Key words: суб- и сверхкритическая вода, гидролиз, лигносульфонат натрия, вератрол
Conversion of veratrol and sodium lignosulphonate (LS) is studied in sub- and supercritical water (SCW) in the temperature range 200÷430 °C at 220 atm and the residence times 2.5÷10 min. Soluble products of the LS depolymerization are analyzed using HPLC and GC-MS. Thermogravimetric, elemental, IR and NMR spectral analyses of insoluble products of LS conversion are carried out. It is shown that methoxyaril ether bonds and aromatic structures do not undergo any destruction in SCW. The formation of insoluble precipitate is related to decarboxylation and desulfonation of lignin polymeric fragments.
Key words: нефть, обессоливание, обезвоживание, сверхкритический С0<sub>2</sub>, экстракция, переработка нефти
A new process for the removal of water, salts and solid admixtures using supercritical carbon dioxide (SC-CO<sub>2</sub>) targeted on the pre-treatment of oil on operating oil refineries is developed. Simultaneously with the removal of mentioned impurities, de-asphaltization and de-metallization of oil is taking place. The process is realized on a pilot plant localized at the Experimental refinery of the Institute of Petrochemical Processes, National Academy of Science (Azerbaijan Republic). Preliminary data and economical evaluation demonstrate the newly developed process has much lower power consumption as compared to conventional technologies.
Key words: регенерация, сверхкритический флюид, цеолитсодержащий катализатор, алкилирование, изобутан, бутан-бутеновая фракция
The results of regeneration by supercritical fluid (CO<sub>2</sub>) of zeolite-containing catalyst for alkylation of isobutane with butane-butylene fraction are presented. The effect of regeneration conditions on the catalytic activity of the investigated catalysts is discussed.
Key words: кислород, азот, водяной пар, оксид углерода, диоксид углерода, водород, термические и калорические уравнения состояния реального газа
Thermal and caloric equations of state (EOS) of main species in gaseous mixtures used in the calculations of various gas dynamic processes, including combustion and detonation as well as internal ballistics, are presented in the analytical formulation. The EOC contain a relatively low number of parameters and exhibit the approximation error which is in average less than 1 % at temperatures from 500 to 2000 — 2500 K and at densities up to the critical density.
Key words: сверхкритический диоксид углерода, сверхгидрофобность, тонкие пленки, гидрофобные полимерные покрытия, газодиффузионные слои, электроды топливных элементов, гидрофобизованная углеродная ткань
In this work a new method for uniform deposition of polymeric hydrophobic agent onto the surface of carbon tissue (a material for gas diffusion layers of fuel cells) from solutions in supercritical carbon dioxide (SC-СO<sub>2</sub>) is developed. The use of Teflon AF 2400 copolymer soluble in SC-СO<sub>2</sub> is compared with a conventional method for hydrophobization of gas diffusion layer by deposition of Teflon 30N from aqueous suspension. Hydrophobic polymer compounds were deposited on rough surface of carbon tissue — a conducting material for gas diffusion layers with good mechanical and longevity characteristics — produced by Saati company. If the coating deposited from SC-СO<sub>2</sub> is annealed at temperature exceeding the glass transition temperature for amorphous Teflon AF 2400 copolymer, a uniform thin fluoropolymer coating on carbon fibers is formed that imparts the most stable superhydrophobic properties to the surface of gas diffusion layer with minimal amounts of deposited agent. Moreover, the contact angles achieved in this work exceed those reported earlier in the literature for materials obtained using similar approaches. Prolonged exposure to water (1000 hours of direct exposure) or washing in the presence of detergent didn't induce any significant loss of the introduced superhydrophobic properties of the gas diffusion layer. Using the developed gas diffusion layer an electrode for phosphoric acid fuel cell was prepared. The achieved voltage-current characteristic of this cell indicates its satisfactory efficiency. The obtained results in general demonstrate good prospects of the developed approach in the production of gas diffusion layers for fuel cells.
Key words: статистическая физика, теория неидеальных систем, локальные флуктуации, критическое и сверхкритическое состояния флюида
The equations for large-scale local fluctuations in fluids — from ideal gas to non-compressible liquids, including near-critical and supercritical (SC) states — are obtained from the first principles. The contemporary notions concerning the critical state are verified and described substantially more accurately. It is demonstrated that in compressible fluids the local density fluctuation is accompanied by non-thermodynamic fluctuations of collective velocity and fluid temperature. The features of the development of such fluctuations near the critical point determine a distinctive behavior of the fluid in critical and SC states.
