Termodynamic and Transport Properties of Supercritical Fluids.<br> Part 1. Thermodynamic Properties.
Key words: изохорная теплоемкость, критическая точка, сверхкритический флюид, уравнение состояния, высокотемпературный адиабатический калориметр
This review presents the results of a detailed analysis of the role of isochoric heat
capacity as a key thermodynamic property of a substance in the study of critical and
supercritical phenomena. A brief historical background is given on the role and
contribution of Russian scientific schools in the experimental study of isochoric heat
capacity in the critical region in the development of the non-classical (scaling) theory
of critical phenomena, which considerably changed our understanding of the physical
nature of critical and supercritical phenomena. The experimental behavior of the
isochoric heat capacity and other thermodynamic properties of fluids associated with
it in the critical and supercritical regions are analyzed in detail. The role of new
experimental studies of two-phase isochoric heat capacity near the critical point in
the development of a “complete” scaling theory is discussed. This theory allows to
understand the physical nature of the liquid-gas coexistence curve asymmetry near
the critical point and to estimate the contribution of the chemical potential to the
divergence of the two-phase isochoric heat capacity at the critical point. The review
also focuses on supercritical phase transitions and the role of isochoric heat capacity
in determining the Widom line, which separates liquid- and gas-like regions in
supercritical states, i.e. defines the boundaries of the coexistence of “liquid-” and “gaslike”
phases in supercritical fluids.
doi:10.34984/SCFTP.2020.15.1.002
Key words: аэрогель, оксид алюминия, оксиды металлов, сверхкритическая сушка, сверхкритический диоксид углерода, удельная площадь поверхности, пористость
Alumina aerogels were obtained using sol-gel synthesis and subsequent supercritical
drying. Sol-gel synthesis was carried out by adding epichlorohydrin to aluminum chloride
dissolved in water and ethanol. Supercritical drying (SCD) of gels was carried out in
supercritical carbon dioxide at 40 °C and 12,0 MPa for 8 hours. The structural
characteristics of aerogels were studied by nitrogen porometry, helium pycnometry
and scanning electron microscopy. The resulting materials have high specific surface
area (up to 764 m<sup>2</sup>/g) and porosity (up to 96,2 %, pore volume up to 4,9 cm<sup>3</sup>/g) and
low density (below 0,066 g/cm<sup>3</sup>). It was found that the structural characteristics of
aerogels can be controlled by changing the «water : precursor» ratio. In particular, an
increase in this ratio leads to an increase in the specific surface area and pore volume.
doi:10.34984/SCFTP.2020.15.1.003
Key words: молекулярная динамика, моделирование, сольватация, разбавленные водные растворы, нормальные условия, сверхкритические условия, растворы вода—этанол, растворы вода—гваякол, растворы вода—фенол, лигнин, коэффициент самодиффузии, кластеризация
Using a classical molecular dynamics method structures of 2 wt. % water solutions of
ethanol, phenol and <i>o</i>-methoxyphenol (guaiacol) were modeled in NVT-ensemble at
densities 0.997 and 0.133 g cm<sup>-3</sup> that corresponds to normal (298 K; 0.1 MPa) and
supercritical (673 K; 23.0 MPa) conditions. Self-diffusion coefficients for individual
components in solutions, radial distribution functions for oxygen atoms of water
molecules, for oxygen atoms in hydroxy-groups and for centers of masses in phenol
molecules are calculated. A possibility of molecule clusterization for diluted substances
is analyzed. The data obtained indicate the heterogeneity of solutions in which clusters
of different composition and structure can exist. It was found that under normal
conditions clustering of up to seven ethanol and phenol molecules can occur, and
dimer formation was detected under SC-conditions. The structural features of solutions
under normal and SC-conditions were compared. The difference between the water
shells of ethanol and phenols molecules was demonstrated. Under normal conditions,
stable shells of water molecules form around ethanol molecules. For phenols, the solvate
shells are unstable and a tendency to clusterization of organic molecules is pronounced.
