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WO2001055073A2 - Oxidation of o-xylol to produce o-tolyl acid - Google Patents

Oxidation of o-xylol to produce o-tolyl acid Download PDF

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Publication number
WO2001055073A2
WO2001055073A2 PCT/EP2001/000707 EP0100707W WO0155073A2 WO 2001055073 A2 WO2001055073 A2 WO 2001055073A2 EP 0100707 W EP0100707 W EP 0100707W WO 0155073 A2 WO0155073 A2 WO 0155073A2
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WO
WIPO (PCT)
Prior art keywords
xylene
oxidation
catalyst
mixture
tolylaldehyde
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PCT/EP2001/000707
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German (de)
French (fr)
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WO2001055073A3 (en
Inventor
Andreas Walch
Ulrich Kammel
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Basf Aktiengesellschaft
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Priority to AU2001228481A priority Critical patent/AU2001228481A1/en
Publication of WO2001055073A2 publication Critical patent/WO2001055073A2/en
Publication of WO2001055073A3 publication Critical patent/WO2001055073A3/en

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    • 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

  • the invention relates to a process for the oxidation of o-xylene with oxygen, preferably in a mixture with an inert gas, in particular air, with the addition of a catalyst.
  • Phthalic anhydride is one of the technically most important aromatic compounds. It is used, for example, in the synthesis of alkyd resins, unsaturated polyester resins, paints, plastics, plasticizers, phthalocyanine dyes, insect repellents, denaturing agents and for the production of numerous fine chemicals. Phthalic anhydride is made by oxidation of o-xylene or naphthalene. Two oxidation processes are common. On the one hand, this is an oxidation in the gas phase on a heterogeneous catalyst, generally a vanadium catalyst. In this process variant, about 20 mol% of the starting material is converted to CO x and is therefore lost as a yield.
  • o-xylene is initially oxidized in the liquid phase with an oxygen-containing gas, mostly air, to o-tolylic acid under homogeneous catalysis.
  • the o-tolylic acid is then evaporated and oxidized to phthalic anhydride in the gas phase in a second stage.
  • Such a two-stage process is described in EP-0 256 352 AI.
  • o-xylene is oxidized in the liquid phase with air at a temperature between 120 and 150 ° C and a pressure between normal pressure and 35 bar with cobalt salts soluble in o-xylene, generally co-naphthenate, as a catalyst.
  • the water formed during the oxidation is condensed together with the o-xylene from the gas phase and separated off.
  • the o-xylene is then fed into the reactor.
  • the reaction mixture obtained from the first stage is distilled, whereby the o-tolylic acid is purified and the unreacted o-xylene is separated off.
  • the o-xylene is again the fed to the first stage, while the o-tolylic acid is fed to the gas phase oxidation of the second stage.
  • a disadvantage of the process according to EP-0 256 352 AI is that the reaction product from the oxidation in the liquid phase of the first stage is contaminated with benzoic acid.
  • Benzoic acid arises from the loss of a carbon atom from the o-xylene.
  • the benzoic acid cannot be removed from the reaction mixture of the first stage, or at least only with great difficulty. It is therefore transferred to the second stage of the oxidation.
  • the benzoic acid is burned to CO x and water. This leads to the formation of "hot spots" and thus to a deterioration in the selectivity of the overall reaction.
  • the object of the invention is therefore to provide a process for the oxidation of o-xylene with oxygen, preferably in a mixture with an inert gas, in particular air, with the addition of a catalyst which enables improved selectivity in the oxidation to phthalic anhydride.
  • the object is achieved in the process in that an aldehyde is added to the o-xylene.
  • Benzoic acid is formed by the oxidation of toluene.
  • the toluene in turn is formed by decarboxylation of o-tolylic acid. If the activity of the catalyst is reduced, the conversion of the side reaction to toluene and thus the amount of benzoic acid formed also decrease. The loss of reactivity can be compensated for by adding o-tolylaldehyde.
  • o-Tolylaldehyde can itself be oxidized to phthalic acid and therefore does not form any troublesome by-products.
  • o-tolylaldehyde is separated from the oxidation products of o-xylene and the o-tolylaldehyde is returned to the reaction.
  • the separation takes place by distillation.
  • the o-tolylaldehyde is preferably separated off from the oxidation products of the o-xylene together with unreacted o-xylene and returned to the reaction.
  • the oxidation process according to the invention is preferably carried out in the liquid phase, in particular with homogeneous catalysis. The process is particularly suitable for the two-stage oxidation of o-xylene to phthalic anhydride described above.
  • the o-xylene is oxidized in the liquid phase to a mixture of different oxidation products. Unreacted o-xylene and o-tolylaldehyde formed are then distilled off and fed back to the first stage. The oxidation products of the o-xylene remaining in the bottom are then evaporated and oxidized to phthalic anhydride in the gas phase in the second stage.
  • the catalyst contains cobalt and / or a cobalt salt.
  • the suitability of this catalyst is also described in EP-0 256 352.
  • the anion used in the cobalt salt is not critical in itself. It mainly serves to make the metal ion soluble in the reaction mixture. Suitable anions are derived, for example, from aliphatic and aromatic carboxylic acids.