Key words: сверхкритический диоксид углерода, аллильное замещение, комплексы палладия, фосфиты, региоселективность
Allylic amination and alkylation catalyzed by Pd complexes is carried out in supercritical carbon dioxide (SC-СO<sub>2</sub>) using phosphite-type ligands. It is shown that Pd-catalysts dissolved in SC-СO<sub>2</sub> provide a high regioselectivity and thus present a useful approach to the synthesis of allylamines.
Key words: теория абсолютных скоростей реакций, неидеальные реакционные системы, релаксация окружения, молекулярная теория
The analysis of the equations for rates of elementary reactions in non-ideal systems demonstrates that traditional notion of the existence of chemical potential of the activated complex in dense phases contradicts real times of molecular and procedure of statistical averaging of molecular distributions. The expressions connecting rate constants of elementary chemical reactions obtained at atmospheric pressure and in supercritical conditions are derived.
Key words: сверхкритические флюиды, фотохромизм, спиросоедине-ния, полярные полимеры, матричная иммобилизация, фотолюминесценция
It is shown that supercritical fluid (SCF) impregnation of polymers containing polar diphenilol and halogen groups (polyoxycarbonate, polytetrafluoroethylene, polyvinylchloride) by spirocompounds leads to conformational changes with the stabilization of merocianine form of photochroms. It is demonstrated also that previously observed effect of the formation of long-living form B of spiroantrooxazine molecules immobilized in polycarbonate matrix is also typical for other similar systems. In this work such effect is observed for a number of spirocompounds incorporated into polar polymer matrixes using the SCF impregnation method. Colored forms of spirocompounds immobilized in halogen-containing matrixes have an intense fluorescence.
Key words: сверхкритическое состояние, особо чистый полистирол, термополимеризация
The possibility and conditions of frontal (thermal) polymerization of styrene in the conditions of the transition of its mixture with carbon dioxide into supercritical state is studied. The experimental procedure is developed and parameters (temperature and pressure) of such transition at different styrene-to-СO<sub>2</sub> ratios are determined. The numerical study of a mathematical model of thermal polymerization of styrene in a tubular reactor is performed. The distributions of temperatures and concentrations along the reactor corresponding to the transition of the styrene — carbon dioxide mixture to the supercritical state are calculated.
Key words: сверхкритический диоксид углерода, квантовые точки, метилметакрилат, стирол, сополимеры, полимерные нанокомпозиты
A new method of synthesis of dispersed fluorescent polymer composites based on dispersion copolymerization of methylmetacrylate and styrene in the presence of quantum dots CdSe/CdS in supercritical carbon dioxide is suggested. A one-step scheme of the formation of fine particles of polymethylmetacrylate/polystyrene/CdSe/CdS composite is carried out and factors controlling their photoluminescent features and photochemical stability at long-term exposition under intense UV and sunlight irradiation on air are investigated.
Key words: зеленый китайский чай, сверхкритический диоксид углерода, чайный лист, целлюлоза, элементный состав, структура
The effect of preliminary treatment in supercritical carbon dioxide (SC-СO<sub>2</sub>) on the elemental composition of tea leafs is studied. FT-IR absorption spectroscopy is employed to study the effect on the structure of green Chinese tea leafs and cellulose.
Key words: до- и сверхкритические водно-солевые равновесия, критические явления, гетерогенизация гомогенных СК флюидов, гидротермальная растворимость, фазовые диаграммы тройных систем
Experimental studies of high temperature phase equilibria in the system BaCl<sub>2</sub>—NaCl—H<sub>2</sub>O determine the conditions when the homogeneous supercritical (SC) fluid, spreading from the binary subsystem BaCl<sub>2</sub>—H<sub>2</sub>O of type 2, transforms into the heterogeneous equilibria. These data also show that liquid-gas equilibria in ternary mixture can be continuously transformed into the immiscibility equilibria in the SC conditions. The comparison of the obtained experimental results with available data for the system K<sub>2</sub>SO<sub>4</sub>—KCl—H<sub>2</sub>O suggests that ternary systems with one volatile component formed by binary subsystems of type 2 with immiscibility and of type 1 without immiscibility have phase diagrams of the same type.
