Background of the Invention Olefins, particularly light olefins, have been traditionally produced from petroleum feedstock by either catalytic or steam cracking. Oxygenates, however, are increasingly becoming an alternative feedstock for making light olefins. In addition to producing light olefms, the oxygenate to olefin process produces a wide variety higher olefin and non-olefin hydrocarbons. In particularly, the oxygenate-to-olefin process produces a substantial amount of C4 hydrocarbons which can be used to produce derivative products.

Maleic anhydride is a versatile monomer and chemical intermediate. The single largest use of maleic anhydride, accounting for over half of its demand, is in the formation of polyester resins. However, maleic anhydride is also used to form lubricating oils, copolymers, fumaric acid, agricultural chemicals, malic acid, and other derivative chemicals. Because of the wide variety of derivative products made from maleic anhydride, demand for maleic anhydride is expected to continue to increase in the future.

Catalysts presently exist for converting straight chain C4 hydrocarbons into maleic anhydride. For example, Felthouse et al., U. S. Patent No. 5,929, 256, discloses a vanadium and phosphorous containing catalyst that is capable of converting n-butane into maleic anhydride. The catalyst is also capable of producing maleic anhydride from unsaturated straight chain hydrocarbons including 1-butene, 2-butene, and 1,3-butadiene.

A maleic anhydride production facility requires a C4 composition stream containing straight chain C4 hydrocarbons. A C4 composition, such as that disclosed above, can be obtained from the effluent of an oxygenate-to-olefin process as part of this invention.

Summary of the Invention The present invention is a method of making maleic anhydride that comprises (1) contacting an oxygenate with an olefin forming catalyst to form an olefin containing product stream; (2) removing water, C2 hydrocarbons, C3 hydrocarbons, and C5+ hydrocarbons from the olefin containing stream to produce a mixed C4 hydrocarbon stream; and (3) contacting the mixed C4 stream with an oxygenating catalyst and an oxygen source to produce maleic anhydride. The advantage of the present invention is that the C4 feedstock produced from the present invention is particularly low in isobutene and isobutane, which produces a superior maleic anhydride product.

According to one embodiment, the oxygenating catalyst is a phosphorus- vanadium-oxide based or promoted catalyst.

According to one embodiment, the C4 stream set forth above, comprises a mixture of two or more of 1-butene, 2-butene, isobutene, 1,3-butadiene, n-butane, and isobutane. In another embodiment, the C4 stream comprises a mixture of 1- butene, 2-butene, isobutene, n-butane, and isobutane.

In another embodiment, the olefin forming catalyst contains a silicoaluminophosphate molecular sieve, and in particular, a silicoaluminophosphate molecular sieve selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO- 31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, metal containing forms thereof, mixtures thereof, and intergrowths thereof.

According to one aspect of the present invention, the mixed C4 hydrocarbon stream comprises less than 10 wt. % isobutane and isobutene.

In another embodiment, the C4 hydrocarbon stream comprises at least 90 wt. % 1-butene, 2-butene, and n-butane.

In yet another embodiment, the mixed C4 hydrocarbon stream is contacted with a hydrogenation catalyst prior to contacting the oxygenating catalyst.

Preferably, the hydrogenation catalyst is a nickel, palladium, platinum or silver based catalyst.

The present invention, according to one embodiment, is a mixed C4 hydrocarbon composition that comprises from 15 wt. % to 35 wt. % 1-butene ; from 50 wt. % to 75 wt. % 2-butene; from 2.0 wt. % to 10.0 wt. % n-butane; and from 0.5 wt. % to 5.0 wt. % 1,3 butadiene. According to this composition, the combined weight of isobutane and isobutene is less than 5. 0 wt % of the composition. In another embodiment, the present invention comprises a mixed Another embodiment of the mixed C4 hydrocarbon composition set forth above, alternatively comprises less than 2.0 wt. % C5+ hydrocarbons. In yet another embodiment, the C4 composition set forth above alternatively comprises less than 2.0 wt. % C3 hydrocarbons.

According to one aspect, the mixed C4 hydrocarbon composition comprises C4 hydrocarbons produced by contacting an oxygenate with a silicoaliminophosphate molecular sieve catalyst. Preferably, the silicoaluminophosphate molecular sieve is selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO- 31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAP0-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, metal containing forms thereof, mixtures thereof, and intergrowths thereof.

