GB2068254A - Catalyst and process for production of alkenyl-substituted aromatic compounds - Google Patents

Abstract

Catalysts for the production of tertiary-butylstyrene by the vapor phase oxydehydrogenation tertiary- butylethylbenzene comprise nickel- cerium phosphate. Similar oxydehydrogenation conversions of other alkyl-substituted aromatic compounds to the respective alkenyl-substituted aromatic compounds may also be performed.

Description

SPECIFICATION Catalyst and process for production of alkenyl-substituted aromatic compounds Alkenyl-substituted aromatic compounds are important starting materials for the producton of resins, plastics, rubbers, solvents, chemical intermediates, and the like.

Processes for the production of alkenylsubstituted aromatic compounds often are characterized by low conversion rates which necessitate the recycle of large quantities of unconverted charge. Many of the known processes require the presence of a large volume of steam or other gaseous diluent which is a cost disadvantage. In some processes the conversion efficiency of alkenyl-substituted aromatic product is diminished because -of the formation of a relatively large proportion of carbon oxides and other byproducts.

In one well-known commercial process, C2-C3 alkylaromatic hydrocarbons (e.g., ethylbenzene, ethyltoluene and isopropylbenzene) are converted to the corresponding styrene.

derivatives by passage of the alkylaromatic hydrocarbon feed and steam over a Fe203 catalyst. the conversion per pass is in the 35-40% range, and comparatively high temperatures are needed for the oxidative dehydrogenation reaction.

Illustrative of other oxidative dehydrogenation processes, U.S. 299,155 describes process for the production of alkenylbenzenes which involves contacting a mixture of an ethyl (or isopropyl) substituted benzene compound and sulfur dioxide in vapor phase with a metal phosphate catalyst such as calcium phosphate.

U.S. 3,409,696 describes a process which involves contacting an admixture of C2-C4 alkylaromatic hydrocarbon and steam at a temperature of 500"-650"C with a catalyst containing 20-60 weight percent of a bismuth compound (e.g., bismuth oxide) on a calcium phosphate support of which at least 90% of the total pore volume is contributed by pores having a diameter of 1000-6000A.

U.S. 3,733,327 describes an oxydehydrogenation process for converting a C2-C6 alkyaromatic compound to the corresponding C2-C6 alkenylaromatic compound which comprises contacting an admixture of starting material and oxygen at 400"-640"C with a cerium phosphate or cerium-zirconium phosphate catalyst.

U.S. 3,957,897 describes a process for oxydehydrogenation of C2-C6 alkylaromatic compounds which involves the use of oxygen, a reaction zone temperature of 450-650"C, a space velocity of 55-2500, and a catalyst which is at least one of calcium, magnesium and strontium pyrophosphate.

More recently, there has been increasing concern with rspect to the potentially harmful environmental effects associated with the manufacture of synthetic resin products. In the molding of large shaped articles, for exam ple, volatile components of a polymerizable monomeric formulation sometimes tend to evaporate from freshly coated mold surfaces which are exposed.

Various means have been contemplated for reducing the level of fugitive vapors in a synthetic resin manufacturing piant. One method involves the replacement of volatile monomers of a formulation with monomers which have a lower vapor pressure. Thus, it is advantageous to substitute an alkenylaromatic compound such as tertiary-butylstyrene for styrene in a polymerizable formulation which contains the volatile styrene as a comonomer.

As a further consideration, it has been found that tertiary-butylstyrene is desirable as a comonomer in the preparation of copolymers or as a curing agent for fiber-reinforced plastics because it improves the moldability of polymerizable formulations and it lessens the mold shrinkage of molded plastic articles.

The advantages of tertiary-butylstyrene as a comonomer in resin systems has stimulated interest in improved processes for synthesizing this type of higher molecular weight alkenylaromatic compound.

U.S. 3,932,549 describes a process for preparing tertiary-butylstyrene which comprises reacting tertiary-butylbenzene with ethylene and oxygen at 50"-300"C in the presence of a catalyst prepared by treating metallic palladium or a fatty acid salt thereof with pyridine.

Other known processes for producing tertiary-butylbenzene involve oxydehydrogenation of tertiary-butylethylbenzene. The type of patent processes described hereinabove for oxydehydrogenation of C2-C6 alkylaromatic compounds are generally applicable for conversion of tertiary-butylethylbenzene to tertiary-butylstyrene.

However, the chemical reactivity of tertiarybutylethylbenzene under oxydehydrogenation conditions is more complex than that of simpler chemical structures such as ethylbenzene or ethyltoluene. The tertiary-butyl substituent of tertiary-butylethylbenzene under oxydehydrogenation conditions is susceptible to cracking so as to yield methane and residual isopropenyl substituent on the benzene nucleus.

