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Synthesis of Gallosilicate and Alumogermanate Zeolites and Investigation of their Activity in the Reaction of Alcohol Dehydration
P.A. Jacobs et al, (Editors), Structure and Reactivity of Modified Zeolites 1984 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
167
SYNTHESIS OF GALLOSILICATE AND ALUMOGERMANATE ZEOLITES AND INVESTIGATION OF THEIR ACTIVITY IN THE REACTION OF ALCOHOL DEHYDRATION Z.G. ZULFUGAROV, A.S. SULEIMANOV, CH.R. SAMEDOV Institute of Inorganic and Physical Chemistry, Academy of Sciences of the Azerbaijan SSR, 370143, Narimanov Prospect 29, Baku (USSR)
ABSTRACT The gallosilicate and alumogermanate analogues of X and ZBK zeolites were obtained by direct synthesis. In the synthesized zeolites aluminium and silicon are completely'substituted by gallium and germanium, respectively. The influence of aluminium and silicon substitution by other atoms (Ga, Ge) on the catalytic activity, selectivity and stability of zeolite catalysts in the conversion of alcohols was investigated. It was established that over gallium zeolites the yield of aromatic hydrocarbons is in~ creased in comp~rison with the alumosilicate zeolites. The alumoQarmanate zeolite exhibits a high selectivity to the propylene yield. ' Some possible reasons for the changes in the activity and selectivity of the zeolites on substitution of aluminium by gallium and silicon by germanium are discussed. INTRODUCTION In (ref.1,2,3,4), the catalytic properties of zeolites inthe alcohol conversion are connected with the state of aluminium in zeolites. The authors of (ref.2) established the dependence of the negative charge on the oxygen atom on the bond length of atoms in the tetrahedra T-O-T. In (ref.3), the determined heterogeneity of acid cent res is connected with that of the states of aluminium atoms. In (ref.4), the dependence of process selectivity on the strength of acid centres has been established. The authors of (ref.5,6) conclude that aluminium atoms in the zeolites with octahedral coordination and deficiency in coordination must act correspondingly as strong Bronsted and Lewis acids. The author of (ref.I) suggested that secondary conversions of olefins take place only in the presence of catalysts containing aluminium atoms in cation positions.
168
From the literature review it follows that at present many special catalytic properties of zeolites are explained by the electron and coordination state of aluminium. In some articles (ref.7,8,9) methods of the synthesis of gallosilicate and alumogermanate analogues of zeolites are desc ribed. The research devoted to the study of the influence of silicon and aluminium substitution by germanium and gallium, respectively, on the zeolite properties is still incomplete (ref.l0). In this connection the synthesis of zeolites, where aluminium is isomorphously substituted by other atoms, is of great interest for the elucidation of the action mechanism of zeolite catalysts. In the course of our work gallosilicate and alumosilicate analogues of Xand ZBK zeolites (zeolites with a high content of silica,i.e.ZSM type) were synthesized and their catalytic activity, selectivity and stability in the conversion of alcohols were studied. THE METHODS OF RESEARCH AND ANALYSIS The zeolites were synthesized by the methods described in (ref.7,8,9). In order to obtain zeolites of higher crystallinity~ the initial gels were kept under the conditions described"in ( re foll ) • The obtained samples were subjected to chemical, X-ray, IRspectroscopic and thermal analysis. To identify the synthesis products containing Ga and Ge the X-ray method was used. Dehydration of alcohols of 99.5% chemical purity was studied in a flow reactorat 360-380 0C, the space velocity of the alcoho supply ranging from 1 to 5 h- 1• The reactor was charged with 3 5 cm of zeolite granul~s of 2 mm diameter. Before the experiment the zeolites were treated with dried air at 550 0C for 4 hours. Calcium ion-exchanged and hydrogen forms of X and ZBK zeolites were used as catalysts. RESULTS AND DISCUSSION In Table 1 the data on the composition of the initial gel and the synthesized zeolites are presented. From them it follows that the gallosilicate zeolite crystallizes at a lower Na 20/Si0 2 ratio than the alumosilicate. As it follows from Table 1, for the synthesis of a pure alumogermanate analogue of X zeolite
169
one should take sermanium oxide 1.5 times less than is the equivalent quantity of 8i0 (3.2 moles) necessary for the synthesis 2 of the alumosilicate X zeolite. On substitution of the silicon by germanium the parameter of a unit cell increases more than on substitution of aluminium by gallium (Table 1). As it is seen from Table 1 in the synthesis of gallium analogues of zeolites with a high content of silica the initial compositions of gels and the synthesis conditions of aluminium- and gallium-containing zeolites are the same. Gallium analogues of zeolites are crystallized from reaction mixtures with a surplus content in Silicon. The synthesis of gallium analogues of zeolites, where in the initial gels 8i0 2/A1 203 ~3, is connected with great experimental difficulties and sometimes fails. In Fig.1 IR-spectra of adsorption of initial alumosilicate zeolites and their gallium and germanium analogues are presented.
