Maleic anhydride mixed oxide catalyst

Mixed Metal Oxides and Propylene Ammoxidation. The best catalysts for partial oxidation are metal oxides, usually mixed metal oxides. For example, phosphoms—vanadium oxides are used commercially for oxidation of / -butane to give maleic anhydride, and oxides of bismuth and molybdenum with other components are used commercially for oxidation of propylene to give acrolein or acrylonitrile. 

The effect of glycols in the organic preparation of V/P mixed oxide, catalyst for the oxidation of n-butane to maleic anhydride... 

Butane-Based Process Selective Oxidation of Butane to Maleic Anhydride 1,4-Butanediol can also be manufactured by hydrogenating maleic acid derivatives obtained by oxidizing -butane. Various methods have been developed, differing in the reaction system or source of maleic anhydride [6]. The selective oxidation of -butane to form maleic anhydride is accomplished in either a fixed or fluid bed reactor containing vanadium/phosphorus mixed oxide catalyst. Formed maleic anhydride is then converted to the diester via esterification with a lower alcohol such as ethanol (Eq. (10.4)). The diester is hydrogenated in the gas phase in a fixed bed reactor filled with a copper catalyst in the gas phase (Eq. (10.5)). The alcohol is released and recycled. Since y-butyrolactone is a reaction intermediate of 1,4-butanediol, hydrogenation conditions can control the product ratio of y-butyrolactone and 1,4-butanediol. The yield of 1,4-butanediol production is ... 

Mazzoni, G., Cavani, F., and Stefani, G. (1997) Process for the tranformation of a vana-dium/Phosphorous Mixed Oxide catalyst precursor into the active catalyst for the production of maleic anhydride, EP0804963B1 (assigned to Lonza). 

Very different catalytic materials have been tested in the selective oxidation of propane, which includes vanadium phosphorous oxide (VPO) catalysts, industrially applied for w-butane oxidation to maleic anhydride. The other catalysts systems include Keggin structure heteropolyoxometalUc compounds (HPCs) and multicomponent mixed oxides (MMOs). These materials have different structure and properties, but have something in common they contain reducible metal 0x0 species. 

Titanium dioxide catalysts were first described in the 1940s and 1950s, when mixed oxide catalysts were being investigated and used in a number of oxidation reactions. Mixtures of vanadium pentoxide with titanium dioxide gave better operation and longer life as phthalic anhydride demand increased. An early catalyst that did not sinter and clearly increased the stability of vanadium pentoxide was described in a patent as Ti0(V03)2. At about the same time vanadium pentoxide/phosphorous pentoxide mixtures were also being developed for use in maleic anhydride processes. 

An interesting practical feature of all mixed oxide catalysts is the very simple preparation from the appropriate ingredients. Maleic anhydride catalyst is prepared as follows ... 

Fresh butane mixed with recycled gas encounters freshly oxidized catalyst at the bottom of the transport-bed reactor and is oxidized to maleic anhydride and CO during its passage up the reactor. Catalyst densities (80 160 kg/m ) in the transport-bed reactor are substantially lower than the catalyst density in a typical fluidized-bed reactor (480 640 kg/m ) (109). The gas flow pattern in the riser is nearly plug flow which avoids the negative effect of backmixing on reaction selectivity. Reduced catalyst is separated from the reaction products by cyclones and is further stripped of products and reactants in a separate stripping vessel. The reduced catalyst is reoxidized in a separate fluidized-bed oxidizer where the exothermic heat of reaction is removed by steam cods. The rate of reoxidation of the VPO catalyst is slower than the rate of oxidation of butane, and consequently residence times are longer in the oxidizer than in the transport-bed reactor. 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

The industrial catalyst for n-butane oxidation to maleic anhydride (MA) is a vanadium/phosphoras mixed oxide, in which bulk vanadyl pyrophosphate (VPP) (VO)2P207 is the main component. The nature of the active surface in VPP has been studied by several authors, often with the use of in situ techniques (1-3). While in all cases bulk VPP is assumed to constitute the core of the active phase, the different hypotheses concern the nature of the first atomic layers that are in direct contact with the gas phase. Either the development of surface amorphous layers, which play a direct role in the reaction, is invoked (4), or the participation of specific planes contributing to the reaction pattern is assumed (2,5), the redox process occurring reversibly between VPP and VOPO4. 

Oxo-metal complexes also intervene as active species in the heterogeneous gas-phase oxidation of hydrocarbons over metal oxide or mixed metal oxide catalysts at high temperatures. Characteristic examples are the bismuth molybdate-catalyzed oxidation of propene to acrolein and the V205-catalyzed oxidation of benzene to maleic anhydride (equations 17 and 18).SJ... 

One of the most important systems which can be prepared advantageously from organic solvents is the (VO)HP04 0.5 H30 precursor for vanadium phosphorus mixed oxides. This is the best known catalyst for the selective conversion of -butanc to maleic anhydride. This system will be discussed in more detail below. 

