CC BY
33
Section 10. Chemistry
Doliyev Golib A.,
Junior researcher, Laboratory of Elemental Analysis of Institute of General and Inorganic Chemistry of Uzbekistan Academy of Sciences;
Rakhmatkariev Gairat U., Dr in Chemistry. Prof., Head of Laboratory of Elemental analysis of Institute of General and Inorganic Chemistry
of Uzbekistan Academy of Sciences;
Rakhmatkarieva Firuza G., PhD, Researcher of Institute of General and Inorganic Chemistry of Uzbekistan Academy of Sciences.
Adsorption mechanism of CO2 and C6H6 on Na-illite
Abstract: The differential heats of adsorption, isotherm and thermokinetics of benzene and carbon dioxide (IV) in the Na-illite at 303K were measured. It is found that the migration of Na+ cations on the basal and lateral faces under the effect of adsorbed water is completely reversible. The amount of Na+ cations on the basal surface is 93 ^mol/g. About 60% of the adsorbed carbon dioxide involved in the interaction of the adsorbate-adsorbate, which is accompanied by the increase of adsorption heat, and passing through a maximum. The mobility of the molecules of CO2 on the surface of Na-illite is higher than in the bulk liquid. Wave like character of the curve of heats of adsorption of benzene vs surface filling are identified. Each stage demonstrates a stoichiometric interaction of benzene with Na+ cation. The first two stages correspond to the benzene adsorption on Na+ cations in the ratio 1:1. Further adsorption occurs in between the adsorbed molecules. In total, about 4 monomolecular layers are formed. The condition of benzene on the Na-illite surface is liquid-like.
Keywords: Na-illite, benzene, carbon (IV) dioxide, adsorption calorimetry
Introduction. The widespread use of minerals to investigate the differential heats (Qd) ofCO2 adsorption (muscovite, illite, etc.) as adsorbents and catalysts for on Na- illite after adsorption-desorption cycle. a number of technological processes of purification, First, it is to be noted that due to the high vapor pres-
drying, in technology and in other fields is possibly due sure of CO2 (P ° = 54086 mm Hg) at 303K, we could to their adsorption properties. Among the recent years not get the full CO2 adsorption isotherm on Na-illite. publications there are papers of detailed study of surface The adsorption isotherm of carbon dioxide in the Na-properties of these minerals and structures of adsorbed illite is shown in semi-logarithmic coordinates (Fig. 1). substances [1-2]. All these studies were conducted with Isotherm in the initial domain is concave, and when fill-micas, having mainly K+ as ion exchange cation. There is ing ~ 80 ^mol/g it is rapidly growing up. Isotherm treat-significant interest to study the effect of Na+ cations on the ment with BET equation demonstrated a specific surface adsorption properties of illite surface. Unlike potassium, area of the sample equal to 99.3 m 2/g. number ofworks devoted to sodium is very limited. In this The differential heats of adsorption (Qd) were
work, we attempted to study the adsorption mechanism measured with a differential automatic calorimeter of carbon dioxide and benzene on Na-illite by means of Tian-Calvet [5; 6]. Isotherms of adsorption were adsorption-calorimetry. Among the precise structure- obtained by volumetric method. The accuracy of sensitive methods, adsorption calorimetry supplies the the measured isotherm was ~ 0.1%, and the heat of most extensive information about chemistry, physics adsorption of ~ 1%. The composition of the studied and crystal chemistry of solid surface [3; 4]. In order to Na-illite was Na1-15 Al4 [Si7-65 Al115O20] (OH)4. The determine how far this process is reversible, we decided adsorption was carried out at 303K.
