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
  • C07C51/215—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of saturated hydrocarbyl groups
• • 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
• • 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
  • C07C51/25—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring
  • C07C51/252—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring of propene, butenes, acrolein or methacrolein

Definitions

• the present invention relates to a process for the preparation of acrolein and / or acrylic acid from propane, in which the propane is subjected to a partial homogeneous and / or heterogeneously catalyzed oxydehydrogenation with molecular oxygen to propene in a first reaction zone and then to the propene formed in the first reaction zone containing, product gas mixture without separation of a product gas mixture component in at least one further reaction zone and in this at least one further reaction zone that in the product gas mixture of the first
• Acrolein and acrylic acid are important intermediates that are used, for example, in the manufacture of active ingredients and polymers.
• the process currently mainly used on an industrial scale for the production of acrolein and / or acrylic acid is the gas-phase catalytic oxidation of propene (e.g. EP-A 575 897), the propene being predominantly produced as a by-product of ethylene production by steam cracking naphtha.
• gas-phase catalytic oxidation of propene e.g. EP-A 575 897
• the propene being predominantly produced as a by-product of ethylene production by steam cracking naphtha.
• US Pat. No. 3,161,670, EP-A 117 446 and DE-A 33 13 573 relate to processes for the production of acrolein and / or acrylic acid, in which propane was first catalyzed by heterogeneous catalysis
• Dehydration is dehydrated to propene in the absence of oxygen.
• the product mixture containing propene is then subjected to heterogeneously catalyzed gas-phase oxidation.
• a disadvantage of this procedure is that the catalyst required for the non-oxidative dehydrogenation of the propane is deactivated relatively quickly by carbon deposits and therefore has to be regenerated frequently.
• Another disadvantage of this procedure is the hydrogen formation associated with the nonoxidative propane dehydrogenation.
• DE-A 33 13 573 does mention the basic possibility of coupling oxidative dehydrogenation of propane to propene with subsequent heterogeneously catalyzed propene oxidation. However, it does not contain any further information on the implementation of such a procedure.
• EP-A 293 224, US-A 5 198 578 and US-A 5 183 936 teach that an increased N content in the diluent gas is disadvantageous in the catalytic gas phase oxidation of propene to acrolein and / or acrylic acid.
• EP-A 293 224 also suggests combining the oxidative dehydrogenation of propane to propene and the catalytic gas phase oxidation of propene for the purpose of producing acrolein and / or acrylic acid.
• Moro-oka et al combine in laboratory tests a homogeneous oxidative dehydrogenation of propane to propene with a subsequent heterogeneously catalyzed oxidation of the dehydrogenation product mixture to acrolein and / or acrylic acid. Recommend the appropriate combination of procedures
• Moro-oka et al in Applied Catalysis, 70 (2), 1991, pp. 175 to 187.
• EP-A 293224, US-A 5 198578 and US-A 5183936 use Moro-oka et al in in all cases, either pure molecular oxygen or nitrogen-depleted air as the oxygen source for the oxide dehydrogenation stage.
• Moro-oka sees in the further course his process before any separation of nitrogen introduced into the process.
• CN-A 1105352 likewise discloses a homogeneous oxidative dehydrogenation of propane to propene with subsequent heterogeneously catalyzed oxidation of the dehydrogenation product mixture to acrolein and / or acrylic acid. Since CN-A 1105352 is a large-scale procedure, CN-A 1105352 follows the recommendation of EP-A 293 224, US-A 5198578 and US-A 5183936 as an exclusively pure molecular source of oxygen Oxygen used.
• WO 97/36849 relates to the combination of a catalytic oxidative dehydrogenation of propane to propene with a subsequent heterogeneously catalyzed oxidation of the dehydrogenation product mixture to acrolein and / or acrylic acid in an industrial scale.
• WO 97/36849 does not rule out the use of nitrogen-containing oxygen (e.g. air) as a source of the molecular oxygen required in the oxydehydrogenation, but advises against it.
• nitrogen-containing oxygen e.g. air
• WO 97/36849 only provides an outlet (purge) of circulating gas and no component separation from the circulating gas in the case of a continuous procedure with recycle gas to suppress undesired leveling of disadvantageous reaction gas mixture components.
