Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978 219
mogeneous nickel complex catalyst to convert propylene to isohexenes (97 RON clear) and to dimerize butylene and co-dimerize C3-C4 olefin streams (Andrews and Bonnifay, 1973). A desirable feature of sulfided Ni-SMM in processing light olefins which contain high concentrations of sulfur impurities is that it is a rugged catalyst that can be used under relatively severe processing conditions and still exhibit good aging performance. Thus, it can catalyze the conversion of propylene to a CI2-Cl8 material to give (after hydrogenation) isoparaffinic high performance jet fuels or a CZl+product for preparing isoparaffinic low pour hydraulic and transformer oils. The excellent aging performance of Ni-SMM is probably associated with its catalytic activity being derived from platelet edges and faces as previously described (Wright et al., 1972). This type of surface morphology provides a mechanism whereby product is easily displaced by solvent and/or more reactant to re-expose the catalytic site, thus, resulting in long catalyst life. Polymer gasoline processes which are still in use employ a solid phosphoric acid catalyst for mainly processing C3-C4 olefin feeds. Noncorrosive and sulfur tolerant Ni-SMM can also accomplish this to give an excellent yield of high octane product as revealed by the data reported in this paper. In summary, as a new catalyst Ni-SMM offers considerable potential for processing low molecular weight
olefins to a variety of useful products and for use in conjunction with H F and H2S04isobutane alkylate processes. It is a noncorrosive catalyst, can result in long process cycle times even with feedstocks containing relatively high levels of sulfur impurities, and is capable of air regeneration. Literature Cited Allum, K. G. (to British Petroleum Company), US. Patent 3816555 (June 1 1 ,
1974). Andrews, J. W., Bonnifay, P., NPRA Meeting, Paper AM-73-31(Apr 1-3, 1973). Barnett, K. W., Glockner, P. W. (to Shell Oil Co.), U.S. Patent 3 527 839 (Sept
8, 1970). Bercik, P. G., Metzger, K. J. (to Gulf Research & Development Co.), US. Patent 3840474 (Oct 8, 1974). Black, E. R., Montagna, A. A., Swift, H. E. (to Gulf Research & Development Co.), U S . Patent 3 966 642 (June 29, 1976). Bronner, C., Derrien, M., Lassau, C., Hydrocarbon Process., 131 (Jan 1977). Capell, R. G., Granquist, W.T. (to Gulf Research 8 Development Co. and N. L. Industries, Inc.), U S . Patent 3 252 889 (May 24, 1966). Choufoer, J. R., deRuiter, H., vanZoonen, D. (to Shell Oil Company), US. Patent 3 161 697 (Dec 15, 1964). Kohn, P. M., Cbem. Eng., 114 (May 23, 1977). Lucki, S. J. (to Mobil Oil Corp.), U S . Patent 3 959 400 (May 25, 1976). Pine, L. A., Roberts Jr., D. T., Jolley, G. B. (to Esso Research & Engineering Co.), U S . Patent 3518323 (June 30, 1970). Swift, H. E., Black, E. R., Ind. Eng. Cbem. Prod. Res. Dev., 13, 106 (1974). Wright, A. C.. Granquist, W. T., Kennedy, J. V., J . Catal., 25, 65 (1972).
Received for review November 29, 1977 Accepted May 8, 1978 Presented at the Division of Petroleum Chemistry, 175th National Meeting of the American Chemical Society, Anaheim, Calif., March 1978.
Ion-Exchanged Ultrastable Y Zeolites. 3. Gas Oil Cracking over Rare Earth-Exchanged Ultrastable Y Zeolites Julius Scherzer' and Ronald E. Rltter W. R. Grace & Co., Davison Chemical Division, Washington Research Center, Columbia, Maryland 21044
The use of rare earth, hydrogen-exchanged ultrastable Y (RE,H-USY) zeolites as catalysts in gas oil cracking has been investigated. Both microactivity and pilot unit data are presented and discussed. The activity and selectivity of these zeolites is compared to that of ultrastable Y and RE,H-Y zeolites. RE,H-USY zeolites are more active than USY. They show good gasoline selectivity, lower coking rates, and higher olefin selectivity than RE,H-Y. The gasoline fractions obtained over RE,H-USY catalysts have a high content of aromatics, olefins, and cyclic allylic hydrocarbons. A possible reaction mechanism is briefly discussed.
