HRP920509A2 - Shaped oxidation catalyst structures for the production of maleic anhydride - Google Patents

Description

The field of technology

The invention belongs to the field of catalytic chemistry.

Technical problem

This invention relates to shaped oxidation catalytic structures. More specifically, it refers to shaped oxidation catalytic structures containing a catalytic material composed of mixed oxides of vanadium and phosphorus suitable for the production of maleic anhydride via the partial oxidation of non-aromatic hydrocarbons in the gas phase with molecular oxygen or a gas containing molecular oxygen.

State of the art

It is known that the physical form of the catalyst in heterogeneous catalysis is a significant factor that determines its activity and productivity. In general, a given catalyst shows an increase in activity in proportion to the decrease in catalyst particle size. However, in fixed bed reactor systems, the reduction in catalyst particle size leads to an increase in the pressure drop across the catalyst bed. This phenomenon results from a better arrangement of the catalyst particles in the catalytic layer. And as the pressure drop across the catalytic bed increases, the amount of reactant gas that can pass through the catalytic bed at the set outlet pressure becomes limited. Conversely, as the size of the catalyst particles increases in order to improve the pressure drop through the catalytic layer, the loss of catalytic activity results, among other things, from the effect of a lower density of the catalytic batch, i.e. amount of catalyst per unit of reactive volume.

In order to overcome the difficulties that arise with regard to catalytic activity and productivity and pressure drop through the catalytic layer, numerous catalytic forms have been described in previous works.

US patents no. 4 370 492 and 4 370 261 describe star or ribbed forms of a catalytic support for use in supporting active metals for the production of vinyl acetate in the gas phase reaction of ethylene with acetic acid and (molecular) oxygen or gases containing (molecular) oxygen.

US patents no. 4,342,603 and 4,328,130 describe a hydrocarbon conversion catalyst having a generally cylindrical shape with a plurality of longitudinal channels running radially from the periphery of the cylinder and forming protrusions between them. The protrusions are described as having a maximum width greater than. maximum channel widths.

US patents no. 4,133,777 and 4,116,819 describe catalysts in the form of elongated extrusions having alternating longitudinal notches and ridges on the surface. Such catalysts reportedly find applications for hydrodesulfurization of residual petroleum oils, liquid coal, shale oil, and sand oil.

US Patent No. 3,966,644 describes shaped porous catalysts that are defined as concave geometric cylinders of polylobular shape. The catalysts are said to be useful in the hydrogenation of hydrocarbons with increased catalytic performance over conventionally designed catalysts.

In US patent no. 3,957,627, a generally spherical catalyst having a hollow center and an opening extending to the outer surface is described as suitable for hydrogenating hydrocarbons containing compounds with carbon-sulfur, carbon-nitrogen and/or carbon-oxygen bonds.

US patent no. 3,347,798 describes hollow ball catalysts suitable for use in a wide range of fluidized bed reactions, e.g., in hydrogenation, oxidation, dehydrogenation, dehydration, polymerization, condensation, amination, reduction of aromatic nitro compounds, cracking, hydrocarbon refining, hydrocarbon alkylation or their derivatives and also aromatic amino, nitro and aminonitro compounds by reduction or reaction with alcohols and also the production of alkanolamines, diamines, diphenylamines and imines.

Despite the above, however, catalysis remains fundamentally an inexact science, i.e. an experiential technique not clarified by the rules that determine the certainty and possibility of expression. Thus, the decisive effect of the shape of the catalyst on a specific catalytic reaction with a specific catalytic material is not unambiguously explained. This is mainly because each catalytic reaction has unique reaction kinetics, and a given catalyst has unique formation characteristics.

The production of maleic anhydride via partial oxidation of hydrocarbons in the gas phase with molecular oxygen or a gas containing molecular oxygen in the presence of a vanadium-phosphorus oxide catalyst is one such reaction. Maleic anhydrite is commercially important worldwide. It is used alone or in combination with other acids in the production of alkyl and polyester resins. It also serves as an intermediate during numerous chemical syntheses. Considerable quantities of maleic anhydride are produced each year to meet these various needs.

Various oxidation catalysts and forms of oxidation catalysts have been used in the production of maleic anhydride, especially partial oxidation of non-aromatic hydrocarbons that have at least 4 carbon atoms in the normal chain (or cyclic structure). Generally, such catalysts contain mixed oxides of vanadium and phosphorus. More precisely, such catalysts in which the valence of vanadium is between +3.8 and +4.8 were considered particularly suitable for the production of maleic anhydride from saturated hydrocarbons that have at least 4 carbon atoms in the normal chain. In many cases, such catalysts also contain additional promoter elements that are thought to be in the form of oxides.

US patent no. 4,283,307 describes an oxidation catalytic structure for the production of maleic anhydride which comprises a cylinder having a cavity therein and is further described as consisting mainly of a catalytic material composed of a phosphorus, vanadium, oxygen complex.

US patents no. 4 181 628 and 4 178 298 describe (solid) pellets (cylinders) as a suitable oxidation catalytic structure for the production of maleic anhydride.

US patent no. 4 632 915 describes catalysts comprising phosphorus, vanadium and oxygen, and a promoter component containing iron and lithium suitable for the partial oxidation of non-aromatic hydrocarbons, especially n-butane with molecular oxygen or a gas containing molecular oxygen in the gas phase to obtain maleic anhydride with extraordinary using it.

US patent no. 4 562 268 refers to the process of producing maleic anhydride from non-aromatic hydrocarbons in the presence of a vanadium/phosphorus mixed oxide oxidation catalyst where the catalyst shows a mass productivity per cycle of at least 70 grams of maleic anhydride per kilogram of catalyst per hour.

