Key words: сверхкритические флюиды, фазовые диаграммы
The main feature of supercritical (SC) fluids is a continuous increase of fluid density at increasing pressure (from values typical for gas to liquid-like) without an appearance of heterogeneity and "liquid - gas" (L-G) equilibria. In binary and more complex systems composed of components of different volatility SC fluid equilibria occur not only at temperatures above the critical point (CP) of less volatile component(s). They can also appear at much lower temperatures - below the melting point of nonvolatile compound, but necessarily above the CP of low-boiling component. Namely these "low-temperature" equilibria occur and are used in various SC fluid technologies. Therefore, an information about the displacement of homogeneity boundaries in SC fluid region, if a third component is added, is very important for practical application of ternary systems. The method of continuous topological transformation of phase diagrams permits to introduce the systematic classification for binary systems and also to derive both fluid and complete phase diagrams for ternary systems with one volatile and two nonvolatile components. The examination of theoretically derived ternary phase diagrams combined with the results of experimental measurements allowed to formulate some general regularities of the behavior of phase diagrams for ternary systems in the region of SC fluid heterogenization.
Key words: сверхкритические флюиды, диоксид углерода, технология, экология
The review summarizes the data on the world development in supercritical fluid technologies (SCFT) since 1980s up to date. During this period SCFT have been developed from laboratory to industrial scale. It should be noticed that these technologies are able to successfully solve current world environmental (ecological) problems. The main directions of supercritical fluid application in food industry, pharmaceutics, medicine, synthesis and development of advanced materials, and some other fields of science and engineering are analyzed.
Key words: сверхкритическая флюидная экстракция, определение органических соединений, ГХ, ГХ/МС
Advantages and limitations of liquid extraction (LE) and conventional supercritical fluid extraction (SFE) from aqueous and solid matrixes (soil, polymers) as applied for gas chromatography (GC) and combined GC-mass-spectrometric analysis (GC/MS) of trace amounts of organic compounds are discussed. Novel method of SFE without use of organic solvent (solvent-free SFE) is developed. This technique allows to transfer the entire amount of extract (concentrate) into the GC injector. Solvent-free SFE and GC (GC/MS) based procedures for determination of manifold target organic compounds of different volatility and polarity in water on the level of 10<sup>-10</sup> - 10<sup>-8</sup>% have been developed. For the determination and quantification of unknown organic impurities in polymers, some pharmaceuticals and in human hair analytical procedures based on GC/MS analysis of the whole concentrate isolated using solvent-free SFE have been developed. It is demonstrated that the newly developed technique permits to increase the number of isolated and analyzed impurities and to lower the detection limits as compared to LE.
Key words: рапсовое масло, переэтерификация, сверхкритический метанол, метиловые эфиры жирных кислот, биодизельное топливо
Modern trends in the development and use of production of motor fuels from renewable bio-materials (bio-mass, various vegetable and seed oils) are discussed. The emphasis is placed on the production of so-called bio-diesel fuel (methyl esters of fatty acids) from rape-seed oil triglycerides. It is demonstrated that the utilization of supercritical fluids can be efficient on stages of both synthesis and isolation (purification) of target methyl esters of fatty acids. Limitations of conventional catalytic re-esterification process are discussed. and possible of Authors' experimental data demonstrate that non-catalytic re-esterification in supercritical methanol can be very efficient and beneficial from the standpoint of practical realization.
Key words: сверхкритический диоксид углерода, полистирол, хитозан, сорастворитель, пористая структура
Processes of porous structure formation in polystyrene and aminopolysaccharide – chitosane – during supercritical carbon dioxide (SC-CO<sub>2</sub>) desorption are investigated. The effect of exposition parameters in SC-CO<sub>2</sub> and desorption rates after exposition onto pore size in polystyrene is studied. It is demonstrated that variations of experimental conditions lead to the formation of porous structures with different morphology. Unlike polystyrene, porous structures in chitosane can be formed only if co-solvents are added to SC-CO<sub>2</sub>.
Key words: рапсовое масло, биодизельное топливо, сверхкритический метанол, метиловые эфиры, жирные кислоты, переэтерификация, сверхкритический диоксид углерода, растворимость, уравнение Пенга-Робинсона
The solubility of bio-diesel fuel components (methyl esters of stearic and palmetic acid) in supercritical carbon dioxide is studied. The results are described in the framework of Peng-Robinson theoretical approach. The possibility of efficient separation of the target compounds (methyl esters of fatty acids, glycerol) from re-esterification reaction mixture and their purification using SC-CO<sub>2</sub> are demonstrated.
Key words: сверхкритический СО<sub>2</sub>, регенерация Pd-содержащих катализаторов, гидрирование ацетилена
Regeneration of Pd-containing catalysts of selective acetylene hydrogenation was for the first time performed by the treatment with supercritical CO<sub>2</sub>. The catalysts have been preliminary poisoned by the mixture of acetylene and ethylene at 80 °С. Their activity and selectivity were regenerated after treatment by supercritical CO<sub>2</sub> (35 °С, 73 at, 80 °С, 110 at and 93 °С, 115 at). The thermo gravimetric study indicated that the treatment with supercritical CO<sub>2</sub> results in removal of the coke precursors from the catalyst surface.
