CC BY
3UOT 546.224-31:549.67:544.723
Dadaeva G. Ch.
Associate Professor, Doctor of Philosophy in Technical Sciences,
Faculty of Chemical Technology, Department of Petrochemical Technology and Industrial Ecology, Azerbaijan State Oil and Industry University, Baku, Republic of Azerbaijan Buniyatov J.S. Master Student, Faculty of Chemical Technology, Department of Petrochemical Technology and Industrial Ecology, Azerbaijan State Oil and Industry University, Baku, Republic of Azerbaijan Melikli Z.E. Laboratory Assistant, Faculty of Chemical Technology, Department of Petrochemical Technology and Industrial Ecology, Azerbaijan State Oil and Industry University, Baku, Republic of Azerbaijan Дадаева Г. Ч.
доцент, доктор философии по техническим наукам, химико-технологический факультет, кафедра «Нефтехимическая технология и промышленная экология», Азербайджанский государственный университет нефти и промышленности,
Баку, Азербайджанская Республика Буниятов Дж. С. магистрант,
химико-технологический факультет, кафедра «Нефтехимическая технология и промышленная экология», Азербайджанский государственный университет нефти и промышленности,
Баку, Азербайджанская Республика
Меликли З.Э. лаборант,
химико-технологический факультет,
кафедра «Нефтехимическая технология и промышленная экология», Азербайджанский государственный университет нефти и промышленности,
Баку, Азербайджанская Республика E-mail: dadayeva750@list.ru
Adsorption of sulfur compounds in acid-modified clinopthalite Адсорбция сернистых соединений в модифицированном кислотой клиноптилолите
Abstract: Based on experimental data on the adsorption of H2S, COS and RSH in modified clinoptilolite and zeolite NaX, it was found that the use of modified clinoptilolite is the most effective. Based on the adsorption temperatures of H2S and COS in modified clinoptilolite, the optimal regeneration temperature was determined at 250°C. At the same time, the price of desorption of sulfur compounds (H2S and COS) from zeolite NaX at 320°C, established in industry, is approximately the same under other equal conditions.
Аннотация: На основании экспериментальных данных об адсорбции H2S, COS и RSH в модифицированном клиноптилолите и цеолите NaX было установлено, что использование модифицированного клиноптилолита является наиболее эффективным. Исходя из температур адсорбции H2S и COS в модифицированном клиноптилолите, оптимальная температура регенерации была определена в 250°С. При этом цена десорбции сернистых соединений (H2S и COS) из цеолита NaX при 320°C, установленная в промышленности, примерно одинакова при других равных условиях.
Keywords: sulfur compounds; adsorption; model mixture; clinoptilolite; synthetic and natural zeolites.
Ключевые слова: сернистые соединения; адсорбция; модельная смесь; клиноптилолит; синтетические и природные цеолиты.
Introduction. In the conditions of rapid development of industry and agriculture, nature protection, rational use of natural resources is becoming one of the most important national tasks. The problem of environmental protection is connected not only with the well-being of present and future generations, but also with their health. These are also the main directions of Azerbaijan's economic and social development, and measures aimed at improving environmental protection and health are constantly being carried out. Taking them into account, research work is
constantly being carried out to improve technological processes in the oil refining industry, including gas purification from harmful compounds in the gas industry. Currently, the natural gas of many newly discovered deposits contains sulfur compounds that reduce the quality of gas as a raw material for various processes, and sulfur compounds cause rapid and irreversible corrosion of equipment. During the combustion of gas containing sulfur compounds, very toxic sulfur oxides are formed, which together with flue gases have a negative impact on the atmosphere and the environment. In this regard, the gas industry faces a number of difficulties, and they are associated with the purification of gases from acidic components.
Currently, there are various methods of extraction of sulfur compounds in the industry. Among them, an important place is occupied by adsorption processes [1]. Synthetic and natural zeolites are most often used as adsorbents, which are distinguished by their polar molecules and have a high absorption capacity at low concentrations. The cost of natural zeolites is very low, they are resistant to high temperatures and aggressive environments. Among natural zeolites, clinoptilolite is of the greatest interest [3]. It was with this in mind that we investigated the adsorption properties of sulfur compounds contained in natural gases using a clinoptilolite type zeolite catalyst having rich deposits in Azerbaijan.
Experimental Part
The experiments were carried out on a flow-through installation (Fig.1), the main element of which was an adsorber — a heat-insulated glass column with a diameter of 10 mm, equipped with an electric heater to maintain a set temperature at the stages of adsorption and regeneration. A crushed adsorbent with a particle size of 0.5 - 1.0 mm is poured into the adsorber. The height of the adsorbent layer was changed from 10 cm to 30 cm. Before each test, the adsorbent was regenerated by purging the fiber with nitrogen at 250°C for four hours. Nitrogen consumption was 0.1-2 l/min. After the regeneration was completed, the adsorber was closed with adsorber cranes and held until the adsorbent cooled to the desired temperature.
Figure 1 — Scheme of the adsorption of sulfur compounds with acid-modified clinoptilolite: 1 — adsorber; 2 — agitator; 3 — rheometer;
4 — "gas container" containing mercaptan
Carbonyl sulfide, hydrogen sulfide, ethyl mercaptan, that is, sulfur compounds most commonly found in natural gas, were used as an adsorbent. Carbonyl sulfide and hydrogen sulfide [6] were synthesized and purified according to the methodology described in the work, dried with CaCl2 and NaA zeolite, and then frozen in a high-pressure tube cooled with a mixture of dry ice and acetone at a temperature of -80°C. Ethyl mercaptan of the brand "T" of factory production was used.
