examined as heat producing components of BM that also contains sodium nitrite as an initiator of nitrate decomposition. Effects of temperature and pressure onto the product distribution and heat evolution in ethanolammonium nitrate decomposition are evaluated. Calculations of parameters in a near-well space taking into account the heat capacity of the surrounding rock layer demonstrate that temperature and pressure can exceed their critical values for both water and main oil fractions. As a result, the conditions for the intense upward flow of water-oil fluid in an artificial gas-lift regime arise.

For the first time the reaction of catalytic oxidative coupling of dimethyl ether (DME) in supercritical conditions is investigated. Oxidation of dimethyl ether by molecular oxygen in the presence of a СаO—SnO₂ catalyst was carried out in the medium of excess reactant (DME) and in its mixtures with carbon dioxide in supercritical (SC) conditions (100 atm, 250—300 °C). At 255 °C a maximum conversion of DME (approaching 40 % at monoglim: diglim ratio about 2:1) is reached at 20-fold (by volume) dilution of DME with SC-CO₂.