The determination of the parameters of sub- and supercritical extraction of plant raw materials

The extraction of biologically active substances by carbon dioxide from various plant raw materials (amaranth seeds, Sophora japonica flower buds, Stephania rotunda stems, and Stevia rebaudiana leaves) was studied at sub- and supercritical parameters. A laboratory unit for the extraction of plant raw materials by liquefied gases and supercritical fluids at 5–35 MPa pressures and 285–350 K temperatures was developed. The maximum yield of the extracted substances from plants specified was obtained at temperature and pressure exceeding the critical parameters of CO₂ (320–330 K, 28–30 MPa).     

Stepwise synthesis of fine crystalline Ce-doped yttrium aluminum garnet in water medium in subcritical and supercritical conditions

In this paper the continuous stepwise method of a production of fine crystalline yttrium aluminum garnet doped with cerium (YAG: Ce³⁺) in supercritical water fluid (SCWF) are represented. The synthesis was carried out in water medium in two stages: first in subcritical conditions and then in an atmosphere of supercritical water fluid. The stoichiometric mixture of yttrium oxide and aluminum hydroxide in a water solution of cerium nitrate was maintained the certain time at 280°C and under vapor water pressure 6.3 MPa. Then temperature and pressure were risen up to a supercritical condition (T = 392–400°C, P_{H2 O}P_{H_2 O} = 22 MPa). The concentration of cerium ions in reaction medium was changed in the interval 0.012–0.706 wt %. The products, obtained on various stages of synthesis, were investigated by physical-chemical methods. During the first stage, the crystals of boehmite and yttrium hydroxide under hydrothermal conditions were arising, and eventually poorly formed YAG: Ce³⁺ were appearing. At this stage, the diffusion of cerium ions into intermediate products takes place. Because of this, at the second step of synthesis, in supercritical conditions, YAG: Ce³⁺, phosphor with high luminescence intensity at 530 nm, was obtained. In supercritical conditions well-faceted crystals of 0.5–3.0 μm with rhombododecahedral habitus were produced.     

Evaluation of the Efficiency of Supercritical Carbon Dioxide Extraction for <Emphasis Type="Italic">Pelargonium graveolens</Emphasis> L’Her Essential Oil Production

The optimal conditions (40°С, 16 MPa, process duration of 30 min) for the extraction of Pelargonium graveolens L’Her essential oil using supercritical (SC) carbon dioxide are determined. GC-MS analysis shows higher concentrations of the target components (e.g., citronellol, geraniol) in the product in comparison to the oil obtained using a traditional method (steam distillation). Additional components, such as camphene, sabinene, and others are also present in the product obtained by the extraction with SC-CO₂.     

Development of technology for large-batch treatment of paper-based information carriers with carbon dioxide ensuring their long-term preservation

A method for nonaqueous neutralization of various brands of paper with alcohol solutions of magnesium methoxide and methoxycarbonate is investigated. The minimum level of alkali reserve (100–150 mg-eq/kg) required for a prolonged preservation of the properties of paper is determined. A method for paper treatment with a neutralizing solution containing Freon, alcohol, and a neutralizing agent and saturated with subcritical carbon dioxide is proposed and experimentally tested. It is shown that, under certain conditions, supersaturation with carbon dioxide leads to the recrystallization of neutralizing agent and its deposition in the pores of paper in the form highly dispersed particles. The method makes it possible to adjust the alkali reserve (AR) level by varying the concentration of neutralizing agent and the degree of saturation of the solution with CO₂. The possibility of using supercritical CO₂ as a solvent and transport medium for neutralizing agent (magnesium methoxycarbonate) to treat paper-based printings is examined. The optimal regimes of dissolution of neutralizing agent in supercritical CO₂ and of paper treatment were selected, and the working parameters in the reactor and the ratio between the components at which the required level of the AR in paper is achieved are determined. The proposed methods for large-batch neutralization of the acidity of paper provide the minimum required AR level capable of ensuring the preservation of paper for a long period (up to 100 years) under conditions of natural aging with minimum amounts of expensive organic solvents, which indicates a high competitiveness of the proposed technologies of large-batch treatment of printed materials.     

