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Isomerization of hydrocarbons in the presence of zeolite-containing catalysts
Petrol. Chem. U.S.S.R. Vol. 23, No. 1, pp. 61-66, 1983 Printed in Poland
0031---6458/83 $ 1 0 . 0 0 + . 0 0 1984 Pergamon Press Ltd.
ISOMERIZATION OF HYDROCARBONS I N THE PRESENCE OF Z E O L I T E - C O N T A I N I N G CATALYSTS
:::
Yrs. M. Z~tOROV, Yrs. N. KARTAStIEVand G. M. PANcItENKOV (dec.) I. M. Gubkin Institute of Petrochemical and Gas Industry, Moscow (Receired I 1 Jamtary 1982)
Low temperatures due to thermodynamic limitations are conducive to the isomerization of hydrocarbons since in equilibrium mixtures both the overall content of isomers and the proportion of technically valuable di- and polysubstituted substances increase. The industrial process of low-temperature isomerization was introduced by ICI using PtAl203C1 as catalyst. An original PtA1203C1 catalyst was developed in the U.S.S.R, which enables technical fractions to be isomerized at temperatures lower than 230~176 [1]. The use of PtAI203CI catalysts, however, requires strict control of sulphur and nitrogen compounds, moisture, as well as aromatic, naphthenic and olefinic hydrocarbons in the raw material. The purification of mixtures produced industrially with PtAI203CI catalysts is difficult when the content of monomethylsubstituted compounds is close to thermodynamic equilibrium. Therefore, the vroblem of developing new heterogeneous catalysts for low temperature isomerization remains pressing and it is natural that zeolites have attracted attehtion for this purpose. Rabo [2] and Minachev et al. [3] showed that zeolite metal catalysts isomerize saturated hydrocarbons. In the presence of alkali-earth, Z- and H-forms of Y zeolite, containing 0.5 ~ platinum or palladium, isomer yield is 50-70 wt. ~o at 280~176 and at a hydrogen pressure of 2-3 MPa. Zeolites with a molar ratio of SiO2 : A1203 of 8-10 (mordenites) in the absence of precious metals are known to isomerize saturated hydrocarbons at 280-380~ [4]. The activity of other-forms of zeolites of different chemical compositions, free from precious metals, has not so far been studied in detail. .. The feasibility of developing efficient isomerization catalysts without precious metals is therefore of scientific and practical interest and forms the purpose of our study. This paper describes the activity of decationized forms of Y zeolite and mordenite in isomerization of cyclohexane and n-hexane. EXPERIMENTAL
NaY zeolite with a molar ratio of SiO2 : A1203 of 4.3 ;~vas used as the starting material for preparing these catalysts. Sodium-decationized samples with. a low degree of decationization were prepared by ion exchange with an NH4CI solution * Neftekhimiya23, No, 2, 166-171, 19~3. 61
Yu. M. ZSOROV et aL
62
in one stage, followed by calcination. Samples with 9 7 ~ .decationization were prepared by two-stage ion-exchange with intermediate calcination. The H-form o f mordenite was produced by three-stage ion-exchange o f mordenite N a M (molar ratio of SiO2 : A1203= 11.9) with NH4CI solution. The degree o f decationization
TABLE 1. RESOLTS OF TRANSFORMATIONS OF tlYDROCARBONS IN TIlE PRESENCE OF H Y
AND
HM
ZEOLrrEs
v 1"5 hr- ~ i
Yield, wt. Yo Hydrocarbon
l~ ~
isomers
cracked products
C7-C9 hydrocarbons
Conversion~
%
:Selectivity of isomerization, ~o
HY Catalyst C'3'clohexane
n-Hexane
200 230 250 280 250 280 320
10.0 25.0 36.0 32-0 15.3 25-2 27.2
0-5 3-5 9.5 13"0 5.2 12-5 16-7
B
1"5 4"3 4"6 1"0 1"4 0"5
10"5 30.0 49-8 49"6 21-5 39.1 44"4
95.2 83,0 73.0 64.5 71-2 64.5 61.2
HM Catalyst Cyclohexane
n-Hexane
200 230 250 320 250 320
8-0 18.0 25.0 34.0 5.3 15.2
m
0-2 0.5 4.0 89.8 28.5
m
0"1 1"0 I'1
8"0 '