Brief Description of the Drawings The invention will be better understood by reference to the Detailed Description of the Invention when taken together with the attached drawings, wherein: FIG. 1 is a flow diagram of the oxygenate to olefin process including a separation processes for obtaining a mixed C4 hydrocarbons composition.

FIG. 2 is a flow diagram of alternative methods of producing maleic anhydride from a mixed C4 hydrocarbon composition produced in an oxygenate to olefin process.

Detailed Description of the Invention This invention provides a method of making maleic anhydride from a mixed C4 hydrocarbon stream produced in an oxygenate to olefin process. The oxygenate to olefin process produces a variety of compounds in addition to the light olefins ethylene and propylene. Other compounds produced during the oxygenate to olefin process in relatively large quantities typically include water, oxygenates, and C2 to C6 alkanes and unsaturates. These other compounds can be separated from the light olefin products and used either alone or together as fuel gas or as feed to derivative process.

A particularly abundant category of hydrocarbons produced during the oxygenate to olefin process are the C4 hydrocarbons. Preferably, from about 2.0 wt. % to 10.0 wt. %, more preferably from about 4.0 wt. % to 8.0 wt. % and most preferably from 5.0 wt. % to 7.0 wt. % of the effluent stream from an oxygenate to olefin reaction process comprise the C4 hydrocarbons 1-butene, 2-butene, isobutene, 1,3-butadiene, n-butane, and isobutane. One or more of these C4 hydrocarbon components can be separated from the oxygenate to olefin reactor effluent to produce a mixed C4 hydrocarbon stream.

The inventors have found that many of the straight chain C4 hydrocarbons produced in an oxygenate to olefin process can be used to produce maleic anhydride. A mixed C4 hydrocarbon stream from an oxygenate to olefin process can be used to produce maleic anhydride directly by contacting the C4 mixture with an appropriate maleic anhydride forming catalyst. Alternatively, an intermediate hydrogenation step can be used to convert a mixed C4 stream containing unsaturated C4 hydrocarbons into a stream higher in n-butane, a saturated C4 hydrocarbon. The hydrogenated C4 stream can then be contacted with an appropriate maleic anhydride forming catalyst. Both the direct oxidation route and the hydrogenation followed by oxidation route have advantages and can be used to effectively produce maleic anhydride from the mixed C4 hydrocarbon stream of this invention.

In this invention, the mixed C4 hydrocarbon composition is obtained by contacting oxygenate with a molecular sieve catalyst. The oxygenate comprises at

least one organic compound which contains at least one oxygen atom, such as aliphatic alcohols, ethers, carbonyl compounds (aldehydes, ketones, carboxylic acids, carbonates, esters and the like). When the oxygenate is an alcohol, the alcohol can include an aliphatic moiety having from 1 to 10 carbon atoms, more preferably from 1 to 4 carbon atoms. Representative alcohols include but are not necessarily limited to lower straight and branched chain aliphatic alcohols and their unsaturated counterparts. Examples of suitable oxygenate compounds include, but are not limited to: methanol; ethanol; n-propanol ; isopropanol ; C4- (: 20 alcohols; methyl ethyl ether; dimethyl ether; diethyl ether; di-isopropyl ether; formaldehyde; dimethyl carbonate; dimethyl ketone; acetic acid; and mixtures thereof. Preferred oxygenate compounds are methanol, dimethyl ether, or a mixture thereof.

The molecular sieve catalyst used in this invention can be any molecular sieve capable of converting an oxygenate to an olefin compound. Such molecular sieves include zeolites as well as non-zeolites, and can be of the large, medium or small pore type. Small pore molecular sieves are preferred in this invention, however. As defined herein, small pore molecular sieves have a pore size of less than about 5.0 Angstroms. Generally, suitable catalysts have a pore size ranging from about 3.5 to about 5.0 angstroms, preferably from about 4.0 to about 5.0 Angstroms, and most preferably from about 4.3 to about 5.0 Angstroms.

Zeolite materials, both natural and synthetic, have been demonstrated to have catalytic properties for various types of hydrocarbon conversion processes.

In addition, zeolite materials have been used as adsorbents, catalyst carriers for various types of hydrocarbon conversion processes, and other applications.

