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Effective Low-Temperature Aromatization of Ethane over H-Galloaluminosilicate(MFI) Zeolites in the Presence of Higher Alkanes or Olefins.

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A).
[17.265(2)
1 = ;= 90, p = 92.580(8) [go'],
Z = 4 [4], V = 4168.0(8)
[4107.8(6) A']]. pLllsd= 1.603 (1.536 MgmF3], T=183(2) [293(2) K); 0-range:
2.20-27 49 [2.36-25.87'1, measured reflections. 5605 1223313, independent
= 0.0409) [3955 (Ri,, = 0.0536)], R values (1>201).
reflections 4540 (R,,,
R1 = 0.041 t [0 02623, wR2 = 0.0752 [0.0524], all data: R1 = 0.0645 [0.0491],
rsR2 = 0.0838 [0.0592]. Diffractometer: Siemens P4 [Stoe IPDS]. Structure
solution with direct methods. Program for structure solution. Siemens
SHELXTL [SHELXS-86 (G. Sheldrick. 1990)],structure refinement: Full-matrix least-squares methods against F Z ;230 [373] parameters, 6 [150] restraints.
Crystallographic data (excluding structure factors) for the structures reported
in this paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-100046. Copies of the data
can be obtained free of charge on application to The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ. UK (fax: Int. code +(1223) 336-033;
e-mail depositki chemcrys.cam.ac.uk).
161 0. J. Scherer. G. Kemeny. G. Wolmershiuser, Chem. Ber. 1995, 128, 11451148
171 a) K Kawaguchi. E. Hirota, M. Ohishi, H. Suzuki, S. Takano, S. Yamamoto,
S. Sailo, J: Mol. Spectrosc. 1988, 130, 81-85; b) D. P. Chong, Chem Phys.
Lzrr. 1994,220,102-108; D. E. Woon, T. H. Dunning, Jr., J Chem. Phys. 1994,
ioi. 8877- 8893.
[8j H. Brunnei-, U. Klement, W. Meier, J. Wachter, 0. Serhadle, M. L. Ziegler,
J Orgunonuv. Chem. 1987, 335, 339-352; H. Brunner, H. Kauermann.
U Klemenc. J. Wachter. T. Zahn, M. L. Ziegler, A n g m Chem. 1985,97, 122;
Angtw Chwn. Inr. Ed. Engl. 1985, 24. 132.
191 D M. P. Mingos. D. J Wales, Introducrion ro Clusrer Chemisrry,Prentice-Hall,
1990. p. 249ff.
[lo] a ) M = Hg. M'L, = Pt(p-CNR)(CNR), n = 0: Y Yamamoto, H. Yamazaki,
7 Akurar. .I. Am Ch<,m.SOC.1982, 104, 2329-2330; b) M = Ag, M L , =
Pt(p-CO)(PK,). n = t A. Albinati, K:H. Dahmen, A. Togni, L. M. Venanzi,
Angrit. Chein. 1985, 97.760-761 ; Angew. Chem. Inr. Ed. Engl. 1985,24,166767; c) M = Cu. Au; M' = Pt(p-CO)(PPh,), n = 1 : M. F. Hallam, D. M. P.
Mingos, 'I Adatia. M. McPartlin, J Chem. Soc. Dulron Trans. 1988,335-340.
[ l l ] R. D. Adams. I T. Horvath, L.-W. Yang, Organomeruflics1983,2, 1257-1258.