Introduction The preparation and physical properties of lanthanum-hydrogen-exchanged ultrastable Y (La,H-USY) zeolites have been previously described and discussed (Scherzer and Bass, 1977). It was shown that such compounds combine properties characteristic to ultrastable Y zeolites with those of lanthanum-exchanged Y zeolites. Infrared studies have shown the presence of both Bronsted and Lewis type acidity in these compounds. They also have high thermal and hydrothermal stability. Such properties would suggest that these compounds can be used as catalysts in processes involving carbonium ion reactions at elevated temperatures. This paper presents and discusses the results obtained by using different rare earth-hydrogen-exchanged ultrastable Y (RE,H-USY) zeolites as catalysts in gas oil cracking. 0019-7890/78/1217-0219$01 .OO/O
Experimental Section A. Materials. A series of lanthanum, cerium, and mixed rare earth exchanged ultrastable Y zeolites have been prepared by methods previously described (Scherzer and Bass, 1977). Different rare earth-exchanged zeolites were prepared by either (a) acid treatment of the ultrastable Y zeolite at a set pH, followed by rare earth exchange, or (b) exchanging the zeolite with a rare earth chloride solution of a certain acidity. Materials prepared by method (a) bear the notation M,H-USY, (M = La, Ce, RE mixture); those by method (b) are designated M,HUSY,. M,H-USY zeolites were also prepared by direct rare earth exchange of USY, without acidity adjustment. They bear the notation M,H-USY,i,. In this case, the exchange pH was close to 4.0. The lanthanum and cerium chloride used in these preparations was obtained from American Potash and 0 1978 American
Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978
Table I. Rare Earth-Exchanged USY Zeolites no.
zeolitea
treat pH
MXO,, mmo1/100 g
unit cell size, A
SiO,/Al,O, mole ratio
1 2 3 4 5 6 7 8 9 10
La,H-USY,i La,H-USY, La,H-USY La,H-USY La,H-USY La,H-USY, La,H-USY, Ce,H-USY,i Ce,H-USY, Ce,H-USY, Ce,H-USY, Ce,H-USY, RE,H-USY,, RE,H-USY,
4.0 3.5 2.5 1.5 3.5 2.5 2.0 4.0 3.5 2.5 2.0 1.5 4.1 3.5
6.3 5.8 5.5 4.5 5.6 4.7 3.7 7.0 6.7 5.1 4.6 2.8 6.2 5.8
24.54 24.52 24.49 24.40 24.53 24.52 24.50 24.53 24.53 24.51 24.50 24.43 24.53 24.52
4.85 5.0 5.9 11.9 4.85 5.5 6.5 4.85 4.85 5.3 6.2 9.4 4.85 4.9
11 12 13 14
, ,
-
M,H-USY,,: prepared by rare earth exchange of USY zeolite without acidity adjustment (pH 4.0). M,H-USY,: prepared by acid treatment of USY zeolite at specified pH, followed by rare earth exchange at pH 4.0. M,H-USY,: prepared by exchanging USY zeolite with rare earth chloride solution at specified pH.