Zeolites are complex crystalline aluminosilicates which form a network of A102- and Si02 tetrahedral linked by shared oxygen atoms. The negativity of the tetrahedral is balanced by the inclusion of cations such as alkali or alkaline earth metal ions. In the manufacture of some zeolites, non-metallic cations, such as tetramethylammonium (TMA) or tetrapropylammonium (TPA), are present during synthesis. The interstitial spaces or channels formed by the crystalline network enable zeolites to be used as molecular sieves in separation processes, as catalyst

for chemical reactions, and as catalyst carriers in a wide variety of hydrocarbon conversion processes.

Zeolites include materials containing silica and optionally alumina, and materials in which the silica and alumina portions have been replaced in whole or in part with other oxides. For example, germanium oxide, tin oxide, and mixtures thereof can replace the silica portion. Boron oxide, iron oxide, gallium oxide, indium oxide, and mixtures thereof can replace the alumina portion. Unless otherwise specified, the terms"zeolite"and"zeolite material"as used herein, shall mean not only materials containing silicon atoms and, optionally, aluminum atoms in the crystalline lattice structure thereof, but also materials which contain suitable replacement atoms for such silicon and aluminum atoms.

Silicoaluminophosphate molecular sieves are preferred embodiments of non-zeolites that can be used in this invention. These sieves generally comprise a three-dimensional microporous crystal framework structure of [SiO2], [A102] and [PO2] tetrahedral units. The way Si is incorporated into the structure can be determined by 29Si MAS NMR. See Blackwell and Patton, J. Phys. Chenu., 92, 3965 (1988). The desired SAPO molecular sieves will exhibit one or more peaks in the 29Si MAS NMR, with a chemical shift 8 (Si) in the range of-88 to-96 ppm and with a combined peak area in that range of at least 20% of the total peak area of all peaks with a chemical shift 5 (Si) in the range of-88 ppm to-115 ppm, where the 8 (Si) chemical shifts refer to external tetramethylsilane (TMS).

Silicoaluminophosphate molecular sieves are generally classified as being microporous materials having 8,10, or 12 member ring structures. These ring structures can have an average pore size ranging from about 3.5-15 angstroms.

Preferred are the small pore SAPO molecular sieves having an average pore size ranging from about 3.5 to 5 angstroms, more preferably from 4.0 to 5.0 angstroms.

These pore sizes are typical of molecular sieves having 8 member rings.

In general, silicoaluminophosphate molecular sieves comprise a molecular framework of corner-sharing [Si02], [A102], and [PO2] tetrahedral units. This type of framework is effective in converting various oxygenates into olefin products.

The [PO2] tetrahedral units within the framework structure of the molecular sieve of this invention can be provided by a variety of compositions.

Examples of these phosphorus-containing compositions include phosphoric acid, organic phosphates such as triethyl phosphate, and aluminophosphates. The phosphorous-containing compositions are mixed with reactive silicon and aluminum-containing compositions under the appropriate conditions to form the molecular sieve.

The [A102] tetrahedral units within the framework structure can be provided by a variety of compositions. Examples of these aluminum-containing compositions include aluminum alkoxide such as aluminum isopropoxide, aluminum phosphates, aluminum hydroxide, sodium aluminate, and pseudoboehmite. The aluminum-containing compositions are mixed with reactive silicon and phosphorus-containing compositions under the appropriate conditions to form the molecular sieve.

The [SiO2] tetrahedral units within the framework structure can be provided by a variety of compositions. Examples of these silicon-containing compositions include silica sols and silicium alkoxides such as tetra ethyl orthosilicate. The silicon-containing compositions are mixed with reactive aluminum and phosphorus-containing compositions under the appropriate conditions to form the molecular sieve.

Substituted SAPOs can also be used in this invention. These compounds are generally known as MeAPSOs or metal-containing silicoaluminophosphates.

The metal can be alkali metal ions (Group IA), alkaline earth metal ions (Group IIA), rare earth ions (Group BOB, including the lanthanoid elements: lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium ; and scandium or yttrium) and the additional transition cations of Groups IVB, VB, VIB, VIB, VIIIB, and IB.

Preferably, the Me represents atoms such as Zn, Mg, Mn, Co, Ni, Ga, Fe, Ti, Zr, Ge, Sn, and Cr. These atoms can be inserted into the tetrahedral framework through a [MeOx] tetrahedral unit. The [MeO2] tetrahedral unit carries

a net electric charge depending on the valence state of the metal substituent.