I121 H. Vahrenkanip. Ad?. Orgummet. Chem. 1983, 22, 169-208, and references
therein. J: Orgunomei Chem. 1989, 370, 65-73. and references therein;
F. G A. Stone. Purr Appl Chem. 1986, 58, 529-536, and references therein.
reactivityr5- 'I and high thermodynamic barrier to aromatization,[6. ethane can be converted and yields of arenes that are
of practical significance obtained only at high temperatures
( 2 600 "C) .I8] Conversion of ethane into arenes with high yield
and selectivity at lower temperatures would not only be of
scientific interest but also have a great impact on the natural gas
conversion technology. Here we show that the thermodynamic
barrier can be overcome and that the conversion and yield of
arenes in the aromatization of ethane over H-galloalluminosilicate of ZSM-5 type (H-GaAIMFI) zeolite at lower temperatures
(400-500°C) can be increased manyfold (4-80 x ) by adding
olefins or higher alkanes to the feed. Furthermore, we show that
the ethane-ethylene conversion mechanism is changed in the
presence of olefins or higher alkanes; the large enhancement in
the reactivity of ethane results from a hydrogen-transfer reaction between ethane and higher (C, +) olefins.
Results showing a large increase in the conversion of ethane
by aromatization over H-GaA1MFI zeolite due to the presence
of various additives A-such as ethylene, propylene, n-butylene,
propane, and n-hexane-at different A/C,H, mole ratios in the
feed are presented in Table 1 and Figures 1 and 2. The increase
A
00
'
Effective Low-Temperature Aromatization of
Ethane over H-Galloaluminosilicate(MF1)
Zeolites in the Presence of Higher Alkanes or
Olefins**
Vasant R. Choudhary*, Anil K. Kinage, and
Tushar V. Choudhary
Over the last seven to eight years, aromatization of lower
alkanes (C, and C,) over Ga-modified zeolites of type ZSM-5
has been widely investigated," - 31 and commercial processes for
aromatizing propane and higher alkanes have been developed.['] Natural gas contains an appreciable amount of ethane
(upto about I0 mol%). In addition, ethane can be produced in
large quantities by oxidative coupling of methane, but, because
of its low concentration, separation of ethane from the product
stream by conventional means is difficult or uneconomical.[41
Ethane is also formed to an appreciable extent in the Cyclar LPG aromatization process as an undesirable byproduct.['] Its conversion into arenes would, therefore, be of
great practical importance. However, because of its very low
(*I
[**I
Dr V. R Choudhary. A. K Kinage, T. V. Choudhary
Chemical Engineering Division
National Chemical Laboratory
Pune-411008 (India)
Fax: Int. code +(212)33-3941, 33-0233, 33-4761
e-mail. vrcw ems.ncl.res.in
A. K K IS grateful to the Council of Scientific and Industrial Research, New
Delhi for the award of senior research fellowship. Editorial note: for a similar
study with propane in phce of ethane see V. R. Choudhary, A. K. Kinage, T. V.
Choudhary. Chem. Commun 1996.2545-2546.
Angew Chem. In,. Ed. Engi. 1997. 36, No 12
60 -
t
XI%
40 -
20 00.0
0.2
0.4
0.6
0.8
1.0
A I C2H6
Figure 1. Enhancement in ethane conversion X and yield of arene based on ethane
over H-GaAlMFI zeolite at 500°C in the presence of nconversion (Y,.,,,,,)
butylene ( 0 ) . propylene (o), and ethylene (A) as additives in the feed at different
A/C,H, ratios. S,, = aromatics selectivity in the overall aromatization of ethane
and additive; conversion of the olefin additives = 9 8 1 2 % .
in ethane conversion is higher when the A/C,H, ratio is larger
and for additives containing a greater number of carbon atoms.
It is interesting that arene selectivity in the simultaneous aromatization of ethane and any of the additives is higher than that
in the aromatization of the additives in the absence of ethane
(Table 1). The ethane conversions and yields of arenes (based on
0 VCH Verlugsge,veIlschuftmbH, 0-69451 Weinheim,1997
05?0-0833/9713612-f30S I
17.50-C .SO/()
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COMMUNICATIONS
b) n-C4H8I CZH6= 0.48
1
I
c) C3H6I C2H6= 0.91
d) C2H4I CzH, = 1.O
100,
I
t
Xf%
t
60
I
400
500
600
I
I
400
500
600
400
500
600
400
500
600
TIQCFigure 2. Influence of temperature on the enhancement of ethane conversion X and yield of arenes based on ethane conversion (Yhr(C2Hal)
over H-GaAIMFI zeolite in the
presence of olefin additives A in the feed.
