MXPA97003089A - Process for the transformation of a vanadium / phosphorus mixed oxide decanterizer in the active catalyst for deanhydride male production - Google Patents

Abstract

The present invention relates to a process for the transformation of a catalyst precursor represented by the formula: (VO) HPO4 to H2OMemPpOy wherein Me is at least one promoter element selected from the group consisting of the elements of group IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIB and VIIIA of the periodic table of elements or mixtures of these elements, a is a number from approximately 0.3 to approximately 0.7, m is a number from approximately 9 to about 0.3, p is a number from about 0 to about 0.3, and y represents the amount of oxygen needed to satisfy the valence requirements of all the elements present, in an active catalyst represented by the formula (VO) 2P2O7Me2mPepOy, where m, pey have the meanings indicated above, a process characterized by comprising the following stages that are carried out in a fluidized bed: a) an initial heating of the precu rsor up to a temperature not exceeding 250 ° C, b) additional heating under superatmospheric pressure from a temperature of approximately 200 ° C to a temperature of at least 380 ° C to 600 ° C, c) maintenance of the temperature reached in stage b) at superatmospheric pressure, and d) cooling the active catalyst

Description

PROCESS FOR THE TRANSFORMATION OF A PRECURSOR OF CATALYZER OF MIXED OXIDE OF VANADIUM / PHOSPHORUS IN THE ACTIVE CATALYST FOR THE PRODUCTION OF ANHYDRID MALEICO Field of the invention The invention relates to a process for the transformation of a catalyst precursor based on a mixed oxide of vanadium / phosphorus into the active catalyst for the production of maleic anhydride, and to a process for the production of maleic anhydride using this activated catalyst.

BACKGROUND OF THE INVENTION Maleic anhydride is a very important intermediate for the manufacture of unsaturated polyester resins or a versatile intermediary for the production of pharmaceutical and agrochemical products. In the prior art a large number of catalysts have been described based on a mixed vanadium oxide / phosphate forum, mainly in the form of REF: 24585 vanadyl pyrophosphate, capable of being used in the conversion of different organic raw materials into maleic anhydride . Therefore, preparation of the active species of the catalyst is generally carried out by a multi-step process comprising: a) the synthesis of a vanadyl acid phosphate as a precursor, which is carried out by contacting vanadium-containing compounds, phosphorus-containing compounds and optionally compounds containing a promoter component under the conditions necessary to reduce the pentavalent vanadium to tetravalent vanadium, b) the transformation of the vanadyl acid phosphate precursor into the active catalyst containing substantially vanadyl pyrophosphate by calcination, and finally, c) the aging of the active catalyst under the reaction conditions.

One of the critical steps in the preparation of the catalyst is the calcination process, i.e., the transformation of the vanadyl acid phosphate precursor into the active catalyst containing substantially vanadyl pyrophosphate. U.S. Patent No. 5,137,860 describes a process for the transformation of the oxidation catalyst precursor based on a mixed vanadium / phosphorus oxide into the active catalyst for the partial oxidation of non-aromatic hydrocarbons to maleic anhydride. The calcination of the precursor material is carried out by a three-stage heating comprising a) an initial heating step and an atmosphere chosen from the group consisting of air, steam, inert gas and mixtures of these components, b) a heating step fast at a programmed heating rate and in an atmosphere containing molecular oxygen / vapor, and c) a final maintenance stage, which is first carried out in an atmosphere containing molecular oxygen / vapor and then in a non-oxidizing atmosphere containing steam. According to what is described in this publication, the calcination is carried out in a fixed bed and at atmospheric pressure. It has been discovered that there are notable temperature gradients in the fixed bed because the removal of water during calcination is endothermic. This inhomogeneity in the temperature profile finally produces a lower efficiency and a decrease in the wear resistance of the catalytic system.

Description of the invention Therefore, the object of the present invention is to avoid these disadvantages of the catalytic systems of the state of the art and to provide an improved process for transforming a catalyst precursor based on a mixed oxide of vanadium / phosphorus into the active catalyst for the production of maleic anhydride. Another object of the invention is to provide a catalyst exhibiting optimum performance during the process of converting a non-aromatic hydrocarbon to maleic anhydride. In addition, an improved process for preparing maleic anhydride is also an object of the invention.