18"2 25-6 39-0 15.1 44"8
100.0 99.0 97.6 87.2 36-0 34.0
of the sample was 98 ~o. Y type zeolite (H form) was dealuminized using ethylenediaminotetraacetic acid (rapid addition by methods previously described [5]).and mordenite, using HCI [6]. Zeolite samples were compressed into pellets of 4 • 3 mm without using binders. The isomerizing activity of these catalysts was studied in the transformation o f cyclohexane and n-hexane in a continuous isothermal reactor at 200~176 at a space velocity of delivery o f 1.5 hr -1, without hydrogen or other carrier-gas. The catalyst was activated in dry air at 540~ for 5 hr after which the hydrocarbon was then passed for 16 rain, the catalyst was then regenerated using atmospheric oxygen at 540~ for 3 hr. Coke deposition />0.8 wt. ~o on feed hydrocarbon (-,-0.5 ~'o'weight of catalyst). After recovery catalyst activity was fully "restored and remained approximately constant during the 16 min reaction period, no irreversible reduction was observed in activity during 30 hr operation (bearing in mind regeneration). Varation
Isomerization of hydrocarbons TABLE 2. EFFECT OF TIlE MOLAR RATIO OF S i O 2 :
AI,O3 IN HY
63
AND
HM oN THEIR
ACTIVITY I,'V.
TRANSFORMATIONS OF CYCLOHEXANE
t 200~ v 1"5 hr-t
Catalyst
HY HM
SiO, : Na20 : A1203, content, mole/mole wt.% 4-3 8.3 9"5 11.9 18.1 25.3 34.6
0"4 0"3 0"2 0"2 0-12 0-08 0.045
Yield, wt. ~o isomers
C7-C9
cracked products
hydrocarbons
0.5 5.0 2.8
0"1 2"6 1"3
0.5 1.6 1.0
0"1 0'6 0-3
10.0 34.0 17.0 8.0 25.0 43.0 38.0
9
Conver- --I. Selectivity sion, of isome~o rization, i
10-6 41.6 21.2 8.0 25.6 45-2 39.3
%
95.2' 81.7 80-5 100.0 97.6 93.0 96.7
in catalyst activity during the experiment is described in a separate paper; stability of the crystalline structure of zeolites was monitored by IR spectra in the range 400--1200 cm - t using methods previously described [8]. Appreciable disintegration ot" the zeolite crystalline structure is only observed in samples decationized above 85 ~o in an H-form of Y type zeolite with a molar ratio of SiO2 : A1203 of 9.5. Product analysis was by gas-liquid chromatography using a capillary column (100 m) coated with squalane (column temperature 60~ carrier-gas-nitrogen). RESULTS
The effect on activity of the extent of decationization of Y type zeolite upon the isomerization of cyclohexane at 250~ is given in Fig. 1. Samples where deca'tionization is lower than 80 ~ are not appreciably active. Increasing decationization to 97 ~o markedly increases isomerization activity, isomer yield at 97 % decationized zeolite is almost 36 wt.~o. The increase in isomerization activity is proportional to the increase in activity for cracking and disproportionation, which may be evidence that these reactions take place on centres of the same type. The H-form of mordenite also has known high activity in isomerization of hydrocarbons [4] .Catalytic properties of HY and HM zeolites were compared in isomerization of naphthenic and paraffinic hydrocarbons (Table 1). These results indicate that the degree of transformation of naphthenic and paraffinic hydrocarbons is higher with HY zeolite than it is with HM at comparable temperatures, however, the latter is more selective for the isomerization of cyclohexane, but not of n-hexane. , The principal cracked products from n-hexane and cyclohexane on HY and HM catalysts are isoparaffinic hydrocarbons. Such products obtained from n-hexane on HY at 280~ have the following composition: CH,, C2H6, C3Ha-20-5; isoC4Hto-40"0, n-C4Hlo-7"5; iso-CsH12-27"3; n-CsHt2-3"7; C2H4+CaH6-1"0 wt. % C7-C9 hydrocarbons arc mainly methylcyclohexaneand dimethylcyclopentanes. The formation of these products using Pd/CaY catalysts has been described [9.1.
