Investigation of the adsorption properties of the sorbent obtained in the process of modification of clinoptilothite in the purification of natural gas from sulfur compounds

. The study of the possibility of using modified clinoptilolite as an adsorbent and the adsorption properties of zeolite in the purification of natural gas supplied to gas processing plants from sulfur compounds contained in it is an urgent task. In the experimental study, the adsorbent fraction was chosen as 0.5÷1.0 mm, density - 0.8 g/cm 3 , adsorbent layer height - 600 mm. Optimal conditions are selected in such a way that the pressure in the experimental process is 0.2-5.0 MPa, the amount of mercaptans in the purified natural gas is 50÷400 mg/nm 3 , the temperature is 20÷25°C, the gas flow rate is 0.2÷250°C. 0.25 m/s. Experiments IR spectroscopic studies were carried out on a NikoletIS-10 IR spectrometer in the frequency range 400-5000cm -1 . The phase composition was studied using a 2DPHASER Bruker X-ray analyzer (CuKa - radiation, 2nd, 20-80 degrees). Electron microscopic images were taken under a Hitachi TM-3000 microscope. Elemental analysis was performed at Oxford Science. The intensity and accuracy of desorption of sulfur compounds adsorbed on clinoptilolite at 250°C, the same results were obtained on NaX zeolite at 320°C. The catalytic activity of regeneration of clinoptilolite at lower temperatures than that of NaX zeolite, although small, made it possible to minimize the decomposition of mercaptans. The purpose of this work is to study the adsorption properties of the sorbent obtained in the process of modifying clinoptilotite during the purification of natural gas from sulfur compounds


Introduction
The study of the structure and properties of the existing and widely used natural raw materials -the class of layered bentonites obtained from clayey rocks -is an important scientific task aimed at creating new multifunctional materials [1,2]. This is mainly due to the specifics of the physicochemical properties of layered bentonites, their ability to have active centers of various nature, adsorption and ion exchange. This opens up wide opportunities for their use, for example, in the creation of new effective materials for water treatment and wastewater treatment, sorbents in pharmacology, anti-migration and filtration barriers for long-term storage of hazardous waste [3][4][5][6][7][8].
Layered silicates are minerals common in nature. They make up to 75% of the sedimentary rocks of the earth's crust. The best-known representatives of layered silicates are clays. Clay has long been used in various fields of human activity. The scope of their application is very wide: the production of ceramic and building products, oil production and processing, metallurgy, chemistry, paper, pharmaceuticals, food and other industries [9].
They are also known as natural sorbents, ion exchangers, catalysts, and catalyst carriers [10][11][12][13]. The development of new methods for changing the structure of layered silicates and changing their physicochemical properties is constantly expanding the scope of their use.
Recently, intensive research has been carried out on the creation and study of multifunctional inorganic 2D nanomaterials related to intercalated layered substrates. Among them are columnar (or columnar) materials, which are distinguished by their unique texture and physicochemical properties. They are characterized by specific surface area, regular distribution of micro-and mesopores, thermal stability, and the presence of active centers of various nature. Therefore, effective sorbents, molecular sieves, catalyst carriers, etc. are obtained from them.
At present, a large number of (columnar) materials of the highest quality are known based on bentonite matrices, the chemical formulas of which are unknown, crosslinked by hydrolysis products of various metals [11].
Among the modification methods, pilling is of great interest to researchers; this technological method opens up wide prospects for the functional application of natural clays in various fields of science and technology. Pillaring is a process of preserving a layered system while simultaneously converting it into a heat-resistant micro-or mesoporous material. The basic ideas about the structure of ivory clays were formed in the studies of Pinnaway [12][13], Sturt [14][15][16] and other scientists.
Regardless of its specific properties, this process can be described by three main stages: 1) hydrolysis of metal polyhydroxo complexes, 2) ion exchange (intercalation) of interlayer cations of layered bentonite, 3) heat treatment (roasting) of layered bentonite.
It should be noted that intercalation is the main stage of clay preparation. Intercalation is a process based on changing the structure of the sludge due to the expansion of the interlayer space due to the introduction of large inorganic complexes. This method was invented in 1977 by scientists from the Brindley sample [17]. During the intercalation of layered silicates, a developed microporous structure is formed, the specific surface area increases, and access to active centers located on the inner surface becomes possible. The most well-known basic molecule of aluminum hydroxide is the Al13 ion, which was originally isolated in the form of sulfate and selenate salts [18][19][20][21].
At present, High Silicon Zeolites (HSZ) are synthesized by thermal, mechanochemical and chemical processing of natural zeolites, for example, bentonites of the Navbakhor region of the Republic of Uzbekistan, and are successfully used in gas cleaning and as a catalyst retainer [22][23][24][25][26][27].

