Make your own free website on Tripod.com
Home | Caso Diseño 2005-I | Nuevo Bolivia dice si al GTL y no al LNG | Gas Natural | Procesos de Separacion | PI 100.- FORMACION DEL INGENIERO QUIMICO | PI-525. DISENO DE PLANTAS | SYLLABUS | Caso Diseno 2004-I | Caso Diseño 2003-II | Caso Diseño 2003- I | Caso de Diseno 2002-II | Caso Diseño 2002-I | Caso Diseno 2001-I | Caso Diseno 2001-II
Ingenieria Quimica
Caso de Diseno 2002-II

Manufactura Estireno

 

DISEÑO DE PLANTAS- PI 525

Ciclo 2002-II

 Memorando

 A:    Ingeniero de Procesos                     Fecha: UNI 30 Setiembre 2002

De:   Jefe Planeamiento

Ref.- Evaluación económica para nueva tecnologías de manufactura de Estireno a partir de  butadieno

 El estireno es un químico orgánico que tiene diversos usos en la industria química. El mayor de sus empleos lo constiuye la producción de poliestireno, aunque también se le emplea en la industria de  de los plàsticos reforzados con fibra de vidrio y en la manufactura de cauchos sintéticos.

 En el año 2001 se importó hacia el Perú:

 Subpartida Nacional : 2902.50.00.00 ESTIRENO.- 1,400 TM a 720 US$/TM

Subpartida Nacional : 3903.11.00.00 POLIESTIRENO EXPANDIBLE, EN FORMAS PRIMARIAS: 950 TM a 1,115 US$/TM

Subpartida Nacional : 3903.19.00.00 POLIESTIRENO NO EXPANDIBLE, EN FORMAS PRIMARIAS:  8,000 US$/TM a 900 US$/TM. 

Se estima quelos volúmenes de poliestireno podrían facilmente multiplicarse por A en caso de existir estireno de manufactura local y que el consumo de estireno monomero podría facilmente Multiplicarse por C para dar un consumo  a partir del tercer año de implantada la manufactura de estireno y poliestireno en el Perú de aproximadamente  D % de la nueva demanda total de estireno, en los años anteriores el incremento de demanda sería gradual desde la atención de la demanda del año  2001  hasta la nueva demanda.

 La forma tradicional de manufacturar estireno ha sido mediante la producción del químico intermedio etilbenceno, el cual tiene dos inconvenientes para emplearlo en el Perú. En primer lugar se requiere de etileno para su manufactura y hasta que no se implante un polo de desarrollo petroquímico que incluya poliolefinas no existirá  una fuente de etileno. La segunda es que en el referido año tuvo un costo en puertos peruanos de aproximadamente 720 US$/TM lo que lo hace sumamente costoso.

 En un pais cercano con una industria petroquímica de poliolefinas recesada existirá en los próximos D años un exceso  de la denominada Corriente  Cruda de C4 proveniente de una Planta de Etileno. En complejos petroquímicos donde se manufactura estireno se parte del Butadieno   (BD), el que es extraido mediante  un proceso costoso de extracción de estas corrientes.  Después del referido tiempo se habrá implantado una industria petroquímica a partir del gas natural que permitirá reducir en E% los precios actuales de la materia prima.

 Una ventaja de esta corriente es que se estima que en los próximos años se la podrá comprar por su valor como componente bien del GLP o del pool de gasolinas (los butanos tienen elevado octanaje), además que esta corriente puede transportarse en buques.

 La Corriente esta constituida de: Butadieno: F%, Isobuteno: G%, Cis 2 Buteno: H%, Trans 2 buteno: I%, N. Butano: J%, Isobutano: K%

 Se desea evaluar la posible utilización de esta corriente, que vendría importada en buques gaseros durante D años, después de lo cual sería reemplazada por una materia prima local, empleando el proceso Dow que se describe en memorando adicional.

 Se desea evaluar la factibilidad económica del Proceso Dow  para la manufactura de estireno en un volumen anual que permita satisfacer la demanda peruana y permitir una exportación a Bolivia y Ecuador del 40% de la capacidad de diseño de la  Planta a partir del 4 año de iniciada las operaciones de la planta referida.

 El diseño de la planta deberá ser tan amigable al medio ambiente como sea posible. Se debe recuperar y reciclar materiales tanto como se aeconomicamente posible. Se deberá minimizar el consumo de energía, simepre que este economicamente justificado. La planta deberá ser segura, es decir no deberán producirse mezclas inflamabes o explosivas.

 La evaluación deberñá realizarse a precios de materias primas y productos constantes del año 2001, las inversiones se  evaluarán al año 2002 y s edeberá efectuar análisis de riesgo e incertidumbre tal como se les explicará después.

 Memorando

 A:    Ingeniero de Procesos                         Fecha: UNI 30 Setiembre 2002

De:   Jefe Planeamiento

Ref.- Proceso Dow para la manufactura de Estireno a partir de una corriente Corriente  Cruda de  C4 proveniente de una Planta de Etileno

La compañía Dow ha desarrollado un proceso para dimerizar el Butadieno (BD) presente en una Corriente Cruda de C4 hacia Vinilciclohexano  (VCH) empleando un catalizador propietario de cobre en zeolitas. En una segunda etapa el VCH se convierte  en Estireno mediante una deshidrogenación oxidativa empleando otro catalizador propietario a base de un óxido de Estaño/antimonio.

Suponga que la Planta se encontrará localizada en el futuro Complejo Petroquímico de Camisea (posiblemente la ciudad de Pisco). Posteriormente se le informará de mayores datos económicos.

Los butanos que no se convierten podrán bien mezclrase con propano de Camisea para venderse como GLP o podrán venderse como octanos a alguna refinería peruana.

El proceso está descrito en al Patente U.S. Patent 5,329,057 del 12.07.94 que se adjunta a continuación:

 

United States Patent

5,329,057

Diesen ,   et al.

* July 12, 1994

Process for the cyclodimerization of 1,3-butadienes to 4-vinylcyclohexenes

Abstract

A process for the cyclodimerization of 1,3-butadienes to 4-vinylcyclohexenes. The process involves contacting butadiene with a copper (I)-aluminosilicate zeolite prepared by (a) an impregnation method, or (b) heating a solid mixture of a copper salt and the zeolite, or (c) contacting vapors of a copper salt with the zeolite. The catalysts exhibit long life and good activity in the claimed process. The impregnated Cu(I)-catalyst is claimed.

Assignee:

The Dow Chemical Company (Midland, MI)

Filed:

September 30, 1992

 Description

BACKGROUND OF THE INVENTION

This invention pertains to a process for the cyclodimerization of 1,3-butadiene or substituted 1,3-butadienes to 4-vinylcyclohexene or a substituted derivative thereof. 4-Vinylcyclohexene (hereinafter referred to as vinylcyclohexene) and substituted vinylcyclohexenes are useful starting materials for the synthesis of styrene and substituted styrenes. Styrene is a well-known monomer for polystyrene plastics and composites.

