Classifications

• • 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
  • C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
  • C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups

Definitions

• carboxylic acids and / or carboxylic anhydrides eg. As benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid or Py- romellithklaanhydrid is technically produced by the catalytic gas phase oxidation of aromatic hydrocarbons such as benzene, xylenes, naphthalene, toluene or durene, in fixed bed reactors.
• a gas stream comprising molecular oxygen and the hydrocarbon to be oxidized is generally passed through a multiplicity of tubes arranged in a reactor in which there is a bed of at least one catalyst.
• the tubes are surrounded by a heat transfer medium, for example a molten salt.
• a heat transfer medium for example a molten salt.
• the catalyst bed is usually brought by external heating to a temperature which is above the later operating temperature.
• the reaction temperature is maintained by the pronounced exotherm of the reaction and the external heating is reduced and eventually shut off.
• start-up phase the formation of a pronounced hot spot hinders a fast start-up phase (start-up phase), since the catalyst can be damaged irreversibly from a certain hot spot temperature. Therefore, the loading of the gas stream with the hydrocarbon to be oxidized is increased in small steps and must be very carefully to be controlled. Typical courses of the loading of the gas stream and the salt bath temperature when starting up a reactor for the oxidation of o-xylene to phthalic anhydride are shown in the appended FIGS. 2A and 2B.
• Start-up time describes the time necessary to stop the supply of the hydrocarbon to the desired final charge, ie. H. bring the oxidation to a steady state without irreversibly damaging the catalyst. Care should be taken to ensure that the hotspot does not exceed a certain critical value, as otherwise the selectivity and the lifetime of the catalyst will be severely impaired.
• the salt bath temperature can not be chosen arbitrarily low when starting, otherwise increased levels of unreacted hydrocarbon or suboxidation occur in the reaction product, which can lead to exceeding emission or quality specifications.
• the salt bath temperature is lowered (to usually 350 0 C) and the load can be increased parallel to the target load.
• WO 00/27753, WO 01/85337 and WO 2005/012216 describe silver vanadium oxide bronzes which selectively catalyze the partial oxidation of aromatic hydrocarbons.
• the silver-vanadium oxide bronzes are expediently used in combination with catalysts based on vanadium oxide and titanium dioxide.
• a gas stream containing a hydrocarbon and molecular oxygen is passed in succession over a bed of a first or upstream catalyst, the active material of which contains the catalytically active silver vanadium oxide bronze, and at least one bed of a second or downstream one which contains catalyst whose catalytically active composition contains vanadium pentoxide and titanium dioxide.
• the hydrocarbon is first reacted at the bed of the first catalyst, with partial conversion to a gaseous reaction mixture. At the bed of the second catalyst, the conversion is then completed.
• the prior art does not provide a method for starting up a gas phase oxidation reactor containing a catalytically active silver vanadium pentoxide bronze.
• Silver vanadium oxide bronzes are very active in comparison to known catalysts based on vanadium pentoxide and titanium dioxide and can therefore be started only at low temperatures. At higher temperatures, exceeding the permissible hot spot temperature in the silver vanadium oxide bronze bed and thus damaging the catalyst would result.
• the object is achieved by a method for starting a Gasphasenoxidati- onsreaktors comprising a bed of a first catalyst whose active material contains a catalytically active silver vanadium oxide bronze, and at least one bed of a second catalyst whose catalytically active material vanadium pentoxide and Ti - Tandioxid contains, and which is tempered by means of a heat transfer medium, to an operating state in which one comprises a gas stream comprising a loading c op of a hydrocarbon and molecular oxygen, at a temperature T op of the heat transfer medium through the bed of the first and second catalyst directs the reactor, wherein one
• the operating state is considered to be the essentially stationary state of the reactor in productive operation after the start-up phase has ended.
• the operating state is characterized by a substantially constant temperature of the heat transfer medium T op and a substantially constant loading of the gas flow c op .
• To compensate for decreasing catalyst activity can be in the operating state the Temperature of the heat transfer medium but increase in the long term (less than 2.5 ° C / year).