Stizza et al. (73,274) have investigated amorphous vanadium phosphates, which are also of interest in relation to a XAS study of the butane-maleic anhydride (V, P)0 catalysts (99a). From the V K edge useful information is obtained about the distortions in the vanadium coordination sphere [molecular cage effect on the pre-edge intensity (312)] and on the vanadium oxidation state. Notably, V4+ is silent to most spectroscopic methods. A mixed V4+-V5+ valence state can be measured from the energy shift of the sharp core exciton at the absorption threshold of the Is level of vanadium due to Is -f 3d derived molecular orbitals localized within the first coordination shell of vanadium ions. 

In the first commercial process, introduced in 1933, maleic anhydride was produced by the catalytic oxidation of benzene with air. Although its appeal declined after the 1970s the benzene process is still operated, particularly where -butane is not available. The catalyst is a mixed oxide (70% V2O5 30% M0O3) deposited on a low surface area carrier to limit side reactions. Atom efficiency is inherently low, as implied by the stoichiometry of the oxidation in which two carbon atoms out of six are lost as CO2 (Equation B4). Molar yields however can be relatively high ca. 73%) and are generally higher than those in the -butane processes. 

A number of commercial oxidation catalysts are based on V and Mo oxides. They are multicomponent materials, such as the mixed oxides Mo-Fe-O (oxidation of methanol to formaldehyde), V-P-O (oxidation of butane to maleic anhydride), Bi-Mo-O (propylene to acrylonitrile), Bi-Fe-Mo-O... 

Similarly, Mota et al. [210] carried out the selective oxidation of butane to maleic anhydride over VPO mixed oxides-based catalysts enclosed in an MFI membrane. Different feed configurations of the zeohte-membrane reactor were tested to outperform the conventional co-feed configuration. The results achieved were rather similar however, the authors pointed out the possibility to take advantage of the O2 distribution, which limits the flammability problems and allows operation with higher butane concentrations than those used in conventional processes. 

This review analyzes the properties which are necessary for heterogeneous catalysts to promote the oxyfunctionalization of light paraffins to valuable chemicals. Three catalytic systems are discussed i) vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation of n-butane to maleic anhydride, which is here also examined for reactions aimed at the transformation of other hydrocarbons ii) Keggin-type heteropolycompounds, which are claimed for the oxidation of propane and isobutane, whose composition can be tuned in order to direct the reaction either to the formation of olefins or to the formation of oxygenated compounds iii) rutile-based mixed oxides, where rutile can act as the matrix for hosting transition metal ions or favour the dispersion of other metal oxides, thus promoting the different role of the various elements in the formation of acrylonitrile from propane. 

Vanadium phosphates (VPO) of different structure are suitable precursors of veiy active and selective catalysts for the oxidation of C4-hydrocarbons to maleic anhydride [e.g. 4] as well as for the above mentioned reaction [5,6]. Normally, VOHPO4 Va H2O is transformed into (V0)2P207 applied as the n-butane oxidation catalyst. Otherwise, if VOHPO4 V2 H2O is heated in the presence of ammonia, air and water vapour a-(NH4)2(V0)3(P207)2 as XRD-detectable phase is formed [7], which is isostructural to a-K2(V0)3(P207)2. Caused by the stoichiometry of the transformation reaction (V/P = 1 V/P = 0.75) (Eq. 2) and the determination of the vanadium oxidation state of the transformation product ( 4.11 [7]) a second, mixed-valent (V 7v ) vanadium-rich phase must be formed. 

Partial Oxidation of ra-Butane to Maleic Anhydride Using SiC-Mixed and Pd-Modified Vanadyl Pyrophosphate (VPO) Catalysts (Case study)... 

Hazbum [2.129] in a U.S. patent, reported ethane and propane partial oxidation to ethylene and propylene oxides using a TiYSZ mixed O Velectron conducting membrane with silver deposited on the hydrocarbon side of the membrane as a catalyst. For the ethane partial oxidation reaction catalyst at 250-400 C, the ethylene oxide selectivity was (>75 %) but the ethane conversion was low (<10 %), limited by the low membrane oxygen flux at these temperatures. For the partial oxidation reaction to propylene oxide yields close to 5 % were reported. Using porous membranes Santamaria and coworkers (Mallada et al. [2.252, 2.253, 2.254, 2.255]), Mota et al. [2.256], and Xue and Ross [2.257] recently studied the oxidation of butane into maleic anhydride. 

Maleic anhydride (72) when mixed with triphenylbismuthine in a ratio ranging from 1 1 to 1 1.5 provided a curing catalyst for a propellant composite comprising an oxidizer, isocyanate curing agent, and a hydroxy-terminated polymer binder. The resulting composite showed improved modulus and/or stress values for use with propellants <91 Ml 208-06). 

Mixed metal oxides are used quite often in industrial partial oxidation reactions, examples being Bi Oj-MoOj for the oxidation of propene to acrolein and V O -MoOj for oxidation of benzene to maleic anhydride. Some mixed oxides also are quite active deep oxidation catalysts, a good example being MnOj-CuO. The difficulties in understanding mixed oxides are of course more formidable than they are for single metal oxides. It is a well-established empirical fact that mixed oxides behave quite differently than as individual oxides in most catalytic reactions. This situation is further complicated by the often dramatic effect of promoters, such as alkali metal oxides that are added to the catalyst intentionally. 

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