• Nitrogen-depleted air possibly in combination with a circulating gas outlet, is very energy-intensive to limit the nitrogen content in the gas phase oxidation of the propene contained in the dehydrogenation product mixture.
• the object of the present invention was therefore a process for the preparation of acrolein and / or acrylic acid from propane, in which the propane is subjected to a partial homogeneous and / or heterogeneously catalyzed oxydehydrogenation with molecular oxygen to propene in a first reaction zone and then in the first reaction zone formed, propene-containing, product gas mixture without separation of a product gas mixture partly leads into at least one further reaction zone and in this at least one further reaction zone the propene contained in the product gas mixture of the first reaction zone, accompanied by all product gas mixture components of the first reaction zone, undergoes a gas-phase-catalytic oxidation to acrolein and / or acrylic acid, from the product gas mixture of the gas-phase catalytic oxidation it contains acrolein and / or separates acrylic acid and water and returns the unreacted propane contained in the residual gas stream to the first reaction zone as part of the residual gas stream, in which the restriction of the nitrogen content in the propene
• Separation of a product gas mixture component leads into at least one further reaction zone and in this at least one further reaction zone the propene contained in the product gas mixture of the first reaction zone, accompanied by all product gas mixture components of the first reaction zone, undergoes a gas phase catalytic oxidation to acrolein and / or acrylic acid, from the product gas mixture of the gas phase catalytic oxidation separates the acrolein and / or acrylic acid contained therein and water and returns the unreacted propane contained in the residual gas stream to the first reaction zone as part of the residual gas stream, which is characterized in that the reaction gas starting mixture fed to the first reaction zone is mixed with that in the first reaction zone required, other than circular oxygen, molecular oxygen as modified nitrogen-containing air, with the proviso that the nitrogen content of the modif ized air is smaller, and the oxygen content of the modified air is greater than the corresponding contents of air, and that at least part of the molecular nitrogen contained in the residual gas stream is separated from the residual gas stream before the residual gas stream is
• the first reaction zone is designed as a homogeneous oxide hydrogenation in the process according to the invention, this can in principle be e.g. as in US-A 3 798 283, CN-A 1 105 352, Applied Catalysis, 70 (2), 1991, pp. 175 to 187, Catalysis Today 13, 1992, pp. 673 to 678 and the older application DE -A 1 96 22 331 described, except 25 that according to the invention air is to be used as an oxygen source (apart from oxygen cycle gas).
• the temperature of the homogeneous oxydehydrogenation is expediently chosen to be in the range from 300 to 700 ° C., preferably in the range from 400 to 30 600 ° C., particularly preferably in the range from 400 to 500 ° C.
• the working pressure can be 0.5 to 100 bar or 1 to 50 bar. Often it will be 1 to 20 bar or 1 to 10 bar.
• the residence time of the reaction gas mixture under oxydehydrogenation conditions is usually 0.1 or 0.5 to 20 sec, preferably 0.1 or 0.5 to 5 sec.
• the implementation of the homogeneous oxydehydrogenation can, for example, take place in a separate reactor.
• the reactor can then be e.g. a tube furnace or a
• tube bundle reactor can be used, e.g. a counterflow tube furnace with flue gas as the heat transfer medium, or a tube bundle reactor with molten salt as the heat transfer medium.
• the propane to oxygen ratio in the reaction gas starting mixture to be used for homogeneous oxide hydrogenation can be 0.5: 1 to 40: 1. It is advantageous according to the invention if the molar ratio of propane to molecular oxygen in the reaction gas starting mixture is ⁇ 6: 1 or ⁇ 5: 1. As a rule, the aforementioned ratio will be> 1: 1 or> 2: 1.
• the nitrogen content in the reaction gas starting mixture is generally a consequence of the aforementioned requirement, since the reaction gas starting mixture normally does not comprise essentially any other gases besides propane and air.
• the reaction gas starting mixture can also comprise other, essentially inert, constituents such as H 2 O, CO 2 , CO, N 2 , noble gases and / or propene.