Key words: сверхкритический CO<sub>2</sub>, полимеры, полиолефины, тетрафенилпорфирин, фотокаталитическая активность
Low-density polyethylene (LDPE) and polypropylene (PP) films are impregnated with tetraphenylporphyrin (TPP) in supercritical carbon dioxide (SC-CO2) medium to obtain composites active in photocatalytic processes. TPP concentration (evaluated from the intensity of Sore line in electronic absorption spectrum) can reach 3 · 10-9 mol/cm2 in LDPE films. The impregnated polymers possess photocatalytic activity in gas-phase singlet oxygen (1O2) generation; measured 1O2 flows reached 3 · 10-9 mol/s ·cm2. Certain changes in structure and mechanical characteristics in LDPE and PP samples were observed after their treatment in SC-CO2. According to X-ray structure analysis (XSA) data (low-angle scattering), such treatment leads to some disordering in amorphous domains of materials under study, especially in the case of LDPE. In turn, according to wide-angle scattering XSA, crystal structures of both polymers remain unchanged. The conclusions about structural changes in polyolefins caused by treatment in SC-CO2 are confirmed by the results of mechanical testing and thermogravimetric analysis.
Key words: сверхкритический СО<sub>2</sub>, метакрилаты, сополимеризация, композиты
Methyl metacrylate and ethylene glycol di-metacrylate are co-polymerized in plastified ultahigh molecular weight polyethylene (UHMWPE) matrix in supercritical carbon dioxide (SC-CO2) medium. Composites with varied ratio of components are obtained. The mechanism of co-polymerization is determined by the way of attaining the supercritical conditions and does not depend on monomer ratio. If temperature is increased in closed volume (initial pressure 3÷4 MPa) from -20 to 120 °C with a subsequent addition of liquid CO2 (20 °C) to final pressure 20 MPa, a «block» polymerization in mass is taking place. On the contrary, if temperature and pressure are risen simultaneously from the initial values (room temperature, 6÷7 MPa) to the same final values (120 °C, 20 MPa), a dispersion polymerization occurs. The data obtained by differential scanning calorimetry demonstrate that metacrylate-impregnated UHMWPE samples have lower degree of crystallinity and reduced crystallization temperature. Atomic-force microscopy is utilized to study the surface structure and micro-mechanical properties of polymer samples. The results demonstrate the possibility of obtaining nano-scale uniform composites of the studied type.
Key words: полимеры, пористость, сверхкритические флюиды, диоксид углерода
New efficient two-stage method for creating a desired porosity in polymeric materials is developed. It consists in polymer treatment with carbon dioxide in supercritical state. The applicability of the method to modification of most practically important glassy polymers is demonstrated on such examples as polymethylmetacrylate, polycarbonate, polystyrene, and dacryl 6. The capability of varying the pore volume depending on the conditions of treatment in supercritical medium and of subsequent heating is among the main features of the suggested method. An easy-to-operate method of measuring the total pore volume in polymer materials is also suggested. It is based on weighing the material treated by water under elevated pressure and room temperature.
Key words: полимеры, пористость, сверхкритические флюиды, диоксид углерода
Previously developed by authors two-stage method for creating a desired porosity is applied to several polymeric materials, such as polytetrafluoroethylene, ultra high-molecular weight polyethylene, polyether ether ketone, polyaryl ether ketone 11, polyamide 6, shock-resistant polystyrene, acrylonitrile-butadiene-styrene co-polymer, and polyvinylchloride. It consists of polymer treatment with carbon dioxide in supercritical state and subsequent heating at atmospheric pressure. It is demonstrated that the method gives different results being applied to crystalline and amorphous polymers: no porosity is formed in crystalline materials, whereas substantial porosity (up to 0.9 cm3·g-1) is formed in polymers, in which amorphous domains dominate.
Key words: сверхкритический, газообразный и твердый диоксид углерода, хитозан, модификация
The influence of different carbon dioxide in different aggregate states (gaseous, solid, supercritical) onto properties of chitosan is studied. The interdependence of the physical and chemical properties of the polymer material under study on its structure and CO2 sorption is demonstrated and analyzed.
Key words: полимерная матрица, полиарилат, растворимость, сверх-критический диоксид углерода, импрегнация, дисперсный краситель Red 13
Impregnation of polymer films (polyarylate DV, polymethylmetacrylate, chitosane, etc.) with some anthraquinone and azobensene dyes from their solutions in supercritical carbon dioxide (SC-CO2) is investigated on qualitative level. Quantitative measurements are carried out with disperse dye Red 13 and polyarylate DV (PAR). The effect of pressure at temperatures ranged from 35 to 40 °C on the dye solubility in SC-CO2 is studied by UV-spectroscopy. It is shown that at 35 °C and 13.8 MPa the dye concentration in PAR can reach 0.2 wt. % (2.8·10-5 mol/l). Kinetic curve of Red 13 diffusion from SC-CO2 solution into PAR matrix at 40 °C and 10 MPa has a monotonic character with saturation. The experimental results are analyzed in the framework of the theoretical model that implies a low solubility of functional additive (in this case dye) in a transportation fluid (SC-CO2).