Before the adsorption column, the adsorbent content in the gas varied within the following limits: H2S 0.01-0.15 mol%, COS and H5SH 0.1-1.0 g/m3. Adsorption processes in the specified range of hardness of sulfur compounds in the gas have high technical and economic indicators based on experimental data. The gas velocity varied from 0.7 m/s to 0.25 m/s, and the temperature - from 20°C to 100°C.
The required concentration of COS and H2S in the gas was obtained by mixing nitrogen and the model mixture in the required proportions. The mixture model is made as follows. The gas cylinder P = 10-2 mm. p.st. it was evacuated to a residual pressure, H2S or COS was injected there from a calibration burette, and then the cylinder was filled with nitrogen of special purification to the design pressure. When
working with ethyl mercaptan, a gas stream is released from a thermostatic "gas cylinder" filled with liquid mercaptan, and then both streams are mixed. The required consistency is achieved by adjusting the ratio of flows and temperature in the "gas cylinder". The gas flow rate was measured by a rheometer. During the experiment, the gas at the inlet and outlet of the adsorber was periodically analyzed. The amount of carbonyl sulfide and hydrogen sulfide was determined in a universal gas chromatograph LC-7A with a thermal conductivity detector. The chromatographic column with a length of 2 m and a diameter of 4 mm is filled with squalane. The mixture was separated at a temperature of 75°C. Helium was used as a gas carrier, the consumption of which was 5 l/h. The amount of mercaptan in the gas was determined by the argentometric method [4].
Based on the experimental results of acid treatment of natural clinoptilolite, modified samples with a degree of 27% and 36% de-lamination were selected for the study. The adsorption of hydrogen sulfide and carbonyl sulfide was obtained in samples with a 27% degree of dealumination. The adsorption of ethyl mercaptan was studied on samples with a degree of 36% de-lamination.
It has been experimentally established that the desorption rate of sulfur compounds from clinoptilolite at 250°C is the same as the desorption rate of sulfur compounds from zeolite NaX at 320°C. This indicates the possibility of reducing energy costs at the regeneration stage when using clinoptilolite in desulfurization processes [2].
Adsorption heat is an important energy characteristic of the adsorption process. Based on this, the amount of heat spent on desorption of absorbed components at the stage of adsorbent regeneration is calculated:
Qg=AHG
where, G is the amount of the adsorbed component.
In addition, the temperature regime of regeneration is selected using the method of relative calculation of desorption curves in the first approximation in accordance with the value of the heat of adsorption [5]. In this method, it is assumed that the desorption rate of two components for an adsorbent or one component for
two adsorbents is the same if the temperature of the regeneration process is proportional to the adsorption temperature (Treq1/Treq2=AH1/AH2).
The regeneration temperature is selected according to the most difficult to desorb component. In the processes of desulfurization of natural gas, such a component is water. Based on experimental data, a temperature of 320°C (593K) is required for effective desorption of water from NaX zeolite. If we assume that the ratio of water adsorption temperatures in modified clinoptilolite and zeolite NaX will be approximately the same as for H2S and COS, then the regeneration temperature of modified clinoptilolite will be equal to
Treg kl = 5 93 ■ -^L s 5 9 3 ■ 0.83 = 492 K (2 2 0°C)
Results and Discussion
The result was verified experimentally, as a result of which it was found that the degree of desorption of sulfur compounds (H2S and COS) from modified clinoptilolite at 250°C and NaX of zeolite at 320°C are approximately the same under other equal conditions.
During the adsorption of ethyl mercaptan in modified clinoptilolite, a slight increase in the adsorption capacity of zeolite was observed with an increase in temperature. This condition is characteristic of chemisorption processes. We have established that the adsorption of ethyl mercaptan in modified clinoptilolite is reversible: the absorbed ethyl mercaptan is completely desorbed at a temperature of 250°C. There was no decrease in the adsorption capacity of zeolite from cycle to cycle. The unusual dependence of the zeolite capacity on the physical adsorption temperature is explained by the sieve effect [7], which is caused by the difficulty of penetration of molecules into the adsorption spaces due to the proximity of the critical diameter of the adsorbent molecules to the diameter of the entrance windows. At the same time, the activation energy of the diffusion process of adsorbent molecules in the zeolite pores AE has a high value, and the effective internal diffusion coefficient De has a low value:
A E
De = A exp(-—)
As a result, true adsorption equilibrium is not achieved, the results obtained should be considered as the results of imbalance. Conclusions
1. Based on experimental data on the adsorption of H2S, COS and RSH in modified clinoptilolite and zeolite NaX, the hardness range of sulfur compounds in which the use of modified clinoptilolite is the most effective is determined.
2. Based on the adsorption temperatures of H2S and COS in modified clinoptilolite, the optimal regeneration temperature is determined.
3. Depending on the temperature, an increase in the adsorption capacity of modified clinoptilolite due to ethyl mercaptan was noted, which is explained by the appearance of the sieve effect. Based on this, it was concluded that the use of modified clinoptilolite for the purification of natural gases from ethyl mercaptan is advisable in cases where the next gas treatment is carried out at high temperatures.
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