Chemical Co. The rare earth chloride solution was a commercial mixture, having the following rare earth distribution (expressed as oxides): 42.8% La203,30.9% Ce02, 18.6% Nd203,5.2% Pr6011,2.4% Sm203,and 0.1% of other rare earth oxides. The composition and certain physical characteristics of ion exchanged zeolites prepared and evaluated catalytically are shown in Table I. For catalytic evaluation, the ion-exchanged zeolites were blended with a semisynthetic matrix, consisting of clay and silica-alumina gel. The zeolite content of the final catalysts varied from 10 to 25 wt %. Prior to catalytic evaluation, the catalysts were submitted to thermal or hydrothermal treatment. The thermal treatment consisted of calcination of 540 "C for 3 h. Two hydrothermal treatments were applied: one consisted of steaming the catalyst at 730 "C for 8 h under 100% steam at 15 psig pressure; the other treatment consisted of steaming at 825 "C for 12 h under 20% steam at atmospheric pressure. B. Catalytic Evaluation. Two methods were used for the evaluation of these zeolites as catalysts for gas oil cracking. One was the microactivity method as described by Ciapetta and Henderson (1967), with some modifications. A glass reactor heated by a Lindberg three-zone furnace was used in the process. The catalyst bed consisted of a weighed amount of about 5 g of powdered catalyst. The feed was a light West Texas Devonian gas oil with a boiling range of 260 to 425 "C and an API gravity of 32.4". A syringe drive assembly allowed the addition of the feed at the desired rate. The liquid products were collected in a tared receiver, weighed, and analyzed by gas chromatography. The gases were passed through a cold trap to remove heavy components and then collected over brine. After measuring their volume, the gases were also analyzed chromatographically. The microactivity method was used primarily to establish the percent conversion of gas oil over the catalyst. The accuracy of the test was f2 numbers. Another method of catalyst evaluation was based on the use of a fluid catalytic cracking (FCC) unit. Such a unit and its operation are described by Magee and Blazek (1976). The data obtained from these tests were used to characterize both the activity and selectivity of different catalysts. Results Microactivity data were obtained for the gas oil conversion over a series of La,H-USY catalysts with variable amounts of lanthanum. The conversion data for La,H-
80
-
70
-
8 > z
0 v)
2
60-
0 0
50-
> z
20
15
IO
25
- SYNTHETIC MATRIX Figure 1. Gas oil conversion over fresh La,H-USY,i,(6.3%La2O3), Ce,H-USY,,i,(7.0% CezO,),and USY. Test conditions: 425 "C, 16 WHSV, 3 cat./oil, West Texas Gas Oil. WEIGHT % ZEOLITE
I
40
1
4.5
I
IN SEMI
I
I
5.8
5.5
1
1
6.I
I
I
I
I
I
I
1.5
2.0
2.5
3.0
3.5
4.0
% Lalo, USYpH
Figure 2. Gas oil conversion over steam-deactivatedLa,H-USY, (15 w t 9'0blend in semisyntheticmatrix). Steaming: 730 "C for 8 h, 100% steam, 15 psig. Test conditions: 480 "C, 16 WHSV, 3 cat./oil, West Texas Gas Oil.
USYa,i,with 6.3% La203are plotted in Figure 1. Results obtained under similar conditions for a catalyst containing USY zeolite are also plotted for comparison. These data show that for a given zeolite level in the catalyst, the lanthanum-exchanged zeolite has considerably better activity than the initial ultrastable form. The activity increases as the zeolite content of the catalyst increases to about 20 wt % zeolite and then tends to level off. For a 20% zeolite containing catalyst, the difference in activity between La,H-USY and USY is about 8 units. A similar increase in activity is observed for a Ce,HUSYa,i,promoted catalyst (Figure 1). In this case, the zeolite contains 7 % Ce203. The activity of this catalyst is very close to that of the above described lanthanum containing catalyst. Sieves with similar lanthanum or cerium levels show similar activities regardless of the preparation method used.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978
221
Table 11. Gas Oil Cracking over Faujasite-Type Zeolites pilot unit data
40 WHSV, 493 'C, 4 cat./oil, West Texas Gas Oil catalyst: zeolite in semisynthetic matrix catalyst deactivation: 8 2 5 'C, 1 2 h, 20% steam, atm. Dress. promoter type La,H- Ce,H- RE: USY USY USY H-Y 20 15 promoter, wt % 25 20 1.1 2.5 catalyst RE,O,, wt % 1.2 70 75 75 I5 conversion, vol% 0.05 0.05 0.05 H,, wt 76 0.04 1.3 e, + c,, wt % 1.4 1.5 2.1 C, olefin, vol % 7.5 7.8 6.5 6.8 C, olefin, vol % 6.9 6.3 4.8 4.9 4.6 5.1 6.4 i-C, ,vol % 4.2 62.5 62.5 62.0 C,\+ gasoline, vol % 61.5 56.0 55.3 56.0 55.5 gravity, API 75 aniline point, "F 75 76 83 76 73 46 bromine no. 81 Coke, wt % 5.6 5.1 6.2 3.8
test conditions:
40
2.8
4.6
5.1 I
I
I
2.0
2.5
3.0
3.5
I
1.5
7.0 % Ce,O,
6.7
I
4.0 EXCH p H
Figure 3. Gas oil conversion over steam-deactivated Ce,H-USY, (15 wt % blend in semisynthetic matrix). Steaming: 730 "C for 8 h, 100% steam, 15 psig. Test conditions: 480 "C, 16 WHSV, 3 cat./oil, West Texas Gas Oil.