Methods
We know that natural gas entering gas processing plants contains sour compounds such as hydrogen sulfide, carbonyl sulfide and mercaptans. Initially, it is purified from impurities containing natural gas, for which an aqueous solution of diethanolamine is used. The total content of natural gas and the proportion of mercaptans (10÷20%) when cleaning mixtures by the above method, the residual content in terms of sulfur in the gas is about 400 mg/nm 3 . After cleaning with an aqueous solution of diethanolamine, the moisture content of natural gas drops to a dew point of -10/-15°C and a pressure of 5.0 MPa. Synthetic zeolite NaX is used in the adsorption method for carrying out the process of post-treatment of natural gas from mercaptans. The residual content of mercaptans in natural gas is not less than 36 mg/nm 3 in terms of sulfur.
The adsorption of mercaptans in the modified clinoptilolite as a result of acid treatment was carried out in the experimental setup described below.
The adsorber is made of stainless steel and has a cylindrical device with an inner diameter of 11 mm and a height of 1 m. The pressure in the process is controlled by a sampling manometer, and the gas flow from the adsorber is measured by a RS-5 rotameter.
In this experiment, an adsorbent fraction of 0.5÷1.0 mm was chosen, the rise was 0.8 g/cm 3 , the height of the adsorbent layer was 600 mm, NaX zeolite was used.
Optimal conditions are selected in such a way that the pressure in the experimental process is 0.2-5.0 MPa, the amount of mercaptans in the purified natural gas is 50÷400 mg/nm 3 , the temperature is 20÷25°C, the gas flow rate is 0.2÷250°C. 0.25 m/s [28,29]. During the experiments, the composition of the gas entering and leaving the adsorber was studied by analyzing mercaptans over a certain period of time. The amount of mercaptans was determined by the argentometric method.
During the experiments, after the completion of the adsorption phase, the adsorbent was cleaned by blowing the bed with purified heated natural gas for 4 hours and then regenerated. The speed of the purified (regenerated) gas is 0.025 m/s, the order of the purification temperature is chosen based on the kinetics of water desorption, which is best adsorbed in zeolites from additives in the gas being purified. In the process of regeneration of clinoptilolite, the temperature of natural gas at the inlet to the adsorber is 0°C, when carried out with NaX zeolite -320°C.
The reason for the temperature difference during the regeneration process is due to the energy difference due to the interaction of water molecules on the surface of the zeolite, which is less than NaX for clinoptilolite.
The amounts of hydrogen sulfide and mercaptans in natural gas leaving the adsorber during purification were compared. The regeneration process was considered completed when the amount of mercaptans in purified natural gas decreased to 20 mg/m 3 .