4
Yu. M. ZHOROV et aL
Tile activity data for dealuminized samples of Y type zeolite and mordenite in isomerization of cyclohexane at 200~ is shown in Table 2. An increase in the molecular ratio of SiO2 : A1203 in H Y zeolite to 8.3 markedly increases its activity at 200~ (isomer yield 34 wt.Yo). Increasing the molecular ratio o f SiO2 : A!203 to 9.5 causes some disintegration of the HY zeolite lattice and isomerization.activity is reduced. The activity change in mordenite is similar: it increases on increasing the molar ratio of SiO: : A1203 to 25.3 and then decreases. Wr q0:% "d ZO
,t 3 t')
.'
qo 60 80 I00 Oeqpee of decatlon&affon ~ %
Effect of the degree of decationization on the activity of Y type zeolites in isomerization of cyclohexane at t 250~ and t, 1-5 hr-i: 1-meth~)lcyclopentane; 2-cracked products; 3--C7-C9 hydrocarbons. The data indicate that dealuminization (modulus being close to 8) of Y type zeolites with 9 7 ~ o f its sodium removed becomes an active and fairly selective catalysts for the isomerization of paraflinic and naphthenic hydrocarbons; this activity is apparent at low temperatures in the absence of hydrogen. Y type zeolites are more active and selective in the isomerization of n-paraffins than is mordenite, but the latter is more selective for the isomerization of naphthenes. An explanation of the varying activity and selectivity of HY and H M catalysts and the effect o f aluminium removal may be explainedas follows. With increasing dealuminization (leaving.crystalline structure intact) catalyst acidity artd the proportion of strong acid ceatres responsible for isomerization and cracking, increases, until in HY zeolites a maximum concentration of acidic centres is observed in a sample with a molar ratio o f SiO2 : A1203 of 7.8 [10]. In dealuminization of H M mordenite tile concentration of strong acidic centres passes through a maximum at a molar ratio of SiO2 : A1203 of 19-25 [11]. At the same time the concentration o f strong acidic centres in H M both on dealuminized and on non-dealuminized samples is noticeably higher than in HY [12]. The increase in the concentration of strong acidic centres is the main factor which determines the superior activity of dealuminized H Y and H M zeolites ill isomerization. It is clear from Table 1 that isomer yield and tile degree of transformation of n-hexane in the presence of HY
Isomerization of hydrocarbons
65
and H M catalysts is lower than in isomerization of cyclohexane, thus stronger centres are needed for isomerization of n-paraffins than those required for isomerization of naphthenes. The catalytic activity of zeolites cannot be explained by their acidic properties alone, particularly when differences o f crystalline structure are taken into account. The data (Table 1) confirm that H Y zeolite is more active than H M for the isomerization of hydrocarbons. However, the measured a m m o n i a irreversibly chemisorbed at 400~ (characterizes strong acidic centres) on H M zeolite (0-2 mmole/g) is almost twice as high as on HY. Therefore if a correlation is sought between acidic properties and isomerization activity for different crystalline structures of H Y and H M zeolites alone no such correlation is observed. TABLE 3. CONVERSIONS OF REFINED PRODUCTS OF CATALYTIC REFORMING IN TIlE PRESENCE OF
HY*
ZEOLITE AT A FEED SPACE VELOCITY OF 1"5 h r - 1
Hydrocarbon
Amount of hydrocarbon,
wt.% Cl-C 3
Isobutane n-Butane Isopentane n-Pentane Dimethylbutanes Methylpentanes n-Hexane Dimethylpentanes Methylhcxanes n-Heptane Other hydrocarbons Coke Catalysate (with 4 ~o isobutane) Octane number of the catalysate: in pure form with 0"4 g/kg TES
0"5 2"7 2"0 5"6 37"2 21 "7 5"7 14"3 6"1 4"2
58"0 67'0
Yield, wt.~ 200~
230~
250~ 3"6 6.2 1.4 11"2
300~
2"2 4'0 0'6 7"8 2"4 7.8 38.0 21"D 2"4 6.8 3.6 2.9 0"4 96"7
3"0 5.3 0'9 12'0 2"8 8.9 37.0 19"0 2"0 3 "8 2.7 2"0 0'6 94"2
9"1 36"4 19-2 2"O 3'4 2.4 2,2 0'9 91 "9
4"7 7"0 2"4 11"0 3"2 8"7 34"1 20"0 1"3 2"2 2"1 2"1 1"4 88"5
63.0 72-0
66-2 75"2
65 "8 74"8
65"0 74"0
3-0
* Chemical composition of the catalyst: N a 2 0 - 0 . 3 w t . ~ , molar ratio of SiO2 : A l c O a = 4 . 3 .
