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• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
  • C07C45/33—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
  • B01J37/033—Using Hydrolysis
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
  • C01B13/14—Methods for preparing oxides or hydroxides in general
  • C01B13/36—Methods for preparing oxides or hydroxides in general by precipitation reactions in aqueous solutions
  • C01B13/366—Methods for preparing oxides or hydroxides in general by precipitation reactions in aqueous solutions by hydrothermal processing
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B19/00—Selenium; Tellurium; Compounds thereof
  • C01B19/002—Compounds containing, besides selenium or tellurium, more than one other element, with -O- and -OH not being considered as anions
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
  • C07C45/33—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties
  • C07C45/34—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds
  • C07C45/35—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds in propene or isobutene
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/215—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of saturated hydrocarbyl groups
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/50—Solid solutions
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/584—Recycling of catalysts

Definitions

• the present invention relates to a process for the preparation of acrylic acid by heterogeneously catalyzed gas-phase oxidation of propane with molecular oxygen at elevated temperature on a multimetal oxide composition of the general formula I,
• M 1 Te and / or Sb
• Multimetal oxide compositions of the general formula I are known (cf., for example, EP-A 608 838, EP-A 529 853, Proceedings ISO'99, Ri ini (Italy), Sept. 10-11, 1999, G. Centi and S. Perathoner Ed ., SCI Pub. 1999, EP-A 767 164, Catalysis Today 49 (1999) pp. 141-153, EP-A 962 253, Applied Catalysis A: General 194 to 195 (2000) pp. 479 to 485, JP- A 11/169716, EP-A 895 809 and DE-A 19835247.
• Multimetal oxide compositions with a composition like Multimetaloxide compositions I are also known from WO 00-29106.
• Acrylic acid is an important ethylenically unsaturated compound which is used both as such and in the form of its alkyl esters for the preparation of polymers.
• Those documents which recommend multimetal oxide compositions of the general formula I as catalysts for the heterogeneously catalyzed gas-phase oxidation of propane to acrylic acid have in common the fact that the multimetal oxide compositions of the general formula I are prepared in such a way that at normal pressure (1 atm) initially from sources
• the intimate mixing of the starting compounds can be carried out in dry or wet form. If it is carried out in dry form, the starting compounds are expediently used as finely divided powders and, after mixing and, if appropriate, compacting, are subjected to the thermal treatment. However, the intimate mixing is preferably carried out in wet, usually in aqueous form. The starting compounds are mixed together in the form of an aqueous solution and / or suspension. The aqueous mass is then dried and thermally treated after drying. It is characteristic of the production method described in the prior art that all production steps are carried out at atmospheric pressure.
• a disadvantage of the multimetal oxide compositions I of the prior art produced in this way is, however, that their selectivity in the formation of acrylic acid cannot be fully satisfied when used as catalysts for the heterogeneously catalyzed gas-phase oxidation of propane to acrylic acid.
• an improvement of the multimetal oxide masses I with regard to their activity when used as catalysts for the heterogeneously catalyzed gas phase amoxidation of propane to acrylonitrile could be achieved by the production of the final to generate the active oxide thermally treated intimate dry mixture is carried out hydrothermally.
• the object of the present invention was to provide an improved process for the heterogeneously catalyzed gas-phase oxidation of propane to acrylic acid, by means of which an increased selectivity of the acrylic acid formation is achieved.
• M 1 Te and / or Sb
• multimetal oxide compositions are favorable according to the invention in which M 2 is Nb, Ta, W and / or titanium.
• M 2 Nb.
• the stoichiometric coefficient b of the multimetal oxide masses I to be used according to the invention is advantageously 0.1 to 0.6.
• the preferred range for the stoichiometric coefficient c is 0.05 to 0.4 and favorable values for d are 0.01 to 0.6.
• Particularly favorable multimetal oxide compositions I to be used according to the invention are those in which the stoichiometric coefficients b, c and d are simultaneously in the aforementioned preferred ranges.
• Further stoichiometries suitable according to the invention for the multimetal oxide compositions I are those which are disclosed in the documents EP-A 608 838, WO 00-29106, JP-A 11/169716 and EP-A 962 253.