When the metal component has a valence state of +2, +3, +4, +5, or +6, the net electric charge is between-2 and +2. Incorporation of the metal component is typically accomplished adding the metal component during synthesis of the molecular sieve. However, post-synthesis ion exchange can also be used.

Suitable silicoaluminophosphate molecular sieves include SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO- 34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, the metal containing forms thereof, and mixtures thereof.

Preferred are SAPO-18, SAPO-34, SAPO-35, SAPO-44, and SAPO-47.

Particularly preferable are SAPO-18 and SAPO-34, including the metal containing forms thereof, and mixtures thereof. As used herein, the term mixture is synonymous with combination and is considered a composition of matter having two or more components in varying proportions, regardless of their physical state.

The silicoaluminophosphate molecular sieves are synthesized by hydrothermal crystallization methods generally known in the art. See, for example, U. S. Pat. Nos. 4,440, 871; 4,861, 743; 5,096, 684; and 5,126, 308, the methods of making of which are fully incorporated herein by reference. A reaction mixture is formed by mixing together reactive silicon, aluminum and phosphorus components, along with at least one template. Generally the mixture is sealed and heated, preferably under autogenous pressure, to a temperature of at least 100°C, preferably from 100-250°C, until a crystalline product is formed.

Formation of the crystalline product can take anywhere from around 2 hours to as much as 2 weeks. In some cases, stirring or seeding with crystalline material will facilitate the formation of the product.

Typically, the molecular sieve product will be formed in solution. It can be recovered by standard means, such as by centrifugation or filtration. The product can also be washed, recovered by the same means and dried.

As a result of the crystallization process, the recovered sieve contains within its pores at least a portion of the template used in making the initial reaction mixture. The crystalline structure essentially wraps around the template,

and the template must be removed so that the molecular sieve can exhibit catalytic activity. Once the template is removed, the crystalline structure that remains has what is typically called an intracrystalline pore system.

The reaction mixture can contain one or more templates. Templates are structure directing agents, and typically contain nitrogen, phosphorus, oxygen, carbon, hydrogen or a combination thereof, and can also contain at least one alkyl or aryl group, with 1 to 8 carbons being present in the alkyl or aryl group.

Mixtures of two or more templates can produce mixtures of different sieves or predominantly one sieve where one template is more strongly directing than another.

Representative templates include tetraethyl ammonium salts, cyclopentylamine, aminomethyl cyclohexane, piperidine, triethylamine, cyclohexylamine, tri-ethyl hydroxyethylamine, morpholine, dipropylamine (DPA), pyridine, isopropylamine and combinations thereof. Preferred templates are triethylamine, cyclohexylamine, piperidine, pyridine, isopropylamine, tetraethyl ammonium salts, and mixtures thereof. The tetraethylammonium salts include tetraethyl ammonium hydroxide (TEAOH), tetraethyl ammonium phosphate, tetraethyl ammonium fluoride, tetraethyl ammonium bromide, tetraethyl ammonium chloride, tetraethyl ammonium acetate. Preferred tetraethyl ammonium salts are tetraethyl ammonium hydroxide and tetraethyl ammonium phosphate.

Materials which can be blended with the molecular sieve can be various inert or catalytically active materials, or various binder materials to form the <BR> <BR> "catalyst. "These materials include compositions such as kaolin and other clays, various forms of rare earth metals, other non-zeolite catalyst components, zeolite catalyst components, alumina or alumina sol, titania, zirconia, quartz, silica or silica or silica sol, and mixtures thereof. These components are also effective in reducing overall catalyst cost, acting as a thermal sink to assist in heat shielding the catalyst during regeneration, densifying the catalyst and increasing catalyst strength. When blended with non-silicoaluminophosphate molecular sieve materials, the amount of molecular sieve that is contained in the final catalyst

product ranges from 1 to 90 weight percent of the total catalyst, preferably 20 to 70 weight percent of the total catalyst.

Other olefin-forming molecular sieve materials which can be used independently, or mixed with the preferred silicoaluminophosphate catalyst, include structural types such as AEI, AFT, APC, ATN, ATT, ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, and substituted forms thereof. These preferred small pore molecular sieves are described in greater detail in the Atlas of Zeolite Strwctural Types, W. M. Meier and D. H. Olsen, Butterworth Heineman, 3rd ed., 1997, the detailed description of which is explicitly incorporated herein by reference. Preferred molecular sieves which can be combined with a silicoaluminophosphate catalyst include ZSM-34, erionite, and chabazite.

