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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 3 2022 99
ISSN 0005-2531 (Print)
UDC 541.64+543.226
ADSORPTION STUDY OF ACETONE ON THE SORBENTS BASED ON
MONTMORILLONITE
N.A.Imanova, F.M.Sadixov
M.Nagiev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
naileimanova91@gmail.com
Received 21.04.2022 Accepted 03.05.2022
Corresponding cation forms of the montmorillonite samples taken from the Ag-Dere bentonite deposit were obtained by processing them with Co2+ and Ni2+ salts. The nature and amount of acid sites formed on the surfaces of the obtained samples were studied by adsorption of acetone using the derivatographic method. The critical diameter of the acetone molecule is d = 5.6A0 and pka = -7.2. Analysis of derivatograms shows that the mass loss changes depending on the ionic radius, nature and temperature of the cation exchanges as follows: Co2+ mont> Ni2+ mont> natural mont. Based on the conducted study it was estableshed that there are weak, medium and strong electron-acceptor centers on the surface of the sorbent which differ energetically. The endothermic effect observed on the DTA curve at a temperature range of 219.3-566.30C characterizes the physical adsorption of an acetone molecule on the surface of a montmorillonite sample. The effects observed at 706.9 and 775.70C characterize the strong acid sites. The amount of electron-acceptor centers formed on the surface of monmorillonite changes depending on the charge of cation exchangers. The number of electron-acceptor centers formed on the surface of Co2+ bentonite is higher than in other samples. The amount (a.mmol.g) and desorption energy (E, kDc, mol-1) of acetone molecule desorbed from the active sites in different temperature ranges were calculated. It was determined that the most capable of adsorbing acetone molecules is Co2+-montimorillonite, which can be used as a sorbent to prevent envoiremental pollution with acetone. Corresponding cation forms of the montmorillonite samples taken from the Ag-Dere bentonite deposit were prepared by processing with Co2+ and Ni2+ salts. The nature and amount of acid sites formed on the surfaces of the obtained samples were studied by adsorption of acetone using the derivatographic method. Based on the conducted study it was estableshed that there are weak, medium, strong electron-acceptor centers on the surface of the sorbent which differ energetically. The amount (a.mmol.\g) and desorption energy (E, kDc, mol-1) of acetone molecule desorbed from the active sites in different temperature ranges were calculated. As a result of the research, it was found that the most capable of adsorbing acetone molecules is Co2+-form of montimorillonite, which can be used as a sorbent to prevent envoiremental pollution with acetone.
Keywords: acetone, modification, montmorillonit, acid-base, sorbent.
doi.org/10.32737/0005-2531-2022-3-99-104 Introduction
The porous structure, physical and mechanical characteristics, low cost make extensive use of natural montmorillonite as catalysts and sor-bents in various sectors of the national economy.
The use of natural clay minerals in sorption processes is promising and relevant due to their low cost and inexhaustible reserves. In this regard, the development of methods for the preparation of new effective sorbents based on natural montmorillonites is of great practical importance for the purification of waste water and liquid waste from heavy metal ions and various toxic substances [1-6].
These works [1-4] are devoted to the preparation of adsorbents and catalysts by processing bentonites with aqueous solutions of various metal salts and the study of their physico-chemical properties using modern physical methods of analysis.
This paper presents the main results of the study on the adsorption properties of natural and modified forms of montmorillonite. Mont-morillonite from Ag-Dere deposit was selected as the object of study.
Despite the widespread use of natural montmorillonite in the petrochemical and gas industries as adsorbents and catalysts, the nature, strength, quantity, and distribution of acid
sites on their surface are not well understood [2-6].
Effective sorbents based on montmoril-lonite have been created by processing them with various metal salts. The nature, strength, number of acid sites were studied by adsorption of various molecular probes such as ammonia, acetone, n-butylamine, carbon dioxide using spectroscopy and derivatography methods [7, 8, 9]. As it s known [10], acetone is a probe of only one type of center (electron-acceptor) existing on the surface of catalysts, sorbents, and the small critical diameter of the molecule (5.6A0) makes it possible to penetrate into the internal cavities of the montmorillonite sample.
Experimental part
The natural montmorillonite samples were crushed, sieved, collecting a fraction with a granule size of 0.25-0.5 mm. Modified forms of montmorillonite were obtained by processing them with corresponding metal salts at 3000C for 6 hours [11] followed by washing the samples with water until a negative reaction for Cl-or SO 4-2and the purpose of the work is to study the acid sites of natural and modified forms of montmorillonite by acetone adsorption using derivatography method. The conditions for the processing of samples with solutions of varions salts and the study of the nature, quantity, strength and concentration of adsorption centers formed on their surfaces bu molecular centers (zonds) are shown in the literature.[12, 20, 21].
X-ray studies of bentonite sorbents were carried out on a diffractometer D2-Phaser using CuKa radiation, and derivatographic studies on a derivatograph STA449F3Yupiter using analysis methods [7, 13, 21, 22] The mineralog-ical composition of the samples was determined by X-ray diffraction and it was found that both samples contain 70-80% montmorillonite and the remaining minerals are quartz, calcite, feldspar and mica and these minerals do not participate in chemical reactions (Table 1).
