Improvement of the demercaptanization process based on kerosene production technology

Introduction. Natural gas in the Republic of Uzbekistan is the main source of energy of the population and industry. For this reason, in order to ensure safety in gas networks, special odorants are added to natural gas – odorizers. An analysis of the literature revealed that the country has a number of unresolved problems, although certain work has been carried out in this direction.First of all, odorants are mainly imported from Russia and other countries. For example, tert-butyl mercaptan and dimethyl disulfide substances are used a lot, but their cost is high and requires additional costs for the country's economy. At the same time, due to the fact that these substances contain sulfur, their release into the atmosphere causes environmental problems. This issue is considered very relevant at a time of increasing environmental standards. [1] First of all, odorants are mainly imported from Russia and other countries. For example, tertbutyl mercaptan and dimethyl disulfide are widely used, but their price is high and requires additional costs for the country's economy. At the same time, since these substances contain sulfur, “Фан ва технологиялар тараққиёти” Илмий–техникавий журнал №6/2025 77 Химия и химические технологии their release into the atmosphere causes environmental problems. This issue is very relevant at a time when environmental standards are becoming stricter. A solvable problem and a statement of the problem. Sulfur-containing organic compounds, including mercaptans, also pose serious environmental problems when they enter the environment. Most people encounter xenobiotics like mercaptans in their daily lives when using natural gas. Natural gas is odorless and colorless, making it difficult to detect in the event of a leak. Therefore, before being supplied to consumers, the gas is odorized at gas distribution stations (GDS) with mercaptans, disulfides, or other compounds. Due to the strong adsorption of mercaptans on various surfaces, they are firmly and permanently retained, causing a persistent unpleasant odor. Currently, organic sulphur compounds (components of formerly applied coal gases) are used as odorants in most countries. This solution ensures that the resulting smell is correctly identified as the “gas smell”. The most widely used sulphur compounds represent the following groups: [1] 1. alkyl mercaptans: a. ethyl mercaptan (ethanethiol) C2H6S, b. n- and iso-propyl mercaptans (1- and 2-propanethiol), C3H8S; c. tert-butyl mercaptan (2-Methyl-2-propanethiol) TBM, C4H10S 2. alkyl sulphides a. diethyl sulphide, DMS, C2H6S, b. diethyl sulphide, C4H10S, c. methylethyl sulphide C3H8S 3. cyclic sulphides a. tetrahydrothiophene, C4H8S. The bulk of sulfur-containing compounds is concentrated in light fractions: gasoline and diesel (Table 1). According to their chemical composition and structure, they are sulfide-type compounds with aliphatic and cyclic radicals. Free sulfur, hydrogen sulfide, low molecular weight mercaptans, and disulfides were also found in small amounts in some fractions. Sulfur accumulates in fractions as a result of the oxidation of hydrogen sulfide, disulfides as a result of the oxidation of mercaptans. [2; 3]. Depending on the presence of mercaptans, oils are divided into mercaptan-containing and mercaptan-free. Mercaptans are mainly concentrated in light fractions of oil, where their amount ranges from 40-50% to 70-75% of the total amount of all sulfur-containing compounds in the fraction. With an increase in the boiling point of the fraction, their amount decreases sharply, and in the fraction boiling at temperatures above 3000C they are almost absent. Currently, more than 50 different mercaptans containing from 1 to 8 carbon atoms in their molecules have been isolated. Of these, more than 40 are alkylthiols, 6 cycloalkylthiols and thiophenol. The bulk of the demerkaptanning process takes place in the "FIBER-FILM" section of the MERICAT II system. Under the condition of the MERICAT process, the micror of the active catalyst solution in the caustic flow in a circular motion to accelerate oxidation reactions is 200 weight.RRM level retention is required. Approximately 0.16 kg (0.68 liters) of the active catalyst must be added every 24 hours through a 12 ms 04 addition mixer. Usually the caustic moves from the lower part of the capacity 12d 01 to the upper part of the contactor 12 ms 01, where it enters into dialogue with kerosene, which contains air [3]. As can be seen from this table, the indicators of the raw materials that will be required for the demercaptation of kerosene are mentioned. Analysis of the experiment and the results obtained. A resiclated solution of kerosene and caustic oxidation catalyst containing air simultaneously flows down through the contact apparatus (contactor), where acidic compounds (naphthenic acids, hydrogen sulfide and mercaptanes) are diffused into the aqueous phase and react with sodium hydrooxide