Table 1. Results of aromatization of ethane in the presence and absence of olefin or higher alkane additlve and aromatizatron of pure additive over a H-GaAIMFI zeolite
(space velocity 6100 cm3g-'h-').
X[%]
TI "Cl
Feed
500
500
500
500
500
500
500
600
600
600
600
600
ethane(33.3Yo)+ N,
n-butylene (31.O %) N,
ethane(33.3 YO)+n-butylene (31.O%) + N,
propylene(29.3%)+ N,
ethane(33.3 %) + propylene (29.3YO)+ N,
ethylene (32.0%) +N,
ethane(33.3%) +ethylene(32.0%)+ N,
ethane (33.3 "/a) + N,
n-hexane(16.3 %)+ N,
ethane (33.3 %) + n-hexane (16.3%) +N,
propane(25.0 YO)iN,
ethane (33.3 %) + propane(25.0 Yo)+N,
~~
+
~
Ya,c*H,,["/.I[al
S A m
Additive A
Ethane
100
100
100
99.2
94.9
97.1
54.6
-
49.6
43.7
11.2
-
-
100
100
90.3
93.9
53.0
-
41.1
0.45
47.9
88.9
92.1
85.1
92.2
90.7
95.9
65.0
71.5
88.6
83 6
86.6
0.94
-
-
50.3
-
45.7
-
41.9
1.3
-
47.0
-
35.6
~
[a] Yield of arene based on the ethane conversion X .
ethane conversion) obtained are much higher than those reported earlier (Table 2 ) . The present results and their comparison
with earlier ones[5*8 , 91 clearly show a highly beneficial effect for
the addition of olefins or higher alkanes to the feed. Because of
the additives, both the limitations-high thermodynamic barrier and very low reactivity of ethane for its aromatization at
lower temperatures-are overcome.
The change in free energy (AG,) for ethane arornatization,
which is positive below 575 "C, approaches zero and becomes
negative (even at lower temperatures, Table 3 ) with increasing
concentrations of the additives. This makes the process thermodynamically more and more feasible. The increase in the ethane
COnverSlOn with higher A/C,H, ratio (Figure 1) and temperature (Figure 2) is consistent with the decrease in AGr ('able 3).
1306
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Table 2. Earlier results of ethane aromatization over Ga-modified zeolites of type
ZSM-5 without addition of alkenes or higher alkanes
Ga/H-ZSM-5
Ga/H-ZSM-5
(Si/AI = 34)
Ga/H-ZSM-5
(Si/Al = 34)
Ga/H-ZSM-5
(SI/AI = 34)
Ga/H-ZSM-5
(Si/AI = 15)
Pt/Ga silicate
600
550
4500
1300
-
15.0
8.0
< 1.0
[91
600
1300
-
3.0
[81
700
1300
21.0
13.0
PI
600
1160
28.2
16.2
PI
500
2000
14.0
5.8
151
[81
[a] Recalculated value (in crn3g-' h - ') in all bur the last case.
0570-0833i9713612-1306 J 17.50+ .SO10
Angew. Chem In1 Ed. Engl. 1997, 36, No. 12
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Table 3. Change In free energy (AG,) for the simultaneous aromatization of ethane
and alkene or higher alkane
A:C,H,
Reaction
-
C,H6+6H,
3C,H,
2C,H6+C,H, + C,H,+ SH,
3C,H,+ 3C,H, --t ZC,H,+9H2
3CzH,+2C,H, ZC,H,+9H2
6C,H,+6C3H, + 5C,H6+21 H,
4C,H6+C,H,
2C,H,+lOH,
C,H, + C,H, + C,H, +4H,
3C,H, +2C3H, 3C,,H, 11 H,
3C,H,+n-C6H,, -2C,H,+IOH,
-
-
+
0.0
0.5
1.o
0.67
I .o
0.2s
1.o
0.67
0.33
AG,[kcalmol- IIbrnzrno
400°C 500'C
600°C
17.6
5.1
-1.2
2.8
-0.16
7.1
-3.5
-
7.2
-2.2
-6.9
-4.4
-6.7
-1.8
-10.8
0.7
-5.2
-3.5
-
-10.0
-15.8
The intrinsic reactivity of ethane is much lower than that of
the higher
The observed enhancement in the
ethane reactivity due to the presence of C, and C, olefins results
from their hydrogen-transfer reaction with ethane [Eq. (a)].
