STUDY OF TEXTURE CHARACTERISTICS OF UNMODIFIED AND MODIFIED BENTONITE

ABSTRACT

In the study, the issues of chemical and physical activation of bentonite, a natural local raw material, texture characteristics and surface morphology were studied. X-ray phase analysis for bentonites was performed to determine the mineralogical composition. In the analysis of natural bentonites, it was found that they contain montmorillonite and a-cristobalite. For samples of heated starting and modified bentonite, the highest values of specific surface area and porosity were observed. The dependence of the surface area and the volume of the pores on the heating temperature showed significant active changes in the texture of all modified samples relative to the original samples during the bentonite plating at very high temperatures.

АННОТАЦИЯ

В ходе исследования изучались вопросы химической и физической активации бентонита, природного местного сырья, текстурные характеристики и морфология поверхности. Рентгенофазовый анализ бентонитов был проведен для определения минералогического состава. При анализе природных бентонитов установлено, что они содержат монтмориллонит и а-кристобалит. Для образцов нагретого исходного и модифицированного бентонита наблюдались наиболее высокие значения удельной поверхности и пористости. Зависимость площади поверхности и объема пор от температуры нагрева показала значительные активные изменения текстуры всех модифицированных образцов по отношению к исходным образцам в процессе бентонитового покрытия при очень высоких температурах.

Keywords: bentonite, activation, surface finish, montmorillonite, α-cristobalite, modified, surface area, porous volume, micro-porosity, cocooning, textures.

Ключевые слова: бентонит, активация, отделка поверхности, монтмориллонит, α-кристобалит, модифицированный, площадь поверхности, пористый объем, микропористость, коконирование, текстуры.

Introduction

Today, the world pays great attention to the creation of waste-free or low-waste, energy and resource-saving technologies. In the successful solution of these problems, the degree of purity of the substances used and formed for the technological process is important. The most important requirements for adsorbent materials are high specific surface area, selectivity and easy regeneration. It is also necessary that the adsorbent is cheap and harmless, has no corrosive properties, can retain its adsorption properties for a long time, and has high mechanical strength. Among the sorbents used in adsorption processes and catalysis, zeolites have a special place in terms of acid resistance, thermal stability and acidity properties. Today, the main problem in the production of zeolites is to reduce its cost and simplify the technology of synthesis, and extensive scientific research is being conducted in this priority area [1-6]. Zeolites are widely used in petrochemistry and as a sorbent and catalyst in the refining of oil, natural gas, petroleum gases, separation and purification of liquid and gaseous media. In recent years, natural and artificial zeolites have been widely used in the refining of hydrocarbon raw materials. One of the most important current directions is the creation of environmentally safe sorbents, retainers and catalysts based on local raw materials [7-12].

Experimental Part

Based on the experiments, laboratory work on adsorption was carried out by the method. Initially, the adsorbent was activated for two and a half hours at a temperature of 500–510 ℃, then cooled in its desiccator to its previous state (to the nearest 0.001g). The process of purification of natural gas from hydrogen sulfide, carbon dioxide and thiols was studied in a device modelled at different temperatures. The natural gas was sent to a column with a total height of 215 mm, a diameter of 32 mm and a volume of 6.64 cm³ filled with 50 g of adsorbent for the adsorption process for 40 minutes. The adsorption temperature was monitored using a thermocouple mounted on the adsorber. The gas passing through the adsorbent layer falls into a gas meter filled with brine (saltwater), at which time the saltwater is compressed in a cylinder. The pressure in the adsorber is equal to atmospheric pressure and it is monitored using a special glass monometer using a saturated solution of table salt in a gasometer. The amount of water and acidic components (H₂S and CO₂) from the second column is determined after the first column after the purified gas is passed to the chromatograph connected to the gas analyzer by a special device after the gas meter. The experiments were performed at given temperatures under atmospheric pressure. Adsorption processes in the device were tested at temperatures of 20, 25, 40, 45, 40 ℃. Before the experiment, the adsorbent was activated by nitrogen spraying for 10 min. Based on the results of the analysis, the dynamic activity of high-silicon zeolite obtained from Navbahor bentonite was determined using the following formula:

А_g=С₀∙ W∙ t ̸ h

In this case, С₀ – the concentration of hydrogen sulfide and carbon dioxide in a mixture of natural gas, g / 100g; W – natural gas flow rate, m / s; t – Time of exposure to adsorbent;  h – the height of the adsorbent layer, m.

Results and Discussion

Bentonites are not considered a pure raw material and the main phase, along with montmorillonite, contains a mixture of different minerals, depending on the deposit to be mined. X-ray phase analysis for bentonites was performed to determine the mineralogical composition. Figure 1 shows X-ray diffractograms of natural bentonites, as well as bentonites fired in an inert argon atmosphere at 550 ℃.

Figure 1. Diffractograms of natural Navbahor bentonite (1) and sample (2) fired in an inert argon atmosphere at 550 ℃

X-ray structural analysis of natural bentonites shows the presence of montmorillonite and α-cristobalite. As a result of firing for activation, a change in the mineralogical composition of bentonites is observed and an illite phase occurs. For both bentonites, a large proportion of the pores are observed in the area of 2–2.2 nm and larger, indicating that these materials are mesoporous. However, the 2nd sample retains a large amount of pores measuring 1.8–7.2 nm. Therefore, the 2nd sample will have a higher specific surface area. The studies were performed on three samples of the same density and thickness prepared based on high-silicon zeolite obtained from bentonite. The first sample was heated to 650 ℃ for 1 h, the second was saturated with methyltretbutyl ether, and the third was taken from a natural sample (Fig. 2).

