Increasing and intensification of the technology of purification of natural gas by composite absorbents

. Today, the urgent task is the synthesis of new nanostructured composite sorbents used for the complete utilization of various wastes of oil and gas refineries, improving the technology of processes for cleaning natural and tail exhaust gases from acidic impurities, increasing the stability of the physicochemical properties of sorbents and improving the environmental conditions for processing secondary absorbents oil and gas refineries. Recently, in the world in oil and gas processing industrial enterprises, the main attention has been focused on the search for methods for purifying natural and waste gas from organic compounds of sulfur, mercaptans, carbonyl sulfide (COS), carbon disulfide (CS 2 ) and sulfides (RSR), as well as the creation of new types of highly effective composite adsorbents for gas purification. for of of in and Absorption The of components in The in


Introduction
Natural gas has already taken a firm place in providing the national economy with fuel and raw materials for petrochemicals. Today, the use of hydrocarbon gases (natural and oil), an environmentally friendly type of fossil fuel and chemical raw materials, accounts for more than 25% of the world consumption of all hydrocarbons.
In industry, in installations for the purification of acid gases, monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) are mainly used as an absorbent. MEA, DEA and MDEA are used at a concentration of 30-35% and the saturation point of these absorbents with acidic components (H2S and CO2) is 0.35 0.55 mol / mol.

Method
During operation, alkanolamine absorbents undergo various thermochemical transformations (degradation) upon contact with H2S, CO2 and other acidic impurities of natural gas. The largest number of studies on this problem is devoted LTSto monoethanolamine (MEEA), significantly less -diethanolamine (DEA) and just a few works of methyldiethanolamine (MDEA) and mixed absorbents -MDEA+ MMEA and MDEA+DEA, MDEA+HMTA (urotropine). Investigation of the thermochemical stability E3S Web of Conferences 258, 12008 (2021) UESF-2021 https://doi.org/10.1051/e3sconf/202125812008 of composite absorbents based on nitrogen-containing water-soluble polymers (ATSP) is not available in the literature. This circumstance is obviously connected with the fact that such absorbents have not yet found wide distribution abroad.