z
80 -
> z
70
-
0 v)
60-
> z o 0
50
40
-
c I
I
I
IO 15 20 WEIGHT % ZEOLITE I N SEMI - S Y N T H E T I C
,
I
25 MATRIX
Figure 4. Gas oil conversion over steam-deactivated RE,H-USY,i. (6.2% RE,O,) and USY. Steaming: 730 "C for 8 h, 100% steam, 15 psig. Test conditions: 480 "C, 16 WHSV, 3 cat./oil, West Texas Gas Oil.
The activity of steam deactivated catalysts containing 15 wt % La,H-USY, with different lanthanum levels is shown in Figure 2. The plot shows an increase in activity with increasing lanthanum content in the zeolite. The conversion of gas oil obtained with steam-deactivated, Ce,H-USY, based catalysts is shown in Figure 3. The catalysts contain 15 wt % Ce,H-USY, zeolites with variable cerium content. As in the case of La,H-USY catalysts, a gradual increase in activity is observed as the cerium content of the zeolite is increased from 2.8 to 7.0% Ce203. Figure 4 compares the activity of steam-deactivated catalysts that have variable amounts of RE,H-USY,i, zeolite to that of steamed USY catalysts. As in the case of lanthanum and cerium exchanged zeolites, the activity of the catalyst with the rare earth-exchanged sieve is considerably higher than that of the corresponding USY sieve. The differences in activity between steam-deactivated RE,H-USY and USY catalysts are even more significant than those observed for the corresponding fresh catalysts: about 13 units vs. 8 units for catalysts containing 20 wt % zeolite. The data obtained from pilot unit evaluation of different rare earth-exchanged USY catalysts are given in Table 11. Data obtained for catalysts containing USY and RE,H-Y are also shown for comparison. Discussion Catalytic Activity. The data presented indicate that the exchange of USY zeolites with lanthanum, cerium, or rare earth mixtures results in a significant increase in catalytic activity for gas oil cracking. In this respect, USY zeolites behave similar to Y zeolites, since the exchange of rare earth into Y zeolites also results in a sharp increase in catalytic activity. However, on a unit weight basis, the activity of RE,H-Y is higher than that of rare earth exchange USY. This is most likely related to the differences in acidity (Scherzer and Bass, 1977), surface area, and rare
I W
u
z a IC
5z
a
K I-
3800
3600
crn-'
Figure 5. Infrared spectra in the OH stretching region of zeolites: A, USY; B, La,H-USY; C, La,H-Y. The La forms have been obtained at exchange pH 3.5 (Scherzer and Bass, 1977).