US patent no. 4 333 853 describes a vanadium/phosphorus mixed oxide catalyst obtained by reducing vanadium mainly in the pentavalent state to the tetravalent state in the presence of a phosphorus-containing compound, and without a corrosive reducing agent in an organic liquid phase suitable for reducing vanadium to a valence state of less than +5, by separating the resulting vanadium/phosphorus mixed oxide catalyst precursor, by drying such precursor and calcining the precursor in order to obtain an active catalyst. Such catalysts are supposedly efficient in the oxidation of C4 hydrocarbons, such as n-butane, 1- and 2-butenes, 1,3-butadiene or their mixtures in order to obtain maleic anhydride with selectivities ranging from 58.7 to 68.1% and yields (mol.%) ranging from 51.4 to 59.5%.

US patent no. 4,135,864 relates to a process for the production of maleic anhydride from C4 normal hydrocarbons in the presence of a vanadium/phosphorus mixed oxide catalyst. The catalyst is obtained by reducing compounds containing pentavalent vanadium in an olefinic liquid medium with oxygen up to a valence of +4, without a corrosive reducing agent, separating the resulting catalytic precursor, drying the catalytic precursor and calcining the precursor to obtain an active catalyst.

US patent no. 4,312,787 describes a catalyst comprising an inert support and a catalytically active mixed oxide material covering vanadium and phosphorus or vanadium, phosphorus and uranium on the outer surface of the support in an amount greater than 50 to about 801 by weight of the support and oxide material. Catalysts within the scope of the patent claim are given with regard to the production of maleic anhydride from n-butane in yields ranging from 53 / to 62.5%, with selectivities ranging from 57.4 to 67.9%.

In US patent no. 4 251 390 a zinc-promoted vanadium-phosphorus-oxygen catalyst is described and protected. The catalyst is obtained by reducing pentavalent vanadium in a mostly dehydrated organic solvent to a lower valence state and destroying the reduced vanadium in the presence of a zinc-promoter compound. The resulting catalyst is activated by bringing it to operating temperatures for the oxidation of n-butane to Malemic anhydride at a rate of 5 to 10º per hour in the presence of a butane-air mixture.

In US patent no. 4 187235 describes a process for obtaining maleic anhydride from n-butane in the presence of a vanadium-phosphorus-oxygen catalyst with a high specific surface area, i.e. 10-100 m2/gram, as determined by the BET method. The catalyst is obtained by reducing pentavalent vanadium to a valency between +4.0 and +4.6 with mostly dehydrated primary or secondary alcohol, and by contacting the reduced vanadium with phosphoric acid, which is followed by the separation and calcination of the resulting vanadium(IV) phosphate compound.

US Patent 4,018,709 describes a gas-phase oxidation process for normal C4 hydrocarbons that uses catalysts containing vanadium, phosphorus, uranium, or tungsten, or a mixture of zinc, chromium, uranium, tungsten, cadmium, nickel, boron, and silicon. In a favorable embodiment, the catalyst also contains an alkali or alkaline earth metal, especially lithium, sodium, magnesium or barium as active components. Typically, such catalysts are prepared in concentrated (37%) HCl.

In US patent no. 3 980 585 describes a process for obtaining maleic anhydride from normal C4 hydrocarbons in the presence of a catalyst containing vanadium, phosphorus, copper, oxygen, tellurium or a mixture of tellurium and hafnium or uranium or a catalyst containing vanadium, phosphorus, copper and at least one element selected from groups consisting of tellurium, zirconium, nickel, cerium, tungsten, palladium, silver, manganese, chromium, zinc, molybdenum, rhenium, samarium, lanthanum, hafnium, tantalum, thorium, cobalt, uranium and tin optionally (and preferably) with the element from Group IA (alkaline metals) or HA (alkaline earth metals).

US patent no. 3,888,866 describes a process for the oxidation of n-butane at a temperature of about 300 to about 600°C with a vanadium/phosphorus/oxygen catalyst having a phosphorus/vanadium atomic ratio of 0.5-2, refined or modified with chromium, iron, hafnium, zirconium, lanthanum and cerium, the promoter metal/vanadium atomic ratio is between 0.0025 and 1. Catalysts are prepared by refluxing a reaction mixture of vanadium oxide, phosphorus, hydrogen halide (usually HCl) and a specific compound containing the promoter metal. The obtained catalytic precursors are separated, dried, formed into spherical structures and calcined to obtain an active catalyst.

US patent no. 3,864,280 describes a vanadium/phosphorus mixed oxide catalyst having an internal specific surface area of about 7 to 50 m 2 /g. Catalysts are obtained by precipitation of a vanadium/phosphorus/oxygen complex from a mostly anhydrous organic solvent. The resulting crystalline precipitate is activated by heating in air and then in a 1.5 mol% butane mixture in air at elevated temperatures.

US patent no. 3 862 146 describes a process for the oxidation of n-butane to maleic anhydride in the presence of a vanadium/phosphorus/oxygen catalytic complex, promoted or activated by zinc, bismuth, copper or lithium as an activator. Phosphorus/vanadium and activator/vanadium atomic ratios are about 0.5-5 and about 0.05-0.5, respectively.

US patent no. 3 856 824 describes a process for the production of maleic anhydride by oxidation of saturated aliphatic hydrocarbons in the presence of a catalyst containing vanadium, phosphorus, iron, oxygen and an additional modifier consisting of chromium in combination with at least one of the elements from the group consisting of nickel, boron, silver, cadmium and barium.