  • Examples include naphthenates, acetates, propionates, butanoates, pentanoates, hexanoates, heptanoates, octanoates, 2-ethylhexanoates, nonanoates, isononaoates, decanoates, laurinoates, palmitates, stearates, benzoates, toluylates, phthalates and citrates.
  • Examples of other groups which cause solubility of the metals are acetylacetonate, porphyrins, salcomine, halls, phthalocyanine and carbonyl groups. However, other groups are also suitable as long as they are capable of causing the metal ion to be soluble.
  • the decarboxylation of tolylic acid to toluene can be suppressed if a manganese (II) compound is added to the catalyst. This lowers the activity of the cobalt catalyst. The loss of activity of the catalyst can be compensated for by adding the aldehyde.
  • II manganese
  • a further metal compound can have a favorable effect on the activity of the reaction.
  • the compound is preferably one of a metal from the group consisting of Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Al, Sc, Y, Ga, In, Tl, Ti, Zr, Hf , Ge, Sn, Pb, V, Nb, Ta, Cr, Mo, W, Tc, Ru, Fe, Re, Os, Rh, Ir, Ni, Pd, Pt and combinations of these metals.
  • the invention is explained in more detail with reference to a drawing. It shows:
  • the process according to the invention can be used particularly advantageously in combination with two-stage oxidation of o-xylene to phthalic anhydride.
  • o-xylene is oxidized with oxygen in the liquid phase to a mixture of oxidation products.
  • the oxidation is catalyzed by cobalt compounds.
  • the mixture of oxidation products in the gas phase is oxidized to phthalic anhydride.
  • This gas phase oxidation can be catalyzed by a vanadium catalyst.
  • the reaction is described by way of example in EP-0 256 352.
  • FIG. 1 shows a representation of the main products of the mixture of oxidation products formed during the oxidation of o-xylene in the liquid phase with atmospheric oxygen.
  • Decarboxylation of o-tolylic acid or decarbonylation of o-tolylaldehyde initially produces toluene as an undesirable by-product, which is then further oxidized to benzoic acid.
  • the benzoic acid is burned to CO 2 and CO and leads to the formation of "hot spots".
  • the proportion of the individual substances in the partially oxidized mixture can be influenced by the choice of the reaction conditions.
  • the illustration shows products which have a larger proportion of the In addition, numerous other products are formed, which, however, are not shown for reasons of clarity.
  • o-tolylaldehyde In the oxidation of o-xylene, one of the oxidation products is o-tolylaldehyde. Depending on the reaction, the o-tolylaldehyde forms a proportion of approximately 1 to 10% by weight of the mixture of the oxidation products, this fraction can be separated off before the further oxidation in the second stage and returned to the first stage of the oxidation in the liquid phase.
  • Fig. 2 shows schematically the structure of a device for performing the method according to the invention.
  • O-xylene is fed to a reactor 2 via the xylene feed 1.
  • the catalyst solution for example a cobalt salt in a mixture with an Mn (II) salt, dissolved in o-xylene, is fed in via a catalyst feed 3.
  • naphthenates, acetate or 2-ethylhexanoate can be used as cobalt salts.
  • the oxidation of the o-xylene takes place in the liquid phase with air, which is injected into the reactor 2 via air supply 4. Suitable forms for the reactor 2 are known per se to the person skilled in the art.
  • the reaction can be carried out in a single reactor, but also in several reactors connected in series.
  • the oxygen-depleted air is led out of the reactor 2 via the exhaust line 5 and condensed more volatile components, in particular o-xylene and toluene, which are condensed by cooling.
  • the exhaust gas depleted in organic volatile constituents can be fed to a combustion for further purification.
  • the condensed components of the exhaust gas are fed to a distillation device 9 via return lines 6.
  • the components of the exhaust gas which have been condensed out can also be combined with the raw product via return line 6a (dashed line), which is led out of the reactor 2 via raw product line 7.
  • the direct feed into the distillation device 9 is omitted.
  • Water which has been condensed out of the exhaust gas in addition to o-xylene and toluene can be led out of the system via water discharge line 8.
  • the crude product which consists of a mixture of o-xylene and oxidation products of o-xylene, is fed to the distillation device 9, in which a separation into different material flows takes place.
  • the distillation device 9 can be constructed from several interconnected columns.
  • toluene is led out of the system via toluene discharge 10 as the first material flow.
  • the toluene is used to carry out azeotropic water that is formed during the oxidation of the o-xylene.
  • the material flows mentioned below are therefore almost water-free.
  • Unreacted o-xylene is separated from the crude product as the second stream and is fed back to the reactor 2 via the xylene return line 11. With the o-xylene, o-tolylaldehyde is distilled off from the mixture of the oxidation products.
  • o-tolylaldehyde has the next higher boiling point of the compounds of the mixture of the oxidation products.
  • a mixture of catalyst and the oxidation products of o-xylene remains in the bottom of the distillation device 9 and is fed to a product separation 13 via the bottom drain 12.
  • the Oxidation products of o-xylene distilled off from the catalyst.
  • the catalyst is returned to the reactor 2 via the catalyst return 14.
  • a portion of the catalyst is led out of the system through catalyst discharge line 15. This portion is replaced in each case by fresh catalyst, which is fed in via catalyst feed 3.
