- Email: [email protected]
Influence of polyelectrolytes on crystallization of zeolite Y
Journal of Crystal Growth 355 (2012) 8–12
Contents lists available at SciVerse ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Influence of polyelectrolytes on crystallization of zeolite Y ¨ z a, A. Nusret Bulutc- u b ¨ ¨ glu a,n, Pembe Hande O Hansu Julide Koro˘ a b
TUBITAK Marmara Research Center, Chemistry Institute P.O. Box 21, 41470, Gebze-Kocaeli, Turkey Istanbul Technical University, Chemical Engineering Department, 80626, Maslak, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 August 2011 Received in revised form 30 April 2012 Accepted 7 May 2012 communicated by S.R. Qiu Available online 16 May 2012
In this study, the influence of polyelectrolytes on the crystallization of zeolite Y is investigated. The prepared synthesis mixtures are aged at room temperature for 24 h and then left to crystallize. The compositional and structural information are provided by elemental analysis obtained by ICP, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), particle size analyzer and adsorption and desorption isotherms of nitrogen by a volumetric adsorption instrument. The first group of synthesis studies is conducted by using solutions containing no additive (WA), nonionic (NI), 100% anionic (100A), and 100% cationic (100C) polyelectrolytes. The crystallization temperature and o crystallization time are kept at 100 % C and 48 h, respectively. The experimental results show that nonionic polyelectrolyte has the most influence on the crystallization of zeolite NaY. In the second group of synthesis studies, the effects of polyelectrolytes with various degrees of anionic properties (10%, 50% and 70%) of the same chemical structure are investigated by conducting crystallization experiments at 100 1C for a duration of 48 h. The results suggest that; particle size, crystallinity and BET surface area (SBET) can be controlled by adding anionic polyelectrolytes to the solution. & 2012 Elsevier B.V. All rights reserved.
Keywords: A1. Characterization A1. Crystal structure A2. Growth from solution B1. Inorganic compounds B1. Polymers
1. Introduction Zeolites occur in nature and have been known for almost 250 years as aluminosilicate minerals. Examples are faujasite, mordenite, offretite, ferrierite, erionite and chabazite. Today, these and other zeolite structures are of great interest in catalysis research, yet their naturally occurring forms are of limited value, because (i) they almost always contain undesired impurity phases, (ii) their chemical composition varies from one stratum to another in the same deposit, and (iii) nature did not optimize their properties for applications [1]. Zeolite Y (faujasite) is one of the most important zeolites in terms of the volume of research activity and the scale of commercial use. The major applications of synthetic zeolite Y are in the fields of fluid catalytic cracking (FCC) of vacuum gasoil and in the adsorption of volatile organics from wet off-gas streams. Faujasite materials are characterized by a high surface area, uniform pore size distributions and high thermal stability [2].Hydrated aluminio silicates in crystalline form referred as ‘‘Molecular sieves’’ exhibit narrow channel in their structure. Zeolite Y (faujasite) is one of the zeolites constructed by joining the interrupted cubic octahedrals with hexagonal prisms [3].Raw materials used in the synthesis process of zeolite Y are reactive silica, alumina and sodium
n
Corresponding author. Tel.: þ90 262 677 29 21. ¨ glu). E-mail address: [email protected] (H.J. Koro˘
0022-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.05.013
hydroxide. As an alumina source, it is possible to use activated alumina, gamma alumina, aluminum hydroxide and sodium aluminates. Sodium silicate, silica gels, silicic acid, hydrated colloidal silica sols and reactive amorphic solid silica can be used as silicate sources [4,5]. The sodium hydroxide procures Na þ ions and controls the pH of the process [6]. The crystallization of zeolite NaY is autocatalytic and crystal growth is characterized by S-shape plots [7]. In many works, seeding is interpreted as a way of reducing the time of aging and used as precrystallization step in the synthesis process [8–12]. Also, the addition of various chemicals is proposed to change some physical and structural properties of synthesized zeolites [13–15]. In the present work, the effect of polyelectrolytes on the crystallization of NaY zeolite is investigated. Polyelectrolytes are an important class of functionalized polymers with charged groups attached to the chains. The physio-chemical behavior of these polymers is dominated by the attractive interactions between the fixed charges and the counterions and by the longrange repulsive interactions between the electric charges located on the macromolecular chains. The interactions between a polyion and the counter-ions can affect the pKa, conductance, colligative properties, and the diffusion of the counterions [16]. In all experiments, the synthesis mixture is prepared by adding polyelectrolytes, aged at room temperature, and then was left to crystallize. Anionic, nonionic and cationic polyelectrolytes with a high molecular weight (106 2.5 107) are used as additives. ICP
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
analysis is done to determine the purity and chemical composition of the raw materials (Al(OH)3, Al2O3, SiO2) and to determine the Si/ Al and Na/Si ratio of the products. The crystallinity of the solid product is determined by X-ray diffraction, and the crystal size and product morphology are determined by scanning electron microscopy. The relationship between polyelectrolyte addition
9
and the particle size of synthesized NaY zeolite is elaborated. The adsorption and desorption isotherms of N2, at liquid N2 temperature, on the solid product were determined by volumetric adsorption instrument connected to a high vacuum system.
