WO2004060839A1 - Dehydrogenation of alkyl aromatic compound over a rare earth catalyst - Google Patents

Abstract

A process for the dehydrogenation of an alkyl aromatic compound, such as ethylbenzene, to a vinyl aromatic compound, such as styrene, involving dehydrogenating an alkyl aromatic compound with a catalyst containing at least one rare earth element on a catalyst support, essentially free of iron oxide and platinum group metal; or with a mixed oxide catalyst containing at least one rare earth element and at least one other metallic element selected from aluminum, cobalt, chromium, manganese, and mixtures thereof; or with a mixture of such catalysts. Optionally, the dehydrogenation feedstream may contain an alkane, such as ethane, which is simultaneously dehydrogenated to an alkene, such as ethylene. The dehydrogenation process can be integrated into a process of producing a vinyl aromatic compound, such as styrene, from a raw material base comprised of an alkane and an aromatic compound, such as, ethane and benzene.

Description

DEHYDROGENATION OFALKYLAROMATIC COMPOUND ONERARAREEARTHCATALYST

Cross-Reference to Related Application: This application claims the benefit of

US Provisional Application Serial No. 60/434875, filed December 19, 2002.

In one aspect, this invention pertains to a novel process of dehydrogenating an alkyl aromatic compound, such as ethylbenzene, to form a vinyl aromatic compound, such as styrene. In a second aspect, this invention pertains to a novel process of dehydrogenating a feedstream containing an alkyl aromatic compound and an alkane to form a product stream containing a vinyl aromatic compound and an alkene, respectively. In this second aspect, the invention can be integrated into a larger process of preparing a vinyl aromatic compound using as raw materials an aromatic compound and an alkane.

The dehydrogenation of alkyl aromatic compounds, for example, ethylbenzene, isopropylbenzene, diethylbenzene, or p-ethyltoluene, finds utility in the preparation of styrene and substituted derivatives of styrene including -methylstyrene, divinylbenzene, and p-methylstyrene. Styrene and its substituted derivatives are useful as monomers in the formation of polystyrenes, styrene-butadiene rubbers (SBR), acrylonitrile-butadiene- styrene (ABS), styrene-acrylonitrile (SAN), and unsaturated polyester resins. The dehydrogenation of alkanes, such as ethane, find utility in the preparation of alkenes, such as ethylene.

Alkenes have well-known utility as monomers in the formation of poly(olefin) polymers and as reactants in various organic processes. Notably, alkenes can be used to alkylate aromatic compounds, such as benzene, to alkylated aromatic compounds, such as, ethylbenzene.

The primary manufacturing route to vinyl aromatic compounds, including styrene, involves the direct catalytic dehydrogenation of alkyl aromatic compounds, such as ethylbenzene. Patents representative of such a process include, for example, US 4,404,123, US 5,171,914, US 5,510,552, and US 5,679,878. The catalyst typically comprises iron oxide and, additionally, may comprise chromium oxide and potassium compounds, such as potassium carbonate, as promoters. Since the process is highly endothermic, energy for the process is obtained by introducing superheated steam into the process reactor, which may typically comprise a fixed or fluidized bed. Steam also functions to promote catalyst regeneration in situ during the dehydrogenation process. Usually, a high steam to ethylbenzene weight ratio is required, typically from greater than about 0.9/1 to about 2.0/1 and possibly higher, which imposes on the process a high energy input and a large water recycle.

Along similar lines, art such as International Patent Application publication no. WO 01/23336 (International Patent Application PCT/EP00/09196, SnamProgetti S.p.A.) 5 discloses the dehydrogenation of ethylbenzene to styrene in a fluidized bed reactor employing a catalyst based on iron oxide optionally promoted with other metal oxides including alkaline oxides, alkaline earth oxides, and/or the oxides of lanthanide rare earth metals supported on alumina. The process, however, does not introduce steam for heat or catalyst regeneration. Instead, the catalyst is cycled to a separate regenerator for regeneration under air. The l o selectivity to styrene achieved in this process is disadvantageously low for commercial applications.

Other art, represented by EP-A1-0,335,130, discloses the oxidative dehydrogenation of ethylbenzene in the presence of oxygen and a mixed oxide catalyst to form styrene. The mixed oxide catalyst may be represented, for example, by the formula:

15 xA.yB.zC.qO wherein, among other requirements, A is an alkali metal; B is a cation with an ionization state 1 greater than the ionization state of C; and B is selected from scandium, yttrium, lanthanum, actinium, aluminum, boron, and mixtures thereof from Group IIIA and IIIB of the Periodic Table, when C is selected from beryllium, magnesium, calcium, strontium,

20 barium, radium, zinc, cadmium, mercury, and mixtures thereof from Groups IIA and IIB of the Periodic Table. Oxidative dehydrogenation processes require the undesirable combination of oxygen and hydrocarbon feed. Moreover, the process produces large amounts of cracking and oxidation by-products, including carbon monoxide and carbon dioxide.

25 Yet other art, represented by US 4,172,853, discloses the dehydrogenation of ethylbenzene in the presence of a catalyst contairiing a platinum group component, a Group IN metallic component, preferably tin; a lanthanide series component, and an alkali or ajkaline earth component on a porous carrier, such as alumina. The disclosed process produces a significant quantity of cracking by-products and a low selectivity to styrene.

30 In respect of alkanes, art represented by US 5,196,634 discloses the oxidative dehydrogenation of alkanes or alkyl aromatics in the presence of oxygen with a catalyst comprising at least one cationic species of a Group IIIB element, for example lanthanum, at least one cationic species of a Group IIA metal, and a cationic species of dun num. Again, the process requires oxygen, which is undesirable for use with hydrocarbons. The examples illustrate alkane oxidative dehydrogenation with high yields of cracking by-products and oxidation products. Additional art, such as US 5,633,421, discloses dehydrogenation of light paraffins, in particular C₂.₅ paraffins, to light olefins in a fluidized bed reactor with a catalyst comprising platinum, tin, potassium, an element of the lanthanide group, and alumina. Again, this process provides for low olefin selectivity.

Yet other art, such as EP-Bl-0,637,578 (SnamProgetti S.p.A.), discloses 0 dehydrogenating a light paraffin, such as propane, over a catalyst comprising gallium, platinum, one or more alkaline or alkaline earth metals, supported on an alumina support to yield light olefins, such as propylene. Although the catalyst activity and selectivity to olefin may be acceptable, the gallium component of the catalyst detrimentally increases catalyst cost. 5 With respect to integrated processes, EP-A1-0905112 (SnamProgetti S.p.A.) discloses a process for producing styrene comprising (a) feeding to an alkylation unit a stream contaming benzene and ethylene; (b) mixing the stream at the outlet of the alkylation unit, containing ethylbenzene, with a stream consisting of ethane; (c) feeding the mixture thus obtained to a dehydrogenation unit containing a catalyst capable of contemporaneously o dehydrogenating ethane and ethylbenzene; (d) feeding the product leaving the dehydrogenation unit to a separation section to produce a stream consisting of styrene and a stream containing ethylene; and (e) recycling the stream containing ethylene to the alkylation unit. As a dehydrogenation catalyst, the process employs either gallium oxide and platinum on alumina, or chromium oxide, tin oxide, alkaline oxide, and silica on alumina. The gallium 5 catalyst is obtainable at high expense; while the chromium catalyst produces low selectivity. While numerous prior art processes are available, a need exists for an improved dehydrogenation process to convert an alkyl aromatic compound, such as ethylbenzene, to a vinyl aromatic compound, such as styrene. It would be desirable if the process did not require steam and oxygen. It would be more desirable if the process employed a catalyst o comprised of inexpensive components of acceptable economics. It would be even more desirable if the process achieved a high conversion of alkyl aromatic compound and a high selectivity to vinyl aromatic compound with little or no selectivity to cracking and oxidation by-products. Finally, it would be most desirable if the dehydrogenation catalyst was capable of simultaneously dehydrogenating mixtures of an alkyl aromatic compound and an alkane, such as ethylbenzene and ethane, to form product mixtures containing vinyl aromatic compound and an alkene, such as styrene and ethylene. Potentially, such a process might be 5 beneficially applicable to an integrated process of producing styrene from a raw materials base comprised of benzene and ethane.