earth content of the two types of zeolite. The different acidities of La,H-Y, La,H-USY, and USY zeolites are shown by the infrared spectra in the OH stretching region of these zeolites (Figure 5). The absorption band at 3640-3650 cm-l is generally assigned to OH groups responsible for Bronsted acidity. This band is considerably stronger in the spectrum of La,H-Y relative to La,H-USY or USY, indicating a higher concentration of Bronsted acidic sites in the former zeolite. Furthermore, acidity measurements by n-butylamine titration also show higher acidity for La,H-Y (Scherzer and Bass, 1977). It is generally agreed that the high Bronsted acidity in RE,H-Y is related to its high rare earth content and is due to the hydrolysis reaction RE3++ H 2 0 [REOHI2++ H+ that takes place in the zeolitic cavities (Plank, 1964). There is about 17% RE203in RE,H-Y vs. 6-7% RE,03 in RE,H-USY and none in USY. Since the catalytic cracking activity of these zeolites is primarily controlled
222
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978
by Bronsted acidity, the higher concentration in Bronsted acidic sites in RE,H-Y results in higher catalytic activity. The higher activity of fresh RE,H-USY vs. USY at equal residence time cannot be explained by an increase in total acidity of the zeolite as a result of rare earth exchange (as in the case of RE,H-Y), since no such increase could be detected by butylamine titration (Scherzer and Bass, 1977). The increased activity of RE,H-USY is most likely related to the rare earth ions, which can generate electrostatic fields of sufficient energy to polarize and activate adsorbed molecules (Pickert et al., 1965; Tung and McIninch, 1968). Furthermore, the presence of highly charged cationic species can also modify the acid strength distribution in the zeolite, due to polarization of OH groups (Hirschler, 1963) or to an inductive effect on these groups (Richardson, 1967). Such a modification in acid strength distribution can result in higher catalytic activity. The higher activity of steam-deactivated RE,H-USY relative to USY catalysts is due not only to the presence of rare earth ions but also to the higher hydrothermal stability of acidic OH groups in RE,H-USY. This difference in stability of acidic OH groups is shown by the infrared spectra in the OH stretching region of steamdeactivated RE,H-USY and USY: the spectrum of steamed La,H-USY shows the presence of an absorption band at about 3650 cm-', characteristic for acidic OH groups, while in the corresponding spectrum of USY this band is much weaker or undetectable (Scherzer and Bass, 1977). Selectivity. The advantages of RE,H-USY over RE,H-Y zeolites become evident by comparing the selectivity of the corresponding catalysts. FCC pilot data show that for similar conversions, the yield in C3 and C4 olefins is increased when using the rare earth-exchanged USY zeolites. In this regard, RE,H-USY is similar to USY, which has higher olefin selectivity than RE,H-Y. The lower acidity of RE,H-USY as compared to that of RE,H-Y zeolites may account for the difference in olefin selectivity of these catalysts (Nace, 1969). Similar to USY, catalysts with RE,H-USY also give lower i-C4/C4 olefin ratios than those with RE,H-Y, a desirable characteristic in cases where C4 alkylate is required. RE,H-USY based catalysts show lower coke yields than those with RE,H-Y, but higher coke yields than USY based catalysts (see Table 11). This is related primarily to the level of rare earth in the zeolite. An increase in rare earth content will generally result in an increased coking rate of the catalyst (Magee et al., 1973). Furthermore, a lower zeolite acidity will also decrease the coking rate of the corresponding catalyst (Moscou and Mon6, 1973). The yield of C1 + C2hydrocarbons is also lower over RE,H-USY and USY catalysts than over RE,H-Y. The RE,H-USY catalysts have good C5+ gasoline selectivity. Moreover, these C5+ gasoline fractions have lower aniline points and higher bromine numbers than those corresponding to C,+ gasoline obtained with RE,H-Y catalysts. The lower aniline points indicate a higher content in aromatic and cyclic allylic hydrocarbons. The higher bromine numbers indicate higher olefin content. This shows again that rare earth exchanged USY zeolites maintain some of the properties of the original USY zeolite. Reaction Mechanism. The gas oil cracking process over zeolitic catalysts has been investigated and discussed by a number of authors (Plank et al., 1964; Thomas and Barmby, 1968; Nace, 1969; Moscou and Mon6,1973; Wang, 1974; John and Wojciechowski, 1975; Magee and Blazek, 1976).
