Crystallization Kinetics and Properties of Na, K-Phillipsites - ACS

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C r y s t a l l i z a t i o n K i n e t i c s a n d P r o p e r t i e s of

Na,

K-Phillipsites

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 25, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0040.ch019

DAVID T. HAYHURST* and L. B. SAND Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Mass. 01609

ABSTRACT Crystallization kinetics are reported for synthetic sodium, potassium p h i l l i p s i t e s , Pure p h i l l i p s i t e was synthesized in the temperature range of 25-175°C under autogenous pressure and with K/(Na+K) ratios in the starting batch composition of 0.05 to 0.35. Reaction rate expressions developed for nucleation and c r y s t a l l i zation were determined to be second order in hydroxide concentration. The kinetic diameter of the synthesized p h i l l i p s i t e s was determined to be 2.60 to 2.65Å. Introduction This paper reports the synthesis conditions, crystallization kinetics and some sorptive properties on Na, K-phillipsites formed in a portion of the soda-potash-silica-alumina-water system with and without chloride additions. P h i l l i p s i t e is one of the most abundant natural zeolites, forming in both sedimentary rocks of marine and continental deposits and in fissures and cavities of extrusive flows, mainly basalts. The name p h i l l i p site was proposed in 1825 by Levy in honor of the British mineralogist W. P h i l l i p s , who discovered the f i r s t crystals of this mineral in Aci Castello, S i c i l y (.1)· P h i l l i p s i t e predominates in low-silica, a l k a l i - r i c h rock, whife the zeolite c l i n o p t i l o l i t e is dominant in high-silica rock (2j. Together, p h i l l i p s i t e and c l i n o p t i l o l i t e form the largest quantity of a l l zeolite deposits. P h i l l i p s i t e contains the 4-ring ( A l , S i ) ^ unit as the smallest structural unit and is classified as a Group I zeolite by Meier {3). The p h i l l i p s i t e framework consists of layers of tetrahedra composed of 4- and 8-membered rings lying approximately in the (100) plane. The layers are linked vertically by 4-rings which form crankshafts with the horizontal 4-rings (4,5). Some confusion has arisen in the literature among the structure types. The same letter has been used to name different synthetic species. *Present address: Cleveland State University, Department of Chemical Engineering, Cleveland, Ohio 44115 219

Katzer; Molecular Sieves—II ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

MOLECULAR

220

SIEVES—II

Thus, zeolite Na-B refers to a synthetic analcime-type zeolite (6); zeolite Β refers to a synthetic phase originally reported by Barrer et a l . (7) who called the same synthetic phase zeolite P . The term zeolite P was used to indicate a "phillipsitetype" structure. However, the framework structure of zeolite P and of zeolite Β is actually that of gismondine (8). The phillipsite reported in this work has an X-ray diTfractogram identical with that reported by Steinfink (9) for natural phillipsite. Although a large amount of work has been done on zeolite synthesis in the last thirty years, the conditions of synthesis for phillipsite had not been clearly established even though it is one of the most common zeolite minerals. There are only two reported syntheses of phillipsite analogues in the literature. Sersale et a l . (10) reports the preparation of a synthetic phillipsite from a high-potassium, high-calcium volcanic glass by treatment with sodium or potassium hydroxide solutions at tem peratures above 240°C for 30 hours. KOhl (JJQ also reports the formation of a synthetic phillipsite, designated ZK-19, whose X-ray powder pattern was found to agree very closely with that of a phillipsite obtained from a marine environment. Pure zeo lite ZK-19 crystallized from mixtures having molar silica/ alumina ratios in the range of 4 to 16 and Na20/(K20+Na20) molar ratios in the range of about 0.3 to 0.85. c

