DE19839782A1 - Metallic reactor tube, useful for the production of (meth)acrolein and/or (meth)acrylic acid by catalytic gas-phase oxidation of alkane or alkene etc. - Google Patents

Abstract

A metallic reactor tube with a catalytic coating of multi-metal oxide material containing molybdenum and bismuth, directly applied to the tube. Independent claims are also included for (a) a pipe bundle reactor with reactor tubes as defined; (b) a process for the production of coated reactor tubes or pipe bundle reactors, comprising (1) preparation of solutions, emulsions and/or dispersions of the elements and/or their compounds required for the catalyst and/or its precursor, (2) possible addition of coupling agents, binders, viscosity regulators and/or pH regulators, (3) application to the tube(s), preferably on the inside, preferably by spraying or dip-coating and (4) drying and possibly sintering or calcining by heating the coated tube at 20-1500 (preferably 200-400) deg C, optionally in presence of inert or reactive gas; (c) a process for the production of (meth)acrolein and/or (meth)acrylic acid by the catalytic gas-phase oxidation of 1-6C alkanes, 2-6C alkenes, 1-6C alkanols and/or alkanals and/or precursors thereof, using a reactor tube or pipe bundle reactor as above.

Description

The invention relates to a metallic reaction tube with a catalytic loading Layering preferred on the inner tube wall, with tube bundle reactors coated reaction tubes, a coating process and a Ver application of the reaction tube or the tube bundle reactor at katalyti Gas phase oxidation for the production of (meth) acrolein and / or (Meth) acrylic acid.

A variety of chemical reactions are carried out in heterogeneous catalysis Reaction tubes carried out. The catalysts are usually called Full or supported catalysts used and as a bed in the reaction pipes inserted. Filled reaction tubes are disadvantageous, however re regarding the increased pressure drop and the increased weight. This usually requires a larger wall thickness, with negati ven effects on heat transfer. These disadvantages are caused by Application of a catalytic coating on the inner tube walls sores.

WO 97/25146 discloses a catalytically active coating which from a layered composite with a metallic base body, for example the Inside of a reaction tube, coupling agent and catalytically active Cover layer consists in particular of oxide ceramic catalyst material. To prevent the catalytically active top layer from flaking off when changing  To avoid temperature stress, it is then imperative on the metallic base body first an adhesion promoter with im essential metallic composition to apply.

From DE-OS 21 18 871 it is known the formation of by-products in the production of carboxylic acids or their anhydrides by gaspha vertical catalytic oxidation of aromatic or unsaturated aliphatic carbons Hydrogen in the presence of supported vanadium pentoxide in a tube bundle reactor by reducing the inner wall of the Pipes are at least partially coated with a catalytic mass, which contains titanium dioxide, preferably in a mixture with vanadium pentoxide. The Process products are obtained in high purity and high yields. The description does not contain any indications of a reduction in heat point temperatures in the pipes.

A commercially important heterogeneously catalyzed reaction is the catalytic gas phase oxidation of C ₁ -C ₆ alkanes, C ₂ -C ₆ alkenes, C ₁ -C ₆ alkanes and / or alkanes and / or precursors thereof for the preparation of ( Meth) acrolein and / or (meth) acrylic acid. These reactions are highly exothermic, which is why, due to the large number of possible parallel or subsequent reactions, it is necessary for a selective reaction to control the course of the reaction temperature. To regulate the temperature, the reaction tubes are surrounded by a heat transfer medium, for example by a molten salt. Despite this thermostatting, so-called hot spots are formed along the catalyst bed, with a higher temperature than the rest of the catalyst bed. On the one hand, this reduces the life of the catalyst in this contact tube section and, on the other hand, affects the selectivity of the acrolein-acrylic acid formation.

Various countermeasures to. Overcoming the disadvantage mentioned are already recommended in the prior art and are for example in DE-A-44 31 949. One suggestion is downsizing of the diameter of the contact tubes, so the heat dissipation per volume unit to increase the catalyst. However, the disadvantage of this method is that that they have the number required for a particular production output catalyst-filled catalyst tubes necessarily increased, both the manufacturing costs of the reactor as well as those for filling and emptying the catalyst tubes in the catalyst increases the time required.

According to another proposed procedure, the training of Try to suppress hotspots by using the volume-specific cal activity of the catalytic feed varies along the catalyst tubes. However, this procedure either requires application at least two catalysts of different activity or the use of Inert material. In addition, this procedure complicates the filling of the Contact tubes. Another obvious way to reduce the Hot spot formation consists in increasing the acrolein load on the reactor to reduce. However, this measure also reduces the space-time Yield of the desired product.