In one aspect, this invention provides for a novel process of dehydrogenating an alkyl aromatic compound to form a vinyl aromatic compound. The novel process comprises contacting a dehydrogenation feedstream comprising an alkyl aromatic compound with a o dehydrogenation catalyst under reaction conditions sufficient to produce a dehydrogenation product stream comprising the vinyl aromatic compound. In one embodiment of this invention, the catalyst comprises at least one rare earth element on a catalyst support, the catalyst being essentially free of iron oxide and platinum group metal, as described hereinafter. In a second embodiment, the catalyst comprises a mixed oxide of at least one 5 rare earth element and at least one other metallic element selected from the group consisting of almninum, cobalt, chromium, manganese, and mixtures thereof. Mixtures of the aforementioned first and second types of catalysts may also be employed.

In a related aspect of this invention, the dehydrogenation feedstream may additionally comprise an alkane, and the dehydrogenation product stream may additionally comprise an o alkene.

The novel dehydrogenation process of this invention finds utility in the preparation of vinyl aromatic compounds of industrial significance, including styrene, p-methylstyrene, α-methylstyrene, and divinylbenzene. Moreover, if an alkane is additionally present in the dehydrogenation feedstream, then both vinyl aromatic compound and alkene may be 5 produced simultaneously. The novel dehydrogenation process of this invention possesses significant advantages as compared with prior art processes. Firstly, the process of this invention does not employ steam in the dehydrogenation feed. Accordingly, the process of this invention eliminates the need for water recycle and may consume less energy than steam- based processes. Secondly, the process of this invention does not employ oxygen. o Accordingly, safety problems associated with handling and processing mixtures of hydrocarbons and oxygen are also eliminated. Additionally, by avoidance of oxygen in the process of this invention, the loss of raw material to oxidized by-products is essentially eliminated. Even more advantageously, the process of this invention does not require expensive catalyst components, such as gallium or platinum group metals, but instead, employs more cost-effective rare earth metals. Most advantageously, the process of this invention achieves acceptable conversion of alkyl aromatic compound and high selectivity to vinyl aromatic compound, preferably styrene, as compared with prior art processes. All of the aforementioned advantages render the dehydrogenation process of this invention attractive for commercial applications.

In a second aspect, this invention provides for a novel integrated process of preparing a vinyl aromatic compound using as a raw material base an aromatic compound and an alkane. In this aspect the process comprises (a) contacting an alkane with a first dehydrogenation catalyst under reaction conditions sufficient to produce an alkene;

(b) contacting the alkene with an aromatic compound in the presence of an alkylation catalyst under reaction conditions sufficient to produce an alkyl aromatic compound; and

(c) contacting the alkyl aromatic compound with a second dehydrogenation catalyst under reaction conditions sufficient to produce the vinyl aromatic compound. The second dehydrogenation catalyst, employed in step (c), comprises at least one rare earth element on a catalyst support, with the proviso that the catalyst is essentially free of iron oxide and platinum group metal, as specified hereinafter; or alternatively, comprises a mixed oxide of at least one rare earth element and at least one other metallic element selected from the group consisting of aluminum, cobalt, chromium, manganese, and mixtures thereof; or comprises a mixture of both types of catalysts.

In a related aspect of the aforementioned integrated process, the first dehydrogenation catalyst for step (a) is identical to the second dehydrogenation catalyst for step (c). In another related aspect of this invention, dehydrogenation steps (a) and (c) are conducted simultaneously in the same reactor with the same dehydrogenation catalyst.

The integrated process described hereinabove can be employed to provide vinyl aromatic compound, such as styrene, from a raw material base comprised of aromatic compound, such as benzene, and alkane, such as ethane. In contrast, prior art processes traditionally produce the vinyl aromatic compound from a raw material base comprised of aromatic compound and alkene, the latter being derived from large, complex, and capital- intensive cracker units. The integrated process of this invention beneficially allows for the production of vinyl aromatic compound without the need for a capital-intensive cracker. Moreover, when the dehydrogenation of alkyl aromatic compound and alkane are conducted simultaneously in one reactor, the entire integrated process to form vinyl aromatic compound beneficially requires only one dehydrogenation unit and one alkylation unit.

The invention described herein involves, in one aspect, a novel process of 5 dehydrogenating an alkyl aromatic compound, such as ethylbenzene, to form a vinyl aromatic compound, such as styrene. Beneficially, the process of this invention can be integrated into a larger process of preparing a vinyl aromatic compound, such as styrene, from a raw material base comprising an aromatic compound, such as benzene, and an alkane, such as ethane. Features of the integrated process will become apparent to those of skill in the art as o the individual aspects of this invention are fully described hereinbelow.

In its first aspect, the novel process comprises contacting a dehydrogenation feedstream comprising an alkyl aromatic compound with a dehydrogenation catalyst under reaction conditions sufficient to produce a dehydrogenation product stream comprising the vinyl aromatic compound. In a first embodiment, the catalyst employed in the process of this 5 invention comprises at least one rare earth element on a catalyst support, the catalyst composition being essentially free of iron oxide and platinum group metal. In this context the term "essentially free of iron oxide" shall mean that the total concentration of iron oxide is less than 1 percent by weight, based on the total weight of the catalyst composition. The term "essentially free of platinum group metal" shall mean that the total concentration of o platinum group metal is less than about 100 parts per million by weight, calculated as metal and based on the total weight of the catalyst composition. In another embodiment, the catalyst employed in the dehydrogenation process of this invention comprises a mixed oxide of at least one rare earth element and at least one other metallic element selected from the group consisting of aluminum, cobalt, chromium, manganese, and mixtures thereof. 5 Mixtures of the aforementioned types of catalysts may also be employed.

In a preferred embodiment, the dehydrogenation process is conducted in the absence of oxygen. The phrase "absence of oxygen" means that oxygen is not fed to the reactor as a co-reactant. Trace amounts of oxygen, however, may be present in the reactor, inasmuch as the process may be conducted at sub-atmospheric pressures, and as such, the total exclusion 0 of oxygen may be difficult to implement. In another preferred embodiment of the dehydrogenation process of this invention, the alkyl aromatic compound is ethylbenzene or isopropylbenzene, and the vinyl aromatic compound is styrene or α-methylstyrene.

In a related aspect, the dehydrogenation feedstream additionally comprises an aJkane, 5 preferably, ethane. Under such circumstances, the dehydrogenation product stream additionally comprises an alkene, preferably, ethylene.

In a second aspect, this invention provides for a novel integrated process of preparing vinyl aromatic compound using as a raw material base an alkyl aromatic compound and an alkane. In this aspect the process comprises (a) contacting an alkane with a first i o dehydrogenation catalyst under reaction conditions sufficient to produce an alkene;

(b) contacting the alkene with an aromatic compound in the presence of an alkylation catalyst under reaction conditions sufficient to produce an alkyl aromatic compound; and

(c) contacting the alkyl aromatic compound with a second dehydrogenation catalyst under reaction conditions sufficient to produce the vinyl aromatic compound. The second

15 dehydrogenation catalyst used in step (c) of this invention may comprise in one form at least one rare earth element supported on a catalyst support, the composition being essentially free of iron oxide and platinum group metal as defined hereinbefore; or the catalyst may comprise a mixed oxide of at least one rare earth element and at least one other metallic element selected from the group consisting of aluminum, cobalt, chromium, manganese, and mixtiires

2 o thereof; or the catalyst may comprise a mixture of the aforementioned types of catalysts. In a related aspect of this invention, the first dehydrogenation catalyst used in step (a) is identical to the second dehydrogenation catalyst used in step (c). In another related embodiment, steps (a) and (c) are conducted simultaneously in the same reactor unit using the same rare earth-contaiiiing catalyst.

25 The novel process of simultaneously dehydrogenating alkyl aromatic compound and alkane is beneficially suited for integrated processes that convert a raw material base of aromatic compound and alkane to vinyl aromatic compound. The process is preferably suitable for converting benzene or substituted benzene and ethane to styrene or substituted styrene. In a preferred embodiment, therefore, the novel integrated process comprises

3 o (a) contacting ethane with a first dehydrogenation catalyst imder reaction conditions sufficient to produce ethylene; (b) contacting ethylene with benzene or a substituted benzene in the presence of an alkylation catalyst under reaction conditions sufficient to produce ethylbenzene or a substituted ethylbenzene; and (c) contacting ethylbenzene or the substituted ethylbenzene with a second dehydrogenation catalyst under reaction conditions sufficient to produce styrene or a substituted styrene; wherein the second dehydrogenation catalyst used in step (c) may comprise at least one rare earth element supported on a catalyst support, the composition being essentially free of iron oxide and platinum group metal as defined hereinbefore; or may comprise a mixed oxide of at least one rare earth element and at least one other metallic element selected from the group consisting of aluminum, cobalt, chromium, and manganese, and mixtures thereof; or may comprise a mixture of the aforementioned types of catalysts. In a most preferred embodiment, steps (a) and (c) for the dehydrogenation of ethane and ethylbenzene or substituted ethylbenzene are conducted simultaneously in the same reactor unit using any of the aforementioned catalysts comprising the rare earth element.

