CC BY
44
Microcalorimetric study of carbon dioxide adsorption in BaY zeolite
References:
1. Mortier W. J. Compilation of Extra-framework Sites in Zeolites. - UK: Guidford, Butterworth Scientific Ltd., 1982, P. 244.
2. Breck, D. W. Zeolite molecular sieves. - New York: Wiley, 1974.
3. Barrer, R. M. Zeolites and Clay Minerals as Sorbent and Molecular Sieves, Academic Press, London, 1978.
4. Mentzen, B. F., Rakhmatkariev, G. U. Localization of Water Sorbed in Barium Exchanged Zeolite Y at Several Loadings. International Neutron Centre ILL. Grenoble. Experiment # 5-22-598, August, 2003.
5. Boddenberg, B., Rakhmatkariev, G. U., etc. A Calorimetrical and Statistical Mechanics Study of Water Adsorption in Zeolite NaY. Physical Chemistry Chemical Physics. 2002, 4, 4171-4180.
6. Moise, J. C., Bellat, J. P. ets. Adsorption of water vapor on X and Yzeolites exchanged with barium. Microporous and Mesoporous Materials. 2001, 43, 91-101.
7. Xianqin Wang, Jonathan C. Hanson, Ja Hun Kwak, Janos Szanyi, and Charles, H. F. Cation Movements during Dehydration and NO2 Desorption in a Ba-Y, FAU Zeolite: An in Situ Time - Resolved X - ray Diffraction Study. J. Phys.Chem. C. 2013,11, 3915-3922.
8. Isirikyan, A. A., Rakhmatkariev, G. U. Energy aspect ofvapor adsorption by A, X and ZSM - 5 zeolites. Proc. 5th Conf. Appl. Chem. unit aperations and processes. Balaton, Hungary, Sept. 3-7, 1989, 1, 61-67.
9. Boddenberg, B., Rakhmatkariev, G. U., etc. Statistical Thermodynamics of Methanol and Ethanol Adsorption in Zeolites NaZSM - 5 and LiZSM - 5. J. Phys. Chem. B, 1997, 101, 1634-1640.
10. Boddenberg, B., Rakhmatkariev, G. U., etc. A Calorimetric and Statistical Mechanics Study ofAmmonia Adsorption in Zeolite NaY. Physical Chemistry Chemical Physics. 2004, 6, (9), 2494-2501.
11. Lyapin, S. B., Rakhmatkarieva, F. G., Rakhmatkariev, G. U. Atomic - Absorption determination of ion - exchange cations in zeolites. Chem. Journal. Kz. 2015, (3), 304-310.
12. Mentzen, B. F., Rakhmatkariev, G. U. Host/Guest interactions in zeolitic nanostructured MFI type materials: Complementarity of X - ray Powder Diffraction, NMR spectroscopy, Adsorption calorimetry and Computer Simulations. Uzbek. khim. zh. 2007, (6). 10-31.
13. Rakhmatkariev, G. U. Mechanism of Adsorption of Water Vapor by Muscovite: A Model Based on Adsorption Calorimetry. Clays and Clay Minerals. 2006, 54. 423-430.
14. Rakhmatkariev, G. U., Isirikyan, A. A. Complete description of the adsorption isotherm by the equations of the volumetric micropore occupancy theory. Izv. AN SSSR, Ser. chem. 1988, (11), 2644-2645.
15. Boddenberg, B., Rakhmatkariev, G. U., Viets J. and Bakhranov Kh. N. Statistical thermodynamics of ammonia-alkali cation complexes in zeolite ZSM-5. Proceedings of the 12th International Zeolite Conference. July 5-10. 1998, Baltimore, Maryland, USA. 481-488.
Rakhmatkarieva Feruza, PhD, Researcher of Institute of general and inorganic chemistry
of Uzbekistan Academy of sciences Rakhmatkariev Gairat, Dr in chemistry, Prof., Head of Laboratory of Elemental analysis of Institute of general and inorganic chemistry of Uzbekistan Academy of sciences;
E-mail: vip.gairat@gmail.com Guro Vitaly Pavlovich,
Dr in chemistry, Head of Laboratory of Non-ferrous metals of Institute of general and inorganic chemistry of Uzbekistan Academy of sciences
Microcalorimetric study of carbon dioxide adsorption in BaY zeolite
Abstract: Differential heats and isotherm of carbon dioxide adsorption in a zeolite BaY have been measured by Tian-Calvet-type microcalorimeter and volumetric system at 303 K. Based on the data obtained, the mechanism of
77
Section 8. Chemistry
(СОД/Ba 2+ complexes formation in the zeolitic matrix of BaY is revealed. The adsorption isotherm is quantitatively reproduced by VOM theory equations.
