Note: Descriptions are shown in the official language in which they were submitted.
S~
PROCESS FOR THE rlANl~'FAClURE OF STYI~ENME
1 Background of the Invention
2 U.S. Patent 3,502,736 discloses the oxidative dehydro-
3 ~enation of vinyl-cyclohexene and of other cyclic non-aromatic
4 hydrocarbons, having at least one double bond in the side chain,
and the consequent formation of styrene or of other aromatic
6 hydrocarbons still having a double bond in the side chain. Said
7 U.S. patent discloses the use of a catalyst which contains about
8 10% by weight of palladium in the form of a compound defined as
9 palladium oxhydrate, carried on different substrates like for
instance asbestos.
11 A big drawback however, has been noted when said
12 catalyst and said operative conditions are reproduced; the
13 formation of a large amount of carbon dioxide has been observed
14 by the applicants a few minutes after the start of the run.
A purpose of the present invention is therefore to
16 lower or to cancel such drawback and to give rise to improved
17 yields. Other advantages will become clear from the following
18 disclosure.
19 . .
Detailed Description of the Invention
21 The invention relates to an improved process for the
22 manufacture of styrene by oxidative dehydrogenation of vinyl-
23 cyclohexene, at a temperature from 100 to 400C, and in the
24 presence of a catalyst containing palladium carried on an inert
substrate, wherein the amount of palladium is comprised between
26 0,1 d 5% by weight with respect to the whole catalyst.
` l~Si4~
1 ~ccordin~ to a preferred embodiment of the invention,
2 the palladium percentage is from 0.1 to 1.5~ by weight and the
3 process temperature is comprised between 140 and 250 C, the
vinyl-cyclohexene being mixed with oxygen or other oxidizing
agent and diluted with an inert gas. ~dvantageously, besides
6 palladium, the catalyst may have an`element selected from the
group consisting of elements of Group Ia of the Periodic System
8 and elements of Groups IIa, IIb, VIa and VIIa of the Periodic
9 Table which further increases the styrene yield and the catalyst
life and lowers considerably the combustion danger. Of the afore-
11 mentioned elements, the preferred are the alkali metal elements of
12 sodium, potassium and mixtures thereof. Very satisfactory results
13 are reached when the inert substrate is alumina and when the cata-
14 lyst is prepared by impregnating the carrier with the solution of
a palladium compound, followed by an activation consisting of a
16 heat treatment for several hours at a temperature from 400 to 600
17 C or more. ~nother satisfactory activation is consisting of a re-
18 duction by means of hydrazine optionally followed by a final treat
19 ment with hydrogen.
The process according to the invention can be performed
21 either on a fixed or on a fluid bed and gives rise to best yields
22 of styrene with a contact time from 0.5 to 5 seconds. Should
23 some ethylbenzene be also present, it can be separated for
24 instance by means of a distillation! and recycled in admixture
with the feed of vinyl-cyclohexene. The catalysts according to
26 the invention are in the first hours more selective
27
` I 105146Z
1 towards the formation of ethylbenzene than of styrene but in a
2 few hours the selectivity to ethylbenzene greatly decreases and
3 the selectivity to styrene increases up to very high values.
4 Should ethylbenzene be passed alone through the catalyst bed,
in admixture with oxygen and inert diluents, no formation of
6 styrene is noted, but if the catalyst has been previously used
7 for the oxidative dehydrogenation of vinyl-cyclohexene to sty-
8 rene, also ethylbenzene can be converted to styrene with satis-
9 factory results. In other words, it has been surprisingly noted
that the catalyst for the conversion of vinyl-cyclohexene is
11 conditioned by vinyl-cyclohexene itself or by some intermediate
12 formed during its oxidative dehydrogenation to styrene.
13 A satisfactory result of the process according to
14 the invention is the possibility to reach the same yields while
using much smaller concentrations of palladium.