2. Experimental Table 1 Polyelectrolytes used in experiments. Trade name
Producer
Physical state
Charge
Chemical structure
F08990
SNF Floerger Cyanamid
Solid
Cationic (%100) Nonionic
PAMþ ADAMMeCl
N100 AN 999 AN 970 AN 956 AN 910
SNF Floerger SNF Floerger SNF Floerger SNF Floerger
Solid Solid
Polyacrylamide (PAM) Hydrolyzed (PAM)
Solid
Anionic (%100) Anionic (%70)
Solid
Anionic (%50)
Hydrolyzed (PAM)
Solid
Anionic (%10)
Hydrolyzed (PAM)
Amorphous silica
Hydrolyzed (PAM)
The colloidal silica sols used in this work are prepared from amorphous silica (EGE Kimya A.S- .) by the method of Iler and Heights [17]. Sodium aluminate solution (13.97% Al2O3, 24.36% Na2O and 61.65% H2O by weight) is prepared using aluminum hydroxide obtained from ET_I Aluminum A.S- . plant in Turkey, sodium hydroxide (99.8%) and distilled water [6–18]. Precipitated silica was initially added to the solution of sodium hydroxide in water in order to obtain a sodium silicate solution, to which finally the sodium aluminate solution was added. The mole composition of the gel is 4.16Na2O:1Al2O3:10SiO2:205H2O. Polyelectrolyte solutions of 0.2% are prepared freshly as stock solution for each experiment. Polyelectrolytes used in this work are listed in Table 1. After the addition of various polyelectrolyte solutions to achieve 10 ppm concentrations, the synthesis mixture is aged under room temperature for 24 h followed by crystallization at 100 1C.
Water NaOH solution Al(OH)3
Sodium aluminate solution
Silica sol
Gel preparation
Polyelectrolyte solution Aging
Crystallization
Filtration
Washing
Drying
Fig. 1. Flow sheet of zeolite NaY synthesis.
Zeolite NaY
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
10
All gel preparations and aging steps are carried out at 20 1C in a polyethylene beaker using a magnetic stirrer. After the crystallization is done at a laboratory type furnace at 100 1C, the produced zeolite is filtered, washed with distilled water and dried at 100 1C for 48 h. The steps of zeolite NaY synthesis is shown schematically in Fig. 1. The first group of experiments is conducted with the solutions containing no additive, nonionic, 100% anionic, and 100% cationic polyelectrolytes. The crystallization temperature and crystallization time were kept at 100 1C and 48 h, respectively. In the case of the second group synthesis studies, the effects of polyelectrolyte with various degrees of anionic properties (10% (10A), 50% (50A), and 70% (70A)), of the same chemical structure are investigated. The experiments are conducted at the same constant crystallization temperature of 100 1C and crystallization time of 48 h. The synthesized samples are compared with sodium Y produced by Aldrich Company as a reference. XRD analysis of the reference and synthesized zeolite samples are conducted using SHIMADZU, XRD-6000. The percent crystallinity and unit cell size are calculated with the ASTM D 3906 and D 3942 using XRD data. Crystallizations are monitored by SEM photographs using JEOL, JSM-5600. The Si/Al ratio of the samples is determined with standard analytical procedures (ASTM D 717, D 718 and D 719)
Volume adsorbed (ml/g, STP)
450 400 350 300 250 200 150 100
WA Adsorption 100A Adsorption NI Adsorption 100C Adsorption
50 0 0.0
0.2
0.4 0.6 Relative pressure P/Po
WA Desorption 100A Desorption NI Desorption 100C Desorption
0.8
1.0
Fig. 2. Adsorption/desorption isotherms of N2 at liquid N2 temperature for zeolites with various types of additives.
Volume adsorbed (ml/g, STP)
450 400 350
using chemical analysis. The particle size distributions of the samples are determined by a laser beam technique, using MALVERN, ZETASIZER-3. Nitrogen adsorption/desorption isotherms are investigated by Quantachrome, Autosorb 1-C.
