## 2 Materials and Methods  
Brief Description of the Hydrotreating Unit of the Catalytic Reforming Cracking Unit LG-35-11/300-95  
The unit for catalytic reforming cracking LG-35-11/300-95 consists of 4 blocks, the main of which is a hydrotreating unit and a reforming unit, which in turn have many interconnected technological units. At the same time, the hydrotreating unit is designed to purify straight-run gasoline coming from the primary oil refining unit from organic compounds of sulfur, oxygen and nitrogen, and in the reforming unit, the process of converting naphthenes and paraffin into aromatic hydrocarbons takes place. In the hydrotreating unit, the process of hydrotreating straight-run gasoline from the primary oil refining unit takes place. At the same time, the quality of straight-run gasoline is improved due to the removal of sulfur, as well as other harmful compounds and impurities from their composition, which worsen the operational characteristics of technological equipment and metal units [22; 23]. Thus, the hydrotreating process can reduce corrosion of metal equipment and pollution of the environment and atmosphere. Therefore, the study and improvement of the processes of hydrotreating oil refining on the basis of scientifically grounded methods, for example, methods of mathematical modeling and optimization, is an urgent task of science and practice of oil refining. A brief description of the process flow diagram of the hydrotreating unit of the catalytic reforming unit of the Atyrau refinery shown in Figure 1, is given. Raw materials from the tank farm are fed by the A16 pump for mixing together with the HCG. The mixture of raw materials and HCG is fed to 3 heat exchangers T-1/1-3 connected in series, here, due to the counterflow of carbonated raw materials from the R-1 reactor and the T-3 reboiler, it is heated to a temperature of 260 \({}^{\circ}\)C, then it enters the F-101 hydrotreating furnace. From the F-101 furnace, a mixture of feedstock and gas with a temperature of 300-343 \({}^{\circ}\)C is fed to the hydrotreating reactor R-1, where the feedstock hydrotreating reaction takes place with the participation of catalyst S-12, i.e., the raw material is preliminarily hydrotreated from sulfur, nitrogen and oxygen-containing compounds. The heat of the mixture of unstable hydrogenate, circulating gas from the outlet of the reactor and the heat of reaction of gases with a temperature of 340-420 \({}^{\circ}\)C is used to heat the mixture of raw materials and gas, first in the heat exchanger T-3 of the stripping column C-1, then in the heat exchangers T-1/1-3 [18]. In gaseous form, the products after cooling in refrigerators XB-101 and X-1 to a temperature of 35 \({}^{\circ}\)C are fed to the separator S-1. There HCG is separated from the liquid  
Figure 1: Technological scheme of hydrotreating unit at the catalytic reforming unit of the Atyrau refinery. and for cleaning it from hydrogen it enters the absorber C-2. The gas from the outlet of this absorber passes through the separator S-4, where it is divided into two streams:  
1. Circulating gas, which, after being compressed in the compressors, is fed back to the feedstock hydrotreating system;
2. Excessive HCG from the unit outlet. The liquid phase of the separator S-1, passing through the heat exchanger T-2, is heated to a temperature of 150 \({}^{\circ}\)C and fed to the 7, 9, 23 trays of the stripping column C-1. From the stripping column C-1, from the hydrogenate at a temperature of up to 270 \({}^{\circ}\)C and a pressure of up to 15 atm, sulfuric hydrogen and water are stripped, and light hydrocarbons are removed from the top of the column C-1. After the stripping column C-1, the total composition of sulfur compounds in the hydrogenation product according to the standard should not exceed 0.0005% by weight.