• the gas stream is passed in succession over a bed of the first or upstream catalyst and at least one bed of a second or downstream catalyst.
• the hydrocarbon is first reacted at the bed of the first catalyst whose active material contains a catalytically active silver vanadium oxide bronze, with partial conversion to a gaseous reaction mixture.
• the resulting reaction mixture is then contacted with at least one second catalyst whose catalytically active composition contains vanadium pentoxide and titanium dioxide.
• Reaction products prepared by gas phase oxidation in the reactor are e.g. B. benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid or pyromellitic anhydride.
• the hydrocarbons used are, in particular, aromatic hydrocarbons, such as benzene, alkylated benzenes, such as toluene, xylenes, durol, or naphthalene.
• a preferred embodiment of the invention relates to the oxidation of o-xylene to phthalic anhydride.
• step b) the procedure is followed
• steps b1) and b2) are optionally repeated one or more times until the temperature of the heat transfer medium is equal to T op and the loading of the gas stream is equal to c op .
• step b the procedure is followed
• the increase in the charge of the gas stream is regulated so that the content of unreacted hydrocarbon and / or of at least one suboxidation product in the reaction product does not exceed a predetermined limit.
• the content of unreacted hydrocarbon and / or Unteroxidationsproduk- th can be determined by condensing at about 23 0 C all condensable at this temperature components of the reaction product and the condensate by gas chromatography in a suitable solvent, such as acetone, analyzed.
• the content of unreacted hydrocarbon and / or suboxidation products herein is based on the total weight of the condensed reaction product.
• Unreacted hydrocarbons such as o-xylene
• Unreacted hydrocarbons are usually not washed out or condensed in the workup apparatus downstream of the reactor; they are therefore emitted and lead to an undesirable environmental impact. For this reason, the content of unreacted hydrocarbon in the reaction product should not exceed a predetermined limit.
• Suboxidation products are considered to be molecules which have the same number of carbon atoms as the desired oxidation product but a lower oxidation state than the desired oxidation product and are further oxidizable to the desired oxidation product. As a rule, suboxidation products can not be separated from the desired oxidation product or only with disproportionate effort. Increased levels of underoxidation products reduce product quality.
• Suboxidation products of phthalic anhydride are in particular o-tolualdehyde, o-toluic acid and phthalide.
• the concentration of unreacted o-xylene is preferably at most 0.1% by weight in the reaction product.
• concentration of phthalide formed is preferably at most 0.20 wt .-% in the reaction product.
• Postreactors are z.
• the concentration is unreacted o-xylene preferably at most 3 wt .-%.
• the concentration of phthalide is preferably at most 1 wt .-%.
• a hot spot ie a temperature maximum
• the further increase in the loading of the gas stream is preferably controlled so that the temperature at the hot spot in the bed of the second catalyst does not exceed a predetermined limit.
• a temperature of 440 0 C is not exceeded, since otherwise the selectivity and the life of the catalyst are greatly impaired.
• a temperature of 400 0 C should not be exceeded, so that the formation of the second catalyst takes place.
• the initial charge is at least 30 g / Nm 3 lower than c op .
• the minimum loading of the gas stream is generally 30 g of o-xylene / Nm 3 , because the uniform atomization of the liquid metered o-xylene is guaranteed only from this amount.
• the initial temperature is at least 8 0 C lower than Top.
• the loading c op is 60 to 110 g / Nm 3 , preferably 80 to 100 g / Nm 3 .
• the temperature T op 340 to 365 0 C preferably 350 to 360 0 C.
• the temperature is increased in step b1) at a rate of 0.5 to 5 ° C / day.
• the loading is increased in step b2) at a rate of 0.5 to 10 g / Nm 3 . Day.
• Silver vanadium oxide bronzes mean silver vanadium oxide compounds having an atomic Ag: V ratio of less than 1. They are generally semiconducting or metallically conductive, oxidic solids which preferentially crystallize in layer or tunnel structures, the vanadium in the [V2 ⁇ 5] host lattice being partially reduced to V (IV).