3. Experimental results Figs. 2 and 3 show the nitrogen adsorption/desorption isotherms of the zeolites synthesized with various types of additives and anionic polyelectrolytes with various degrees of anionic properties. The isotherms are similar to Type I according to IUPAC classification. The shapes of the adsorption/desorption isotherms indicate that the prepared zeolites are mainly microporous however they also contain some mesopores. Micropore filling and therefore high uptakes are observed at relatively low pressures, because of the narrow pore width and high adsorption potential. The limiting uptake is being governed by the accessible micropore volume rather than by the internal surface area [19–20]. The maximum nitrogen adsorption/desorption isotherm is achived at WA zeolite (Fig. 2). The volume of nitrogen adsorbed at any relative pressure is decreasing as the degree of anionic property of the additive increased (Fig. 3). The results obtained in the first and second group of experiments are given in Tables 2 and 3. The BET surface area and pore structure parameters are determined from the nitrogen adsorption isotherms and summarized in Table 2. For the first group of experiments WA zeolite has the maximum BET surface area, but the maximum microporosity is achieved with the addition of 100% cationic polyelectrolytes. As anionicity decreases, the BET surface area, the total pore volume (Vt), the micropore volume (Vmic), and the mesapore volume (Vmes) increased all, but microporosity decreases (Fig. 3). The zeolite 10A, which is prepared with the addition of polyelectrolytes having 10% anionic degree possesses the highest BET surface area (1258 m2/g) and largest total pore volume (0.668 cm3/g). The pore size distribution is determined by a non-local density functional theory (NLDFT) model using nitrogen adsorption data. Table 2 BET surface areas and pore structure parameters of the synthesized zeolites. Sample
SBET (m2/g)
Vt (cm3/g)
Vmic (cm3/g)
Vmes (cm3/g)
Microporosity Vmic/Vt
WA NI 100C 100A 70A 50A 10A
1155 827 991 609 604 818 1258
0.663 0.405 0.458 0.324 0.296 0.453 0.668
0.408 0.310 0.410 0.239 0.230 0.310 0.447
0.183 0.141 0.030 0.048 0.058 0.104 0.143
0.615 0.765 0.895 0.737 0.777 0.684 0.668
300
Table 3 Physical and chemical properties of zeolites synthesized with various types of additives and with various degrees of anionic properties.
250 200 150 100A Adsorption 70A Adsorption 50A Adsorption 10A Adsorption WA Adsorption
100 50 0 0.0
0.2
0.4
0.6
100A Desorption 70A Desorption 50A Desorption 10A Desorption WA Desorption 0.8
1.0
Relative Pressure P/Po Fig. 3. Adsorption/desorption isotherms of N2 at liquid N2 temperature for zeolites with various degrees of anionic properties.
Sample
Crystallinity (%)
Unit Cell Constant ˚ (ao, A)
SiO2/Al2O3 (mol/mol)
Na2O/SiO2 (mol/mol)
Particle Size (mm)
WA NI 100C 100A 70A 50A 10A
92 83 84 82 90 91 92
24.71 24.76 24.72 24.71 24.67 24.68 24.66
4.34 4.20 4.24 4.50 4.23 4.23 4.34
0.195 0.190 0.191 0.185 0.185 0.177 0.193
1.93 5.89 2.19 2.53 2.04 1.99 1.77
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
The NLDFT pore size distribution curves of samples with various degrees of anionic properties are given in Fig. 4. The pore sizes of the samples are mainly located in the range of micropores. The evolution of the pore structure can be clearly observed. For all of ˚ the zeolite samples, there are two peaks at around 9.8 and 11.2 A, showing the validity of the DFT method for estimating the pore sizes of microporous materials. The area under the pore size distribution curve and two known abscissa values are related to the relative amount of micropores having sizes that fall into the range defined by abscissa limits. The peak about 11.2 A˚ is gradually increased by decreasing of the anionic degrees of the polyelectrolytes and the results are compatible with micropore volume given in Table 2. The molar composition, particle size and calculated values of crystallinity and unit cell constant for various types of additives and for various degrees of anionic properties of synthesized
zeolites are given in Table 3. Molar compositions of the sample that have similar crystallinity are also similar. A comparison of crystallinity of the products indicates that increasing the degree of anionicity in the reaction mixtures decreases the crystallinity. Also, crystallinity of these products is shown to be higher than the zeolite NaY obtained with nonionic and 100% cationic polyelectrolyte. Decreasing the anionicity of the polyelectrolyte to 10% gives similar crystallinity as the one with no additive. The maximum mean particle size is obtained by adding nonionic polyelectrolytes (Fig. 5). The unit cell constant of without additive, nonionic, 100% cationic, 100%, 70%, 50% and 10% anionic polyelectrolytes additive ˚ products is calculated as 24.75 A. The BET surface area (S) and crystallinity (C) of NaY zeolites synthesized decrease in the order of without additive, 100% cationic, nonionic, and 100% anionic. Accordingly, the particle size (P) increases in the same order. SWA 4 S100C 4 SNI 4 S100A
0.18 Differential pore volume dV/dD (cc/A/g)
11
100A 70A 50A 10A WA
0.16 0.14 0.12
C WA 4 C 100C 4C NI 4C 100A P WA oP 100C oP 100A o PNI
4. Conclusions
0.10 0.08 0.06 0.04 0.02 0.00 8
9
10
11 12 13 Pore diameter (Å)
14
15
16
Fig. 4. Pore size distribution curves of zeolites with various degrees of anionic properties.