• Propene as a component of the reaction gas outlet - a mixture is given, for example, if the C 3 fraction from the refinery or the C 3 fraction from the light hydrocarbons of the oil field, which contains a proportion of propene of up to 10 wt . -% can have. It can also result from the recycle gas recycle required according to the invention. Components returned to the oxydehydrogenation are generally referred to in this document as circulating gas. As a result of recycle gas recycle, the nitrogen content in the reaction gas starting mixture can be up to 60 mol% or up to 50 mol%, for example.
• the recycle gas recycle according to the invention can also result in the reaction gas starting mixture having up to 5 mol% of gases such as CO, CO, ethene and H 2 O in a continuous procedure. It is favorable for a homogeneous oxidative dehydrogenation of propane to propene if the ratio of the surface of the reaction space to the volume of the reaction space is as small as possible. This is a consequence of the radical mechanism of homogeneous oxidative propane dehydrogenation, as reaction surface surfaces generally act as radical scavengers. Aluminum oxide, quartz glass, borosilicate, stainless steel and aluminum are particularly favorable surface materials.
• the first reaction stage is designed as a heterogeneously catalyzed oxydehydrogenation in the process according to the invention, this can in principle be carried out, for example, as in US Pat. Nos. 4,788,371, CN-A 1073893, Catalysis Letter 23 (1994) 103-106, W. Zhang, Gaodeng Xuexiao Huaxue, 14 (1993) 566, Z. Huang, Shiyou Huagong, 21 (1992) 592, WO 97/36849, DE-A 1 97 53 817, US-A 3 862 256, US-A 3 887 631, DE-A 1 95 30 454, US-A 4 341 664, J.
• Oxydehydrogenation catalysts which are particularly suitable according to the invention are the multimetal oxide compositions or catalysts A of DE-A 1 97 53 817, the multimetal oxide compositions or catalysts A mentioned as preferred in the abovementioned publication being very particularly favorable.
• multimetal oxide compositions of the general formula I come in particular as active compositions Ml a M ⁇ -b M 2 b O x (I),
• M 1 Co, Ni, Mg, Zn, Mn and / or Cu,
• active compositions I which are suitable according to the invention can be prepared in a simple manner by generating an as intimate, preferably finely divided, dry mixture as possible according to their stoichiometry from suitable sources of their elemental constituents and calcining them at temperatures of 450 to 1000.degree.
• the calcination can be carried out either under an inert gas or under an oxidative one
• Atmosphere such as air (mixture of inert gas and oxygen) and also under a reducing atmosphere (eg mixture of inert gas, oxygen and NH 3 , CO and / or H 2 ).
• the calcination time can range from a few minutes to a few hours and usually decreases with temperature.
• Suitable sources for the elementary constituents of the multimetal oxide active compositions I are those compounds which are already oxides and / or those compounds which can be converted into oxides by heating, at least in the presence of oxygen.
• such starting compounds are, above all, halides, nitrates, formates, oxalates, citrates, acetates, carbonates, amine complex salts, ammonium salts and / or hydroxides (compounds such as NHOH, (NH) 2 CO 3 , NH 4 NO 3 , NH 4 CH0 2 , CH 3 COOH, NH 4 CH 3 C0 and / or ammonium oxalate, which can decompose and / or decompose to form completely gaseous compounds at the latest during later calcination, can also be incorporated into the intimate dry mixture).
• the intimate mixing of the starting compounds for the production of multimetal oxide masses I can take place in dry or in wet form.
• the starting compounds are expediently used as finely divided powders and, after mixing and optionally compacting, are subjected to the calcination.
• the intimate mixing is preferably carried out in wet form.
• the starting compounds are usually in the form of an aqueous solution and / or suspension mixed together.
• particularly intimate dry mixtures are obtained if only sources of the elementary constituents present in dissolved form are used.
• Water is preferably used as the solvent.
• the aqueous composition obtained is then dried, the drying process preferably being carried out by spray drying the aqueous mixture at exit temperatures of 100 to 150 ° C.
• Particularly suitable starting compounds of Mo, V, W and Nb are their oxo compounds (molybdates, vanadates, tungstates and niobates) or the acids derived from them. This applies in particular to the corresponding ammonium compounds (ammonium molybdate, ammonium vanadate, ammonium tungstate).