Consequently, one of the ultimate byproducts of tertiary-butylethylbenzene oxydehydrogenation is a dialkenylbenzene derivative such as isopropenylstyrene.

Because of the presence of two or more polymerizable alkenyl groups, a compound such as isopropenylstyrene tends to undergo crosslinking activity and form insoluble byproducts during the high temperature cycles of starting material conversion and product recovery in an oxydehydrogenation process.

Heat exchangers and distillation columns can be rendered inoperative by the deposition of high molecular weight polymeric residues.

Further, the presence of an isopropenylstyrene type of contaminant, particularly a variable quantity of such material, in purified tertiary-butylstyrene can complicate or even prohibit the application of the contaminated tertiary-butylstyrene product as a comonomer in polymerizable formulations.

Accordingly, it is an object of the invention to provide a process for oxydehydrogenation of C2-C6 alkyl-substituted aromatic compounds to the corresponding alkenyl-substituted aromatic derivatives.

The present invention provides a process for the production of tertiary-butyistyrene which comprises contacting a feed stream containing tertiary-butylethylbenzene and oxygen in vapor phase with a catalyst comprising nickelcerium phosphate.

In a more specific embodiment, this invention provides a process for the production of tertiary-butylstyrene under oxydehydrogenation conditions which comprises contacting a feed mixture of tertiary-butylethylbenzene and oxygen at a temperature in the range between about 350"C and 650"C with a coprecipitated nickel-cerium phosphate catalyst, wherein the conversion selectivity to tertiary-butylstyrene is at least 80 mole percent, and the conversion selectivity to dialkenylbenzene byproducts is less than one mole percent.

A preferred reaction temperature for the oxydehydrogenation reaction is one which is in the range between about 400"C and 600"C.

The feed admixture of tertiary-butylethylbenzene and oxygen can contain quantities of other hydrocarbons which do not adversely affect the invention oxydehydrogenation reaction, e.g., compounds such as octane, decene, naphthene, benzene, toluene, pyridine, thiophene, and the like, which may be present in commercially available alkylbenzenes.

The molecular oxygen component of the feed admixture preferably is present in a quantity between about 0.2-5 moles per mole of tertiary-butylethylbenzene, and most preferably in,a molar ratio of 0.8-2:1. The oxygen can be supplied as air, commercially pure oxygen, or air enriched with oxygen.

It is advantageous to include à gasiform diluent in the feed stream. Illustrative of suitable diluents are carbon dioxide, nitrogen, noble gases and steam, either individually or in admixture. thediluent is normally employed in a quantity between about 2-20 moles per mole of tertiary-butylethylbenzene in the feed stream.

The pressure utilized in the vapor phase oxydehydrogenation process can be subatmospheric, atmospheric or superatmospheric. A convenient pressure for the vapor phase process is one which is in the range between about 1 and 200 psi.

Suitable reactors for the vapor phase process include either fixed bed or fluid bed reactors which contain the invention nickelcerium phosphate catalyst composition. The process can be conducted continuously or noncontinuously, and the catalyst may be present in various forms such as a fixed bed or a fluidized system.

The residence time (i.e., catalyst contact time) of the feed stream in the vapor phase process generally will vary in the range of about 0.5-20 seconds, and preferably will average in the range between about 1-15 seconds. Residence time refers to the contact time adjusted to 25"C and atmospheric pressure. The contact time is calculated by dividing the volume of the catalyst bed (including voids) by the volume per unit time flow rate of the feed stream at NTP.

An important aspect of the present invention process is the use of a novel coprecipitated nickel-cerium phosphate catalyst composition. The catalyst can exhibit unique properties for the conversion of tertiary-butylethylbenzene to the tertiary-butylstyrene with a high conversion efficiency, and with little or no production of dialkenylbenzene type of byproducts. The presence of a cerium component in the invention metal phosphate catalyst appears to enhance the reactivity and selectivity of the catalyst for conversion of tertiarybutylethylbenzene to tertiary-butylstyrene.

The atomic ratio of metals in the catalyst composition can vary in the range of about 5-20:1 of nickel:cerium. The phosphate component is present in a quantity at least sufficient to satisfy the valences of the metal elements in the catalyst.

The catalyst can be prepared by adding to an aqueous solution of ammonium phosphate an aqueous solution of water soluble or partially water-soluble compounds of nickel and cerium metals, respectively. Illustrative of wa ter-sojuble or partially water-soluble compounds are the chlorides, nitrates, sulfates and acetates of nickel and cerium.

In a preferred procedure, the pH of the resultant solution of nickel, cerium, and phosphate compounds is adjusted to about 7 with an alkaline reagent such as ammonium hydroxide. The coprecipitate which forms is recovered, washed with water, and dried.

It has been found that the activity of the catalyst composition is enhanced if the coprecipitate preparation is calcined in an inert atmophere at a temperature between about 300"C and 600"C for a period of about 1-24 hours.