In a most preferred embodiment, this invention comprises an integrated process of preparing styrene comprising (a) feeding ethane to a dehydrogenation reactor wherein the ethane is dehydrogenated in the presence of a dehydrogenation catalyst under reaction conditions sufficient to prepare ethylene; (b) feeding the ethylene to an alkylation reactor wherein the ethylene is contacted with benzene in the presence of an alkylation catalyst under reaction conditions sufficient to prepare ethylbenzene; and (c) feeding the ethylbenzene to the dehydrogenation reactor of step (a) wherein the ethylbenzene is dehydrogenated with the dehydrogenation catalyst under reaction conditions sufficient to prepare styrene; the dehydrogenation catalyst comprising at least one rare earth element on alumina, the catalyst being essentially free of iron oxide and essentially free of a platinum group metal; or the catalyst comprising a rare earth aluminate; or the catalyst comprising a mixture of the aforementioned catalysts. In a preferred embodiment of the aforementioned inventions, the dehydrogenation catalyst support comprises an alumina support, more preferably, a transitional diimina support, as described hereinafter.

In another preferred embodiment, the rare earth metal is selected from lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. In yet another preferred embodiment, the dehydrogenation catalyst composition further comprises one or more promoters selected from Group LA, Group IIA, and zinc elements of the Periodic Table, as referenced, for example, in the Periodic Table of the Elements illustrated in the CRC Handbook of Chemistry and Physics, 75th edition, CRC Press, 1994-1995.

In yet another preferred embodiment, the dehydrogenation catalyst composition has a surface area of greater than about 20 m²/g and less than about 280 m²/g. 5 Any alkyl aromatic compound can be employed in the dehydrogenation process of this invention, provided that a vinyl aromatic compound is produced. The aromatic moiety of the vinyl aromatic compound can comprise, for example, a monocyclic aromatic ring, such as benzene; a fused aromatic ring system, such as naphthalene; or an aromatic ring assembly, such as biphenyl. Preferably, the aromatic moiety is a monocyclic aromatic ring, more o preferably, benzene. The alkyl segment of the alkyl aromatic compound can comprise any saturated, straight, or branched chain hydrocarbon radical, or cyclic hydrocarbon radical, provided that the alkyl radical can be dehydrogenated to a vinyl radical. Non-limiting examples of suitable alkyl radicals include ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, cyclopentyl, cyclohexyl, and higher homologues thereof. Preferably, the alkyl radical 5 is a C₂-Cιo alkyl radical, more preferably, a C₂-C₅ alkyl radical, and most preferably, ethyl or isopropyl. Optionally, the alkyl aromatic compound may be substituted on the aromatic ring with one or more substituents in addition to the alkyl radical; or the alkyl radical itself may be substituted with one or two substituents. The substituents may be active or inactive towards dehydrogenation; but preferably should not interfere with the desired dehydrogenation o process. Suitable substituents include, for example, alkyl moieties, such as methyl, hydroxy, ether, keto, and acid moieties. Non-limiting examples of alkyl aromatic compounds that may be beneficially employed in the process of this invention include ethylbenzene, isopropylbenzene, t-butylbenzene, ethyltoluene, ethylxylene, ethylnaphthalene, ethylbiphenyl, isopropylnaphthalene, isopropylbiphenyl, diethylbenzene, and the like. Preferably, the alkyl 5 aromatic compound is a C₈-C₃₀ alkyl aromatic compound, more preferably, a Cg-ds alkyl aromatic compound, and most preferably, ethylbenzene or a substituted derivative thereof (herein to include ethyltoluene, ethylxylene, diethylbenzene, and α-methylethylbenzene, for instance, isopropylbenzene).

As an optional reactant, the dehydrogenation feed may also contain an alkane, which o for this invention shall be defined as any saturated aliphatic hydrocarbon having two or more carbon atoms that is capable of being dehydrogenated to an alkene (olefin). The alkane may be straight-chained, branched, or cyclic. The alkane may be substituted at any carbon with one or more substitutents, provided that such substituents do not substantially interfere with the dehydrogenation of the alkyl aromatic compound or the alkane itself. Suitable non- limiting examples of alkanes include ethane, propane, butane, pentane, hexane, heptane, and octane, including straight and branched isomers thereof and higher homologues thereof; as well as cyclopentane and cyclohexane; and any mixtures of the foregoing compounds.

Preferably, the alkane is a C₂-ι₀ alkane, more preferably, a C₂.₆ alkane, most preferably, ethane or propane.

Optionally, a diluent may be provided with the alkyl aromatic feedstream. The diluent functions to dilute the reactants and products for improved selectivity. Alternatively, the diluent may aid in the transfer and equilibration of heat. Any gas that is substantially inert with respect to the dehydrogenation process may be suitably employed as the diluent including, for example, nitrogen, argon, helium, carbon dioxide, methane, and mixtures thereof. The concentration of diluent in the alkyl aromatic feedstream can vary depending, for example, upon the specific diluent, alkyl aromatic compound, catalyst, and dehydrogenation conditions selected. Typically, the concentration of diluent is greater than about 20 volume percent, preferably, greater than about 40 volume percent, and more preferably, greater than about 75 volume percent, based on the dehydrogenation feedstream comprising alkyl aromatic compound, diluent, and optional feed, such as alkane. Typically, the concentration of diluent is less than about 98 volume percent, preferably, less than about 90 volume percent, based on the dehydrogenation feedstream comprising alkyl aromatic compound, diluent, and optional feed, such as alkane.

Oxygen is not required for the dehydrogenation process of this invention. Preferably, the process is conducted in the absence of oxygen, which shall be taken to mean that oxygen is not fed to the reactor as a co-reactant. Likewise, steam is not required for the dehydrogenation process of this invention, and preferably, is not fed to the reactor. For clarification, it is noted that air or oxygen is typically employed in a separate regenerator to burn off coke on the dehydrogenation catalyst, and steam is produced during such regeneration.

The catalyst employed in the dehydrogenation of the alkyl aromatic compound may be provided in any of the following forms described herein. In a first form, the catalyst comprises one or more rare earth elements, deposited on a catalyst support. The rare earths are a group of 17 elements consisting of scandium (atomic number 21), yttrium (atomic number 39) and the lanthanides (atomic numbers 57-71) [James B. Hedrick, U.S. Geological Survey - Minerals Information - 1997, "Rare-Earth Metals"]. For the purposes of this invention, the "rare earth elements" shall be selected from scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, 5 holmium, erbium, thulium, ytterbium, and lutetium. The preferred rare earth element for this invention is selected from lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. More preferably, the rare earth element comprises lanthanum or a mixture of lanthanum with other rare earth elements.

The description herein of the rare earth as an "element" is not meant to imply that the i o rare earth is present substantially in an elemental or zerovalent state on the catalyst support. For the purposes of this invention, the rare earth element may be present in any available oxidation or valence state, or mixture of valences, provided that the catalyst is operable in the dehydrogenation process described herein. Valences ranging from zerovalent to the highest valence available to the specific rare earth, typically, about +3, are acceptable.

15 Typically, however, the rare earth elements are not readily susceptible to reduction to elemental metal; and in fact, the more irreducible rare earths tend to yield catalysts of higher stability. Additionally, in this form of the catalyst the rare earth element is typically not detectable by X-ray diffraction as a pure oxide phase; but such an observation should not limit the invention in any manner.

2 o The loading of the rare earth element(s) on the catalyst support can be any loading that gives rise to a dehydrogenation catalyst composition selective for vinyl aromatic compound. The loading of rare earth element(s) is usually greater than about 0.05 weight percent, and preferably, greater than about 1 weight percent, calculated as metal and based on the total weight of the catalyst composition. The loading of rare earth element(s) is 25 usually less than about 20 weight percent, preferably, less than about 15 weight percent, calculated as metal and based on the total weight of the catalyst composition.