  • the distilled off oxidation products of o-xylene are removed via product line 16 and fed to a second reaction stage (not shown) in which the oxidation products of o-xylene are oxidized to phthalic anhydride.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
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Abstract

The invention relates to a method for oxidizing o-xylol with oxygen, preferably mixed with an inert gas, especially air, while adding a catalyst, in order to produce a mixture of oxidation products of the o-xylol. The selectivity of the reaction can be increased by adding an aldehyde to the o-xylol.

Description

Oxidation von o-Xylol zu o-Tolylsäure Oxidation of o-xylene to o-tolylic acid
Die Erfindung betrifft ein Verfahren zur Oxidation von o-Xylol mit Sauerstoff, vorzugsweise im Gemisch mit einem inerten Gas, insbesondere Luft, unter Zusatz eines Katalysators.The invention relates to a process for the oxidation of o-xylene with oxygen, preferably in a mixture with an inert gas, in particular air, with the addition of a catalyst.
Phthalsäureanhydrid gehört zu den technisch wichtigsten aromatischen Verbindungen. Es wird z.B. bei der Synthese von Alkydharzen, ungesättigten Polyesterharzen, Lacken, Kunststoffen, Weichmachern, Phthalocyanin-Farbstoffen, Insektenabwehrmitteln, Denaturierungsmitteln sowie zur Herstellung zahlreicher Feinchemikalien verwendet. Phthalsäureanhydrid wird durch Oxidation von o-Xylol oder Naphthalin hergestellt. Es sind dabei zwei Oxidationsverfahren üblich. Dies ist zum einen, eine Oxidation in der Gasphase an einem heterogenen Katalysator, im Allgemeinen einem Vanadium- Katalysator. Bei dieser Verfahrensvariante werden ca. 20 Mol-% des Ausgangsmaterials zu COx umgesetzt und gehen damit als Ausbeute verloren. Wegen der besseren Selektivität der Oxidationsreaktion wird als Alternative eine zweistufige Reaktionsführung vorgeschlagen, bei der zunächst in flüssiger Phase o-Xylol mit einem sauerstoffhaltigen Gas, meist Luft, unter homogener Katalyse überwiegend zu o-Tolylsäure oxidiert wird. Die o-Tolylsäure wird anschließend verdampft und in der Gasphase in einer zweiten Stufe zu Phthalsäureanhydrid oxidiert.Phthalic anhydride is one of the technically most important aromatic compounds. It is used, for example, in the synthesis of alkyd resins, unsaturated polyester resins, paints, plastics, plasticizers, phthalocyanine dyes, insect repellents, denaturing agents and for the production of numerous fine chemicals. Phthalic anhydride is made by oxidation of o-xylene or naphthalene. Two oxidation processes are common. On the one hand, this is an oxidation in the gas phase on a heterogeneous catalyst, generally a vanadium catalyst. In this process variant, about 20 mol% of the starting material is converted to CO x and is therefore lost as a yield. Because of the better selectivity of the oxidation reaction, a two-stage reaction is proposed as an alternative, in which o-xylene is initially oxidized in the liquid phase with an oxygen-containing gas, mostly air, to o-tolylic acid under homogeneous catalysis. The o-tolylic acid is then evaporated and oxidized to phthalic anhydride in the gas phase in a second stage.
Ein derartiges zweistufiges Verfahren wird in der EP-0 256 352 AI beschrieben. In der ersten Stufe wird o-Xylol in flüssiger Phase mit Luft bei einer Temperatur zwischen 120 und 150°C und einem Druck zwischen Normaldruck und 35 bar mit in o-Xylol löslichen Kobaltsalzen, im allgemeinen Co-Naphthenat, als Katalysator oxidiert. Das während der Oxidation gebildete Wasser wird zusammen mit dem o-Xylol aus der Gasphase kondensiert und abgetrennt. Das o-Xylol wird dann in den Reaktor zimickgeführt. Die aus der ersten Stufe erhaltene Reaktionsmischung wird destilliert, wodurch die o-Tolylsäure gereinigt und das nicht umgesetzte o-Xylol abgetrennt wird. Das o-Xylol wird wieder der ersten Stufe zugeführt, während die o-Tolylsäure der Gasphasenoxidation der zweiten Stufe zugeführt wird.Such a two-stage process is described in EP-0 256 352 AI. In the first stage, o-xylene is oxidized in the liquid phase with air at a temperature between 120 and 150 ° C and a pressure between normal pressure and 35 bar with cobalt salts soluble in o-xylene, generally co-naphthenate, as a catalyst. The water formed during the oxidation is condensed together with the o-xylene from the gas phase and separated off. The o-xylene is then fed into the reactor. The reaction mixture obtained from the first stage is distilled, whereby the o-tolylic acid is purified and the unreacted o-xylene is separated off. The o-xylene is again the fed to the first stage, while the o-tolylic acid is fed to the gas phase oxidation of the second stage.
