Vol 12, No 8 (2018)

The mechanism of synthesis of fine-crystalline corundum from aluminum hydroxide under induced nucleation conditions in a supercritical water fluid at 400°C and initial pressure of 26.4 MPa followed by exposure in the synthesis medium was studied. The crystal size distribution was analyzed by electron microscopy. The use of the lognormal function to describe the crystal size distribution of the synthesized corundum particles was substantiated. The possibility of using the lognormal particle size distribution function and the time dependence of its parameters to reveal the routes of product formation was analyzed. The dimensional spectrum of microcrystals has four components, whose appearance is associated with different routes of product formation. The number of distribution components remains unchanged during prolonged exposure, but their average characteristics have different time dependences. The mass redistribution during recrystallization, generally leading to a decrease in the average crystal size, is explained by differences in the crystal structure mobility of different components. It was concluded that the states of corundum in the newly formed crystals and in the overgrown layer on the particles of the inducing additive are different.

The thermal stability of 1,4-dioxane below and above its critical temperature (300–500°C) and at different fluid densities was studied. It was established that at 300–350°C dioxane is thermally stable during 80–100 min; at higher temperatures during this time, uncontrolled growth of pressure begins in the system due to the thermal cracking of dioxane. The analysis of he liquid and gas phases that remained in the reactor after heat treatment of dioxane showed the presence of a wide range of products.

A study was made of the applicability of supercritical antisolvent precipitation to producing microparticles of the antiasthmatic drug salbutamol sulfate that are suitable for manufacturing the drug in inhalation dosage form. Depending on the salbutamol concentration in the initial solution, the flow rate of the solution, and pressure, either spherical or needle-like particles 0.7–8.5 μm in size form. The dependence of the average particle size on the salbutamol concentration in the initial solution is nonmonotonic. The conditions were determined under which the obtained salbutamol particles meet the shape and size requirements for fabrication of inhalation dosage forms.

The structure and morphology of fine-crystalline barium titanate synthesized in a subcritical water fluid at 230°C and 2.9 MPa were studied. Barium oxide, barium hydroxide octahydrate (Ba(OH)₂ · 8H₂O), and two modifications of titanium oxide (rutile and anatase) were used as starting reactants. Relationships between the composition and properties of the reactants and the characteristics of the product (barium titanate) were revealed. They indicate that the product structure in the subcritical water is formed via a solidphase mechanism.

Selective solvation of ortho-hydroxybenzoic, meta-hydroxybenzoic, para-hydroxybenzoic, protocatechal, gallic, lilac, para-coumaric, and caffeic acids with a polar cosolvent (methanol) in supercritical carbon dioxide was studied at 318 K at a density of 0.7 g/cm³ and a methanol concentration of 3.5 mol % with conventional molecular dynamics. We studied the localization of a cosolvent in the nearest environment of a solute, the formation of cosolvent clusters around the solute, and the number and nature of hydrogen bonds between molecules of the solute and cosolvent. We also considered the structural features of hydrogen-bound complexes associated with a molecular structure of a solute (the number and the arrangement of hydroxyl groups, the substitution of hydroxyl hydrogen atoms with methyl moieties, and the presence of an ethylene group).

The process of saturation of high-density polyethylene and polyethylene terephthalate with suband supercritical freons and supercritical carbon dioxide was investigated for the first time. The subcritical freon R22 was shown to be absorbed by these polymers in much larger amounts compared to subcritical freon R410a, as well as supercritical R23 and carbon dioxide, which makes it promising for use in the processes of impregnation and sterilization of polymers.

A small-volume cyclone separator with changeable extract collection reservoirs for supercritical fluid extraction has been designed. A method for manufacturing the designed separator by 3D-printing from an available polymer is proposed. It is shown that the designed small-volume separator allows a greater extract recovery compared to a standard large volume cyclone separator in supercritical fluid extraction.