Key words: <i>PVT</i>-свойства, <i>н</i>-пентан, вода, критическое состояние, критическая точка
Thermal properties of the binary system <i>n</i>-pentane + water (1 : 4 by weight) re phase equilibria of hydrocarbon liquid—vapor and aqueous liquid—vapor have been studied in a wide temperature range 303—674 K under elevated pressures (up to 60 MPa) along 9 isochors. The phase equilibrium lines and critical points for the system were obtained and the phase diagrams are described.
Key words: сверхкритическая флюидная хроматография, фурокумарины, метоксипсоралены, механизмы удерживания
A method for separation of isomeric psoralen methoxy-derivatives, namely bergapten, xanthotoxin and isopimpinellin, is developed. The results of sorbent screening allow one to consider a normal phase elution regime as optimal for separation of these compounds in SFC. The analysis of methoxypsoralen (MOP) retention mechanisms showed that the same one is responsible for MOP’s separation on all tested silica sorbents containing polar groups, except 2-ethylpyridine and pentafluorophenyl. A possible explanation of the observed MOP’s retention phenomena is given. In the case of pentafluorophenyl sorbent π-electron intermolecular interactions play a key role in separation of closely related MOPs. It is likely that the same effects are responsible for a specific order of MOP’s elution observed when 2-ethylpyridine sorbent is used.
Key words: сверхкритический диоксид углерода, биодеградируемые полимеры, СКФ микронизация, поли-3-гидроксибутират, SAS
Micronization of poly-3-hydroxybutyrate (PHB) using SAS technique with supercritical carbon dioxide as an antisolvent is studied experimentally. The possibility of PHB particle fabrication with different morphology (including hollow spheres) and predetermined sizes varied from 100 nm to 20 μm is demonstrated. The effect of various mechanisms of the formation of solid phase during the SAS micronization process onto the size and morphology of poly-3-hydroxybutyrate particles is evaluated and discussed.
Key words: сверхкритический диоксид углерода, алифатические полиэфиры, матрицы для тканевой инженерии
A novel method for fabrication of highly porous bioresorbable polymer matrixes for tissue engineering is proposed and developed. It is shown that injection of polymer compositions plasticized in sub- or supercritical carbon dioxide at 20—40 °C through the nozzle of certain diameter to the moulds at atmospheric or elevated (up to 6 MPa) CO<sub>2</sub> pressure enables to fabricate highly reproducible polymer matrixes with desirable structure and morphology and mean porosity up to 96 % without use of organic solvents. The effect of chemical composition and molecular weight of initial polymers, as well as, carbon dioxide temperature and pressure in reaction and receiver chambers onto the morphology and internal structure of fabricated matrixes is studied using a scanning electron microscopy.
Key words: ЭПР, сверхкритическая вода, спектроскопия <i>in situ</i>, VO<sup>2+</sup>, VOSO<sub>4</sub>, кластеризация, гетерогенные катализаторы, температурный градиент
Temperature variations of the EPR spectra of VO<sup>2+</sup> ions in sub- and supercritical water, under isothermal and temperature gradient conditions are investigated using an <i>in situ</i> EPR. A broadening of the hyperfine structure at increasing temperature and appearance of an unresolved broad low intensity line (Δ<i>H<sub>pp</sub></i> ≈ 300 Oe) in the supercritical state are observed in the absence of temperature gradients, indicating the increase of exchange interaction between VO<sup>2+</sup> ions in supercritical water. Exchange-narrowed anisotropic absorption line is observed under the temperature gradient conditions in the subcritical water near the transition to supercritical state. The shape of this line is close to that observed in the solid salt VOSO<sub>4</sub>·3H<sub>2</sub>O. It is shown that <i>in situ</i> EPR allows us to investigate the effects of changing the local environment of paramagnetic ions, which is preceding a well-known process of clustering and formation of amorphous oxide particles in sub- and supercritical conditions.
Key words: субкритическая вода, эхинацея пурпурная, кафтаровая кислота, цикориевая кислота, высокоэффективная жидкостная хроматография
New method for extraction of caftaric acid and cichoric acid using subcritical water is developed. This method is environmentally benign and more efficient than traditional extraction methods based on the utilization of expensive and toxic organic solvents.
Key words: субкритическая вода, регенерация сорбентов, капролактам, нитробензол, сверхсшитые полистирольные сорбенты
Subcritical water is tested as an agent for caprolactam and nitrobenzene desorption from hyper-cross-linked polystyrene sorbents MN-202 and MN-270. The efficiencies of desorption of two mentioned compounds by subcritical water and by water solution of isopropanol are compared.