c


c

EXPERIMENTAL The reactants used for phillipsite synthesis were an amor phous silica-alumina gel (Al203-10.38Si02-5.18ΗοΟ, Davison Chemi cal), sodium aluminate (1.lNa20-Al203-2.98H20-Nalco Co.), sodium silicate solution (N-type, Na20-3.326Si02-24.12H?0, Philadelphia Quartz Co.), microfine precipitated silica{Quso G20, Philadelphia Quartz Co.), and reagent grade sodium and potassium hydroxide and sodium and potassium chloride. Syntheses were made in modified Morey-type autoclaves of 3 and 15 ml capacity at autogenous pressures. For some runs below 100°C, runs were made in a mechanically stirred triple-neck distilling flask under reflux. For the quiescent runs, the reactants were mixed with a mortar and pestle into a homogeneous mix and loaded into the autoclaves. Crystallization kinetics at 100°C in a stirred flask were determined by first mixing the soluble salts with water and heating the solution to temperature. When at temperature, the gels were added and this was considered time zero. Crystallization was followed by analyzing the solid product quantitatively by X-ray powder diffraction. Prepared mixtures of a well-character!zed sample of phillipsite and the amorphous substrate of near-phillipsite composition were used to establish a calibration curve for quantitative phase identifica tion based on a summation of X-ray peak intensities. Crystalli zation curves were obtained by analyzing the solid product from either a number of identically charged autoclaves kept at the


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crystallization temperature for different times or from aliquots taken from the stirred flask at various times. Adsorption tests were conducted with a constant-pressure, constant-volume adsorption balance in which the weight change of the adsorbent was measured. Samples typically were activated overnight by heating to 300°C under 3 χ 10- torr vacuum. The activated zeolite then was cooled to the temperature at which the adsorption determination was made. Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 25, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0040.ch019

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RESULTS AND DISCUSSION Synthesis. Na, K-phil1ipsites were synthesized using a variety of starting batch compositions in the Na2-0-K20-Al20 S i O o - r ^ O system over a temperature range of 25°C to 175°C, with sodium and potassium chloride added in some cases. Typical batch compositions, times, temperatures, and starting materials that produced phillipsite as a pure phase are listed in Table 1. A ternary diagram of the batch compositions used in the synthesis of phillipsite is shown in Figure 1. Phillipsite formed as the stable phase from the less siliceous starting batch compositions. As the amount of silica was in creased in the batch, phillipsite was more metastable, with other zeolitic phases forming with or completely replacing it. These other phases were mordenite, erionite and zeolite L. Clinoptilolite was indicated in some of the high-silica runs in which calcium, usually in the form of salt, was added to the system. In order to determine the critical parameters in phillipsite synthesis, batch compositions were varied with respect to sodiumpotassium ratios, and chloride addition. The sodium-potassium ratio was varied from the pure sodium to the pure potassium endmembers while maintaining constant all other system parameters such as temperature and silica-alumina ratios. The K/(Na+K) ratios used were 1.00, 0.75, 0.50, 0.45, 0.40, etc. to 0. The metastable phase transformations were studied in the system with a starting batch composition of 3.2 (Na20, K20)-Al203-10.38Si0 150H 0-6(NaCl,KC1) and reaction temperature of 120°C. This diagram is shown in Figure 2. Approximately 200 experimental runs were used to establish the phase boundaries. The phases that were found to coexist with phillipsite were zeolite L, mordenite, gismondine and analcime. Phillipsite formed stably (or persisted metastably for 1000 hours) in a K/(Na+K) range of 0.10 to 0.20, although it formed metastably over the K/(Na+K) range of 0.05 to 0.40. As the amount of potassium was increased, nhillipsite was replaced by mordenite and subsequently by zeolite L. At the high potassium contents, phillipsite did not form and zeolite L was the only crystalline phase observed. From the high sodium compositions, sodium gismondine formed, which was replaced in time by analcime. 3

2

2



MOLECULAR

(Να, K , l / 2 C a ) 0

A

2

Figure 1.

1

2°3

Ternary diagram of the starting batch compositions used in synthesis

O

20

40

60

80

TIME,

100

1000

HOURS

Figure 2. Metastable phase transformation diagram for the system 3.2 (Na 0, K O)-Al O -10.38 Si0 150 H 0-6 (NaCl, KCl) reacted at 120°C 2

2

2

$

2

2


SIEVES-

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Table I.-Typical Synthesis Runs Producing Pure Phillipsite Run No.