16 Such low concentrations and the part~cular method of
17 coating the carrier by means of impregnation lead advantageously
18 to a high dispersion of the active portion on the substrate
19 sur~ace.
Another satisfactory result is the possibility to
21 avoid the sintering of the catalyst and the starting of com-
22 bustion~ polymer~zation or cracking reactions; the cracking
23 of the reactants is particularly well repressed if some potas-
24 siu~ or sodium is present on the surface of the carrier. Beside
alumina many other carriers can be used, like silica, silica-
26 ~el, silica-alumina compositions, zeolites, kieselguhr, activa-
27 ted carbon, pumice, polyamides 9 li~e for instance, polypara-
11 -3- ~ I
1051462
1 ¦ fen en-terephthalamide, and similar natural or synthetic com-
2 pounds.
3 As a palladium compound, palladium chloride may be
4 used as well as sodium or potassium tetrachloro-palladite,
palladium nitrate, palladium sulphate, and palladium complexes
6 having ammoniacal ligands or ligands of other type. The impreg-
7 nation of the carrier can be performed by means of the incipient
8 wetting technique or soaking the carrier in the solution. The
9 carrier can be impregnated wlth a single solution containing a
palladium and an alkaline compound, but the impregnation can
11 be also carried out in two steps, the one with an alkaline so-
12 lution and the othex with a palladium solution.
13 The alkaline solution may contain potassium hydroxide
14 as well as sodium hydroxide~ sodium chloride or potassium chlo-
ride. When palladium chloride is used its solubility can be
16 improved by means of hydrogen chloride, sodium chloride, potas-
17 sium chloride or similar halogenides. By this procedure, chloro-
18 ~ palladous acid or a chloropalladite is formed at least in part. ¦ .
19 After the impregnation, the catalyst is advantageously
dried with nitrogen, with air or under vacuum and the activa-
21 tion can be performed by means of a heating treatmentor by means
;22 of different reducing agents, e.g., hydrazine, hydrogen, sodium
23 borohydride, formaldehyde and similar compounds.
24 The true nature of the catalyst during the reaction
is not known; it must be remembered that the true catalyst is
26 very active and selective only after the conditioning with a
27 run of a few hours of the ~xidative dehydrogenation of vinyl-
_~_
1()5146Z
1 cyclohexene, under the operating conditions necessary for the
2 formation of styrene.
3 The process according to the present invention can be
4 performed at a pressure comprised between 0.1 and 5 atmospheres
and preferably at atmospheric level. The oxidizing agent can
6 be oxygen or other similar oxidant like sulphur dioxide. When
7 oxygen is used, it can be added as air or as a mixture ~ith
8 diluting gases like carbon dioxide, nitrogen or steam. The
9 molar ratio between oxygen, or other equivalent oxidant, and
the vinyl-cyclohèxene, is suitably comprised between 1 and 15;
11 the concentration of vinyl-cyclohexene in the gaseous mixture
12 ed to the catalyst should be comprised fro~ 1 to 10% by volume.
13
14 Description of the Preferred Embodiments
The following examples are given for illustrating
16 purposes and do not limit in any way the scope of the invention.
17 The performance of the catalysts described in the examples im-
18 proves after a short initial run of less of an hour up to three .
19 hours; all the results hereinabelow have been reached after said
2~ initial run period. The wording "conversion" refers to the
21 molax percentage of vinyl-cyclohexene converted in any way to
22 different compounds and the wording "selectivity" refers to the
23 molar percentage of the converted vinyl-cyclohexe~e, which is
24 selectively transformed into styrene or other single and well
defined end product.