Catalyzed processes are known for the dimerization of butadiene. For example, British Patent 1,554,942 and U.S. Pat. No. 4,125,483 disclose a process for the catalytic dimerization of butadiene to vinylcyclohexene in the presence of a cation-exchangeable aluminosilicate into which copper(I) ions and ions of an alkali metal having an atomic number of at least 19, preferably, cesium, have been introduced. The aluminosilicate includes natural and synthetic zeolites, such as faujasite, as well as clay minerals, such as montmorillonite, and other synthetic silica aluminas. It is taught that copper is introduced into the aluminosilicate via ion-exchange with a copper(I) or copper(II) salt.

U.S. Pat. No. 3,444,253 also discloses the dimerization of butadiene to vinylcyclohexene in the presence of copper(I) zeolites X or Y. The catalyst in taught to be prepared by ion-exchanging of sodium zeolite X or Y with cuprous iodide in liquid ammonia or by the reduction of copper(II) zeolite X or Y with carbon monoxide, ammonia, acetylenic hydrocarbon or an olefinic hydrocarbon.

U.S. Pat. No. 4,664,247 relates to a process for the cyclodimerization of butadiene to vinylcyclohexene under Diels-Alder conditions in the presence of a copper-containing ZSM-12 zeolite catalyst. It is taught that the ZMS-12 zeolite is ion-exchanged or impregnated with copper(II) cation.

P. Renger, R. Janowski, F. Wolf and E. Jahn report in Z. Chem., 19 (1979), 194-195, that butadiene is cyclodimerized to vinylcyclohexene in the presence of silica gel impregnated with copper(II) cations.

All of these processes suffer from the same manifold disadvantages. First, and most importantly, the lifetime of these catalysts is short, and the catalyst easily deactivates from coking and fouling. Second, the preparations of the catalysts are difficult and expensive. For example, the catalysts prepared by ion-exchange with copper(II) salts must be reduced to the copper(I) oxidation state, which is the active form of the catalyst. Disadvantageously, the reduction process in the ion-exchanged material is inefficient. Alternatively, the catalysts may be prepared without reductants by ion-exchange with copper(I) salts; however, this route is disadvantageous because copper(I) salts oxidize easily and are not readily solubilized without expensive solubilizing ligands. Third, regeneration of these catalysts typically requires burning off the coked material at high temperatures, usually at least about 400.degree. C. Such a procedure oxidizes copper(I) to copper(II), and therefore a reduction procedure is again necessitated to bring the catalyst back into the active cuprous form. Finally, in certain instances the catalysts may possess low activity and even low selectivity.

SUMMARY OF THE INVENTION

In a first aspect this invention is a process for the cyclodimerization of 1,3-butadiene or substituted 1,3-butadiene to 4-vinylcyclohexene or a substituted derivative thereof. The process comprises contacting 1,3-butadiene or a substituted 1,3-butadiene with a catalytic amount of a copper(I)-aluminosilicate zeolite prepared as described hereinbelow. The zeolite is selected from the group consisting of faujasites, mordenite, zeolite L, zeolite .OMEGA., and zeolite beta. The contacting of the butadiene and the copper(I)-zeolite occurs under reaction conditions such that 4-vinylcyclohexene or a substituted derivative thereof is formed.

The copper(I)-aluminosilicate zeolite employed in the first aspect of this invention can be prepared by one of three general methods. In the first method, a dried aluminosilicate zeolite selected from the group consisting of faujasites, mordenite, zeolite L, zeolite .OMEGA., and zeolite beta and having a framework silica to alumina molar ratio of at least about 15 is impregnated with a solution of a copper(II) salt. Thereafter, the copper(II)-impregnated zeolite is calcined under reaction conditions sufficient to remove the anion of the copper salt. After calcination the copper(II)-impregnated zeolite is reduced under reaction conditions such that a portion of the copper(II) ions are converted to copper(I). As a second method, the catalyst can be prepared by heating a solid mixture containing a copper salt and the above-identified aluminosilicate zeolite in the absence of liquid solvent. As a third method, the catalyst can be prepared by contacting vapors of a copper salt with the above-mentioned aluminosilicate zeolite.

In a second aspect this invention is a process for the cyclodimerization of butadiene or substituted 1,3-butadiene to 4-vinylcyclohexene or a substituted derivative thereof. The process comprises contacting 1,3-butadiene or a substituted 1,3-butadiene with a catalytic amount of copper(I) ions supported on a carrier. The contacting also occurs in the presence of a promoting amount of a hydroxylic solvent and under reaction conditions such that the activity of the catalyst, as measured by the rate constant for the formation of vinylcyclohexene, is increased when compared to a control process conducted with a minimum level of hydroxylic solvent. The control process and minimum hydroxylic solvent level are described in detail hereinafter.

The processes of this invention produce vinylcyclohexenes in a steady high rate of formation, heretofore not possible with the catalysts of the prior art. Vinylcyclohexenes are valuable as precursors to styrenes. In addition, the preferred catalysts in the process of this invention possess many advantageous features, described hereinbelow.

In a third aspect, this invention is a catalyst composition comprising copper(I) ions impregnated onto an aluminosilicate zeolite. The zeolite is selected from the group consisting of faujasites, mordenite, zeolite L, zeolite omega (.OMEGA.), and zeolite beta (.beta.). The zeolite is characterized by a silica to bulk alumina molar ratio in the range from about 5 to about 50, and a silica to tetrahedral framework alumina molar ratio of at least about 15. The "bulk" ratio includes alumina from both tetrahedral framework sites as well as excess or non-framework alumina located in the pores. Optionally, the catalyst composition contains a binder.

In a fourth aspect, this invention is a method of preparing the above-identified catalyst comprising (a) drying an aluminosilicate zeolite to remove water, the zeolite being selected from the group consisting of faujasites, mordenite, zeolite L, zeolite .OMEGA. and zeolite .beta. and being characterized by a silica to bulk alumina molar ratio in the range from about 5 to about 50 and a silica to framework alumina molar ratio of at least about 15, (b) impregnating the dried zeolite with a solution containing a copper(II) salt, (c) calcining the copper(II)-impregnated zeolite under conditions such that the anion of the soluble salt is removed, and (d) reducing the calcined copper(II)-impregnated zeolite under conditions such that a portion of the copper(II) ions are converted to copper(I). Optionally, a promoting amount of hydroxylic solvent may be added after calcination and prior to reduction.

The catalyst of this invention is useful in the aforementioned cyclodimerization of butadiene and substituted butadienes, and surprisingly maintains a long lifetime in that process before deactivating. A catalyst half-life on the order of at least about 200 hours is readily achieved. In addition, the above-identified catalyst is advantageously prepared without expensive solubilizing ligands. More advantageously, the reduction of the copper(II)-zeolite catalyst precursor prepared by this invention is efficient. In some preparative embodiments, a separate reduction step is not required or the reduction is conducted in situ in the aforementioned cyclodimerization process. Most advantageously, the catalyst of this invention is easily regenerated. All that is required is an oxygen burn-off at low temperatures, typically less than about 350.degree. C., followed by reduction, and the activity of the catalyst is restored essentially to its original level. Consequently, the combined beneficial properties of the catalyst of this invention make it desirable for commercial applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 depict graphs of the rate constant for the formation of vinylcyclohexene plotted versus the concentration of water in the catalyst, as described in detail in Examples E-1(a-b), E-2(a-d), E-3(a-f), E-4(a-i), and E-9(a-f).