Figure 2. Diffractogram of bentonite fractions

Influence of heating temperature on the parameters of the porous structure of columnar bentonites. Treatment of Navbahor modified bentonite at temperatures above 700 ℃ results in the release of water between the layers and the deterioration of texture characteristics with the occurrence of irreversible adhesion of the layers. However, as can be seen from the figures (Fig. 3), no significant changes were observed in the porous structure parameters of the initial sludge samples in the heating temperature range of 70–500 ℃.

Figure 3. The effect of heating temperature on the surface of bentonite

Regardless of the chemical composition and modification conditions of natural bentonites, the average mesopore diameter of all bentonites remains unchanged and varies in the range of 4.0–4.2 nm (Fig. 4). It should be noted that as a result of tabletting, the size of the mesentery is reduced.

Figure 4. Dependence of the distribution curve of the diameter of the pores on the size of unmodified bentonite on the ratio ОН^-:Меⁿ⁺

For samples of initial and modified bentonite heated to 400 ℃, the highest values of specific surface area and porosity were observed. The specific surface area and micropore volume dependence for the modified sample are very high, depending on the heating temperature, during the bentonite plating process at a maximum temperature of 400 ℃, all modified samples showed significant changes in texture properties compared to the original samples. Due to the increase in the adsorption capacity of the obtained materials, the specific energy of nitrogen adsorption in modified bentonites increased by 1.3-1.5 times compared to the original samples.

Figure 5. Isotherms of nitrogen adsorption at 77 K in linear coordinates of Dubinin-Radushkevich equation of natural and modified bentonite

Adsorption testing in equilibrium mode allows to determine the maximum amount of adsorbed substance and to calculate the thermodynamic parameters of adsorption in the low-temperature range.

Conclusion

Experiments in laboratory work showed that the adsorbent was first activated for two and a half hours at a temperature of five hundred and above, then cooled in a desiccator and then the process of purification of natural gas from hydrogen sulfide, carbon dioxide and thiols was studied in a simulated device at different temperatures. In order to determine the mineralogical composition, X-ray phase analysis for bentonites was carried out. X-ray diffractograms of natural bentonites and calcined bentonites in an inert argon atmosphere were obtained. The effect of temperature and temperature of the bentonite on the surface was directly studied on the size of the micro-pores, the specific surface area and the porosity of the pores were observed for the samples of heated primary and modified bentonite. Due to the increase in the adsorption capacity of the obtained materials, the specific energy of nitrogen adsorption in modified bentonites increased by 1.3-1.5 times compared to the original samples.

References:

1. Busca G. Zeolites and other structurally microporous solids as acid-base materials //Heterogeneous Catalytic Materials. – 2014. – Т. 1. – С. 197-249.
2. Ayari F., Srasra E., Trabelsi-Ayadi M. Characterization of bentonitic clays and their use as adsorbent //Desalination. – 2005. – Т. 185. – №. 1-3. – С. 391-397.
3. Везенцев А.И., Воловичева Н.А. Вещественный состав и сорбционные характеристики монтмориллонит содержащих глин // Сорбционные и хроматографические процессы. 2007. Т. 7. № 4. С. 639–643.
4. Садыков Т.Ф., Конькова Т.В., Алехина М.Б. Монтмориллонит со слоистостолбчатой структурой для процесса фентона // Успехи в химии и химической технологии. 2012. Т. 26. № 8 (137). С. 50–54.
5. Mamadoliyev I. Synthesis of high-silicone zeolites //Збірник наукових праць ΛΌГOΣ. – 2020. – С. 16-20.
6. Mamadoliev I. I., Khalikov K. M., Fayzullaev N. I. Synthesis of high silicon of zeolites and their sorption properties //International Journal of Control and Automation. – 2020. – Т. 13. – №. 2. – С. 703-709.
7. Mamadoliev I. I., Fayzullaev N. I. Optimization of the activation conditions of high silicon zeolite //International Journal of Advanced Science and Technology. – 2020. – Т. 29. – №. 3. – С. 6807-6813.
8. Ibodullayevich F. N., Ilkhomidinovich M. I., Bo’riyevna P. S. Research of sorption properties of high silicon zeolites from bentonite //ACADEMICIA: An International Multidisciplinary Research Journal. – 2020. – Т. 10. – №. 10. – С. 244-251.
9. Файзуллаев Н. и др. Каталитическая дегидроароматизация нефтянного попутного газа //Збірник наукових праць ΛΌГOΣ. – 2020. – С. 122-126.
10. Ilkhomidinovich M. I. Study of the sorption and textural properties of bentonite and kaolin //Austrian Journal of Technical and Natural Sciences. – 2019. – №. 11-12. – С. 33-37.
11. Fayzullaev N. I., Mamadoliev I. I. Yuqori kremniyli seolitning faollanish sharoitini maqbullashtirish //SamDU ilmiy axborotnoma. – 2019. – Т. 3. – №. 115. – С. 8-12.
12. Fayzullaev N.I., Mamadoliev I.I. Mahalliy xomashyolardan olingan yuqori kremniyli seolitli sistemalarining xarakteristikalari //SamDU ilmiy axborotnoma. – 2020. –№.119. – 52-56.