Key words: сверхкритические флюиды, импульсный нагрев, теплообмен
A technique based on pulse heating of the wire probe (resistance thermometer) in the constant heating power mode is developed and applied for the studies of comparative heat transfer intensity in supercritical fluids (SCF) in the pressure and temperature ranges from 1<i>р</i><sub>с</sub> to (4—6) <i>р</i><sub>с</sub> and from 0,6<i>T</i><sub>с</sub> to 1,6<i>T</i><sub>с</sub>, respectively (<i>р</i><sub>с</sub> and <i>T</i><sub>с</sub> — critical pressure and temperature). Characteristic parameters of the setup used are as follows: heating pulse length — 1—10 ms; density of the heat flux through the probe surface — 1—10 MW/m<sup>2</sup>; repeatability of the selected power value in a series of pulses — not worse than 0,1 %. A sharp decrease in the heat transfer intensity in SCF compared to that observed at subcritical temperatures is revealed.
Key words: локальная молекулярная динамика, ИК-Фурье спектроскопия, полимеры, релаксационный переход, метод конформационных зондов, сверхкритический диоксид углерода
To study the local molecular mobility of polysulphone and polycarbonate processed in
supercritical carbon dioxide the FTIR-spectroscopic method of conformational probes
is applied. The temperatures and nature of secondary relaxation transitions are determined.
The effect of supercritical fluid processing on relaxation transitions in polymers and on
the difference in conformation enthalpies of probe molecules is analyzed.
Key words: критические параметры, сверхкритические растворы, концентрация, уравнение состояния, фактор сжимаемости, приведенные параметры, относительное отклонение
The <i>p</i>, ρ, <i>T</i>, <i>x</i>-relationshi ps for water + aliphatic alcohol (methanol, ethanol, <i>n</i>-propanol) mixtures in near-critical and supercritical conditions obtained by compressibility measurements using the piezometric setup are analyzed. It is demonstrated that thermodynamic surface (<i>p</i>, ρ,<i>T</i>)<sub><i>x</i></sub> or (<i>Z</i>, ρ,<i>T</i>)<sub><i>x</i></sub> in supercritical region can be satisfactory described (average relative error 0.83 %) by the equation of state in the form of polynomial decomposition of compressibility factor <i>Z = p/RT</i> to the series of degrees of density and temperature:
\(Z=1+\sum_{i=1}^{m}\sum_{j=0}^{n_i}a_{ij}\omega^i/\tau^j\), where
\(\omega=\rho_m/\rho_{m_{cr}}, \tau=T/T_{cr}\)
Key words: сверхкритические флюиды, крекинг нефти, водно-углеводородные флюиды, выращивание кристаллов кварца, синтетические включения, нефть, углеводородные газы, твердые битумы, термобарогеохимия флюидных включений
An experimental research was conducted to study the features of the hydrocarbons
behaviour and their phase states at temperatures from 220 up to 500 °C and saturated
vapour pressure and above (up to 150 MPa). The study was realized using the synthetic
fluid inclusions in the quartz crystals which had been grown simultaneously with the
interaction between the water solutions and crude oil. It was shown that the aqueoushydrocarbonic
fluids generated at temperatures below 320 °C (approximate pressure of
30—50 MPa), depending on the thermobaric parameters and ratio of the water solution
(L1), oil (L2) and the gas phase (G) (presented by water vapour), could exist as the
three-phase (from L1>G≥L2 up to L2≥L1>G) and two-phase (from L1≥L2 up to
L2≥L1) states. The cracking of oil in such aqueous-oil fluids is not observed. The
fluids formed at temperatures above 330 °C (and especially at 380—450 °C) have higher
amount of light oil fractions, gaseous hydrocarbons and residual solid bitumen. This
means that the hydrocarbons in the hydrothermal systems are exposed to the cracking
at the specified temperatures. Reheating of such multi phase inclusions to temperatures
240—280 °C leads to the complete dissolution of the liquid hydrocarbons in the gaseous
and aqueous phases. Therefore, the fluid becomes bi phasic (water solution + gaseous
hydrocarbons saturated by liquid hydrocarbons). The consecutive increase of
temperature from 350 up to 380 °C transfers the fluid in homogeneous liquid or gaseous
state, or in supercritical state. Fluid cooling results in its heterogenization, and all
intermediate phases are consecutively restored. As a whole, the experimental studies
confirm influence of the hydrocarbons cracking on the occurrence in the earth interior
of the vertical zonal distribution of various types of the oil-and-gas deposits.
Key words: сверхкритическая флюидная экстракция, жидкий и сверхкритический диоксид углерода, переработка оксидного ядерного топлива, комплексообразование, трибутилфосфат, водные растворы нитрата железа(III)
Solubility of UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>-tributyl phosphate (TBP) complex in liquid and supercritical
(SC) carbon dioxide as a function of temperature and pressure is measured. This
complex is formed during the dissolution of uranium oxide in two-phase system consisting
of aqueous iron nitrate solution and liquid or supercritical CO<sub>2</sub> saturated with
TBP. Kinetics of ceramic UO<sub>2</sub> dissolution in such two-phase solvent is studied. The
feasibility of the recovery of uranium from spent oxide nuclear fuels via its dissolution
in sub-acid iron nitrate aqueous solutions accompanied by simultaneous extraction of
the above mentioned complex into «TBP — SC-CO<sub>2</sub>» phase is demonstrated.