DE-A-44 31 949 describes a reduction in hot spot temperatures in the tubes of a tube reactor with heat exchange circuit in the Contact tubes surrounding space through a meandering guide of the Heat exchangers in cocurrent with the reaction gases as well Compliance with certain, low temperature differences in the heat exchange by means of from the entry point to the exit point from the reactor beard.

It is an object of the invention to provide a reaction tube or a tube bundle freak Tor to provide with reaction tubes that out in the way stalten that when carrying out heterogeneously catalyzed gas phase senoxidations in such reaction tubes the occurrence of "hot spots" is largely or completely avoided. This task is said to be in a facher way, by a suitable design of the reaction tubes, without special requirements for temperature profile and flow control of the Heat exchange circuit can be solved.

The object is achieved by providing a metalli reaction tube with catalytic coating, the coating contains a multimetal oxide mass that is directly on the reaction tube is applied.

Surprisingly, it has been found that a coating containing a Contains multimetal oxide mass and that directly on a metallic reak tion tube is applied without an adhesion-promoting intermediate layer, a represents long-term stable composite, which at temperatures up to approx. 600 ° C, like they usually occur during catalytic gas phase oxidation is.

A coating process for the production of the corresponding metallic reaction tubes or tube bundle reactors provided become.

The term "multimetal oxide mass" used here denotes oxidi mixtures containing two or more, preferably three or more chemical Elements included, generally not more than 50 different chemical elements are contained in a proportion of more than 1 wt .-%. The transition metal elements molybdenum and bismuth are in the  Always contain multimetal oxide materials used according to the invention. More common wise, the multimetal oxide masses are not simple physical gemi of oxides of elementary constituents, but heterogeneous mixtures complex poly compounds of these elements.

The multimetal oxide compositions used according to the invention generally contain molybdenum, calculated as MoO ₃ , in a proportion of 20 to 90% by weight, preferably 30 to 80% by weight, particularly preferably 40 to 70% by weight.

The catalytic coating containing the multimetal oxide mass is applied directly to the reaction tube, d. H. without in between ordered subcarriers or adhesive intermediary layers.

The inner tube wall of the metallic reaction tube is preferably provided with the catalytic coating.

With regard to the metallic materials for the reaction tube, there are basically no restrictions, but preference is given to steel, in particular stainless steel, such as V ₂ A steel, and ferritic steel.

The catalytic coating according to the invention preferably has one Layer thickness of 10 to 1000 microns, preferably from 20 to 500 microns, particularly preferably from 50 to 350 microns.

In a preferred embodiment, the invention relates to a tube bundle reactor ren with metallic reaction tubes, which correspond to the above Aus guides are provided with a catalytic coating that a directly on the reaction tubes, preferably on the inner wall of the tube, applied multimetal oxide mass contains. The reaction tubes of the Rohrbün delreactor can have any cross section, but in the  Usually round, especially circular. The inside pipe diameter is preferably 0.2 to 70 mm, in particular 10 to 50 mm, especially before pulls 15 to 30 mm. The tube bundle reactor can usually up to 50,000 Reaction tubes, preferably 50 to 40,000, particularly preferably 500 to Contain 30,000 reaction tubes. The pipe length is usually 0.1 to 10 m, preferably 0.3 to 8 m, particularly preferably 0.5 to 6 m.

According to a particular embodiment, it is possible in the reaction pipes in their entirety prefer a fill made of multimetal oxide or to insert catalysts, in particular with a fill level of 5 to 90%, preferably from 10 to 70%, especially from 20 to 50% of the entire reactor tube length. The catalyst bed is preferably in area located on the gas outlet side.

According to a further preferred embodiment is a tube bundle reactor with fully or partially coated reaction tubes, a second reactor, in particular a tube bundle reactor, connected with a bed is provided from full or shell multimetal oxide catalysts. This The arrangement of two reactors connected in series offers the advantage that differed according to the degree of progress of the reaction at union, specially adapted process conditions can be worked. In particular, in the first reactor, the pipes of which the invention wear catalytic coating as a result of avoiding the hot spot Danger at temperatures that are usually around 20 to 100 ° C higher compared to conventional gas phase oxidation to (meth) acrolein and / or (Meth) acrylic acid, typically from 200 to 450 ° C, are worked. As a result, less educt is lost due to improved desorption Total combustion instead.  

