Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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F-534
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PROCESS FOR STABILIZING CATALYSTS OF THE SILICALITE TYPE
The present invention relates to a process for stabilizing
catalysts of the silicalite type. More particularly, the present invention
concerns a process for stabilizing crystalline silica polymorph catalysts
of the silicalite type, in order to use them in catalytic processes
conducted under pressure higher than atmospheric pressure.
The present invention also relates to the stabilized catalysts
of the silicalite type obtained in accordance with the process of the
invention, in order to use them in the processes of catalytic treatment
conducted under pressure.
It is well known in the art that the catalysts of the silicalite
type are relatively stable when used in catalytic processes which are
conducted at atmospheric pressure. It is thereiore the reason why
silicaIite has alreaty been used in processes such as isomerization of
hydrocarbons, olefin dimerization, aromatization and reforming of paraffinic
feedstocks, ant more particularly hydrocarbon conversion, insofar as the
process is conducted at atmospheric pressure.
However, it is generally interesting to conduct these processes
at higher pressures than atmospheric pressure.
In order to operate at higher pressures whils keeping the catalyst
of the silicalite type reasonably stable and active, it has already been
proposed in US patent 4,414,423 to incorporate a metal of Group IIB of the
Periodic Table of the Elements, usually zinc or cadmium. The incorporation
may be realized by any known method, as for instance impregnation or other
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usual techniques. This type of catalyst has been used in a catalytic
process for treating feedstocks containing gaseous olefins. While one
has tried to stabilize the silicalite, an important decrease of the yield
has been noted after a relatively short operating time.
It would be therefore interesting to possess a process to stabilize
silicalite in order to use it in catalytic processes which are conducted
at high pressure.
An obiect of the present invention is to provide a process to
stabilize silicalite type catalysts.
Another object of the present invention is to provide a process
to stabilize silicalite type catalysts by halogenating it with a chlorinated,
brominatet or fluorinated terivative.
Another object of the present invention is to provide stabilized
silicalite type catalysts in accordance with the process of the invention.
The foregoing objects are achieved by providing a process for
stabilizing the crystalline silica polymorph of the silicalite type which
comprises the steps of :
a) halogenating said silicalite by contacting it with a gaseous stream
comprising
(i) an halogenation agent selected from the group comprising the
~ saturatet chlorinated aliphatic organic compounds, the saturated
! brominated aliphatic organic compounds, the saturatet fluorinatet
aliphatic organic compounds and mixtures thereof, having a vapor
pressure of at least 13 kPa at a temperature of 200 to 230-C and
having a low hydrogen content; and
(ii) a non-reducing gaseous vehicle;
at a temperature comprised between 200 and 500C and during a
sufficient period of time to fix from 0.1 to 1% by weight of
halogen on the silicalite;
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b) recovering or u .g the so-formed stabilized and 'logenated silicalite.
In the process of the invention, one uses 8 silicalite, in other
terms a crystalline silica polymorph which has no exchange capacity by
comparison with zeolites. Aluminum may be present in these catalysts, but
only under the form of impurities coming from the starting products and
particularly from the source of silica used. The methods to obtain those
materials are disclosed in US 4061724 to Grose and Flanigen.
Silicalites are microporous materials, hydrothermally prepared
by using a reaction mixture comprising tetrapropylammonium cations, alkali
metals cations, water and a source of reactive silica.
According to the process of the invention, stabilization of
silicalite is carried out by halogenating it at a temperature coDprised
between about 200C and about 500C, preferably comprised between about
250C ant about 300C when chlorinated or brominated agents are used,
ant preferably between about 450 and about 500C when fluorinated agents
are uset.
The halogenation of silicalite is carried out by contacting
silicalite with a gaseous stream comprising the halogenating agent and a
non-retucing gaseous vehicle. It has been found that this treat~ent has
to be carried out under specific conditions in order to obtain
halogenated ant stabilizet catalysts which are active during long periods
~ of time when used in processes which are conducted under pressure.