It is generally agreed that the mechanism of hydrocarbon cracking reactions over zeolites requires the initial formation of carbonium ions, primarily at Bronsted acid sites. For example, in the case of paraffin cracking, this involves the addition of a proton from a Bronsted acid site to some olefinic species produced by thermal cracking or present as an impurity. The resulting carbonium ion can react with a paraffin molecule and form another carbonium ion, which subsequently undergoes C-C bond cleavage. The cracking product is an olefin and a new carbonium ion, which continues the chain of reaction; e.g. initiating step
+ H+
RlCH=CHR2
-
RlCH2CH+RZ
reaction with paraffin (intermolecular hydride transfer) RlCHZCH+R2 + R3CH2CHZR4 RlCH2CHzR2 + R&H2CH+R4 cracking step R3CH2CH+R4
-
R3+ + CH2=CHR4
Olefins crack easier than paraffins, since olefins are easier converted to carbonium ions. The catalytic cracking of cyclic hydrocarbons (naphthenes, cycloolefins, and others) involves the initial formation of cyclic carbonium ions. Side chains crack easier than rings. Benzene rings are very difficult to crack. Besides the primary cracking reactions, a number of secondary reactions take place during the gas oil cracking process. According to Thomas and Barmby, the secondary reactions occur in the zeolitic cavities and are mainly hydrogen-transfer reactions: intra- and intermolecular hydrogen transfer, cyclodehydrogenation, aromatization reactions. These are accompanied by skeletal isomerization, dismutation, condensation, and polymerization reactions. It is generally assumed that many of the hydrogen-transfer reactions involve the formation of carbonium ions and require the presence of acid sites on the catalyst. In the initial stage, the hydrogen-transfer reactions involve the conversion of olefins to paraffins and h y drogen-deficient products (aromatics and cyclic allylic hydrocarbons). Such reactions can be of the following type 4CnHZn olefins
+
3CnH2,+, + CnH2n-6 paraffins aromatics
(a)
3CmH2m-2 +.2CrnHzm + CmHzm-6 cyclocycloaromatics olefins paraffins
(b 1
Further loss of hydrogen to olefins by part of the hydrogen-deficient products results in more paraffins and coke, as illustrated schematically by reactions c and d.
olefins
c
C
c , condensed polycycles
(c)
C "Co-ke"
H, addition
CnH,n olefins
+
CnHzn+z
(d 1
The occurrence of reactions a and b during gas oil cracking is supported by the fact that simple olefinic
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978
molecules, like ethylene, have been converted into paraffins and aromatics over faujasite-type zeolites (Venuto et al., 1966). Reactions c and d involve carbonium ions and require the presence of acid sites. There is spectroscopic evidence for the interaction of zeolitic acidic OH groups with Pelectron systems of adsorbed olefins and aromatics (Venuto and Landis, 1968). Such an interaction is likely to facilitate the subsequent conversion of these molecules, leading to paraffins and condensed, hydrogen-deficient aromatics (coke). This explains why over strongly acidic zeolites, such as RE,H-Y, the rate of these hydrogen-transfer reactions is high. The presence of metals also facilitates these reactions. We have shown that USY zeolites have a lower overall acidity than RE,H-Y zeolites. The lower density of acid sites in USY zeolites reduces the rate of conversion of olefins into paraffins and of aromatics into condensed polycycles, thus allowing the olefins and aromatics to diffuse out of the zeolite and to desorb. The higher content in aromatic and allylic hydrocarbons in the gasoline fraction obtained from gas oil cracking over ultrastable zeolites, as well as the lower coke yield and higher olefin selectivity, is in agreement with this interpretation. Exchange of rare earth into the zeolite will increase the rate of these hydrogen-transfer reactions, resulting in more coke and higher conversions. This effect will be more pronounced as the rare earth content of the ultrastable zeolite increases.