doi:10.34984/SCFTP.2020.15.1.004
Key words: сверхкритическая флюидная пластификация, квази-изотермическое расширение, пена, аморфный полилактид, диоксид углерода, уравнение состояния, показатель политропы, коэффициент поверхностного натяжения, коллапс
The results of experimental and theoretical studies of the behavior of the amorphous
D,L-polylacide fo am are presented. D,L-polylacide was preliminary plasticized using
sub- or supercritical carbon dioxide under the constant temperature (313,3 K) and
various pressures from 4 MPa to 20 MPa; after plasticization, it was foamed using the
quasi-isothermal depressurization under the low depressurization rates (from 0,005
to 0,05 MPa/s). It was established that, in the case of polylactide plasticization in the
supercritical domain (with the pressures of carbon dioxide above 8 MPa), the transition
from the expansion of the polylactide foam to collapse occurs in the course of
depressurization. Using the equation of state for a thermodynamically equilibrium
foam, which was pioneered by S. Ross, the criterion of the expansion-to-collapse transition
was established. It was shown that this phenomenonis caused by asignificant increase
in the surface tension of polymer during a slow decrease in the pressure of carbon
dioxide.
doi:10.34984/SCFTP.2020.15.1.005
Key words: сверхкритические флюидные технологии, биорезорбируемые матриксы и микрочастицы, инкапсуляция гентамицина и левофлоксацина, кинетика высвобождения в физиологические среды
Gentamicin and levofloxacin were encapsulated into bioresorbable polymer scaffolds
and microparticles by SCF methods — PGSS and plasticization and subsequent foaming
of amorphous polymers using supercritical carbon dioxide. Release kinetics of
incorporated drug substances into model physiological media was studied. It was shown
that the use of the developed methods of SCF-encapsulation of drugs in bioresorbable
carriers allows varying the size, shape and morphology of formed structures and
accordingly the rate of release of drugs into physiological environments. In our opinion,
this approach can be very promising for the development of components of new
highly effective antibacterial prolonged dosage forms.
doi:10.34984/SCFTP.2020.15.1.006
Key words: хрящ свиньи, децеллюляризация, поверхностно-активные вещества, сверхкритические флюиды, этанол, гистологические исследования, ДНК, мезенхимальные стромальные клетки
At obtaining tissue-specific scaffolds of dense tissues from decellularized porcine
articular cartilage it was found that full decellularization of tissue takes surfactant
treatment followed by supercritical fluides treatment. An introduction of ethanol as a
polarity modifier enables to increase significantly a completeness of cartilage
decellularization backgrounded by reduction of the destructive changes in the
extracellular matrix. Preservation of morphology and active proliferation of mesenchymal
stromal cells of human adi pose tissue in the presence of tissue-specific scaffold of
porcine cartilage evidence an opportunity of its use as a cell carrier for tissue
engineering of cartilage.
doi:10.34984/SCFTP.2020.15.2.001
Key words: реакционная способность, оксид титана, оксид алюминия, гидратация, водный флюид, титанаты щелочноземельных элементов
The synthesis of strontium and barium titanates supported on the porous carrier
(α-Al<sub>2</sub>O<sub>3</sub>) was performed via the treatment of the previously deposited precursors
(titanium oxide, strontium nitrate, barium nitrite) in the water fluid medium at 400 °C.
The obtained samples were characterized using the X-Ray Powder Diffraction (XRD)
and Scanning Electron Microscopy combined with Energy Dispersion X-Ray analysis
(SEM-EDX) techniques. It was found that in the presence of titanium oxide α-alumina
undergoes a partial hydration with the formation of the basic aluminum hydroxide
AlO(OH) (boemite) that was not found using the XRD method after the treatment
of the pure α-Al<sub>2</sub>O<sub>3</sub> in the same conditions. Using the SEM-EDX method we
demonstrated that in spite of much higher content of alumina in the samples, strontium
ions preferably interact with titania forming SrTiO<sub>3</sub>. It was shown that samples with
different spatial distribution of the supported component inside the carrier particle
can be obtained by varying the method of the preliminary deposition of the titania
precursor (titanium tetra-<i>iso</i>-propoxide).
doi:10.34984/SCFTP.2020.15.2.002
Key words: квази-изотермическое вспенивание, аморфный полилактид, диоксид углерода, нуклеация, энергия Гиббса, бинодаль, спинодаль
Mechanisms controlling the nucleation kinetics in the foamed amorphous D,L-polylactide,
which is preliminary plasticized using sub-ical or supercritical carbon
dioxide, are established using analysis of videodata on the depressurization-induced
quasi-isothermal (313,3 K) foaming of the polymer. Possible scenarios of the phase
separation in the polylatide—carbon dioxide system at the stage, which precedes the
expressed foam formation, are considered.