European patent application no. 98 039 describes a process for obtaining a vanadium-phosphorus mixed oxide catalyst optionally containing a promoter element selected from the group consisting of group IA (alkali metals), group IIA (alkaline earth metals), titanium, chromium, tungsten, mobium, tantalum, manganese, thorium , uranium, cobalt, molybdenum, iron, zinc, hafnium, zirconium, nickel, copper, arsenic, antimony, tellurium, bismuth, tin, germanium, cadmium and lanthanides and their mixtures. Catalysts having a phosphor/vanadium atomic ratio of about 0.8 to about 1.3 and a promoter/vanadium atomic ratio of about 0.01 to about 0.5 are obtained in an organic solvent reaction mixture capable of reducing vanadium in a valence state of about +4 into the form of an insoluble catalytic precursor, by bringing an organic liquid containing an insoluble catalytic precursor into contact with water, for the purpose of building a two-phase system that has an organic layer as the upper phase and a lower aqueous phase containing an insoluble catalytic precursor, by drying the catalytic precursor and calcining the precursor in order to obtain an active catalyst.

The oxidation catalysts described in the cited references refer to a number of well-known solid catalytic forms used in fluidized bed maleic anhydride production processes, such as spheres, spheroids, tablets and pellets. Although the catalysts and catalytic forms from the described techniques are generally successful in the production of maleic anhydride, the commercial use of the catalytic system and catalytic process is highly dependent on the price of the catalyst, the conversion of reactants, and the utilization of the reaction or, in other words, the actual productivity of the catalytic system. In many cases, a reduction in the cost of a catalytic system in a given catalytic process of the order of a few cents per kilogram or pound, or a small increase in the amount of product obtained relative to the amount of catalyst, represents a huge economic advance in a commercial operation. Therefore, the efforts of researchers are continuously directed towards finding new or improving existing catalytic systems and procedures, in order to reduce the cost, improve the activity, selectivity and/or productivity. The disclosure of the shaped oxidation catalytic structures of the present invention is therefore believed to be an advance in the art.

Description of solutions with examples of implementation

Sl. 1A shows a solid cylindrical structure with voids as equally spaced circular grooves located in the outer surface, running generally vertically from top to bottom.

Sl. 1B shows a top view of a solid cylindrical structure with voids as equally spaced circular slots located in the outer surface, running generally vertically from top to bottom.

Sl. 2A shows a variation of the structure shown in Fig. 1A with the voids as equally spaced circular grooves located in the outer surface running vertically from top to bottom.

Sl. 2B shows a top view of a variation of the structure shown in Fig. 1B with the voids as equally spaced circular grooves located in the outer surface, running vertically from top to bottom.

Sl. 3A shows a solid cylindrical structure with voids as equally spaced circular grooves located in the outer surface, and a centrally located opening.

Sl. 3B shows a top view of a solid cylindrical structure with voids as equally spaced circular grooves in the outer surface, and a centrally located opening.

Sl. 4A shows a solid cylindrical structure with void space as a centrally located opening.

Sl. 4B shows a top view of a solid cylindrical structure with void space as a centrally located opening.

Sl. 5A shows a solid cylindrical structure with voids as equally spaced angular grooves located in the outer surface, running generally vertically from top to bottom.

Sl. 5B shows a top view, solid cylindrical structure with voids as equally spaced angular grooves located in the outer surface and running generally vertically from top to bottom.

Sl. 6A shows a solid cylindrical structure with void space arranged as a continuous angular spiral, located on the outer surface from top to bottom.

Sl. 7A shows a solid cylindrical structure with an empty space arranged as a circular groove on the outer surface, in communication with a centrally placed opening.

Sl. 7B shows a top view of a solid cylindrical structure with a void space provided as a circular groove on the outer surface in communication with a centrally located opening.

Sl. 8A shows a solid pyramidal structure with a square base with voids as equally spaced circular grooves in the outer surface at the corner edges.

Sl. 8B shows a top view of a solid pyramidal structure with a square base and void spaces arranged equally as circular grooves located in the outer surface at the corner edges.

Sl. 9A shows a solid pyramidal structure with a square base with voids as equally spaced circular slots in the outer surface laterally, along slanted surfaces from top to bottom.

Sl. 9B shows a top view, a solid pyramidal structure with a square base with voids as equally spaced circular grooves in the outer surface laterally, along slanted surfaces from top to bottom.

Sl. 10A shows a solid conical structure with voids equally placed as circular grooves in the outer surface along the inclined faces from top to bottom.

Sl. 10B shows a top view, a solid conical structure with voids equally placed as circular grooves in the outer surface along the inclined surfaces from top to bottom.

Sl. 11A shows a solid cubic structure with voids equally placed as corner slots located in the outer surface on the sides, from top to bottom generally vertically.

Sl. 11B shows a top view, a solid cubic structure with voids equally placed as corner slots located in the outer surface on the sides, from top to bottom generally vertically.

Sl. 12A shows a solid cubic structure with voids equally spaced as corner slots in the outer surface on the sides, from top to bottom generally vertically.

Sl. 12B shows a top view, a solid cubic structure with voids equally spaced as corner slots in the outer surface on the sides, from top to bottom generally vertically.

Sl. 13A shows a solid cubic structure with voids equally placed as dimples in the outer surface on the sides, top and bottom.

Sl. 13B shows a top view, a solid cubic structure with voids equally placed as dimples in the outer surface on the sides, top and bottom.

Sl. 14A shows a solid spherical structure with voids uniformly placed as circular dimples in the outer surface.

Sl. 14B shows a cross-section in the middle, a solid spherical structure with voids equally placed as circular dimples in the outer surface.

This invention is directed to shaped oxidation catalytic structures. Therefore, it is a primary object of the present invention to provide shaped oxidation catalytic structures comprising a catalytic material comprising vanadium and phosphorus oxides suitable for the production of maleic anhydride via the partial oxidation of non-aromatic hydrocarbons in the gas phase with molecular oxygen or a gas containing molecular oxygen. Such catalytic structures have enhanced catalytic activity, as demonstrated by the mass/mass productivity ratio compared to conventional oxidation catalytic forms for the production of maleic anhydride.