Since ethylene and propane or butane are much more reactive
than ethane, they are further converted into arenes over the
zeolite according to Equations (b) and (c).
-
C2H6 +C,Hz, --*
CnH2n+2
C,H,,
3
C,
C2H4 +C,H,, + 2
CnH2n+H2
olefins
--f
arenes
GH-+H'
C,Hl
C2H: + G H G+H,
e C2H4+ H'
C2H4 or (C,H,,)+C,H:
(6)
(CNHZN+
I)+
(c)
The desorption of Ha, atoms from the zeolite surface as
molecular hydrogen, which controls the formation of aromatics
and hence the aromatics sele~tivity,["~is facilitated by their
spillover to the Ga sites followed by recombinative desorption
[Eqs. (k) and (l)].[I6. ' '1 The very high arene selectivity observed
(4
(el
(f)
Because of the very low reactivity of ethane, the activation of
ethane by reaction (d) is slow and, hence, limits its conversion.
Angeu Chem fnr Ed Engl 1997, 36. No 12
ethylene with the release of a proton. The activation of ethane
according to Equation (h) is much faster than that by Equation (d). Because of its high reactivity, the higher alkane formed
in reaction (h) is converted back into the olefin by reactions
similar to that in the ethane-ethylene conversion in the absence
of olefin additive [Eqs. (d)-(f)].
Ethylene and higher olefins are converted into arenes on the
Brernsted acid sites by oligomerization [Eq (i), N = 6- 101. SUCcessive dehydrogenation of the carbonium ions"61 by reaction (j) results in formation of the arenes, release of protons,
and adsorbed H atoms that remain unchanged.
(a)
However, the enhancement in the ethane conversion due to
the presence of ethylene in the feed was expected due to the
hydrogen-transfer reaction of its dimer butylene, which is
formed by ethylene dimerization over the zeolite. In the case of
higher-alkane addition, the enhancement also results from the
hydrogen-transfer reaction of ethane with the olefin formed
from the alkanes by dehydrogenation over the zeolite [Eq (b)],
which is a bifunctional catalyst with both dehydrogenation and
acid functions.
The reactivity of the olefins in the hydrogen-transfer reaction
is higher for that with a larger number of carbon atoms.["]
Therefore, the observed larger enhancement due to the longer
carbon chain in the additive and the higher A/C,H, ratio (Figure 1) is consistent with the above-mentioned hypothesis. It is
also consistent with the fact that the pentasil zeolites of ZSM-5type show high activity for the hydrogen-transfer reaction between alkane and olefin, even at 400°C."03 '']
A path and elementary reaction steps for ethane aromatization over the zeolite, which contains both Lewis (extraframework Ga sites) and Brunsted (zeolitic protons) acid sites, are
proposed here for explaining the beneficial effect of the additive.
In the absence of additive, dehydrogenation of ethane is expected to occur by interaction with the Lewis acid site G located
close to the zeolitic proton; this is similar to that proposed for
dehydrogenation of propane."'- 15] The steps involve C-H
bond cleavage (which is facilitated in the presence of a proton)
and abstraction of H - by the Lewis acid site [Eq. (d)], regeneration of the Lewis acid site by interaction with the nearby proton and H, desorption [Eq. (e)], and finally desorption of
ethylene by the release of proton from the carbonium ion
[Eq. (01.
