Published February 2010
Supercritical fluids in petrochemistry and oil refining
S.Y.RashidovaSupercritical fluids are the fourth form of aggregative state of the matter, into which many organic compounds are able to pass while achieving certain temperature and pressure. A point, at which this transition occurs, is called critical, and a state of a substance, which is above this point, is called supercritical. Critical point is the point at which the boundary, dividing a liquid and a space, filled with a gas, disappears, and all volume is filled up with milky-white opalescent liquid. At subsequent increasing the temperature it quickly becomes transparent and mobile, consisting of constantly overflowing streams. Though it is like a liquid outwardly, at present in use a special term – supercritical fluid (SCF) – is used. The properties of supercritical fluid may be adjusted by pressure increase. The dissolving ability of a solvent increases sharply, and in the SCF state it has an ability to dissolve organic compounds. Along with this, SCFs processes a high diffusion coefficient, that allows to penetrate into deep layers of a substance. Despite of this phenomenon is known since XIX century, only from the 80s of XX century the development of supercritical technologies began. At present SCF-extraction is widely pharmaceutical and food industries, in radio- and polymer chemistry. In the processes of oil and gas refining the SCF-extraction is used in petrochemistry industry, extraction of mineral deposits, separation processes, synthesis of polymer materials, etc. A development of supercritical technologies is effective in ecology for solving a problem of creation of non-waste technologies in oil processing. The directions, in which the SCF-extraction is used, are deasphalting, demetallization, purification of oily soils, purification of gases, paraffines and oil fractions. CO2 differs by relatively low critical temperature, high recoverability, low viscosity, and it is also non-toxic, environmentally safe, non-flammable, cheap and available. Using the unique properties of CO2 in the supercritical state, in the Institute of Petrochemical Processes of NAS, Azerbaijan, the preparative method of determination of asphaltenes in the petroleum and its heavy residues has been patented. The information about this method and laboratory installation is presented in the published paper of authors. The basis of the process constitutes that raw material – petroleum and its heavy residues were dissolved in the light hydrocarbon solvent, and the process of asphaltene precipitation was conducted in supercritical parameters (T=31 оC, п =7.3 MPa) of carbon dioxide. By small changing the critical parameters of the solvent it is possible to adjust its solubility. The investigations on determining the influence of deasphaltization process basic parameters and demetallization of petroleum and its heavy residue have been conducted. The influence of raw material dilution degree by hydrocarbon solvent, and also pressure and temperature on the process result have been studied. A microelemental composition of a raw material and products of supercritical extraction have been determined. So the use of heavy oil stock processing with the use of supercritical extraction (CO2) allows to remove the disadvantages of an existing method, provides high level of purification from asphaltenes and metals, increases the yield of the product. This method may be recommended for wide usage in oil refining, as an alternative upon preparing the petroleum to processing.
