Aleksandrova, N. V.

Bursian, N. E.

Daragan, V. K.

Feoktistov, N. N.

Kogan, S. B.

Kozlova, N. I.

Ždanov, S. P.

English

Ždanov S. P.

Feoktistov N. N.

Kozlova N. I.

Bursian N. E.

Kogan S. B.

Daragan V. K.

Aleksandrova N. V.

University of Szeged

CATALYTIC PROPERTIES OP ZSM-TYPE ZEOLITES FORMED UNDER DIFFERENT CONDITIONS IF REACTIONS OP CONVERSION OP PARAFFINIC AND AROMATIC HYDROCARBONS S.P. ZHDANOV3,, N.N. Feoktistovaa, N.I. Kozlova®, N.E. Bursianb, " V V V S.B. Kogan , V.K. Daragan , N.V. Aleksandrova Institute for Chemistry of Silicates, U.S.S.S. Academy of Soiences, Leningrad^ U.S.S.B. (a) All-Union Scientific and Research Institute for Pdtrochemioal Proces-ses, Leningrad, U.S.S.R. (b) ABSTRACT Research has been made to compare oatalytio properties of Et-ZSM-5 type zeolites, H-mordenite (SiOgtAlgO^ = 9-100) and silioalite,in reactions of paraffinic and aromatic hydrooarbons in hydrogen media at P = 3.5 MPa and T = 533-613 K. The H-ZSM-zeolite possesses much higher destruction aotivity in n-hezahe conversion at much lower pro-duct isomerization degree whioh is noticed also with corresponding platinum catalysts. The difference between H-ZSM-zeolites and H-mor-denites consists in the different qualitative composition of alkyl benzenes formed by the reaction between n-hezane and benzene. The re-sults demonstrate the variety in chemical nature of n-hezane conver-sion over the tested zeolites. INTRODUCTION On the basis of the previously published data, it might be assu-med that zeolites ZSM-5 oould be synthesized only in the presence of quaternary ammonium bases or their derivatives. Later it became known that ZSM-5 zeolites might be easily cristallized from aluminosilioate mixtures either containing other organio compounds or without them. It might be ezpeoted that the usage of different organic compounds would lead to the formation of ZSM-5-type zeolites distinguished not only by their constitution, but also by their catalytic properties. EXPERIMENTAL In the present work, in order to investigate catalytic proper-ties of ZSM-5 zeolites, the samples with various S10?:A190~ ratios were synthesized» In order to eliminate the possible influence of or-ganic compounds, butyl alcohol was used as organic component in all cases. Silicalite was also synthesized in the silicate system in the presence of tetrapropylammonium hydroxide. In all cases, the synthesis was conducted at 423 K in steel autoclaves with teflone inserts. The analytical data on the compo-sition of initial mixtures and crystals are shown in Table 1. Table 1 Chemical composition of initial mixtures and crystals of ZSM samples Moles per 1 mole Samples — Initial mixtures Crystals Na20 Si02 1^0 C^HgOH Na20 Si02 ZSM-5 1.28 20 512 34.7 0.87 17 ZSM-5 3.62 60 1453 98.4 0.99 49 ZSM-5 4.10 100 1652 86.2 1.00 97.1 z)lnoineration losses are to be neglected. The composition of silicalite crystals corresponds to 0.011 moles Na90 per 1 mole Si09« ZSM-5 zeolites containing organios are stable to temperatures up to 973-1073 K, their thermostability inoreases with the increase in Si02:Al20j ratio in orystals. By means of ohemioal modification of ZSM-5 orystals, their thermostability oan be risen up to 1273-1373 K. In the present work, the properties of pentasiles have been in-vestigated in conditions of paraffin hydrocracking which goes through disproportionation stages resulting mainly in the formation of initial hydrooarbon with the minimum yield of destruction products (C^-Cg). The similar conversion of n-hexane has been studied over the catalyst on the base of H-mordenite under hydrogen pressure and at the tempera-ture of 593-623 K C1, P. 341 ;23. The experiments with mordenites (H-S) were used in this work as reference standards. The sample with silicate modulus 13 (standard), and mordenite obtained by dealuminizing of the standard with a ratio Si02:Al203 = 59 were studied. Zeolite powdered was formed together with jf-AlgÔ  (3:1, mass.). The tests were conducted in an ordinary unit of flow-through type. The amounts of catalyst from 1 to 8 cn̂  with particle size 0.1-0«>2 cm were used. Test conditions are listed in notes to Tables 2, 3 and Figures 1-3. RESULTS AND DISCUSSION The most significant difference of H-ZSM zeolites as opposed to H-M consists in their much higher destructive aotivity in conversion of n-hexane at lower (compared with H-M) product isomerization degree (Table 2). Although the optimum value of silicate modulus approaches 50, the above conclusion is practically true for entire interval of its values (except the low-active silicalite), and also with the changing of conversion degree (10-70$) acoording to the experimental condi-tions (T = 533-613 K, LHSV » 4-16 hrs"1). Table 2 Conversion of n-hexane over H-M- and H-ZSM-type zeolites1̂  No. Zeoli- Conv. Selectivity, $6 iso/n te/SiOgJAlgOj of n-C6, C3 IC4 I05 I1G6 C4 C5 Cg mass$ 1 H-M/13 16.5 13.1 13.5 10.5 62.9 2.3 2.8 0.1 2 H-M/59 23.1 7.1 18.7 14.2 59.7 3.4 3.7 0.2 3 H-ZSM/17 33.4 19.8 39.8 25.2 15.2 0.7 0.8 0.1 4 H-ZSM/49 50.6 16.0 40.8 28.1 15.1 0.8 0.9 0.1 5 H-ZSM/100 37.3 15.9 40.3 28.2 15.6 0.8 0.9 0.1 6 Sili-caliteA40 000 0.5 6.4 17.0 12.8 63.8 3.0 4.0 0.01 X>T = 573 K, LHSV = 8 hrs"1, P„ = 3.5 MPa H2 The increase in conversion degree as a funotion of modulus (in the interval of 9-49) when passing from mordenite to ZSM is observed for corresponding platinum catalyst with the difference that platinum favours the formation of iso-hexane (in accordance with data C3] ) with maximum selectivity for SiOgiAlgO^ =13 (Pt/H-M, Fig. 1). The data on the comparison of catalitic activity between H-ZSM-and H-ffi-type zeolites support the conclusion [4,5] that the decline in number of acidic oenters due to deorease in aluminium concentration, is followed by the increase in their acidio strength. In the publications, this problem still remains controversial C4-73. Pig, 1. Conversion of n-hexane over Pt/H-M and Pt/H-ZSM 1 - Selectivity of iso-Og formation 2 - Selectivity of 2,2-dimethylbutane formation I-IV - Pt/H-M V-TL - Pt/H-ZSM N We have previously shown that, when n-hexane destruction, pro-ducts reaot with benzene over dealuminized H-M, the main initial pro-duot is ethylbenzene [3]* The similar produot distribution is obser-ved over standard H-M with modulus equal to 13 (Pig. 2, 1-2). The zeolites of H-ZSM-type are at the similar conditions cha-racterized by the formation of mainly propylbenzenes along with the formation of higher alkylbenzenes and minimum quantities of ethylben-zene irrespective to conversion degree and silioate modulus (Pig. 2, 3-5). The conversion of benzene without paraffin at these conditions is negligible, so the composition of aUylbenzenes (if seoondary reac-tions are restricted) depiots the composition of n-hexane distributioi products, whioh are Intermediates in the formation of final products, paraffins Ĉ -̂ Ĉ e Thus, the prevalence of propyl benzenes over H-ZSM shows the significant difference in ohemioal mechanisms on n-hexane destruction over H-ZSM and over H-M at the same conditions. 