The objects and advantages of the invention are achieved with the new process for transforming a catalyst precursor based on a mixed vanadium oxide / phosphorus into the active catalyst as described in claim 1, with the catalyst described in claim 12 and obtained by the transformation process of the invention, and with the process for preparing maleic anhydride that is described in claim 13 and employing the catalyst transformed according to the present invention. The process of the invention comprises the transformation of a catalyst precursor represented by the formula (VO) HP04 to H20 MemPpOy I, where Me represents at least one promoter element chosen from the group consisting of the elements of group IA, IB, HA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIB and VIIIA of the periodic table of elements or mixtures of these elements, a is a number from about 0.3 to about 0.7, m is a number from about 0 to about 0.3, p is a number from about 0 to about 0.3, and y represents the amount of oxygen needed to meet the requirements of valence of all the elements present, in an active catalyst represented by the formula (VO) 2P207Me2mP2pOy II, where m, p and y have the meanings indicated above, a process comprising the following steps carried out in a fluidized bed: a) an initial heating of the precursor up to a temperature not exceeding 250 ° C approximately b) an additional heating at superatmospheric pressure from a temperature of approximately 200 ° C to a temperature of at least 380 ° C to 600 ° C, c) maintaining the temperature reached in stage b) at superatmospheric pressure and d) cooling the activated catalyst.

The expression "Periodic table of elements" used in this text refers to the periodic table of elements published in Rump Chemie Lexikon 9a ed., Georg Thieme Verlag, Stuttgart, volume 4, p. 3285. I preferably represent lithium, zirconium, titanium, iron or niobium, or mixtures of these elements, a is a number that is preferably around 0.5 m is preferably a number from about 0 to about 0.1 and p is preferably a number from approximately 0.1 to 0.2.

Thus, the most convenient ratio of phosphorus atoms to vanadium atoms, or the atomic ratio P / V, is in a range of about 1 to 1.3, preferably about 1.1 to about 1.2. The catalyst precursor materials that are suitable for use in the process of the present invention are those known in the prior art, for example, those described in U.S. Pat. 4,594,433; 5,137,860 or 4, 668, 652. Accordingly, the preparation of the precursors includes the reaction of the vanadium component, the phosphorus component and optionally the promoter component in either aqueous or organic medium. In general, organic reaction media such as, for example, a primary alcohol, a secondary alcohol or mixtures thereof are preferred. Isobutyl or benzyl alcohol or mixtures of both are particularly preferred. Depending on the preparation conditions, the alcohol can be trapped or intercalated considerably within the structure of the precursor. As is known in the prior art, the vanadium component of the precursor can be obtained from a trivalent, tetravalent or pentavalent vanadium compound. As representative but not limiting examples, mention may be made of vanadium trichloride, vanadium tetrachloride, vanadium dioxide, vanadium pentoxide or vanadium oxytribromide. Vanadium pentoxide is preferred. Non-limiting examples of the phosphorus compound are phosphorous acid and phosphoric acid.

Depending on the valence of the vanadium compound, the reaction can be carried out under non-oxidizing conditions or under reducing conditions in order to reduce a pentavalent vanadium compound to the tetravalent form. Once the catalyst precursor has been prepared, recovered and dried it is preferably carried, in view of its activation treatment in the fluidized bed of the invention, to defined structures with defined properties with respect to wear resistance or mechanical properties. Such processes include, in general, a wet milling process of the dry precursor until a particle size of less than 10 μm is reached., preferably less than 3 μm. At this stage additives can also be added to improve the wear resistance as described, for example, in US Pat. No. 4,511,670. Following this preliminary step, a recovery step may be carried out, for example, a spray drying, calcination, further milling in the presence of a controlled amount of an acid, usually phosphoric acid, and a final recovery step. and structuring the precursor material, for example, by spray drying. The precursor is preferably obtained in a spherical form which is most suitable for the use thereof in a fluidized bed reactor. In general, the transformation of the precursor material of general formula I into the active catalyst comprises four steps carried out in a fluidized bed, namely: a) an initial heating of the precursor to a temperature not exceeding about 250 ° C, b ) an additional heating at superatmospheric pressure from a temperature of approximately 200 ° C to a temperature of at least 380 ° C to 600 ° C, c) maintenance of the temperature reached in stage b) under superatmospheric pressure and d) cooling of the activated catalyst .