doi:10.34984/SCFTP.2020.15.2.003
Key words: сосна обыкновенная, сверхкритическая флюидная экстракция, эфирное масло, терпены, антибактериальная активность
The paper presents a comparative analysis of influence of extraction methods that
meet the princi ples of «green chemistry» on the extraction degree of components
from the wood greenery of <i>Pinus sylvestris</i>. Analysis of the obtained alcohol extract,
essential oil and supercritical extracts by GC-MS method showed that differences are
observed in both the quantitative and qualitative composition of the studied objects.
The highest selectivity of the diterpene fraction extraction and the expansion of the
spectrum of individual components extracted from wood greenery by supercritical
fluid extraction with carbon dioxide compared to traditional extraction methods while
maintaining a high antimicrobial activity of the resulting extract to suppress <i>Escherichia
coli</i> strains is shown.
doi:10.34984/SCFTP.2020.15.2.004
Key words: ароматизация, дегидроциклодимеризация, <i>н</i>-бутан, ZSM-5, Ga/H-ZSM-5, сверхкритические условия
A comparative study of <i>n</i>-butane conversion into aromatic hydrocarbons over ZSM-5
zeolite in H-form and modified with gallium and platinum at 530 °C in gas phase
(1 atm) and under supercritical conditions (190 atm) was carried out. The catalysts
demonstrate high activity, stability, and productivity under supercritical conditions. In
contrast to the gas phase process, modification of ZSM-5 zeolite with gallium and
platinum had no affect on the distribution of n-butane aromatization products in
supercritical conditions.
doi:10.34984/SCFTP.2020.15.2.005
Key words: водно-солевые системы, фазовые равновесия, расслаивание растворов, критические явления
The study concerns phase equilibria and critical phenomena in the
Na<sub>2</sub>SO<sub>4</sub>—Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>—H<sub>2</sub>O
system with two boundary subsystems: Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>—H<sub>2</sub>O (type 1 with liquid phase
immiscibility of solutions) and Na<sub>2</sub>SO<sub>4</sub>—H<sub>2</sub>O (type 2) at 350—460 °C and pressure
up to 100 MPa. It is shown that there are two three-phase regions — (l<sub>1</sub>-l<sub>2</sub>-s) adjacent
to two aqueous salt subsystems and separated by a fluid region at the temperatures
from 440 °C (critical point Q (l<sub>1</sub>=l<sub>2</sub>-s) of the type 2 binary system) to ~455 °C when
these regions integrate with each other. The three-component system is characterized
by two critical curves in saturated solutions. The curves extend from different critical
points of the type 2 binary subsystem — g=l-s (point p) and l<sub>1</sub>=l<sub>2</sub>-s (point Q). These
curves end at the ternary critical points — pR (g=l<sub>1</sub>-l<sub>2</sub>-s) and QN (g-l<sub>1</sub>=l<sub>2</sub>-s), respectively,
with a four-phase equilibrium (g-l<sub>1</sub>-l<sub>2</sub>-s) between them in the temperature
range of 350—380 °C, according to the visual observations in sealed quartz ampoules.
doi:10.34984/SCFTP.2020.15.2.006
Key words: пропиленгликоль, сверхкритическая пропан/бутановая смесь, фазовое равновесие, растворимость, уравнение состояния Пенга —Робинсона, закон смешивания Мухопадхъяи и Рао
The phase equilibrium of the propylene glycol—propane/butane system and the solubility
of propylene glycol in supercritical propane-butane mixture at temperatures 403, 423
and 443 K using a high-pressure optical cell were studied. The results were described
using the Peng—Robinson equation of state and the Mukhopadhyay and Rao mixing
law.