Nachteilig an dem Verfahren gemäß der EP-0 256 352 AI ist, daß das Reaktionsprodukt aus der Oxidation in flüssiger Phase der ersten Stufe mit Benzoesäure verunreinigt ist. Die Benzoesäure entsteht durch Verlust eines Kohlenstoffatoms aus dem o-Xylol. Die Benzoesäure lässt sich nicht oder zumindest nur sehr aufwendig aus dem Reaktionsgemisch der ersten Stufe abtrennen. Sie wird daher in die zweite Stufe der Oxidation mit überführt. Bei der Oxidation in der Gasphase wird die Benzoesäure zu COx und Wasser verbrannt. Dies führt zur Ausbildung von „hot spots" und damit zu einer Verschlechterung der Selektivität des Gesamtreaktion.A disadvantage of the process according to EP-0 256 352 AI is that the reaction product from the oxidation in the liquid phase of the first stage is contaminated with benzoic acid. Benzoic acid arises from the loss of a carbon atom from the o-xylene. The benzoic acid cannot be removed from the reaction mixture of the first stage, or at least only with great difficulty. It is therefore transferred to the second stage of the oxidation. During the oxidation in the gas phase, the benzoic acid is burned to CO x and water. This leads to the formation of "hot spots" and thus to a deterioration in the selectivity of the overall reaction.
Aufgabe der Erfindung ist es daher, ein Verfahren zur Oxidation von o-Xylol mit Sauerstoff, vorzugsweise im Gemisch mit einem inerten Gas, insbesondere Luft, unter Zusatz eines Katalysators zur Verfügung zu stellen, das eine verbesserte Selektivität bei der Oxidation zu Phthalsäureanhydrid ermöglicht.The object of the invention is therefore to provide a process for the oxidation of o-xylene with oxygen, preferably in a mixture with an inert gas, in particular air, with the addition of a catalyst which enables improved selectivity in the oxidation to phthalic anhydride.
Die Aufgabe wird bei dem Verfahren dadurch gelöst, daß dem o-Xylol ein Aldehyd zugegeben wird.The object is achieved in the process in that an aldehyde is added to the o-xylene.
Benzoesäure wird durch Oxidation von Toluol gebildet. Das Toluol entsteht wiederum durch Decarboxylierung von o-Tolylsäure. Senkt man die Aktivität des Katalysators, sinkt auch der Umsatz der Nebenreaktion zu Toluol und damit auch die Menge an entstehender Benzoesäure. Durch den Zusatz von o-Tolylaldehyd kann der Reaktivitätsverlust wieder ausgeglichen werden. o-Tolylaldehyd kann selbst zu Phthalsäure oxidiert werden und bildet daher keine störenden Nebenprodukte.Benzoic acid is formed by the oxidation of toluene. The toluene in turn is formed by decarboxylation of o-tolylic acid. If the activity of the catalyst is reduced, the conversion of the side reaction to toluene and thus the amount of benzoic acid formed also decrease. The loss of reactivity can be compensated for by adding o-tolylaldehyde. o-Tolylaldehyde can itself be oxidized to phthalic acid and therefore does not form any troublesome by-products.
Bei einer besonders bevorzugten Ausfuhrungsform wird aus den Oxidationsprodukten des o-Xylols o-Tolylaldehyd abgetrennt und der o-Tolylaldehyd in die Reaktion zurückgeführt. Die Abtrennung erfolgt destillativ. Dabei wird bevorzugt der o-Tolylaldehyd zusammen mit nicht umgesetztem o-Xylol von den Oxidationsprodukten des o-Xylols abgetrennt und wieder in die Reaktion zurückgeführt. Das erfindungsgemäße Oxidationsverfahren wird bevorzugt in flüssiger Phase durchgeführt, insbesondere unter homogener Katalyse. Besonders geeignet ist das Verfahren für die oben beschriebene zweistufige Oxidation von o-Xylol zu Phthalsäureanhydrid. Dabei wird das o-Xylol in der ersten Stufe in flüssiger Phase zu einem Gemisch verschiedener Oxidationsprodukte oxidiert. Anschließend wird nicht umgesetztes o-Xylol sowie entstandener o-Tolylaldehyd abdestilliert und der ersten Stufe wieder zugeführt. Die im Sumpf verbleibenden Oxidationsprodukte des o-Xylols werden anschließend verdampft und in der zweiten Stufe in der Gasphase zu Phthalsäureanhydrid oxidiert.In a particularly preferred embodiment, o-tolylaldehyde is separated from the oxidation products of o-xylene and the o-tolylaldehyde is returned to the reaction. The separation takes place by distillation. The o-tolylaldehyde is preferably separated off from the oxidation products of the o-xylene together with unreacted o-xylene and returned to the reaction. The oxidation process according to the invention is preferably carried out in the liquid phase, in particular with homogeneous catalysis. The process is particularly suitable for the two-stage oxidation of o-xylene to phthalic anhydride described above. In the first stage, the o-xylene is oxidized in the liquid phase to a mixture of different oxidation products. Unreacted o-xylene and o-tolylaldehyde formed are then distilled off and fed back to the first stage. The oxidation products of the o-xylene remaining in the bottom are then evaporated and oxidized to phthalic anhydride in the gas phase in the second stage.