Fig. 1. IR-spectra of adsorption of initial alumosilicate zeolites and their gallic and germanic zeolites.
170
From the comparison of the spectra it follows that in the spectrum of gallosilicate zeolite (Ga-NaX) the band, corresponding to the bond vibration Si(Al)-04 and located at 1000 cm- 1, undergoes a noticeable change,i.8.it expands considerably. The observed changes reflect a mixed character of the tetrahedra. The absorption bands of silicon tetrahedra interfere with the bands of gallium tetrahedra. As it is seen from Fig.l,for the substitution of silicon by germanium (Ge-NaX) the absorption bands, when compared to an alumosilicate zeolite spectrum, shift towards low-frequency regions of the spectrum. The peaks of absorption bands shift approximately by 100cm- 1. Such experimental results are in a good agreement with the theory of IR-spectra. From the theory of IR-spectra (ref.12,13) it follows that a variation of atomic mass, in general, affects the frequency of atomic vibrations. In Fig.l, IRspectra of absorption of the initial and gallium zeolites of ZBK type are also presented. IR-spectra of these zeolites are in a satisfactory mutual agreement. Fig.2 illustrates the curves of differential thermal analysis of alumosilicates and their gallium- and germanium-substitu-
o x
w t
~ ~
o+
'0
z
w
100 200
400
600
800
Fig.2. DTA curves of the alumosilicate, gallosilicate and alumogermanate zeolites of X and ZBK types.
171
ted forms. Endoeffects corresponding to the dehydration of sodium forms of the alumosilicate (NaX), alumogermanate (Ge-NaX) and 0C, gallosilicate (Ga-NaX) zeolites appear at 246 190 0C and 160 0C, respectively. Mass losses when heating the alumosilicate and its alumogermanate and gallosilicate analogues are correspondingly equal to 25.3%, 22.5% and 18%, respectively. The decrease of the adsorption volume of a zeolite seems to be determined by the difference in the ionic radii of the isomorphously substituted atoms (see Table 1). Gallium and germanium atoms occupy a relatively larger volume in the zeolite lattice and thus decrease the volumes of free cavities. After heating at 760 0C the zeolite NaX becomes amorphous and recrystallizes into carnegeite at 800 0 e, and into nepheline at 1000 0C (ref.14). In contrast to NaX, the alumogermanate and gallosilicate analogues of X zeolite recrystallize only once into germanate and sodium gallate and at 800 0C their crystal structure is destroyed (see Fig.2). Thus, it is established that on substitution of aluminium and silicon in X zeolites by gSllium and germanium, respectively, the thermostability of zeolites decreases in the order: NaX (760 0C) > Ge-NaX (7400Cl > Ga-NaX (650 0Cl. In Fig.2 the curves of differential thermal analysis of the initial and gallium zeolites of ZBK type are presented too. Fig.2 shows that both gallosilicate ZBK and alumosilicate form are characterized by a high thermostability. Catalytic properties of the gallosilicate and alumogermanate analogues~f X and ZBK ~eolites were investigated in the dehydration reactions of isopropyl and methyl alcohols. The catalytic results are given in Table 2. Comparing the activities (Table 2) of the sodium form of the gallium and germanium X zeolites with the initial zeolite we may see that the sodium form of gallium- and germanium-containing X zeolites has not'a very high activity. It is shown in Table 2 that the activity of calcium forms of all three zeolites (NaX, Ga-NaX and Ge-NaX) rises with increasing degree of exchange by exchange for calcium. X zeolite and gallium zeolite exhibit a high activity when 70% of sodium has been exchanged by calcium. On the contrary, the alumogermanate zeolite exhibit a high activity at lower degree of sodium exchange by calcium (50%). All these three zeolites (CaNaX, Ga-CaNaX and Ge-CaNaX) show almost the same high activity in isopropanol conversion. In the case of alumosilicate and gallosilicate zeolites, the activity was sta-