To convert an oxygenate to an effluent containing light olefins and C4 hydrocarbons, conventional reactor systems can be used, including fixed bed, fluid bed or moving bed systems. Preferred reactors are co-current riser reactors and short contact time, countercurrent free-fall reactors. Desirably, the reactor is one in which an oxygenate feedstock can be contacted with a molecular sieve catalyst at a weight hourly space velocity (WHSV) of at least about 1 hr~l, preferably in the range of from about 1 hr i to 1000 ho 1, more preferably in the range of from about 20 hr 1 to 1000 hr 1, and most preferably in the range of from about 20 hr~l to 500 hr~l. WHSV is defined herein as the weight of oxygenate, and hydrocarbon which may optionally be in the feed, per hour per weight of the molecular sieve content of the catalyst. Because the catalyst or the feedstock may contain other materials which act as inerts or diluents, the WHSV is calculated on the weight basis of the oxygenate feed, and any hydrocarbon which may be present, and the molecular sieve contained in the catalyst.

Preferably, the oxygenate feed is contacted with the catalyst when the oxygenate is in a vapor phase. Alternately, the process may be carried out in a liquid or a mixed vapor/liquid phase. When the process is carried out in a liquid phase or a mixed vapor/liquid phase, different conversions and selectivities of feed-to-product may result depending upon the catalyst and reaction conditions.

The process can generally be carried out at a wide range of temperatures.

An effective operating temperature range can be from about 200°C to 700°C, preferably from about 300°C to 600°C, more preferably from about 350°C to 550°C. At the lower end of the temperature range, the formation of the desired olefin products may become markedly slow. At the upper end of the temperature range, the process may not form an optimum amount of product.

The mixed C4 composition of this invention comprises various C4 hydrocarbons from the effluent of an oxygenate to olefin process, and is designed as a feed to produce maleic anhydride by partial oxidation. The effluent obtained by reacting oxygenates with molecular sieve catalysts is generally high in water and various oxygenates which can be detrimental to the formation of maleic anhydride by partial oxidation. Consequently, it is desirable to separate such components from the effluent stream to form the preferred mixed C4 composition of this invention.

Preferably, the mixed C4 stream of this invention is low in C3. hydrocarbon components (hydrocarbons having 3 or less hydrocarbons). This is because maleic anhydride production by partial oxidation according to this invention utilizes hydrocarbons having a straight chain of four or more carbon atoms. C3- hydrocarbons lack this four carbon chain and therefore cannot be used to produce maleic anhydride by partial oxidation. Further, the preferred mixed C4 stream of this invention will also be low in C5+ hydrocarbons (hydrocarbons having five or more hydrocarbons). Not all of the carbon atoms in a C5+ hydrocarbon is utilized in the formation of maleic anhydride. Their presence in high amounts can result in an inefficient use of these hydrocarbons and may necessitate additional cleanup of the maleic anhydride produced.

The effluent stream from an oxygenate to olefin process can be fractionated to produce the mixed C4 hydrocarbon stream of this invention using any known fractionation technique including distillation, absorption, adsorption and combinations thereof.

In one embodiment of this invention, the mixed C4 composition comprises greater than about 80.0 wt. % l-butene, 2-butene, 1, 3-butadiene, and n-butane

and no more than about 20.0 wt. % of isobutane and isobutene. In another embodiment, the C4 composition comprises greater than about 90 wt. %, 1-butene, 2-butene, 1,3-butadiene, and n-butane and no more than about 10 wt. % isobutane and isobutene.

C4 hydrocarbons with a straight chain of at least four hydrocarbons can be used to produce maleic anhydride according to this invention. Accordingly, a preferable C4 hydrocarbon stream is rich in the straight chain hydrocarbons, for example, 1-butene, 2-butene, 1,3-butadiene, and n-butane, and less rich in the branched hydrocarbons, for example isobutane and isobutene. However, some branched C4 hydrocarbons can be present in the mixed C4 composition because in low amounts their presence does not harm the formation of maleic anhydride.