Previous explanations of similar observations assumed [11] that the strongest acidic eentres were mostly deactivated; consequently H M catalysts containing many of these centres are less active in isomerization than HY. One other important factor, which explains the differences in the activity and selectivity of H Y and H M catalysts, is the rate of transport of reactants in the crystalline lattice channels of mordenite. Diffusion inhibition in the transformations of hydrocarbons on mordenite is known [10]. Hence the partial removal of aluminium and sodium f r o m mordenite skeleton makes it easier for reactants to diffuse to active centres and explains sudden increase in the activity o f dealuminized catalyst compared with HY.
66
Yu. M. ZHOROV eta/.
The H Y catalyst described has both isomerizing, and cracking activity, p e r m i t ting its use for increasing the co~itent of isomers even in cases, where the reactant composition is close to thermodynamic equilibrium. Thus refined products from platforming contain n- and monomethyl-substituted paraffins in.proportions close to thermodynamic equilibrium. With a combination of mild cracking and isomerizatlon, it is possible to upgrade the octaue number by 8 points to 75 by the formation o f desirable high-octane components like isopentane and dimethylbutanes. The catalysate (yields ground 94 wt.~o) is consequently a good blending c6mponent of high-octane light petroleum spirit (Table 3). SUMMARY
1. Y-type zeolites with 97 ~ of the sodium removed and after aluminium removal (modulus close to 8) and without precious metal a c t i v a t i o n - a r e active and fairly selcctive catalysts for the isomerization of paraffinic and naphthenic hydrocarbons at 200~176 2. The isomerization activity of H Y and H M zeolites correlates with the concentration of strong acid sites; the isomerization of paraffins requires stronger centrcs sites than are needed for the isomerization of naphthenes. 3. H Y Catalysts may be used for increasing the octane number of refined oils in catalytic reforming. REFERENCES
1. N. R. BURSIAN, Izomerizatsiya parafinovykh uglevodorodov. Terhaticheskii obzor (Isomcrization of Paraffinic Hydrocarbons. P,eview), p. 70, TsNIITENeftekhim., Moscow, 1979 2. J. A. RABO, P. E. PICKERT and P. L. iMAYS, Ind. Eng. Chem. 53, 9, 733, 1961 3. Kh. M. MINACHEV, V. I. GARANIN and Ya. I. ISAKOV, Uspekhi khimii 35, 12, 21512177, 1966 4. Kh. M. MINACHEV, V. V. KIIARLAMOV and V. I. GARANIN, Neftekhimiya 20, 1, 313, 1980 5. G. T. KERR, J. Phys. Chem. 72, 7, 2594-2597, 1968 6. P. E. EBERLY, C . N . KIMBERLIN and A. VOORHIES, J. Catal. 22, 3, 419-426, 1971 7. Yu. N . KARTASHEV, Yu.M. ZHOROV and G. M. PANCHENKOV, Kinetika i kataliz 22, 5, 1343-1345, 1981 8. A. A. KUBASOV, Vestnik MGU, Ser. 2, Khimiya 22, 1, 21-31, 1981 9. Kh. M. MINACHEV and Ya. I. ISAKOV, Metallsoderzhashchiye tseolity v katalize, p. 152, Nauka, Moscow, 1976 10. Khimiya tseolitov i kataliz ua tseolitakh (ed. by Dzh. M. Rabo), vol. 1, p. 506, Mir, 1980 I I. A. M. TSIBULEVSKII, A. L. KLYACHKO and V. I. BEREZHNAYA, Izv. AN SSSR, Ser. khim., 12, 2690-2694, 1980 12. K. V. TOPCHIYEVA and KHO SHI TKIIUANG, Aktivnost' i fiziko-khimicheskiye svoistva vysokokremnistykh tseolitov i tscolitsoderzhasbchikh katalizatorov, p. 176, lzd. MGU, Moscow, 1976
0031---6458/83 $ 1 0 . 0 0 + . 0 0 1984 Pergamon Press Ltd.