95 120
Temperature of the synthesis ,oc 78 80 Nax Ga-NaX Ge-NaX Ga-ZBK
c?m~os~t~on
Phase
Ga-CaNaX
I I
O,~2
Radius of t.qe ion A 0,57 0,62 0,44
Ge-CaNaX
5H
Na 20A1 20 Al 32,6Si026Hz0 Na 20 Ga;0324 8i02 20 Ga~+ Na 20 A12032Ge025H20 Ge4+ O,9Na20 Ga 20 Ga 3 + 362Si02
Ion
3 type 3+
The composition of zeolite,mole/A1 20
37 79 86.6 92 93
74 77 78 78 77
20 75.2 83.4 92 92
72 74 77 75 73 30 85,7 57 93 92.4
56 58 57 57 56
20 83.6 88.5 90.3 90.1
Conversion was taken after a
53 54 56 55 55
27 94.6 98 93 94
86 88 96 95 94
18 87 81 72 69
cycle of periodic regeneration, total time of which was 50-60 hours.
:;-Temp~rature of the reaction is 350 oC, space velocity is 1 hour-l,
0 20 50 70 100
0/0 84 82 92 91 91
Selectivity to propylene
25,04 25,51 a=b=20,2 c=13,5
of .u. c. a A 24,86
Parameter
Substi- Conver- Selecti-I;>Conver- Selecti- Conver- Selecti-- bConver_ Selecti- Conver- Selecti-bConvertution sion % vity to sion, % vity to sion, % vity to sion, % vity to sion % vity to sion, % of sodi- initial propypropyinitial propypropyinitial propyurn by lene lene lene lene % lene % calcium
C<:tNaX
TABLE 2: Isopropanol dehydration over zeolite X and analoguesa
7,6Na20 Al20~ 5,28i02 500H20 6,5Na 20 Ga20 4,58 i 0 2 500 H20 3 5,21Na20 A120 2,2Ge0 347 H20 2 3 10Na20 9,3TBA Ga 20 3 100 8i02 2700 H 20
20 3
The composition of the reaction mixture,mole/A1
TABLE 1: The composition of the reaction mixture and of the zeolite X and analogues
-J l'.'
.....
173
ble during the investigation. while the activity of the germanate zeolite decreased with time. As germanium zeolites are less thermostable. they undergo a partial destruction on the heat treatment and activation. In Table 2 the selectivity to propylene in dehydration of isopropyl alcohol is also presented. From the table it follows that among the investigated zeolites the alumogermanate zeolite exhibits the highest selectivity. Otner conditions being the same. on complete substitution of aluminium by gallium the selectivity to propylene yield decreses when compared with alumosilicate zeolite (see Table 2). Different selectivity in the propylene yield can be explained perhaps by the different strength of acidity of the investigated zeolites and by their ability to give rise to secondary reactions. A similar picture is observed in the case of the gallium ZBK. In Table 3, the data on the catalytic properties of alumosilicate and gallium zeolites of the ZBK type are presented. Comparing the activities of the hydrogen forms of gallosilicate zeolites BK and alumosilicate ZBK we may see that the yield of liquid hydrocarbons decreases by 3%. Comparing the compositions of the hydrocarbon fraction of the reaction products we may see that in the case of gallium zeolite more aromatic and isoparaffine hydrocarbons are formed on Ga-ZBI<. Thus, it is established that activity. selectivity and stability of zeolite catalysts depend noticeably on the cationic composition of the zeolite frame. TABLE 3 The selectivity of rrethanol conversion over alurrosilicate and gallosilicate analogues of BK zeolite Reaction conditions
ZBK*
GaZBK
T,OC space velocity,hr- 1 conversion, % Reaction products, % Gas Hydrocarbons > C5 Methanol Water
380 2 100
380 2 100 16.4 22
56
56
a
2.7
Coke *Si0 2
14.5 25
Al 203
62
a
3.6
(hydrogen forms)
The composition of hydrocarbons, % ;;:BK Ga ZBK methane 1 ethane-ethylene 1 15.2 12.1 propane 2 propylene i-butane 16.7 19.6 6.6 3.5 n-butane 2.3 1 butenes 14.6 12.6 hydrocarbons C5-C9 aromatics 39.8 48