Results
The quality of composite solutions of absorbents determines not only the quality of gas cleaning, but also the loss of amines, their corrosive properties. In this connection, in this paper, the results of studies on this problem are presented.
The proposed compositional absorbent based on MDEA and DEA is prepared as follows: in a 20-25% aqueous solution of MDEA and DEA, a 0.1-10% mixture of a nitrogen-containing water-soluble polymer (AVRP) at 50-60 ° C is mixed in a stirred tank reactor for 20-30 minutes, after passing through the filter, the absorbent is dosed into the absorption unit for purifying natural gas from hydrogen sulphide. Laboratory conditions for the purification of gases from H2S and CO2 using a composite absorbent based on nitrogen-containing GRP established that the absorption capacity for acidic gas components will increase by 0.1-0.2 mol / mol, the foaming decreases comparatively (H = 0.6-1, 4 cm), the lifetime of the foam (0.5-1.0 sec), and other physicochemical parameters of the purification process. The initial absorption rate of H2S is almost twice as large as that of CO2. Thus, this fact confirms that high selectivity for H2S is achieved in a solution of a composite absorbent at low saturation with an acid gas, the selectivity depends on the kinetics of the process. The conditions for regeneration of a solution saturated with acidic components with an activator-AIPP do not require additional process costs, and also the temperature of the process can be reduced by 8-12°C, i.e. 120-130°C.
The study of the kinetics of sulfur absorption was carried out by a change in the electrical conductivity of the absorber solution ( As follows from the data given, the specific resistance of the aqueous solution of ATSP sharply decreases when a spent solution appears in the initial reagent. After the proportion of the spent solution in the starting reagent exceeds 20%, the resistivity decreases more smoothly. In this regard, the resistivity index of the solution can serve as an indicator of the processing of the initial reagent during gas desulfurization. Based on the study of the kinetics of sulfur absorption of a composite absorbent with the use of AVRP in small plants of gas processing plants, it was found that the main factors influencing the value of the specific consumption factor are the parameters that contribute to the increase in the phase contact surface of the gas and reagent, such as the viscosity of the AVRP, the height of the reaction zone, And the linear velocity of the gas, the residence time of the gas in the reaction zone. In connection with this, the thermochemical stability of the AWSP was studied (  The data obtained by gas chromatography on a capillary column with polyethylene glycol (PEG) and published data show that the temperature and concentration of CO2 have a decisive influence on the degradation of amines. And degradation is mainly subject to DEA and MIEA. Composite absorbent (AVRP+MDEA+DEA) practically does not undergo transformations. So at a temperature of 160 ɨ ɋ and exposure in an atmosphere of ɋɈ2 of 94 hours in an absorber remains unconverted amine (%): AWSP -91%, MDEA-90.9; DEA-22.1; MIEA-11.4. In the absence of CO2 amines are stable. In the presence of one H2S, the amines do not degrade in the temperature range 80-160° C. In the presence of CO2, the AWSP and MDEA are practically stable, whereas DEA and MIEA undergo significant transformations. The experimental sulfur content in the waste AWSP samples was 6-7% by weight. The IR spectra of the AVPP sample of the absorption bands are given in Table. 3. Table 3. Reference of bands of absorption of AWSP samples in the IR-spectrum. From the analysis of the IR spectrum, it can be assumed that the sample contains mainly 1,3,5-tris (2-hydroxyethyl) hexahydrotriazine and residual oxazolidines. Possible the presence of other compounds, the determination of which from the IR spectrum is difficult. The nature of their absorption bands indicates that the products formed are present in the polymer form, i.e. In the form of polycondensates.
In connection with the planned carrying out of pilot-industrial tests of the composite absorbent DEA+MDEA+AVRP, their corrosion aggressiveness was investigated.
The experiments were carried out in glass ampoules and autoclaves according to the procedure [1][2][3][4]. The use of ampoules allowed obtaining preliminary information with limited time and reagents, and autoclaves -information close to real conditions.
The results of the investigations are shown in Fig. 2,3 and in Table 4 (experiments in ampoules), as well as in table 4 and in fig. 4 (experiments in autoclaves). Analysis of the data obtained in ampoules shows that the corrosion rate of st.10 in the absorbents-DEA+MDEA, MDEA+DEA is higher if the absorbent is saturated with one H2S, than in the case of saturation with one CO2 ( fig. 1.2). In the presence of H2S and CO2, the maximum corrosion rate was observed at the ratio H2S/CO2 = (1.5-4): 1. The addition of 10% AWP to this absorbent reduces the rate of corrosion of steel by 2 times, and the addition of 20% ~ 3 times. In addition, the corrosive aggressiveness of the DEA+MDEA solution containing more than 40% MDEA increases. Stainless steel is practically not corroded. Addition of 1% by weight. Hexamethylenediamine to the MDEA+DEA absorbent (60x40%), which showed the highest corrosion rate of 12 GF-1.0 mm/ year steel, reduces it to 0.11-0.12 mm/year. This fact requires additional special research.

Conclusion
The results of the experiments showed that the sample of the composite absorbent DEA+MDEA+AVRP even after 1.5 months of storage showed a stable desulfurization efficiency. All the experiments were carried out to the end, until the reagent was fully developed. As a result of the experiments, real consumption coefficients were obtained for the AWSP. When analyzing the results, it was found that the range of preferred consumption coefficients DEA+MDEA+AVRP (0.015-0.018 l/g H2S) is in the region of E3S Web of Conferences 258, 12008 (2021) UESF-2021 https://doi.org/10.1051/e3sconf/202125812008 low linear gas velocities (0.02-0.04 m/s), which corresponds to a sufficiently long residence time Gas in the reaction contact zone (10-18 sec). The use of a composite absorbent on the basis of DEA and MDEA with the AWSP activator shows the following parameters in the technology for the purification of a little sulfur dioxide: the absorption capacity of the solution in H2S and CO2 is 0.4-0.5 mol/mol; Absorption temperature -40-45°C; The desorption temperature is 125-130°C; The content of acidic components in the regenerated solution is -0.006-0.01%; The content of acidic components in purified gas is 0.0009-0.0018%.