Als geeignet hat sich erwiesen, wenn der Katalysator Kobalt und/oder ein Kobaltsalz enthält. Die Eignung dieses Katalysators ist auch in der EP-0 256 352 beschrieben. Das im Kobaltsalz verwendete Anion ist an sich unkritisch. Es dient hauptsächlich dazu, das Metallion im Reaktionsgemisch löslich zu machen. Geeignete Anionen leiten sich beispielsweise von aliphatischen und aromatischen Carbonsäuren ab. Beispiele dafür umfassen Naphthenate, Acetate, Propionate, Butanoate, Pentanoate, Hexanoate, Heptanoate, Octanoate, 2-Ethylhexanoate, Nonanoate, Isononaoate, Decanoate, Laurinoate, Palmitate, Stearate, Benzoate, Toluylate, Phthalate und Citrate. Beispiele für andere Gruppierungen, die eine Löslichkeit der Metalle bewirken, sind Acetylacetonat, Porphyrine, Salcomin, Sälen, Phthalocyanin und Carbonylgruppen. Es sind jedoch auch andere Gruppen geeignet, solange diese in der Lage sind, eine Löslichkeit des Metallions zu bewirken.It has proven to be suitable if the catalyst contains cobalt and / or a cobalt salt. The suitability of this catalyst is also described in EP-0 256 352. The anion used in the cobalt salt is not critical in itself. It mainly serves to make the metal ion soluble in the reaction mixture. Suitable anions are derived, for example, from aliphatic and aromatic carboxylic acids. Examples include naphthenates, acetates, propionates, butanoates, pentanoates, hexanoates, heptanoates, octanoates, 2-ethylhexanoates, nonanoates, isononaoates, decanoates, laurinoates, palmitates, stearates, benzoates, toluylates, phthalates and citrates. Examples of other groups which cause solubility of the metals are acetylacetonate, porphyrins, salcomine, halls, phthalocyanine and carbonyl groups. However, other groups are also suitable as long as they are capable of causing the metal ion to be soluble.
Die Decarboxylierung von Tolylsäure zu Toluol läßt sich zurückdrängen, wenn dem Katalysator eine Mangan(II)-Verbindung beigegeben ist. Dadurch wird die Aktivität des Kobalt-Katalysators abgesenkt. Der Aktivitätsverlust des Katalysators kann durch die Zugabe des Aldehyds wieder ausgeglichen werden.The decarboxylation of tolylic acid to toluene can be suppressed if a manganese (II) compound is added to the catalyst. This lowers the activity of the cobalt catalyst. The loss of activity of the catalyst can be compensated for by adding the aldehyde.
Weiterhin kann sich die Zugabe einer weiteren Metallverbindung günstig auf die Aktivität der Reaktion auswirken. Die Verbindung ist dabei vorzugsweise eine eines Metalls aus der Gruppe bestehend aus Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, AI, Sc, Y, Ga, In, Tl, Ti, Zr, Hf, Ge, Sn, Pb, V, Nb, Ta, Cr, Mo, W, Tc, Ru, Fe, Re, Os, Rh, Ir, Ni, Pd, Pt sowie Kombinationen dieser Metalle. Die Erfindung wird anhand einer Zeichnung näher erläutert. Dabei zeigt:Furthermore, the addition of a further metal compound can have a favorable effect on the activity of the reaction. The compound is preferably one of a metal from the group consisting of Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Al, Sc, Y, Ga, In, Tl, Ti, Zr, Hf , Ge, Sn, Pb, V, Nb, Ta, Cr, Mo, W, Tc, Ru, Fe, Re, Os, Rh, Ir, Ni, Pd, Pt and combinations of these metals. The invention is explained in more detail with reference to a drawing. It shows:
Fig. 1 : eine Aufstellung der Hauptkomponenten der bei der Oxidation von o-Xylol entstehenden Oxidationsprodukte;1: a list of the main components of the oxidation products formed in the oxidation of o-xylene;
Fig. 2: eine schematische Darstellung einer Vorrichtung zur Oxidation von o-Xylol zu Phthalsäureanhydrid.2: a schematic representation of a device for the oxidation of o-xylene to phthalic anhydride.
Das erflndungsgemäße Verfahren läßt sich besonders vorteilhaft in Kombination mit zweistufigen Oxidation von o-Xylol zu Phthalsäureanhydrid anwenden. Dabei wird in der ersten Stufe o-Xylol mit Sauerstoff in flüssiger Phase zu einem Gemisch von Oxidationsprodukten oxidiert. Die Oxidation wird durch Kobaltverbindungen katalysiert. In der zweiten Stufe wird das Gemisch von Oxidationsprodukten in der Gasphase zu Phthalsäureanhydrid oxidiert. Diese Gasphasenoxidation kann durch einen Vanadiumkatalysator katalysiert werden. Die Reaktion wird beispielhaft in der EP-0 256 352 beschrieben.The process according to the invention can be used particularly advantageously in combination with two-stage oxidation of o-xylene to phthalic anhydride. In the first stage, o-xylene is oxidized with oxygen in the liquid phase to a mixture of oxidation products. The oxidation is catalyzed by cobalt compounds. In the second stage, the mixture of oxidation products in the gas phase is oxidized to phthalic anhydride. This gas phase oxidation can be catalyzed by a vanadium catalyst. The reaction is described by way of example in EP-0 256 352.
