CC BY
15
https://doi.org/10.29013/AJT-23-1.2-21-23
Makhmudov Mukhtor Jamolovich, Doctor of Chemical Sciences, Associate Professor of the Bukhara Institute of Engineering and Technology,
Bukhara, Uzbekistan Nematov Khusan Ibodullaevich, scientific competitor, Karshi Engineering and Economic Institute,
Karshi, Uzbekistan
MODERN INDUSTRIAL ADSORBENTS FOR DRYING NATURAL GAS CLEANING
Abstract. As oil resources are depleted, natural gas is steadily moving to the forefront of the global economy. This article presents the results of the degree of gas drying under dynamic conditions by various adsorbents.
Keywords: natural gas, adsorbent, dew point, gas hydrate, water, dynamic conditions, zeolite, silica gel, aluminum oxide.
Along with the drying of gases by the absorption method, installations using the adsorption method are widely used in technology for drying various media [1].
Drying plants by the adsorption method have a number of advantages compared to the absorption method: they achieve a very low dew point - minus 70 °C and below; increasing the pressure in the system has little effect on the process; the equipment is not difficult to manufacture and there are practically no losses of chemicals.
Solid dryers - adsorbents - are preferred ifit is necessary to remove other harmful chemical compounds from the gas, along with drying, since acetylene, aliphatic, aromatic and sulfur-containing hydrocarbons are simultaneously removed selectively [2].
To adsorbents used in the gas industry, there are certain requirements: large pore surface, high selectivity and rate of mass transfer, stability of adsorption properties during long-term operation, low resistance to gas flow, high mechanical strength.
In addition, adsorbents should be cheap, non-corrosive, non-toxic, chemically inert, and easily regenerated.
In each case, when choosing adsorbents, it is necessary to take into account also the cost of equipment, service life and prices of the adsorbent, goals process, etc. [3].
Adsorbents can be divided into the following general categories [4]:
- bauxite (natural minerals, consisting mainly ofAl 2O3);
- activated alumina (purified bauxite);
- gels (substances consisting of silicon oxide or aluminum gel and obtained through chemical reactions).
- molecular sieves (sodium-calcium silicates, or zeolites);
- carbon (charcoal), the adsorption properties of which are obtained as a result of activation. All these substances, except coal, are used for gas dehydration.
Activated charcoal is used to extract hydrocarbons from natural gas and gas purification from some impurities.
The activity of coal with respect to water is very low [1].
Section 3. Technical sciences in general
To clean natural gas from sulfur compounds from all range of industrial adsorbents currently in use, mainly synthetic zeolites, as other adsorbents (activated carbons, silica gels and alumogels) have a significantly lower adsorption capacity for sulfur compounds. This is explained non-selective co-adsorption of other components of natural gas. So, for example, the adsorption capacity of activated carbons for mercaptans decreases by 5-6 times during their adsorption from natural gas in comparison with their absorption from a gas stream that does not contain hydrocarbons, for example, nitrogen [4].
From modern industrial adsorbents - activated carbons, silica gels, alumogels, zeolites - the latter show the most high selective ability to absorb polar substances (H2 S, RSH, etc.) even when the temperature rises to 100 °C [5]. This property of zeolites is due to the presence of a strong electrostatic fields in the channels of their aluminosilicate crystals [6]. Under the action of this field, electron-donor atoms of polar substances are firmly are chemisorbed on the inner surface of zeolites, and sorption increases in the series H2O > R2 S > RSH > H2S > COS > CO2 > > hydrocarbons.
Synthetic zeolites also have the unique property comparability of the diameter of the entrance windows in the cavity of the zeolite with the size molecules of the extracted impurity, which allows for selective adsorption [7; 8].
The advantages of molecular sieves (zeolites) when used in industries are a decrease in the specific volume of the adsorbent, more low pressure drop across the adsorbent bed, elimination of gas losses due to adsorption ofvaluable components, long service life of molecular sieves, more reliable and stable operation of drying plants [8].
Molecular sieves containing a high proportion of silicon are usually used for drying sulphurous natural gases due to stability of these adsorbents to H2S. In this case, two types of zeolites: A and X [1; 2]. The most common type A zeolite has mouths of pores of approximately the same effective diameter, equal to
0.4 nm. For type X zeolites, the effective diameter of the pore mouths lies in the range 0.9-1.0 nm. In the event that it is necessary to extract only water, it should be use type 3 A zeolite, since HS and CO, , ,
' £ 1 2 2 molecules
cannot pass into adsorbent pores.
At natural gas desulfurization plants, the most widely synthetic zeolites NaA (4A), CaA (5A), NaX (13 A) are used.
The greatest influence on the capacity of zeolites for sulfur compounds render H2O vapors. In the case of cleaning wet hydrocarbon gases H2O sorbed in the frontal layers of the zeolite, almost completely displacing sulfur compounds. Significant effect on the capacity of zeolites sulfur compounds are also affected by the presence of heavy vapors in the gas hydrocarbons. The sorption capacity of hydrocarbons increases as increase in their molecular weight [4].
For the first time, molecular sieves (zeolites) were used in the world industrial practice for drying natural gas [1-5]. Molecular sieves also have the ability to remove some impurities from the water.
A valuable property of molecular sieves is the removal ofwater from natural gases enriched with acid gases (H2S and CO2).
At many foreign installations that prepare gas for pumping through pipelines, previously used as an adsorbent aluminum oxide or silica gel was replaced by molecular sieves in order to increasing the productivity of existing equipment and adsorbent service, reducing liquid hydrocarbon losses and lowering dry gas dew point [7].
Foreign scientific and technical literature describes a significant number of industrial installations for the purification of natural gases from sulfur compounds using synthetic adsorbents zeolites [4]. Such installations are widely used in the USA, France, Japan, Saudi Arabia [8]. Type used in installations desulfurization of zeolites depends on the nature of sulfur compounds. For purification from hydrogen sulfide and carbon sulfide, 4A zeolites and 5A (NaA and CaA), for purification from mercaptans -
zeolites 13A (NaX). Term service life of zeolites is liquid hydrocarbons (C5+ ) and moisture, showed
1000-2000 cycles. that at present for this purification, mainly adsorp-
The above review of scientific, technical and pat- tion technology is used, consisting in the absorption
ent literature, dedicated to the purification of natural of impurities by a layer of adsorbent, predominantly
sulfur dioxide from impurities H2S, thiols, vapors of zeolite Na X.
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