• Suitable first catalysts whose active material contains a catalytically active silver vanadium oxide bronze are described in WO 00/27753, WO 01/85337 and WO 2005/012216.
• the silver-vanadium oxide bronze is obtainable by thermal treatment of suitable multimetal oxides. The thermal transformation of the multimetal oxides to silver vanadium oxide bronzes proceeds through a series of reduction and oxidation reactions, the in detail are not yet understood.
• the multimetal oxide is applied as a layer to an inert support to obtain a so-called precatalyst.
• the conversion of the precatalyst into the active catalyst can be carried out in situ in the gas phase oxidation reactor under the conditions of the oxidation of aromatic hydrocarbons. Alternatively and preferably, the conversion of the precatalyst into the active catalyst takes place ex situ prior to introduction into the gas phase oxidation reactor, as described in WO 2007/071749.
• the multimetal oxide has the general formula I:
• a has a value of 0.3 to 1.9, preferably 0.5 to 1.0, and more preferably 0.6 to 0.9;
• Q is an element selected from P, As, Sb and / or Bi,
• b has a value of 0 to 0.3, preferably 0 to 0.1
• M for at least one of alkali and alkaline earth metals, Bi, Tl, Cu, Zn, Cd, Pb, Cr, Au, Al, Fe, Co, Ni, Mo, Nb, Ce, W, Mn, Ta, Pd, Pt, Ru and / or Rh is selected metal, preferably Nb, Ce, W, Mn and Ta, in particular Ce and Mn, of which Ce is most preferred
• c has a value of 0 to 0.5, preferably 0.005 to 0.2, in particular 0.01 to 0.1; with the proviso that (a-c) is> 0.1,
• d is a number which is determined by the valency and frequency of the elements other than oxygen in the formula I, and
• e has a value of 0 to 20, preferably 0 to 5.
• the silver vanadium oxide bronze is present in a crystal structure whose powder X-ray diffraction pattern at the interplanar spacings d is 4.85 ⁇ 0.4, 3.24 ⁇ 0.4, 2.92 ⁇ 0.4, 2.78 ⁇ 0 , 04, 2.72 ⁇ 0.04, 2.55 ⁇ 0.04, 2.43 ⁇ 0.04, 1, 95 ⁇ 0.04 and 1, 80 ⁇ 0.04 ⁇ .
• the indication of the Röntgenbeugungsre- Flexe takes place in this application in the form of independent of the wavelength of the X-rays used interplanar spacings d [ ⁇ ], which can be calculated from the measured diffraction angle by means of the Bragg ''s equation.
• a suspension of vanadium pentoxide (V2O5) is generally heated with the solution of a silver compound and optionally a solution of a compound of the metal component M and a compound of Q.
• the solvent for this reaction water is preferably used.
• Silver nitrate is preferably silver nitrate, the use of other soluble silver salts, eg. As silver acetate, silver perchlorate or silver fluoride is also possible.
• salts of the metal component M are usually selected those which are soluble in the solvent used. If water is used as solvent in the preparation of the multimetal oxides according to the invention, it is possible to use, for example, the perchlorates or carboxylates, in particular the acetates, of the metal component M.
• the nitrates of the relevant metal component M are preferably used.
• the amounts of V2O5, silver compound and the compound of the metal component M resulting from a and c of formula I are reacted with one another for its preparation.
• the multimetal oxide thus formed can be isolated from the reaction mixture and stored until further use. Particularly advantageously, the isolation of the resulting multimetal oxide suspension is carried out by spray drying. The spray-dried powder is then applied to an inert support.
• Catalysts based on vanadium pentoxide and titanium dioxide contain vanadium pentoxide in addition to titanium dioxide (in the form of its anatase modification). Furthermore, small amounts of other oxidic compounds may be present, which, as promoters, influence the activity and selectivity of the catalyst.
• the activity reducing and the selectivity increasing promoters are usually alkali metals, such as cesium, lithium, potassium and rubidium, and in particular cesium used.
• As the activity increasing additives phosphorus compounds are usually used.