The catalyst support can be any conventional support that functions as a carrier for the rare earth element(s) and that does not inhibit the dehydrogenation process of this invention. Suitable supports include, without limitation, alumina, silica, sinca-aliiminas,

3 o aluminosilicates, zirconia, titania, and the like. Preferably, the support comprises alumina, more preferably a transitional aliimina, suitable examples of which include gamma, delta, theta, and eta aluminas, and mixtures thereof. Mixtures of the aforementioned transitional alii inas with alpha alumina are also suitable. More preferably, the alumina comprises a delta or theta transitional alumina or mixture thereof, optionally combined with alpha alumina. Mixtures of dumina with other support materials, such as silica, in any suitable combination, may also be employed. 5 The aforementioned dehydrogenation catalyst composition comprising one or more rare earth elements on a catalyst support is required to be essentially ree of iron oxide, which means that the concentration of iron oxide in the catalyst is typically less than about 1 weight percent, preferably, less than about 0.1 weight percent, and more preferably, less than about 0.01 weight percent, based on the total weight of the catalyst composition. The o presence of iron oxide tends to decrease selectivity to vinyl aromatic compound and increase by-product formation.

Likewise, the aforementioned catalyst comprising one or more rare earth elements on a catalyst support is required to be essentially free of platinum group metal, that group to include ruthenium, rhodium, palladium, osmium, iridiuin, platinum, and any mixture thereof. 5 The phrase "essentially free of platinum group metal" means that the total concentration of platinum group metal is typically less than about 100 parts per million (ppm) by weight, calculated as metal and based on the total weight of the catalyst composition. Preferably, the concentration of platinum group metal is less than about 50 ppm by weight. The presence of platinum group metal tends to increase cracking by-products while decreasing selectivity to o vinyl aromatic product.

Optionally, the dehydrogenation catalyst described hereinabove may be provided in a form that is essentially free of Group INA metals. In this context, Group INA metals are intended to include tin, germanium, and lead. (Silicon shall not be included in this description, as the use of silica in the catalyst support is acceptable.) In this context, the 5 phrase "essentially free of Group INA metals" means that the total concentration of

Group INA metals, preferably tin, is typically less than about 100 parts per million (ppm), preferably, less than about 50 ppm, and more preferably, less than about 25 ppm by weight, calculated as the oxide and based on the total weight of the catalyst composition. The presence of tin tends to increase cracking by-products while decreasing the formation of o vinyl aromatic product.

The dehydrogenation catalyst of this invention comprising at least one rare earth element supported on a catalyst support can be prepared by conventional methods, including for example impregnation, deposition precipitation, and ion-exchange. Preferably, the catalyst is prepared by impregnation, which is known in the art and described, for example, by Charles N. Satterfield in Heterogeneous Catalysis in Practice, McGraw-Hill Book Company, New York, 1980, 82-84. A more preferred impregnation method involves impregnation to incipient wetness, wherein the impregnation solution containing one or more soluble compounds or salts of the desired rare earth element(s) (and optional promoter element(s) as described hereinafter) is wetted onto the support to the point of beginning wetness. One or more impregnating solutions may be employed, as needed. Soluble rare earth compounds and salts that may be suitably employed in the impregnation solution 0 include, for example, the rare earth halides, preferably the chlorides; and rare earth nitrates, bicarbonates, sulfates, and carboxylates. The impregnation solutions may be prepared with aqueous or non-aqueous solvents; although typically water is preferred. The concentration of selected rare earth or promoter element in the impregnation solution typically ranges from about 0.01 M to the solubility limit of the selected soluble compound or salt. The 5 impregnation may be conducted at any convenient temperature and pressure. Generally, the impregnation temperature is greater than about 10°C and less than about 100°C, more preferably, about ambient temperature, taken as about 22°C. The impregnation is typically conducted at ambient pressure, but other pressures may also be suitable. Following impregnation with the desired rare earth metal(s), the support is calcined at a temperature o sufficient to yield the dehydrogenation catalyst of the invention. Generally, the calcination temperature is greater than about 400°C, preferably, greater than about 500°C. Generally, the calcination temperature is less than about 1,100°C, and preferably, less than about 850°C.

In a second embodiment of this invention, the catalyst employed in the dehydrogenation of the alkyl aromatic compound may comprise a mixed oxide of at least one 5 rare earth element and at least one other metallic element, the rare earths being identified hereinbefore. The additional metallic element may be selected from aluminum, cobalt, chromium, manganese, and mixtures thereof. At the current time, aluminum is more preferred. The mixed oxide composition may be a stoichiometric compound or a non- stoichiometric composition. The mixed oxide may be crystalline, quasi-crystalline, or o amorphous, as determined by X-ray diffraction. Preferably, the mixed oxide is a rare earth aluminate, more preferably, a rare earth duminate of stoichiometric ratio RAlO₃, wherein R is the rare earth element or mixture of rare earth elements. A most preferred rare earth aluminate is lanthanum aluminate (LaAlO₃). The percentage rare earth in the mixed oxide may be any percentage determined by the composition stoichiometry; for example, the percentage lanthanum in lanthanum aluminate equals about 65 mole percent. The mixed oxides, including the preferred rare earth aluminate, may be obtained commercially or 5 prepared by synthetic methods described in the art, including for example, by precipitation from basic solution.

Optionally, the dehydrogenation catalyst, either in the form of supported rare earth or rare earth mixed oxide, may further comprise one or more promoters selected from the group consisting of Group IA, Group IIA, and zinc elements of the Periodic Table, and o mixtures thereof. The Group IA and IIA promoter element(s) may function to increase catalyst activity, or increase selectivity to the desired dehydrogenation product, or increase catalyst lifetime, or provide a combination of such positive effects. Preferred Group IA elements include lithium, sodium, potassium, rubidium, and cesium, more preferably, potassium. Preferred Group IIA elements include magnesium, calcium, strontium, and 5 barium. When one or more Group IA and/or Group IIA promoters are employed, then the total quantity of such elements is typically greater than about 0.01 weight percent, and preferably, greater than about 0.1 weight percent, calculated as oxide and based on the total weight of the catalyst composition. If one or more Group IA and/or Group IIA promoters are employed, then the total quantity thereof is typically less than about 20 weight percent, o and preferably, less than about 10 weight percent, calculated as oxide and based on the total weight of the catalyst composition.

Additionally, zinc has been found to be a useful promoter, being especially effective in enhancing the dehydrogenation of alkane present in the feed. If zinc is employed, then the zinc loading is typically greater than about 0.01 weight percent, and preferably, greater than 5 about 0.1 weight percent, calculated as zinc oxide and based on the total weight of the catalyst composition. If zinc is employed, then the zinc loading is typically less than about 20 weight percent, and preferably, less than about 10 weight percent, calculated as zinc oxide and based on the total weight of the catalyst composition.

The incorporation of promoter elements into the catalyst composition may be o effected by conventional techniques, for example, in a manner analogous to that described hereinabove in connection with impregnation of the rare earth elements. In yet another embodiment, any of the aforementioned dehydrogenation catalyst compositions can be bound, compacted, or extruded with or deposited onto a secondary support that may function, for example, to bind and strengthen the catalyst particles and improve attrition resistance. Non-limiting examples of suitable secondary supports include 5 alumina, silica, silica-alumina, silicon carbide, titanium oxide, zirconium oxide, zirconium silicate, as well as other similar refractory oxides and ceramic supports, and combinations thereof. A preferred secondary support is silica. The quantity of secondary support that may be used can vary depending upon the specific catalyst components; but typically, the quantity of secondary support comprises greater than about 1 weight percent, and preferably, greater o than about 5 weight percent, based on the total weight of the catalyst composition and secondary support. Typically, the quantity of secondary support comprises less than about 30 weight percent, and preferably, less than about 20 weight percent, based on the total weight of the catalyst composition including secondary support.

The catalyst used for the dehydrogenation of alkane in step (a) of the integrated 5 process may be any catalyst that functions in such capacity, for example, as described in

US 5,196,634, US 5,633,421, and EP-Bl-0,637,578, incorporated herein by reference. In a preferred embodiment, however, the catalyst used in the dehydrogenation of alkane is identical to any form of the rare earth catalysts described herein for the dehydrogenation of alkyl aromatic compound. o Various conventional reactor designs are acceptable for the dehydrogenation of alkyl aromatic compound and alkane including fixed bed, transport bed, and fluidized bed reactors, operating under continuous flow or intermittent flow modes. A fluidized bed reactor is preferred. More preferably, the fluidized bed reactor contains internal structures (internals) that facilitate plug flow behavior. In a preferred embodiment, the reactor is designed for 5 countercurrent flow, such that the dehydrogenation feed and the catalyst are fed at opposite ends of the reactor and flow in opposite directions. Preferably, the dehydrogenation catalyst is continuously transported out of the reactor to a regenerator for regeneration; after which the regenerated catalyst is recycled back to the dehydrogenation reactor.