CLAIMS
1. A process for the cyclodimerization of 1,3-butadiene or substituted 1,3-butadiene to 4-vinylcyclohexene or a substituted derivative thereof, the process comprising contacting 1,3-butadiene or a substituted 1,3-butadiene with a catalytic amount of a copper(I)-aluminosilicate zeolite wherein the zeolite is selected from the group consisting of faujasites, mordenite, zeolite L, zeolite .OMEGA., and zeolite beta, and wherein the zeolite has a framework silica to alumina molar ratio of at least about 15, the catalyst being prepared by:

I) impregnating the aluminosilicate zeolite with a solution of a copper(II) salt, calcining the copper(II)-impregnated zeolite under conditions sufficient to remove the anion of the copper(II) salt, and reducing the calcined copper(II)-impregnated zeolite under conditions such that a portion of the copper (II) ions are converted to copper(I); or

II) heating a solid mixture containing a copper salt and the aluminosilicate zeolite in the absence of liquid solvent; or

III) contacting vapors of a copper salt with the aluminosilicate zeolite; the contacting of the butadiene and the copper(I)-zeolite occurring under reaction conditions such that 4-vinylcyclohexene or a substituted derivative thereof is formed.

2. The process of claim 1 wherein 1,3-butadiene, chloroprene or isoprene is employed.
3. The process of claim 1 wherein the concentration of 1,3-butadiene or substituted 1,3-butadiene ranges from about 10 to about 80 volume percent of the feedstream.

4. The process of claim 1 wherein the zeolite is a faujasite zeolite.

5. The process of claim 4 wherein the bulk SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of the zeolite is in the range from about 5 to about 50.

6. The process of claim 5 wherein the bulk SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of the zeolite is in the range from about 10 to about 45 and the framework SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio is at least about 22.

7. The process of claim 1 wherein the catalyst exhibits a half-life of at least about 200 hours and the rate constant for the formation of 4-vinylcyclohexene or substituted derivative thereof is at least about 0.1 (mole-hr).sup.-1.

8. The process of claim 1 wherein the catalyst exhibits a half-life of at least about 500 hours.

9. The process of claim 1 wherein the process temperature is in the range from about 70.degree. C. to about 190.degree. C.

10. The process of claim 1 wherein the process is conducted in the liquid phase, the process pressure is in the range from about 100 psig to about 1000 psig, and the weight hourly space velocity is in the range from about 0.01 hr.sup.-1 to about 100 hr.sup.-1.

11. The process of claim 1 wherein the catalyst is prepared by impregnating an aluminosilicate zeolite with a solution of a soluble copper(II) salt, calcining the copper(II)-impregnated zeolite under conditions sufficient to remove the anion of the copper(II) salt, and reducing the calcined copper(II)-impregnated zeolite with an olefinic reducing agent under conditions such that a portion of the copper(II) ions are converted to copper(I).

12. The process of claim 11 wherein the reducing agent is butene, propylene, or butadiene.
13. The process of claim 12 wherein the reducing agent is butadiene, the reduction is conducted in situ in the cyclodimerization process, and the concentration of water on the catalyst is from 3 to about 14 weight percent.

14. The process of claim 12 wherein the reducing agent is propylene or 1-butene, and the concentration of water on the catalyst is less than 6weight percent.

15. The process of claim 1 wherein the catalyst is prepared by heating a solid mixture containing a copper salt and the zeolite at a temperature in the range from about 250.degree. C. to about 800.degree. C. in the absence of liquid solvent.

16. The process of claim 15 wherein the copper salt is selected from the group consisting of cuprous and cupric halides and oxides.

17. The process of claim 16 wherein the copper salt is cuprous or cupric chloride and the heating is conducted under an inert atmosphere.

18. The process of claim 16 wherein the copper salt is cuprous or cupric oxide and the heating is conducted under ammonia and the resulting copper(I)-zeolite is thereafter stripped of excess ammonia by further heating.

19. The process of claim 1 wherein the catalyst is prepared by contacting the vapors of a copper salt with the zeolite.

20. The process of claim 1 wherein the catalyst is regenerated by an oxygen burn-off at a temperature less than about 350.degree. C. followed by reduction.

21. The process of claim 1 wherein the rate constant for the formation of vinylcyclohexene is at least about 0.50 (mole-hr).sup.-1.

22. A process for the cyclodimerization of 1,3-butadiene to 4-vinylcyclohexene, the process comprising contacting 1,3-butadiene in the liquid phase with a catalytic amount of a copper(I)--faujasite zeolite having a framework silica to alumina molar ratio of at least about 15, the catalyst being prepared by (a) impregnating the aluminosilicate zeolite with a solution of a copper (II) salt, (b) calcining the copper(II)-impregnated zeolite under conditions sufficient to remove the anion of the copper(II) salt, and (c) reducing the calcined copper(II)-impregnated zeolite with propylene or butene under conditions such that a portion of the copper(II) ions are converted to copper(I); the contacting of butadiene and the copper(I)-zeolite occurring at a temperature between 80.degree. C. and 150.degree. C., a pressure between 100 psig and 1000 psig, and a weight hourly space velocity between 0.1 hr.sup.-1 and 10 hr.sup.-1, such that the rate of formation of 4-vinylcyclohexene is at least about 0.5 (mole-hr).sup.-1 and the half-life of the catalyst is at least about 500 hours.

 

United States Patent

5,336,822

Hucul

August 9, 1994

Process for the production of styrene

4-Vinylcyclohexene is converted to styrene in the presence of a catalyst comprising tin, antimony, and oxygen. The feed stream to be contacted with the catalyst comprises water, 4-vinylcyclohexene, and oxygen. A ratio of water to 4-vinylcyclohexene above about 12:1, preferably above about 14:1, significantly increases the half-life of the catalyst. The catalyst is prepared by coprecipitating a tin chloride and an antimony chloride followed by calcination of the precipitate at a temperature in the range from 850.degree. C. to 1000.degree. C.

Inventors:

Hucul; Dennis A. (Midland, MI)

Assignee:

The Dow Chemical Company (Midland, MI)

 

 

 

June 14, 1993

 References Cited

 U.S. Patent Documents

3094565

Jun., 1963

Bethell et al.

260/604.

3258432

Jun., 1966

Gasson et al.

252/461.

3308183

Mar., 1967

Bajars

260/680.

3309325

Mar., 1967

Gasson et al.

252/461.

3328478

Jun., 1967

Barclay et al.

260/680.

3346513

Oct., 1967

Hadley

252/461.

3370103

Feb., 1968

Callahan et al.

260/680.

4036901

Jul., 1977

Kawakami et al.

260/669.

4165441

Aug., 1979

Okano et al.

585/444.