; Cne of the contitions resides in the selection of the
halogenating agent. This agent is preferably a volatile organic saturated
aliphatic chlorinated, brominated or fluorinated compound, having a
vapor pressure of at least 13 kPa at a temperature of about 200 to 230C.
It is preferable to use an halogenated compound having a vapor pressure
of about 40 to 53 kPa or even more, in the same range of temperatures.
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As active halogenating agent, it may be cited volatlle halogenated
compounts having an halogen/carbon atomic rat'o equal to or hi8her than 1,
containing from 1 to 4 carbon atoms and which may contain oxygen. ~s
halogenating agents, particularly suitable to produce the catalysts of - -
the invention, it may be cited the halogenated paraffins containing from
l to 4 carbon atoms and the halogenated ethers containing from 2 to 4 carbon
atoms and which fulfill the hereabove conditions regarding volatility
ant number of halogen atoms. By way of typical examples of halogenated
paraffins, it may be cited carbon tetrachloride, carbon tetrabromide,
carbon tetrafluoride, chloroform, bromoform, fluoroform, hexachloroethane,
pentachloroethane and C~2F2. As other halogenating agents, it may
also be cited di-trichloromethyl ether, di-pentachloroethyl ether, ant
their brominated homologs.
Among the hereabove citet compounts, carbon tetrachlorite and
ti-trichloromethyl ether are particularly suitable as halogenating agents,
whlle molecular chlorine or bromine together with hytrogen chloride or
bromite are less effective.
The non-retucing gaseous vehicle which may be used is generally
nitrogen, carbon dioxite, oxygen or mixtures thereof.
The total a~ount of halogenating agent which has to be uset,
s well as the contact time with silicalite are also atjustet in order to
produce catalysts containing from about 0.1 to about 5% by weight of
chlorin- ant/or bro~ine ant/or fluorine. The necessary contact time
depends on various factors such as the number of halogen atoms within
the halogenating agent ant the concentration of halogenating agent in
the gaseous stream, or the vapor pressure of sait agent. Generally, it
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is compriset between 1/2 hour and 96 hours. more particularly between
; 1 ant 12 hours. The preferret halogen content in the catalyst depends
on various f-ctors. In most cases, the higher the activity of the
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catalyst, the higher the halogen content.
However, it has been noted that in most cases, it is more
interesting to have a halogen content comprised between 0.1 and 1% by
weight.
If the catalyst is not prepared in situ in the reactor to
be used for carrying out the process conductet under pressure~ the
catalyst is withdrawn from the halogenation reactor and is introduced
in storage tanks.
The catalysts prepared in accordance with the process of the
invention may be producet under any known form such as pellets, powder,
beads or other analogs.
It has been found that the halogenated catalysts prepared in
accordance with the process of the invention were particularly suitable
to be used in hydrocarbon conversion processes, such as for instance
olefin isomerization or dimerization, the reforming or aromatization of
paraffinic feedstoc~s, when these processes are conducted under a high
pressure compriset between about 2.105 and 7.106 Pa and particularly
when steam is cofed with the feed, as disclosed in~Unieed state~ Patent
No. 4,748,291.
Indeet, there exists an essential difference between zeolites
and the halogenatet catalyst preparet in accortance with the process of
the invention : the zeolites cannot be uset in the presence of water
(whether in the form of steam or liquit) while the catalysts of the
invention can be uset ant even present an improved stability).
It has been found that the activity of the halogenatet stabilizet
silicalites was maintained over a longer period of time when the a~ount
of steam cofet was so that the molar ratio water/feed is compriset
between about 0.5 ant 1.5.
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If, despite the stabilization provided by the process of the
invention, it is desirable to regenerate an halogenated silicalite type
catalyst as hereabove described, it may be regenerated in accordance
with well known methods, by burning the hydrocarbon products which have - -
been accumulated, e.g. by calcining them at temperatures comprised between
about 450C and 550C under a nitrogen stream containing progressively
increasing amounts of oxygen, until the CO2 content in the effluent
gaseous stream is lower than 0.1% by volume.
The following examples are given to better illustrate the process
of the present invention.