The coating method according to the invention comprises the following steps

• 1. Preparation of solutions, emulsions and / or dispersions of elements and / or element connections in the multime talloxide catalyst and / or catalyst precursor present Elements,
• 2. if necessary, adding adhesion promoters, binders, Viscosity regulators and / or pH regulators in the solution genes, emulsions and / or dispersions,
• 3. Application of the solutions, emulsions and / or dispersions on the reaction tube or tubes of the tube bundle reactor, preferably on the inside, preferably through Spraying or dipping, and
• 4. Heating the coated reaction tube, optionally in Presence of inert or reactive gases, at one temperature in the range from 20 to 1500 ° C, preferably to 200 to 400 ° C, for drying and optionally sintering or calcining the Multimetal oxide catalysts and / or catalyst precursors.

First, a liquid starting mixture is produced in the form a solution, emulsion and / or dispersion corresponding to that in DE-A 198 05 719 described manner. The liquid mixtures contain in generally a liquid chemical component that acts as a solvent, Emulsifying agents or dispersing agents for the other components the mixture is used. Water is preferably used for this and / or one or more organic compounds, their boiling point or Sublimation temperature at normal pressure <100 ° C, preferably <150 ° C is. The organic proportion of the is preferably according to the invention using liquid chemical components 10 to 80 wt .-%, ins particularly 10 to 70% by weight, and particularly preferably 20 to 50% by weight.  

Except for the chemical elements of the solvent or dispersing aid the liquid mixtures contain one or more, preferably 2 or more, preferably 3 or more chemical elements, in general but no more than 50 different chemical elements with one Amount of more than 1 wt .-% are included. The are preferably chemical elements in the mixtures in very intimate mixing, e.g. B. in the form of a mixture of different miscible solutions, intimate emulsions with small droplet size and / or preferably as Suspension (dispersion) containing the chemical elements in question general in the form of a fine precipitation, e.g. B. in the form of a chemi mixed precipitation. The use has also proven particularly useful of sols and gels, in particular those that chemi elements contained in a largely homogeneous distribution and preferred of those that are favorable for the subsequent coating Show adhesion and flow behavior. As starting compounds for the out chosen chemical elements come in principle the elements themselves, preferably in finely divided form, moreover all connections in Question the selected chemical elements appropriately contain, such as oxides, hydroxides, oxide hydroxides, inorganic salts before adds nitrates, carbonates, acetates and oxalates, organometallic compounds gene, alkoxides, etc. The respective starting compounds can be in solid Form, in the form of solutions, emulsions and / or in the form of suspensions sions are used.

In addition, the liquid mixture can contain further compounds which influence the adhesive properties and the flow behavior of the liquid mixture on the surface to be coated. Here are z. B. ethylene glycol or glycerin, as described in DE-A 44 42 346, or z. B. maleic acid copolymers and as inorganic compounds such. B. SiO ₂ , Si organic compounds or siloxanes.

Furthermore, the mixtures used can additionally contain an inorganic one and / or contain organic binder or a binder system which the used mixture stabilized. For this, z. B. Binder or Binder systems, the metal salts, metal oxides, metal oxide hydroxides, metal oxide hydroxide phosphates and / or at the operating temperature of the catalyst contain melting eutectic compounds.

The mixture can also be added by adding acids and / or bases a defined pH range. In many cases pH-neutral suspensions are used. The mixture can be more advantageous indicate a pH between 5 and 9, preferably between 6 and 8, can be set. Special results are with the invention Achieve process when the mixture has a high solids content up to 95 wt .-%, preferably 50 to 80 wt .-% at low viscosity having.

In a preferred embodiment of the invention, the mixture gradually and in general also during production and their Flowability continuously, but measured at least at the end of production sen. This can e.g. B. by measuring the current consumption of the stirrer respectively. With the help of this measurement, the viscosity of the suspension z. B. adjusted by adding further solvents or thickeners be that optimal adhesion, layer thickness and layer thickness even liquid on the surface to be coated results.

In a further process step, the coating is carried out put mixtures, preferably by means of a spray process or Immersion, on different parts of a metallic reaction tube or the Tubes of a tube bundle reactor, in particular on the tube inner walls, in a 10 to 1000 microns, preferably 20 to 500 microns, particularly preferred 50 to 350 µm thick layer.  