Keywords: zeolite BaY, isotherm of adsorption, carbon dioxide, differential heats
Introduction. Host/guest complexes of Ba 2+ with normal and branched hydrocarbons in the Y zeolites are the most studied. However, there is too little number of papers on the adsorption of small molecules. Among them the special place is occupied by water, which due to its small size can penetrate into the sodalite cages [1]. Review of the problem of participation of the sodalite and supercages in the adsorption process is an extremely complex task, which has not found out its final decision. An attempt to solve this problem by the method of adsorption calorimetry was undertaken [2], but unsuccessfully due to the strong dispersion of experimental points of energy data. Synchrotron — based in situ time — resolved X — ray diffraction and Rietveld analysis were used to probe the interactions between Ba-Y, FAU zeolite frameworks and H2O molecules [3]. These results provide information on the formation of double rings of hexagonal ice like clusters [(H2O)6] in the 12 ring openings of the supercage. The attempt to face this issue was made by us as well. The results are presented in [4].
The next step in the study of BaY zeolite would be the application as a molecular probe relatively large molecules of carbon dioxide. It is expected that this quadrupole molecule as well as water can selectively interact with the positively charged cations ofbarium, but in contrast to carbon dioxide, water does not penetrate into the cavity sodalite BaY due to steric factors. Consequently, the test will be subject only to adsorption sites, which are located in the original supercage or appear there due to the migration of cations of hexagonal prisms and sodalite cavities.
Objective: Present work is devoted to revealing the detailed mechanism of carbon dioxide adsorption in BaY zeolite in a wide range of filling of the pore space by means of adsorption calorimetry. Among the precise structure — sensitive methods of investigation, adsorption calorimetry is unique [5] because it provides the most detailed information about the surface, crystal chemistry, and mechanism of host/guest clusters formation. Due to the differential adsorption heats of such probe molecules as water, methanol and ammonia [1; 6; 7] energetically uniform sites (cations) at monotypic crystallographic positions of zeolites were established stoihiometrically.
Subjects and methods. The original material for a specified sample obtaining was a NaY zeolite. The NaY (Si: Al=2.43) was a binder — free commercial product
(Linde LZ — Y52). The crystalline structure of this material was proved by X — ray powder diffraction, and the absence of extra — framework aluminum species was examined by 27Al MAS NMR spectroscopy. NaY was subjected to repeated treatment with a solution of BaCl2 Chemical analysis showed a full exchange of Ba 2+ on Na+. The chemical composition of the fully dehydrated Ba,A^t,SFff„, zeolite has been verified by elemental analysis. The method of sample decomposition of synthetic zeolites with simultaneous determination of moisture content and organic impurities, followed by atomic — absorption determination (Perkin — Elmer 3030B) of exchangeable cations Na and Ba content has been developed [8]. It eliminates the influence of structure — forming elements (Al, Si) and fluctuations in the moisture content of the probes on the analysis’ results.
Prior to admission of water, the BaY sample was heated under high vacuum at 450° C for 10 h in an all — glass apparatus. The adsorption isotherm was obtained by the volumetric method, on a basis of mass difference between the amounts of water introduced into the cell and remained in its dead space at equilibrium. The details of measuring the adsorption isotherms as well as the differential heats of adsorption using a differential microcalorimeter of the Tian — Calvet type have been described elsewhere [9; 10]. The application of compensating heat flux method based on Peltier effect allowed increasing the accuracy of adsorption heat measurement more than 10 times.
Results and discussions. Interpretation of data obtained using neutron powder diffraction data for increasing water amount have been realized by the Rietveld technique (modified DBW and GSAS codes) [11] showed the same framework coordinates of structural Si and O, that are usually observed for the Y zeolite. Positions of the Ba 2+ cations were determined when using profile simulation and by considering theoretical versus experimental intensities ratios. It has been found that in dehydrated condition of the zeolite the best distribution of the cations being calculated for 1/8 unit cell (uc) or supercage the following: 0.8 BaI 2+ in hexagonal prisms (D6R, position I), 0.5 Bar 2+ in the sodalite cages (position I’) and 2.2 BaII 2+ in the supercages (position II).
