GB2068767A - 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 of tertiary- butylethylbenzene comprise an aluminum-calcium 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 alkenylsubstituted aromatic compounds Alkenyl-substituted aromatic compounds are important starting materials for the production 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 to alkenylsubstituted 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 Fe2O3 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. 3,299,155 describes a 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 alkylaromatic compound to the corresponding C2-C6 alkenylaromatic compound which comprises contacting an admixture of starting material and oxygen at 400"-650"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 respect to the potentially harmful environmental effects associated with the manufacture of synthetic resin products. In the molding of large shaped articles, for example, 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 plant. 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 tertiarybutylstyrene 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 tertiarybutyl benzene 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 tertiarybutylethylbenzene to tertiary-butylstyrene.

However, the chemical reactivity of tertiarybutylethylbenzene underoxydehydrogenation conditions is more complex that that of simpler chemical structures such as ethylbenzene or ethyltoluene.

The tertiary-butyl substituent of tertiarybutylethylbenzene underoxydehydrogenation conditions is susceptible to cracking so as to yield methane and a 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 correspounding alkenyl-substituted aromatic derivatives.

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

In a more specific embodiment, this invention provides a process for the production oftertiary 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 aluminum-calcium phosphate catalyst, wherein the conversion selectivity to tertiary-butylstyrene is at least 80 mole percent, and the conversion selectivity to dialkenylbenzene byproducts is essentially zero 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 organic compounds 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 tertiarybutylethylbenzene, 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 a gasiform diluent in the feed stream. Illustrative of suitable diluents are carbon dioxide, nitrogen, steam and noble gases, either individually or in admixture. The diluent 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 aluminum-calcium 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 generally will vary in the range of about 0.5-20 seconds, and pref erablywill average in the range between about 1-15 seconds. Residence time refers to the contact time adjusted to 250C 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 pro cess is the use of a novel coprecipitated aluminum calcium phosphate catalyst composition. The catal yst can exhibit unique properties for the conversion of tertiary-butylethylbenzene to the tertiary butylstyrene product with a high conversion effi ciency, and with little or no production of dialkenyl benzene type of byproducts.

The atomic ratio of metals in the catalyst composition can vary in the range of about 1-10:1-5 of aluminum:calcium. 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 the addition of an aqueous solution of ammonium phosphate to an aqueous solution of water-soluble or partially water-soluble compounds of aluminum and calcium metals, respectively. Illustrative of water-soluble or partially water-soluble compounds are the chlorides, nitrates, sulfates, and acetates of aluminum and calcium. Alternatively, the solution of aluminum and calcium compounds can be added to the phosphate solution, preferably at a slow rate and with efficient stirring.

In one process embodiment, the pH of the resultant solution of aluminum, calcium 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 atmosphere at a temperature between about 300"C and 600"C for a period of about 1-24 hours.

The coprecipitated aluminum-calcium 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 during the 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) crystafline zeolitic aluminosilicates 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, FeAI204, ZnAl2O4, MnAl2O4, CaAI2O4, and other like compounds having the formula MO A1203 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 preferred catalyst composition of the present invention is one which corresponds to the formula: Al1-10Ca1-5(PO4) wherein xis 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 forth oxydehydrogenation of tertiary-butylethylbenzene and ethyltoluene under mild oxidation conditions.

The presence of the aluminum metal component in an invention AI1-10Ca1-5(PO4) catalyst composition as defined above contributes attrition-resistance and extends 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 an aluminum-calcium phosphate oxidation catalyst.

A.

A solution is prepared by dissolving 200 grams of aluminum nitrate [0.53 M, Al(NO3)3 9H20] and 128 grams of calcium nitrate [0.54 M, Ca(NO3)2 4H20] in 400 grams of water. A second solution is prepared by dissolving 160 grams of dibasic ammonium phosphate [1.21 M, NH4)2P04] in 400 grams of water.

One half of the first solution is added to one half of the second solution with stirring over a 45 minute period. Ammonium hydroxide is added to raise the pH above about 6. The reaction medium is stirred for an additional 45 minutes at atemperature of about 80"C. The solid catalyst precursor which has precipitated is collected by filtration, and the filter cake is washed with water. The wet filter cake is pressed through an 8 mesh screen to produce uniformly divided catalyst precursor, which is then dried in a vacuum oven at 1200C. The dried catalyst precursor is calcined at 550"C under a nitrogen atmosphere for a period of 5 hours to yield a composition identified as catalyst A.

When a carrier substrate is being employed it is preferably incorporated during the initial solution blending and solids precipitation stage.

The remaining halves of the two solutions are combined by addition ofthe ammonium phosphate solution to the metal nitrate solution with stirring over a 45 minute period. Without the addition of ammonium hydroxide, a catalyst precursor coprecipitate is separated as described above, and subdivided, dried and calcined to yield a composition identified as catalyst B. The acidic filtrate of the catalyst preparation medium has a pH of about 3.

B.

A 1 cm3 portion of catalyst A as prepared above is charged to an electrically heated reactor, and the reactor is heated to a temperature of about 450"C.

An airflowof 10 milliliters/minute and atertiary- butylethylbenzene flow of 1 milliliter/hour are introduced into the inlet of the reactor. The effluent stream from the reactor is cooled and the resultant liquid components are collected and identified.