C,H6+G
However, the enhancement in ethane conversion in the presence
of higher (C3+)olefins results from a change in the mechanism
of ethane activation. First, the olefin is activated by interaction
with a zeolitic proton to form a carbonium ion by the equilibrium reaction (g). The carbonium ion then undergoes a hydrogen-transfer reaction with ethane IEq. (h)]. The ethyl carbonium ion undergoes reaction according to Equation (f) to form
H,,+G
2H-G
[or (C,H2,+,)+I
(CNHZN+l)-
C N H 2 N -(arenes)+H+
6
+6H,,
e H-G
eH 2 + 2 G
(1)
ti)
(k)
(1)
is, therefore, attributed to the presence of well-dispersed nonframework Ga sites in the zeolite channels in a close vicinity of
the zeolitic protons.
Since the aromatization of ethylene is exothermic and the
ethane dehydrogenation or overall ethane aromatization is endothermic, there is a coupling of exothermic and endothermic
reactions in the simultaneous aromatization of ethane and
ethylene. This makes the process most energy efficient, which is
similar to the case of the methane-syngas1'81 and ethaneethylene["] conversion processes.
This investigation clearly shows that ethane, which has very
low reactivity (compared to higher hydrocarbons), can be converted into arenes with high conversion, yield, selectivity, and
productivity (because of the high space velocity) at low temperatures (400-500°C) if enough olefins or higher alkanes are
present in the feed. This concept would have great practical
implications, particularly for the conversion of ethane from natural gas, which contains appreciable amount of higher hydrocarbons along with methane and ethane, and from the OCM
(oxidative coupling of methane) product stream, which contains
comparable amounts of ethane and ethylene along with smaller
amounts of higher hydrocarbons.
Experimental Section
H-GaAIMFI zeolite [framework (FW) Si/Ga 49.9, FW Si/Al 40.3, non-FW Ga
2.2 wt%, Na/(AI+Ga) 0.03, crystal shape spherical hexagonal, and crystal size
5.5 + 1.5 pm] was prepared and characterized by methods described earlier [20].The
zeolite was pretreated in a flow of hydrogen (space velocity 1 0 3 0 c m 3 g ~ ' h - ' )at
600'C for 1 h and then in air for 0.5 h. The number of strong acid sites (in terms of
the pyridine chemisorption at 400°C) in the zeolite is 0.46 mmolg- I . The ethane
aromatization reaction over the zeolite was carried out under steady-state conditions at atmospheric pressure in a continuous-flow quartz reactor with a mixture of
VCH Verlagsgesellschufr mbH. D-69451 Wernherm, 1997
0570-0833/97~3612-1307$1750+5010
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ethane (33.3 mol%) and nitrogen, with or without any additive (higher alkanes or
olefins), as the feed at a space velocity of 6100+_100 cm3g - ' h- * w'ith a squarepulse technique descrlbed earlier [21]. The space velocity was measured at 0 "C and
1 atm. Conversion X in %, S,, in %, and yield of arene based on ethane conversion
( YArlCIHs)
in %) were determined as follows: X = [{(wt% of reactant in the feed
hydrocarbons) - (wt% of reactant in the product hydrocarbons)}/(wt% of reactant in the feed hydrocarbons)] x 100; S,, = [(wt% of arenes in the hydrocarbon
products)/{l00 - wt% of reactant(s) in the hydrocarbon products]] x 100;
YAr,Cz",, = (XS*,)/~OO.
Received: December 3, 1996 [Z9849IE]
German version: Angew Chem. 1997. f09, 1362-1 365
-
-
Keywords: arenes cyclizations ethane heterogeneous catalysis zeolites
-
[I] M. Guisnet, N. S . Gnep, F. Alario, Appl. Catal. A . Gen 1992, 89, 1-30.
[2] Y. Ono, Catal. Rev. Sci.Eng. 1992, 34, 179-226.
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[6] M . S. Scurrell, Appl. Catal. 1988, I f , 89-98.
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87. 255-270.
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279-290.
[lo] D. B. Lukynov, J Cutai. 1994, 147, 494-499.
[ l l ] D. B. Lukynov, J Catul. 1994, f45, 54-57.
[12] C. R. Bayense, A. J. H. P. van der Pol, J. H. C. van Hooff, Appl. Curul. 1991,
72, 81 -98.