Preferably, the mixed C4 composition of this invention comprises greater than about 80 wt. % straight chain C4 hydrocarbons. More preferably, the C4 composition comprises greater than about 90 wt. % straight chain C4 hydrocarbons, and most preferably, the C4 composition comprises greater than about 95 wt. % straight chain C4 hydrocarbons.

Preferably, the mixed C4 composition of this invention comprises less than about 20 wt. % branched C4 hydrocarbons. More preferably, the mixed C4 composition comprises less than about 10 wt. % branched C4 hydrocarbons, and most preferably, the mixed C4 composition comprises less than about 5 wt. % branched C4 hydrocarbons. Most preferably, the composition contains no branched C4 hydrocarbons.

Preferably, the mixed C4 composition of this invention comprises less than about 2.0 wt. % C3 hydrocarbons. More preferably, the mixed C4 composition comprises less than about 1.0 wt. % C3 hydrocarbons, and most preferably, the mixed C4 composition comprises less than about 0.7 wt. % C3 hydrocarbons.

Preferably, the mixed C4 composition of this invention comprises less than about 2.0 wt. % C5+ hydrocarbons. More preferably, the mixed C4 composition comprises less than about 1.0 wt. % C5+ hydrocarbons, and most preferably, the mixed C4 composition comprises less than about 0.7 wt. % C5+ hydrocarbons.

Preferably, the mixed C4 composition of this invention comprises less than about 1.0 wt. % oxygenates. More preferably, the mixed C4 composition comprises less than about 0.5 wt. % oxygenates, and most preferably, the mixed C4 composition comprises less than about 0.2 wt. % oxygenates.

Typically, some of the most difficult separations in a hydrocarbon manufacturing process are the separation of hydrocarbons having the same number of carbon atoms. Hydrocarbons having the same number of carbon atoms typically have similar characteristics, including boiling points, that are used to separate different hydrocarbons from one another. Since the mixed C4 composition of this invention comprises a low level of branched C4 components, the separation of C4 components from one another to produce the mixed C4 composition is reduced or even eliminated.

A mixed C4 composition stream containing straight chain hydrocarbons can either be directly converted into maleic anhydride by partial oxidation, or the straight chain hydrocarbons can first be converted into n-butane by complete hydrogenation. The n-butane can then be converted into maleic anhydride by partial oxidation. The n-butane route can result in a higher maleic anhydride yield, but requires the added hydrogenation step.

A mixed C4 hydrocarbon composition from an oxygenate to olefin process comprises one or more of the straight chain C4 hydrocarbons 1-butene, 2-butene, 1., 3-butadiene, and n-butane. These hydrocarbons can all be directly oxidized to produce maleic anhydride according to idealized equation (1), (2) and (3): C4H8 (1-butene or 2-butene) +3 02 + maleic anhdride + 3 H20 (1) C4H6 (1,3-butadiene) +3.5 02+ maleic anhydride + 2 H20 (2) CH3CH2CH2CH3 (n-butane) + 3. 5 02maleic anhydride +4 H20 (3) Since maleic anhydride is a four carbon hydrocarbon like 1-butene, 2-butene, 1,3- butadiene, and n-butane the idealized processes are an efficient use of carbon.

Unfortunately, the production of maleic anhydride competes against the more complete oxidation reactions that produce carbon monoxide and carbon dioxide.

The n-butane route to maleic anhydride is less susceptible to the complete oxidation reactions that produce the carbon oxides and is also less susceptible to other reactions that produce organic salts from the C4 hydrocarbons. N-butane is therefore a more preferable feedstock compared to 1-butene, 2-butene, and 1,3 butadiene for producing maleic anhydride.

In one preferred embodiment the mixed C4 hydrocarbon composition is directed to a hydrogenation unit before maleic anhydride is produced. The hydrogenation unit converts 1-butene, 2-butene, and 1,3-butadiene in the mixed C4 hydrocarbon composition into n-butane The hydrogenation unit comprises a reactor and a hydrogenation catalyst capable of converting the butenes and butadienes in the C4 hydrocarbon stream to n-butane. Conventional hydrogenating processes can be used. The effluent stream from the hydrogenation unit comprises a mixture of n-butane and isobutane. It is desirable that at least about 80 wt. %, more preferably at least about 90 wt. % and most preferably at least 95 wt. % of the hydrogenated mixed C4 composition comprise n-butane.

The hydrogenation catalyst is preferably a transition metal supported on alumina. Examples of metals include nickel, palladium, platinum and silver.

