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The IMPA-ModFD-2 model of the feedstock mixture for mathematical modeling of selective treatment of deasphalted product was developed and combined with laboratory modeling on real mixtures and allows using the advantages of both methods for developing new and improving existing processes and equipment. A general description of the mixture and its structural-group composition are presented. A special feature of the mixture is the presence of sulfur-containing components. This allows calculating one of the key indexes in treatment of deasphalted product -the sulfur content, which is significantly limited in selective treatment raffinates. The results of the mathematical modeling shows the acceptable agreement with the analytical data.Extraction treatment of oil distillates and deasphalted products with selective solvents from polycyclic aromatic hydrocarbons and naphthene-aromatic hydrocarbons with short side chains and resinous, organosulfur, and organometallic compounds is the basic manufacturing process for production of petroleum oils. Such very important performance properties of lube oils as the viscosity-temperature properties and stability against oxidation are formed in this process.One problem in obtaining high-quality mineral oils is related to the increase in the proportion of refining of high-sulfur crudes with limitation of the sulfur content in the raffinates from selective treatment of highly viscous distillates and deasphalted products. The development of new and optimization of existing selective treatment technologies by mathematical modeling will solve this problem to a great degree. 153Determining the composition of the feedstock is a first and important step in mathematical modeling. Oil distillates have a complex group chemical composition. They contain a large number of components, many of which cannot be identified. For this reason, in modeling the process, model mixtures [1] with a set of characteristic components are usually used as the feedstock. The results of modeling the process are directly dependent on the accuracy of the composition of the model mixture.Modern analytical equipment was used to determine the group chemical composition of the deasphalted product: a Gradient liquid chromatograph, a G-800 gas chromatograph, an instrument for determining the elemental composition from Carlo Erba (Italy), a Trio-1000 chromatograph-mass spectrometer from VG (Great Britain). The basic classes of hydrocarbons of n-and isoparaffins, naphthenes, alkylbenzenes, naphthalene derivatives, phenanthrenes, and resins, organosulfur and other compounds were taken into consideration. Each class of hydrocarbons was represented by the individual hydrocarbon defining it, whose empirical formula was determined from experimental data on the molecular weight of the hydrocarbons in the corresponding group.The method of determining the group chemical composition of complex multicomponent systems includes [2]:

In 2003, the problem of increasing takeoff of residual raffinate while preserving its quality and reducing power consumption in the selective treatment section of the combined KM-2 unit for production of lube oils and waxes was set before Slavneft'-Yaroslavnefteorgsintez Co. The bid of IMPA Engineering Ltd. -a specialized enterprise for development of modern extraction equipment whose efficiency was confirmed by experience in industrial operation -was selected to solve this problem [1].After examining operation of the extraction unit in this section, IMPA Engineering developed a plan for modernizing the extraction tower and fabrication and installation of internals and master assembly. Extraction treatment of deasphalted product with N-methylpyrrolidone is conducted in the tower (23.7 m high, 2.4 m in diameter). Inspection of operation of the tower before and after modernization included generalizing the process parameters in a wide feedstock charge range -from 12.5 to 17.5 m 3 /h -and laboratory studies of selected industrial samples.Several operating regimes that differed by the feedstock charge and quality of the treated feedstock were distinguished (Table 1). With an increase in the charge, the overall unit load of contacting phases increases so that the efficiency of their reaction increases and the ratio of solvent to feedstock decreases. The quality of the feedstock additionally affects the tower operating indexes: to obtain raffinate of standardized quality -carbon residue of 0.40-0.45 wt. % from deasphalted product with high carbon residue -from 1.14 to 1.42%, the ratio of solvent to feedstock must be increased from 1.14 to 1.42 %.Laboratory modernization of selective treatment of the feedstock was conducted with the psendoreflux method in [2,3]. The essence of the method consists of varying the number of theoretical treatment plates to determine its effect on the quality indexes and product takeoff. The efficiency of operation of the tower in