This and other objects, aspects and advantages of the present invention will become apparent to those skilled in the art by the following description and conditions.

The above objectives are achieved by the shaped oxidation catalytic structures of the present invention which comprise a solid geometric shape having at least one (1) void space placed in the outer surface. The shaped structure is characterized by (a) containing a catalytic material consisting of mixed oxides of vanadium and phosphorus and (b) exhibiting (i) a geometric volume of about 30 to about 90% of that expected for a solid geometry without void space, (ii) external geometric specific surface area/geometric volume ratio of at least about 15 cm-1 (iii) specific gravity of about 0.4 to about 1.4 g/cm3 and (iv) mechanical resistance sufficient to maintain mainly the structural integrity of the molded structure under the conditions of handling and use.

Description of preferred performances

Through this invention, designed oxidation catalytic structures for the production of maleic anhydride by partial oxidation of non-aromatic hydrocarbons in the gas phase with molecular oxygen or a gas containing molecular oxygen have been solved. Shaped structures comprise a solid geometric shape that has at least one (1) void space placed in the outer surface. In addition, such designed structures feature a combination of effective properties to increase catalytic activity, as determined by the mass/mass productivity ratio compared to conventional oxidation catalytic forms for the production of maleic anhydride.

For the purposes of this invention, the term "void space" means unoccupied space in a solid geometric shape, which is not normally present pores and cracks in such geometric shape. The term mass/mass productivity means the mass of maleic anhydride (MAN) expressed in grams that is produced in one cycle of hydrocarbon batch processing over the catalyst per unit mass of the catalyst expressed in kilograms per unit time expressed in hours, the term expressed as g maleic anhydride/kg catalyst- hours or g MAN/ kg cat. an hour. The term "yield" means (a) the ratio of moles of maleic anhydride obtained to the moles of hydrocarbon charge introduced into the reactor, multiplied by 100, expressed as mol%, and (b) the ratio of the mass of maleic anhydride obtained to the hydrocarbon charge introduced into the reactor multiplied by 100, the term expressed as mass%. The term "selectivity" means the ratio of the moles of maleic anhydride obtained to the moles of the hydrocarbon that entered the reaction or its conversion, multiplied by 100, is expressed as mol.%. The term "conversion" means the ratio of the moles of the hydrocarbon batch that entered the reaction to the moles of hydrocarbon introduced into the reactor multiplied by 100, the term is expressed as mol%. The term "space velocity" or "gas space velocity per hour" or "GHSV" means the volume of the gas batch expressed in cubic centimeters (cm3) at 20[image] C and atmospheric pressure, divided by the mass volume of the catalyst, expressed as cm[image ] /cm3/hour.

Geometrical solid shapes suitable in representative base structures of the molded oxidation catalytic structures of the present invention include solid geometry in which voids may be placed in the outer surface to provide the molded oxidation catalytic structures of the present invention. Non-limiting examples of solid geometric shapes include cylinders, cones, cones, frustum cones, pyramids, frustum pyramids, spheres, prisms, and the like.

The decisive feature of this invention is the placement of empty spaces in the outer surface of a solid geometric shape. Suitable voids include slots, cavities, dimples and the like. The outdoor spaces are usually evenly distributed over the outdoor areas where such empty spaces are located. The number and shape of empty spaces placed in the outer surface of a solid geometric shape is not of decisive importance. The basic thing that is required is that the obtained oxidation catalytic structure has certain inherent properties as stated in the following text. Therefore, the shape of the corners of the empty spaces, as well as the protrusions connected with them, can be angular or circular, and the number of such empty spaces, which must be at least one (1), can be some practical number, taking into account the dimensions of the empty spaces and the available external geometric surface in to which they are placed. It is generally preferable to have the shape of rounded corners.

In connection with the placement of voids in the outer surface of the solid geometric shape, the geometric volume of the required formed oxidation catalytic structures must be reduced to a value smaller than that of the solid geometric shape without void space. According to the present invention, the shaped oxidation catalytic structures of the present invention must exhibit a geometric volume of about 30 to 90%, preferably about 40 to 80%, of that of non-void geometries. The retention of such geometric volume, combined with other characteristic features of the shaped oxidation catalytic structures of this invention, provides structures that exhibit improved catalytic activity as demonstrated by mass/mass productivity ratios, when compared to conventional oxidation catalytic shapes, including solid geometries without of empty space, for the production of maleic anhydride.

The shaped oxidation catalytic structures of the present invention exhibit characteristic geometric volume and geometric specific surface area as a consequence of the cross-sectional shape and associated dimensions. Geometric volume and geometric specific surface area are easily calculated from appropriate measurements associated with appropriate perfect geometric shapes. The shaped oxidation catalytic structures of the present invention close to such shapes and their geometric specific surface areas and volumes can be closely estimated from the corresponding geometric models. The ratio (external) geometric specific surface/geometric volume should be about 15 cm-1, and preferably at least about 20 cm-¹.

The specific gravity of the formed catalytic structures is an indicator of the amount of catalytic material contained in a particular catalytic form. It is clear that for shaped structures with clearly defined dimensions, a larger amount of catalytic material (or material in general, whether it is a catalytic material or a combination of catalytic material and filler or inert material) means a higher specific weight. On the other hand, with all other constant factors, a higher specific gravity means a denser packing of the contained material. This is naturally associated with a reduction in porosity, which prevents the movement of reactive gas molecules in and out of the formed catalytic structure. The molded oxidation catalytic structures of the present invention, however, do not have this drawback because such structures have a specific gravity of about 0.4 to about 1.4 g/cm 3 , preferably about 0.5 to about 1.1 g/cm 3 .