ISOMERIZATION OF HYDROCARBONS I N THE PRESENCE OF Z E O L I T E - C O N T A I N I N G CATALYSTS
:::
Yrs. M. Z~tOROV, Yrs. N. KARTAStIEVand G. M. PANcItENKOV (dec.) I. M. Gubkin Institute of Petrochemical and Gas Industry, Moscow (Receired I 1 Jamtary 1982)
Low temperatures due to thermodynamic limitations are conducive to the isomerization of hydrocarbons since in equilibrium mixtures both the overall content of isomers and the proportion of technically valuable di- and polysubstituted substances increase. The industrial process of low-temperature isomerization was introduced by ICI using PtAl203C1 as catalyst. An original PtA1203C1 catalyst was developed in the U.S.S.R, which enables technical fractions to be isomerized at temperatures lower than 230~176 [1]. The use of PtAI203CI catalysts, however, requires strict control of sulphur and nitrogen compounds, moisture, as well as aromatic, naphthenic and olefinic hydrocarbons in the raw material. The purification of mixtures produced industrially with PtAI203CI catalysts is difficult when the content of monomethylsubstituted compounds is close to thermodynamic equilibrium. Therefore, the vroblem of developing new heterogeneous catalysts for low temperature isomerization remains pressing and it is natural that zeolites have attracted attehtion for this purpose. Rabo [2] and Minachev et al. [3] showed that zeolite metal catalysts isomerize saturated hydrocarbons. In the presence of alkali-earth, Z- and H-forms of Y zeolite, containing 0.5 ~ platinum or palladium, isomer yield is 50-70 wt. ~o at 280~176 and at a hydrogen pressure of 2-3 MPa. Zeolites with a molar ratio of SiO2 : A1203 of 8-10 (mordenites) in the absence of precious metals are known to isomerize saturated hydrocarbons at 280-380~ [4]. The activity of other-forms of zeolites of different chemical compositions, free from precious metals, has not so far been studied in detail. .. The feasibility of developing efficient isomerization catalysts without precious metals is therefore of scientific and practical interest and forms the purpose of our study. This paper describes the activity of decationized forms of Y zeolite and mordenite in isomerization of cyclohexane and n-hexane. EXPERIMENTAL
NaY zeolite with a molar ratio of SiO2 : A1203 of 4.3 ;~vas used as the starting material for preparing these catalysts. Sodium-decationized samples with. a low degree of decationization were prepared by ion exchange with an NH4CI solution * Neftekhimiya23, No, 2, 166-171, 19~3. 61
Yu. M. ZSOROV et aL
62
in one stage, followed by calcination. Samples with 9 7 ~ .decationization were prepared by two-stage ion-exchange with intermediate calcination. The H-form o f mordenite was produced by three-stage ion-exchange o f mordenite N a M (molar ratio of SiO2 : A1203= 11.9) with NH4CI solution. The degree o f decationization
TABLE 1. RESOLTS OF TRANSFORMATIONS OF tlYDROCARBONS IN TIlE PRESENCE OF H Y
AND
HM
ZEOLrrEs
v 1"5 hr- ~ i
Yield, wt. Yo Hydrocarbon
l~ ~
isomers
cracked products
C7-C9 hydrocarbons
Conversion~
%
:Selectivity of isomerization, ~o
HY Catalyst C'3'clohexane
n-Hexane
200 230 250 280 250 280 320
10.0 25.0 36.0 32-0 15.3 25-2 27.2
0-5 3-5 9.5 13"0 5.2 12-5 16-7
B
1"5 4"3 4"6 1"0 1"4 0"5
10"5 30.0 49-8 49"6 21-5 39.1 44"4
95.2 83,0 73.0 64.5 71-2 64.5 61.2
HM Catalyst Cyclohexane
n-Hexane
200 230 250 320 250 320
8-0 18.0 25.0 34.0 5.3 15.2
m
0-2 0.5 4.0 89.8 28.5
m
0"1 1"0 I'1
8"0 '
18"2 25-6 39-0 15.1 44"8
100.0 99.0 97.6 87.2 36-0 34.0