• the catalysts based on vanadium oxide and titanium dioxide may also contain antimony compounds. Typical catalysts based on vanadium oxide and titanium dioxide and their preparation are described in DE 198 23 262.
• the catalytically active material of the second catalyst contains from 1 to 40% by weight of vanadium oxide, calculated as V2O5, from 60 to 99% by weight of titanium dioxide, calculated as TiC "2, up to 1% by weight of a cesium compound, calculated as Cs, up to 1 wt .-% of a phosphorus compound, calculated as P, and up to 10 wt .-% antimony oxide, calculated as Sb2 ⁇ 3.
• the bed of the second catalyst comprises at least two layers of catalysts whose catalytically active composition has different Cs content, the Cs content decreasing in the flow direction of the gas stream.
• the components are used in the form of their oxides or in the form of compounds which convert to oxides when heated or when heated in the presence of oxygen.
• vanadium component vanadium oxides or vanadium compounds which convert to vanadium oxides upon heating may be used singly or in the form of their mixtures.
• V2O5 or NH4VO3 are used.
• a reducing agent such as formic acid or oxalic acid
• Suitable promoter (precursor) compounds are the corresponding oxides or compounds which, upon heating, convert to oxides, such as sulfates, nitrates, carbonates. Suitable examples are Na 2 CO 3, K 2 O, CS 2 O, CS 2 CO 3, Cs 2 SO 4 , P 2 O 5 , (N HU) 2 H PO 4 , Sb 2 O 3 .
• an aqueous slurry of the compound of the vanadium component, of the titanium dioxide and of promoter (precursor) compounds is generally prepared in suitable amounts and the slurry is stirred until sufficient homogenization has been achieved. The slurry may then be spray dried or used as such for coating.
• the catalysts used in the process according to the invention are generally coated catalysts in which the catalytically active composition is applied in the form of a dish on an inert support.
• the layer thickness of the catalytically active composition is generally 0.02 to 0.2 mm, preferably 0.05 to 0.1 mm.
• the catalysts have a cup-shaped active mass layer of substantially homogeneous chemical composition.
• Virtually all known support materials can be used as the inert support material, for example quartz (SiO 2 ), porcelain, magnesium oxide, tin dioxide, silicon carbide, rutile, alumina (Al 2 Os), aluminum silicate, steatite (magnesium silicate), zirconium silicate, cerium silicate or mixtures of these carrier materials.
• the carrier material is usually non-porous.
• Particularly advantageous support materials are steatite and silicon carbide.
• the shape of the support material is generally not critical. For example, catalyst supports in the form of spheres, rings, tablets, spirals, tubes, extrudates or chippings can be used.
• catalyst supports are the same as the catalyst supports commonly used to prepare shell catalysts for the gas phase partial oxidation of aromatic hydrocarbons.
• Steatite is preferred in the form of spheres with a diameter of 3 to 6 mm or of rings used with an outer diameter of 5 to 9 mm and a length of 4 to 7 mm.
• the application of the active material layer on the carrier can be carried out by any known methods, for. B. by spraying solutions or suspensions in the coating drum or coating with a solution or suspension in a fluidized bed.
• organic binders preferably copolymers, advantageously in the form of an aqueous dispersion of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate / maleate, vinyl acetate / ethylene and hydroxyethyl cellulose can be added to the catalytically active composition, with Advantage binder amounts of 3 to 20 wt .-%, based on the solids content of the solution of the active ingredient components, are used.
• the applied binder burn after filling the catalyst and start-up of the reactor within a short time.
• the addition of binder also has the advantage that the active material adheres well to the carrier, so that transport and filling of the catalyst are facilitated.
• the gas phase oxidation reactor is heatable by means of a heat transfer medium.
• the bed of the first catalyst and the bed of the second catalyst are heatable by a common heat transfer medium, for. B. by means of a single Salzbadniklaufs.
• the reactor used is preferably a salt bath-cooled tubular reactor. This comprises a tube bundle circulated by a heat transfer medium in the form of a salt bath.
• the individual catalyst-filled tubes end in a top tube sheet or a bottom tube sheet.