No limitations need be placed on catalyst particle size, shape, or density, provided o that the catalyst is suitable for the selected reactor design and active in the dehydrogenation process. If the catalyst is provided to a fluidized bed reactor, as is the preferred mode of operation, then the catalyst average particle diameter, shape, and density should be such as to provide for acceptable attrition resistance and acceptable flow and transport properties. Preferably, the catalyst has the properties of, and is classified as, a Group-A particle according to Geldart (Gas Fluidization Technology, D. Geldart, John Wiley & Sons). Accordingly, the average catalyst particle diameter is typically greater than about 5 microns (μm), and preferably, greater than about 50 μm. Typically, the average catalyst particle diameter is less than about 500 μm, and preferably, less than about 300 μm. The surface area of the catalyst typically exceeds about 20 m²/g, as determined by the BET (Brunauer- Emmet-Teller) method, described by S. Brunauer, P. H. Eromett, and E. Teller, Journal of the American Chemical Society, 60, 309 (1938). Preferably, the surface area is greater than about 40 m²/g, more preferably, greater than about 60 m²/g, and most preferably, greater than about 80 m²/g. Typically, however, the surface area is less than about 280 m²/g, and more preferably, less than about 150 m²/g. Preferably, the catalyst particles are smooth with rounded edges, are substantially non-cohesive, and possess an attrition resistance appropriate for use in a fluidized bed reactor, as known to those of skill in the art. When a fluidized bed reactor is employed for the dehydrogenation process, then optionally a sweeping gas may be used in the process of this invention. Fluidized bed reactors usually comprise at least two zones: a reaction zone for the fluidized bed and a freeboard zone above the fluidized bed. The freeboard zone comprises a free space that allows for expansion of the catalyst volume on fluidization. The sweeping gas is typically introduced into the freeboard zone and primarily functions to remove products from the freeboard zone so as to minimize undesirable thermal reactions. Any gas that is substantially inert with respect to the dehydrogenation process may be suitably employed as the sweeping gas, including, for example, nitrogen, argon, helium, carbon dioxide, and mixtures thereof. The concentration of sweeping gas in the freeboard zone can vary widely, depending, for example, upon the specific alkyl aromatic and/or alkane feeds and specific process conditions employed, particularly, temperature and gas velocity. Typically, the concentration of sweeping gas in the freeboard zone is greater than about 10 volume percent, and preferably, greater than about 20 volume percent. Typically, the concentration of sweeping gas in the freeboard zone is less than about 90 volume percent, and preferably, less than about 70 volume percent.

If desired, the dehydrogenation feedstream may be preheated before entry into the dehydrogenation reactor. Any preheat temperature can be used, provided it lies below the temperature at which thermal cracking of the alkyl aromatic and/or alkane becomes measurable. Typical preheat temperatures are greater than about 150°C, preferably, greater than about 250°C, and more preferably, greater than about 350°C. Typical preheat temperatures are less than about 500°C, and preferably, less than about 400°C. The temperature of the dehydrogenation zone can be any operable temperature, provided that a vinyl aromatic compound and/or alkene are produced in the process. The operable dehydrogenation temperature will vary with the specific catalyst and reactant feed. Typically, the dehydrogenation temperature is greater than about 400°C, and preferably, greater than about 425°C. Typically, the dehydrogenation temperature is less than about 0 750°C and, preferably, less than about 675°C. Below about 400°C, the conversions of alkyl aromatic compound and alkane may be too low; whereas above about 675°C, thermal cracking of the reactants may occur. In fluidized bed reactors, the temperature is typically measured on the catalyst bed in fluidized form.

The dehydrogenation process can be conducted at any operable total pressure, 5 ranging from subatmo spheric to superatmospheric, provided that the vinyl aromatic product is produced, and if desired, the alkene. If the total reactor pressure is too high, the equilibrium position of the dehydrogenation process may be shifted backwards towards alkyl aromatic compound and/or alkane. Preferably, the process is conducted under vacuum to maximize the yield of vinyl aromatic product and alkene. Preferably, the total pressure is o greater than about 1 psia (6.9 kPa), more preferably, greater than about 3 psia (20.7 kPa). Preferably, the total pressure is less than about 73 psia (503.3 kPa), more preferably, less than about 44 psia (303.4 kPa). Most preferably, the total pressure is subatmospheric, ranging between about 3 psia (20.7 kPa) and about 13 psia (90.6 kPa). In a fluidized bed reactor, the pressure throughout the freeboard and reaction zones may vary depending upon 5 process factors, such as the weight and buoyancy of the catalyst and frictional effects.

The gas hourly space velocity of the dehydrogenation reactant feedstream will depend upon the specific alkyl aromatic compound and catalyst employed, the specific vinyl aromatic product formed, the reaction zone dimensions (for example, diameter and height), and the form and weight of the catalyst particles. For the dehydrogenation of alkane to o alkene, analogous variations in space velocity are found. It is desirable to remove the reactant and products quickly from the reactor, so as to reduce thermal cracking and other undesirable side reactions. In fluidized bed reactors specifically, gas flow should be sufficient to induce fluidization of the catalyst bed. Generally, the space velocity of the dehydrogenation feedstream varies from the minimum velocity needed to achieve fluidization of the catalyst particles to a velocity just below the minimum velocity needed to achieve pneumatic transport of the catalyst particles. Fluidization occurs when the catalyst particles 5 are disengaged, when the particles move in a fluid-like fashion, and when the bed pressure drop is essentially constant along the bed. Pneumatic transport occurs when an unacceptable quantity of catalyst particles are entrained in the gas flow and transported out of the reactor. Preferably, the space velocity of the dehydrogenation feedstream varies from the minimum bubbling velocity to a bubbling velocity just below the minimum turbulent flow velocity. o Bubbling occurs when gas bubbles can be seen in the fluidized bed, but little back-mixing of gas and solids occurs. Turbulent flow occurs when there is both substantial bubbling and substantial back-mixing of gas and solids. More preferably, the flow is sufficient to cause bubbling, but not substantial back-mixing.

In view of the above, the normal gas hourly space velocity (GHSV), calculated as the 5 total flow of dehydrogenation feedstream comprising alkyl aromatic compound, optional diluent, optional sweeping gas, and optional alkane is typically greater than about 60 ml total feed per ml catalyst per hour (h^"1), measured at standard conditions of atmospheric pressure and 0°C. Preferably, the GHSV of the dehydrogenation stream is greater than about 120 h^"1, and more preferably, greater than 300 h^"1 at standard conditions. Generally, the GHSV of o the dehydrogenation stream is less than about 10,000 h^"1, preferably, less than about

3,600 h^"1, and more preferably, less than 700 h^"1, measured as total flow at standard conditions.

For this invention, the gas residence time in the dehydrogenation zone may be calculated as the height of the reaction zone times the reaction zone voidage fraction divided 5 by the superficial gas velocity of the reaction feedstream. The "reaction zone voidage fraction" is the fraction of the reaction zone which is empty. The "superficial gas velocity" is the gas velocity through the empty reactor. Typically, the gas residence time in the reaction zone is greater than about 0.3 seconds (sec), measured at operating conditions. Preferably, the gas residence time in the reaction zone is greater than about 1 sec, more preferably, o greater than about 2 sec, measured at operating conditions. Generally, the gas residence time in the reaction zone is less than about 60 sec, preferably, less than about 30 sec, and more preferably, less than about 5 sec, measured at operating conditions. When an alkyl aromatic compound is contacted with the dehydrogenation catalyst in the manner described hereinbefore, a vinyl aromatic compound is produced. Ethylbenzene, for example, is converted primarily to styrene. Likewise, ethyltoluene is converted to p-methylstyrene (p-vinyltoluene); t-butylethylbenzene is converted to t-butylstyrene; 5 isopropylbenzene (cumene) is converted to α-methylstyrene; and diethylbenzene is converted to divinylbenzene. Hydrogen is also formed during dehydrogenation. By-products produced in lower yields include benzene, toluene, tar, and coke.