26 __
27
105146Z
1 ¦ EXAMPLE 1
2 25 g of a Ketjen-grade A alumina, wlth a surface
3 area of 49 m /g, are impregnated with a solution of 0.14 g of
4 palladium chlorlde and 1.2 cm3 of concentrated hydrogen chlDride
in 7.5 cm3 of water. The composition obtained by this way is
6 dried for 2 hours at 110C, quickly reduced with an alkaline
7 solution of hydrazine in water, then washed~ dried under vacuum
8 and finally treated with hydrogen at 250C for 8 hours. A mix-
9 ture of vinyl-cyclohexene, oxygen and nitrogen, in a molar ratio
1:4:38, is made to pass at 175C and atmospheric pressure with
11 a contact time of 3 seconds, through a fixed bed reactor con-
12 sisting of a pipe having a diameter of lO mm, loaded with the
13 catalyst prepared as above. 83.7% of the vinyl-cyclohexene is
14 selectively transformet in~o styrene, the balance being ethyl-
benzene.
16
17 EXAMPLE 2
18 25 g of the alumina of Example l are impregnated with
19 a solution of 0.42 g of palladium chloride and 3.5 cm3 of con-
centrated hydrogen chloride in 7.5 cm3 of water The compo-
21~ sition obtained by this way is dried under vacuum at 110C for
22 2 hours, quickly reduced with an alkaline solution of hydrazine
23 ~ ~n water (at room temperature) and then washed and dried at
24 150C for S hours under vacuum. A mixture of vinyl-cyclohexene,
oxygen and nitrogen9 in a molar ratio 1:3:29, is made to pass
26 at 150C and atmospheric pressure, with a contact time of 3.2
27 seconds, through the reactor of Example 1, loaded with the
iO514~i2
1 catalyst prepared as above. The conversion is 97.3% and the
2 selectivity to styrene 72%, the remaining portion being trans-
3 formed into ethylbenzene.
4 With a fe~ ratio 1:4:38, a contact time of 3.1 seconds
and a reaction temperature of 175C the conversion is 70.5% and
6 the selectivity to styrene 72.6%. -
8 EXAMPLE 3
9 25 g of the alumina of Example 1 are impregnated with
a solution of 0.42 g of palladium chloride and 0.28 g of sodium
11 chloride in 7.5 cm of water. The composition obtained by this
12 way is dried under vacuum for 2 hours at 110C, quickly reduced
13 with an alkaline solution of hydrazine at room temperature, then
14 washed and dried for 5 hours under vacuum at ~50C. A mixture
of vinyl-cyclohexene, oxygen and nitrogen, in a molar ratio
16 1:4:38, is made to pass at 175C and atmospheric pressure, with
17 a contact time of 3.1 seconds, through the react~r of Example 1
18 loaded with the catalyst prepared as above The conversion is
19 94.8% and the selectivity to styrene is 60%, the balance being
ethylbenzene.
21
22 EXAMPLE 4
23 25 g of the alumina of Example 1 are impregnated
24 with the solution of 0 21 g of palladium chloride and 0.48 g
potassium chloride in 7.5 cm of water. The composition
26 obtained by this way is dried for 4 hours at llO~C and then
27 activated at 500C for 8 hours in air. A pre-heated mixture
28 of vinyl-cyclohexene, oxygen and nitrogen, in a molar ratio
-7-
10514~Z
1 1:3:29, is made to pass at 210C and atmospheric pressure, with
2 a contact time of 2 8 seconds, through the reactor of Example 1,
3 loaded with the catalyst prepared as above. The conversion is
4 79.5% and the selectivity to styrene 81~8D/o the balance being
ethylbenzene. Data and results of Examples 1 through 4 are re-
6 ported in Table I.
8 EXAMPLE 5 ~Comparative)
9 A mixture of vinyl-cyclohexene, oxygen and nitrogen
in a molar ratio 1:6:18, is made to pass at 160C and atmos-
11 pheric pressure, with a contact time of 2 seconds, through the
12 reactor of Example 1, loaded with a palladium catalyst supported
13 on asbestos, prepared exactly as described in the first example
14 of U.S. Patent 3,502,736. The conversion of vinyl-cyclohexene
is 34/O~ the selectivity to styrene is 47%, the selectivity to
16 ethylbenzene is 11% and the selectivity to carbon dioxide is
17 41.9%. When increasing the temperat~re to 170C, the conver-
18 sion jumps to 100% and the formation of carbon dioxide is noted, .
l9 but neither styrene nor ethylbenzene or other similar aromatic
compounds are retrievable in the reaction mixture.