174
REFERENCES
1 K.r .MoH8 nOJm~HInUI.OHaJlcHhli! xaranas aa U80JrnTaX. I13.n. "HaYRa" HOBOCHCHPCR, ~982, 68-84.
2 G.V. Gibbs, E.P. Meagher, J.V. Smi~h, J.J. Plu~h, in Molecular Sieves. II ACS Symp.Ser•• 40 (197W, 19-20. 3 R. Beaumont, D. Barthomeuf, J. Catal., 26 (1972),218-225 4 P. Jacobs, M.Tielen, J.B. Uytterhoeven, J. Catal., 50(1977)
98-108. 5 E. Dempsey, J .Catal., 39 (1975)
'155-157.
6 D.W. Breck! G.W. Skeels, Preprints of 6th Intern.Congr.on Ca~a lysis 2 (°1976), 1-155. 7 R.M. Barrer, J.W.Baunham, F.R. Bul~itude and W.M. Meier, J. Chem.Soc., 1 (1959) 195-2U~. 8 L. Lero~, G.Poncelet, J.J. Fripia~, Mater.Res.BuII., 9 (1974)
N7, 979-987.
9 J. Selbin and R.B. Mason, J.lnorg.Nucl.Chem., 20 (1961)
228.
10 G. Poncelet, M.L.Dubru, G.Somme, (Szeged), 24 (1978) 273-280
L.~erot,
222-
Acta Phys. et Chern.
YillH8THRa n RaTaJli13 20 (I9?9) II88-II93. JI.C..MaflHD;, T80PR.fI. paC1!8T8 I
11 X~~.CaM8~OB, A.C.CY~8HMaHOB, 12 13 14
D.W. Breck, Zeolite Molecular Sieves, Wiley, New York 1974,
p , 493-498.
167
SYNTHESIS OF GALLOSILICATE AND ALUMOGERMANATE ZEOLITES AND INVESTIGATION OF THEIR ACTIVITY IN THE REACTION OF ALCOHOL DEHYDRATION Z.G. ZULFUGAROV, A.S. SULEIMANOV, CH.R. SAMEDOV Institute of Inorganic and Physical Chemistry, Academy of Sciences of the Azerbaijan SSR, 370143, Narimanov Prospect 29, Baku (USSR)
ABSTRACT The gallosilicate and alumogermanate analogues of X and ZBK zeolites were obtained by direct synthesis. In the synthesized zeolites aluminium and silicon are completely'substituted by gallium and germanium, respectively. The influence of aluminium and silicon substitution by other atoms (Ga, Ge) on the catalytic activity, selectivity and stability of zeolite catalysts in the conversion of alcohols was investigated. It was established that over gallium zeolites the yield of aromatic hydrocarbons is in~ creased in comp~rison with the alumosilicate zeolites. The alumoQarmanate zeolite exhibits a high selectivity to the propylene yield. ' Some possible reasons for the changes in the activity and selectivity of the zeolites on substitution of aluminium by gallium and silicon by germanium are discussed. INTRODUCTION In (ref.1,2,3,4), the catalytic properties of zeolites inthe alcohol conversion are connected with the state of aluminium in zeolites. The authors of (ref.2) established the dependence of the negative charge on the oxygen atom on the bond length of atoms in the tetrahedra T-O-T. In (ref.3), the determined heterogeneity of acid cent res is connected with that of the states of aluminium atoms. In (ref.4), the dependence of process selectivity on the strength of acid centres has been established. The authors of (ref.5,6) conclude that aluminium atoms in the zeolites with octahedral coordination and deficiency in coordination must act correspondingly as strong Bronsted and Lewis acids. The author of (ref.I) suggested that secondary conversions of olefins take place only in the presence of catalysts containing aluminium atoms in cation positions.