 

 

Other References

CA 93:149958w (1980) Mitsubishi Chem. Ind. Co., Ltd. (abstract only of Japan Kokai Tokkyo Koho 80 57,522).
CA 92:23138q (1980) Kageyama et al. (abstract only of Japan Kokai Tokkyo Koho 79,119,422).
CA 90:138404z (1979) Okano et al.
(abstract only of Japan Kokai Tokkyo Koho 78,144,534).
CA 94:65292g (1981) Mitsubishi Chem. Ind. Co., Ltd. (abstract of Japan Kokai Tokkyo Koho 80 72,123).
CA 92:198074t (1980) Kageyama et al.
(abstract only of Jpan Kokai Tokkyo Koho 79,144,326).
CA 93:71239r (1980) Kageyama et al.
(abstract only of Japan Kokai Tokkyo Koho 79,163,530).
CA 93:168840t (1980) Mitsubishi Chem. Ind. Co., Ltd. (abstract only of Japan Kokai Tokkyo Koho 80 94,322).
CA 91:40085s (1979) Nakatomi et al. (abstract only of Japan Tokkyo Koho 79 29,893).
J7 4039-248 (Derwent 81728V, abstract only) Asahi Dow Ltd., Mar. 18, 1969.
Berry, "Tin-Antimony Oxide Catalysts" Advances in Catalysis, vol. 30, 97-129 (1981).
Weng et al., "Cooperation Between Phases in Mixed SnSbO Selective Oxidation Catalysts" New Developments in Selective Oxidation, 797-806 (1990).
Viswanathan et al., "Some Reflections on Mixed Tin and Antimony Oxide Catalysts" Surface Technology, vol. 23, 231-244 (1984).

Claims

What is claimed is:

1. A process for the production of styrene from 4-vinylcyclohexene, comprising contacting a feed stream in the gas phase with a catalyst comprising tin, antimony, and oxygen under conditions sufficient to produce styrene, the feed stream comprising 4-vinylcyclohexene, water, and molecular oxygen, the molar ratio of water to 4-vinylcyclohexene in the feed stream being at least about 12:1 and less than about 30:1, the catalyst having a half-life of at least about 1000 hours, and the catalyst having been prepared by coprecipitating a tin halide and an antimony halide to form a precipitate and calcining the precipitate at a temperature in the range from about 850.degree. C. to about 1000.degree. C.

2. The process of claim 1 wherein the molar ratio of water to 4-vinylcyclohexene in the feed stream is at least about 4:1.
3. The process of claim 1 wherein the tin halide is stannic chloride and the antimony halide is antimony pentachloride.
4. The process of claim 1 wherein the temperature at which the feed stream is contacted with the catalyst is in the range from about 300.degree. C. to about 500.degree. C.

5. The process of claim 1 wherein the catalyst is calcined at a temperature in the range from about 900.degree. C. to about 1000.degree. C. prior to use in the process.

6. The process of claim 1 wherein the catalyst has a atomic ratio of tin to antimony in the range from about 1:1 to about 20:1.

7. The process of claim 1 wherein the catalyst has a atomic ratio of tin to antimony in the range from about 1:1 to about 16:1.

8. The process of claim 1 wherein the catalyst has a atomic ratio of tin to antimony in the range from about 5:1 to about 16:1.

9. The process of claim 1 wherein the catalyst has a atomic ratio of tin to antimony in the range from about 7:1 to about 11:1.

10. The process of claim 1 wherein the molar ratio of oxygen to 4-vinylcyclohexene is in the range from about 0.5:1 to about 3:1.

11. The process of claim 1 wherein the catalyst has a half-life of at least about 1500 hours.
12. The process of claim 1 wherein the catalyst has a half-life of at least about 2000 hours.
13. The process of claim 1 wherein the catalyst has a half-life of at least about 2500 hours.
14. The process of claim 1 wherein the feed stream further comprises a diluent.
15. The process of claim 1 wherein the molar ratio of water to 4-vinylcyclohexene is at least about 14:1.
16. The process of claim 8 wherein the catalyst consists essentially of tin antimony, oxygen, and a binder.
17. The process of claim 9 wherein the catalyst consists of tin antimony, oxygen, and a binder.
18. A process for the production of styrene from 4-vinylcyclohexene, comprising contacting a feed stream in the gas phase at a temperature of from about 300.degree. C. to about 500.degree. C. with a catalyst consisting essentially of tin, antimony, oxygen, and a binder under conditions sufficient to produce styrene, the catalyst having a tin/antimony atomic ratio in the range from about 7:1 to about 11:1, the feed stream comprising 4-vinylcyclohexene, water, and oxygen, the molar ratio of water to 4-vinylcyclohexene being at least about 14:1 and less than about 30:1, the catalyst having a half-life of at least about 1000 hours, and the catalyst having been prepared by coprecipitating a tin halide and an antimony halide to form a precipitate and calcining the precipitate at a temperature in the range from about 850.degree. C. to about 1000.degree. C.

19. The process of claim 18 wherein the tin halide is stannic chloride and the antimony halide is antimony pentachloride.
20. The process of claim 18 wherein the catalyst was calcined at a temperature of from about 900.degree. C. to about 1000.degree. C. prior to the process.

21. The process of claim 18 wherein the binder is selected from the group consisting of calcium sulphate, silicas alumina, magnesium oxide, boron oxide, titanium oxides zirconium oxide, and combinations thereof.
22. The process of claim 18 wherein the molar ratio of oxygen has 4-vinylcyclohexene is in the range from about 0.5:1 to about 3:1.

23. The process of claim 18 wherein the catalyst has a half-life of at least about 1500 hours.
24. The process of claim 18 wherein the catalyst has a half-life of at least about 2000 hours.
25. The process of claim 18 wherein the catalyst has a lifetime of at least about 2500 hours.
26. The process of claim 18 wherein the feed stream further comprises a diluent.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the gas phase catalytic production of styrene from 4-vinylcyclohexene.

Styrene is an important monomer useful in the production of polymers such as polystyrene. Owing to its important commercial value, effective processes for the production of styrene are highly sought.

An example of a process useful for the production of styrene is disclosed in U.S. Pat. No. 4,165,441. This patent discloses a process for the gas phase oxidative dehydrogenation of 4-vinylcyclohexene in the presence of a catalyst containing tin, antimony, and oxygen. The patent describes the use of water as a component in the feed stream containing 4-vinylcyclohexene. The molar ratio of water to 4-vinylcyclohexene in the feed stream is about 8.5:1. While the patent reports reasonable yields with a variety of catalysts containing tin, antimony, and oxygen, the examples only report data for runs up to a few hours of continuous production of styrene. It is known, however, that under the conditions employed in U.S. Pat. No. 4,165,441, the half-life of the catalyst is quite low. Thus, the process disclosed in U.S. Pat. No. 165,441 results in poor yields after an undesirably short amount of time when the process is run continuously. Similarly, the process disclosed in U.S. Pat. No. 4,165,441 requires frequent stoppage of the process to regenerate the catalyst. Hence, to enable effective commercial use of such a process, it is desirable to increase significantly the half-life of said catalyst and thereby provide a process capable of being used to commercial advantage.

SUMMARY OF INVENTION

This invention, in one respect, is a process for the production of styrene from 4-vinylcyclohexene, comprising contacting a feed stream in the gas phase with a catalyst comprising tin, antimony, and oxygen under conditions sufficient to produce styrene, the feed stream comprising 4-vinylcyclohexene, water, and molecular oxygen, the molar ratio of water to 4-vinylcyclohexene in the feed stream being at least about 12:1 and less than about 30:1, the catalyst having a half-life of at least about 1000 hours, and the catalyst having been prepared by coprecipitating a tin chloride and an antimony chloride to form a precipitate and calcining the precipitate at a temperature in the range from about 850.degree. C. to about 1000.degree. C.