Furthermore, the mixture can be poured into the individual tubes and at Speeds between 200 and 1000 rpm, preferably at speeds between 300 and 800 r.p.m. In a preferred one Embodiment are the coatings on the inside of the reak tion pipes by spraying the above-mentioned liquid mixture manufactured. The sprayed mixture material presses into the Roughness of the subsurface, with air bubbles under the Coating can be prevented. The mixture used can adhere completely to the sprayed inside. But it can also, ins especially with lower adhesion and / or low viscosity of the mixture part of the mixture can be discharged again by dripping down. The auxiliary carrier to be coated, e.g. B. in the form of inner tubes can be full be coated continuously or only partially. In particular, the respective reactor tube inlet and reactor tube outlet by a ge suitable device from the coating to be left out later occurring sealing problems with the supply and Prevent drainage devices for the fluid. Has also proven itself a coating in which the mixture is poured into the preheated tube is sprayed or this mixture by immersion in the preheated pipe is introduced. To do this, the metallic base body is opened spray the suspension to 60 to 500 ° C, preferably 200 to 400 ° C and more preferably 200 to 300 ° C preheated and at this temperature coated with the mixture described above. In doing so, a Much of the volatile components of the mixture evaporate and one preferably 10 to 2000 microns, preferably 20 to 500 microns, especially before draws in 50 to 350 µm thick layer of the catalytically active metal oxides the metallic base body. This type of manufacture can be like described in DE-A-25 10 994, with the variant that the Mi not on a preheated support, but on a preheated one metallic base body is applied.  

To achieve particularly thick layers or particularly homogeneous loading The reaction tubes can also be coated several times be carried out in succession. You can choose between the individual Coatings of a reaction tube separate drying and / or calci kidney and / or sintering steps are interposed. The inner wall In the case of spraying, layering is advantageous with the help of an or several spray lances, preferably with one or more movable Spray lances carried out. The spray lance is used during spraying gangs z. B. with the help of an automatic device with a defined constant or varying speed due to the coating Tube pulled.

The thickness of the applied layer after drying and if necessary Calcination or sintering is preferably 10 to 1000 microns, especially preferably 20 to 500 microns.

In addition, the adhesion of the catalytic layer through a chemical, physical or mechanical pretreatment of the inner tube be increased before coating. With chemical pretreatment can the inner tubes z. B. pickled with alkali or preferably with acids become. Furthermore, e.g. B. the inner tube by blasting with a dry blasting medium, in particular corundum or quartz sand roughened to support liability. Beyond that too Detergent proven that a suspension of hard particles, for. B. Corundum, in a dispersion liquid.

When heating the coated tube bundle reactor under vacuum or under a defined gas atmosphere at temperatures from 20 to 1500 ° C, preferably 60 to 1000 ° C, particularly preferably 200 to 600 ° C, very particularly the previously applied coating is more preferably 250 to 500.degree  freed from the preferably aqueous solvent by drying. With increased Temperature can also be a sintering or calcination of the Coating particles take place. In this process, the Usually get the actual catalytically active coating.

In one embodiment of the invention with respect to a process for the production of (meth) acrolein and (meth) acrylic acid by catalytic gas phase oxidation of C ₁ -C ₆ alkanes, C ₂ -C ₆ alkenes, C ₁ -C ₆ alkanols and / or -alkanals and / or precursors using an above-described metallic reaction tube with a catalytic coating or a tube-bundle reactor described above with reaction tubes with a catalytic coating. Since the danger of the formation of hot spots is avoided in this method, it is possible to work at an elevated temperature, in particular around 20 to 100 ° C. higher temperature than in the conventional catalytic gas phase oxidation, typically in the range from approximately 200 to 250 ° C. Due to the increased temperature, an improved educt desorption takes place with less total combustion.

The invention is explained in more detail below on the basis of exemplary embodiments explained.

A reaction gas with an inner diameter of 21 mm and a length of 90 cm was mixed with 300 Nl / h of the composition:
3% by volume propene,
9.5 vol% oxygen and
Rest of nitrogen added.

A multimetal oxide catalyst with a gross composition of Mo ₁₂ W ₂ Bi ₁ Co _5.5 Fe ₃ Si _1.6 K _0.08 O _x was introduced into the reaction tube in the form specified. The reaction temperatures and the selectivity of the reaction to acrolein and acrylic acid or to CO ₂ are shown in the table below.

Example 1 (comparison)

The catalyst was in the form of a full catalyst in the form of rings, with the dimensions: Outer diameter × height × inner diameter = 5 × 3 × 2 mm in the Filled reaction tube.

With this conventional reaction procedure, the proportion of total combustion expressed by the selectivity of the reaction of CO _x (4.8% and 6.5%) is relatively high.