The percent conversion of tertiarybutylethylbenzene is 31, and the mole percent selectivity to tertiary-butylstyrene is 85. The relative selectivity yield of d ialkenylbenzene byproduct is less than about 0.6 mole percent.

When the hydrocarbon flow rate is decreased by a factor of 10, the mole percent selectivity to tertiarybutylstyrene is 85, and there is no detectable presence of dialkenylbenzene byproducts at the 100 ppm level as determined by gas chromatographic analysis.

Employing the same hydrocarbon oxidation procedure and reactor as described above, a feedstream of air and tertiary-butylethylbenzene is contacted with a 1 cm3 portion of catalyst B in the reactor.

The percent conversion of tertiarybutylethylbenzene is 40, and the mole percent selectivity to tertiary-butylstyrene is 86. There is no detectable presence of dialkenylbenzene byproducts as determined by gas chromatographic analysis.

EXAMPLE Il A 100 cm3 portion of aluminum-calcium phosphate catalyst A from Example I is charged to a reactor which is a 0.5 inch stainless steel pipe of 24 inch length. The reactor and a part of each of the feed lines are immersed in a molten salt bath.

Feedstreams of oxygen, tertiarybutylethylbenzene, and nitrogen are blended at the inlet and fed into the reactor, and the proportions of feed components are varied over several runs.

Another series of runs is conducted employing a 100 cm3 portion of catalyst B in the reactor.

The reaction parameters and product yields of the two series are listed in Table 1. Only in one run is there a detectable presence of dialkenylbenzene (DAB) byproducts.

When ethyltoluene is substituted for tertiarybutylbenzene in the above described oxidation process, an average mole percent selectivity to vinyltoluene of at least 80 is obtained.

TABLE 1 Mol fraction Moss 02/ Reactor LHSV Selectivity, % Run Catalyst t-BEB in feed Mol t-BEB C, max. giglhr T-BS DAB * 1 A 0.09 0.6 520 0.96 87.6 0 2 A 0.04 1.4 530 0.83 75.3 0.11 3 A 0.04 1.4 536 0.80 81.5 0 4 B 0.062 0.9 530 1.17 80.8 0 5 B 0.055 T.0 523 1.03 80.5 0 6 B 0.053 11 502 1.0 82.5 0 * Less than GC detectable level of 100 ppm.

EXAMPLE ffl In the same manner as in Example I, a larger quantity of catalyst A is prepared. A 250 cm3 portion of the catalyst is charged to the reactor described in Exam ply 11.

Air, tertiary-butylethylbenzene and either carbon dioxide or steam diluent are metered into the reactor inlet in a preheated condition as previously described.

The reaction parameters and product yields are listed in Table II. In none of the runs is the presence of dialkenylbenzene byproducts (DAB) detectable by gas chromatographic analysis.

In the same manner, additional runs are conducted with aluminum-calcium phosphate catalysts having an Al/Ca ratio of 4:1 and 9:1, respectively. In each run, the mole percent selectivity to tertiarybutylstyrene is at least 82, and there is little or no detectable presence of dialkenylbenzene byproducts as determined by gas chromatographic analysis.

TABLE2 Mols O21 Mol Fraction Max Reactor LSHV Selectivity, % Run Diluent Mol t-BEB t-BEB in feed Temp., "C giglhr T-BS DAB* 7 CO2 .90 .072 539 .48 82.5 0 8 CO2 .83 .078. 505 .52 85.1 0 9 H2O .90 .074 576 .95 83.3 0 10 H2O .90 .098 653 .95 70.5 0 11 H20 .90 .093 578 .95 79.9 0 * Less than GC detectable level of 100 ppm.

Claims (18)

1. A process forthe production of tertiarybutylstyrene which comprises contacting a feed stream containing tertiary-butylethylbenzene and oxygen in vapor phase with a catalyst comprising aluminum-calcium 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 about350 C and 650"C with a coprecipitated aluminum-calcium phosphate catalyst, wherein the conversion selectivity to tertiary-butylstyrene is at least 80 mole percent, and the conversion selectivity to dialkenylbenzenes is essentially zero 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 tertiarybutylethylbenzene.

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 a gaseous inert diluent.

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 aluminum and calcium metal elements, respectively, are present in the catalyst in an atomic ratio of about 1-10:1-5.

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

9. A process forthe production of vinyltoluene which comprises contacting a feed stream containing ethyl-toluene and oxygen in vapor phase with a catalyst comprising aluminum-calcium phosphate.

10. 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 composition corresponds to the formula: Al1 ~10Ca1 ~5(PO4)x wherein x is a number sufficient to satisfy the valences of the metal elements in the catalyst.

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

13. Acoprecipitated catalyst in accordance with claim 11 or claim 12, wherein said composition has had its activity enhanced by calcining in an inert atmosphere.

14. A coprecipitated catalyst composition, substantially as described in either of the foregoing Examples I and III.

15. Aprocessforthe productionoftertiarybutylstyrene, the process being substantially as described in any one of the foregoing Examples I to 111.

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

17. Tertiary-butylstyrene, whenever produced by a process in accordance with any one of claims 1 to 8 and 15.

18. Vinyltoluene, whenever produced buy a process in accordance with any one of claims 9, 10 and 16.