21
22 EXAMPLE 6 (Comparative)
23 A catalyst containing 8% by weight of palladium
24 carried on al~mina is prepared, according to Example 2, by
impregnation of the carrier with a solution of palladium chlo-
26 ride and hydrogen chloride in water. The composition obtained
27 by this way is dried for 4 hours at 110C, quickly reduced with
-8-
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1 an alkaline solution of hydrazine in water at room temperature, .
2 then washed and dried for 5 hours under vacuum at 150C.
.3 A mixture of vinyl-cyclohexene, oxygen and nitrogen,
4 in the molar ratio 1:3:29, is made to pass at 137C and atmos-
pheric pressure, with a contact time of 2.5 seconds, through
6 the reactor of Example l, loaded with the catalyst prepared as
7 above; the conversion of vinyl-cyclohexene is 61.4%, the selec-
8 tivity to styrene 52.1%, the selectivity to ethylbenzene is 32.5%
9 and the selectivity to carbon dioxide is 15.4%.
At 150C, under same operating conditions, conversion
11 is 95 4%, selectivity to styrene 30.3~, selectivity to ethyl-
12 benzene is 35 5% and selectivity to carbon dioxide is 34.2%.
13 At 158C, under same operating conditions, after a few minutes
14 of run, the temperature increases abruptly and spontaneously, .
vinyl-cyclohexene is wholly converted and the only retrievable
16 end produc~, when using a gas-cromatograph, is carbon dioxide;
17 aromatic compounds as styrene, ethylbenzene, toluene, benzene
18 and xylene are absolutely absent.
19 . ' . .
EXAMPLE 7
21 100 g of the alu~ina of Example 1 are impregnated
22 with a solution of 1 g of potassium hydroxide in 30 cm3 of
23 water; the resulting composition i9 dried for 4 hours at 110C
24 under vacuum, ~hen impregnated with a solution of 0.5 g of
palladium chloride and 1.15 g of potassium chloride in 30 cm3
26 of water and finally dried for 4 hours at 110C in air and
27 activated for 8 hours at 550C. A mixture of vinyl-cyclohexene
_~Q_
10514~;2
1 oxygen and ni~rogen, in a molar ratio of 1:3:29 is made to pass,
2 at 250C and atmospheric pressure, with a-contact t-ime of 2.6
3 seconds, through the reactor of Example 1, loaded with the
4 catalyst prepared as above. After a run of 9 hours, the con-
version of vinyl-cyclohexene is 90.6% and 85.6% of the converted
6 vinyl-cyclohexene'is retrievable as styrene, the balance being
7 ethylbenzene. As to the ethylbenzene, its selectivity decreases
8 about 3 points percent each hour.
9 . ` .
EXAMPLE 8
11 A catalyst is prepared as in Example i, but for the
12 amount of palladium chloride (0.84 g), the amount of potassium
13 chloride (1.92 g) and the activation temperature (600C).
14 The conversion of vinyl-cyclohexene is carried out as
in Example 7, while modifying the temperature (210C) and the
16 contact time (2.8"). After 6 hours, vinyl-cyclohexene conver-
17 sion is 86.5Z and styrene selectivity is 84.5%, the balance
18 being ethylbenzene; ethylbenzene selectivity, at the end of .
19 the reaction, is one quarter of the value noted after the first
hour of react~on. -
21
22 EXAMPLE 9
23 100 g of alumina of Example 1 are impregnated with
24 a solutîon of 0.84 g of palladium chloride and 1.92 g of potas-
sium chloride in 30 cm of water; the resulting composition is
26 dried for 4 hours at 110C under vacuum, activated in air for
27 8 hours at 500C, then impregnated again with a solution of 1 g
iS)Sl~iZ
1 of potassium chloride in 30 cm of water and finally dried for
2 4 hours at 110C under vacuum and activated for 8 hours at 600C.