Key words: сверхкритический диоксид углерода, экстракция, растворимость, капли воды, дифракционная картина, диаметр капли
The formation of water droplets of micron size in supercritical carbon dioxide (SC-CO<sub>2</sub>)
in high-pressure cell with sapphire windows is studied experimentally using in
situ laser diffractometry. According to the analysis of diffraction patterns of laser
radiation scattered on water droplets in SC-CO<sub>2</sub> and optical microscopy data at 10.0 MPa
and 40 °C, the mean diameter of water droplets is 55±3 mm.
Key words: водные растворы NaF и Li<sub>2</sub>CO<sub>3</sub>, растворимость и критические явления в двойных и тройных системах
Experimental studies of binary and ternary water-salt systems containing NaF or
Li<sub>2</sub>CO<sub>3</sub> demonstrate that these salts belong to the type 2, which is characterized by
negative temperature coefficient of salt solubility in water, by critical phenomena in
salt-saturated aqueous solutions and by a wide region of fluid equilibria where
homogeneous supercritical fluid solutions are stable at any pressure variation. However,
the behavior of these two salts of type 2 differs from that of alkali metals sulfates and
carbonates, which is complicated by immiscibility phenomena in stable and metastable
states. It is shown that the immiscibility phenomena in hydrothermal binary systems
with NaF and Li<sub>2</sub>CO<sub>3</sub> are absent and the second critical end-point Q in solid saturated
solutions appears at very high temperature and pressure (above 500 °C and 150 MPa).
Key words: сверхкритический диоксид углерода, полилактид, атомносиловая микроскопия полимеров
Microstructure and properties of amorphous D,L-polylactide processed different routes
in supercritical carbon dioxide (SC-CO<sub>2</sub>) are studied. Atomic force microscopy analysis
demonstrated polymer plasticization that follows its swelling in SC-CO<sub>2</sub> and leads to
significant internal structure changes caused by polylactic acid supramolecular
transformations. A developed pore structure formation and an accompanying increase
of polylactide void volume are directly related to a destruction of initial intermolecular
polymer bonds during the release of carbon dioxide. These changes are reflected in
significant (1.7—5-fold) increase of exothermal effects detected by differential scanning
calorimetry in the temperature ranges between -30 °C and -10 °C and around 30—40 °C.
Key words: сверхкритические условия, плотность, волоконно-оптический денситометр, изобутан, бутены, алкилирование
The applicability of a fiber-optic densitometer for monitoring of the reaction mixture density in the course of heterogeneous catalytic reactions is demonstrated on an example of isobutane alkylation with butene in supercritical conditions at 150 °C and 80 atm. Density measurements are carried out in two points — before and after the fixed bed of the H-USY zeolite catalyst. Temperature and pressure dependencies of density and refraction index of butene-isobutane mixture are revealed.
Key words: ионный фосфит, гидроформилирование, сверхкритический диоксид углерода, ионные жидкости, родий
A new method for the preparation of ionic phosphite ligands is developed. The first example of the use of this type of ligands in the hydroformylation catalyzed by rhodium complexes in organic solvents, ionic liquid and supercritical carbone dioxide is described. It is shown that the hydroformylation reaction in biphasic mixtures «ionic liquid/supercritical carbon dioxide» leads to a higher activity of the catalyst.
Key words: ацизол, сверхкритический диоксид углерода, ИК-Фурье спектроскопия
Dissolution of the pharmaceutical substance Acizol® — bis(1-vinylimidazole-N) zinc diacetate — in supercritical carbon dioxide (SC-CO<sub>2</sub>) is studied using the FTIR spectroscopy. Via the analysis of temporal dependences of integral intensities of IR absorption analytical band (1650 сm<sup>-1</sup>) at varied acizol shot its molar fraction in saturated solution in carbon dioxide at 40 °C and 10,0 MPa is evaluated as (4,9 ± 1,3) • 10<sup>-3</sup>.
Key words: сверхкритическая сушка, автоклав, аэрогель на основе диоксида кремния, мезопористое кварцевое стекло, оптическое кварцевое стекло, синтетический опал
The supercritical drying technology applied in the synthesis of materials based on pure silica, such as aerogel, mesoporous silica glass, optical quartz glass, and noble opal is described. The parameters of supercritical drying for the case of silica material synthesis in ethanol and methanol are optimized.
Key words: сверхкритические среды, каротиноиды, экстракция, морковь, параметры процесса
The effect of process parameters on the efficiency of carotenes extraction from carrot samples by supercritical CO<sub>2</sub> is studied. The degree of carotenes extraction increases to approximately 35 % at rising temperature (in the range between 60 and 80 °C) and pressure (up to 350 atm) at nearly stable fraction of β-carotene (64—70 %) in the obtained extracts.