The differential heats (Qd) of carbon dioxide adsorption per 1/8 unit cell (N) in BaY at 303 K are presented at Figure. Qd curve has a complex wave-like appearance.
78
Microcalorimetric study of carbon dioxide adsorption in BaY zeolite
Each piece in the curve reflects the stoichiometric ratio between the number of energy-homogeneous adsorption centers and the number of adsorbed molecules. Total 5 pieces are allocated: 0-0.71, 0.71-3.48, 3.48-6.26, 6.26-7.43 and 7.43-8.16 CO2/1/8 uc.
Exchangeable cations of zeolites do create a high gradient electrostatic field and for quadruple molecules present the adsorption centers of varying strength depending on the degree of coordinative unsaturation. Against the background of high energy adsorption now energy of interaction with the active sites is imposed, giving a monotonous Qd curve an stepped appearance. These differential heats of adsorption of the quadruple molecules must also be of discrete nature (the stepped shape of the curve Qd) and must stoichiometrically reflect the number of homogeneous active sites in the adsorbent cavities of zeolites. For zeolites along with a universal thermodynamic approach the study of adsorption systems in molecular structural aspect is also indicative. The latter direction in which clear correlations are estab-
lished between the heats of adsorption and the number of homogeneous active sites in an adsorbent has been our priority over since 1969.
As can be seen from Figure, the curve of differential heats of carbon dioxide adsorption in the zeolites also has a stepped appearance, where each step on the curve Qd reflects certain stage of carbon dioxide adsorption on Ва 2+. Let us consider the mechanism of carbon dioxide adsorption on adsorption energy of stoichiometric interrelations basis with the construction of molecular — structural model. In accordance with the coordination non-saturation of cations in different crystallographic positions the first high-energy fragment is attributed to the adsorption of CO2 on the cations in the position S, the second one — on cations S, which are screened more by oxygen atoms of six-membered oxygen ring. At this stage all of Ва 2+ (3.5 Ва 2+ on 1/8 uc) do participate in the adsorption process to form a monomeric complex (CO2)/Ba 2+ in positions Sm, (0.71 CO2/1/8 uc) and SII (2.77 CO2/1/8 uc).
Fig. Differential heats of adsorption, Qd, of carbon dioxide molecules, (N), in BaY zeolite at 303 K. The horizontal dashed line is the heat of condensation of bulk water. Top: corresponding differential molar entropy of adsorption. The entropy of liquid carbon dioxide is taken as zero. Dashed line is an integral mean molar entropy
From this it follows that already at an early stage of adsorption of carbon dioxide Ва 2+ cations are leaving their positions in the six-membered oxygen prisms (SI) and sodalite cavities (Sr) and do migrate into supercages where “settle” in the S, and S positions. Ba 2+ cations do migrate under the effect of adsorption of relatively large (0 = 0.45 nm) non-penetrating into the sodalite cavity (0 = 0.26 nm) of a molecule of carbon dioxide. Despite the relatively weak charge on the oxygen atoms at the ends of the quadrupole molecule of CO2, compared with the oxygen atom of a polar molecule H2O, it is capable of pulling double-charged cations Ba 2+ from the sodalite cavities and hexagonal prisms in the supercages and form there adsorption systems (CO2)n/Ba 2+. Previously, basing on the example of NaY molecular sieve [7],
it was established that the quadrupolic carbon dioxide molecule is not able to extract the monovalent cation Na from hexagonal prisms and sodalite cavities.
The third fragment in length exactly corresponds to the second one and is responsible for formation of the complex with a second molecule СО2 — (СО2)2/Ва 2+. Attaching of a second molecule of CO2 to Ba 2+ in the position S, takes place at the final fifth stage of adsorption (7.43-8.14 CO2/1/8 uc), where 0.71 CO2/1/8 uc is attached to and forms a complex dimer (СО2)2/Ва 2+
Passage of Qd curve through a maximum in the fourth fragment (6.26-7.43 CO2/1/8 uc) occurs quite often in the adsorption of CO2 adsorbents of different nature (for example, [9]), and is caused by the formation of an ideal or distorted T — shaped configuration
79
Section 8. Chemistry
of two molecules of carbon dioxide, which leads to an increase in the heat of adsorption on the additional apart adsorbent-adsorbate mutual interactions of adsorbed molecules. The length of the fifth segment is correlated with the number of vacancies (free cations) at position SII — 1.17 СО2/1/8 uc.