The results show that the addition of polyelectrolytes and the anionicity of the additives affect the BET surface area and microporosity of the NaY zeolites. All of the synthesized zeolites ˚ have microporous structures having pore sizes smaller than 12 A. The maximum BET surface area at 10% anionic additive is determined as 1258 m2/g. The BET surface area increases and microporosity decreases with the decrease of anionicity. The particle size in 100% anionic polyelectrolytes are affected less than the same polyelectrolytes assuring lower degree of ionicity in the reaction mixtures. The main interaction is via polyamide structure; thus the effects of additives containing more poliacrylamide are more pronounced. Therefore, nonionic polyacrylamide affects the particle size more than the others.
1µm
WA
1µm
100A
1µm
NI
1µm
100C
Fig. 5. SEM photograph of zeolite NaY crystallized at 48 h without additive (WA), with nonionic (NI), 100% anionic (100A) and 100% cationic (100C) polyelectrolyte additive (x10.000).
12
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
If the interaction were only via polyacrylamide groups, anionic and cationic additives of the same ionic property should have given similar results. However, the addition of polyelectrolytes with 10% and 50% anionicity results in higher crystallinities compared to cationic additives. This indicates that polyacrylate groups are also effective. High crystallinity requires highly anionic polyelectrolytes at low concentrations. However, as the crystallinity increases, the mean particle size of the zeolite decreases. When the anionic property of the additive is low, the effect of concentration is negligible. On the other hand, high anionicity affects considering both particle size and crystallinity. References [1] J. Weitkamp, Solid State Ionics 131 (2000) 175–188. [2] D. Karami, S. Rohani, Chemical Engineering and Processing: Process Intensification 48 (2009) 1288–1292. [3] L. Puppe, Ullman’s Encyclopedia der Technishcen Chemie, Molecularsiebe, 4. Neubearbeitete und erweierte Auflage, Volume 17, Germany, 1967, pp. 9–19. [4] D.W. Breck, Zeolite Molecular Sieves, Structure, Chemistry and Use, John Wiley and Sons, New York, 1974, pp. 25–80.
[5] E. Roland, P. Kleinschmit, Ullman’s Encyclopedia of Industrial Chemistry A28 (1996) 47–504. [6] D.W. Breck, United State Patent no. 3 130 007, 1964. [7] J.S. Magee, Studies in surface science and catalysis, fluid catalytic cracking, Science and Technology, The Netherlands, 76, 1993 (Chapter 4), pp. 105–145. [8] C.V. Mc Daniel, P.K. Maher, J.M. Pilato, United State Patent no. 4 166 099, 1979. [9] C.H. Elliott, United State Patent no. 4 164 551, 1979. [10] D.E.W. Vaughan, G.C. Edwards, M.G. Barrett, United State Patent no. 4 178 352, 1979. [11] G.C. Edward, D.E.W. Vaughan, E.W. Albers, United State Patent no. 4 175 059, 1979. [12] P.K. Maher, E.W. Albers, C.V. Mc Daniel, United State Patent no. 3 671 191, 1972. [13] G.J. Myatt, P.M. Budd, C. Price, Zeolites 14 (1994) 190–197. [14] R. Szostak, Molecular Sieves Principles of Synthesis and Identification, Van Nosrand Reinhold International Company Limited, New York, 1989. [15] M.E. Davis, R.F. Lobo, Chemistry of Materials (1992) 4. [16] A.M. Mika, R.F. Childs, J.M. Dickson, B.E. McCarry, D.R. Gagnon, Journal of Membrane Science 108 (1995) 37–56. [17] R.K. Iler, C. Heights, United State Patent, 2 597 872, dated 27.5.1952. [18] Gmelins Handbuch, Der Anorganischem Chemie, Aluminium, Teil B, SystemNumber 35 (1934) 360–364. [19] F. Su, X.S. Zhao, L. Lv, Z. Zhou, Carbon 42 (2004) 2821–2831. [20] S. Lowell, J.E. Shields, M.A. Thomas, M. Thommes, Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density, Kluwer Academic Publishers, Dordrecht, 2004 p.12.