Fig. 1 zeigt eine Darstellung der Hauptprodukte des bei der Oxidation von o-Xylol in flüssiger Phase mit Luftsauerstoff entstehenden Gemisches von Oxidationsprodukten. Durch Decarboxylierung von o-Tolylsäure bzw. Decarbonylierung von o-Tolylaldehyd entsteht als unerwünschtes Nebenprodukt zunächst Toluol, das dann weiter zur Benzoesäure oxidiert wird. In der zweiten Stufe wird die Benzoesäure zu CO2 und CO verbrannt und führt zur Ausbildung von „hot spots". Der Anteil der einzelnen Substanzen im teiloxidierten Gemisch lässt sich durch die Wahl der Reaktionsbedingungen beeinflussen. Die Darstellung zeigt Produkte, die einen größeren Anteil am Gemisch der Oxidationsprodukte bilden. Daneben entstehen noch zahlreiche andere Produkte, die aus Gründen der Übersichtlichkeit jedoch nicht dargestellt sind. Bei der Oxidation von o-Xylol entsteht als eines der Oxidationsprodukte o-Tolylaldehyd. Je nach Reaktionsführung bildet der o-Tolylaldehyd einen Anteil von ungefähr 1 bis 10 Gew.-% am Gemisch der Oxidationsprodukte. Dieser Anteil kann vor der Weiteroxidation in der zweiten Stufe abgetrennt werden und wieder zur ersten Stufe der Oxidation in flüssiger Phase, zurückgeführt werden. Fig. 2 zeigt schematisch den Aufbau einer Vorrichtung zur Durchfuhrung des erfindungsgemäßen Verfahrens. Über den Xylol-Zulauf 1 wird o-Xylol einem Reaktor 2 zugeführt. Die Katalysatorlösung, beispielsweise ein Kobaltsalz im Gemisch mit einem Mn(II)Salz, gelöst in o-Xylol, wird über einen Katalysatorzulauf 3 zugeführt. Als Kobaltsalze können beispielsweise Naphthenate, das Acetat oder das 2-Ethylhexanoat verwendet werden. Die Oxidation des o-Xylols erfolgt in flüssiger Phase mit Luft, die über Luftzufuhr 4 in den Reaktor 2 eingedüst wird. Geeignete Formen für den Reaktor 2 sind dem Fachmann an sich bekannt. Die Reaktion kann in einem einzelnen Reaktor, jedoch auch in mehreren hintereinander geschalteten Reaktoren durchgeführt werden. Die an Sauerstoff abgereicherte Luft wird über Abgasleitung 5 aus dem Reaktor 2 herausgeführt und durch Kühlen mitgefühlte leichter flüchtige Anteile, insbesondere o-Xylol und Toluol, auskondensiert. Das an organischen flüchtigen Bestandteilen abgereicherte Abgas kann zur weiteren Reinigung einer Verbrennung zugeführt werden. Die auskondensierten Bestandteile des Abgases werden über Rückführungsleitungen 6 einer Destillationsvorrichtung 9 zugeführt. Als Alternative können die auskondensierten Bestandteile des Abgases auch über Rückführungsleitung 6a (gestrichelte Darstellung) mit dem Rohprodukt vereinigt werden, das über Rohproduktleitung 7 aus dem Reaktor 2 herausgeführt wird. In diesem Fall entfallt die direkte Zuleitung in die Destillationsvorrichtung 9. Wasser, das neben o- Xylol und Toluol aus dem Abgas auskondensiert wurde, kann über Wasserableitung 8 aus dem System herausgeführt werden. Das Rohprodukt, das aus einem Gemisch von o-Xylol und Oxidationsprodukten des o-Xylols besteht, wird der Destillationsvorrichtung 9 zugeführt, in der eine Auftrennung in verschiedene Stoffströme erfolgt. Die Destillationsvorrichtung 9 kann aus mehreren miteinander verschalteten Kolonnen aufgebaut sein. In der Destillationsvorrichtung 9 wird als erster Stoffstrom Toluol über Toluolableitung 10 aus dem System herausgeführt. Mit dem Toluol wird azeotrop Wasser ausgeschleppt, das bei der Oxidation des o-Xylols entsteht. Die im Weiteren genannten Stoffströme sind daher nahezu wasserfrei. Als zweiter Stoffstrom wird nicht umgesetztes o-Xylol aus dem Rohprodukt abgetrennt und über Xylolrückführungsleitung 11 wieder dem Reaktor 2 zugeführt. Mit dem o-Xylol wird o-Tolylaldehyd aus dem Gemisch der Oxidationsprodukte abdestilliert. o-Tolylaldehyd weist nach o-Xylol den nächsthöheren Siedepunkt der Verbindungen des Gemisches der Oxidationsprodukte auf. Im Sumpf der Destillationsvorrichtung 9 bleibt ein Gemisch aus Katalysator sowie den Oxidationsprodukten des o-Xylols zurück und wird über Sumpfableitung 12 einer Produktabtrennung 13 zugeführt. In der Produktabtrennung werden die Oxidationsprodukte des o-Xylols vom Katalysator abdestilliert. Der Katalysator wird über Katalysatorrückführung 14 wieder dem Reaktor 2 zugeführt. Ein Anteil des Katalysators wird jeweils durch Katalysatorausleitung 15 aus dem System herausgeführt. Dieser Anteil wird jeweils durch frischen Katalysator, der über Katalysatorzulauf 3 zugeführt wird, ersetzt. Die abdestillierten Oxidationsprodukte des o-Xylols werden über Produktleitung 16 abgenommen und einer (nicht dargestellten) zweiten Reaktionsstufe zugeführt, in der die Oxidationsprodukte des o-Xylols zu Phthalsäureanhydrid oxidiert werden. 