Those skilled in the art will appreciate that the formed oxidation structures must have sufficient mechanical strength or physical durability to withstand handling, transfer from the source of production to the reactor in which they are used, and loading into the reactor. In addition, the molded structures must be able to support their own mass in the reactor. In other words, they must have mechanical resistance sufficient to maintain the substantially structural integrity of the molded structure under conditions of handling and use. If the molded structures have insufficient mechanical resistance, breakage may occur. Of course, the economic consequences in that case are negative, such as an increase in the pressure drop and a decrease in the reactive gas flow rate, an increase in the production price of formed oxidation catalytic structures due to the loss of small broken pieces, and less efficiency of the reactor operation due to hot spots in the catalytic layer. In general, sufficient mechanical resistance, as determined by measuring breaking strength—the strength of force required to tear or break a molded structure—there are structures that exhibit a lateral breaking strength of about 4.45 to about 222.4 Newtons (N) (about 1-50 pounds ), preferably from about 13.3 to about 89 N (3-20 pounds). In other words, the mechanical resistance of the molded structure is sufficient to maintain mainly its structural integrity, which at the same time is not excessive in the sense that the porosity of the molded structure is reduced to such values that the movement of reactive gas molecules in and out of the molded structure is impossible.

The shaped oxidation catalytic structures of the present invention can be of practical size and dimensions, given the dimensions of the particular reactor tube in which they are used. In general, a base width (ie, the widest part of the structure) of about 3.175 mm to about 6.35 mm and a height to base width ratio of about 0.5 to 2.0 are favorable for use.

Catalytic materials suitable for use in this invention are known in the art. In general, these are materials suitable for catalysis in the gas phase where partial oxidation of hydrocarbons to maleic anhydride occurs under oxidizing conditions. Such materials are generally vanadium phosphorus oxide complexes, and usually contain a promoter element. A common expression of the empirical formula of a suitable catalytic material is expressed as VPxOyMz, where M is a promoter element selected from the group consisting of elements from groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, and VIIIB of the periodic table of elements , x is a number from about 0.5 to 2.0, preferably from about 0.95 to 1.35, y is a number taken to satisfy the valences of V, P and M in the oxidation states in which they exist in the preparation, and z is a number from zero to about 1.0, preferably about 0.5.

Specific, although non-limiting, examples of suitable catalytic materials are those described in multiple references provided in "Description of the Prior Art" - US Patent Nos. 4632915, 4562268, 4333853, 4315864, 4312787, 4251390, 4187235, 40187-u, 3980585, 3888866, 3864280, 3862146, 3856824 and European patent application no. 98039 - it is understood, however, that the same are not given as limiting, but for purposes of practicality and illustration of this invention. Among such catalytic materials, those described in US Pat. Nos. 4632915 and 4562268.

The shaped oxidation catalytic structures of the present invention can be obtained by mixing the catalytic material with shaped structures made of known materials such as graphite or stearic acid with a suitable inert filler material by pressing in a mold (a press containing a suitable mold) or by extrusion or casting by methods known in the art. technique. In general, the push-in-mold (compaction) technique is preferred because it is easier to obtain molded structures with properties corresponding to this invention. In the same sense, it is preferable not to use an inert filler material, because the partial oxidation reaction of hydrocarbons into maleic anhydride is optimally performed in a way that maximizes the amount of active catalytic material that is in a certain volume of the reactor, and thus achieves the largest amount of hydrocarbons converted into maleic anhydride within of one reactor cycle.

The designed oxidation catalytic structures of this invention can be applied in various reactors for the purpose of converting non-aromatic hydrocarbons to maleic anhydride. A typical reactor used for this process is a tube type, fixed bed, with central cooling and heat transfer. The details of the operation of this type of reactor are well known to experts. The tubes of such reactors can be made of iron, stainless steel, nickel, glass (Vycor, etc.), and their diameter can vary from 0.635 to 3.81 cm, and their length from 15.24 to 762 cm. The oxidation reaction is very exothermic even in the course of one reaction, and in order to maintain the desired temperature of the reactor, a medium is needed to remove heat from the reactor. Suitable heat transfer media are well known to those skilled in the art. These are usually materials that remain in a liquid state at reaction temperatures and have a relatively high thermal conductivity. Examples of such materials include various heat transfer oils, molten sulfur, mercury, molten lead, and alkali metal salts such as nitrates and nitrites. Salts are preferred due to their high boiling point. A mixture of potassium nitrate, sodium nitrate and sodium nitrite is particularly desirable, which not only has the necessary high boiling point, but also a sufficiently low freezing point, so that it remains in a liquid state even during reactor downtime. Another method of temperature control is the use of a metal block reactor, in which the metal surrounding the reaction part of the reactor acts as a temperature regulator.

In general, the reaction for the conversion of non-aromatic hydrocarbons into maleic anhydride involves sieving a mixture of non-aromatic hydrocarbons having at least 4 carbon atoms in a normal or cyclic structure, a gas containing molecular oxygen, and a reactor supplied with a heat removal medium and a reaction zone consisting of formed oxidation catalytic structures of this invention. In addition to hydrocarbons and molecular oxygen, other gases such as nitrogen or water vapor may be present in the reaction mixture. Typically, the hydrocarbon is mixed with a gas containing molecular oxygen at a concentration of 1 to 10 mol% hydrocarbon. Contact with the catalyst is achieved at a space velocity (GHSV) of about 100 to 5000/hour and at a temperature of 300 to 600 C. It is optimal between 1000 and 3000/hour and 325 to 500 C.

Initially, the yield of maleic anhydride may be small. In this case, the catalyst can be prepared for the production process itself in such a way that the formed oxidation catalytic structures are brought into contact with low concentrations of hydrocarbons and gas containing molecular oxygen, at low space velocities.

Pressure is not critical in the reaction of conversion of non-aromatic hydrocarbons into maleic anhydride. The reaction can be carried out either at atmospheric, higher or lower pressure. It is generally preferable to operate at a pressure close to atmospheric. Pressures between 1.24 x 102 and 2.068 x 102 kPa are preferred.