223
The data presented show that the rare earth-exchanged USY zeolites combine the catalytic properties of USY zeolites with those of RE,H-Y. By varying the rare earth input into the zeolite, a series of yield-oriented catalysts can be prepared, each tailored to meet the demand of a particular segment of the refining industry. Acknowledgment
The authors express their appreciation to the Davison Division of W. R. Grace & Co. for permission to publish the results of this study. Literature Cited Ciapetta, F. G., Henderson, D., OilGas J., 88 (Oct 16, 1967). Hirschler, A. E., J. Catal., 2, 428 (1963). John, T. M.. Wojciechowski, B. W., J. Catal., 37, 240, 348. 358 (1975). Magee, J. S.,Blazek, J. J., Ritter, R. E., Oil Gas J., 48 (July 23, 1973). Magee, J. S.,Blazek, J. J., ACS Monogr., No. 171, 646 (1976). Moscou, L.. MonB, R., J. Catal., 30, 471 (1973). Nace, D. M., Ind. Eng. Chem. Prod. Res. Dev., 8 , 37 (1969). Name, D. M., Ind. Eng. Chem. Prod. Res. Dev., 9, 203 (1970). Pickett, P. E., Rabo, J. A., Dempsey, E., Schomaker, V., Roc. Int. Congr. Catal., 3rd, 7964, 1, 714 (1965). Plank, C. J., Proc. Int. Congr. Catal., 3rd, 1964. 1, 727 (1965). Plank, C. J., Rosinski, E. J., Hawthorne, W. P., Ind. Eng. Chem. Prod. Res. Dev., 3 , 165 (1964). Richardson, J. T., J. Catal., 9, 182 (1967). Scherzer, J., Bass, J. L., J. Catal., 46, 100 (1977). Thomas, C. L., Barmby. D. S.,J. Catal., 12, 341 (1968). Tung, S.E., McIninch, E., J. Catal., 10, 166, 175 (1968). Venuto, P. B., Hamilton, L. A., Landis, P. S.,J. Catal., 5 , 484 (1966). Venuto, P. B., Landis, P. S.,Adv. Catal.. 18, 303 (1968). Wang, I.. P h D Thesis, University of Utah, 1974.
Received for reuieu! December 7, 1977 Accepted May 30,1978
Synthesis of Mordenite Type Zeolite Pramod K. Bajpal and M. Someswara Rao' Department of Chemical Engineering, Indian Institute of Technology, Kanpur-2080 16, UP., India
K. V. G. K. Gokhale Deparfment of Civil Engineering, Indian Institute of Technology, Kanpur-2080 16, UP., India
I n spite of the availability of vast literature on mordenite type zeolite, information on its synthesis and stability, and
also the role of different parameters on its formation, is limited. I n the present investigation the mordenite was synthesized between 135 and 165 O C involving several compositions for starting mixture, temperature, and varied periods of time. The roles of different parameters such as the composition of the starting mixture, temperature, and duration of synthesis on the formation of sodium mordenite and its stability are investigated. The progress of the reaction for different conditions was tracked using X-ray diffraction technique, and the crystallization kinetics for mordenite formation was also studied.
molecules, and x + y is the total number of tetrahedra per unit cell. The ratio y / x ranges between 1 and 10 for natural and synthetic zeolites. These are structurally classified according to the openness of their framework as measured by their water sorption capacity (Meier, 1968; Barrer, 1968). Mordenite type zeolites have a water sorption capacity of 0.27-0.33 cm3 of H20/cm3of zeolite. Several forms of mordenite reported in literature are the derivatives of the original sodium form after ion exchange. The unit cell of the sodium form of mordenite has the dimensions: a = 18.13 A, b = 20.49 A, and C = 7.52 A, and
Introduction
The utilization of synthetic crystalline zeolites as molecular sieves and as catalysts finds extensive potential in adsorption separations, ion exchange, hydrocarbon catalysis, recovery of radioactive ions from waste solutions, separation of hydrogen isotopes, and other purifications (Breck, 1974; Kladning, 1975). The internal pore space available in any particular zeolite is governed by its structure. The zeolites are characterized by the general formula M,,,[ (A102)x.(Si02)y]-wH20, where M is the exchange cation of valency n, w is the number of water 0019-7890/78/1217-0223$01.00/0
@
1978 American Chemical Society