[13] P. Meriaudeu, C. Naccache, J. Mol. Catul. 1991,59, L31 -L38.
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[19] V. R. Choudhary, B. S . Uphade, S . A. R. Mulla, Angew Chem. 1995,107,721723; Angew. Chem. In]. Ed. Engl. 1995,34,665-666.
[20] V . R. Choudhary, A. K. Kinage, C. Sivadinarayana, M. Guisnet. J. Curd.
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[21] V. R. Choudhary, A. K. Kinage, C. Sivadinarayana, P. Devadas, S D.
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structure and related molecules of biological relevance.['] Foltemlowing the pioneering work of Schill and Wa~serrnan,[~'
plate-directed strategies that used transition metal complexation,14. 51 x-donor-acceptor interactions,[61 and hydrogen
bonding''' have not only made the synthesis of interlocking
rings more accessible but have also allowed the introduction of
various functional groups. In most cases, the cyclization reaction is restricted to the formation of ether and amide bonds or
quaternary ammonium salts by an intermolecular pathway.
Ring-closing metathesis (RCM) has been established as an efficient approach to macroX Y 3
'*.
*.Ph
cyclic systems with intramolecular formation
C F y -H
of carbon-carbon double bonds.[sr9J The
PCY3
ruthenium benzylidene catalyst 1 (Cy = cyclohexyl) is particularly attractive in these reac1
tions, due to its high activity and tolerance to
an array of functional groups.f8- Although RCM was initially
applied in the synthesis of small five- to eight-membered
rings,["] this methodology has recently been extended to larger
ring systems incorporating up to 38 atoms.[121
The approach presented here utilizes a combination of a transition metal based template strategy and RCM to provide access
to [2]catenanes (Figure 1). The building blocks are the 30-mem-
'
n
High-Yield Synthesis of 12lCatenane.s by
Intramolecular Ring-Closing Metathesis**
Bernhard Mohr, Marcus Weck, Jean-Pierre Sawage,*
and Robert H. Grubbs*
The development of effective approaches to interlocked
molecular rings, catenanes, constitutes a great challenge in
preparative chemistry,"' especially in light of their role in DNA
[*I Dr. J:P. Sauvage, Dr. B. Mohr
Laboratoire de Chimie Organo-Minerale, UA 422 au CNRS
Faculte de Chimie
Universite Louis Pasteur
4, rue Blaise Pascal, F-67070 Strasbourg (France)
Fax: Int. code +(388)607-312
e-mail: sauvage@chimie.u-strasbg.fr
Prof. R. H. Grubbs, M Weck
Arnold and Mabel Beckman Laboratories of Chemical Synthesis
Division of Chemistry and Chemical Engineering
California Institute of Technology
Pasadena, CA 91125 (USA)
Fax: Int. code +(818)564-9297
e-mail: rhg@starbasel .caltech.edu
["*I This work was supported by a postdoctoral fellowship from the European
Community and by the United States Air Force.
1308
0 VCH i4rlagsgesdschaft mhH. 0-69451 Weinheim.1997
Figure 1. Schematic drawing of the approach utilizing a combination of a transition metal based template strategy and RCM to provide access to [2]catenanes:
a) formation of a threaded complex followed by RCM and decomplexation;
b) formation of an intertwined complex followed by twofold RCM and decomplexation. The black circle represents the transition metal ion.
bered macrocycle 2, bearing a 2,9-diphenyl-1,I 0-phenanthroline
(dpp) bidentate chelate in its backbone, and the acyclic ligands
3 and 4,in which the dpp moiety is symmetrically substituted
with ethylene oxide groups with a terminal olefin (Scheme
The threaded complexes 5 and 6 were formed quantitatively
by the reaction of 2 with a stoichiometric amount of
[Cu(MeCN),]PF, in CH,Cl,/MeCN followed by addition of
diolefins 3 and 4, respectively. Analogously, the intertwined
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Angew. Chem. Int. Ed. Engl. 1997, 36, No. 12
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