Batch Composition Starting Na 0/K20/Al 03/Si02/H20/NaCl/KCl Materials

N-3

2.4/0.8/1.0/10.38/150/4.5/1.5


N-6 N-7

N-10

2

2

6.4/0/

1.0/10.38/150/6/ 6

6.95/3.50/1.0/20/325/0/

10.0/0/

0

1.0 20.0/300/5/5

Temp Time (Hours) °C

Davison Gel, NaOH, 120 KOH

36

Davison Gel, NaOH

120

48

Na-silicate Na-aluminate KOH 100

68

Davison Gel, Quso NaOH

175

2.2

N-10

II

II

II

II

125

4.5

N-10

II

II

II

II

100

3.3

N-10

II

II

II

II

60

96

N-10

II

II

II

II

25

744

The effect of the addition of chloride was evaluated by developing a metastable phase transformation diagram for the system 3.2(Na 0,K 0)-Al 0 -10.38Si02-150Hp0-0.20(NaCl,KC1) using the same reaction temperature of 120°C. The composition was essentially the same as that used in Figure 2, except the amount of chloride was substantially reduced. This diagram is shown in Figure 3. In this low-chloride case, the phases that were found to coexist with phillipsite were erionite, zeolite L, gismondine and analcime. As found in the high-chloride system, phillipsite persisted as a phase over the K/(Na+K) range of 0.10 to 0.20. However, phillipsite formed with co-existing phases over the much wider range of K/(Na+K) of 0.05 to 0.80. Zeolite L formed as a single phase only at the K/(Na+K) ratios greater than 0.80. In the high-sodium region, gismondine persisted as a phase for a greater time, again being replaced by analcime. It is in teresting to note that in the low-chloride system erionite formed with phillipsite, vhile in the higher-chloride system mordenite replaced phillipsite. The phillipsites that were synthesized had silica-alumina ratios from 4.51 to 5.24, and these are summarized in Table II. It was found that during synthesis, phillipsite selectively took up potassium from the reacting solution. Λ plot of this selec tive uptake is given in Figure 4. 2

2

2

3


224

MOLECULAR

S I E V E S —-II ]

1.00


0.75

+

0.50

PHILLIPSITE /+AM /

/—t/

0.25

/

+

ERIONITE

I ι

Ί

I

ι

PHILLIPSITE

Figure 3. Metastable phase trans formation diagram for the system, 3.2 (Να Ο,Κ Ο)-ΑΙ,Ο -10.38 St0 150 H O-0.20 (NaCl, KCl) reacted at 120°C 2

:

3

AM /

2

Ο

20

|G'SM0ND1NE 40

60

80

11 A N A L C I Μ Ε 1000

100

2

TIME, H O U R S

0.40

1 1 1

•

0.30 X

ο < ω ±

y

0.20

/

/

• 0.10

• Figure 4. Selected uptake of po tassium by phillipsite from the syn thesis batch

0.2

0.4

K / Κ + Να

0.6

IN

0.8

PHILLIPSITE


1.0

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Table II.-Silica-Alumina Ratios of Synthetic Phillipsites Run Number

Silica/A1umina


N-7 N-6 N-10

5.24 5.01 4.51

Activation energies for nucleation and crystallization were calculated for Run Number N-10 using an Arrhenius relationship at three temperatures. The data are plotted in Figure 5 where 0 is the induction time. Results are summarized in Table III. Table III.-Apparent Activation Energies

Stirred Non-Stirred

Nucleation, E (Kcal/gmole) 13.46 14.30

n

Crystallization, E (Kcal/gmole) 15.25

c

14.76

Crystal 1ization Kinetics. The functional dependence of the zeolite crystal1ization kinetics on alkalinity was developed for phillipsite synthesis. In Figure 6, crystallization curves for phillipsite are shown in which the same starting batch composition is reacted, but the alkalinity of the system is varied. This was accomplished by replacing hydroxide with chloride and assuming that for this range of concentrations, the chlorides do not affect the alkalinity significantly and therefore also do not significantly affect the nucleation or crystallization reactions. The mixture was reacted at 100°C under reflux while maintaining temperature and stirring rate constant. The batch compositions used are listed in Table IV. Table IV.-Batch Compositions Used in the Kinetic Studies Batch Compositions (Na20/Al 0 /Si02/H20/NaCl/KCl) 2

3

Hydroxide Concentration (gmoles/1iter)

9.0/1.0/20.0/300/7/5

3.50

10.0/1.0/20.0/300/5/5

3.89

11.0/1.0/20.0/300/3/5

4.30

As can be seen in Figure 6, the rates of nucleation and crystallization increased as the alkalinity of the system was increased; therfore, a functional dependence of nucleation and