Fig. 1. Adsorption isotherm
The differential heats of CO2 adsorption on the Na-illite (fig. 2), in total, have a stepwise character. However, a plateau at the level of 34 kJ/mol is interrupted with a maximum, reaching to 51.5 kJ/mol, which starts with 10 ^mol/g and ends at 54 ^mol/g. In addition, the rapid fall happens at the initial stage of adsorption, starting from 70 kJ/mol to 37 kJ/mol at a = 10 ^mol/g. Plateau ends at 93 ^mol/g, wherein the heat drops to 27.7 kJ/mol, and remains at this level till about 140 ^mol/g. Domain of inhomogeneity (0-10 ^mol/g) at low surface coverage of Na-illite with carbon dioxide, apparently happens due to the presence of mixed cations on the surface on which CO2 is adsorbed with high heats. Taking into consideration very high adsorption energy (70 kj/mol), it is possible to assume that mixed
70 i
«
T3
O)
of œ2 on Na-illite at 303К
cations are the polyvalent cations, as far as monovalent cations such as Na + or Li +, arranged in hexagonal cavities are adsorbed with the heat ~36 kJ/mol. Further adsorption occurs on Na+ cations with the constant heat of ~ 34 kJ/mol. The reason of the maximum on the Qd curve is the tendency of adsorbed CO2 molecules to associate with each other. Incidentally, the adsorption energy of CO2 on Na-illite impose additional interaction energy adsorbate-adsorbate, leading to an increase in heat. Starting from 10 ^mol/g and up to 54 ^mol/g adsorption of CO2 is accompanied by the interaction of the adsorbed molecules among yourselves. Such a high maximum of the curve Qd is explained with association of CO2 molecules adsorbed on the high energy centers and their neighboring Na+ cations.
45
20 <D
30 60 90 a, /zmol/g
120 150
Fig. 2. Ddifferential heats of CO2 adsorption on illite at 303 K. Dashed line is the heat of condensation of bulk water
Fig.3. Ddifferential molar entropy of CO2 adsorption on Na-illite at 303 K. Dashed line is integral mean molar entropy. The entropy of liquid CO2 is taken as zero
The heat of condensation of CO2 is equal to 27 kJ/mol. Heats of adsorption, greater than this dimension, correspond to the absorption on active centers of the adsorbent surface, in our case on the Na+ cations. Consequently, a plateau at 34 kJ/mol, which extends up to 93 ^mol/g, is responsible for adsorption on the Na+ cations, which are in hexagonal holes of basal Na-illite surface. This value corresponds with the data of the low-temperature adsorption of nitrogen on the initial sample of Na-illite until water adsorption. Since the initial surface of Na-illite and surface after adsorption of water
contain the same quantity of cations--93 ^mol/g, we
can conclude that the adsorption of water is a reversible process. Consequently, migration of cations to the Na-illite surface coming from the adsorption of water molecules is a reversible process, the cations, migrating from the bulk volume of Na-illite to the surface, return during desorption. In total, the entropy curve is above zero. Average integral mean molar entropy is equal to 27 J/mol*K. It can be concluded that, the mobility of the adsorbate on the surface of Na-illite is higher than the mobility in liquid carbon dioxide.
Fig. 4. Adsorption Isotherm of 0MC on Na-illite at 303К
In Fig. 4 represented isotherm of benzene adsorption on Na-illite in semi-logarithmic coordinates. Isotherm in coordinates of BET equation is linear in the range of relative pressures 0,046 < P/Po < 0.36. Capacity of monomolecular layer (am) was 615 ^mol/g, energetic constant equaled to 1.05. If the area occupied
by a benzene molecule in a dense monomolecular layer (wm) is accepted as 48 A 2, specific surface by benzene equals to 180 m 2/g.
The differential heats of adsorption of benzene on Na-illite in monomolecular coverage of the surface possess wavelike falling view (Fig. 5).
Fig. 5. Differential heats of C6H6 adsorption on Na
The differential heats of adsorption ofbenzene on Na-illite in the initial domain overstated (~ 70 kJ/mol) and falls until 40.4 kJ/mol at 107.2 ^mol/g. As on the basal surface of the Na-illite contained 92 ^mol/g of Na+ cations, it is not difficult to figure out that the lateral surface fits to 15.2 (107,2-92 = 15.2) ^mole/g ofNa+ cations. This fragment is determined with the formation ofn-complexes of benzene with the Na+ cations, located on the basal and lateral faces. Further happens the filling process of the vacant ditrigonal holes on the surface ofillite with Na cations, migrated from the neighboring layers. By the adsorption 536 ^mol/g, all vacant holls are filled with n-benzene complexes with Na+ cations. The adsorption process is very complicated and is accompanied with the migration of cations, thus in the curve Qd we observe undulating decrease of absorption heat. Formation of the second layer also proceeds with undulating changes of adsorption heat, indicating the participation of Na+ cations in the formation
-illite at 303K. Da-shed line is a heat of condensation
of the second layer. Further adsorption continues with formation of the 3rd and 4th layers. Using the isotherm and the differential heats of adsorption ofbenzene on Na-illite, we calculated differential molar entropy of adsorption ASd (Fig. 6). In the domain of monomolecular filling, curve is close to the entropy ofliquid benzene, demonstrating that the mobility of benzene is close to the mobility in the liquid. During the completion of the 2nd layer, the entropy is lower that the entropy of liquid benzene. Hence, the mobility of benzene in this layer is slightly slows down comparing to the mobility in the liquid benzene.