• the reaction gas is generally from top to bottom, d. H. in the direction of gravity, passed through the pipes; but it is also a reverse flow direction conceivable.
• the term "temperature of the heat transfer medium” is the lowest temperature of the heat transfer medium in the region of the reactor, which is generally the temperature in the inlet of the molten salt in the reactor.
• the catalysts are filled in the reaction tubes of the tubular reactor. About the thus prepared catalyst bed, the reaction gas is passed.
• the reaction gas fed to the reactor is generally made by mixing a molecular oxygen-containing gas which is still suitable in addition to oxygen Reaction moderators and / or diluents, such as water vapor, carbon dioxide and / or nitrogen may contain, produced with the aromatic hydrocarbon to be oxidized, wherein the molecular oxygen-containing gas is generally 1 to 100 vol .-%, preferably 2 to 50 vol. % and more preferably 10 to 30% by volume of oxygen, 0 to 30% by volume, preferably 0 to 20% by volume of steam and 0 to 50% by volume, preferably 0 to 1% by volume of carbon dioxide, balance Nitrogen, may contain. It is particularly advantageous to use air as the molecular oxygen-containing gas.
• Fig. 1 shows the time course of the salt bath temperature and the loading of the gas stream in one embodiment of the inventive method for the oxidation of o-xylene to phthalic anhydride.
• Fig. 2A shows the time course (days) of the loading of the gas stream (g / Nm 3 ) and Fig. 2B the time course (days) of the salt bath temperature ( 0 C) when starting a reactor for the oxidation of o-xylene to phthalic anhydride, the contains exclusively catalysts based on vanadium pentoxide and titanium dioxide.
• Fig. 3 shows a typical local temperature profile ( 0 C) in a reaction tube (cm from the reactor inlet) at a constant loading of 30 g / Nm 3 , while increasing the salt bath temperature of 346 0 C to 356 0 C within 6 days.
• Fig. 4 shows a typical local temperature profile ( 0 C) in a reaction tube (cm from the reactor inlet) at a constant salt bath temperature of 356 0 C, while increasing the loading of 30 g / Nm 3 to 76 g / Nm 3 .
• a reactor was used with 100 tubes of 360 cm length surrounded by a salt bath.
• a catalyst based on vanadium pentoxide and titanium dioxide was introduced into the tubes up to a filling height of 240 cm.
• the catalyst comprised an active composition of the composition of 5.75 wt .-% V2O5, 1, 58% by weight of Sb 2 O 3, 0.11 wt .-% P, 0.41 wt .-% Cs, 0.027 wt % K, the remainder TiO 2 , which was applied to support supports in the form of hollow cylinders (8x6x5 mm); the active mass fraction was 9% by weight.
• the catalyst was filled up to a filling height of 320 cm, the active mass of which comprised a silver vanadium oxide bronze having the composition Ago, 68V 2 O 5 (see WO 00/27753 for its preparation).
• the reactor also included a thermal tube that allowed temperature measurement axially along the catalyst beds.
• the thermal tube contained, in addition to the fixed catalyst bed, a thermal sleeve fed only with a temperature sensor and centered along the same in the thermowell.
• the salt bath was heated to 200 0 C, passing 2 m 3 / h / tube air through the pipes. Subsequently, the salt bath temperature was increased within 25 h without passing air to 380 0 C. Then, at 30 min 3.81 Nm 3 / h / pipe air at 380 0 C salt bath temperature through the tubes. In this case, the salt bath reactor cools down. When reaching a temperature of 346 0 C 30 g / Nm 3 o-XyIoI were added to the air stream. Due to the exothermic nature of the initiation of the oxidation reaction, the temperature of the reactor did not drop further.

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• 2009
  • 2009-04-07 WO PCT/EP2009/054170 patent/WO2009124947A1/de active Application Filing
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  • 2009-04-07 EP EP09730240A patent/EP2274265A1/de not_active Withdrawn
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  • 2009-04-07 US US12/936,648 patent/US20110028740A1/en not_active Abandoned
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