• hydrothermal preparation of multimetal oxide active material precursors is familiar to the person skilled in the art (see, for example, Applied Catalysis A: 194 to 195 (2000) 479-485, Kinetics and Catalysis, Vol. 40, No. 3, 1999, pp. 401 to 404, Chem . Commun., ' 1999, 517 to 518, JP-A 6/227819 and JP-A 2000/26123).
• this includes the thermal treatment of a, preferably intimate, mixture of sources of the elemental constituents of the desired multimetal oxide mass I in an overpressure vessel (autoclave) in the presence of water vapor at superatmospheric pressure, usually at temperatures in the range from> 100 ° C. to 600 ° C, understood.
• the pressure range typically extends up to 500 at, preferably up to 250 atm.
• temperatures above 600 ° C. and water vapor pressures above 500 atm can also be used, but this is not very practical in terms of application technology.
• the hydrothermal treatment according to the invention is particularly advantageously carried out under conditions under which water vapor and liquid water coexist.
• the hydrothermal treatment advantageously takes place at temperatures of> 100 to 300 ° C, preferably at temperatures of 150 to 250 ° C (e.g. 160 to 180 ° C).
• the proportion by weight of the latter in the autoclave according to the invention is generally at least 1% by weight.
• the aforementioned proportion by weight is usually not above 90% by weight.
• Typical proportions by weight are from 3 to 60% or from 5 to 30% by weight, frequently from 5 to 15% by weight.
• the starting compounds (sources) for the hydrothermal production variant according to the invention are especially all those that are able to form oxides and / or hydroxides when heated under pressure with water.
• oxides and / or hydroxides of the elemental constituents can also be used or used exclusively as starting compounds for the hydrothermal production according to the invention.
• the sources are used in finely divided form.
• Suitable sources for the element Mo according to the invention are e.g. Molybdenum oxides such as molybdenum trioxide, molybdates such as ammonium heptamolybdate tetrahydrate and molybdenum halides such as molybdenum chloride.
• Molybdenum oxides such as molybdenum trioxide
• molybdates such as ammonium heptamolybdate tetrahydrate
• molybdenum halides such as molybdenum chloride.
• Suitable starting compounds according to the invention for the element V are, for example, vanadylacetylacetonate, vanadates such as ammonium metavandate, vanadium oxides such as vanadium pentoxide (V0s), vanadium halides such as vanadium tetrachloride (VCI 4 ) and vanadium oxyhalogenides such as V0C1 3 .
• the vanadium starting compounds used are those which contain the vanadium in the oxidation state +4.
• tellurium oxides such as tellurium dioxide, metallic tellurium, tellurium halides such as TeCl 2 , but also telluric acids, ie orthotelluric acid H 6 TeO 5, are suitable as sources for the element tellurium.
• antimony starting compounds are antimony halides such as SbCl 3 , antimony oxides such as antimony trioxide (Sb 2 0 3 ), antimonic acids such as HSb (OH) 6 , but also antimony oxide salts such as antimony oxide sulfate (Sb0 2 ) S0 4 .
• Niobium sources suitable according to the invention are, for example, niobium oxides such as niobium pentoxide (NbOs), niobium oxide halides such as NbOCl 3 , niobium halides such as NbCls, but also complex compounds composed of niobium and organic carboxylic acids and / or dicarboxylic acids such as oxalates and alcoholates.
• NbOs niobium pentoxide
• NbOCl 3 niobium oxide halides
• NbCls complex compounds composed of niobium and organic carboxylic acids and / or dicarboxylic acids such as oxalates and alcoholates.
• Nb-containing solutions used in EP-A 895809 can also be used.
• suitable starting compounds according to the invention are, in particular, their halides, nitrates, formates, oxalates, acetates, carbonates and / or hydroxides. Suitable starting compounds are often also their oxo compounds, such as tungstates or the acids derived from them. Ammonium salts are also frequently used as starting compounds. Also suitable as starting compounds for the hydrothermal variant according to the invention are polyanions of the Anderson type, as described, for example, in Polyhedron Vol. 2, pp.