• the multimetal oxide masses I can for the invention
• solid catalysts can be produced from the powder form of the active composition or its uncalcined precursor composition by compression to the desired catalyst geometry (e.g. by tableting, extrusion or extrusion), where appropriate auxiliaries such as e.g. Graphite or stearic acid as lubricants and / or molding aids and reinforcing agents such as microfibers made of glass, asbestos, silicon carbide or
• Suitable full catalyst geometries are e.g. Solid cylinder or hollow cylinder with an outer diameter and a length of 2 to 10 mm. In the case of the hollow cylinder, a wall thickness of 1 to 3 mm is appropriate.
• Suitable hollow cylinder geometries are e.g. 7 mm x 7 mm x 4 mm or 5 mm x 3 mm x 2 mm or 5 mm x 2 mm x 2 mm (each length x outer diameter x inner diameter).
• the full catalyst can also have a spherical geometry, the spherical diameter being 2 to 10 mm.
• the powdery active composition or its powdery, not yet calcined, precursor composition can also be shaped by application to preformed inert catalyst supports.
• the coating of the support bodies for the production of the coated catalysts is generally carried out in a suitable rotatable container, as is known, for example, from DE-A 2909671 or from EP-A 293859.
• the powder mass to be applied can expediently be moistened and dried again after application, for example by means of hot air.
• the layer thickness of the powder mass applied to the carrier body is expediently in the range from 50 to 500 ⁇ m, preferably in the range from 150 to 250 ⁇ m.
• porous or non-porous aluminum oxides silicon dioxide, thorium dioxide, zirconium dioxide,
• Silicon carbide or silicates such as magnesium or aluminum silicate can be used.
• the carrier bodies can have a regular or irregular shape, with regularly shaped carrier bodies with a clearly formed surface roughness, e.g. Balls 10 or hollow cylinders are preferred. It is suitable to use essentially non-porous, rough-surface, spherical supports made of steatite, the diameter of which is 1 to 8 mm, preferably 4 to 5 mm.
• reaction temperature of the heterogeneously catalyzed oxydehydrogenation of the propane will advantageously be in the range from 300 to 600 ° C., frequently in the range from 350 to 500 ° C.
• 0.5 to 10 bar or 1 to 10 bar or 1 to 5 bar is recommended as the working pressure.
• the heterogeneously catalyzed oxydehydrogenation of the propane takes place on a fixed catalyst bed.
• the latter is expediently heaped up in the tubes of a tube bundle reactor, such as those e.g. in EP-A 700 893 and in EP-A 700 714 and in these documents
• the average residence time of the reaction gas mixture in the catalyst bed is normally from 0.5 to 20 seconds.
• the reaction gas starting mixture can be 0.5: 1 to 40: 1. It is advantageous according to the invention if the molar ratio of propane to molecular oxygen in the reaction gas starting mixture is ⁇ 6: 1 or ⁇ 5: 1. As a rule, the aforementioned ratio will be> 1: 1 or 2: 1.
• reaction gas starting mixture 35 in the reaction gas starting mixture is generally a consequence of the aforementioned requirement, since the reaction gas starting mixture normally does not comprise essentially any other gases besides propane and air.
• the reaction gas starting mixture can also contain other, essentially inert, constituents such as H0,
• Propene as a component of the reaction gas starting mixture is given, for example, when the C 3 fraction coming from the refinery or the C 3 fraction from the light hydrocarbons of the oil field, which contains a proportion of propene, is used as the starting propane
• the nitrogen content in the Reaction gas starting mixture of the heterogeneously catalyzed propoxydehydrogenation in the context of the process according to the invention can be up to 60 mol% or up to 50 mol% when carried out continuously.
• the recycle gas recycle according to the invention can also lead to the reaction gas starting mixture having up to 5 mol% of gases such as CO, CO, ethane, methane, ethene and / or H 2 O in a continuous procedure.
• the modified air to be used as an oxygen source according to the invention can e.g. Contain> 0.05% by volume to> 78% by volume or> 0.1% by volume to> 75% by volume of N. That is, the nitrogen content of the modified air to be used as an oxygen source according to the invention can be> 1% by volume to ⁇ 70% by volume or> 5% by volume to ⁇ 60% by volume or> 10% by volume. -% to ⁇ 50 vol.% or> 15 to 15 vol.% to ⁇ 40 vol.% or> 20 vol.% to ⁇ 30 vol.%.