226 MOLECULAR


SIEVES—Π

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crystallization rates on alkalinity could be derived. To inves tigate the kinetics, crystal growth was considered to be indepen dent of nucleation, as suggested by the uniform particle size (3.1 to 3.5 ym) of the synthetic phillipsite crystals. Therefore, the rate of nucleation can be expressed by the equation

where Ν is the number of nuclei (a critical number of nuclei are required for crystal growth to begin), Κη is a reaction rate constant, C was taken to be the hydroxide concentration and a is the reaction order. The induction period is taken to be equivalent to the nucleation rate. The order of the reaction was evaluated by plotting log (dN/dt)y versus log (OH"). The nucleation reaction was found to be second order in hydroxide concentration as shown in Figure 7, where 0 again is the induc tion time (when crystal growth commences). In a similar manner, an expression was developed for the rate of crystallization as a function of alkalinity. The crystal growth rate can be expressed by the equation n

dW

T

"

K

ccac

where W is the crystal growth, Κς is a reaction rate constant, CQ is trie concentration of the hydroxide and a is the reaction order. The quantity (dWç/dtW is the rate of crystallization and was taken to be equal to the maximum slope of the crystallization curve which was found to occur at 50% crystallization. The reaction order for crystallization was evaluated in the same manner as that for nucleation, and from Figure 7 the order was found to be 1.75 or approximately second order. The values of the reaction rate constants and orders are summarized in Table V. c

Table V.-Reaction Rate Orders and Rate Constants for FRTllipsite Nucleation and Crystal!izatTon Reaction Order Nucleation

TM

Rate Constant 100°Ç 0.013 1^/hr mole*

Crystallization

1.75

6.748 %xM /hr mole

a

K

?

1

2

2

From these experimental data for phillipsite crystallization, it was concluded that (1) the nucleation and growth rates increased with hydroxide concentration, (2) the rates of nucleation and crystallization were proportional to the hydroxide concentration according to second-order kinetics and (3) as the phillipsite crystals were not found to be pseudomorphic with the



228

MOLECULAR

SIEVES—II

reacting alumina-silica gel, nhillipsite probably was formed by a condensation-polymerization reaction with some dissolved aluminosilicate species. These data are consistent with those of Ciric (12) for zeolite A crystallization, in which at relativelyTow alkalinities, the growth rate of zeolite A was found to be second order in hydroxide concentration. Ciric concluded from this second order relationship that dimers or cyclic tetramers possibly are the building blocks for the zeolite. The experimentally determined order for crystallization was 1.75. As crystal growth takes place very rapidly, the difference between the expected reaction order of 2.00 and the observed 1.75 may reflect mass transfer limitations in the availability of nutrients for the crystal growth. Properties. The synthetic phillipsite was characterized with respect to thermal stability and sorptive properties and some comparisons were made with natural K, Na-phi11ipsite from Rome, Oregon. The thermal stabilities of the phillipsites were determined by heating a sample to a set temperature, maintaining it at this temperature for eighteen hours, cooling, and measuring the crystallinity of the activated sample by X-ray techniques. Samples were heated to progressively higher temperatures and the results of this thermal treatment are shown in Figure 8. The synthetic phillipsites are stable to 300°C, with the one having the higher silica-alumina ratio being somewhat more stable. The natural phillipsite from Rome, Oregon, demonstrated a high thermal stability due to its high silica-alumina ratio of 6 to 7. The phillipsites were characterized further by determining their effective port diameters by adsorbing molecules of various dimensions into the activated zeolite. At the low gas pressures (less than one atmosphere), it was found that the only gases that any of the phillipsites tested would adsorb were water and ammonia. From this, i t can be concluded that the effective port diameter of phillipsite is 2.60 to 2.65 j(, which is consistent with the crystal structure of phillipsite. The effect of activation temperature on adsorption capacity was determined on a synthetic phillipsite (Run Number N-7) using ammonia as the sorbate gas. The phillipsite was activated by heating to a set temperature while under a vacuum of less than 0.003 mmHg and maintained at that temperature and pressure for 12 hours. The sample was allowed to cool to 25°C and the adsorption capacity was determined at 100 mmHg. As also can be seen in Figure 8, the adsorption capacity for phillipsite was found to be sensitive to activation temperature, with a maximum capacity achieved with a 300°C to 350°C activation. This sensitivity indicates the high degree of coordination of water to the cations. Equilibrium adsorption isotherm data were developed for synthetic N-7 phillipsite at 25°C using ammonia as the sorbate.


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Crystallization Kinetics and Properties of Na, K-Phillipsites - ACS

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