Example 2

A calcined catalyst of the gross composition given above was ground, then 100 g of this powder were mixed with 100 g Clycerin intimately mixed and the resulting suspension by immersion on the inside of a reaction tube with the dimensions given above solutions applied at room temperature. The pipe was then at Annealed at 300 ° C for two hours. The coating process was then repeated and after double coating a multimetal oxide Obtain catalyst layer (35 g active mass).

By using the catalyst according to the invention as a coating of the Inner wall of the reaction tube is the selectivity of the reaction with respect to Acrolein and acrylic acid significantly improved. Even with increased response temperature (400 ° C) compared to Comparative Example 1 becomes a higher Selectivity to acrolein and acrylic acid (95.6%) over a selectivity  only 93.2% at a lower reaction temperature, 360 ° C, he enough.

Example 3

In a tube coated according to Example 2 was a stainless steel spiral Wall width 1.5 cm and wall thickness 2 mm for intensive gas swirling installed and examined.

The gas mixing improved by the installation of the stainless steel spiral leads to an improved selectivity of the reaction to acrolein and acrylic acid.

Example 4

The spiral from Example 3 was used in the same way as the coating in Example 2 a catalyst powder / clycerin mixture coated by immersion (10 g Active compound on the spiral spiral) and tested.

By coating the stainless steel spiral with the multimetal oxide catalyst the selectivity is significantly improved again.

Example 5

In a tube that was coated analogously to Example 2 (35 g active mass on the inside of the tube) 100 g of conventional full catalyst were ent speaking example 1 installed in the reactor outlet. The dumping height was 30 cm.  

Through the combined use of the catalyst as a coating and at the same time as a full catalyst there will be a significant improvement in selectivity compared to the conventional use of the catalyst as a full catalyst, reached.

The improvement in selectivity achieved with the reaction tubes coated according to the invention leads to a significant improvement in the economy of large-scale processes.

Claims (9)

1. Metallic reaction tube with catalytic coating, characterized in that the coating contains a multimetal oxide mass with molybdenum and bismuth, which is applied directly to the reaction tube. 2. Reaction tube according to claim 1, characterized in that the multi metal oxide mass molybdenum, calculated as MoO ₃ , in a proportion of 20 to 90 wt .-%, preferably 30 to 80 wt .-%, particularly preferably 40 to 70 wt .-% %, contains. 3. Reaction tube according to claim 1 or 2, characterized in that the catalytic coating is applied to the inner tube wall. 4. Reaction tube according to one of claims 1 to 3, characterized in net that the catalytic coating a layer thickness of 10 to 1000 microns, preferably 20 to 500 microns, particularly preferably 50 to 350 µm. 5. tube bundle reactor with reaction tubes according to one of claims 1 to 4th 6. tube bundle reactor according to claim 5, characterized in that in the Reaction tubes, preferably in their entirety, a bed Multimetal oxide full or shell catalysts is introduced, in particular  those with a fill level of 5 to 90%, preferably 10 to 70%, specifically 20 to 50% of the reactor tube length. 7. tube bundle reactor according to one of claims 5 or 6, with a downstream second reactor, in particular tube bundle reactor with a bed of full or shell multimetal oxide catalysts. 8. A process for the production of coated reaction tubes according to one of claims 1 to 4 or of tube bundle reactors according to one of claims 5 to 7, which comprises the following steps:

• 1. Preparation of solutions, emulsions and / or dispersions of elements and / or element compounds of the elements present in the multimetal oxide and / or catalyst precursor,
• 2. if necessary, adding adhesion promoters, binders, viscosity regulators and / or pH regulators to the solutions, emulsions and / or dispersions,
• 3. Applying the solutions, emulsions and / or dispersions to the reaction tube or tubes of the tube bundle reactor, preferably the inside thereof, preferably by spraying or dipping, and
• 4. Heating the coated reaction tube, optionally in the presence of inert or reactive gases, to a temperature in the range from 20 to 1500 ° C., preferably to 200 to 400 ° C., for drying and optionally sintering or calcining the multimetal oxide catalysts and / or catalyst precursors .

9. Process for the preparation of (meth) acrolein and / or (meth) acrylic acid by catalytic gas phase oxidation of C ₁ -C ₆ alkanes, C ₂ -C ₆ alkanes, C ₁ -C ₆ alkanols and / or alkanes and / or precursors thereof using a reaction tube according to one of claims 1 to 4 or a tube bundle reactor according to one of claims 5 to 7.