In another respect, this invention is a process for the production of styrene from 4-vinylcyclohexene, comprising contacting a feed stream in the gas phase at a temperature of from about 300.degree. C. to about 500.degree. C. with a catalyst consisting essentially of tin, antimony, oxygen, and a binder under conditions sufficient to produce styrene, the catalyst having a tin/antimony molar ratio in the range from about 7:1 to about the feed stream comprising 4-vinylcyclohexene, water, and oxygen, the molar ratio of water to 4-vinylcyclohexene being at least about 14:1 and less than about 30:1, the catalyst having a half-life of at least about 1000 hours, and the catalyst having been prepared by coprecipitating a tin chloride and an antimony chloride to form a precipitate and calcining the precipitate at a temperature in the range from about 850.degree. C. to about 1000.degree. C.

The half-life of a catalyst containing tin, antimony, and oxygen in a process for the production of styrene from 4-vinylcyclohexene is at least about 1000 hours in a continuous operation when the molar ratio of water to 4-vinylcyclohexene is at least about 12:1. Advantageously this invention provides enhanced half-life of the catalyst employed herein and reduces the frequency at which the catalyst is in need of regeneration.

A catalyst prepared by coprecipitation in accordance with this invention provides higher activity than other methods in processes for the production of styrene from 4-vinylcyclohexene.


DETAILED DESCRIPTION OF THE INVENTION

The catalyst used in this invention comprises tin, antimony, and oxygen. Preferably, the molar ratio of tin to antimony is in the range from about 1:1 to about 20:1, preferably the molar ratio of tin to antimony is in the range from about 1:1 to about 16:1, more preferably the molar ratio of tin to antimony is in the range from about 4:1 to about 16:1, and most preferably the molar ratio of tin to antimony is in the range from about 7:1 to about 11:1. If one or more metals other than tin and antimony are present in the catalyst, the one or more metals can be present in an amount in the range from about 0.01 to about 10 weight percent based on the total weight of the catalyst.

The catalyst can be prepared by a number of techniques such as the mastecation method evaporation-to-dryness method, immersion method, or deposition method.

The tin component of the catalyst can be provided from tin oxides such as stannous oxide and stannic oxide, or pyrolyzed products of organic tin compounds such as tin oxalate or tin acetate. The organic tins may be dissolved in an inorganic acid such as hydrochloric acid and then neutralized with an alkali such as ammonia water. It is also possible to use the products obtained by oxidizing tin metal with nitric acid. Preferably, the tin component of the catalyst is provided from easily hydrolyzable tin halides such as stannous chloride, stannic chloride, etc. Most preferably, the tin component is provided from stannic chloride.

The antimony component of the catalyst can be provided from various sources, for example antimony oxides such as antimony oxide and antimony pentoxide, hydrous antimony oxides such as metaantimonic acid, orthoantimonic acid, and pyroantimonic acid, and the products obtained by oxidizing antimony metals with nitric acid. Preferably, the antimony component is provided from easily hydrolyzable antimony halides such as antimony trichloride and antimony pentachloride. Most preferably, the antimony component is provided from antimony pentachloride.

The catalyst can also contain metals other than tin and antimony. Examples of such metals include iron, molybdenum, manganese, coppery zinc, tellurium, cobalt, and vanadium. These metals can be added to the tin and antimony catalyst from a variety of sources including metal oxides, inorganic salts such as chlorides and nitrates, and organic salts such as acetates and oxalates.

While the catalyst of this invention can contain other metals, it has been found that a catalyst essentially free from added metals other than tin and antimony performs better than a catalyst having metals added thereto. A catalyst containing a metal other than tin and antimony is less productive and deactivates faster than a catalyst free of metals other than tin and antimony.

It is preferred that the catalyst be formed by the coprecipitation method from tin and antimony halides. In the coprecipitation method, the tin and antimony halides are thoroughly admixed in appropriate molar proportions. The resulting admixture is then added to stirred water. Typically, the temperature of the water is about 25.degree. C. The pH of the water should be maintained in the range from about 5 to about 10, as by addition of concentrated ammonium hydroxide or other base as the tin and antimony halide admixture is added to the water. Preferably, the pH is maintained in the range from about 7 to about 8.

The admixture can be added to the water at any rate so long as the pH can be maintained in the range from about 5 to about 10. The proportion of the tin and antimony halide admixture to water has a significant bearing on activity of the final catalyst. While proportions in the range from about 0.03 to about 3.0 total moles of admixture to one liter of water is desirable, it is preferred that the proportion be in the range from about 0.07 to about 0.6 total moles of admixture to one liter of water. As the admixture is added to the stirred water, a gel precipitate forms. This gel is collected by conventional techniques such as filtration and then washed. If a metal other than tin and antimony is desired in the final catalyst, a solution containing a salt of said metal can be added to the precipitate. Typically, the solution is added to the precipitate by pouring the solution over the precipitate in a closed vessel to thereby impregnate the precipitate with metal salt solution. The amount of metal salt present in the solution can be varied depending on the amount of metal desired in the final catalyst. Finally, the precipitate, with or without a metal salt solution admixed thereto, is dried.

The dried precipitate, as well as a precipitate or mass recovered from and prepared by a technique other than the coprecipitation method, is next subjected to a calcination treatment to further enhance the catalyst activity. Calcination can be accomplished by calcining the prepared catalyst composition with an oxygen-containing gas, such as airy at a temperature in the range from about 800.degree. C. to about 1200.degree. C. for a time in the range from about 1 to about 24 hours. Preferably, the catalyst is calcined at a temperature in the range from about 850.degree. C. to about 1000.degree. C. for a time in the range from about 1 to about 6 hours. Most preferably, the catalyst is calcined at a temperature in the range from about 900.degree. C. to about 1000.degree. C. for a time in the range from about 1 to about 3 hours. The shape of a catalyst is not critical to the invention, but the catalyst can be formed by conventional methods to produce a final catalyst. For example, the catalyst can be shaped into the form of pellets convenient for use in a fixed bed reaction or can be shaped into granules for use in a fluidized bed reaction.

The catalyst of this invention may be bound with conventional binders such as calcium sulphate, various clays, and refractory oxides, such as silica, alumina, magnesium oxide, zirconium oxide, titanium oxide, and boron oxide. Combinations of two or more binders may be employed such as silica-alumina and silica-magnesia. Typically, the binder is in an amount in the range from about 0.1 to about 50 weight percent of a finished catalyst. The weight percent of binder varies depending on the particular binder employed.

The process of this invention for the production of styrene can be carried out in any known manner used for gas phase processes and the catalyst can be used either as a fixed bed, a fluidized bed, or a moving bed. Likewise, multiple beds and multiple reactant injection sites can be employed. The temperature in this process is usually from about 250.degree. C. to about 600.degree. C., preferably from about 300.degree. C. to about 500.degree. C. This process can be performed under sub-atmospheric, atmospheric, or super-atmospheric pressures.

For purposes of this invention, "gas hourly space velocity" ("GHSV") is defined as the value of the volume of feed stream which passes per hour per unit volume over the catalyst. In case of using the catalyst of this invention in a process for the production of styrene from 4-vinylcyclohexene, GHSV is in the range from about 50,000 hr.sup.-1 to about 100 hr.sup.-1, preferably about 5,000 hr.sup.-1 to about 1,000 hr.sup.-1.

