Production of tertiary-butylstyrene

This invention provides an improved oxydehydrogenation process for the production of tertiary-butylstyrene which involves the contacting of a vapor phase mixture of tertiary-butylethylbenzene and oxygen with a novel coprecipitated aluminum-calcium-cerium phosphate catalyst composition. The tertiary-butylstyrene is produced with a high conversion selectivity, and concomitantly there is little or no dialkenylbenzene byproducts produced.

BACKGROUND OF THE INVENTION 
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 alkenyl-substituted 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 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, C.sub.2 -C.sub.3 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 Fe.sub.2 O.sub.3 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. Pat. No. 
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. Pat. No. 3,409,696 describes a process which involves contacting an 
admixture of C.sub.2 -C.sub.4 alkylaromatic hydrocarbon and steam at a 
temperature of 500.degree.-650.degree. 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 1000-6000 A. 
U.S. Pat. No. 3,733,327 describes an oxydehydrogenation process for 
converting a C.sub.2 -C.sub.6 alkylaromatic compound to the corresponding 
C.sub.2 -C.sub.6 alkenylaromatic compound which comprises contacting an 
admixture of starting material and oxygen at 400.degree.-650.degree. C. 
with a cerium phosphate or cerium-zirconium phosphate catalyst. 
U.S. Pat. No. 3,957,897 describes a process for oxydehydrogenation of 
C.sub.2 -C.sub.6 alkylaromatic compounds which involves the use of oxygen, 
a reaction zone temperature of 450.degree.-650.degree. 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 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. Pat. No. 3,932,549 describes a process for preparing 
tertiary-butylstyrene which comprises reacting tertiary-butylbenzene with 
ethylene and oxygen at 50.degree.-300.degree. 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 C.sub.2 -C.sub.6 
alkylaromatic compounds are generally applicable for conversion of 
tertiary-butylethylbenzene to tertiary-butylstyrene. 
However, the chemical reactivity of tertiary-butylethylbenzene 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 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 C.sub.2 -C.sub.6 alkyl-substituted aromatic 
compounds to the corresponding alkenyl-substituted aromatic derivatives. 
It is another object of this invention to provide a process for converting 
tertiary-butylethylbenzene to tertiary-butylstyrene under moderate 
conditions with a high level of starting material conversion and product 
selectivity. 
It is another object of this invention to provide a process for converting 
tertiary-butylethylbenzene to tertiary-butylstyrene with little or no 
production of dialkenylbenzene byproducts. 
It is a further object of this invention to provide a novel catalyst 
adapted for oxydehydrogenation processes. 
Other objects and advantages of the present invention shall become apparent 
from the accompanying description and examples. 
DESCRIPTION OF THE INVENTION 
One or more objects of the present invention are accomplished by the 
provision of a process which comprises contacting a feed stream containing 
tertiary-butylethylbenzene and oxygen in vapor phase with a catalyst 
comprising aluminum-calcium-cerium 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.degree. C. and 
650.degree. C. with a coprecipitated aluminum-calcium-cerium phosphate 
catalyst, wherein the conversion selectivity to tertiary-butylstyrene is 
at least 80 mole percent, and the selectivity to dialkenylbenzene is 
essentially zero mole percent. 
A preferred reaction temperature for the oxydehydrogenation reaction is one 
which is in the range between about 400.degree. C. and 600.degree. 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 a gasiform diluent in the feed stream. 
Illustrative of suitable diluents are carbon dioxide, nitrogen, noble 
gases and steam, 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-cerium 
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 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.degree. 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 aluminum-calcium-cerium phosphate catalyst composition. The 
catalyst exhibits 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 atomic ratio of metals in the catalyst composition can vary in the 
range of about 5-20:5-20:1 of aluminum:calcium: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 the addition to an aqueous solution of 
ammonium phosphate of an aqueous solution of water soluble compounds of 
aluminum, calcium and cerium metals, respectively. Illustrative of 
water-soluble or partially water-soluble compounds are the chlorides, 
nitrates and sulfates of aluminum, calcium and cerium. 
In a preferred procedure, the pH of the resultant solution of aluminum, 
calcium, 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 atmosphere at a 
temperature between about 300.degree. C. and 600.degree. C. for a period 
of about 1-24 hours. 