Sorption and Diffusion of Supercritical Carbon Dioxide in a Biodegradable Polymer

A gravimetric method was used to study the sorption and diffusion of supercritical carbon dioxide in a temperature range from 40°C to 80°C and a pressure range from 8.0 to 18.0 MPa in a biodegradable polymer, namely poly(butylene adipate-co-terephthalate) (PBAT). The PBAT presented Fickian behavior and Fick's diffusion model was applied to determine the amount of carbon dioxide present in the samples after a predetermined exposure time as well as the diffusion coefficients. The variations of diffusion coefficients of CO₂ for the sorption under supercritical conditions and desorption at ambient conditions as well as equilibrium sorption amounts of CO₂ with variations of pressure and temperature were determined and compared.     

High-temperature vibrational densitometer for high-pressure aggressive media

High-temperature vibrational densitometer for chemically active media was developed. The principle of operation of the densitometer is based on recording and analyzing the natural frequency of a U-shaped high-pressure capillary filled with the test medium. The placement of the capillary in a thermostat capable of maintaining its temperature to within ±0.1°C makes it possible to measure the density and study the phase behavior of aggressive media over pressure and temperature ranges of 0.1–50 MPa and 20–500°C, respectively. Measurements of the carbon dioxide density with the densitometer developed at temperature below, near, and above its critical point (31°C), as well as water density measurements at temperatures up to 375°C demonstrated good agreement with the data from the NIST (National Institute of Standards and Technology) interactive database. The density of a methanol-water mixture was measured at temperatures up to 300°C.     

Separation of low-molecular-weight fractions of ultrafine polytetrafluoroethylene with supercritical carbon dioxide

The separation of low-molecular-weight fractions of FORUM® ultrafine polytetrafluoroethylene (UPTFE) in supercritical carbon dioxide (SC-CO₂) was studied under static conditions. The experiments were performed over temperature and pressure ranges of 318–383 K and 10–70 MPa, respectively. Over the entire pressure and temperature ranges covered, a behavior typical of solid substance-SC-CO₂ systems was observed: as the pressure and temperature of the solvent increased, so did the concentrations of low-molecular-weight UPTFE fractions in it. The experimental data were interpreted within the framework of three models establishing a relationship between the solubility of a substance with the supercritical fluid density, those proposed by Chrastil, Bartle, and Mendez-Santiago. The experimental data were closely described by the Bartle and Mendez-Santiago models.     

Thermal conductivity of ozone-safe C10M1 refrigerant in liquid and gaseous phases

Thermal conductivity of ozone-safe refrigerant C10M1 in liquid (303.9–342.4 K, 1.23–4.257 MPa) and gaseous (324–398.15 K; 0.672–2.107 MPa) states was studied by the methods of high-frequency thermal waves and coaxial cylinders. The estimated measurement errors for the temperature, pressure, and thermal conductivity are ±0.02 K, ±1.5 kPa, and ±1.5–2.5 %, correspondingly. Approximation dependencies for thermal conductivity were obtained over the studied range of temperatures and pressures as well as on the dew and bubble lines. It is shown that thermal conductivity in the liquid state is additive relative to mass concentrations of components. The work was financially supported by the Russian Foundation for Basic Research (grant No. 04-02-16355).     

Fabrication of two types of one-dimensional Si–C nanostructures by laser ablation

Two types of one-dimensional (1D) nanostructures—amorphous silicon carbide (SiC) nanowires, 5–30 nm thick and 0.5–2 μm long, and carbon nanotubes (CNTs) filled completely with crystalline SiC nanowires, 10–60 nm thick and 2–20 μm long—were synthesized by the laser ablation of carbon-silicon targets in the presence of high-pressure Ar gas up to 0.9 MPa. All the CNTs checked by transmission electron microscopy contained SiC, and no unfilled CNTs were produced. We discuss the growth of the two nanostructures based on the formation of molten Si–C composite particles and their instabilities leading to the precipitation of Si and C.     