The conversion of the alkyl aromatic compound in the process of this invention can vary depending upon the specific feed composition, catalyst, reactor, and process conditions o used. For the purposes of this invention, the term "conversion of alkyl aromatic compound" is defined as the mole percentage of alkyl aromatic compound converted to all products. In this process, the conversion of alkyl aromatic compound is typically greater than about 30 mole percent, preferably, greater than about 40 mole percent, and more preferably, greater than about 50 mole percent. 5 Likewise, the selectivity to products will vary depending upon the specific feed composition, catalyst, reactor, and process conditions. In this context, "selectivity" is

' defined as the mole percentage of converted alkyl aromatic compound that forms a specific product, preferably, vinyl aromatic compound. In the process of this invention, the selectivity to vinyl aromatic compound, preferably styrene or substituted styrene, is typically o greater than about 70 mole percent, preferably, greater than about 80 mole percent, and more preferably, greater than about 90 mole percent.

All of the aforementioned dehydrogenation process conditions may be employed as described or modified by those of skill in the art to facilitate the dehydrogenation of the alkane to alkene. Conventional alkane dehydrogenation catalysts may be used in step (a) of 5 the integrated process; however, advantageously, the rare earth catalysts described herein may be suitably employed for alkane dehydrogenation, preferably, simultaneously with alkyl aromatic dehydrogenation (step (c)). The conversion of alkane and selectivity to alkene achieved varies analogously as well. Typically, the alkane conversion, defined as the mole percentage of alkane converted to all products, is greater than about 0.1 mole percent, o preferably, greater than about 1.5 mole percent. Typically, the selectivity to alkene, defined as the mole percentage of converted alkane that forms alkene, is greater than about 1 mole percent, preferably, greater than about 1.5 mole percent, and more preferably, greater than about 2.0 mole percent.

When the dehydrogenation catalyst is sufficiently deactivated, it may be transported to a separate zone for regeneration. Regeneration typically involves burning out the catalyst 5 under air or oxygen, or some diluted variation thereof. The regeneration feedstream comprising deactivated catalyst, optional diluent and sweeping gas can be preheated prior to introduction into the regenerator. A typical preheat temperature is greater than about 200°C, preferably, greater than about 300°C, and more preferably, greater than about 400°C. The preheat temperature is typically less than about 650°C, and preferably, less than about 630°C. o Typically, the regeneration temperature lies below the minimum temperature for thermally cracking the alkyl aromatic compound and vinyl aromatic product and any optional alkane and alkene. Accordingly, the regeneration temperature is typically greater than about 400°C, and preferably, greater than about 570°C. Typically, the regeneration temperature is less than about 850°C and, preferably, less than about 775°C. 5 The gas hourly space velocity of regeneration gas comprising air, oxygen, or diluted variation thereof, through the regenerator can be broadly varied, provided that the catalyst is regenerated at least in part. Typically, the gas hourly space velocity (GHSV), calculated as the total of the regeneration gas, is greater than about 60 nil total feed per ml catalyst per hour (h^"1), and preferably, greater than about 100 h^"1, measured under standard conditions o (0°C, 1 atm). Generally, the gas hourly space velocity of the regeneration gas is less than about 5,000 h^"1, preferably, less than about 1,000 h^"1, measured under standard conditions.

In the regeneration zone, the gas residence time, calculated as the height of the regeneration zone times the regeneration zone voidage fraction divided by the superficial gas velocity of the total of the regeneration gas is greater than about 0.3 sec, measured at 5 operating conditions. The "regeneration zone voidage fraction" is the fraction of the regeneration zone which is empty. Preferably, the gas residence time in the regeneration zone is greater than about 1 sec, and more preferably, greater than about 5 sec. Generally, the gas residence time in the regeneration zone is less than about 60 sec, preferably, less than about 30 sec, and more preferably, less than about 10 sec, measured at operating conditions. 0 In the integrated process contemplated in this invention, an alkane is dehydrogenated to an alkene; thereafter, an aromatic compound is alkylated with the alkene to form an alkyl aromatic compound; and the alkyl aromatic compound is dehydrogenated to form a vinyl aromatic compound. As noted above, alkane dehydrogenation can be conducted using prior art process methods, or the methods disclosed in this invention. The alkylation step can be conducted with any conventional alkylation catalyst and process conditions known to those of skill in the art, as illustrated for example, in US 5,430,211, US 4,409412, US 5,157,185, 5 US 4,107,224, US 5,856,607, and EP-B1-0,432,814, incorporated herein by reference. Other prior art alkylation processes may also be employed.

The invention will be further clarified by a consideration of the following examples, which are intended to be purely illustrative of the use of the invention. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of this l o specification or practice of the invention as disclosed herein.

Preparation of Catalyst Support

A micro spheroidal alumina support was prepared by spray drying a mixture of hydrated alumina and Ludox® silica (1.4 + 0.2 weight percent) and then heating the resulting spray dried particles at 1,100°C sufficient to achieve a particle surface area of 100 + 10 m²/g. 15 X-ray diffraction analysis of the alumina product detected theta and delta phases (34 and

66 weight percent, respectively) as the major components. The alumina support was dried at 150°C for a minimum of 12 hours prior to use. The catalysts of Examples 1-3 were prepared by incipient wetness techniques using aqueous solutions and the prepared alumina support, as described hereinafter.

20 EXAMPLE 1

A catalyst was prepared comprised of lanthanum (7 weight percent as lanthanum metal) and potassium (1 weight percent as potassium metal) on the alumina support prepared as described hereinabove. The alumina support (200 g) was impregnated with an aqueous solution (80 niL) containing lanthanum nitrate hexahydrate (46.86 g, 0.1082 mol), potassium

25 nitrate (5.91 g, 0.0584 mol) and enough deionized water to make 80 mL of impregnating liquor. The impregnating solution was added to the alumina support in 1 to 2 mL aliquots over the course of 45 min while the sample was continuously mixed at room temperature in a rotary tumbler. After being impregnated, the support was mixed for an additional 45 min while a low flow of compressed air was passed over the sample. The impregnated sample

3 o was then dried for 3 h at 80°C, dried for 12 h at 120°C, and finally calcined for 4 h at 750°C before cooling to room temperature to obtain a catalyst embodiment of this invention. A sample (1.00 g) of the catalyst (density approx. 1.1 g/mL) was loaded into a quartz fixed-bed reactor (0.64 cm O.D.). The reactor was heated to 550°C, as monitored and controlled by an external thermocouple mounted on the side of the reactor tube in the middle of the catalyst bed, under a flow of argon (10 standard cubic centimeters per min, seem). 5 After the reactor reached 550°C, a stream of ethylbenzene (15 volume percent in argon) was fed to the reactor. This feed stream was produced by vaporizing ethylbenzene at a flow of 0.0065 inL/min in an argon flow of 6.75 seem in a vaporizer maintained at 130°C. The sum of the ethylbenzene and argon flows gave a gas hourly space velocity of 500 h^"1 based on the packed volume of the catalyst. One evaluation cycle consisted of a reaction period and a o regeneration period separated by an argon purge. After a reaction period of 11 min, the reactor was flushed with argon (10 seem), and the temperature of the reactor was raised to 650°C, whereupon the reactor was fed a flow of compressed air (8.5 seem). Thereafter, the regeneration period followed with compressed air lasting 20 min. The reactor was then flushed with argon (10 seem) as the temperature of the reactor was lowered to the next 5 reaction temperature. Catalyst testing consisted of twelve evaluation cycles. The reaction temperature of the first six cycles was 550°C, and the reaction temperature of the second six cycles was varied between 520°C and 600°C as shown in Table 1.

Analysis of the reaction products was conducted on stream during the reaction phase of the cycle. A portion of the reactor effluent was periodically diverted to a gas o chromatograph (GC) by means of a six-port valve equipped with a sample loop. Products were analyzed at 3 min and 8 min on stream. The product stream was analyzed for ethylbenzene, styrene, benzene and toluene, and the results were quantified using external standards.

Ethylbenzene conversion was calculated as the ratio of the sum of the styrene, 5 benzene, and toluene concentrations to the sum of the ethylbenzene, styrene, benzene and toluene concentrations, as measured by gas phase chromatography (GC). The selectivity to a given reaction product was calculated as the ratio of the measured concentration of that product versus the sum of the styrene, benzene, and toluene peaks, as measured in the GC. The first four reaction cycles were considered a break-in period and the data were not used 0 in conversion and selectivity calculations. The resulting data are shown in Table 1. Table 1. Dehydrogenation of Ethylbenzene Over Lanthanum Catalyst (Example 1) 1,2

1. Reaction Conditions: Catalyst - La (7 wt%), K (1 wt%), balance alumina; atmospheric pressure; total gas hourly space velocity, 500 h^{' 1} (argon plus ethylbenzene); ethylbenzene, 15 vol gas feed,

2. EB = ethylbenzene

The data in Table 1 illustrate the activity of the rare earth catalyst comprising lanthanum on alumina, absent iron oxide and any platinum group metal, in the dehydrogenation of ethylbenzene to styrene. The catalyst exhibited a styrene selectivity greater than 95 mole percent at acceptable ethylbenzene conversions.