The coprecipitated aluminum-calcium-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 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) 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 MgAl.sub.2 O.sub.4, FeAl.sub.2 O.sub.4, ZnAl.sub.2 O.sub.4, MnAl.sub.2 
O.sub.4, CaAl.sub.2 O.sub.4, and other like compounds having the formula 
MO.Al.sub.2 O.sub.4 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: 
EQU Al.sub.5-20 Ca.sub.5-20 Ce.sub.1 (PO.sub.4).sub.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 C.sub.3 -C.sub.10 
alkenes, C.sub.4 -C.sub.10 cycloalkenes and C.sub.2 -C.sub.6 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 
aluminum-calcium-cerium phosphate catalyst composition appears to enhance 
the reactivity of the catalyst, and the presence of the aluminum metal 
component 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 
A. 
A solution is prepared by dissolving 25 grams of aluminum nitrate [0.07 M, 
Al(NO.sub.2).sub.3.9H.sub.2 O], 16 grams of calcium nitrate [0.07 M, 
Ca(NO.sub.3).sub.2.4H.sub.2 O] and 3 grams of cerium(III) nitrate [0.007 
M, Ce(NO.sub.3).sub.3.6H.sub.2 O] in 150 milliliters of water. The 
solution is blended with 150 milliliters of an aqueous solution of dibasic 
ammonium phosphate [0.3 M, (NH.sub.4).sub.2 HPO.sub.4 ] having a pH of 
7.6. The pH of the resultant blended solution is adjusted to a pH of 7 
with ammonium hydroxide. 
The solution is heated to the boiling point, maintained at that temperature 
for a period of about one hour, and then cooled to room temperature. The 
solid material which has precipitated is separated by filtration. The 
recovered precipitate is washed with water, and then dried in a vacuum 
oven at 120.degree. C. The dried solids are calcined at 550.degree. C. 
under a nitrogen atmosphere for a period of 5 hours. 
B. 
A portion of the calcined solids is ground and sieved to a mesh size in the 
range of 10-20. A 1 cm.sup.3 quantity of the catalyst is charged to an 
electrically heated reactor, and the reactor is heated to a temperature of 
about 450.degree. C. 
An air flow of 10 milliliters/minute and a tertiary-butylethylbenzene 
(meta:para ratio of 3:97) 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 analyzed by a gas 
chromatograph/mass spectrometer system. 
The molar percent conversion of tertiary-butylethylbenzene is 45.6 and the 
mole percent selectivity to tertiary-butylstyrene is 86.4. The relative 
selectivity yield of dialkylbenzenes is less than about 0.03 mole percent. 
When an aluminum-calcium-cerium phosphate catalyst contains Ce(IV) rather 
than Ce(III) metal component, the yield of dialkenylbenzene byproducts 
tends to increase. 
EXAMPLE II 
An aluminum-calcium-cerium phosphate catalyst is prepared in the same 
manner as Example I, employing an eight-fold increase in the relative 
proportions of chemical components. 
The atomic ratio of the metals in the catalyst composition are in a ratio 
of 9.8:9.6:1 of Al:Ca:Ce. 
A 100 cm.sup.3 portion of the catalyst powder (10-20 mesh) is charged to a 
reactor which is a 0.5 inch stainless steel pipe of 24 inch length. The 
reactor and a part of the feed line are immersed in a molten salt bath. 
Variable quantities of tertiary-butylethylbenzene between about 30-120 
milliliters/hour are fed to the reactor, together with a gas stream 
consisting of about 400-800 milliliters/minute of air and about 500-1000 
milliliters/minute of nitrogen. Assay of the liquid products and of the 
effluent gas from the condenser are employed to calculate the conversion 
and selectivity results. The reaction conditions and data calculations 
from 3 runs are summarized in the following Table. 
TABLE 
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Oxidative Dehydrogenation of Tertiary-butylethylbenzene 
1 2 3 
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Hydrocarbon feed rate, g/hr 
31 56 83 
Mols O.sub.2 /mol t-BEB 
1.09 0.61 0.41 
Mol fraction t-BEB in feed 
0.052 0.090 0.127 
Reactor temp., inlet, .degree.C. 
494 465 464 
Peak temperature 560 515 505 
Liquid hourly space 
velocity g/g/hr 1.15 2.07 3.06 
Conversion, % 49.7 39.8 32.4 
tert-Butylstyrene assay % 
42.6 35.2 28.8 
Dialkenylbenzenes 0 0 0 
Selectivity, mole % 
CO 3.5 2.7 1.8 
CO.sub.2 9.2 6.8 5.4 
Light By-products 4.8 2.7 3.2 
tert-Butylstyrene 80.6 86.5 88.6 
Heavy By-products 1.9 1.3 1.0 
Dialkenylbenzenes 0 0 0 
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