Solubility of ammonium palmitate in supercritical carbon dioxide

The solubility of ammonium palmitate in supercritical carbon dioxide is studied in the dynamic regime at 308.15–333.15 K and 10.0–35.0 MPa. Experimental data are described in the framework of the Peng–Robinson equation of state.     

Thermal quenching of photoluminescence of Eu3+ ions in an Eu(fod)3 complex

We have studied the photoluminescence (PL) spectra of Eu³⁺ ions in the complex Eu(fod)₃ (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadione) and also in polymers doped with Eu(fod)₃ with the help of supercritical carbon dioxide. We have established that in the temperature range 20°C–100°C, we observe thermal quenching of the photoluminescence of Eu³⁺ ions, and this quenching is most efficient in polycrystalline Eu(fod)₃ powder and Eu(fod)₃-doped polypropylene. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 315–319, May–June, 2006.     

Autoignition of ethylene in shock waves

The delay time of ignition of various C₂H₄-O₂-Ar mixtures behind reflected shock waves were measured at temperatures of 1090–1520 K and a pressure of 0.65 ± 0.05 MPa. A kinetic scheme of the ignition of ethylene based on the known rate constants of the key elementary reactions was developed. The scheme satisfactorily describes our own and published data on the ignition of ethylene in shock waves over wide ranges of temperature (1100–2400 K), pressure (0.006–0.64 MPa) and ethylene (0.1–17.4 vol %) and oxygen (0.6–20.7 vol %) concentrations.     

Low temperature improvement method on characteristics of Ba(Zr0.1Ti0.9)O3 thin films deposited on indium tin oxide/glass substrates

To improve the electrical properties of as-deposited BZ1T9 ferroelectric thin films, the supercritical carbon dioxide fluid (SCF) process were used by a low temperature treatment. In this study, the BZ1T9 ferroelectric thin films were post-treated by SCF process which mixed with propyl alcohol and pure H₂O. After SCF process treatment, the remnant polarization increased in hysteresis curves, and the passivation of oxygen vacancy and defect in leakage current density curves were found. Additionally, the improvement qualities of as-deposited BZ1T9 thin films after SCF process treatment were carried out XPS, C–V, and J–E measurements.     

Some Thermodynamic Characteristics of Paracetamol Dispersing with the SEDS Method

The solubility of paracetamol in supercritical carbon dioxide and its mixtures with acetone is experientially studied. The isobaric heat capacity of paracetamol and the systems “paracetamol–CO₂” and “paracetamol–acetone–CO₂” is measured under pressures 7–29 MPa and temperatures 303–523 K. The results of paracetamol dispersing using the SEDS method (Solution Enhanced Dispersion by Supercritical Fluids) are presented.     

Fuel quality and operational issues for polymer electrolyte membrane (PEM) fuel cells

Polymer electrolyte membrane (PEM) fuel cells are susceptible to degradation due to the catalyst poisoning caused by CO present in the fuel above certain limits. Although the amount of CO in the fuel may be within the permissible limit, the fuel composition (% CO₂, CH₄, CO and H₂O) and the operating conditions of the cell (level of gas humidification, cell temperature and pressure) can be such that the equilibrium CO content inside the cell may exceed the permissible limit leading to a degradation of the fuel cell performance. In this study, 50 cm² active area PEM fuel cells were operated at 55–60 °C for periods up to 250 hours to study the effect of methane, carbon dioxide and water in the hydrogen fuel mix on the cell performance (stability of voltage and power output). Furthermore, the stability of fuel cells was also studied during operation of cells in a cyclic dead end / flow through configuration, both with and without the presence of carbon dioxide in the hydrogen stream. The presence of methane up to 10% in the hydrogen stream showed a negligible degradation in the cell performance. The presence of carbon dioxide in the hydrogen stream even at 1–2% level was found to degrade the cell performance. However, this degradation was found to disappear by bleeding only about 0.2% oxygen into the fuel stream.     