In this case, it is possible at the same time on CO2 adsorption cations in positions S, и S.
Totally BaY holds 8.14 CO2 molecules/1/8 uc which are screened more oxygen atoms by six-membered oxygen ring.
Adsorption isotherm of carbon dioxide in the BaY zeolites is satisfactorily described by two — term equation of the theory of volumetric micropore occupancy (VMOT) [12].
N = 6.39 exp [-(A/25,55) 4] + 4.05 exp [-(A/13,79)4],
where N is the adsorption in micropores in CO2/(1/8) uc; A= RTln (po/p) — is the adsorption energy, kJ/mol.
Using precise values of the isotherms and differential heats of adsorption, we calculated differential molar entropy of adsorption (ASd) of carbon dioxide in BaY according to the equation of Gibbs — Helmholtz, ASd = = — (Qd — A H/T — R ln (p/po), wherepo is the pressure of carbon dioxide at saturation. The entropy of adsorption (Fig. top) is deferred from the entropy of liquid carbon dioxide at the measured temperature. The whole
curve is located above the level of entropy of liquid carbon dioxide.
The average molar integral entropy is 25J/mol*K. Differential and integral entropy indicates that the mobility of the carbon dioxide in the molecular sieve matrix is above its mobility in the liquid state.
Conclusion. The heat of adsorption of water in the zeolite have a stepwise appearance and every step meets the stoichiometric formation of adsorption complexes (C°2)i,/Ba2* in the matrix of BaY zeolite. The heat of adsorption of carbon dioxide at zero filling at S , ~ 56 kJ/mol. Ba 2+ cations in the zeolite BaY position S ~52 kJ/mol, and cations in position S .~ 56 kJ/mol. Differential adsorption heat have four fragments (1, 2, 3 and 5), corresponding to the formation of mono- and dimeric complexes with CO2 Ba 2+ cations at position S ,and S The fourth fragment is responsible for the formation of CO2 bidentate complex with cations S .and S, which are located in a vacant position of the cations S. The adsorption of carbon dioxide leads to a migration of Ba 2+ of hexagonal prisms and sodalite cavities of supercages into position S .and S for small fills the pore space. The adsorption isotherm is fully described with binomial equation VMOT. The mobility of the carbon dioxide in the matrix of the molecular sieve possesses high mobility in liquid carbon dioxide. Total supercage BaY holds 8.14 molecules of carbon dioxide.
References:
1. Boddenberg, B., Rakhmatkariev, G. U., etc. A Calorimetric and Statistical Mechanics Study of Water Adsorption in Zeolite NaY. Physical Chemistry Chemical Physics. 2002, 4, 4171-4180.
2. Moise, J. C., Bellat, J. P. ets. Adsorption of water vapor on X and Y zeolites exchanged with barium. Microporous and Mesoporous Materials. 2001, 43, 91-101.
3. Xianqin Wang, Jonathan C. Hanson, Ja Hun Kwak, Janos Szanyi, and Charles, H. F. Cation Movements during Dehydration and NO2 Desorption in a Ba-Y, FAU Zeolite: An in Situ Time - Resolved X-ray Diffraction Study. J. Phys.Chem. C. 2013,11, 3915-3922.
4. Rakhmatkarieva, F. G., Rakhmatkariev, G. U., Guro V. P. Microcalorimetric study of water vapor adsorption in BaY zeolite. Austrian Journal of Technical and Natural Sciences. 2015, № 11-12, 73-77.
5. Isirikyan, A. A., Rakhmatkariev, G. U. Energy aspect of vapor adsorption by A, X and ZSM - 5 zeolites. Proc. 5th Conf. Appl. Chem. unit aperations and processes. Balaton, Hungary, Sept. 3-7, 1989,1, 61-67.
6. Boddenberg, B., Rakhmatkariev, G. U., etc. Statistical Thermodynamics of Methanol and Ethanol Adsorption in Zeolites NaZSM - 5 and LiZSM - 5. J. Phys. Chem. B, 1997, 101, 1634-1640.
7. Boddenberg, B., Rakhmatkariev, G. U., etc. A Calorimetric and Statistical Mechanics Study ofAmmonia Adsorption in Zeolite NaY. Physical Chemistry Chemical Physics. 2004, 6, (9), 2494-2501.