Contents lists available at SciVerse ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Influence of polyelectrolytes on crystallization of zeolite Y ¨ z a, A. Nusret Bulutc- u b ¨ ¨ glu a,n, Pembe Hande O Hansu Julide Koro˘ a b
TUBITAK Marmara Research Center, Chemistry Institute P.O. Box 21, 41470, Gebze-Kocaeli, Turkey Istanbul Technical University, Chemical Engineering Department, 80626, Maslak, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 August 2011 Received in revised form 30 April 2012 Accepted 7 May 2012 communicated by S.R. Qiu Available online 16 May 2012
In this study, the influence of polyelectrolytes on the crystallization of zeolite Y is investigated. The prepared synthesis mixtures are aged at room temperature for 24 h and then left to crystallize. The compositional and structural information are provided by elemental analysis obtained by ICP, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), particle size analyzer and adsorption and desorption isotherms of nitrogen by a volumetric adsorption instrument. The first group of synthesis studies is conducted by using solutions containing no additive (WA), nonionic (NI), 100% anionic (100A), and 100% cationic (100C) polyelectrolytes. The crystallization temperature and o crystallization time are kept at 100 % C and 48 h, respectively. The experimental results show that nonionic polyelectrolyte has the most influence on the crystallization of zeolite NaY. In the second group of synthesis studies, the effects of polyelectrolytes with various degrees of anionic properties (10%, 50% and 70%) of the same chemical structure are investigated by conducting crystallization experiments at 100 1C for a duration of 48 h. The results suggest that; particle size, crystallinity and BET surface area (SBET) can be controlled by adding anionic polyelectrolytes to the solution. & 2012 Elsevier B.V. All rights reserved.
Keywords: A1. Characterization A1. Crystal structure A2. Growth from solution B1. Inorganic compounds B1. Polymers
1. Introduction Zeolites occur in nature and have been known for almost 250 years as aluminosilicate minerals. Examples are faujasite, mordenite, offretite, ferrierite, erionite and chabazite. Today, these and other zeolite structures are of great interest in catalysis research, yet their naturally occurring forms are of limited value, because (i) they almost always contain undesired impurity phases, (ii) their chemical composition varies from one stratum to another in the same deposit, and (iii) nature did not optimize their properties for applications [1]. Zeolite Y (faujasite) is one of the most important zeolites in terms of the volume of research activity and the scale of commercial use. The major applications of synthetic zeolite Y are in the fields of fluid catalytic cracking (FCC) of vacuum gasoil and in the adsorption of volatile organics from wet off-gas streams. Faujasite materials are characterized by a high surface area, uniform pore size distributions and high thermal stability [2].Hydrated aluminio silicates in crystalline form referred as ‘‘Molecular sieves’’ exhibit narrow channel in their structure. Zeolite Y (faujasite) is one of the zeolites constructed by joining the interrupted cubic octahedrals with hexagonal prisms [3].Raw materials used in the synthesis process of zeolite Y are reactive silica, alumina and sodium
n
Corresponding author. Tel.: þ90 262 677 29 21. ¨ glu). E-mail address: [email protected] (H.J. Koro˘
0022-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.05.013
hydroxide. As an alumina source, it is possible to use activated alumina, gamma alumina, aluminum hydroxide and sodium aluminates. Sodium silicate, silica gels, silicic acid, hydrated colloidal silica sols and reactive amorphic solid silica can be used as silicate sources [4,5]. The sodium hydroxide procures Na þ ions and controls the pH of the process [6]. The crystallization of zeolite NaY is autocatalytic and crystal growth is characterized by S-shape plots [7]. In many works, seeding is interpreted as a way of reducing the time of aging and used as precrystallization step in the synthesis process [8–12]. Also, the addition of various chemicals is proposed to change some physical and structural properties of synthesized zeolites [13–15]. In the present work, the effect of polyelectrolytes on the crystallization of NaY zeolite is investigated. Polyelectrolytes are an important class of functionalized polymers with charged groups attached to the chains. The physio-chemical behavior of these polymers is dominated by the attractive interactions between the fixed charges and the counterions and by the longrange repulsive interactions between the electric charges located on the macromolecular chains. The interactions between a polyion and the counter-ions can affect the pKa, conductance, colligative properties, and the diffusion of the counterions [16]. In all experiments, the synthesis mixture is prepared by adding polyelectrolytes, aged at room temperature, and then was left to crystallize. Anionic, nonionic and cationic polyelectrolytes with a high molecular weight (106 2.5 107) are used as additives. ICP
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
analysis is done to determine the purity and chemical composition of the raw materials (Al(OH)3, Al2O3, SiO2) and to determine the Si/ Al and Na/Si ratio of the products. The crystallinity of the solid product is determined by X-ray diffraction, and the crystal size and product morphology are determined by scanning electron microscopy. The relationship between polyelectrolyte addition
9
and the particle size of synthesized NaY zeolite is elaborated. The adsorption and desorption isotherms of N2, at liquid N2 temperature, on the solid product were determined by volumetric adsorption instrument connected to a high vacuum system.