Results and discussion
The output curves of the adsorption process are shown in Fig.1. As can be seen from the figure, the output curves have a high value, which is typical for the process of adsorption of a mixture of substances as a result of the displacement of one substance from one adsorbed phase to another.
According to the output curves of the adsorption state, G, % wt. Mercaptans (1) can be used to calculate the dynamic activity of the zeolite and the maximum activity Gmax (2).
We accept tpr and tr like this: tpr is the amount of mercaptan in natural gas leaving the adsorber, Cexit = 10 mg/nm 3 tr-time to equalize the amount of mercaptan in natural gas entering and leaving the adsorber, Cexit = Co As can be seen from the figure, mercaptans adsorb 200 mg/nm 3 in less than 30 minutes in modified clinoptiolite, which can be observed in 150 minutes in NaX zeolite. As the rate of the process decreases with time, it can be seen that the adsorption did not change for 90 min in clinoptilolite and for 500 min in NaX zeolite.
From the data presented in Table. 1, it is known that the dynamic activity of the modified clinoptilolite obtained by acid treatment at high concentrations of mercaptans in natural gas is about six times less than the size of the NaX zeolite. But at medium concentrations, this difference is equal. The data in the table are consistent with the experimental data in the laboratory. According to the results of the study of the regeneration process, kinetic curves are formed that characterize the presence and speed of movement of sulfur-containing substances (Fig.  2).
As can be seen from Figure 2, when using clinoptilolite as an adsorbent with a maximum amount of mercaptans in the regeneration gas of 6 g/m 3 , it is possible to achieve a temperature of the gas leaving the adsorber equal to 0°C. It is known that the main component of mercaptans, i.e. 80%, desorbed in one hour. The temperature curve (3) has a parametric horizontal section as follows: within 20 minutes the temperature is 0°C. These valuescorrespond to the temperature and time of intense desorption of mercaptans adsorbed on the zeolite.
As can be seen from Fig.2, hydrogen sulfide is formed in the regeneration gas at a temperature of 140°C (curve 2), which indicates the possibility of calculating the product of the thermal catalytic process of mercaptan decomposition. When calculating the material balance, it was found that after four hours the mercaptans are desorbed; only 2% of them are cracked. When using NaX zeolite, the maximum amount of mercaptans in the regeneration gas is 14 g/nm 3 , and these results can be achieved at a temperature of gases leaving the adsorber of 150°C. After three hours, 90% of the mercaptans are desorbed, about 10% of which we can observe cases of decomposition. Comparison of the data in the above figures showed that the intensity and accuracy of desorption of sulfur compounds adsorbed on clinoptilolite at 250°C can achieve the same results as on NaX zeolite at 320°C. The catalytic activity of clinoptilolite regeneration at lower temperatures than that of NaX zeolite, although small, allows minimizing the decomposition of mercaptans. This factor is of great practical importance, on which the service life of the zeolite mainly depends. During the decomposition of mercaptans, along with hydrogen sulfide, olefinic hydrocarbons are formed, which polymerize in small amounts at high temperatures with the formation of carbon-like layers in the zeolite, thereby causing its deactivation.
Experimental results show that the use of modified acid-treated clinoptilolite in combination with synthetic zeolites in desulfurization processes leads to positive results: the first layer is synthetic zeolite at the inlet of purified natural gas, in the connecting layersclinoptilolite. Since the adsorbent treatment rate in the binder layers is low, the replacement of synthetic zeolite with clinoptilolite has little effect on the overall sulfur absorption of the layer. The use of a mixed bed during countercurrent regeneration in cracking processes also contributes to an increase in the service life of adsorbents, taking into account the high thermal stability of clinoptilolite, i.e. thermochemical stability and very low catalytic activity.

Conclusion
1. The degree of dealumination of the modified clinoptilolite used as an adsorbent in the purification of sulfur compounds present in natural gas was 36%, and the adsorption properties of NaX zeolite were studied.
2. Adsorption of 200 mg/nm 3 mercaptans in modified clinoptiolite in less than 30 minutes, this figure was recorded in 150 minutes in NaX zeolite.
3. It was studied that the adsorption did not change after 90 minutes in clinoptilolite and after 500 minutes in NaX zeolite.