168
From the literature review it follows that at present many special catalytic properties of zeolites are explained by the electron and coordination state of aluminium. In some articles (ref.7,8,9) methods of the synthesis of gallosilicate and alumogermanate analogues of zeolites are desc ribed. The research devoted to the study of the influence of silicon and aluminium substitution by germanium and gallium, respectively, on the zeolite properties is still incomplete (ref.l0). In this connection the synthesis of zeolites, where aluminium is isomorphously substituted by other atoms, is of great interest for the elucidation of the action mechanism of zeolite catalysts. In the course of our work gallosilicate and alumosilicate analogues of Xand ZBK zeolites (zeolites with a high content of silica,i.e.ZSM type) were synthesized and their catalytic activity, selectivity and stability in the conversion of alcohols were studied. THE METHODS OF RESEARCH AND ANALYSIS The zeolites were synthesized by the methods described in (ref.7,8,9). In order to obtain zeolites of higher crystallinity~ the initial gels were kept under the conditions described"in ( re foll ) • The obtained samples were subjected to chemical, X-ray, IRspectroscopic and thermal analysis. To identify the synthesis products containing Ga and Ge the X-ray method was used. Dehydration of alcohols of 99.5% chemical purity was studied in a flow reactorat 360-380 0C, the space velocity of the alcoho supply ranging from 1 to 5 h- 1• The reactor was charged with 3 5 cm of zeolite granul~s of 2 mm diameter. Before the experiment the zeolites were treated with dried air at 550 0C for 4 hours. Calcium ion-exchanged and hydrogen forms of X and ZBK zeolites were used as catalysts. RESULTS AND DISCUSSION In Table 1 the data on the composition of the initial gel and the synthesized zeolites are presented. From them it follows that the gallosilicate zeolite crystallizes at a lower Na 20/Si0 2 ratio than the alumosilicate. As it follows from Table 1, for the synthesis of a pure alumogermanate analogue of X zeolite
169
one should take sermanium oxide 1.5 times less than is the equivalent quantity of 8i0 (3.2 moles) necessary for the synthesis 2 of the alumosilicate X zeolite. On substitution of the silicon by germanium the parameter of a unit cell increases more than on substitution of aluminium by gallium (Table 1). As it is seen from Table 1 in the synthesis of gallium analogues of zeolites with a high content of silica the initial compositions of gels and the synthesis conditions of aluminium- and gallium-containing zeolites are the same. Gallium analogues of zeolites are crystallized from reaction mixtures with a surplus content in Silicon. The synthesis of gallium analogues of zeolites, where in the initial gels 8i0 2/A1 203 ~3, is connected with great experimental difficulties and sometimes fails. In Fig.1 IR-spectra of adsorption of initial alumosilicate zeolites and their gallium and germanium analogues are presented.
Fig. 1. IR-spectra of adsorption of initial alumosilicate zeolites and their gallic and germanic zeolites.
170
From the comparison of the spectra it follows that in the spectrum of gallosilicate zeolite (Ga-NaX) the band, corresponding to the bond vibration Si(Al)-04 and located at 1000 cm- 1, undergoes a noticeable change,i.8.it expands considerably. The observed changes reflect a mixed character of the tetrahedra. The absorption bands of silicon tetrahedra interfere with the bands of gallium tetrahedra. As it is seen from Fig.l,for the substitution of silicon by germanium (Ge-NaX) the absorption bands, when compared to an alumosilicate zeolite spectrum, shift towards low-frequency regions of the spectrum. The peaks of absorption bands shift approximately by 100cm- 1. Such experimental results are in a good agreement with the theory of IR-spectra. From the theory of IR-spectra (ref.12,13) it follows that a variation of atomic mass, in general, affects the frequency of atomic vibrations. In Fig.l, IRspectra of absorption of the initial and gallium zeolites of ZBK type are also presented. IR-spectra of these zeolites are in a satisfactory mutual agreement. Fig.2 illustrates the curves of differential thermal analysis of alumosilicates and their gallium- and germanium-substitu-
o x
w t
~ ~
o+
'0
z
w
100 200
400
600
800
Fig.2. DTA curves of the alumosilicate, gallosilicate and alumogermanate zeolites of X and ZBK types.