Maleic anhydride produced using the oxidation-formed catalytic structures of this invention can be isolated in various ways known to those skilled in the art, for example by direct condensation or adsorption in a suitable medium, with further separation and purification.

In order to compare the efficiency of maleic anhydride production using the present invention, mass ratios/mass productivity and maximum reaction yields under standardized conditions were compared. In this case, the concentration of hydrocarbons in the air was 1.5 mol% with a space velocity of 2000/hour, and the hydrocarbon conversion was adjusted to about 70 to 90 mol%, which is just enough to obtain the maximum yield of maleic anhydride. Of course, the values of the mass/mass productivity ratio and the maximum reaction yield can also be determined under conditions other than those specified. However, the values obtained will usually not be equal to those obtained with the above reaction conditions. Therefore, a direct comparison of mass ratio/mass productivity values and maximum yields for different catalytic structures can only be made if the measurements were made under identical conditions.

A wide variety of non-aromatic hydrocarbons containing 4 to 10 carbon atoms can be converted to maleic anhydride using the oxidation-patterned catalytic structures of this invention. It is only necessary that the given hydrocarbon contains no less than 4 carbon atoms in the chain or ring. For example n-butane is satisfactory, but isobutane (2-methyl propane) is not suitable for conversion to maleic anhydride, although its presence does not interfere. In addition to n-butane, pentanes, hexanes, heptanes, octanes, nonanes, decanes and their mixtures are suitable for conversion. It is essential that at least 4 carbon atoms are in a normal chain within a saturated hydrocarbon molecule.

Certain unsaturated hydrocarbons are also suitable for conversion to maleic anhydride using the present invention. These are butenes (1-butene and 2-butene), 1,3-butadiene, pentenes, hexenes, octenes, nonenes, decenes and their mixtures with or without butene, and of such a length that they contain at least 4 carbon atoms in the normal chain.

Cyclic hydrocarbons such as cyclopentane and cyclopentene can also be used in the production of maleic anhydride using the designed oxidation catalytic structures of this invention.

Of all the above, it is optimal to use n-butane from saturated, and n-butene from unsaturated compounds suitable for this reaction.

It is important to note that it is not necessary to work with pure substances, but it is sufficient for the hydrocarbons to be of a technical degree of purity.

The main oxidation product of the above-mentioned materials is maleic anhydride, although smaller amounts of citraconic anhydride (methyl maleic anhydride) can be formed if the starting material is a hydrocarbon containing more than 4 carbon atoms.

The following specific examples describe the best currently known method of using this invention, and are described in detail in order to facilitate a clearer understanding of the invention. It is to be understood, however, that the detailed descriptions of the practice of the present invention are provided by way of illustration only and not as limitations, and possibilities of alteration and modification will be apparent to those skilled in the art after a review of the descriptions below.

Example 1

A 12-liter round-bottomed flask equipped with a ball stirrer, thermometer, thermal insulation, and reflux condenser is charged with 900 mL of isobutyl alcohol, 378.3 g (4.20 moles) of oxalic acid (C2H2O4), and 843.4 g of vanadium pentoxide (V2O5 ). 997.6 g (10.76 mol) of phosphoric acid (H3PO4, 105.7% by mass) is added to this mixture. The resulting mixture is refluxed for about 15 hours, until it becomes light blue in color. After extracting 6 L of isobutyl alcohol within three hours, the mixture is cooled and quantitatively transferred to a flat porcelain dish and dried for 48 hours at 110 C in nitrogen, and then for 48 hours at 150 C in air. The dried material is transferred to another box-type furnace and heated in air at 250-260 C for one hour to obtain a gray-black catalytic precursor powder.

Catalytic precursor powder is mixed so that it contains about 4.0 wt.% graphite, and is pressed on a Stokes 512 tableting machine, which has appropriate molds and punches for the purpose of obtaining the catalytic structure of the desired shape, and 1.27 cm cylinders with tablet density from 1.30 to 1.50 g/cm3. The 1.27 cm nuggets are milled to produce a batch powder tablet between 18 and 30 mesh (600 microns) in size and batched into a tableting machine. The compaction pressure is adjusted to obtain structures with an average (lateral) breaking strength of 13.3 to 89 N (3 to 20 pounds). The characteristic properties of the produced molded catalytic structures are given in Table 1.

Any designed catalytic structure produced must be activated. The molded catalytic structure is placed on a 30.48 cm x 30.48 cm x 2.54 cm substrate made of stainless steel mesh that has about 40% open area. The substrate is transferred to a box-type furnace through which air preheated to about 425ºC passes. This temperature is maintained for 1-2 hours. Then the base of the formed oxidation catalytic structures is removed from the furnace and cooled. After that, it is transferred to a box-type furnace through which gaseous nitrogen passes, and it is heated to about 275ºC, at which temperature the atmosphere in the furnace changes to a mixture of 50% air and 50% water vapor. Within one to two hours, the temperature rises to 425ºC, and is maintained at this value for 6 hours. The base of the formed oxidation structures is cooled to room temperature, while dry nitrogen passes through the furnace. The formed catalytic structures are charged into a tubular fixed bed reactor, 2.10 cm internal diameter and 121.9 cm long, and the properties are tested as described in Example no. 5.

Example 2

In this example, the production of vanadium phosphorus oxide is described in accordance with the procedure described for examples 1-7 of US patent no. 4333853.

A 12-liter bottle with a round bottom and the equipment described in Example 1 is filled with 7340 ml of isobutyl alcohol and 513.5 g (2.82 moles) of V2O5. 663.97 g of 100% phosphoric acid in 1129 ml of isobutyl alcohol is added with stirring. The resulting reaction mixture is refluxed for about 16 hours until it acquires a light blue color. The mixture is cooled, the precipitate is filtered and dried at ambient temperature under vacuum. The dried residue is then washed with about 1200 ml of isobutyl alcohol, dried at about 145ºC for two hours, and calcined for about 1 hour in a stream of air at 400ºC.