132-Pig. 2. Distribution of alltylbenzenes in the product of reac-tion between n-hexane and benzene (86 mole fc n-CgH^ + 14 mo-le it CgHg) over zeolites of H-ZSM- and H-M-type Si02:Al203 T, K LHSV, n-C6H14 C6H6 hrs 1 conver- conver-sion, sion, mass £ mass $ 1 - H-M 13 613 8 18.4 12.1 2 - H-M 59 613 8 28.0 15.0 3 - H-ZSM 17 533 16 20.0 19.4 4 - H-ZSM 49 533 16 22.0 21.7 5 - H-ZSM 17 613 4 70.0 67.2 T h i s effect m a y be e x p l a i n e d b y means of t h e sohemes listed b e -l o w : I (over H - M ) t 0 G + i s o m e r i z a t i o n Y d e s t r u c t i o n j C-C-C-C-C-C C-$-C-C-C C - j - 0 + G = C I I (over H - Z S M ) : + d e s t r u c t i o n + C - C - C - C - C - G O - C - C + C « = C - C It is s u p p o s e d that the f o r m a t i o n of b r a n o h e d structures o n H - Z S M - z e o l i t e s compared t o H - M faces d i f f i c u l t i e s due t o t h e r e d u c -t i o n of e f f e c t i v e channel r a d i i i n t h e Z S M s t r u c t u r e , w h i o h is e v i -denced by t h e s u p p r e s s i o n of 2,2-dimethylbutane f o r m a t i o n . At t h e sane t i m e , s t r o n g aoidio o e n t e r s of fr-ZSM catalyze oleavage w i t h t h e f o r m a t i o n of Co f r a g m e n t s ( i . e . Scheme I I p r e v a i l s ) . 133-It should be noticed that introduction of small amounts of ben-zene (14$) into the hydrocarbon does not affect the conversion of n-hexane over H-ZSM. Only an excess of benzene (88$) causes some reaction retardation (Table 3). Table 3 Conversion of n-hexane over zeolites of H-M- and ZSM-type in the presence of benzenex^ No. Zeoli- Benzene n-Hexane Selectivity, $ te/Si05:Al90^ alkyla- oonver-* * J tion sion, C3 C^ C5 iCg degree, mass $ mass $ Feedstock: 86 mole$ n-•°6H14 + 14 mole$ CgHg 1 H-M/13 3.8 10.5 10.4 15.4 10.5 63 2 H-M/59 6.0 14.6 6.9 13.4 9.2 70 3 H-ZSM/17 36.3 34.9 17.4 37.5 25.7 19 4 H-ZSM/49 67.5 53.6 15.3 41.1 28.7 14 Feedstock: 12 mole$ n-•°6H14 + 88 mole$ CgHg 5 H-ZSM/17 1.5 29.3 15.4 28.2 22.2 34.2 x)T „ 5 7 3 K j L H S V 3 8 to8-1 The formation of higher alkylbenzenes is the result of benzene alkylation by the products of oligomerization that also observed in the reaction of benzene alkylation by ethylene on acidio catalysts [1, p. 392]. Actually, in the experiments with mixture containing exoess of benzene, there was observed an abrupt decrease in higher alkylbenjzene yield with the formation of equal amount of ethylbenzene (Pig. 3). Therefore, the presence of ethyl- and butylbenzenes in the pri-mary products formed over H-ZSM points to the fact that n-hexane con-version in this case partially follows Scheme (I). The faot,that ethylene oligomerization at relatively low ben-zene concentration (12$ compared to 80$ over H-ZSM) is prevented over H-M, agrees well with the above conolusion that H-ZSK-type zeo-lites have acidic centers with higher strength. Pig. 3. The effect of bezene concentration on the distribution of alkylbenzenes over H-ZSM zeolite Si02:Al203 = 17, T = 573 K, LHSV = 8 hrs"1 1 - 14 mole <f> CgHg, 2 - 8 8 mole $ CgHg REFERENCES 1. Bolton, A.P. Gidrokreking, izomerizatsiya i drugie promyshlennye protsessy. - In: KMmiya tseolitov i kataliz na tseolitakh. J.Ra-bo ed. Russ. translation, Kh.M.Minachev ed., Mosoow, Mir Publ., 1980, Vol. 2, p. 341, 392. 2. Bursian,N.R., Kogan,S.B., Lastovkin, G.A., Orlov, D.S., Khimiya i tekhnologiya topliv i masel, No. 10, 7 (1981). 3. Sharikhina, M.A., Loginova, A.N., Dyrin, V.G., Levinter, M.E., Nefedov, B.Z., Alekseeva, T.V., Neftekhimiya, 22., 485 (1983). 4. Minachev, Kh.M., Kondratiev, D.A., Uspekhi Khimii, 52, 1921 (1983). 5. Kazansky, V.B., Kinetika i kataliz, 23, 1334 (1982). 6. Hidalgo, C.V., It oh, H., Hattori, T., Niwa, M., Murakami, J., J. Catal., 85, 362 (1984). 7. Vedrine, J.C., Auroux, A., Boles, V., Dejaifie, P., Berg, J.P., van den, J. Catal., 59, 248 (1979). 8. Kogan, S.B., Daragan, V.K., Bursian, N.R., Neftekhimiya, 24, 32 (1984). 

Catalytic properties of ZSM-type zeolites formed under different conditions in reactions of conversion of paraffinic and aromatic hydrocarbons

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Catalytic properties of ZSM-type zeolites formed under different conditions in reactions of conversion of paraffinic and aromatic hydrocarbons

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