to form sodium sulfide, sodium naphthenate and sodium Mercaptide. “Развитие науки и технологий” Научно–технический журнал №6/2025 78 Кимё ва кимёвий технологиялар Table 1 Description of chemical composition, reagents, catalysts, organic materials, polymer oils, materials used in production Mandatory quality indicator name for control The value of the indicator according to the regulatory document Definition of a regulatory document Naming of raw materials, materials, products Unit of measurement Scope of application 1. Density in 20oS kg/m3 Not less than 775 КSt 16472899-003:2008 0S 1500S 1650S 1950S 2300S 2500S raw materials for kerosene demercapting device 2. Fractional content: the beginning of driving -10 %, not higher than - 50%, not higher than - 90%, not higher than - 98%, not higher than Kerosene driven directly 3. Kinematic meltdown at 20 0S mm2/s Not less than 1.25 4. Detectable flash temperature in a closed Crucible 0S Not less than 28 5. Mass fraction of aromatic hydrocarbons weight % Not less than 22 6. Mass fraction of mercaptane sulfur % Not more than 0.01 (100) 7. Crystallization 0 S minus 50. 8. 100 cm3 flammable acid aluminum does Mg КОН not cover from 0.7 mg The bulk of the demerkaptanning process takes place in the "FIBER-FILM" section of the MERICAT II system (fiber-pleated contactor). Such Cleaning makes it possible to ensure the acidity number and mercaptane sulfur content in commodity kerosene in technical demand. When kerosene is treated with caustic (NaOH) in the MERICAT II device, two types of reactions occur: - extraction of naphthenic acids and hydrogen sulfide; -Extraction of R-SH and regeneration of caustic. More naphthenic acids in paraffin are extracted according to the following reaction: R-COOH+NaOH  R-COONa+H2O If the kerosene is found to contain hydrogen sulfide, it reacts quickly and intensively with caustic (NaOH), thereby reducing its amount in the reaction mixture. [2] The following reaction occurs: 2NaOH + H2S  Na2S+2H2O Purification of light hydrocarbons from mercaptans is performed by their extraction with an alkaline solution with alkali regeneration by oxidation of mercaptides to disulfides in the presence of a catalyst: RSH+NaOH  NaSR+H2O 2NaSR+ H2O+1/2O2  RSSR+2NaOH “Фан ва технологиялар тараққиёти” Илмий–техникавий журнал №6/2025 79 Химия и химические технологии Catalyst The resulting disulfides are insoluble in alkaline solution. They are removed from the regenerated alkali by extraction with gasoline. When using homogeneous catalysts dissolved in alkali, disulfide formation continues outside the regenerator—in pipelines or in the extractor itself. The resulting disulfides are transferred from the circulating alkaline solution into the purified feedstock in the extractor, increasing the total sulfur content in the purified product. The removal of mercaptans by alkaline leaching is associated with great difficulties.The acidic properties of mercaptans decrease with increasing length of the hydrocarbon chain, and therefore the upper mercaptans do not react with alkalis. In addition to the reaction of mercaptanide formation in the presence of atmospheric oxygen, the oxidation of mercaptans to form disulfides is also observed. RSH+O2  RSSR+H2O2 RSH+ H2O2 RSSR+H2O Disulfides are insoluble in water and migrate into the distillate being purified, thereby reducing the efficiency of mercaptan removal [4]. Table 2 Obtained product control Naming of the product under analysis Sampling site Indicator in control Control method 1. Density at 20 oS, kg / m3 GOST 3900 or Own OU 0372: 2008 ASTM d1298 2.Fractional content: os - temperature, - 10% expelled; - 50% expelled; - 90% expelled; Demercaptanated kerosene 12SC14 GOST 2177 or ASTM D86 on 3.Detectable flash temperature in closed tigel, os GOST 2177 or GOST 17323 or 0369:2008 ASTM D3227 4.Mass fraction of mercaptane sulfur, % ppm As a result of the research, it was possible to improve the quality of stable sulfur condensates supplied to oil refineries and ensure the production of import-substituting products based on local raw materials. A sample of the resulting mercaptan mixture was collected and analyzed for its composition using method a of GOST 2177. The composition of the results is given in Table 2.The administration of the Bukhara oil refinery tested odorant obtained from a mixture of mercaptans containing kerosene. Conclusion. In conclusion, sulfur compounds contained in oil and gas condensate are of great importance as an available, cheap and renewable raw material for the production of odorants. Mercaptan and disulfide derivatives obtained as a result of their processing are the most effective components that give odor to natural and liquefied gases. Therefore, the processing of sulfur compounds should be considered not only as a purification process, but also as a productive chemical conversion stage. This direction has strategic prospects for energy security, the development of waste-free technologies and the improvement of environmental control systems