of the sample was 98 ~o. Y type zeolite (H form) was dealuminized using ethylenediaminotetraacetic acid (rapid addition by methods previously described [5]).and mordenite, using HCI [6]. Zeolite samples were compressed into pellets of 4 • 3 mm without using binders. The isomerizing activity of these catalysts was studied in the transformation o f cyclohexane and n-hexane in a continuous isothermal reactor at 200~176 at a space velocity of delivery o f 1.5 hr -1, without hydrogen or other carrier-gas. The catalyst was activated in dry air at 540~ for 5 hr after which the hydrocarbon was then passed for 16 rain, the catalyst was then regenerated using atmospheric oxygen at 540~ for 3 hr. Coke deposition />0.8 wt. ~o on feed hydrocarbon (-,-0.5 ~'o'weight of catalyst). After recovery catalyst activity was fully "restored and remained approximately constant during the 16 min reaction period, no irreversible reduction was observed in activity during 30 hr operation (bearing in mind regeneration). Varation
Isomerization of hydrocarbons TABLE 2. EFFECT OF TIlE MOLAR RATIO OF S i O 2 :
AI,O3 IN HY
63
AND
HM oN THEIR
ACTIVITY I,'V.
TRANSFORMATIONS OF CYCLOHEXANE
t 200~ v 1"5 hr-t
Catalyst
HY HM
SiO, : Na20 : A1203, content, mole/mole wt.% 4-3 8.3 9"5 11.9 18.1 25.3 34.6
0"4 0"3 0"2 0"2 0-12 0-08 0.045
Yield, wt. ~o isomers
C7-C9
cracked products
hydrocarbons
0.5 5.0 2.8
0"1 2"6 1"3
0.5 1.6 1.0
0"1 0'6 0-3
10.0 34.0 17.0 8.0 25.0 43.0 38.0
9
Conver- --I. Selectivity sion, of isome~o rization, i
10-6 41.6 21.2 8.0 25.6 45-2 39.3
%
95.2' 81.7 80-5 100.0 97.6 93.0 96.7
in catalyst activity during the experiment is described in a separate paper; stability of the crystalline structure of zeolites was monitored by IR spectra in the range 400--1200 cm - t using methods previously described [8]. Appreciable disintegration ot" the zeolite crystalline structure is only observed in samples decationized above 85 ~o in an H-form of Y type zeolite with a molar ratio of SiO2 : A1203 of 9.5. Product analysis was by gas-liquid chromatography using a capillary column (100 m) coated with squalane (column temperature 60~ carrier-gas-nitrogen). RESULTS
The effect on activity of the extent of decationization of Y type zeolite upon the isomerization of cyclohexane at 250~ is given in Fig. 1. Samples where deca'tionization is lower than 80 ~ are not appreciably active. Increasing decationization to 97 ~o markedly increases isomerization activity, isomer yield at 97 % decationized zeolite is almost 36 wt.~o. The increase in isomerization activity is proportional to the increase in activity for cracking and disproportionation, which may be evidence that these reactions take place on centres of the same type. The H-form of mordenite also has known high activity in isomerization of hydrocarbons [4] .Catalytic properties of HY and HM zeolites were compared in isomerization of naphthenic and paraffinic hydrocarbons (Table 1). These results indicate that the degree of transformation of naphthenic and paraffinic hydrocarbons is higher with HY zeolite than it is with HM at comparable temperatures, however, the latter is more selective for the isomerization of cyclohexane, but not of n-hexane. , The principal cracked products from n-hexane and cyclohexane on HY and HM catalysts are isoparaffinic hydrocarbons. Such products obtained from n-hexane on HY at 280~ have the following composition: CH,, C2H6, C3Ha-20-5; isoC4Hto-40"0, n-C4Hlo-7"5; iso-CsH12-27"3; n-CsHt2-3"7; C2H4+CaH6-1"0 wt. % C7-C9 hydrocarbons arc mainly methylcyclohexaneand dimethylcyclopentanes. The formation of these products using Pd/CaY catalysts has been described [9.1.