2. Experimental Table 1 Polyelectrolytes used in experiments. Trade name
Producer
Physical state
Charge
Chemical structure
F08990
SNF Floerger Cyanamid
Solid
Cationic (%100) Nonionic
PAMþ ADAMMeCl
N100 AN 999 AN 970 AN 956 AN 910
SNF Floerger SNF Floerger SNF Floerger SNF Floerger
Solid Solid
Polyacrylamide (PAM) Hydrolyzed (PAM)
Solid
Anionic (%100) Anionic (%70)
Solid
Anionic (%50)
Hydrolyzed (PAM)
Solid
Anionic (%10)
Hydrolyzed (PAM)
Amorphous silica
Hydrolyzed (PAM)
The colloidal silica sols used in this work are prepared from amorphous silica (EGE Kimya A.S- .) by the method of Iler and Heights [17]. Sodium aluminate solution (13.97% Al2O3, 24.36% Na2O and 61.65% H2O by weight) is prepared using aluminum hydroxide obtained from ET_I Aluminum A.S- . plant in Turkey, sodium hydroxide (99.8%) and distilled water [6–18]. Precipitated silica was initially added to the solution of sodium hydroxide in water in order to obtain a sodium silicate solution, to which finally the sodium aluminate solution was added. The mole composition of the gel is 4.16Na2O:1Al2O3:10SiO2:205H2O. Polyelectrolyte solutions of 0.2% are prepared freshly as stock solution for each experiment. Polyelectrolytes used in this work are listed in Table 1. After the addition of various polyelectrolyte solutions to achieve 10 ppm concentrations, the synthesis mixture is aged under room temperature for 24 h followed by crystallization at 100 1C.
Water NaOH solution Al(OH)3
Sodium aluminate solution
Silica sol
Gel preparation
Polyelectrolyte solution Aging
Crystallization
Filtration
Washing
Drying
Fig. 1. Flow sheet of zeolite NaY synthesis.
Zeolite NaY
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
10
All gel preparations and aging steps are carried out at 20 1C in a polyethylene beaker using a magnetic stirrer. After the crystallization is done at a laboratory type furnace at 100 1C, the produced zeolite is filtered, washed with distilled water and dried at 100 1C for 48 h. The steps of zeolite NaY synthesis is shown schematically in Fig. 1. The first group of experiments is conducted with the solutions containing no additive, nonionic, 100% anionic, and 100% cationic polyelectrolytes. The crystallization temperature and crystallization time were kept at 100 1C and 48 h, respectively. In the case of the second group synthesis studies, the effects of polyelectrolyte with various degrees of anionic properties (10% (10A), 50% (50A), and 70% (70A)), of the same chemical structure are investigated. The experiments are conducted at the same constant crystallization temperature of 100 1C and crystallization time of 48 h. The synthesized samples are compared with sodium Y produced by Aldrich Company as a reference. XRD analysis of the reference and synthesized zeolite samples are conducted using SHIMADZU, XRD-6000. The percent crystallinity and unit cell size are calculated with the ASTM D 3906 and D 3942 using XRD data. Crystallizations are monitored by SEM photographs using JEOL, JSM-5600. The Si/Al ratio of the samples is determined with standard analytical procedures (ASTM D 717, D 718 and D 719)
Volume adsorbed (ml/g, STP)
450 400 350 300 250 200 150 100
WA Adsorption 100A Adsorption NI Adsorption 100C Adsorption
50 0 0.0
0.2
0.4 0.6 Relative pressure P/Po
WA Desorption 100A Desorption NI Desorption 100C Desorption
0.8
1.0
Fig. 2. Adsorption/desorption isotherms of N2 at liquid N2 temperature for zeolites with various types of additives.
Volume adsorbed (ml/g, STP)
450 400 350
using chemical analysis. The particle size distributions of the samples are determined by a laser beam technique, using MALVERN, ZETASIZER-3. Nitrogen adsorption/desorption isotherms are investigated by Quantachrome, Autosorb 1-C.