The feed stream of this invention comprises 4-vinylcyclohexene, oxygen, and water. The 4-vinylcyclohexene used in this process need not be high in purity and may contain other cyclic or chain hydrocarbons. The molar ratio of oxygen to 4-vinylcyclohexene in the feed stream is in the range from about 0.5:1 to about 10:1, preferably in the range from about 0.5:1 to about 3:1. In addition, the feed stream can further comprise a diluent gas which is essentially inert to the reaction of this invention. An example of a diluent gas is nitrogen.

It is critical to the present invention that the amount of water in the feed stream be maintained such that the molar ratio of water to 4-vinylcyclohexene is at least about 12:1, most preferably the molar ratio of water to 4-vinylcyclohexene is at least about 14:1. The molar ratio of water to 4-vinylcyclohexene is preferably less than about 50:1, more preferably less than about 30:1. When the molar ratio of water to 4-vinylcyclohexene is at least about 12:1 in a process to produce styrene from 4-vinylcyclohexene in the presence of a catalyst used in this invention and under conditions sufficient to produce styrene, the half-life of the catalyst is at least about 1000 hours, preferably at least about 1500 hours, more preferably at least about 2000 hours, even more preferably at least about 2500 hours. It is understood, however, that half-life will vary depending on reaction conditions such as temperature. For purposes of this invention, "half-life" is defined as the time required for conversion to be reduced by half under steady state conditions (constant feed rates, reaction temperature, and pressure). For example, if the conversion is 90 percent initially, the half-life is obtained when the conversion drops to 45 percent. Half-life can be estimated by extrapolation of the data as recognized by skilled artisans.

The catalyst can be regenerated as needed by methods known to those skilled in the art. For examples, the catalyst can be regenerated by passing an oxygen-containing gas, such as air, over the catalyst at elevated temperatures.

For purposes of this invention, "conversion " is defined as the mole percentage of the moles of reactant, such as 4-vinylcyclohexene, lost from the feed stream as a result of reaction divided by mole percentage of reactant in the feed times 100. The conversion can vary widely depending upon the reactants, the form of the catalyst, and the process conditions such as temperature, pressure, flow rate, and catalyst residence time. Within the preferred gas hourly space velocity range, as the space velocity increases the conversion generally decreases. Typically, the conversion of 4-vinylcyclohexene is at least about 30 mole percent. Preferably, the conversion is at least about 40 mole percent, more preferably at least about 50 mole percent, and most preferably at least about 60 mole percent. The styrene formed from the process can be separated from feed stream components by well known methods such as by distillation. The 4-vinylcyclohexene recovered after the first pass conversion can be recycled into the feed stream. Hence, by recycling unconverted 4-vinylcyclohexene, the conversion can approach 99-100 percent in a commercial operation.

For the purposes of this invention, "selectivity" is defined as the mole percentage of converted 4-vinylcyclohexene that forms styrene. Typically, selectivities also vary widely depending upon the reactants, the form of the catalyst, and the process conditions. Within the preferred space velocity range, as the space velocity increases the selectivity for styrene generally increases. Typically, the selectivity to styrene is at least about 80 mole percent. Preferably, the selectivity to styrene is at least about 85 mole percent.

The concept of simultaneous high conversion and high selectivity can be conveniently expressed in terms of yield. For the purposes of this invention, the term "yield" refers to the numerical product of the single-pass conversion and selectivity. For example, a process according to the present invention operating at a conversion of 90 mole percent, and a selectivity to styrene of 90 mole percent, would have a styrene yield of 81 mole percent. Typically, the yield of styrene achieved in the process of this invention is at least about 30 mole percent. Preferably, the yield of styrene achieved in the process of this invention is at least about 50 mole percent.

The rate at which a desired product is produced in the process of this invention can be expressed in the concept of productivity. The "productivity" is defined as the weight of styrene formed divided by the volume of catalyst per hour. Preferably, the productivity of styrene in the process of this invention is at least about 5 pounds per cubic foot per hour (0.08 grams per cubic centimeter per hour), more preferably, at least about 10 pounds per cubic foot per hour (0.16 grams per cubic centimeter per hour), and most preferably, at least about 15 pounds per cubic foot per hour (0.24 grams per cubic centimeter per hour).

The following examples are given to illustrate the process of this invention and should not be construed as limiting its scope. All percentages in the examples are mole percent unless otherwise indicated.

Preparation of Catalysts

(a) A series of catalysts, A-G, were prepared according to the following general procedure. For each catalyst, the moles of tin and antimony were adjusted according to the tin/antimony molar ratio desired. The tin/antimony molar ratios, as well as results of Examples 1-10, described hereinbelow, are reported in Table I.

Antimony pentachloride (8.5 ml, 0.0664 mole) and stannic chloride (68.5 ml, 0.585 mole) were thoroughly mixed. The admixture was added dropwise to 4 liters of rapidly mixed, 25.degree. C. deionized water maintained at a constant pH of 7.2 by adding concentrated ammonium hydroxide. The gel precipitate formed was then filtered, washed, dried, and calcined at 950.degree. C. in a flowing stream of air for two hours to form the final catalyst. The catalyst had a tin/antimony molar ratio of about 9:1.

(b) The general procedure of (a) was followed to form catalyst H except 900 ml of deionized water was used instead of 4 liters.

(c) The general procedure of (a) was followed to form catalyst I except the calcination temperature was 750.degree. C. instead of 950.degree. C.

(d) Catalyst J was prepared by adding 47.4 g of tin metal and 6.02 g of antimony metal to 400 ml of concentrated nitric acid (Sn/Sb mole ratio of 8.1:1). After heating the solution for 1 hour at 80.degree. C., the excess liquid was removed. The catalyst was placed in a quartz tube and was calcined in air at 950.degree. C. for two hours.

(e) Catalyst K having a tin/antimony molar ratio of 9:1 was prepared via precipitation. A mixture was made from antimony pentachloride (4.25 ml 0.033 moles) and tin tetrachloride (34.25 ml, 0.29 moles). This mixture was added dropwise to 2 liters of rapidly mixed deionized water maintained at a constant pH of 7.2 by adding concentrated ammonium hydroxide. The gel precipitate formed was then filtered and was washed with deionized water. Before drying an aqueous solution containing 1.28 gram of cupric chloride dihydrate was added. The catalyst was then dried and calcined at 950.degree. C. in a flowing stream of air for two hours. The finished catalyst had a tin/antimony molar ratio of about 9:1 and contained about 1.5 weight percent copper.

(f) The procedure of (e) was repeated to form Catalyst L except 1.49 gram of ferrous chloride tetrahydrate was substituted for cupric chloride dihydrate. The final catalyst contained 1.5 weight percent iron.

(g) Catalyst M having a tin/antimony molar ratio of 9:1 was prepared via precipitation. A mixture was made from antimony pentachloride (4.16 ml 0.032 moles) and tin tetrachloride (34.25 ml, 0.29 moles). This mixture was added dropwise to 2 liters of rapidly mixed deionized water maintained at a constant pH of 7.2 by adding concentrated ammonium hydroxide. The gel precipitate formed was then filtered and washed with deionized water. Before drying, an aqueous solution containing 1.9 gram of calcium sulfate was added. The catalyst was then dried and calcined at 950.degree. C. in a flowing stream of air for two hours. The finished catalyst had a tin/antimony molar ratio of about 9:1 and contained about 1 weight percent calcium.