The coprecipitated nickel-cerium phosphate composition described above can be used as the catalyst per se, or the said composition can be combined with a suitable internal diluent or carrier substrate. The carrier substrate is preferably incorporated just prior to the catalyst precursor coprecipitate formation step of the catalyst preparation.

The carrier substrate should be relatively refractory to the conditions utilized in the invention process. Suitable carrier substrate materials include (1) silica or silica gel, silicon carbide, clays, and silicates including those synthetically prepared and naturally occurring, which may or may not be acid treated such as attapulgus clay, china clay, diatomaceous earth, Fuller's earth, kaolin, asbestos and kieselguhr; (2) ceramics, porcelain, crushed firebrick and bauxite; (3) refractory inorganic oxides such as alumina, titanium dioxide, zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide, cesium oxide, hafnium oxide, zinc oxide, molybdenum oxide, bismuth oxide, tungsten oxide, uranium oxide, magnesia, boria, thoria, silica-alumina, silica-magnesia, chromia-alumina, alumina-boria and silica-zirconia; (4) crystalline zeolitic alumino-silicates such as naturally occurring or synthetically prepared mordenite and/or faujasite, either in the hydrogen form or in a form which has been treated with multivalent cations; and (5) spinels such as MgAl2O4, FeAl2O4, ZnAl204, MnAl2O4, CaAl2O4, and other like compounds having the formula MO.AI203 where M is a metal having a valence of 2.

The catalyst as employed in the invention process can be in the shape of granules, pellets, extrudate, powders, tablets, fibers, or other such convenient physical form.

A preferre catalyst composition of the present invention is one which corresponds to the formula: Ni5 ~ 20Ce1 ( PO4)x wherein x is a number sufficient to satisfy the valences of the metal components.

The preferred catalyst composition of the present invention is adapted for oxydehydrogenation of hydrocarbon compounds such as C3-C10 alkenes, C4-C10 cycloalkenes and C2-C6 alkylaromatic compounds, and has particular advantage for the oxydehydrogenation of tertiary-butylethylbenzene and ethyltoluene under mild oxidation conditions.

The presence of the cerium metal component in an invention nickel-cerium phosphate catalyst composition appears to enhance the reactivity of the catalyst, and have the further advantage of extending the life of the catalyst under hydrocarbon oxydehydrogenation conditions.

The following examples are further illustrative of the present invention. The reactants and other specific ingredients are presented as being typical, and various modifications can be derived in view of the foregoing disclosure within the scope of the invention.

EXAMPLE I This Example illustrates the preparation and application of a nickel-cerium phosphate oxidation catalyst.

A.

A solution of 233 grams of nickel nitrate [0.8 M, Ni(NO3)2.6H20] and 35 grams of cerium(lll) nitrate [0.08 M, Ce(NO3)3.6H2O in 400 milliliters of water is. added to a solution of 1 82 grams of dibasic ammonium phosphate [1.4 M, (NH4)2HPO4] in 500 milliliters of water at 40"C over a 30 minute period with stirring. A total of about 50 milliliters of ammonium hydroxide is added as necessary to maintain the pH of the aqueous slurry of precipitated catalyst precursor in the range between about 6-7.

After the aqueous slurry is cooled to room temperature, the precipitated catalyst precursor is isolated by filtration, washed with water, and then dried in a vacuum oven at 120"C. The dried catalyst precursor is calcined at 550"C under a nitrogen atmosphere for a period of about five hours.

When a carrier substrate is being employed, it is preferably incorporated as an internal diluent component during the initial solution blending stage.

B.

A portion of the nickel-cerium phosphate catalyst is ground and sieved to a mesh size in the range of 10-20. A one cm3 quantity of the catalyst is charged to a stainless steel pipe reactor, and the reactor is heated to a temperature of about 460"C.

An air flow of 10 milliliters/minute and a tertiary-butylethylbenzene flow of 1 milliliter/ hour are blended and introduced into the reactor as a feed stream. The effluent stream from the reactor is cooled and the resultant liquid components are collected.

The percent conversion of tertiary-butylethylbenzene is 37, and the mole percent seletivity to tertiary-butylstyrene is 89. The relative selectivity yield of divinylbenzene type of byproducts is about 0.2 mole percent.

EXAMPLE II Another nickel-cerium phosphate catalyst is prepared in the same manner as Example I.

A 100 cm3 portion of the catalyst power (10-20 mesh) is charged to a reactor which is 0.75 inch stainless steel pipe of 24 inch length. The reactor and part of the feed line are immersed in a molten salt bath.

The feed stream is a blend of 45 milliliters/ hour of tertiary-butylethylbenzene, 400 milliliters/minute of air, and 1000 milliliters/ minute of nitrogen, and the peak temperature in the oxidation reaction zone is about 475"C.