3. Experimental results Figs. 2 and 3 show the nitrogen adsorption/desorption isotherms of the zeolites synthesized with various types of additives and anionic polyelectrolytes with various degrees of anionic properties. The isotherms are similar to Type I according to IUPAC classification. The shapes of the adsorption/desorption isotherms indicate that the prepared zeolites are mainly microporous however they also contain some mesopores. Micropore filling and therefore high uptakes are observed at relatively low pressures, because of the narrow pore width and high adsorption potential. The limiting uptake is being governed by the accessible micropore volume rather than by the internal surface area [19–20]. The maximum nitrogen adsorption/desorption isotherm is achived at WA zeolite (Fig. 2). The volume of nitrogen adsorbed at any relative pressure is decreasing as the degree of anionic property of the additive increased (Fig. 3). The results obtained in the first and second group of experiments are given in Tables 2 and 3. The BET surface area and pore structure parameters are determined from the nitrogen adsorption isotherms and summarized in Table 2. For the first group of experiments WA zeolite has the maximum BET surface area, but the maximum microporosity is achieved with the addition of 100% cationic polyelectrolytes. As anionicity decreases, the BET surface area, the total pore volume (Vt), the micropore volume (Vmic), and the mesapore volume (Vmes) increased all, but microporosity decreases (Fig. 3). The zeolite 10A, which is prepared with the addition of polyelectrolytes having 10% anionic degree possesses the highest BET surface area (1258 m2/g) and largest total pore volume (0.668 cm3/g). The pore size distribution is determined by a non-local density functional theory (NLDFT) model using nitrogen adsorption data. Table 2 BET surface areas and pore structure parameters of the synthesized zeolites. Sample
SBET (m2/g)
Vt (cm3/g)
Vmic (cm3/g)
Vmes (cm3/g)
Microporosity Vmic/Vt
WA NI 100C 100A 70A 50A 10A
1155 827 991 609 604 818 1258
0.663 0.405 0.458 0.324 0.296 0.453 0.668
0.408 0.310 0.410 0.239 0.230 0.310 0.447
0.183 0.141 0.030 0.048 0.058 0.104 0.143
0.615 0.765 0.895 0.737 0.777 0.684 0.668
300
Table 3 Physical and chemical properties of zeolites synthesized with various types of additives and with various degrees of anionic properties.
250 200 150 100A Adsorption 70A Adsorption 50A Adsorption 10A Adsorption WA Adsorption
100 50 0 0.0
0.2
0.4
0.6
100A Desorption 70A Desorption 50A Desorption 10A Desorption WA Desorption 0.8
1.0
Relative Pressure P/Po Fig. 3. Adsorption/desorption isotherms of N2 at liquid N2 temperature for zeolites with various degrees of anionic properties.
Sample
Crystallinity (%)
Unit Cell Constant ˚ (ao, A)
SiO2/Al2O3 (mol/mol)
Na2O/SiO2 (mol/mol)
Particle Size (mm)
WA NI 100C 100A 70A 50A 10A
92 83 84 82 90 91 92
24.71 24.76 24.72 24.71 24.67 24.68 24.66
4.34 4.20 4.24 4.50 4.23 4.23 4.34
0.195 0.190 0.191 0.185 0.185 0.177 0.193
1.93 5.89 2.19 2.53 2.04 1.99 1.77
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
The NLDFT pore size distribution curves of samples with various degrees of anionic properties are given in Fig. 4. The pore sizes of the samples are mainly located in the range of micropores. The evolution of the pore structure can be clearly observed. For all of ˚ the zeolite samples, there are two peaks at around 9.8 and 11.2 A, showing the validity of the DFT method for estimating the pore sizes of microporous materials. The area under the pore size distribution curve and two known abscissa values are related to the relative amount of micropores having sizes that fall into the range defined by abscissa limits. The peak about 11.2 A˚ is gradually increased by decreasing of the anionic degrees of the polyelectrolytes and the results are compatible with micropore volume given in Table 2. The molar composition, particle size and calculated values of crystallinity and unit cell constant for various types of additives and for various degrees of anionic properties of synthesized
zeolites are given in Table 3. Molar compositions of the sample that have similar crystallinity are also similar. A comparison of crystallinity of the products indicates that increasing the degree of anionicity in the reaction mixtures decreases the crystallinity. Also, crystallinity of these products is shown to be higher than the zeolite NaY obtained with nonionic and 100% cationic polyelectrolyte. Decreasing the anionicity of the polyelectrolyte to 10% gives similar crystallinity as the one with no additive. The maximum mean particle size is obtained by adding nonionic polyelectrolytes (Fig. 5). The unit cell constant of without additive, nonionic, 100% cationic, 100%, 70%, 50% and 10% anionic polyelectrolytes additive ˚ products is calculated as 24.75 A. The BET surface area (S) and crystallinity (C) of NaY zeolites synthesized decrease in the order of without additive, 100% cationic, nonionic, and 100% anionic. Accordingly, the particle size (P) increases in the same order. SWA 4 S100C 4 SNI 4 S100A
0.18 Differential pore volume dV/dD (cc/A/g)
11
100A 70A 50A 10A WA
0.16 0.14 0.12
C WA 4 C 100C 4C NI 4C 100A P WA oP 100C oP 100A o PNI
4. Conclusions
0.10 0.08 0.06 0.04 0.02 0.00 8
9
10
11 12 13 Pore diameter (Å)
14
15
16
Fig. 4. Pore size distribution curves of zeolites with various degrees of anionic properties.