1 shows a representation of the main products of the mixture of oxidation products formed during the oxidation of o-xylene in the liquid phase with atmospheric oxygen. Decarboxylation of o-tolylic acid or decarbonylation of o-tolylaldehyde initially produces toluene as an undesirable by-product, which is then further oxidized to benzoic acid. In the second stage, the benzoic acid is burned to CO 2 and CO and leads to the formation of "hot spots". The proportion of the individual substances in the partially oxidized mixture can be influenced by the choice of the reaction conditions. The illustration shows products which have a larger proportion of the In addition, numerous other products are formed, which, however, are not shown for reasons of clarity. In the oxidation of o-xylene, one of the oxidation products is o-tolylaldehyde. Depending on the reaction, the o-tolylaldehyde forms a proportion of approximately 1 to 10% by weight of the mixture of the oxidation products, this fraction can be separated off before the further oxidation in the second stage and returned to the first stage of the oxidation in the liquid phase. Fig. 2 shows schematically the structure of a device for performing the method according to the invention. O-xylene is fed to a reactor 2 via the xylene feed 1. The catalyst solution, for example a cobalt salt in a mixture with an Mn (II) salt, dissolved in o-xylene, is fed in via a catalyst feed 3. For example, naphthenates, acetate or 2-ethylhexanoate can be used as cobalt salts. The oxidation of the o-xylene takes place in the liquid phase with air, which is injected into the reactor 2 via air supply 4. Suitable forms for the reactor 2 are known per se to the person skilled in the art. The reaction can be carried out in a single reactor, but also in several reactors connected in series. The oxygen-depleted air is led out of the reactor 2 via the exhaust line 5 and condensed more volatile components, in particular o-xylene and toluene, which are condensed by cooling. The exhaust gas depleted in organic volatile constituents can be fed to a combustion for further purification. The condensed components of the exhaust gas are fed to a distillation device 9 via return lines 6. As an alternative, the components of the exhaust gas which have been condensed out can also be combined with the raw product via return line 6a (dashed line), which is led out of the reactor 2 via raw product line 7. In this case, the direct feed into the distillation device 9 is omitted. Water which has been condensed out of the exhaust gas in addition to o-xylene and toluene can be led out of the system via water discharge line 8. The crude product, which consists of a mixture of o-xylene and oxidation products of o-xylene, is fed to the distillation device 9, in which a separation into different material flows takes place. The distillation device 9 can be constructed from several interconnected columns. In the distillation device 9, toluene is led out of the system via toluene discharge 10 as the first material flow. The toluene is used to carry out azeotropic water that is formed during the oxidation of the o-xylene. The material flows mentioned below are therefore almost water-free. Unreacted o-xylene is separated from the crude product as the second stream and is fed back to the reactor 2 via the xylene return line 11. With the o-xylene, o-tolylaldehyde is distilled off from the mixture of the oxidation products. After o-xylene, o-tolylaldehyde has the next higher boiling point of the compounds of the mixture of the oxidation products. A mixture of catalyst and the oxidation products of o-xylene remains in the bottom of the distillation device 9 and is fed to a product separation 13 via the bottom drain 12. In the product separation, the Oxidation products of o-xylene distilled off from the catalyst. The catalyst is returned to the reactor 2 via the catalyst return 14. A portion of the catalyst is led out of the system through catalyst discharge line 15. This portion is replaced in each case by fresh catalyst, which is fed in via catalyst feed 3. The distilled off oxidation products of o-xylene are removed via product line 16 and fed to a second reaction stage (not shown) in which the oxidation products of o-xylene are oxidized to phthalic anhydride.