The percent conversion of tertiary-butylethylbenzene is 34, and the mole percent selectivity to tertiary-butylstyrene is 90.2. Gas chromatographic analysis of the effluent product mixture indicates that any presence of dialkenylbenzene compounds is less than about 0.5 percent.

When ethyltoluene is substituted for tertiary-butylethylbenzene in the above described oxidation process, a mole percent selectivity to vinyltoluene of at least 80 is obtained.

EXAMPLE 111 This Example illustrates that the production of dialkenylbenzene byproducts increases if a nickel-cerium phosphate catalyst contains Ce (IV) rather than Ce(lll) metal.

A solution of 233 grams of nickel nitrate [Ni(NO3)2.6H20, 0.80 M] and 44 grams of cerium acid sulfate [Ce(HSO4)4, 0.08M] in 400 milliliters of water is added to a solution of 1 82 grams of dibasic ammonium phosphate [(NH4)2HPO4, 1.38 M in 500 milliliters of water. Ammonium hydroxide is added to maintain the pH between 6 and 7. The resulting precipitate is collected on a filter and washed with 3 liters of water. The washed filter cake is dried and then calcined at a temperature of 550"C for 5 hours.

One cubic centimeter of the catalyst (0.28 gram) is placed in an electrically heated reaction chamber at 460"C. A flow of air (10 milliliters/minute) and a flow of tertiary-butylethylbenzene (1 milliliter/hour) is passed through the catalyst bed. About 35 percent of the tertiary-butylethylbenzene is converted with a percent selectivity to tertiary-butylstyrene of 86.3.

The selectivity to dialkenylbenzenes is 0.76 percent, which is a higher yield of byproduct than is obtained in Examples l-ll where a Ce(lil) metal component is employed in the nickel-cerium phosphate catalyst.

Claims (14)

1. A process for the production of tertiarybutylstyrene which comprises contacting a feed stream containing tertiary-butylethylbenzene and oxygen in vapor phase with a catalyst comprising nickel-cerium phosphate.

2. A process for the production of tertiarybutylstyrene under oxydehydrogenation conditions which comprises contacting a feed mixture of tertiary-butylethylbenzene and oxygen at a temperature in the range between about 350"C and 650"C with a coprecipitated nickel-cerium phosphate catalyst, wherein the conversion selectivity to tertiary-butylstyrene is at least 80 mole percent, and the conversion selectivity to dialkenylbenzenes is less than one mole percent.

3. A process in accordance with claim 2, wherein the feed mixture contains between about 0.2-5 moles of molecular oxygen per mole of tertiary-butylethylbenzene.

4. A process in accordance with claim 2 or claim 3, wherein the feed mixture contains a gaseous inert diluent.

5. A process in accordance with any one of claims 2 to 4, wherein the feed mixture contains nitrogen and/or carbon dioxide and/ or steam as an additional component.

6. A process in accordance with any one of claims 2 to 5, wherein the contact time between the feed stream and the catalyst is in the range between about 0.5 and 20 seconds.

7. A process in accordance with any one of claims 2 to 6, wherein the nickel and cerium metal elements, respectively, are present in the catalyst in an atomic ratio of about 5-20: 1.

8. A process in accordance with any one of claims 2 to 7, wherein the catalyst is supported on a carrier substrate.

9. A process for the production of vinyltoluene which comprises contacting a feed stream containing ethyltoluene and oxygen in vapor phase with a catalyst comprising nickelcerium phosphate.

1 0. A process in accordance with claim 9, wherein the conversion selectivity to vinyltoluene is at least 80 mole percent.

11. A coprecipitated catalyst composition adapted for oxydehydrogenation reactions, which catalyst corresponds to the formula: Ni5 - 20Ce1 (PO4)x wherein x is a number sufficient to satisfy the valences of the metal elements in the catalyst.

1 2. A coprecipitated catalyst composition in accordance with claim 11, wherein the cerium metal is substantially in the plus three valence state.

1 3. A coprecipitated catalyst composition in accordance with claim 11 in combination with a carrier substrate.

14. A coprecipitated catalyst composition in accordance with any one of claims 11 to 13, wherein said composition has had its activity enhanced by calcining in an inert atmosphere.

1 5. A coprecipitated catalyst composition, substantially as described in any one of the foregoing Examples I to III.

1 6. A process for the production of tertiary-butylstyrene, the process being substantially as described in any one of the foregoing Examples I to Ill.

1 7. A process for the production of vinyltoluene, the process being substantially as described in the foregoing Example II.

1 8. Tertiary-butylstyrene, whenever produced by a process in accordance with any one of claims 1 to 8 and 16.

1 9. Vinyltoluene, whenever produced by a process in -accordance with the one of claims 9, 10 and 17.