EXAMPLE 2

A sample (93 mL; 1.11 g/mL packed, bulk density) of the catalyst prepared in Example 1 was loaded into a fluidized bed reactor (1 inch (2.5 cm) ID up-flow fluidized bed 5 quartz reactor). The reactor was heated to 550°C as monitored and controlled from an internal thermocouple placed in the center of the reactor and two inches (5.0 cm) from the bottom of the catalyst bed. The ethylbenzene flow was 0.68 n-L/min, and this stream was vaporized and mixed with ethane at 195°C prior to introduction to the reactor. The ethane gas had a flow rate of 0.645 L/min (0°C, 1 atm). The sum of ethane and ethylbenzene flows o gave a gas hourly space velocity of 500 h^"1, based on the packed volume of the catalyst and ideal gas volumes based on normal conditions described above for the diluent flow. One evaluation cycle consisted of a reaction segment and a regeneration segment that were separated by nitrogen purges used to sweep the reactor with an inert gas. The reaction segment lasted for 10 min. Thereafter, a nitrogen purge was passed through the reactor for 15 min. The liquid products were condensed in a liquid nitrogen trap and the residual gaseous products were captured in a gas sampling bag. The nitrogen feed was switched to air at the same flow rate, and the reactor temperature was increased to 650°C for the regeneration segment, which was maintained for 30 min and followed by a second nitrogen purge. The gas stream was collected in a separate bag during the regeneration portion of the cycle. The liquid sample was weighed and analyzed by GC; each of the gas sampling bags was also analyzed by GC. The results were quantified using external standards. Compilation of the three analyses allowed for the calculation of an overall conversion and selectivity for the entire cycle. The main products were styrene, benzene, toluene, alpha-methyl styrene, tar, and coke. Tar was defined as the sum of peaks eluted after alpha-methyl styrene to the end of the temperature ramp of 230°C. The molecular weight of stilbene was used for the average molecular weight of tar. Coke was measured as CO₂ formed during the regeneration. The reactor was then cooled to the next reaction temperature while being purged with nitrogen. The temperature was then set for the next cycle and the above process was repeated again to generate another data point. Cycles were completed at selected reaction temperatures between 550°C and 605°C. The resulting data are shown in Table 2, with the exception that the first six catalytic cycles were used as a break-in period and the data are not recorded.

Table 2. Dehydrogenation of Ethylbenzene in Ethane Stream Over Lanthanum Catalyst

(Example 2)¹'²

1. Reaction Conditions: Catalyst - La (7 wt%), K (1 wt%), balance alumina; atmospheric pressure; total gas hourly space velocity, 500 h^"1 (ethane + ethylbenzene); ethylbenzene, flow 0.68 mL/min

2. EB = ethylbenzene, Eth = ethane, Sty = styrene, Ben = benzene, Tol = toluene, AMS = alpha methyl styrene

The data in Table 2 illustrate the activity of a rare earth catalyst of this invention, absent iron o oxide and any platinum group metal, in the dehydrogenation of ethylbenzene to styrene in a feedstream containing ethane. The catalyst achieved high selectivity to styrene (>85 mole percent) and low selectivities to by-products and tar. Additionally, the activity of the catalyst, measured by ethylbenzene conversion, is acceptable at about 50 mole percent. The catalyst also showed activity for ethane dehydrogenation. 5 EXAMPLE 3

A catalyst comprised of a mixture of rare earth elements (7 wt%) and potassium (metal basis, 1 wt%) on alumina was prepared in the following manner. The impregnating solution was prepared by suspending 1.747 g of a hydrated, mixed rare earth carbonate (30% lanthanum, 2.6% cerium, 1.5% neodymium, 9% praseodymium expressed as weight percent 0 on a metals basis) in deionized water (1 mL). Concentrated nitric acid was added drop wise with stirring until gas evolution ceased and all of the solids had dissolved. To this solution was added potassium nitrate (0.236 g) and enough deionized water to make 4.0 rnL of solution. The alumina support (10.00 g), prepared as described hereinabove, was impregnated by adding the solution several drops at a time, with hand mixing, over the 5 course of 15 min. After being impregnated, the support was dried for 2 h at room temperature followed by drying for 3 h at 80°C, drying for 12 h at 120°C, and finally calcination for 4 h at 750°C. The sample was then tested for catalytic activity in the manner described in Example 1 with the results shown in Table 3.

Table 3. Dehydrogenation of Ethylbenzene Over Mixed Rare Earth Catalyst (Example 3) 1,2

Reaction Conditions: Catalyst - rare earth mixture (lanthanum, praseodymium, neodymium, cerium) (7 wt%), K (1 wt%), balance alumina; atmospheric pressure; total gas hourly space velocity, 500 h^"1 (argon + ethylbenzene); ethylbenzene flow,

0.68 ml/min

EB = ethylbenzene

l o The data in Table 3 illustrate the activity of a mixed rare earth catalyst containing lanthanum, cerium, neodymium, and praseodymium, absent iron oxide and platinum group metal, in the dehydrogenation of ethylbenzene to styrene. The catalyst achieved high selectivity to styrene (>95 mole percent) with low selectiviti.es to by-products and tar.

COMPARATIVE EXPERIMENT 1

15 For comparative purposes, a catalyst comprising iron oxide, yttrium oxide, and potassium oxide supported on dumina was evaluated for catalytic activity in the dehydrogenation of ethylbenzene to styrene. The catalyst comprised iron oxide (3 wt% Fe₂O₃), potassium oxide (3 wt% K₂O), and yttrium oxide (1.1 wt% Y₂O₃). The catalyst was prepared by impregnating the alumina support described in Example 1 (180 g) with an aqueous solution (72 mL) containing iron(III) nitrate nonahydrate (29.44 g, 0.07287 mol), potassium nitrate (12.47 g, 0.1233 mol), yttrium nitrate tetrahydrate (6.32g, 0.01822 mol) and enough deionized water to make 72 mL of impregnating solution. The impregnating solution was added in 1 to 2 mL aliquots over the course of 45 min while the sample was continuously mixed at room temperature in a rotary tumbler. After being impregnated, the support was dried, with occasional mixing, for 4 h at room temperature. The impregnated sample was then dried for 3 h at 80°C, dried for 12 h at 120°C, and then calcined for 4 h at 750°C before cooling to room temperature to obtain the comparative catalyst.

The sample of comparative catalyst (90 mL, 1.12 g/mL packed, bulk density) was 0 tested for catalytic activity in the manner described in Example 2, with the exceptions that nitrogen gas was used in place of ethane and the sum of nitrogen and ethylbenzene flows gave a gas hourly space velocity of 400 h^"1. The resulting data are shown in Table 4.

Table 4. Ethylbenzene Dehydrogenation Over Catalyst Containing Iron Oxide and Rare

Earth (Comparative Experiment)¹'²

5 1. Reaction Conditions: Catalyst - 3 wt% Fe₂O₃, 3 wt% K₂0, 1.1 wt% Y₂O₃, balance alumina; atmospheric pressure; T as shown; GHSV, 400 h^"1 (nitrogen + ethylbenzene); ethylbenzene flow, 0.68 inL/min.

2. EB = ethylbenzene, Sty = styrene, Ben = benzene, Tol = toluene, AMS = alpha methyl styrene o When Comparative Experiment 1 is compared with Example 2, it is seen that the presence of iron oxide in the catalyst lowers the selectivity to styrene and raises selectivities to cracking products, by-products, and tars.