4
Yu. M. ZHOROV et aL
Tile activity data for dealuminized samples of Y type zeolite and mordenite in isomerization of cyclohexane at 200~ is shown in Table 2. An increase in the molecular ratio of SiO2 : A1203 in H Y zeolite to 8.3 markedly increases its activity at 200~ (isomer yield 34 wt.Yo). Increasing the molecular ratio o f SiO2 : A!203 to 9.5 causes some disintegration of the HY zeolite lattice and isomerization.activity is reduced. The activity change in mordenite is similar: it increases on increasing the molar ratio of SiO: : A1203 to 25.3 and then decreases. Wr q0:% "d ZO
,t 3 t')
.'
qo 60 80 I00 Oeqpee of decatlon&affon ~ %
Effect of the degree of decationization on the activity of Y type zeolites in isomerization of cyclohexane at t 250~ and t, 1-5 hr-i: 1-meth~)lcyclopentane; 2-cracked products; 3--C7-C9 hydrocarbons. The data indicate that dealuminization (modulus being close to 8) of Y type zeolites with 9 7 ~ o f its sodium removed becomes an active and fairly selective catalysts for the isomerization of paraflinic and naphthenic hydrocarbons; this activity is apparent at low temperatures in the absence of hydrogen. Y type zeolites are more active and selective in the isomerization of n-paraffins than is mordenite, but the latter is more selective for the isomerization of naphthenes. An explanation of the varying activity and selectivity of HY and H M catalysts and the effect o f aluminium removal may be explainedas follows. With increasing dealuminization (leaving.crystalline structure intact) catalyst acidity artd the proportion of strong acid ceatres responsible for isomerization and cracking, increases, until in HY zeolites a maximum concentration of acidic centres is observed in a sample with a molar ratio o f SiO2 : A1203 of 7.8 [10]. In dealuminization of H M mordenite tile concentration of strong acidic centres passes through a maximum at a molar ratio of SiO2 : A1203 of 19-25 [11]. At the same time the concentration o f strong acidic centres in H M both on dealuminized and on non-dealuminized samples is noticeably higher than in HY [12]. The increase in the concentration of strong acidic centres is the main factor which determines the superior activity of dealuminized H Y and H M zeolites ill isomerization. It is clear from Table 1 that isomer yield and tile degree of transformation of n-hexane in the presence of HY
Isomerization of hydrocarbons
65
and H M catalysts is lower than in isomerization of cyclohexane, thus stronger centres are needed for isomerization of n-paraffins than those required for isomerization of naphthenes. The catalytic activity of zeolites cannot be explained by their acidic properties alone, particularly when differences o f crystalline structure are taken into account. The data (Table 1) confirm that H Y zeolite is more active than H M for the isomerization of hydrocarbons. However, the measured a m m o n i a irreversibly chemisorbed at 400~ (characterizes strong acidic centres) on H M zeolite (0-2 mmole/g) is almost twice as high as on HY. Therefore if a correlation is sought between acidic properties and isomerization activity for different crystalline structures of H Y and H M zeolites alone no such correlation is observed. TABLE 3. CONVERSIONS OF REFINED PRODUCTS OF CATALYTIC REFORMING IN TIlE PRESENCE OF
HY*
ZEOLITE AT A FEED SPACE VELOCITY OF 1"5 h r - 1
Hydrocarbon
Amount of hydrocarbon,
wt.% Cl-C 3
Isobutane n-Butane Isopentane n-Pentane Dimethylbutanes Methylpentanes n-Hexane Dimethylpentanes Methylhcxanes n-Heptane Other hydrocarbons Coke Catalysate (with 4 ~o isobutane) Octane number of the catalysate: in pure form with 0"4 g/kg TES
0"5 2"7 2"0 5"6 37"2 21 "7 5"7 14"3 6"1 4"2
58"0 67'0
Yield, wt.~ 200~
230~
250~ 3"6 6.2 1.4 11"2
300~
2"2 4'0 0'6 7"8 2"4 7.8 38.0 21"D 2"4 6.8 3.6 2.9 0"4 96"7
3"0 5.3 0'9 12'0 2"8 8.9 37.0 19"0 2"0 3 "8 2.7 2"0 0'6 94"2
9"1 36"4 19-2 2"O 3'4 2.4 2,2 0'9 91 "9
4"7 7"0 2"4 11"0 3"2 8"7 34"1 20"0 1"3 2"2 2"1 2"1 1"4 88"5
63.0 72-0
66-2 75"2
65 "8 74"8
65"0 74"0
3-0
* Chemical composition of the catalyst: N a 2 0 - 0 . 3 w t . ~ , molar ratio of SiO2 : A l c O a = 4 . 3 .