Figure 1 shows the derivatogram of natural montmorillonite after acetone adsorption. As can be seen from the derivatogram obtained by heating the sample, the DTA curve shows two endothermic effects with a maximum at temperatures of 158.40C and 223.60C.
After treatment of montmorillonite with nickel salt and acetone adsorption on it, the endothermic effect on the DTA curve with a maximum at temperature 158.40C shifts to 228.90C with increasing intensity.
Furthermore, an additional minimum appears on the DTA curve, in comparison with natural montmorillonite at temperatures 484.2 and 732.10C (Figure 2).
During the retining of montmorillonite with an aqueous solution of a cobalt salt,the appearance of new electroacceptor centers was observed upon its surface..
Figure 3 shows the derivatogram of cobalt form of montmorillonite after acetone adsorption. After processing natural montmorillonite with a cobalt salt and heating it with adsorbed acetone, an endothermic effect with a maximum at 219.30C and three exothermic effects with a maximum at 566.3 , 706.9, 775.70C appear on the DTA curve.
The observed endothermic effects on the DTA curve in the temperature range of 219.3-566.30C characterize the desorption of physically adsorbed acetone molecules from the surface of the investigated montmorillonite samples.
The appearance of endothermic effect with a maximum at 706.90C, 775.70C, 887.90C on the DTA curve shows that after the treatment of natural montmorillonite with aqueous solutions of cobalt salts, the surface properties of natural montmorillonite change, and new electron-acceptor centers appear.
The appearance of endothermic effect at a temperature of 566.30C indicates that two processes of oxidation and desorption take place simultaneously.
Table 1. Mineralogical composition % of the presented samples.
Conventional terms SiO2(a quartz) Feldspar montmorillonite CaCO3 calcite Fe2O3 NaCl
Agdere bentonite 6.2 10.8 75,6 4.2 4.5 0.4
Fig.2. Derivatogram of Ni-montmorillonite after acetone adsorption.
BO
i: 01.21 % (S9B.3 "<
Fig. 3. Derivatogram of Co-montomorillonite after acetone adsorption.
The exothermic effect in the range of 775.7-887.90C is associated with the rate maximum of acetone thermal-oxidative degradation. It should be noted that the critical diameter of an acetone molecule (5.6A0) makes it possible to interact with acid centers located on the internal and external surfaces of the sample.
The temperature maximum of the endo-thermic effect in the range of 566.3-06.90C corresponds to the desorption of acetone molecules held with an average strength of electron-acceptor centers and in the range of 706.3-775.70C it characterizes the desorption of acetone molecules from strong electron-acceptor centers on sorbents based on natural montmoril-lonite. Endothermic effects with temperature maximum in the range of 775.7-887.90C, in our opinion, characterize the desorption of acetone with very strong electron-acceptor centers located in the secondary pores of its compaction product.
Based on the obtained derivatograms, the amounts of acetone molecules desorbed from the active centers of sorbents at different temperatures have been calculated and the results are presented in Table 2. Experimental study
indicates that the amount of acetone desorbed from montmorillonite samples, depending on the ionic radius, changes as follows:
2+ 9+
Co -montm>Ni -montm>natural. montmore.
It was found that the number of desorbed acetone molecules from montmorillonite samples obtained on the basis of Co -montmorillonite is greater than other forms.
The desorption energy (E), the number of adsorbed acetone molecules related with electron-acceptor centers on the studied montmoril-lonite samples were determined in accordance with the area of endothermic effects based on reference samples (Table 3).
Determination of the desorption energy of adsorbed molecular probes from the surface of catalysts and sorbents is described in detail[14, 20]. Based on the comparison of acetone desorption energy (E) from the electron-acceptor centers of sorbents obtained on the basis of montmorillonite, it was found that the acetone desorption energy related with electron-acceptor centers existing on samples of the Co form is greater than in others.
Table 2. The number of acetone molecules desorbed from modified forms of montmorillonite samples at different desorption temperatures (a, mmol/g-1)._
Samples Temperature, C0
20-00 200-300 300-500
a ( mmol.g-1)
1. Montmorillonite 2.36 0.10 0.20
2. Co2+-Montmorillomte 2.87 1.23 0.60
3. Ni2+-Montmorillomte 2.50 1.18 0.45
Samples Temperature maximum of endothermic effects, C0
Montmorillonite 220 520 770
a 0.83 0.19 0.19
E 66.40 74.7 107.2
Ni+2 - form of montmorillonite 230 484 732
a 1.50 0.08 0.4
E 72.63 83.0 116.9
Co+2 - form of montmorillonite 219 706 775
a 1.83 0.17 0.08
E 72.63 95.5 132.3
Table.3 Amount (a, mol.kg-1) and desorption energy (E, kJ.mol-1) of acetone from sorbents at different temperatures in accordance with the area of endothermic effects.