Catalytic precursor powder is mixed so that it contains about 2.54% by weight of stearic acid and placed in a Stokes 512 Rotary Tableting machine which is equipped with suitable molds and punches in order to obtain the desired shaped catalytic structure. The pressure during the compaction process is adjusted to produce structures with average lateral breaking strengths of 13.3 to 89 N (3-20 pounds). The characteristic properties of the catalytic structures produced in this way can be found in Table 1. The catalytic structures obtained in this way are placed in a tubular stationary bed reactor with an internal diameter of 2.10 cm and a length of 121.9 cm. Properties are tested as specified in Example 5.

Example 3

This example describes the production of a lithium/zinc promoter vanadium phosphorus oxide catalyst, in accordance with the process described for examples 1-7 of US Pat. 4333853.

A 12 liter round-bottomed bottle, equipped as described in Example 1, plus a Dean Stark piston and gas dispersion tube, is charged with 6500 ml of isobutyl alcohol and 1145 g (6.29 moles) of vanadium pentoxide. Mixing begins, and dry hydrogen chloride (HCl) is passed through the mixture at a rate sufficient to maintain the reaction temperature at about 50°C. After 6 hours and 43 minutes of reaction with hydrogen chloride, the color of the reaction mixture becomes reddish-brown. Then a solution containing 1089.5 g (9.51 mol) of 85.5% phosphoric acid, 422.0 g (2.97 mol) of phosphorus pentoxide dissolved in 1500 ml of isobutyl alcohol is added. An additional 100 ml of isobutyl alcohol is used to wash the phosphorus-containing solution into the vanadium-containing solution. Zinc chloride (ZnCl2, 17.17 g, 0.13 mol) and 1.07 g (0.025 mol) of lithium chloride (LiCl) are added to the reaction mixture. This solution is refluxed for about two hours, after which 5.33 L of isobutyl alcohol is separated over a period of about 4 hours. The mixture is cooled and quantitatively transferred into a porcelain container, and dried at 150°C.

The catalytic precursor powder is mixed so that it contains about 4% by weight of graphite. Tableting is done on a Stokes 512 Rotary Tableting machine equipped with appropriate molds and punches to obtain the desired shaped catalytic structures, 1.27 cm cylinders with a tablet density of about 1.90 g/cm3. The 1.27 cm nuggets are milled to obtain a tablet batch powder with a particle size between 18 and 30 mesh (600 microns) and charged into a tableting machine equipped with appropriate dies and punches to obtain the desired shaped oxidation catalytic structure. The compaction pressure is adjusted to produce structures with average (lateral) breaking strengths of 13.3 - 89 N (3-20 pounds). The characteristic properties of the formed catalytic structures are given in Table 1. The thus obtained structures are activated according to the activation procedure described in US patent no. 4333853 by placing them in a tubular reactor with a fixed bed, with an internal diameter of 2.10 cm and a length of 121.9 cm. The reactor is heated slowly up to 400°C while at the same time a gas containing 0.5-0.7 mol.% n-butane in air passes over the formed catalytic structures, starting at 280ºC. After the temperature reaches 400 degrees Celsius, the molded structures undergo aging in a stream of n-butane in air. The properties of the catalytic structures thus activated and conditioned are tested as described in Example 5.

Example 4

This example describes the preparation of an iron/lithium promoted vanadium phosphorus oxide catalyst in accordance with the procedure described in Example 1 of US Pat. 4632915.

A 12-liter round-bottom bottle supplied as described in Example 1, except that it also contains a Dean Stark plunger and a coarsely porous gas dispersion tube, is filled with 8300 ml of isobutyl alcohol. Mixing begins and the isobutyl alcohol is cooled to a temperature of about 10 to 15°C. A solution of 901.8 g (7.87 moles) of 85.5% phosphoric acid and 343.4 g (2.42 moles) of phosphorus pentoxide maintained at room temperature is added to the cooled isobutyl alcohol. The resulting solution is cooled to about 5 to 10°C. 953.0 g (5.29 moles) of vanadium pentoxide, 1.35 g (0.032 moles) of lithium chloride, 0.96 g (0.017 gram atoms) of iron powder and an additional 1.0 L of isobutyl alcohol are added to the cooled solution with stirring. Anhydrous HCl (2037.0 g or 55.81 mol) was added to the reaction mixture through a gas dispersion tube for 4.67 hours while maintaining the temperature between 40 and 50ºC. The solution is heated and maintained at reflux for about 2 hours. Then, 5.4 L of distillate is removed at atmospheric pressure over 5 hours, which is followed by additional refluxing for 1.38 hours. After that, an additional 1.5 L of distillate is removed over 2.35 hours. The mixture is cooled and quantitatively transferred into a porcelain bowl, and dried in a box-type oven at 150 degrees Celsius for 5.5 hours. The dried material is transferred to another furnace of the same type and heated in nitrogen at a temperature between 250 and 260°C for about 3 hours, which is followed by replacing the nitrogen with air. Additional heating for 3 hours is performed in order to obtain a gray-black catalytic precursor powder.