Previous explanations of similar observations assumed [11] that the strongest acidic eentres were mostly deactivated; consequently H M catalysts containing many of these centres are less active in isomerization than HY. One other important factor, which explains the differences in the activity and selectivity of H Y and H M catalysts, is the rate of transport of reactants in the crystalline lattice channels of mordenite. Diffusion inhibition in the transformations of hydrocarbons on mordenite is known [10]. Hence the partial removal of aluminium and sodium f r o m mordenite skeleton makes it easier for reactants to diffuse to active centres and explains sudden increase in the activity o f dealuminized catalyst compared with HY.
66
Yu. M. ZHOROV eta/.
The H Y catalyst described has both isomerizing, and cracking activity, p e r m i t ting its use for increasing the co~itent of isomers even in cases, where the reactant composition is close to thermodynamic equilibrium. Thus refined products from platforming contain n- and monomethyl-substituted paraffins in.proportions close to thermodynamic equilibrium. With a combination of mild cracking and isomerizatlon, it is possible to upgrade the octaue number by 8 points to 75 by the formation o f desirable high-octane components like isopentane and dimethylbutanes. The catalysate (yields ground 94 wt.~o) is consequently a good blending c6mponent of high-octane light petroleum spirit (Table 3). SUMMARY
1. Y-type zeolites with 97 ~ of the sodium removed and after aluminium removal (modulus close to 8) and without precious metal a c t i v a t i o n - a r e active and fairly selcctive catalysts for the isomerization of paraffinic and naphthenic hydrocarbons at 200~176 2. The isomerization activity of H Y and H M zeolites correlates with the concentration of strong acid sites; the isomerization of paraffins requires stronger centrcs sites than are needed for the isomerization of naphthenes. 3. H Y Catalysts may be used for increasing the octane number of refined oils in catalytic reforming. REFERENCES
1. N. R. BURSIAN, Izomerizatsiya parafinovykh uglevodorodov. Terhaticheskii obzor (Isomcrization of Paraffinic Hydrocarbons. P,eview), p. 70, TsNIITENeftekhim., Moscow, 1979 2. J. A. RABO, P. E. PICKERT and P. L. iMAYS, Ind. Eng. Chem. 53, 9, 733, 1961 3. Kh. M. MINACHEV, V. I. GARANIN and Ya. I. ISAKOV, Uspekhi khimii 35, 12, 21512177, 1966 4. Kh. M. MINACHEV, V. V. KIIARLAMOV and V. I. GARANIN, Neftekhimiya 20, 1, 313, 1980 5. G. T. KERR, J. Phys. Chem. 72, 7, 2594-2597, 1968 6. P. E. EBERLY, C . N . KIMBERLIN and A. VOORHIES, J. Catal. 22, 3, 419-426, 1971 7. Yu. N . KARTASHEV, Yu.M. ZHOROV and G. M. PANCHENKOV, Kinetika i kataliz 22, 5, 1343-1345, 1981 8. A. A. KUBASOV, Vestnik MGU, Ser. 2, Khimiya 22, 1, 21-31, 1981 9. Kh. M. MINACHEV and Ya. I. ISAKOV, Metallsoderzhashchiye tseolity v katalize, p. 152, Nauka, Moscow, 1976 10. Khimiya tseolitov i kataliz ua tseolitakh (ed. by Dzh. M. Rabo), vol. 1, p. 506, Mir, 1980 I I. A. M. TSIBULEVSKII, A. L. KLYACHKO and V. I. BEREZHNAYA, Izv. AN SSSR, Ser. khim., 12, 2690-2694, 1980 12. K. V. TOPCHIYEVA and KHO SHI TKIIUANG, Aktivnost' i fiziko-khimicheskiye svoistva vysokokremnistykh tseolitov i tscolitsoderzhasbchikh katalizatorov, p. 176, lzd. MGU, Moscow, 1976