Examples 1-12

Conversion of 4-Vinylcyclohexene to Styrene

The following general procedure was repeated for Examples 1-12. The results of each run, corresponding to catalysts A-D and F-M, are reported in Table I. In Examples 1-12, standard feed conditions were defined as: 4-vinylcyclohexene ("VCH") feed rate of 3 ml/hr; water feed rate of 6 ml/hr, and a feed rate of 187 ml/minute of a gaseous mixture having 93 percent nitrogen and 7 percent oxygen. The standard feed had a water/VCH/oxygen/nitrogen molar ratio of 14.4:1:1.506:19.9. The standard feed was flowed over 10 ml of catalyst in a fixed bed reactor. The reported conversions, selectivities, and yields were those obtained at the indicated times after start of the runs.

                                     
                           TABLE I
   
                           __________________________________________________________________________
              Sn:Sb    Hours of    Selectivity        Styrene
              Molar        Temp.    
                           Continuous     VCH  
                           to    Yield     
                           Productivity
   
                           Example  Catalyst  Ratio  (.degree.C.)  Operation  Conversion   Styrene   
                           (%) (g/cc-hr)
   
                           __________________________________________________________________________
     1 (a)
         A    1:3  398 8    
                           70    89    62  0.149
     
                           (b)          377 5     67    84    56  0.135
     2 (a)
         B    1:1  378 46   
                           82    87    71  0.171
     
                           (b)          396 12    90    90   
                           81  0.194
     3   C    3:1  400 24   
                           85    83    71  0.171
    
                           4 (a)
        
                           D    4.9:1
                  
                           399 21    90   
                           83    75  0.180
      (b)          382 29   
                           92    73    67  0.161
    
                           5   F    9:1  380 24    98    93    91 
                           0.218
    
                           6 (a)
        
                           G    19:1 398 20   
                           56    84    47  0.113
      (b)         
                           376 32    38   
                           85    32  0.077
     7  
                           H    9:1  398 24    60    84    50  0.120
     8   I    9:1  380 37    65    85   
                           55  0.132
     9   J    8.1:1
                  
                           400 2     93.3  92.6  86.4
                         
                                              0.208
                      
                           25    92.5  92.7  85.7
                                            
                           0.206
                      
                           46    91.8  92.5  84.9
                                            
                           0.204
                      
                           64    91.1  92.9  84.7
                                            
                           0.204
                      
                           96    89.9  92.5  83.2
                                            
                           0.200
                      
                           101   89.4  92.6  82.8
                                            
                           0.199
    10   K    9:1 with
                  
                           399 6     90.6  90.7  82.2
                                            
                           0.199
             
                           1.6      24   
                           90.2  90.3  81.5
                                            
                           0.196
             
                           percent  43.5  89.3  90.1  80.5
                                            
                           0.193
             
                           copper   61    88.8  90.1  80.0
                                            
                           0.192
                      
                           96    87.9  89.8  79.0
                                            
                           0.190
     
                                            99    87.8  89.8  78.9
                                            
                           0.190
   
                           11   L    9:1
                           with
                  
                           380 1.0   97.2  96.8  94.1
                                            
                           0.226
             
                           1.5      17.0 
                           95.8  94.2  90.3
                                            
                           0.217
             
                           percent  25.0  92.1  92.3  85.0
                                            
                           0.204
             
                           iron     44.0  83.6  91.4  76.4
                                            
                           0.184
         
                                        68.0  73.9  88.7 
                           65.5
                                            
                           0.157
                      
                           73.0  72.7  88.4  64.3
                                            
                           0.154
   
                           12   M    9:1
                           with
                  
                           399 3.0   61    89.2  56  0.134
             
                           1        20.5 
                           60    90.5  56  0.134
             
                           percent  25.5  60    90.5  56 
                           0.134
             
                           calcium
             
                           sulphate
             
                           binder
   
                           __________________________________________________________________________



It can bee seen in Table I the catalyst prepared by coprecipitation in Example 5, catalyst F, exhibited superior activity compared with the catalyst of Example 9, catalyst J, catalyst J having been prepared by the method noted above wherein antimony and tin metals are place in nitric acid followed by recovery and calcination at 950.degree. C. Thus it is seen that catalyst J required a temperature of 400.degree. C. to achieve a productivity of about 0.2, whereas catalyst F (calcined at 950.degree. C., having a slightly higher Sn:Sb mole ratio) produces a higher productivity of 0.218 at 380.degree. C. Thus it is readily seen that catalysts prepared by coprecipitation produce superior productivity in the process.

EXAMPLE 13-14

Conversion of 4-Vinylcyclohexene to Styrene

The procedure of Examples 1-12 was repeated except the flow rates were doubled: VCH, 6 ml/hr; water, 12 ml/hr; 93 percent nitrogen and 7 percent oxygen, 375 ml/min. The water/VCH molar ratio is 14.4:1. The results are reported in Table II.

      
                                                          TABLE
                           II
    __________________________________________________________________________
             
                           Sn:Sb   Hours of   
                           Selectivity
                                           
                           Styrene
             
                           Molar    Temp.   
                           Continuous  VCH   to    Yield Productivity
 
    Example  
                           Catalyst  Ratio    (.degree.C.)   Operation     Conversion    Styrene    (%) (g/cc-hr)
    _________________________________________________________________________
    13  
                           E    8.5:1
                 
                           400 3     96.9  93.8  91  0.437
                     
                           31.5  96.5  94.3  91  0.437
                     
                           75.5  95.2  94.0  90  0.430
                     
                           121   94.3  94.0  90  0.430
                     
                           145   94.2  94.5  89  0.428
                     
                           169   94.1  93.8  88  0.424
                     
                           176   94.0  93.6  88  0.423
    14  
                           F    9:1 400 24   
                           97.1  93.7  91  0.437
                     
                           31.5  96.6  94.0  91  0.437
                     
                           96.0  96.2  93.9  90  0.434
                     
                           121.0 95.4  94.0  90  0.431
                     
                           145.0 94.2  94.0  89  0.426
                     
                           176.0 94.0  93.6  88  0.423
                     
                           200.0 93.2  93.6  87  0.414
                     
                           268.0 92.8  93.5  87  0.417
                     
                           300.0 92.5  93.4  86  0.415
   
                           __________________________________________________________________________


In Example 13, the half-life of the catalyst was estimated to be 2900 hours by extrapolation of the data points. In Example 14, the half-life was estimated to be 2800 hours by extrapolation of the data points.

Comparative Experiment 1 (Not an embodiment of the invention)

The general procedure of Example 13 using catalyst E was repeated except the water feed rate was 6 ml/hour; thus, the water/VCH molar ratio was 7.2:1. The following data was obtained.

    ______________________________________
                                     
                           Styrene
                         
                           Yield       Productivity
    Time (Hours)
             
                           Conversion (%)
                         
                           Styrene (%) (g/cc-hr)
   
                           ______________________________________
    
                           4        97.2       
                           91.4        0.439
     23      
                           96.6        90.3        0.434
     28      
                           95.3        89.7        0.431
     55      
                           94.0        88.0        0.423
     95      
                           87.6        80.6        0.387
    100      
                           86.2        79.3        0.318
    119      
                           82.3        74.7        0.354
    124      
                           81.4        73.9        0.355
    143      
                           76.8        68.6        0.329
    148      
                           76.6        67.9        0.326
    172       71.5        62.7        0.301
    ______________________________________


The half-life of this catalyst, when the water/VCH molar ratio was 7.2:1 was estimated to be about 215 hours.