According to the invention, the transformation in the active catalyst is carried out in a fluidized bed, that is to say that it is conveniently carried out under conditions that allow the optimal fluidization of the catalytic bed. Such conditions are preferably expressed by means of the surface velocity which is defined as the volume of the gaseous feed at the given conditions of temperature and pressure per second, which is expressed in m3s "x, divided by the surface area of the catalytic bed expressed in m2, thus obtaining the superficial velocity expressed in ms "1. As a general rule, the surface velocity is usually adjusted to a range between approximately 0.01 ms "1 and 0.5 ms" ~, preferably between approximately 0.02 ms "1 and 0.2 ms" "1 during the entire transformation stage of the precursor in the catalyst During the initial heating stage a) the precursor is heated in a conventional atmosphere, ie air, steam, inert gas or mixtures thereof, at atmospheric or superatmospheric pressure and at any convenient heating rate until reaching a temperature which not exceeding approximately 250 ° C. In the following, superatmospheric pressure is expressed as absolute pressure, In a preferred embodiment of the invention, the precursor is heated in air, at a superatmospheric pressure of at least 1.1 bar, more preferably 2 a 3 bars, and at a heating rate of approximately 1 ° C / minute at 5 ° C / minute until reaching a temperature not exceeding 200 ° C During activation stages b) and c) superatmospheric pressure is a mandatory parameter, which exerts the surprising effect of increasing the performance of the catalytic system. In these steps it is convenient to apply a superatmospheric pressure of at least 1.1 bar, preferably from approximately 2 to approximately 3 bar. Step b) comprises an additional heating step in which the temperature reached in the previous stage is increased from approximately 200 ° C to a temperature of at least 380 ° C and without exceeding approximately 600 ° C, preferably heated from about 200 ° C to about 400 ° C to 450 ° C, at a controlled heating rate, in a defined atmosphere, in a fluidized bed as described above and under the pressure conditions indicated above. It is expedient to operate at a heating rate of between approximately 0.1 ° C / minute and approximately 10 ° C / minute, preferably between approximately 1 ° C / minute and approximately 4 ° C / minute. The atmosphere required for step b) is composed of oxygen or an oxygen-containing gas, an inert gas and vapor, conveniently containing 1 to 20% by volume, preferably 2 to 10% by volume of oxygen, 10 to 80% by volume, preferably 30 to 70% by volume of steam (calculated as H20) and the rest of the inert gas. The oxygen source can be air or molecular oxygen, preferably air. As an inert gas, nitrogen or a noble gas such as helium or argon can be used. During the isothermal stage c) the temperature reached in stage b) is maintained for at least 0.5 hours, preferably for a period of 3 to 5 hours, in a controlled atmosphere and in the fluidized bed and pressure conditions indicated above. The atmosphere required for stage c) is a composition of vapor and an inert gas and, if necessary, also of oxygen or of an oxygen-containing gas. Said atmosphere conveniently contains from 10 to 80% by volume, preferably from 30 to 70% by volume of steam (calculated as H20) and from 0 to 20% by volume, preferably from 2 to 10% by volume of oxygen, and the rest It is completed with the inert gas. The oxygen source can be air or molecular oxygen, preferably air. As an inert gas, nitrogen or a noble gas such as helium or argon can be used. During the cooling step d) the activated catalyst is brought to room temperature. Although the conditions of this stage are not critical, it is preferred to carry it out in an inert atmosphere and under the fluidized bed and pressure conditions described above. It is preferred that the cooling rate does not exceed 5 ° C / minute. After carrying out the transformation described by the present invention, the catalyst is ready to be used in the conversion of non-aromatic hydrocarbons to maleic anhydride. Another important aspect of the invention is that under the conditions of the process, the catalyst surprisingly does not need further aging. From the beginning of the conversion, the catalyst exhibits an immediate activity and selectivity providing excellent yields of maleic anhydride. The process for the conversion of non-aromatic hydrocarbons to maleic anhydride is known and described in the prior art, for example, in US Patent Nos. 4,594,433, 5,137,860 and 4,668,652. In general, the conversion of the non-aromatic hydrocarbon to maleic anhydride is carried out with oxygen or an oxygen-containing gas at a temperature comprised between approximately 320 ° C and 500 ° C. As the non-aromatic hydrocarbon, it is conveniently used in saturated or unsaturated hydrocarbon having 4 to 10 carbon atoms or mixtures thereof. The particularly preferred hydrocarbon is n-butane. In general, the feed gas is composed of a mixture of the hydrocarbon and oxygen or a gas containing oxygen, preferably air, in an oxygen: hydrocarbon ratio usually from 15: 1 to 1: 1. The conversion can be carried out at in a fixed or fluidized bed reactor, but in particular it is carried out in a fluidized bed reactor.

