CA1051462A

CA1051462A - Process for the manufacturer of styrene

Info

Publication number: CA1051462A
Application number: CA248,884A
Authority: CA
Inventors: Arsenio Castellan; Giorgio R. Tauszik; Enrico Moretti; Paolo Marinozzi; Romano Covini
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1975-05-07
Filing date: 1976-03-23
Publication date: 1979-03-27
Also published as: DE2612082C3; FR2310328A1; FR2310328B1; NL7602095A; BE839667A; GB1514373A; ES447644A1; DE2612082B2; IT1037920B; JPS51133236A; DE2612082A1

Abstract

Abstract of the Disclosure The present invention refers to an improved process for the manufacture of styrene by oxidative dehydrogenation of 4-vinyl-cyclohexene-1, hereinafter vinyl-cyclohexene, at a temperature from 100 to 400°C, and in the presence of a catalyst which contains palladium carried on an inert substrate. Advan-tageously, besides palladium, the catalyst may have an element selected from the group consisting of the alkali metal elements.

Description

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.

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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 ` 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

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.

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 __ 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.

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%. -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.

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 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.

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 ' .~ 10~14~;2 . ~ ~ ~ o~ o '~ ~U~ o o ~ ~00 1~ _ q _ o~ o U~ ~
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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 . ' . .

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 . ` .

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. -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.
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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.

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%, ~''.15 . .
l6 . ' . ., Il I

Claims

WHAT WE CLAIM IS:

1. A process for the manufacture of styrene by oxidative dehydrogenation of vinyl-cyclohexene at a temperature from 100 to 400°C, in the presence of a catalyst containing palladium carried on an inert substrate, said process com-prising the use of an amount of palladium from 0.1 to 5.0%
with respect to the weight of the catalyst.

2. A process according to claim 1, wherein the amount of palladium is comprised from 0.1 to 1.5% with respect to the catalyst weight and wherein the dehydrogenation is per-formed at from 140 to 250°C.

3. A process according to claim 1, wherein the vinyl-cyclohexene is admixed with oxygen diluted with an inert gas.

4. A process according to claim 1, wherein said catalyst is prepared by impregnating said inert substrate with the solution of a palladium compound.

5. A process according to claim 1, wherein said catalyst is prepared by impregnating said inert substrate with the solution of a palladium compound and wherein the compo-sition obtained by this way is activated by means of a reduc-tive treatment.

6. A process according to claim 5, wherein the re-ductive treatment is carried out by means of hydrazine.

7. A process according to claim 1, wherein said catalyst is prepared by impregnating said inert substrate with the solution of a palladium compound and wherein the compo-sition obtained by this way is activated by a healing treatment.

8. A process according to claim 1, wherein the manu-factured styrene is separated from the process by-products, containing a major proportion of ethylbenzene, and wherein said ethylbenzene is recycled and brought into contact with said catalyst, in admixture with said vinyl-cyclohexene.

9. A process according to claim 8, wherein said catalyst is activated by a preliminary run of said oxidative dehydrogenation of vinyl-cyclohexene, and wherein said ethyl-benzene is made to pass over the activated catalyst in admixture with vinyl-cyclohexene or alone.

10. A process according to claim 1, wherein said cata-lyst contains an element selected from the group consisting of the alkali elements.

11. A process according to claim 10, wherein the element is selected from the group consisting of potassium, sodium and mixtures thereof.

12. A process according to claim 1, wherein said catalyst is prepared by impregnating said inert substrate with the solution of a compound containing an element selected from the group consisting of the alkali metal elements and by impre-gnating in a second step the resulting composition with a solu-tion containing palladium.

13. A process according to claim 12, wherein the compound is potassium hydroxide.

14. A process according to claim 1, wherein said catalyst is prepared by impregnating said inert substrate with a solution containing palladium and by impregnating in a second step the resulting composition with a solution of a compound containing an element selected from the group con-sisting of the alkali metal elements.

15. A process according to claim 1, wherein said inert substrate is alumina.

16. A process according to claim 1, wherein said inert substrate is a polyamide.

17. A process according to claim 16, wherein the polyamide is parafenylen-terephthalamide.

18. A process according to claim 9 wherein catalyst activation by said preliminary run of oxidative dehydrogenation is conducted for a period of at least 1 hour.