Conventional catalyst systems can be used. The hydrogenation of the mixed C4 hydrocarbon stream can occur in the liquid or gas phase. A preferable hydrogenation process occurs in a liquid phase over a promoted palladium catalyst. Typical hydrogenation reactions are carried out from about 1 bar to about 300 bar and at a temperature in the range of about 40DC to about 380°C.

A preferred catalyst for producing maleic anhydride from C4 hydrocarbons, whether an unhydrogenated mixed C4 stream or a hydrogenated mixed C4 stream, is a phosphorous-vanadium-oxide (PVO) based catalyst.

Especially preferred among these type of catalysts are those comprising divanadyl pyrophosphate ( (VO) 2P2 07) as the active component. These catalysts themselves are generally known and used. Details of these catalysts including production processes are disclosed, for example, in Chem. Rev., 88, pp. 55-80 (1988), and

U. S. Pat. Nos. 4,472, 527 and 4,520, 127, such details being incorporated herein by reference.

An alkali or alkaline promoter is preferably combined with the basic catalyst to improve the overall catalyst performance. The structure of the catalyst, the phosphorous/vanadium ratio, and the oxidation state of the vanadium oxide system affect the mechanism and the kinetics for the formation of maleic anhydride. Preferably a catalyst that best balances the activity (how quickly the C4 hydrocarbons in the stream react) with selectivity (the percentage of maleic anhydride produced relative to other chemical compositions) is chosen.

The partial oxidation of the mixed C4 hydrocarbon composition, whether hydrogenated or unhydrogenated, to produce maleic anhydride can be accomplished in a variety of known reactors. Preferable reactors include fixed- bed and fluidized bed reactors. Typically a PVO based catalyst is loaded into the chosen reactor in either a spherical or pelletized form. The mixed C4 hydrocarbon composition and an oxygen-containing gas, are preferably fed to the reactor in such a proportion as to result in a C4 hydrocarbon concentration of from about 1.5 to 10 wt. %. Preferably, the oxygen containing gas is air, however, air diluted with an inert gas, air enriched with oxygen, or the like can also be used.

Preferably the C4 hydrocarbons are contacted with the oxidation catalyst at a temperature of between 250 and 600°C, more preferably between 300 and 500°C and most preferably between 350 and 450°C. Methods for the formation of maleic acid in a fluidized-bed or fixed-bed reactor are generally known and used.

The effluent from the maleic anhydride reactor comprises a mixture of the unreacted oxygen containing gas, unreacted feedstock hydrocarbons, by-products such as carbon monoxide, carbon dioxide, and water, and other reaction products, along with maleic anhydride. The maleic anhydride in the effluent from the maleic anhydride reactor can be recovered by any known technique. Preferred techniques include cooling the gas effluent to condense the maleic anhydride, bringing the gas effluent into contact with water to collect the maleic anhydride as maleic acid in the water, or contacting the gas effluent with an organic solvent to collect maleic anhydride in the organic solvent.

Detailed Description of the Preferred Embodiments One preferred process for separating the effluent from an oxygenate to olefin process to produce the preferred mixed C4 composition of this invention is shown in Figure 1. In Figure 1, an oxygenate containing stream 10 is fed into a reaction unit 12. The reaction unit 12 contains a reactor and molecular sieve catalyst capable of converting oxygenates in the oxygenate containing stream 10 into olefins. The effluent stream 14 from reaction unit 12 contains an assortment of hydrocarbon and non-hydrocarbon components including water. The effluent stream 14 is sent to a quench tower 15 where the effluent stream comes into contact with cooling water 16. The cooling water 16 cools the effluent stream 14 below the condensation temperature of water. Water from stream 14 condenses in quench tower 15 and leaves along with the cooling water 16 as stream 18. The compounds which remain in the gas phase in quench tower 15 leave the quench tower as stream 20.

Stream 20 is sent to a compressor 22 which compresses stream 20 forming compressed stream 24. The compressed stream 24 is then sent to a drying unit 26 where water remaining in stream 24 is removed, forming a dry stream 28. The dry stream 28 is then sent to a C1 separator 30. The C1 separator 30 produces two streams, a stream 32 comprised of methane and components with boiling temperatures lower than methane and a stream 34 comprised of C2+ hydrocarbons.