Key words: сверхкритический диоксид углерода, инженерия костной ткани, композиты, наноразмерный гидроксиапатит, полилактид, механические характеристики
Composite materials for biomedical applications based on bioresorbable polymer and nano-sized calcium phosphates (hydroxyapatite) are prepared using supercritical carbon dioxide. The stress-strain while bending dependence are investigated for the composites with different ratios of polymer and mineral parts. The elastic modulus of composites obtained in supercritical conditions from bioresorbable polymer and bioactive nanoceramics were in the range of elastic modulus of natural bone tissues. Experiments on human embryonic fibroblasts demonstrated the suitability of sintered samples for using in tissue engineering and regenerative medicine.
Key words: сверхкритическая вода, природный асфальтит, продукты превращения, состав
Natural asphaltite and the products of its conversion in supercritical water (400 °С, 40 MPa) are comparatively analyzed using a complex of methods including analyses of elemental and component compositions, pyrolytic and X-ray diffraction analyses, spectrophotometry, IR-, EPR-spectroscopy and gas chromatography/mass spectrometry. It is demonstrated that under indicated conversion conditions of asphaltite various products, such as gases, carbene-carboids; heavy, highly resinous and sulfur-rich petroleum are produced. The yields of the conversion products are roughly identical. The obtained petroleum and carbene-carboids are characterized by lower sulfur and oxygen content and higher content of nitrogen and paramagnetic centers as compared to the initial asphaltite. Components of the same names (oils, resins and asphaltenes) composing petroleum and asphaltite noticeably differ by the content of heteroatoms (elemental analysis), aromatic and carbonyl-containing structural fragments (IR-spectroscopy). The analysis of molecular compositions of hydrocarbon and heteroorganic compounds present in oils of the obtained petroleum evidence that compositions of nearly all classes of compounds substantially differ from those present in the initial asphaltite other reasons apart — due to the appearance of new compounds. The revealed differences are mainly caused by the generation of such compounds via thermal destruction of resin-asphaltene substances. The process prolongation from 0.5 to 1 hour causes noticeable changes both in the yields of the main groups of products and in the compositions of the most of analyzed compounds.
Key words: сверхкритическая флюидная экстракция, сверхкритический СО<sub>2</sub>, волосы, хлорорганические пестициды, фосфорорганические пестициды, ГЖХ-МС
A supercritical fluid extraction process using supercritical carbon dioxide for isolation of chloro-organic and phosphoro-organic pesticides in the human hair is developed. The effect of process parameters (temperature, pressure, duration) on the efficiency of pesticide extraction is studied. Gas chromatography-mass spectrometry technique is used for quantitative analysis of pesticide concentration.
Key words: рапсовое масло, пальмовое масло, сверхкритические метанол и этанол, переэтерификация, метиловые и этиловые эфиры жирных кислот, биодизельное топливо, теплоемкость
Syntheses of methyl and ethyl esters of fatty acids via trans-esterification of vegetable oils in supercritical methanol and ethanol are carried out on the pilot installation with a continuous flow reactor. Corresponding procedures are described and results are analyzed. The effect of preliminary ultrasonic treatment of the initial mixture on the product yield is studied, and the correlation between the stability of obtained emulsions and the composition of the initial mixture, as well as the intensity of ultrasonic treatment is determined. Isobaric heat capacity of mixtures «supercritical alcohol (methanol, ethanol) — vegetable oil» is measured.
Key words: сверхкритические флюиды, фазовое равновесие, диспергирование, поликарбонат, метод SAS
The results of phase equilibria investigation in the systems «methylene dichloride — СO<sub>2</sub>», «methylene dichloride — polycarbonate», «polycarbonate — СO<sub>2</sub>», and «polycarbonate — methylene dichloride — СO<sub>2</sub>» are presented. Based on them, the conditions for polycarbonate dispersing process using SAS method are determined. Experimental data for polycarbonate dispersing process carried out in the pressure range from 8.0 to 25 MPa at 313, 333 and 355 K using SAS method are obtained and analyzed.