Vol 11, No 7 (2017)

Sub- and supercritical freons can be successfully used in the bone matrix cleaning process. In the case of freon R22 the duration of bone matrix cleaning significantly decreases as compared to the same procedure with supercritical carbon dioxide. Freons R23, R134 and R407c which do not contain chlorine atoms are almost ineffective in this process.

The features and mechanisms of microcrater formation in optical silicate glass by laser-induced backside wet etching (LIBWE) are determined in a wide range of energy densities (Φ) from 4 to 10³ J/cm² for laser pulses of 5 ns length and 1 kHz repetition rate. The existence of two different mechanisms of laserinduced microcrater formation is revealed: (i) chemical etching in supercritical water (SCW), and (ii) cavitation. At Φ > 10² J/cm² irregular craters of 1–20 μm in depth with rough walls and distinct cracks around microcrater are formed testifying that in such mode (“hard”) laser induced cavitation plays a dominant role in glass removal. At Φ < J/cm² neat glass craters with smooth walls are formed, their size and shape are easily reproducible, cracks are not formed, and the processing area is limited to the laser spot area. In this mode (“soft mode with active cavitation”), a microcirculation of water is stimulated by cavitation without causing undesirable shock breakage. The latter is achieved thanks to the fast removal of glass etching products by microcirculation, and the inflow of “fresh” etchant (SCW) to the glass surface in the vicinity of the formed microcraters. Such mode is optimal for highly controlled laser microstructuring of glass and other optically transparent materials.

A study of esterification process of dicarboxylic acids with 2-ethylhexanol under supercritical conditions is presented. It was shown that the esterification reaction can be carried out without a catalyst. The esters formed with greater rate and selectivity.

The general hydrodynamic equations of a mathematical model for supercritical fluid extraction are derived within the framework of the continuum mechanics approach. The shrinking core concept is used to describe the mass transfer on the solid-liquid interface. The complete system of macroscopic differential mass-balance equations is reduced to a one-dimensional approximation and accounts for the axial dispersion effect. Correlation formulas available in the literature are used to calculate the axial dispersion coefficient for the conditions of supercritical CO₂ filtration. The effect of axial dispersion on the characteristics of the macroscopic process is analyzed for the typical laboratory-scale extraction conditions in the framework of the suggested model. The numerical simulations demonstrate that the difference between the values of the current mass of accumulated extract calculated in terms of the complete approach, which accounts for the axial dispersion, and the one related to the simplified model (in which the axial dispersion is neglected), is less than 10%. The same comparison is made for the outlet concentrations of the target compounds; the difference reaches 200%.

The specific features of the transformation of risperidone polymorphs as a result of micronization and encapsulation into aliphatic polyesters (polylactides and polylactoglycolide) have been studied using supercritical (SC) carbon dioxide. It has been shown that the micronization of risperidone, which originally is polymorph A, via the rapid expansion of supercritical solutions (RESS) and the supercritical antisolvent (SAS) precipitation leads to its crystallization in less thermodynamically stable polymorph B. This transition is complete for SAS and only partial for RESS. When these micronized samples are encapsulated into polylactides and polylactoglycolides via the formation of particles from gas-saturated solutions (PGSS) and monolithization with further cryogrinding (MCG), risperidone polymorph B is partially converted back into polymorph A. At the same time, the micronization of initial risperidone polymorph A via cryogrinding and its further PGSS and MCG encapsulation into polylactides or polylactoglycolides does not result in any change in the polymorphic state of risperidone, and it always remains in initial polymorph A.

The fatty acid composition of arctic brown algae was studied using supercritical (SC) fluid extraction. A method for fractionating the SC extract based on the differences in the solubility of its components (fatty acids, polyphenols) was proposed. The composition and biological activity of the fractions were studied.

The effect of supercritical water and pyrite on the transformations of propylene upon the uniform heating (1.5 K/min) of reagents to 718 K is studied. The products are analyzed by IR and ¹H NMR spectroscopy, mass-spectrometry and gas chromatography/mass-spectrometry. It is established based on the temperature dependences of the pressure of reagents that the addition of pyrite in the absence of water gives rise to a decrease in the starting temperature of propylene oligomerization. In the absence of pyrite, the addition of water suppresses propylene oligomerization. A synergetic effect of supercritical water and pyrite on the degree of conversion of propylene is revealed. It is shown that hydrogen sulfide, thiols, and methyl-derivatives of thiophene are formed in the presence of pyrite, as well as the yield of aromatic and polyaromatic hydrocarbons increases. The mechanisms of the observed processes are discussed.

The kinetics of inactivation of Escherichia coli under the action of pressurized gases (CO₂, O₂ and N₂) is studied. It is demonstrated that the concentration of surviving cells decreases by seven orders of magnitude in the case of CO₂ and less than by one order in the case of O₂ and N₂. An assumption about how bacterial cells are inactivated in the presence of CO₂ is proposed.

Cytotoxicity and in vitro degradation rate of porous matrices based on lactide and ε-caprolactone copolymers formed via supercritical foaming are determined. A high biocompatibility of materials obtained by the above method is demonstrated.

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.