Vol 11, No 8 (2017)

The process of wood drying is studied in supercritical (SC) CO₂ and SC-CO₂ containing 5 vol % ethanol at temperatures of 323, 343, and 353 K and pressures of 10, 20, and 30 MPa. It is established that 40–87% of moisture is removed from wood in the first cycle of drying. An increase in the duration of the decompression stage of the drying process decreases the number of cracks in the wood samples. The solubility of propiconazole is studied in SC-CO₂ at 323, 343, and 353 K in the pressure range of 10–30 MPa using a dynamic method. Rather high saturation concentrations of (3–5) × 10^–3 mol/mol CO₂ are obtained, which indicates the potential benefits of using SC-CO₂ as a solvent in wood impregnation with propiconazole. Continuous impregnation is achieved when impregnating wood with propiconazole from SC-CO₂. The impregnation efficiency increases with increasing pressure and duration of the process.

The composition of oily fractions (OFs) formed by the Kashpir oil shale conversion in a flow of water vapor and supercritical water under uniform heating from 300 to 550°C is studied by means of gas-chromatography/ mass-spectrometry, IR, and 1H NMR spectroscopy. The maximum yield of the oil fraction is observed at 360–390°C. Alkanes, alkenes, and alkyl-derivatives of naphthalene and benzothiophene are the major components of the OFs formed below 440°C. A significant predominance of even alkanes and alkenes over their odd homologies is detected above 440°C. The peculiarities in the varying of the content of specific groups and individual polyaromatic substances are discussed.

The conversion of high-sulfur oil shale in a flow of supercritical benzene under pressure of 10 MPa and temperatures up to 400°C is studied. The composition of the formed liquid products is characterized by the methods of IR- and ¹H NMR-spectroscopy, structural group analysis, and chromato-mass spectrometry. It is shown that the content of resin and asphaltene compounds in the pyrolyzates decreases with the increase of temperature and the fraction of aromatic fragments in their composition increases, while the fraction of aliphatic fragments decreases. The amount of polar components decreases in the oily fraction. The compounds identified in the oils are represented by normal and branched alkanes; alkenes; saturated and unsaturated naphthenes; and mono-, bi-, tri-, tetra-, and pentacyclic aromatic hydrocarbons; as well as compounds of thiophene-, benzo-, dibenzo-, and naphthothiophene series, aliphatic ethers, and ketones.

The work is devoted to exploring the possibility of using supercritical fluids as media for modification of polymers offering promise for production of gas-separation membranes with the goal to improve selectivity towards CO₂. The possibility is demonstrated for introduction of fragments of quaternary ammonium salts into the structure of poly(4-methyl-2-pentyne) with the help of a two-stage process: bromination of the initial polymer with N-bromosuccinimide followed by the addition of the tertiary amine—N-butylimidazol— conducted in supercritical fluids as a medium. The use of trifluoromethane as the reaction medium provides the highest degree of modification of the brominated polymer with the amine. The polymer produced under the optimized conditions demonstrates a threefold increase of the calculated selectivity of separation of CO₂ and N₂ in comparison with the initial poly(4-methyl-2-pentyne).

The method of thermoplasmonic laser-induced backside wet etching (TPLIBWE) is applied for effective and well-controlled microstructuring of sapphire. The method is based on the generation of highly absorbing silver nanoparticles in the course of the pulsed-periodic laser irradiation. The silver nanoparticles are formed as a result of the reduction of a water-dissolved precursor, AgNO₃. The process of sapphire etching occurs via the formation of supercritical water at ultrahigh temperatures and pressures (which significantly exceed the critical values for water) and the formation of silver nanoparticles at the sapphire/water interface as a result of the absorption of laser radiation. The mechanism of TPLIBWE is considered and the etching rate, which reaches ~100 nm/pulse, is determined. The formation of aluminum nanoparticles, which indicates a deep destruction of Al₂O₃ as a result of TPLIBWE, is observed.

The process of carbon dioxide supercritical fluid extraction (SFE) of secondary metabolites from the lichen of Cladonia genus is studied. The yield of solid extract during SFE with carbon dioxide is significantly higher than during the extraction with acetone, ethanol, and petroleum ether on the Soxhlet apparatus. The maximum content of the target component—usnic acid (UA)—in the extract (91%, yield—2.5% of absolutely dry raw material) is obtained under pressure of 35 MPa, temperature 40°C, and duration of the process of 40 min. Introduction of cosolvents (acetone, ethanol, methylene chloride) to carbon dioxide increases the yield of the target product to 3%.

Supercritical phase equilibria in the ternary system K₂SO₄–KOH–H₂O at 420–500°C and up to 130 MPa pressure with binary boundary subsystems of different types are studied. The binary subsystem of type 1 features no critical phenomena in saturated (l = g) aqueous solution and no phase separation (l1–l2) (KOH–H₂O); the binary subsystem of type 2 is characterized by immiscibility of the liquid phase and has two critical end-points \(p(g = l-_{S_{K_{2}SO_{4}}})\) and \(Q(l_{1} = l_{2}-_{S_{K_{2}SO_{4}}})\) in saturated aqueous solution (K₂SO₄–H₂O). The ternary system has two three-phase equilibria (g–l–s) and (l1–l2–s), separated by a two-phase supercritical fluid region \((fl-_{S_{K_{2}SO_{4}}})\), and two types of monovariant critical curves \((g=l-_{S_{K_{2}SO_{4}}})\) and \((l_{1}=l_{2}-_{S_{K_{2}SO_{4}}})\). The three-phase regions approach each other upon temperature increase up to the point where the two-phase supercritical equilibrium disappears, and the two mentioned monovariant critical curves are joined into a double homogeneous critical point \((g=l-_{S_{K_{2}SO_{4}}} \leftrightarrow l_{1} = l_{2}-_{S_{K_{2}SO_{4}}})\) at maximum temperature ~445°C and 51–52 MPa.