BezugszeichenlisteLIST OF REFERENCE NUMBERS
1 Xylolzulauf1 xylene feed
2 Reaktor2 reactor
3 Katalysatorzulauf3 catalyst feed
4 Luftzufuhr4 air supply
5 Abgasleitung5 exhaust pipe
6 Kondensatrückführungsleitung6 condensate return line
7 Rohproduktleitung7 Raw product line
8 Wasserableitung8 water drainage
9 Destillationsvorrichtung9 distillation device
10 Toluolableitung10 toluene discharge
11 Xylolrückführungsleitung11 xylene return line
12 Sumpfableitung12 swamp drainage
13 Produktabtrennung13 Product separation
14 Katalysatoirückführung14 Catalyst recycle
15 Katalysatorausleitung15 Catalyst rejection
16 Produktleitung 16 Product management

Claims

Patentansprüche claims
1. Verfahren zur Oxidation von o-Xylol mit Sauerstoff, vorzugsweise im Gemisch mit einem inerten Gas, insbesondere Luft, unter Zusatz eines Katalysators, zu einem Gemisch von Oxidationsprodukten des o-Xylols, dadurch gekennzeichnet, daß dem o-Xylol o-Tolylaldehyd zugegeben wird.1. A process for the oxidation of o-xylene with oxygen, preferably in a mixture with an inert gas, in particular air, with the addition of a catalyst, to a mixture of oxidation products of o-xylene, characterized in that the o-xylene is added to o-tolylaldehyde becomes.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß aus dem Gemisch von Oxidationsprodukten des o-Xylols o-Tolylaldehyd und nicht umgesetztes o-Xylol abgetrennt wird und zur Oxidation von o-Xylol rückgeführt wird.2. The method according to claim 1, characterized in that o-tolylaldehyde and unreacted o-xylene is separated from the mixture of oxidation products of o-xylene and is recycled to the oxidation of o-xylene.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Oxidation von o-Xylol in flüssiger Phase, vorzugsweise unter homogener Katalyse, durchgeführt wird.3. The method according to claim 1 or 2, characterized in that the oxidation of o-xylene is carried out in the liquid phase, preferably with homogeneous catalysis.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß der Katalysator ein Kobalt-Katalysator ist.4. The method according to any one of claims 1 to 3, characterized in that the catalyst is a cobalt catalyst.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß eine Kobaltverbindung eines Anions verwendet wird, die eine im Reaktionsmedium lösliche Verbindung ergibt, vorzugsweise ein Anion einer aliphatischen oder aromatischen Carbonsäure, insbesondere Naphthenate, Acetate, Propionate, Butanoate, Pentanoate, Hexanoate, Heptanoate, Octanoate, 2-Ethylhexanoate, Nonanoate, Isononaoate, Decanoate,5. The method according to claim 4, characterized in that a cobalt compound of an anion is used which gives a compound soluble in the reaction medium, preferably an anion of an aliphatic or aromatic carboxylic acid, in particular naphthenates, acetates, propionates, butanoates, pentanoates, hexanoates, heptanoates, Octanoates, 2-ethylhexanoates, nonanoates, isononaoates, decanoates,
Laurinoate, Palmitate, Stearate, Benzoate, Toluylate, Phthalate und Citrate, oder ein Anion aus der Gruppe bestehend aus Acetylacetonat, Porphyrinen, Salcomin, Sälen, Phthalocyanin und Carbonylgruppen.Laurinoates, palmitates, stearates, benzoates, toluylates, phthalates and citrates, or an anion from the group consisting of acetylacetonate, porphyrins, salcomine, halls, phthalocyanine and carbonyl groups.
6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß der Katalysator mindestens eine Mangan(II)-Verbindung enthält. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß der Katalysator weiterhin eine Verbindung enthält eines Metalls aus der Gruppe bestehend aus Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, AI, Sc, Y, Ga, In, Tl, Ti, Zr, Hf, Ge, Sn, Pb, V, Nb, Ta, Cr, Mo, W, Tc, Ru, Fe, Re, Os, Rh, Ir, Ni, Pd, Pt und Kombinationen davon. 6. The method according to any one of claims 1 to 5, characterized in that the catalyst contains at least one manganese (II) compound. Method according to one of claims 1 to 6, characterized in that the catalyst further contains a compound of a metal from the group consisting of Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Al, Sc, Y, Ga, In, Tl, Ti, Zr, Hf, Ge, Sn, Pb, V, Nb, Ta, Cr, Mo, W, Tc, Ru, Fe, Re, Os, Rh, Ir, Ni, Pd, Pt and combinations thereof.
PCT/EP2001/000707 2000-01-24 2001-01-23 Oxidation of o-xylol to produce o-tolyl acid WO2001055073A2 (en)

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DE2000102807 DE10002807A1 (en) 2000-01-24 2000-01-24 Catalytic oxidation of o-xylene, especially in manufacture of phthalic anhydride, comprises adding o-tolualdehyde to o-xylene to compensate for catalyst activity loss
DE10002807.1 2000-01-24

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB680571A (en) * 1949-03-22 1952-10-08 Monsanto Chemicals Improvements in or relating to liquid phase oxidation
GB815198A (en) * 1957-06-13 1959-06-17 Du Pont Improvements in or relating to the production of aromatic acid esters
GB890387A (en) * 1958-08-23 1962-02-28 Basf Ag Improvements in the production of terephthalic acid
EP0351627A1 (en) * 1988-07-16 1990-01-24 Bayer Ag Process for the recovery of ortho-toluic acid by distillation
US5679847A (en) * 1995-05-30 1997-10-21 Mitsubishi Gas Chemical Company, Inc. Process for producing terephthalic acid

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB680571A (en) * 1949-03-22 1952-10-08 Monsanto Chemicals Improvements in or relating to liquid phase oxidation
GB815198A (en) * 1957-06-13 1959-06-17 Du Pont Improvements in or relating to the production of aromatic acid esters
GB890387A (en) * 1958-08-23 1962-02-28 Basf Ag Improvements in the production of terephthalic acid
EP0351627A1 (en) * 1988-07-16 1990-01-24 Bayer Ag Process for the recovery of ortho-toluic acid by distillation
US5679847A (en) * 1995-05-30 1997-10-21 Mitsubishi Gas Chemical Company, Inc. Process for producing terephthalic acid

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