The C2+ stream 34 is fed into a Ca separator 36. The C2 separator 36 produces two streams from stream 34, a stream 38 comprised of C2 hydrocarbons, and a stream 40 comprised of C3+ hydrocarbons. The C2 hydrocarbon stream 38 is sent to an ethylene/ethane splitter 42. The ethylene/ethane splitter 42 produces an ethylene stream 44 and an ethane stream 46.

The C3+ stream 40 from the C2 splitter is fed to a C3 separator 48. The C3 separator produces a C3 stream 50 and a C4+ stream 52. The C4+ stream is then fed into a C4 splitter 54 which produces a C4 stream 56 and a C5+ stream 58. The C4 stream 56 comprises a mixed C4 composition. All or part of stream 56 may be used as a feed to make maleic anhydride according to this invention.

Figure 2 shows two preferred embodiments of how maleic anhydride is produced from a mixed C4 composition from an oxygenate to olefin process.

Stream 202 is a C4 stream from an oxygenate to olefin process. Stream 202 is fed either directly into a partial oxidation reactor 220 to produce maleic anhydride or is first fed into a hydrogenation reactor 204 to make butanes out of any unsaturated C4 hydrocarbons in stream 202. If the C4 stream 220 is directed to hydrogenation reactor 204, the stream is mixed with a hydrogen containing stream 206 and contacted with a hydrogenation catalyst within the reactor. The hydrogenation reactor 204 converts the unsaturated C4S in stream 202 into a butane stream 208. Butane stream 208 is then fed into partial oxidation reactor 210, which converts the butanes into a maleic anhydride and carbon oxide containing stream 214. Stream 214 is then sent to a recovery section 216 which recovers a maleic anhydride product stream 218.

Alternatively, C4 stream 202 can be directed into a partial oxidation reactor 220 without the additional hydrogenation step. In the partial oxidation reactor, straight chain C4 hydrocarbons, for example n-butane, 1-butene, 2-butene, and 1,3-butadiene, are converted into a maleic anhydride and carbon oxide containing stream 224. Stream 24 is sent to a recovery section 226 which recovers a maleic anhydride product stream 228.

This invention will be better understood with reference to the following example.

Example 1 A methanol feed stream was contacted with a SAPO-34 catalyst in a fluidized bed reactor. The percent of methanol conversion was varied with each trial. For trial one, 98.98% methanol conversion occurred within the reactor; for trial two, 97.32% methanol conversion occurred within the reactor; and for trial three, 87.80% methanol conversion occurred within the reactor. For each trial, the effluent from the reactor contained several compositions including water, oxygenates, C2 hydrocarbons, C3 hydrocarbons C4 hydrocarbons and C5+ hydrocarbons. The distribution of the individual C4 hydrocarbon compositions in the effluent are shown in Table 1.

TABLE 1

C4 hydrocarbon Trial #1 (wt. %) Trial #2 (wt. %) Trial #3 (wt. %) 1-butene 25. 26 25. 44 26. 13 2-butene 59. 92 59. 82 60. 85 Isobutene 4. 14 4. 06 3. 47 1, 3-butadiene 1. 95 2. 49 2. 74 n-butane 7. 79 6. 6 # 5.8 Isobutane 0. 94 1. 6 # 1 After each trial, the effluent from the reactor is contacted with water in a quench tower, which condenses most of the water and unreacted methanol in the effluent. After being quenched, the effluent is fractionated into individual hydrocarbon streams. A C1 separator removes methanol and lighter compounds from the effluent. A C2 separator, removes the C2 hydrocarbons from the effluent, leaving C3+ hydrocarbons. The effluent containing C3+ hydrocarbons is sent to a C3 separator, which removes C3 hydrocarbons from the effluent leaving C4+ hydrocarbons. The C4+ effluent is then sent to a C4 separator, which produces two streams a C4 hydrocarbon stream and a Cs+ hydrocarbon stream.

The C4 hydrocarbon stream from the C4 separator is then contacted with a hydrogenation catalyst to produce a butane rich composition. The butane rich composition is then contacted with a PVO based catalyst to produce a maleic anhydride containing composition. The data shows that the streams produced have considerably low levels of isobutene and/or isobutane.

Having now fully described this invention, it will be appreciated by those skilled in the art that the invention can be performed within a wide range of parameters within what is claimed, without departing from the spirit and scope of the invention.