• polyanions suitable as starting compounds are e.g. those of the Dawson or Keggin type. According to the invention, preference is given to using those starting compounds which, at elevated temperatures, convert into their oxides either in the presence or in the absence of oxygen with the liberation of gaseous compounds.
• the hydrothermal treatment itself usually takes from a few hours to a few days. A typical period is 48 hours.
• the inside of the autoclave to be used for the hydrothermal treatment is coated with Teflon.
• the autoclave including the aqueous mixture it contains if necessary, can be evacuated. Then it can be filled with inert gas (N 2 , noble gas) before the temperature rises. Both measures can also be omitted.
• the aqueous mixture can also be purged with inert gas for inertization prior to hydrothermal treatment.
• the aforementioned inert gases can expediently also be used to pre-set the hydrothermal treatment in the autoclave above atmospheric pressure.
• the treatment required according to the invention of the newly formed in the course of the hydrothermal treatment and after the end of the hydrothermal treatment (after the end of the hydrothermal treatment, the autoclave can either be quenched to room temperature or slowly, ie over a longer period of time (for example, left by itself) to room temperature separated) solid is advantageously carried out at a temperature of 350 to 700 ° C, often at a temperature of 400 to 650 ° C, or 400 to 600 ° C. It can be carried out under an oxidizing, reducing or inert atmosphere. Examples of suitable oxidizing atmospheres are air, air enriched with molecular oxygen or air depleted in oxygen.
• the thermal treatment is preferably carried out under an inert atmosphere, ie, for example under molecular nitrogen and / or noble gas.
• the thermal treatment can of course also be carried out under vacuum.
• the thermal treatment takes place in a gaseous atmosphere, it can both stand and flow.
• the thermal treatment can take up to 24 hours or more.
• the thermal treatment is preferably carried out first under an oxidizing (oxygen-containing) atmosphere (e.g. under air) at a temperature of 150 to 400 ° C or 250 to 350 ° C. Thereafter, the thermal treatment is expediently continued under inert gas at temperatures of 350 to 700 ° C or 400 to 650 ° C or 400 to 600 ° C.
• an oxidizing (oxygen-containing) atmosphere e.g. under air
• the thermal treatment is expediently continued under inert gas at temperatures of 350 to 700 ° C or 400 to 650 ° C or 400 to 600 ° C.
• the thermal treatment of the hydrothermally produced catalyst precursor can also be carried out in such a way that the catalyst precursor mass is first tabletted, then thermally treated and subsequently split.
• the solid obtained in the course of the hydrothermal treatment is split up for subsequent thermal treatment.
• the multimetal oxide compositions I prepared according to the invention generally have a higher selectivity of the acrylic acid formation and an increased activity.
• the multimetal oxide compositions I obtainable according to the invention can be used as such (for example ground into powder or chippings) or shaped into shaped bodies for the process according to the invention.
• the catalyst bed can be a fixed bed, a moving bed or a fluidized bed.
• reaction gas mixture with which the multimetal oxide active composition according to the invention is used at reaction temperatures of e.g. 200 to 550 ° C or 230 to 480 ° C or 300 to 440 ° C can e.g. have the following composition:
• Reaction gas mixtures containing water vapor are preferred.
• compositions of the reaction gas mixture are:
• a product gas mixture is obtained which does not consist exclusively of acrylic acid. Rather, the product gas mixture contains secondary components such as propane, acrolein, CO 2 , CO, H 2 O, acetic acid, propionic acid, etc., from which the acrylic acid must be separated.
• the acrylic acid contained can be taken up from the product gas mixture by absorption with water or by absorption with a high-boiling inert hydrophobic organic solvent (e.g. a mixture of diphenyl ether and diphyl which may also contain additives such as dimethyl phthalate).
• a high-boiling inert hydrophobic organic solvent e.g. a mixture of diphenyl ether and diphyl which may also contain additives such as dimethyl phthalate.
• the resulting mixture of absorbent and acrylic acid can then be worked up in a manner known per se by rectification, extraction and / or crystallization to give pure acrylic acid.
• the basic separation of the acrylic acid from the product gas mixture can also be carried out by fractional condensation, as it is e.g. is described in DE-A 19 924 532.