LaAK Catalyst Preparation

An aqueous solution (100 ml) containing lanthanum nitrate hexahydrate (1M, 43.3 g) 5 and an aqueous solution (100 ml) containing aluminum nitrate nonahydrate (1 M, 37.5g) were mixed together and then added slowly and with rapid stirring to an aqueous ammonium hydroxide solution (2M, 500 ml). The resultant slurry was stirred at 20°C for 1 hour. A solid was recovered by centrifugation and washed three times with deionized water (1 liter each wash). The resultant wet cake was dried at 80°C for 12 hours and then calcined at 700°C for 4 hours. The nitrogen BET surface area of the calcined solid was 30 m²/g and the material exhibited an X-ray diffraction powder pattern characteristic for lanthanum aluminate, LaAlO₃. EXAMPLE 4

The lanthanum aluminate composition prepared hereinabove was evaluated as a catalyst for the dehydrogenation of ethylbenzene. A sample (0.10 g) of the LaAlO₃ catalyst (density approx. 1.1 g/mL) was loaded into a quartz fixed-bed reactor (0.64 cm O.D.) and the dehydrogenation was conducted in a manner closely similar to that in Example 1. The reactor was heated to 550°C under a flow of argon (10 seem). After the reactor reached 550°C, a stream of ethylbenzene (20 mole percent in ethane) was fed to the reactor. This feed stream was produced by vaporizing ethylbenzene at a flow of 0.01703 niL/min in an ethane flow of 12.14 seem in a vaporizer maintained at 130°C. The sum of the ethylbenzene and ethane flows gave a gas hourly space velocity of 10,120 h^"1 based on the packed volume of the catalyst. One evaluation cycle consisted of a reaction period (11 min) and a regeneration period (10 min (8.5 seem compressed air, 650°C ) separated by an argon purge. Analysis of the reaction products was conducted on stream during the reaction phase of the cycle as described in Example 1. Products were analyzed at 1.5, 4.5 and 7.5 min on stream. The product stream was analyzed for ethylbenzene, styrene, benzene, toluene, ethane and ethylene. Catalyst testing consisted of six evaluation cycles. Reactor conditions and the resulting data are shown in Table 5.

Table 5. Dehydrogenation of Ethylbenzene (EB) Over Lanthanum Aluminate Catalyst

(Example 4)¹

1. Reaction Conditions: Catalyst - LaAlO₃; atmospheric pressure; total gas hourly space velocity, 10120 h^"1 (ethane plus ethylbenzene); ethylbenzene, 20 vol% gas feed.

The data in Table 5 illustrate the activity of the rare earth catalyst comprising lanthanum aluminate in the dehydrogenation of ethylbenzene to styrene. The catalyst exhibited a styrene selectivity greater than 95 mole percent at acceptable ethylbenzene conversions.

Claims

Claims:

1. A process of preparing a vinyl aromatic compound comprising contacting a dehydrogenation feedstream comprising an alkyl aromatic compound and optionally a diluent with a dehydrogenation catalyst under reaction conditions sufficient to prepare a dehydrogenation product stream comprising a vinyl aromatic compound; the catalyst comprising at least one rare earth element supported on a catalyst support, the catalyst being essentially free of iron oxide and platinum group metal; or the catalyst comprising a mixed oxide of at least one rare earth element and at least one other metallic element selected from the group consisting of aluminum, cobalt, chromium, and manganese, or a mixture thereof; 0 or the catalyst comprising a mixture of the aforementioned catalysts.

2. The process of Claim 1 wherein the alkyl aromatic compound is a C₈-₃o alkyl aromatic compound.

3. The process of Claim 1 wherein the alkyl aromatic compound is selected from ethylbenzene, ethyltoluene, ethylxylene, diethylbenzene, isopropylbenzene, and mixtures 5 thereof.

4. The process of Claim 1 wherein the rare earth metal is selected from lanthanum, praseodymium, neodymium, yttrium, and combinations thereof.

5. The process of Claim 1 wherein the loading of rare earth metal on the catalyst support is greater than about 0.05 and less than about 20 weight percent, calculated as metal o and based on the total weight of the catalyst composition.

6. The process of Claim 1 wherein the catalyst support is selected from alumina, silica, silica-alumina, aluminosilicates, titania, zirconia, and mixtures thereof.

7. The process of Claim 6 wherein the catalyst support comprises a transitional alumina. 5

8. The process of Claim 1 wherein iron oxide comprises less than about 0.1 weight percent, based on the total weight of the catalyst composition.

9. The process of Claim 1 wherein platinum group metal comprises less than about 50 parts per million, calculated as metal and based on the total weight of the catalyst composition.

10. The process of Claim 1 wherein the mixed oxide catalyst comprises at least one rare earth element and aluminum.

11. The process of Claim 10 wherein the mixed oxide catalyst is a rare earth almninate.

5 12. The process of Claim 1 wherein the catalyst further comprises a promoter selected from Group IA, Group IIA, zinc, and combinations thereof.

13. The process of Claim 12 wherein the loading of promoter metal is greater than about 0.01 and less than about 20 weight percent, calculated as metal oxide and based on the total weight of the catalyst composition. 0 14. The process of Claim 1 wherein the catalyst has a surface area greater than about

20 m²/g and less than about 280 m²/g.

15. The process of Claim 1 wherein the catalyst has an average particle diameter of greater than about 5 microns and less about 500 microns.

16. The process of Claim 1 wherein the temperature ranges from greater than about 5 400°C to less than about 750°C.

17. The process of Claim 1 wherein the pressure ranges from greater than about 1 psia (6.9 kPa) to less than about 73 psia (503.3 kPa).

18. The process of Claim 1 wherein the gas hourly space velocity of the dehydrogenation feedstream is greater than about 60 h^"1 and less than about 10,000 h^"1. o

19. The process of Claim 1 wherein a diluent is used, and the diluent is selected from nitrogen, argon, helium, methane, carbon dioxide, and mixtures thereof.

20. The process of Claim 1 wherein the process is conducted in a fluidized bed reactor.

21. The process of Claim 1 wherein the process is conducted in the absence of 5 co-fed oxygen and/or steam.

22. The process of Claim 1 wherein the catalyst is transported to a regenerator for regeneration under air or oxygen at a temperature greater than about 400°C to less than about 850°C.

23. The process of Claim 1 wherein the vinyl aromatic compound comprises styrene, vinyltoluene, vinylxylene, t-butylstyrene, divinylbenzene, Dmethyl styrene, or mixtures thereof.

24. The process of Claim 1 wherein the vinyl aromatic compound is produced in a 5 selectivity of greater than about 90 mole percent.

25. The process of Claim 1 wherein the dehydrogenation feedstream comprises an alkane, and the dehydrogenation product stream comprises an alkene.

26. The process of Claim 1 wherein the dehydrogenation feedstream comprises ethylbenzene and ethane, and the dehydrogenation product stream comprises styrene and 0 ethylene.

27. An integrated process of preparing vinyl aromatic compound comprising (a) dehydrogenating an alkane in the presence of a first dehydrogenation catalyst under reaction conditions sufficient to prepare an alkene; (b) contacting the alkene with an aromatic compound in the presence of an alkylation catalyst under reaction conditions sufficient to 5 prepare an alkyl aromatic compound; and (c) dehydrogenating the alkyl aromatic compound with a second dehydrogenation catalyst under reaction conditions sufficient to prepare a vinyl aromatic compound; the catalyst for step (c) comprising at least one rare earth element on a catalyst support, the catalyst being essentially free of iron oxide and essentially free of platinum group metal; or the catalyst comprising a mixed oxide of at least one rare element o and at least one other metallic element selected from duminum, cobalt, chromium, manganese, and mixtures thereof; or the catalyst comprising a mixture of the aforementioned catalysts.

28. The process of Claim 27 wherein the alkane is ethane; the alkene is ethylene; the aromatic compound is benzene; the alkyl aromatic compound is ethylbenzene; and the vinyl 5 aromatic compound is styrene.

29. The process of Claim 27 wherein the rare earth metal is selected from lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof.

30. The process of Claim 27 wherein the alkane dehydrogenation step (a) occurs simultaneously in the same reactor and with the same catalyst as the alkyl aromatic 0 dehydrogenation step (c).

31. An integrated process of preparing styrene or substituted styrene comprising

(a) feeding ethane to a dehydrogenation reactor wherein the ethane is dehydrogenated in the presence of a dehydrogenation catalyst under reaction conditions sufficient to prepare ethylene; (b) feeding the ethylene to an alkylation reactor wherein the ethylene is contacted with benzene or substituted benzene in the presence of an alkylation catalyst under reaction conditions sufficient to prepare ethylbenzene or substituted ethylbenzene; and (c) feeding the ethylbenzene or substituted ethylbenzene to the dehydrogenation reactor of step (a) wherein the ethylbenzene or substituted ethylbenzene is dehydrogenated with the dehydrogenation catalyst under reaction conditions sufficient to prepare styrene or substituted styrene; the dehydrogenation catalyst comprising at least one rare earth element on alumina, the catalyst being essentially free of iron oxide and essentially free of a platinum group metal; or the catalyst comprising a mixed oxide of at least one rare earth element and aluminum; or the catalyst comprising a mixture of the aforementioned catalysts.

32. The process of Claim 31 wherein the rare earth is lanthanum or a mixture of lanthanum with other rare earth elements.