doi:10.34984/SCFTP.2020.15.2.007
Key words: альгинат натрия, хитозан, сверхкритическая сушка, аэрогель, интерполимерный комплекс, фурацилин
Composite aerogel materials based on the alginate-chitosan interpolyelectrolyte
complex with calcium carbonate using supercritical fluids were obtained. Aerogels have
developed mesoporous structure. The specific surface area of the samples is 400 m<sup>2</sup>g<sup>-1</sup>,
the average pore size is 19.3 nm, and the total pore volume is 1.93 cm<sup>3</sup>g<sup>-1</sup>. New
materials are superadsorbents. 1 g of aerogel retains 60 g of liquid while maintaining
its shape. The possibility of using the obtained composite aerogels to create wound
coatings with the inclusion of an antiseptic medicinal substance (furacilin) was
shown. It was found that for all samples of aerogels, the furacilin release profile from
the aerogel matrix corresponds to the dynamics of controlled release. It was shown
that within 5 hours there is almost complete release of furacilin (88—95 %) from the
aerogel matrix, which is due to the developed surface of the material.
doi:10.34984/SCFTP.2020.15.3.002
Key words: бионефть, конверсия, переходные металлы, пропанол-2, сверхкритический растворитель
This paperis devoted to the study of the catalytic conversion of bio-oil obtained by the
pyrolysis of pine wood waste using supercritical propanol-2. The method proposed in
this work is suitable for the production of monoaromatics mixture from the pyrolysis
liquid. The oxygen removal degree was found to beca. 80 %.
doi:10.34984/SCFTP.2020.15.3.003
Key words: сверхкритическое антисольвентное осаждение, углеродные нанотрубки, полимерные композиты
The possibility to obtain polyurethane—carbon nanotube composites using supercritical
antisolvent preci pitation (SAS) is demonstrated. The influence of solvent, polymer concentration
in the solution, spraying nozzle and suspension flow rate on composites
preparation efficiency and morphology is investigated.
doi:10.34984/SCFTP.2020.15.3.004
Key words: диоксид углерода, сверхкритическое состояние, сольватохромные параметры, красители, полярность, донорно-акцепторные свойства, температура, давление
Kamlet—Taft solvatochromic polarity parameters are determined for carbon dioxide in
sub- and supercritical state at 22, 40, 60 and 80 °С and 10,0—30,0 MPa. As solvatochromic
indicators, 2,6-di phenyl-4-(2,4,6-triphenyl-1-pyridino)-phenolate (Reichardt’s betaine)
and benzophenone were used to determine <i>E<sub>T</sub></i>, and to determine β and π parameters,
respectively, 4-nitrophenol and 4-nitroanisole were used. It was found that the values of
the parameters characterizing the polarity and donor-acceptor properties of CO<sub>2</sub> are
practically independent of the state parameters, since these properties are determined by
the structure of the molecule.
doi:10.34984/SCFTP.2020.15.3.005
Key words: гетерогенные катализаторы, субкритический синтез, сверхсшитый полистирол
The current paper is devoted to the study of the influence of temperature and pressure
of subcritical synthesis on the structure of polymeric supports and the composition of
the active phase of the synthesized catalysts. During the investigation, the optimal
synthesis conditions were chosen for the deposition of the metal-containing phase on
the surface of hypercrosslinked polystyrene.
doi:10.34984/SCFTP.2020.15.3.006
Key words: импрегнация, полиметилметакрилат, карбамазепин, сверхкритический CO<sub>2</sub>
In this work we performed an impregnation of polymethylmethacrylate with carbamazepine
in SC-CO<sub>2</sub> medium. Impregnation was carried out at two temperatures of 75 °C and
105 °C and SC-CO<sub>2</sub> density equal 1.3 of its critical value. In the first stage, in order to
define the kinetic parameters of CO<sub>2</sub> sorption by polymer matrix, we applied high pressure
NMR spectroscopy. Two impregnated polymethylmethacrylate samples were obtained
upon impregnation process and further they were analyzed by Raman spectroscopy and
powder X-Ray diffraction.
Basing on the results of Raman spectroscopy we found that both impregnated samples
contain carbamazepine, at that its concentration in polymethylmethacrylate impregnated
at 105 °C is in ∼2.7 times higher than in polymethylmethacrylate processed at 75 °C. It
was also discovered that carbamazepine does not crystallize in the confinement of polymer
matrix. Its solution in polymethylmethacrylate is formed instead. Moreover, processing
temperature also affects on conformational state of carbamazepine molecules entrapped
into polymer matrix.
doi:10.34984/SCFTP.2020.15.3.007