3 A mixture of vinyl-cyclohexene, oxygen and nitrogen, in a molar
4 ratio of 1:1:16, is made to pass at 245C and atmospheric pres-
sure, with a contact time of 2.2 seconds, through the reactor
6 of Example 1, filled with the catalyst prepared as above. After
7 2 hours the conversion is 70~ and the styrene selectivity is ~4%,
8 the balance being substantially ethylbenzene. Data and results
9 of Examples 7, 8 and 9 are reported in Table II.
,10 . ,,
11 EXAMPLE 10 (Ethylbenzene Conversion)
12 A mixture of ethylbenzene, oxygen and nitrogen, in
13 a molar ratio between 1:1.5:29 and 1:3:29 is made to pass at
14 atmospheric pressure and with a contact time of 2.8 seconds
through the reactor of Example 1, filled with the catalyst of
16 Example 7, in a temperature range between 200 and 240C; ethyl-
17 benzene conversion is co~prised ~etween 0 and 17.8% but the re-
18 sulting product is almost nearly pure carbon dioxide and no
19 styrene at all is found.
The feed is changed replacing ethylbenzene by vinyl-
21 cyclohexene during a test run of some hours; then the ethyl-
22 benzene, oxygen and nitrogen feed is repristinated at a molar
23 ratio of 1:1.5:29. At 200C and a contact time of 2.8" ethyl-
24 benzene conversion is 15.3Z and 97.7% of the converted ethyl-
benzene is retrievable as styrene.
26 __ ~ l2 -
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1 EXAMPLE 11
2 A mixture of v~nyl-cyclohexene~ oxygen and nitrogen,
3 in a molar ratio 1:1:16, is made to pass at atmospheric pressure
4 and with a residence time of 3 seconds through the reactor o~
S Example 1 loaded with the catalyst of Example 8, while main-
6 taining the temperature within the range from 210 to 230C.
7 Vinyl-cyclohexene is then replaced by ethylbenzene and 20% of
8 the ethylbenzene is dehydrogenated to styrene, while ethyl-
9 benzene combustion to carbon dioxide is limited to 1%. Tests
10 and 11 prove that vinyl-cyclohexene has an activating action
11 on the catalyst. Furthermore, they are likely to teach that
12 the presence of ethylbenzene, ~oint to the presence of vinyl-
13 cyclohexene, does not hinder but énhance the styrene yields;
14 the presence of ethylbenzene alone is not sufficient for the
starting of the formation of styrene.
16
17 EXAMPLE 12 ~
18 14.3 g of poly-parafenylen-terephthal-amide are sus-
19 pended under vigorous stirring at room temperature in a solution
of 1 g of palladium chloride in 450 cm of water and 50 cm of
21 glacial acetic acid. The stirring is continued for 18 hours,
22 the suspension is then filtered and the resulting composition
~23 is washed with ethyl alcohol and dried under vacuum at 90DC.
24 The concentration of the palladium is 4.2% by weight. A mix-
ture of Y~nyl-cyclohexene, oxygen and nitrogen, in a molar ratio
26 1:14:18, is made to pass at 217C and atmospheric pressure, with
27 a contact time of 3 seconds, through* the reactor of Example 1,
10514~Z
1 loaded with the catalyst prepared as above. The conversion is .
2 79.,1% and the selectlvlty to styrene 89.2%, the balance being
3 ethylbenzene.
4 When lowering the temperature to 177C, under same
operating conditions, the conversion is 86.5% and the selectivity
6 ~ to tyr e 68,5%,
0
~''.15 . .
l6
. ' . .,
19
22
24
26
Il I