Synthesis of silver nanocomposites by SCF impregnation of matrices of synthetic opal and Vycor glass by the Ag(hfac)COD precursor

Silver-containing nanocomposites were prepared by impregnating Vycor glass (a pore diameter of 4 nm) and synthesized opal matrices (an interstitial void size of 40 nm) with cyclooctadiene complex of silver hexafluoroacetylacetonate (Ag(hfac)COD), a silver precursor, dissolved in supercritical carbon dioxide and were examined by optical absorption spectroscopy, atomic force microscopy, and electron spin-resonance spectroscopy. It was demonstrated that the absorption spectra of Vycor glass and opal matrices impregnated with Ag(hfac)COD molecules and subjected to thermal treatment in air at temperatures above 50°C exhibit plasmon resonances characteristic of Ag nanoparticles at 420–430 nm. The peculiarities of the plasmon resonance band for both types of samples were attributed to the morphology of the pore space in which silver particles are formed. Paramagnetic Cu(hfac)₂ molecules (copper hexafluoroacetylacetonate) were used as a spectroscopic probe for estimating the distribution of the precursor in the pores of Vycor glass and opal matrices during supercritical fluid impregnation.     

Influence of impurities on the low-temperature deformation of nanocrystalline copper

The influence of ZrO₂ particles on the low-temperature deformation of nanocrystalline copper produced by strong plastic deformation is investigated using equichannel angular pressing. A comparison is made between the deformation characteristics in tension and compression in the temperature range 4.2–400 K, measured for copper and the composite Cu:0.3 vol. % ZrO₂. It is shown that within 4.2–200 K the yield point σ _sm of the composite is higher than that for copper, attaining 680 MPa at 4.2 K, then the yield points are close in value up to room temperature, and diverge again as the temperature is raised. Possible causes of the dissimilar influence of an impurity on the strength and plasticity characteristics of nanocrystalline copper in various temperature intervals are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1639–1641 (September 1998)     

Experimental study of pressure and density of saturated and superheated vapor of refrigerant R-236ea from 20 to 150 °C

The saturation pressure, pressure and density of superheated vapor of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea, R-236ea) were studied by an isochoric piezometer within the temperature range of 294–423 K up to the pressure of 4.0 MPa. The uncertainties of temperature, pressure, and density measurements were estimated as ±20 mK, ±1.5 kPa, ±(0.1–0.2) %, and ±(0.1–0.2) %, correspondingly. The purity of studied samples was 99.68 mass %. The obtained experimental data are shown as tables and analytical equations. Coefficients of the virial state equation were calculated for R-236ea on the basis of these data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-02-16355).     

Mass-spectrometric analysis of diffusion and solubility of helium in cerium-gadolinium ceramics with a submicrocrystalline structure

Diffusion and solubility of helium in Ce_0.8Gd_0.2O_{1.9 − δ} ceramics (δ = 0, 0.015) with a submicrocrystal structure are studied by thermodesorption of helium from preliminarily saturated (in the gas phase) crystals at temperatures of 613 and 673 K in the saturated pressure range 0–21 MPa. It is shown that, in this ceramics (δ = 0), the defect-trap diffusion mechanism operates. The main positions for dissolution are neutral anion vacancies formed as a result of thermal dissociation of impurity-vacancy complexes and saturated up to ∼1 × 10¹⁹ cm⁻³ at P = 6 MPa and T = 673 K. The dissociation energy of the complex and the energy of helium dissolution in the neutral anion vacancy are estimated at ∼2 eV and below −0.3 eV, respectively.     

Treatment of Cotton Fabrics by Ammonium Palmitate in a Supercritical CO<Subscript>2</Subscript> Medium

Experimental results on the solubility of ammonium palmitate as a potential fabric water-repellent agent in supercritical carbon dioxide (SC-CO₂)—pure and modified with acetone and dimethyl sulfoxide—are presented. The measurements are performed at temperatures 318.2 and 328.2 K in the pressure range from 10.0 to 32.5 MPa in a dynamic regime. The experimental solubility data are described using the Peng–Robinson equation of state. The results of treatment of various types of cotton fabrics by ammonium palmitate in SC-CO₂ are presented. The contact (wetting) angle of the treated samples is determined and the increase in their hydrophobicity is demonstrated.