Comparative Experiment 2 (Not an embodiment of the invention)

The procedure of Example 9 using catalyst J was repeated except the water feed rate was 6 ml/hour; thus, the water/VCH molar ratio was 7.2:1. The following data was obtained.

    ______________________________________
                                     
                           Styrene
                         
                           Yield       Productivity
    Time (Hours)
             
                           Conversion (%)
                         
                           Styrene (%) (g/cc-hr)
   
                           ______________________________________
   
                           2.0       95.8       
                           90.6        0.436
    8.0      
                           94.4        88.7        0.426
    24.0      91.7        85.3       
                           0.410
   
                           48.0      86.3       
                           79.7        0.383
    56.0     
                           83.8        76.5        0.368
    75.0      79.1        70.9       
                           0.341
   
                           106.0     73.1       
                           64.1        0.308
    ______________________________________

It can be seen from Comparative Experiments 1 and 2 that the molar ratio of water to VCH in the feed stream had a dramatic effect on the half-life of the catalyst. In Examples 9 and 13 the water/VCH mole ratio was 14.4 in the feed stream. In Comparative Experiments 1 and 2, however, the water/VCH mole ratio was 7.2. In both comparative experiments 1 and 2, conversion and yield had dropped significantly as compared to Examples 9 and 13.

Comparative Experiment 3 (Not an embodiment of the invention)

The procedure of Example 10 using catalyst K was repeated except the water feed rate was 6 ml/hour; thus, the water/VCH molar ratio was 7.2: 1. The following data was obtained.

   ______________________________________
                                      Styrene
                         
                           Yield       Productivity
    Time (Hours)
             
                           Conversion (%)
                         
                           Styrene (%) (g/cc-hr)
   
                           ______________________________________
   
                           5         83.2        73.2        0.352
   
                           26        79.6        69.0       
                           0.331
   
                           31        79.3        68.8       
                           0.331
   
                           50.5      79.2       
                           68.4        0.329
    55.5     
                           78.9        68.0        0.327
    74.5      78.6        67.6       
                           0.325
   
                           81        78.5        67.5        0.324
    ______________________________________


It can be seen from Comparative Experiment 3 when compared to Example 10, that the increase of water in the feed stream also increased half-life for a metal-doped catalyst.

EXAMPLE 15
The procedure of Example 14 was repeated using catalyst F at 400.degree. C. with the proviso that the amount of water was varied to correspond with those shown in Table III below. In Table III the phrase "Styrene Produced" represents the integrated amount of styrene produced in arbitrary units, over a 175 hour time period. Data with an asterisk were from short runs and were extrapolated to 175 hours assuming no catalyst deactivation.

                 
                           TABLE III
   
                           ______________________________________
   
                           Water/VCH mole ratio
                    
                           Styrene Produced
   
                           ______________________________________
   
                           2.2              
                           83*
    7.2              151
    8.6             
                           154
    12.0             160
    14.4            
                           167
    21.6              162*
    28.8             
                           156*
   
                           36.1             
                           150*
   
                           72.1             
                           122*
   
                           144.3             79*
    ______________________________________


It can be seen from the data in Table III that the water/VCH mole ratio had an important impact on the amount of styrene produced in a given time period. A maximum was observed in the range from 12.0 to approximately 30.0, inclusive. Below 12.0 and above 28.8 the styrene produced decreases.

EXAMPLE 16
The procedure of Example 14 was repeated except the feed rate over the catalyst was increased such that the VCH feed rate was 9.6 mL/hr, the water feed rate was 19.2 mL/hr, and the feed rate of a nitrogen/oxygen mixture (93% nitrogen and 7% oxygen) was 600 cc/min. Under these conditions, the conversion decreased to 85.1 mole percent; selectivity to styrene is 92.2 mole percent; which corresponds to a styrene productivity of 0.603 grams per cubic centimeter per hour.


Comparative Experiment 4 (Not an embodiment of the invention)

A catalyst was prepared by the slow addition of 47.4 grams of tin metal and 5.4 grams of antimony metal to 500 mL of rapidly stirred concentrated nitric acid. The mixture was heated to 90.degree. C. with continual stirring to completely digest the metal. The mixture was then dried at 100.degree. C. and then calcined, in flowing air, by heating at 2.5.degree. C./minute from room temperature to 950.degree. C. and then holding isothermally at 950.degree. C. for two hours. After cooling a 10.0 cc sample of this catalyst (tin/antimony mole ratio of 9:1) was tested under identical conditions as for Example 14. The results were as follows.

   
                           ______________________________________
                                     
                           Styrene
                         
                           Yield       Productivity
    Time (Hours)
              Conversion (%)
                         
                           Styrene (%) (g/cc-hr)
   
                           ______________________________________
     3       
                           88.4        82.8        0.398
   
                           21        86.1        80.3       
                           0.386
    27        85.7       
                           80.1        0.385
    45        83.9       
                           78.1        0.375
    48       
                           83.8        77.8        0.374
   
                           62        83.1        77.0       
                           0.370
    ______________________________________



When a comparison is made between the results of Example 14 and Comparative Experiment 4, it is seen that the catalyst prepared by coprecipitation is superior to the catalyst prepared in Comparative Experiment 4 (the mole ratio of antimony to tin the calcination temperature, and the conditions being the same in Example 14 and Comparative Experiment 4). For instance, at 21 hours and 27 hours in Comparative Experiment 4 the styrene yield is 80.3 percent and 80.1 percent, respectively, whereas in Example 14 the yield was over 10 percent greater being 91 percent at 24 hours. This data shows a catalyst prepared by coprecipitation is superior to a catalyst prepared by the procedure in Comparative Experiment 4.


In addition, another experiment was performed using the catalyst of Comparative Experiment 4 using the same procedure above to make styrene except that the flow rates were changed from initial gas space velocity of 3820 sec.sup.-1 to lower values until a conversion was reached that was the same as in Example 14 at 200 hours wherein the productivity was 0.419 g/cc-hr, this lower rate being 2290 sec.sup.-1 (VCH flow rate of 3.6 mL/hr, water flow rate of 7.2 mL/hr and gaseous 7 percent oxygen in nitrogen of 224 cc/minute). Thus, at a space velocity of 2290 sec.sup.-1, the catalyst of Comparative Experiment 4 produced a 93.3 percent VCH conversion and a productivity of 0.256 g/cc-hr. This difference in space velocities is significant in that the ratio of space velocities (3820 sec.sup.-1 /2290 sec.sup.-1 =1.668) shows the catalyst of Example 14 to be at least 67 percent more active than the catalyst prepared according to Comparative Experiment 4 because the catalyst of Example 14 achieves the same conversion as the catalyst of Comparative Experiment 4 except that the catalyst of Example 14 can do so at a much higher space velocity. Likewise, the productivity in Example 14 was 0.419 g/cc-hr whereas the catalyst of Comparative Experiment 4 at a gas hourly space velocity of 2290 sec.sup.-1 was less being 0.256 g/cc-hr.


Enter supporting content here