171
ted forms. Endoeffects corresponding to the dehydration of sodium forms of the alumosilicate (NaX), alumogermanate (Ge-NaX) and 0C, gallosilicate (Ga-NaX) zeolites appear at 246 190 0C and 160 0C, respectively. Mass losses when heating the alumosilicate and its alumogermanate and gallosilicate analogues are correspondingly equal to 25.3%, 22.5% and 18%, respectively. The decrease of the adsorption volume of a zeolite seems to be determined by the difference in the ionic radii of the isomorphously substituted atoms (see Table 1). Gallium and germanium atoms occupy a relatively larger volume in the zeolite lattice and thus decrease the volumes of free cavities. After heating at 760 0C the zeolite NaX becomes amorphous and recrystallizes into carnegeite at 800 0 e, and into nepheline at 1000 0C (ref.14). In contrast to NaX, the alumogermanate and gallosilicate analogues of X zeolite recrystallize only once into germanate and sodium gallate and at 800 0C their crystal structure is destroyed (see Fig.2). Thus, it is established that on substitution of aluminium and silicon in X zeolites by gSllium and germanium, respectively, the thermostability of zeolites decreases in the order: NaX (760 0C) > Ge-NaX (7400Cl > Ga-NaX (650 0Cl. In Fig.2 the curves of differential thermal analysis of the initial and gallium zeolites of ZBK type are presented too. Fig.2 shows that both gallosilicate ZBK and alumosilicate form are characterized by a high thermostability. Catalytic properties of the gallosilicate and alumogermanate analogues~f X and ZBK ~eolites were investigated in the dehydration reactions of isopropyl and methyl alcohols. The catalytic results are given in Table 2. Comparing the activities (Table 2) of the sodium form of the gallium and germanium X zeolites with the initial zeolite we may see that the sodium form of gallium- and germanium-containing X zeolites has not'a very high activity. It is shown in Table 2 that the activity of calcium forms of all three zeolites (NaX, Ga-NaX and Ge-NaX) rises with increasing degree of exchange by exchange for calcium. X zeolite and gallium zeolite exhibit a high activity when 70% of sodium has been exchanged by calcium. On the contrary, the alumogermanate zeolite exhibit a high activity at lower degree of sodium exchange by calcium (50%). All these three zeolites (CaNaX, Ga-CaNaX and Ge-CaNaX) show almost the same high activity in isopropanol conversion. In the case of alumosilicate and gallosilicate zeolites, the activity was sta-
95 120
Temperature of the synthesis ,oc 78 80 Nax Ga-NaX Ge-NaX Ga-ZBK
c?m~os~t~on
Phase
Ga-CaNaX
I I
O,~2
Radius of t.qe ion A 0,57 0,62 0,44
Ge-CaNaX
5H
Na 20A1 20 Al 32,6Si026Hz0 Na 20 Ga;0324 8i02 20 Ga~+ Na 20 A12032Ge025H20 Ge4+ O,9Na20 Ga 20 Ga 3 + 362Si02
Ion
3 type 3+
The composition of zeolite,mole/A1 20
37 79 86.6 92 93
74 77 78 78 77
20 75.2 83.4 92 92
72 74 77 75 73 30 85,7 57 93 92.4
56 58 57 57 56
20 83.6 88.5 90.3 90.1
Conversion was taken after a
53 54 56 55 55
27 94.6 98 93 94
86 88 96 95 94
18 87 81 72 69
cycle of periodic regeneration, total time of which was 50-60 hours.
:;-Temp~rature of the reaction is 350 oC, space velocity is 1 hour-l,
0 20 50 70 100
0/0 84 82 92 91 91
Selectivity to propylene
25,04 25,51 a=b=20,2 c=13,5
of .u. c. a A 24,86
Parameter
Substi- Conver- Selecti-I;>Conver- Selecti- Conver- Selecti-- bConver_ Selecti- Conver- Selecti-bConvertution sion % vity to sion, % vity to sion, % vity to sion, % vity to sion % vity to sion, % of sodi- initial propypropyinitial propypropyinitial propyurn by lene lene lene lene % lene % calcium
C<:tNaX
TABLE 2: Isopropanol dehydration over zeolite X and analoguesa
7,6Na20 Al20~ 5,28i02 500H20 6,5Na 20 Ga20 4,58 i 0 2 500 H20 3 5,21Na20 A120 2,2Ge0 347 H20 2 3 10Na20 9,3TBA Ga 20 3 100 8i02 2700 H 20
20 3
The composition of the reaction mixture,mole/A1
TABLE 1: The composition of the reaction mixture and of the zeolite X and analogues
-J l'.'