The examples given below are only illustrative and not limiting, since from this description the person skilled in the art can carry out various modifications that are included within the limits of the present invention.

EXAMPLES Example 1 (comparison) Into a 5 liter three-neck flask, fitted with a thermometer, mechanical stirrer, glass distillation column with reflux condenser and Dean-Stark water separator, 2 liters of isobutanol and 404 g of H3P04 are introduced. (100%) The mixture is heated to reflux and then a suspension of 326 g of V205 in 1000 ml of isobutanol is added slowly (for about 1 hour). During the addition of V205, an equal amount of isobutanol is distilled into the V2O5, removing the water formed during the reaction from the reaction mixture. Once the V205 addition is complete, heating to reflux is continued for two hours, separating more water formed during the reaction. The residue is cooled and the blue solid which is dried at 140 ° C is filtered. This gives the catalyst precursor based on a complex oxide of V-P-O. The catalyst precursor, once prepared, is brought to a structure with defined wear resistance properties by means of a spray drying process as described in US Patent No. 4,654,425 (Example 1). The material recovered from the spray drying was introduced into stainless steel containers and placed in a forced ventilation oven. During the calcination in the furnace, an N2 atmosphere was maintained and the precursor was heated at a programmed heating rate of approximately 9 ° C / minute, starting from room temperature to 550 ° C. The catalyst was maintained at 550 ° C under isothermal conditions for 5 hours and then cooled to room temperature. This procedure is called the normal calcination procedure.

Example 2 (comparison) This example illustrates the transformation of a vanadium oxide and phosphorus precursor, prepared according to Example 1, into an active catalyst according to the process described in Example 3, Part D, of US Pat. 5, 137, 860. The material recovered from the spray drying was placed inside a stainless steel vessel and introduced into the furnace. The precursor was subjected to a hydrothermal treatment according to the following procedure: a) heating from 25 ° C to 275 ° C in air and without any control of the heating step; b) heating from 180 ° C to 425 ° C in a mixture of air (75% in mol) and steam (25% in mol), at a programmed speed of 4 ° C / min .; c) isothermal stage at 425 ° C in the same mixture described above, for 1 hour; d) isothermal stage at 425 ° C in nitrogen (50% in mol) and steam (50% in mol), for 6 hours.

Example 3 (comparison) The procedure described below is called the hydrothermal method of calcination in a fluidized bed at atmospheric pressure. The procedure consists of a thermal treatment in the presence of steam. The treatment was carried out at temperatures not exceeding 450 ° C. The material recovered from the spray drying was introduced in a stainless steel fluidized bed reactor and at atmospheric pressure it was subjected to a hydrothermal treatment according to the following process: a) heating from 25 ° C to 180 ° C in air and in 40 '; b) heating from 180 ° C to 425 ° C in a mixture of air (27% by volume) and steam (73% by volume), at a programmed speed of 1.5 ° C / min.; c) isothermal stage at 425 ° C in the same mixture described above, for 2 hours; d) isothermal stage at 425 ° C in nitrogen (27% by volume) and steam (73% by volume), for 3 hours; e) cooling in a mixture of nitrogen and steam.

Example 4 (invention) The process described below is called the hydrothermal method of calcination in a fluidized bed with pressure. The procedure consists of a thermal treatment in the presence of steam. The treatment was carried out at temperatures not exceeding 450 ° C. The material recovered from the spray drying was introduced in a stainless steel fluidized bed reactor and subjected to a hydrothermal treatment with pressure (3 bars) maintaining a surface velocity of 0.03 ms "1 according to the following process: a) heating from 25 ° C up to 180 ° C in air at a programmed speed of 4 ° C / min, b) heating from 180 ° C to 425 ° C in a mixture of air (70% by volume) and steam (30% by volume) , at a programmed speed of 1.5 ° C / min; c) isothermal stage at 425 ° C in the same mixture described above, during 2 hours; d) isothermal stage at 425 ° C in nitrogen (70% by volume) and steam (30% by volume), for 3 hours; e) cooling in a mixture of nitrogen and steam, at a programmed speed of 2 ° C / min.

Example 5 (invention) The precursor was treated in a manner similar to that of Example 4, with the exception that the surface velocity was 0.05 ms "1.

Example 6 (invention) The precursor was treated in a manner similar to that of Example 4, with the exception that step d) was carried out in a mixture of nitrogen and steam for 6 hours.