During the adsorption of acetone on a montmorillonite sample, an interaction occurs
2+ 2+
between the acetone molecule and Ca , Mg ions located in the interlayer space of bentonite. An ion-dipole interaction is formed.
A coordination bond is formed between the adsorbed acetone and the electron-acceptor center of the sample due to the interaction of a lone pair of electrons of the carbonyl oxygen atoms with a free orbital of metal atoms on montmorillonite (CH3)2C=O:Me
When studying the physicochemical properties of the samples, it was found that there are acid centers on their surface, which are actively involved in the cleaning process.
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MONTMORÍLLONÍT OSASINDA ALINMI§ SORBENTLORÍN ASETONUN ADSORBSÍYASI
VASÍTOSÍ ÍLO TODQÍQÍ
N.a.imanova, F.M.Sadiqov
Ag-Dara bentonit yatagindan götürülmü;? montmorillonit nümunasini Co2+ va Ni2+- metallannin duzlan ila i§lamakla müvafiq kation formalari hazirlanmi§dir.Onlain sathlarinda amala galan tur§u markazlarinin tabiati,miqdari derivatoqrafik üsulla asetonun adsorbsiyasi vasitasila tadqiq edilmi§di.Aseton molekulasinin kritik diametri d=5.6A va pk^-7.2 dir. Asetonun kritik diametri ham daxilda,ham sathdaki tur§u markazlarinin öyranilmasina imkan verir. Derivatoqrammalann analizi göstarir ki, kütla itkisi mübadila kationlanmn ion radiusundan, tabiatindan va temperaturdan asili olaraq a§agidaki kimi dayi§ir: Co2+mont> Ni+2mont>tabii-mont. Co2+, Ni2+ formali sorbentlarinin asetonun adsorbsiyasi vasitasila tadqiqi zamani nümunalarin sathinda zaif, orta,qüvvatli elektron akseptor markazlarin olmasi müayyan eilmi§dir. DTA ayrisi üzarindaki 219.3-566.30C temperaturda mü§ahida olunan endotermik effekt, montmorillonit nümunasinin sathina aseton molekulasinin fiziki adsorbsiyasini xarakteriza edir.706.9 va 775.70C temperaturda mü§ahida olunan effeklar isa qüvvatli tur§u markazlarini xarakteriza edir.Montmorillonitin sathinda amala galan elektron akseptor markazlarinin miqdan mübadila kationlanmn yükündan asili olaraq dayi§ir. Co2+ formali bentonitin sathinda amala galan eletron akseptor markazlarinin miqdan digar nümunalarla müqayisada daha da goxdur. Müxtalif temperatur intervallannda adsorbsiya olunan aseton molekulasinin miqdan (a mmol./q) va desorbsiyasina sarf olunan enerji (E, kc mol -1) hesablanmi§di. Aseton molekullanni an gox adsorbsiya etma qabiliyyatina malik olan Co2+ formali montmorillonitdi va ondan atraf mühitin asetonla girklanmasinin qar§isini almaqda sorbent kimi istifada etmak olar.
Agar sözlar: aseton, modifikasiya, montmorillonit, aktiv m3rk3z, sorbent.
ИСЛЕДОВАНИЕ АДСОРБЦИИ АЦЕТОНА НА СОРБЕНТАХ ПОЛУЧЕННЫХ НА ОСНОВЕ МОНТМОРИЛЛОНИТА
Н.А.Иманова, Ф.М.Садыхов
Путем обработки образцов монтмориллонита взятых из бентонитового месторождения Аг-дере солями кобальта и никеля были получены соответствующие катионные формы. Природа и количество кислотных центров образованных на поверхности полученных образцов исследованы дериватографическим методом адсорбцией ацетона. Критический диаметр молекулы ацетона составляет d = 5.6 A и pka = -7.2. Анализ дериватограмм показывает, что потерие массы в зависимости от ионного радиса, природы и температуры катионообменников меняется следующим образом: ^^^^^^^природный монт. В результате проведенного исследования установлено, что на поверхности сорбента в зависимости от ионного радиуса катионо -обменников имеются слабые, средние и сильные электроноакцепторные центры которые отличаются друг от друга энергетически. Наблюдающиеся эндотермические эффекты на DTA в интервале температур 219.3 -566.30C характеризуют физическую адсорбцию молекулы ацетона на поверхности монтмориллонитового образца. Эффекты, наблюдающиеся при температурах 706.9 и 775.70C, характеризуют сильные кислотные центры. Количество электроноакцепторных центров, образующихся на поверхности монтмориллонита, меняется в зависимости от заряда катионообменников. Были рассчитаны количество (а,ммоль/г) и энергия десорбции (Е,кДж/моль1-) молекул ацетона десорбированных с активных центров в различном интервале температур. В результате проведенных исследований установлено, что молекулы ацетона лучше всего адсорбируются кобальтовой формой монтмориллонита и его можно использовать в качестве сорбента для предотвращения загрязнения окружающей среды ацетоном.
Ключевые слова: ацетон, модификация, монтмориллонит, активные центр, сорбент.