Catalytic precursor powder is mixed to contain about 4 by mass of graphite and subjected to tableting on a Stokes 512 Rotary Tableting machine equipped with appropriate dies and punches to obtain the desired shaped catalytic structure, 1.27 cm cylinders with a tablet density of about 1.90 g/cm3 . The 1.27 cm nuggets are milled to obtain a tablet batch powder with a particle size between 18 and 30 mes (600 microns) and fed into a tableting machine equipped with appropriate dies and punches to obtain the desired shaped oxidation catalytic structure. The compaction pressure is adjusted to produce structures with average (lateral) breaking strengths of 13.3 - 89 N (3-20 pounds). The characteristic properties of the formed catalytic structures are given in Table 1. The thus obtained structures are activated according to the activation procedure described in US patent no. 4632915, except that they are placed in a tubular reactor with a fixed bed of 2.10 cm internal diameter, 121.9 cm long. After activation, the molded catalytic structures are conditioned by heating the reactor at 1 degree Celsius/hour to 400 degrees, while passing a gas stream containing 0.6 mol% n-butane in air over the molded catalytic structures, starting at about 280ºC. After the temperature rises to 400 degrees Celsius, the molded structures undergo aging by passing a continuous stream of n-butane in air over the catalyst for 24 hours. The properties of the catalytic structures thus activated and conditioned are tested as described in Example 5.

Example 5

Each type of molded catalytic structure is tested under a standardized set of reaction conditions - 1.5 mol% n-butane, 1.034 x 102 kPa (15.0 psig) inlet pressure and 2000 GHSV. The desired formed oxidation catalytic structure is placed in a reactor with an internal diameter of 2.10 and a length of 121.9 cm, to its useful height of 121.9 cm. The amount of catalyst placed in the reactor is a direct result of the characteristics of the tube being filled with the desired shaped catalytic structure. The catalyst works for at least 200 hours under standardized test conditions before performing yield optimization. The maximum yield value is determined for each structural subspecies by increasing n-butane conversion until no further increase in reaction yield is observed. Parameters and results are listed in Table 2.

A comparison of ma sa values/mass productivity with various shaped oxidation catalytic structures (compare Examples 1A with 1B, 1C, 1D or 1E and 2A with 2B or 2C) clearly demonstrates the advantages of the shaped oxidation catalytic structures of this invention over conventional catalytic forms. In general, a similar comparison of the wt% yield of maleic anhydride shows equal or better results of the designed oxidation catalytic structures of this invention over the conventional catalytic forms of the prior art. Therefore, the advantage of an equal or higher reaction yield with the use of a smaller amount of catalyst provides considerable economic convenience.

It is clear that the present invention provides designed oxidation catalytic structures that fully satisfy the above objectives and advantages. Although the invention has been described with reference to various specific examples and embodiments, it is to be understood that it is not limited thereto. Many alternative modifications and variations will become apparent to those skilled in the art in light of the above description.

Claims (18)

1. A shaped oxidation catalytic structure for the production of maleic anhydride comprising a solid geometric shape having at least one empty space positioned on the outer surface, characterized in that (a) contains a catalytic material comprising mixed oxides of vanadium and phosphorus, and (b) exhibits (I) a geometric volume that is 30 to 90% of that for the void-free geometry, (II) an external specific surface area/geometric volume ratio of at least about 15/cm, (III) a density of about o.4 g/cm3 and (IV) mechanical resistance sufficient to substantially maintain the structural integrity of the molded structure under conditions of use and handling. 2. A shaped oxidation catalytic structure according to claim 1, characterized in that the solid geometric shape is selected from the group consisting of cylinders, cones, cones, tapered cones, pyramids, tapered pyramids, spheres and prisms. 3. Formed oxidation catalytic structure according to claim 1, characterized in that the empty spaces are equally placed over the outer surface on which they are located. 4. The formed oxidation catalytic structure according to claim 1, characterized in that the empty spaces are selected from the group consisting of grooves, cavities and dimples. 5. A shaped oxidation catalytic structure according to claim 1, characterized in that the empty spaces are selected from the group consisting of angular and rounded shapes. 6. Shaped oxidation catalytic structure according to claim 3, characterized in that the empty spaces are rounded. 7. Formed oxidation catalytic structure according to claim 1, characterized in that its geometric volume is about 40 - to 80% of that of the quay structure does not contain empty space. 8. Formed oxidation catalytic structure according to claim 1, characterized in that the ratio of external geometric specific surface area/geometric volume is at least 20/cm. 9. The formed oxidation catalytic structure according to claim 1, characterized in that its density is about 0.5 to 1.1 g/cm3. 10. The molded oxidation catalytic structure of claim 1, wherein the mechanical strength, as determined by lateral breaking strength, is about 4.45 to about 222.2 N. 11. The molded oxidation catalytic structure of claim 10, wherein the lateral breaking strength is about 13.3 to 89 N. 12. The molded oxidation catalytic structure of claim 1, wherein the molded structure exhibits a base width of about 3.175 to about 6.35 mm and a height/base width ratio of about 0.5 to about 2.0. 13. Formed oxidation catalytic structure according to claim 1, characterized in that the material is denoted by an empirical formula VPxOyMz where M is at least one promoter element selected from the group consisting of elements from groups IA, IB, IIA, IIB, IIIA, IIIB, IVB, VA, VB, VIB and VIIIB of the periodic table of elements, x is a number from about 0.5 to 2,0, y is a number chosen to correspond to the valences of V, P and M in the oxidation states in which they are in the preparation, and, finally, z is a number from 0 to 1. 14. The shaped oxidation catalytic structure according to claim 13, wherein x is a number of about 0.95 to 1.35 and z is a number of about 0.5. 15. Formed oxidation catalytic structure according to claim 13, characterized in that M is selected from the group consisting of elements from group IA and IIB of the periodic system of elements. 16. Formed oxidation catalytic structure according to claim 15, characterized in that M from group IA is lithium, and from group IIA zinc. 17. Formed oxidation catalytic structure according to claim 13, characterized in that M is selected from the group consisting of elements of groups IA and VIIIB of the periodic system of elements. 18. Formed oxidation catalytic structure according to claim 17, characterized in that M from group IA is lithium, and from group VIIIB is iron.