The results show that the addition of polyelectrolytes and the anionicity of the additives affect the BET surface area and microporosity of the NaY zeolites. All of the synthesized zeolites ˚ have microporous structures having pore sizes smaller than 12 A. The maximum BET surface area at 10% anionic additive is determined as 1258 m2/g. The BET surface area increases and microporosity decreases with the decrease of anionicity. The particle size in 100% anionic polyelectrolytes are affected less than the same polyelectrolytes assuring lower degree of ionicity in the reaction mixtures. The main interaction is via polyamide structure; thus the effects of additives containing more poliacrylamide are more pronounced. Therefore, nonionic polyacrylamide affects the particle size more than the others.
1µm
WA
1µm
100A
1µm
NI
1µm
100C
Fig. 5. SEM photograph of zeolite NaY crystallized at 48 h without additive (WA), with nonionic (NI), 100% anionic (100A) and 100% cationic (100C) polyelectrolyte additive (x10.000).
12
H.J. K¨ orog˘ lu et al. / Journal of Crystal Growth 355 (2012) 8–12
If the interaction were only via polyacrylamide groups, anionic and cationic additives of the same ionic property should have given similar results. However, the addition of polyelectrolytes with 10% and 50% anionicity results in higher crystallinities compared to cationic additives. This indicates that polyacrylate groups are also effective. High crystallinity requires highly anionic polyelectrolytes at low concentrations. However, as the crystallinity increases, the mean particle size of the zeolite decreases. When the anionic property of the additive is low, the effect of concentration is negligible. On the other hand, high anionicity affects considering both particle size and crystallinity. References [1] J. Weitkamp, Solid State Ionics 131 (2000) 175–188. [2] D. Karami, S. Rohani, Chemical Engineering and Processing: Process Intensification 48 (2009) 1288–1292. [3] L. Puppe, Ullman’s Encyclopedia der Technishcen Chemie, Molecularsiebe, 4. Neubearbeitete und erweierte Auflage, Volume 17, Germany, 1967, pp. 9–19. [4] D.W. Breck, Zeolite Molecular Sieves, Structure, Chemistry and Use, John Wiley and Sons, New York, 1974, pp. 25–80.
[5] E. Roland, P. Kleinschmit, Ullman’s Encyclopedia of Industrial Chemistry A28 (1996) 47–504. [6] D.W. Breck, United State Patent no. 3 130 007, 1964. [7] J.S. Magee, Studies in surface science and catalysis, fluid catalytic cracking, Science and Technology, The Netherlands, 76, 1993 (Chapter 4), pp. 105–145. [8] C.V. Mc Daniel, P.K. Maher, J.M. Pilato, United State Patent no. 4 166 099, 1979. [9] C.H. Elliott, United State Patent no. 4 164 551, 1979. [10] D.E.W. Vaughan, G.C. Edwards, M.G. Barrett, United State Patent no. 4 178 352, 1979. [11] G.C. Edward, D.E.W. Vaughan, E.W. Albers, United State Patent no. 4 175 059, 1979. [12] P.K. Maher, E.W. Albers, C.V. Mc Daniel, United State Patent no. 3 671 191, 1972. [13] G.J. Myatt, P.M. Budd, C. Price, Zeolites 14 (1994) 190–197. [14] R. Szostak, Molecular Sieves Principles of Synthesis and Identification, Van Nosrand Reinhold International Company Limited, New York, 1989. [15] M.E. Davis, R.F. Lobo, Chemistry of Materials (1992) 4. [16] A.M. Mika, R.F. Childs, J.M. Dickson, B.E. McCarry, D.R. Gagnon, Journal of Membrane Science 108 (1995) 37–56. [17] R.K. Iler, C. Heights, United State Patent, 2 597 872, dated 27.5.1952. [18] Gmelins Handbuch, Der Anorganischem Chemie, Aluminium, Teil B, SystemNumber 35 (1934) 360–364. [19] F. Su, X.S. Zhao, L. Lv, Z. Zhou, Carbon 42 (2004) 2821–2831. [20] S. Lowell, J.E. Shields, M.A. Thomas, M. Thommes, Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density, Kluwer Academic Publishers, Dordrecht, 2004 p.12.