Example 7 (invention) The precursor was treated in a manner similar to that of Example 4, with the exception that the amount of oxygen in the feed was 4% by volume. The activity test was carried out as in Example 1 and the behavior of the catalyst is indicated in Table 1.

Evaluation of the catalysts activated in the conversion of n-butane to maleic anhydride: The catalytic tests were carried out at atmospheric pressure in a glass piston type spent reactor of a fluidized bed pilot plant, which had been charged with 500 ml of the catalyst. The products that were absorbed in water were collected and analyzed by gas chromatography. The performance of the catalysts was determined based on the weight of the butane with which the reactor was fed, the amount of maleic anhydride (AM) recovered in the wash water (acidimetry) and the amount of butane in the gases outside the reactor. reaction in a given period of time. During the activity tests, the following conditions were maintained in order to establish a comparison: reaction temperature: 360-440 ° C concentration of n-butane in the feed: 4% by volume air flow rate: 75 Nl / h superficial speed: 0.03 ms "1.

The reaction conditions and results are summarized in the table below. This table shows the temperature at which 81% of the conversion of n-butane is reached, as well as the yield of maleic anhydride and the selectivity to maleic anhydride at this degree of conversion. Table It is noted that in relation to this date, the best method known by the applicant to carry out the present invention is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property:

Claims (13)

1. Process for the transformation of a catalyst precursor represented by the formula (V0) HP0 to H20 MemPp0? I, where Me is at least one promoter element chosen from the group formed by the elements of group IA, IB, HA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIB and VIIIA of the periodic table of elements or mixtures of these elements, a is a number from about 0.3 to about 0.7, m is a number from about 0 to about 0.3, p is a number from about 0 to about 0.3, and y represents the amount of oxygen necessary to satisfy the valence requirements of all the elements present, in an active catalyst represented by the formula (VO) 2P2? 7Me2mP2pO? I I, where m, p and y have the meanings indicated above, a process characterized by comprising the following steps that are carried out in a fluidized bed; a) an initial heating of the precursor to a temperature not exceeding 250 ° C, b) an additional heating under superatmospheric pressure from a temperature of approximately 200 ° C to a temperature of at least 380 ° C to 600 ° C, c) maintenance of the temperature reached in stage b) at superatmospheric pressure, and d) cooling of the activated catalyst.

2. The process according to claim 1, characterized in that the superatmospheric pressure is maintained during all stages a), b), c) and d).

3. The process according to claim 1 or 2, characterized in that a superatmospheric pressure of at least 1.1 bar is applied.

4. The process according to claims 1 to 3, characterized in that a superatmospheric pressure of about 2 bars to about 3 bars is applied.

5. The process according to claims 1 to 4, characterized in that the surface velocity of the fluidized bed is adjusted to a range between 0.01 ms "1 to 0.5 ms" 1.

6. The process according to claims 1 to 5, characterized in that in step a) an initial heating of the precursor is carried out up to a temperature not exceeding 200 ° C.

7. The process according to claim 6, characterized in that in step a) an initial heating of the precursor is carried out in an air atmosphere.

8. The process according to claims 1 to 7, characterized in that in step b) subsequent heating is carried out from about 200 ° C to about 400 ° C to 450 ° C, with a heating rate of about 0.1 ° C / minute at 10 ° C / minute.

9. The process according to claim 7, characterized in that in step b) a subsequent heating is carried out in an atmosphere containing from 1 to 20% by volume of oxygen or of an oxygen-containing gas, from 10 to 80% in volume of steam and the rest of inert gas.

10. The process according to claims 1 to 9, characterized in that in step c) the temperature reached in stage b) is maintained in an atmosphere containing 0 to 20% by volume of oxygen or of an oxygen-containing gas, from 10 to 80% in volume of steam and the rest of inert gas.

11. The process according to claims 1 to 10, characterized in that in step d) the activated catalyst is cooled in an inert atmosphere, at a speed not exceeding 5 ° C / minute.

12. Active catalyst obtainable by the process of claims 1 to 11, characterized by the formula (VO) 2 P2? 7Me2mP2pOy I I, where m, p and y have the meanings indicated above.

13. Process for the production of maleic anhydride, characterized in that the feed gas composed of a non-aromatic hydrocarbon and oxygen or an oxygen-containing gas is converted in the presence of the active catalyst obtainable by the process of claims 1 to 11, a temperature between about 320 ° C and about 500 ° C.