8. Lyapin, S. B., Rakhmatkarieva, F. G., Rakhmatkariev, G. U. Atomic - Absorption determination of ion - exchange cations in zeolites. Chem. Journal. Kz. 2015, (3), 304-310.
9. Mentzen, B. F., Rakhmatkariev, G. U. Host/Guest interactions in zeolitic nanostructured MFI type materials: Complementarity of X - ray Powder Diffraction, NMR spectroscopy, Adsorption calorimetry and Computer Simulations. Uzbek. khim. zh. 2007, (6). 10-31.
80
Investigation of physicochemical properties of synthesized amphoteric ion exchangers
10. Rakhmatkariev, G. U. Mechanism of Adsorption of Water Vapor by Muscovite: A Model Based on Adsorption Calorimetry. Clays and Clay Minerals. 2006, 54. 423-430.
11. Mentzen, B. F., Rakhmatkariev, G. U. Localization of Water Sorbed in Barium Exchanged Zeolite Y at Several Loadings. International Neutron Centre ILL. Grenoble. Experiment # 5-22-598, August, 2003.
12. Rakhmatkariev, G. U., Isirikyan, A. A. Complete description of the adsorption isotherm by the equations of the volumetric micropore occupancy theory. Izv. AN SSSR, Ser. chem. 1988, (11), 2644-2645.
Eshkurbonov Furkat Bozorovich, Teacher Termez State University, Uzbekistan Surhondarinskaya region, Termez, E-mail: furqat-8484@mail.ru Turaev Hayit Hudaynazarovich, Professor, Doctor of Chemistry, Dean of the Engineering Faculty of Termez State University, Uzbekistan Surhondarinskaya region, Termez, E-mail: hhturaev@mail.ru Jalilov Abdulahat Turapovich, Professor, Doctor of Chemistry, Director of the State Unitary Enterprise of the Tashkent Scientific Research Institute of Chemical Technology, Uzbekistan, Tashkent
E-mail: gup_tniixt@mail.ru
Investigation of physicochemical properties of synthesized amphoteric ion exchangers
Abstrast: The paper studied the process of obtaining amphoteric ion exchangers based on hydrolyzed polyacrylonitrile (GIPAN) and polyethylene polyamine (PEPA) and epichlorohydrin (EXG). The presence of hydroxyl, epoxy and amino groups in starting materials, reaction mixture and the final product was studied IR, UV spectroscopic analysis methods. When using the hydrolyzed polyacrylonitrile in a molar ratio of 1.0:1.25 exchange capacity of the ion exchanger reaches 4-4,2 mg-ekv/g. By increasing the hydrolyzed polyacrylonitrile to 2.5 m. r. resins obtained have a lower mechanical strength, but with a sufficiently high exchange capacity, up to 5.2 mg-ekv/g.
Keywords: amphoteric ion exchangers, hydrolyzed polyacrylonitrile (GIPAN), polyethylene polyamine (PEPA), epichlorohydrin (EXG), sorption, infrared spectra obtained, the epoxide groups.
Currently, one of the promising directions of the ion-exchange material is the use of reactive oligomers containing ionic groups. Using them as a starting material allows the reaction under mild conditions without using, during this reaction, the polymer analogous reactions. The use of hydrolyzed polyacrylonitrile products of interaction with nitrogen-containing compounds allows to obtain resins which are promising in the process of sorption of some metals from a variety of solutions. As is known, by reacting compounds containing an amino group with a halogen-containing compounds occurs molecular nucleophilic substitution of alkyl halides and increase the primary amine. Thus, in contrast to primary and secondary amines, tertiary amines to form quaternary salts, alkyl group attaching. Interaction with polyethylene polyamine epichlorohydrin results in the
disclosure of the stress cycle oksiaranovogo epichlorohydrin under the influence of a nucleophilic group to form chlorohydrins [1; 2]. Polycondensation of hydrolyzed polyacrylonitrile (GIPAN) and polyethylene polyamine (PEPA.) With epichlorohydrin (EXG) obtained carboxyl and nitrogen-containing oligomeric compounds. In order to identify regularities in the formation of condensate odds, we studied the effect of synthesis conditions on the condensation reaction of the hydrolyzed polyacrylonitrile and polyethylene polyamine with epichlorohydrin (the duration and temperature of reaction, ratios of starting components and others.). The temperature was varied between 80-100 °C. Thus, we investigated the change in molecular weight and intermediates forkon-densatov obtained, the concentration of epoxy groups (Table 1.).
81