Adsorption without cations leads to an increase of entropy and it crosses the zero point, and increases towards the positive region, indicating the increase benzene mobility as compared with its mobility in the liquid. Mean molar integral entropy is -6.41 J/mol*K, thus in the whole system benzene-Na-illite, the condition of benzene is close to liquid-like.
Fig.6. Differential molar entropy of C6H6 adsorption on Na-illite at 303K Dashed line is integral mean molar entropy. The entropy of liquid C6H6 is taken as zero
Synthesis of phosphoric acid cation- exchange polymer of polycondensation type
The time to establish adsorption equilibria during
As a result of high-precision measurements of
the formation of monomolecular layer slowed ~ 4 hours, and the second layer is formed for ~ 2 h.
Conclusion In this work we determined that the migration of Na+ cations on the basal and lateral faces under the influence of adsorbed water is completely reversible. The number of Na+ cations on the basal surface equals 93 ^mol/g. About 60% of the adsorbed carbon dioxide is involved in the adsorbate-adsorbate interactions, which is accompanied with the growth of the adsorption heat and its passing through a maximum. The mobility of the CO2 molecules on the surface of Na-illite is higher than in the liquid.
References:
the adsorption heats of benzene on illite, we revealed wavelike property of heats ofbenzene when the surface is filled.
Each stage reflects the stoichiometric interaction of benzene with Na+ cations. First two stages correspond to adsorption.of benzene with Na+ cations in the ratio 1:1. Further adsorption takes place in the intermediates between the adsorbed molecules. On the total surface approximately 4 monomolecular layers are formed. The condition of benzene on the surface of Na-illite is liquidlike.
1. Diaz M., Farmer V.C, Prost R. Characterization and assignment of far infrared absorption bands of K+ in muscovite//Clays and Clay Minerals. - 2000. - V. 48, №. 4. - P. 433-438.
2. Pluijm Ben A., Lee J. H., Peacor D. R. Analytical electron microscopy and the problem of potassium diffusion/Clays and Clay Minerals. 1988. V.36. No. 6. P. 498-504.
3. Boddenberg B., Rakhmatkariev G. U., Viets J. Thermodynamics and Statistical Mechanics ofAmmonia in Zeolites NaZSM-5//Ber.Bunsenges Phys. Chem. - 1998. - V. 102. - P. 177-182.
4. Boddenberg B., Rakhmatkariev G. U., Greth R. Statistical Thermodynamics of Methanol and Ethanol Adsorption in Zeolite NaZSM-5//J. Phys.Chem. B. -1997. - V. 101. - P. 1634-1640.
5. Mentzen B. F., Rakhmatkariev G. U. Host/Guest interactions in zeolitic nonostructured MFI type materials: Complementarity of X-ray Powder Diffraction, NMR spectroscopy, Adsorption calorimetry and Computer Simulations//Uzbek. Khim. Zh. - 2007. - № 6. - C. 10-31.
Turobjonov Sadriddin Maxamaddinovich, Tashkent Institute of Chemical Technology, Rector E-mail: [email protected] Rakhimova Latofat Sobirdjanovna, Tashkent Institute of Chemical Technology, Senior lecturer
E-mail: [email protected]
Synthesis of phosphoric acid cation- exchange polymer of polycondensation type
Abstract: Were studied the reaction of phosphorylation obtained diphenyloxide-furfural polymer for produce the new phosphoric acid exchange polymer with capacity of 5,8-6,0 mg-eq/g. Investigated the influence of the nature and concentration of the phosphorylating agent, the temperature and duration of the phosphorylation reaction, concentration and nature of the catalyst on the properties of phosphoric acid cation exchange polymer. On the basis of studies to determine the optimum conditions for obtaining cation exchanger.
Keywords: Diphenyloxide-furfural polymer, phosphorylation, cation exchanger, swelling, static exchange capacity.
Introduction. Among the known phosphoric acid cation ion exchangers have a special meaning. They are characterized by a number of valuable properties: high capacity, selectivity to ions of certain metals. It should be also noted chemical and thermal stability
of the cation exchanger from the carbon-phosphorus, especially aromatic-phosphorus which is significantly higher than for ion-exchange polymers with carbon-sulfur, carbon-nitrogen or carbon-carbon, thermal destruction of which begins with the destruction of