.....
173
ble during the investigation. while the activity of the germanate zeolite decreased with time. As germanium zeolites are less thermostable. they undergo a partial destruction on the heat treatment and activation. In Table 2 the selectivity to propylene in dehydration of isopropyl alcohol is also presented. From the table it follows that among the investigated zeolites the alumogermanate zeolite exhibits the highest selectivity. Otner conditions being the same. on complete substitution of aluminium by gallium the selectivity to propylene yield decreses when compared with alumosilicate zeolite (see Table 2). Different selectivity in the propylene yield can be explained perhaps by the different strength of acidity of the investigated zeolites and by their ability to give rise to secondary reactions. A similar picture is observed in the case of the gallium ZBK. In Table 3, the data on the catalytic properties of alumosilicate and gallium zeolites of the ZBK type are presented. Comparing the activities of the hydrogen forms of gallosilicate zeolites BK and alumosilicate ZBK we may see that the yield of liquid hydrocarbons decreases by 3%. Comparing the compositions of the hydrocarbon fraction of the reaction products we may see that in the case of gallium zeolite more aromatic and isoparaffine hydrocarbons are formed on Ga-ZBI<. Thus, it is established that activity. selectivity and stability of zeolite catalysts depend noticeably on the cationic composition of the zeolite frame. TABLE 3 The selectivity of rrethanol conversion over alurrosilicate and gallosilicate analogues of BK zeolite Reaction conditions
ZBK*
GaZBK
T,OC space velocity,hr- 1 conversion, % Reaction products, % Gas Hydrocarbons > C5 Methanol Water
380 2 100
380 2 100 16.4 22
56
56
a
2.7
Coke *Si0 2
14.5 25
Al 203
62
a
3.6
(hydrogen forms)
The composition of hydrocarbons, % ;;:BK Ga ZBK methane 1 ethane-ethylene 1 15.2 12.1 propane 2 propylene i-butane 16.7 19.6 6.6 3.5 n-butane 2.3 1 butenes 14.6 12.6 hydrocarbons C5-C9 aromatics 39.8 48
174
REFERENCES
1 K.r .MoH8 nOJm~HInUI.OHaJlcHhli! xaranas aa U80JrnTaX. I13.n. "HaYRa" HOBOCHCHPCR, ~982, 68-84.
2 G.V. Gibbs, E.P. Meagher, J.V. Smi~h, J.J. Plu~h, in Molecular Sieves. II ACS Symp.Ser•• 40 (197W, 19-20. 3 R. Beaumont, D. Barthomeuf, J. Catal., 26 (1972),218-225 4 P. Jacobs, M.Tielen, J.B. Uytterhoeven, J. Catal., 50(1977)
98-108. 5 E. Dempsey, J .Catal., 39 (1975)
'155-157.
6 D.W. Breck! G.W. Skeels, Preprints of 6th Intern.Congr.on Ca~a lysis 2 (°1976), 1-155. 7 R.M. Barrer, J.W.Baunham, F.R. Bul~itude and W.M. Meier, J. Chem.Soc., 1 (1959) 195-2U~. 8 L. Lero~, G.Poncelet, J.J. Fripia~, Mater.Res.BuII., 9 (1974)
N7, 979-987.
9 J. Selbin and R.B. Mason, J.lnorg.Nucl.Chem., 20 (1961)
228.
10 G. Poncelet, M.L.Dubru, G.Somme, (Szeged), 24 (1978) 273-280
L.~erot,
222-
Acta Phys. et Chern.
YillH8THRa n RaTaJli13 20 (I9?9) II88-II93. JI.C..MaflHD;, T80PR.fI. paC1!8T8 I
11 X~~.CaM8~OB, A.C.CY~8HMaHOB, 12 13 14
D.W. Breck, Zeolite Molecular Sieves, Wiley, New York 1974,
p , 493-498.