• the resulting aqueous acrylic acid condensate can then e.g. be further purified by fractional crystallization (e.g. suspension crystallization and / or layer crystallization).
• fractional crystallization e.g. suspension crystallization and / or layer crystallization.
• the residual gas mixture remaining in the basic separation of acrylic acid contains, in particular, unreacted propane. This can be done from the residual gas mixture, for example by fractional pressure rectifiers. tion separated and then recycled into the gas phase oxidation according to the invention. However, it is more favorable to bring the residual gas into contact with a hydrophobic organic solvent in an extraction device (for example by passing it through), which the propane is able to absorb preferentially. Through subsequent desorption and / or stripping with air, the absorbed propane can be released again and returned to the process according to the invention. In this way, economic total propane sales can be achieved.
• the method according to the invention enables increased selectivity of the acrylic acid formation for identical propane conversions related to a single pass.
• the X-ray diffractogram of the multimetal oxide materials I according to the invention generally corresponds essentially to those from the documents ⁇ P-A 529 853, DE-A 19 835 247 and EP-A 608 838.
• the multi-metal oxide catalysts to be used according to the invention are also suitable for the gas-phase catalytically oxidative production of methacrylic acid from its C 4 precursors, such as, for example, isobutene or isobutane.
• multimetal oxide compositions (I) to be used according to the invention are also used in finely divided, e.g. colloidal, materials such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, niobium oxide diluted form can be used in the process according to the invention.
• the dilution mass ratio can be up to 9 (thinner): 1 (active mass). Ie, possible dilution mass ratios are also 6 (thinner): 1 (active mass) and 3 (thinner): 1 (active mass).
• the diluents can be incorporated before and / or after the calcination. As a rule, the thinner is incorporated before the hydrothermal treatment. If the incorporation is carried out before the calcination, the thinner must be selected so that it is essentially retained as such during the calcination. The same applies to the hydrothermal treatment when it is worked in before carrying out the same. This is usually the case, for example, in the case of oxides fired at correspondingly high temperatures. Examples
• solution 2 was stirred into solution 1. Then, also at 50 ° C, the solution 3 within 1 to 2 min. dripped into the mixture of solution 1 and solution 2. 1
• the resulting mixture was immediately transferred to an autoclave (Hastelloy C material, internal volume 2.5 l). Without stirring, the aqueous mixture was heated to 175 ° C. in a closed autoclave (within 60 min).
• the total amount (80 g) of the solid dried overnight was kept in an air flow (50 Nl / h) at 250 ° C. in a heatable rotating ball (internal volume: 1 liter, see enclosed FIG. 1). Heating from room temperature to 250 ° C was carried out at a heating rate of 10 ° C / min.
• the 50 Nl / h air flow was then replaced by 50 Nl / h of molecular nitrogen and the temperature was increased from 250 ° C to 600 ° C at a heating rate of 10 ° C / min.
• the temperature of 600 ° C was also maintained for 2 hours. like the molecular nitrogen flow. Then it was passively cooled to a temperature of 25 ° C. (room temperature).
• the resulting multimetal oxide active composition had the composition o ⁇ V 0 , 29 ten, ⁇ 3 Nbn, i 6 0 n . It was crushed into chippings in a mortar and the grain fraction, which still fell through square sieve meshes with an edge length of 1.2 mm, but was no longer allowed through from square sieve meshes with an edge length of 0.6 mm, was separated off by sieving.
• the tablets were thermally treated and processed into chippings, from which the grain fraction "0.6 mm - 1.2 mm" was in turn separated by sieving as a multimetal oxide active material.
• the stoichiometric composition was Mo ⁇ Vo, 9 Teo, os bo, ⁇ 6 On- B) Heterogeneously catalyzed gas phase oxidation of propane to acrylic acid
• a tube reactor (V2A steel, wall thickness 2.5 cm, length 140 cm, inside diameter) was added to each 35 g of the separated multimetal oxide active mass fraction from A) 1. or A) 2.
• reaction tube wall temperature (reaction temperature) required for propane conversion with a single pass of 25 mol% was then linearly heated within 2 h.

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