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ExamPle 1
A reactor was fed with silicalite which has been heated at
500C during 3 hours under a nitrogen stream at a gaseous hourly space
velocity (G~SV) of 500 (ml/ml.h).
After cooling at 280C while maintaining the nitrogen flow rate,
the nitrogen stream fed to the reactor has been saturated with CC14
during 4 hours.
A C4 hydrocarbon feed was passed on the obtained chlorinated
silicalite, which contains 0.8% by weight chlorine, at a temperature of
340C, under a pressure of 14,7.105 Pa, and a liquid hourly space
velocity (LHSV) of 30. The feed composition was
53.3 % by weight of n-butenes
1.2% isobutene
44.6Z butanes
0.9% lighter hydrocarbons.
Steam was cofet in a molar ratio water/feed of 1/1.
The values of the n-butenes conversion and of the gasoline
selectivity (hytrocarbons having a boiling point ranging between 36-C and
200C) are indicated in the following table, together with the
calculated gasoline yielt (~ conversion x selectivity)
Time ConversionSelectivity Yield
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After 9 hours 94.6% 86.8% 82.1
29 91.6 ~7.6 80.2
53 90.0 85.4 76.9
73 89.5 84.8 75.9
; 95 90.1 81.9 73.8
~ 143 88.7 78.1 69.3
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Comparative Exam~le 1
The same feed as in Example 1 together with steam in a molar
ratio water/feed of 1/1, was passed over an untreatet silicalite, at a
- temperature of 325C under a pressure of 14.8x105 Pa and at a LHSV - -
of 41.2.
The following results were obtained (~ by weight)
n-butene gasoline gasoline
conversion selectivity yield
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aftes 12 hours 91.6 % 65.2 æ 59.7 Z
26 hours 87.3 % 80.7 ~ 70.5 ~
52 hours 60.7 % 80.4 % 48.8 %
75 hours 20.4 Z 88.6 % 18.1 %
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Com~arative Exam~le 2
The same feed as in Example 1 together with steam in a molar ratio
wates/feed of O.S/1, was passed over an untreated silicalite at a
temperature of 323C, under a pressure of 14.8 x 105 Pa and at a LHSV
of 31.
After 7 hours, the n-butenes conversion was of 70.6 % by weight
and the gasoline selectivity was of 87.8Z. After 25 hours, the n-butene
conversion was only of 6.85 %.
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Examole 2
The experiment described in Example 1 was repeated, but with a
molar ratio watertfeed of 0.45/1.
The following results were o6tained (Z by weight).
N-bùtenes Gasoline Gasoline
conversion selectivity yield
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after 10 hours 89.2 Z 80.3 % 71.6 %
24 hours 88.6 % 84.1 % 74.5 %
54 hours 82.0 % 81.8 % 67.1 %
78 hours 79.1 % 81.1 % 64.2 %
97 hours 76.2 % 79.8 % 60.8 %
122 nours 66.5 % 80.4 % 53.5 %
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Example 3
A reactor was loaded with silicalite; then the silicalite was
- heated to 500~C during 3 hours under a nitrogen stream at a GHSV of 500.
After cooling at 284C while maintaining the nitrogen flow rate, the . .
nitrogen stream fed into the reactor was saturated with CC14 during
t 110 minutes.
The same C4hydrocarbon feed as in Example 1 was passed over
the hereabove silicalite, containing 0.4~ chlorine.
The feed was passed at 340C under a pressure of 14.9 x 105 Pa~ .
ant at a LHSV of 30.
Steam was cofed at a molar ratio water/feed o~ 0.7/1.
The following results were obtainet (% by weight)
N-butenes gasoline gasoline
conversion selectivity yield
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After 8 hours 94.5 % 84.3 % 79.7 %
24 hours 92.9 % 8S.3 % 79.2 %
48 hours 91.5 % 82.3 % 75.3 %
75 hours 90.8 % 83.9 % 76.2 %
96 hours 89.4 ~ 84.7 % 75.7 %
126 ~ours 89.2 % 80.2 % 71.5 %
149 hours 88.2 % 80.6 % 71.1 %
:; 157 hours 87.4 % 80.5 % 70.4 %
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