• the oxygen content of the modified air to be used as an oxygen source according to the invention can be> 20.95 vol.% To 99.95 vol.% Or> 25 vol.% To ⁇ 99.9 vol.% Or> 20 30 vol. -% to ⁇ 99 vol.% or> 40 vol.% to ⁇ 95 vol.% or> 50 vol.% to ⁇ 90 vol.% or> 60 vol.% to ⁇ 85 vol. % or> 70 vol .-% to ⁇ 80 vol .-%.
• the modified air to be used according to the invention can also contain the other constituents, such as noble gases, carbon dioxide, water vapor, etc., which are usually present in small amounts in air.
• the aforementioned components may also have been partially or completely removed as part of the modification.
• the modified air to be used according to the invention as an oxygen source can e.g. by fractional distillation of air, preferably under pressure.
• the methods of EP-A 848 981 and 35 of EP-A 848 639 can also be used.
• Both the 0 2 conversion of the homogeneous and the catalytic oxidative propane dehydrogenation can be> 50 mol% or> 40 70 mol% within the scope of the process according to the invention (with a single pass). That is, the aforementioned 0 conversion can be> 75 mol% or> 80 mol% or> 85 mol% or> 90 mol% or> 95 mol% or> 97 mol% or > 99 mol%.
• both the 0 conversion of the homogeneous and the 45 catalytic oxidative propane dehydrogenation in the process according to the invention will be> 70 mol%. It goes without saying that homogeneous and catalytic Propane oxydehydrogenation can also be used in combination.
• the propane and unreacted propane-oxyhydrogen product gas mixture (as a rule it contains C0 2 , CO, H 2 O, N 2 , 0, ethane, ethene, methane, acrolein, acrylic acid, ethylene oxide, butane, acetic acid, formaldehyde as further constituents , Formic acid, propylene oxide and butene) are passed directly into at least one further reaction zone in order to subject the propene contained therein to catalytic gas phase oxidation to acrolein and / or acrylic acid.
• the aforementioned gas phase catalytic propene oxidation can e.g. be carried out as is known in the art, e.g. is described in WO 97/36849 or CN-A 1105352.
• this gas phase catalytic propene oxidation can also be carried out as described in EP-A 117146, US-A 5 198578 or US-A 5183936.
• it can also be carried out in analogy to DE-A 3313578, CA-A 1217502, US-A 3 161 670 or US-A 4532365.
• connections such as other lower hydrocarbons essentially function as an inert diluent gas.
• acrylic acid is the desired target product
• two gas-phase-catalytic oxidation zones will generally follow the oxide dehydration, although one-step gas-phase-catalytic oxidation of propene to acrylic acid is also known in the prior art.
• acrolein is the desired target product, usually only a gas-phase-catalytic oxidation zone will follow.
• the aforementioned catalytic gas phase oxidation zones can e.g. can be realized in separate reactors.
• the catalytic gas phase oxidation of the propene contained in the propane oxide hydrogenation product gas mixture to an amount of acrolein which is predominant over acrylic acid can, for example, as described in EP-A 731 082, DE-A 44 31 957, DE-A 29 09 597 or EP-A 575 897.
• the gas phase oxidation is advantageously carried out in a multi-contact tube fixed bed reactor.
• the volume (Nl) ratio is 1: (1.0 to 3.0): (5 to 25), preferably 1: (1.7 to 2.3 ): (10 to 15), worked.
• the propane oxyhydrogen product gas mixture containing the propene before it is introduced into the propene oxidation stage.
• This can be in the form of air, in the form of nitrogen-depleted air or in the form of pure oxygen.
• additional dilution gases known essentially as indifferent, can be added at this point.
• the reaction temperature is expediently chosen to be 300 ° C. to 450 ° C., preferably 320 ° C. to 390 ° C.
• the reaction pressure is usually 0.5 to 5 bar, preferably 1 to 3 bar.
• the total space load is often 1500 to 2500 Nl / l / h.
• Suitable catalysts for this oxidation stage are e.g. those of DE-A 29 09 592, especially those from Example 1 of this document.
• the multimetal oxide catalysts II or II 'of DE-A 1 97 53 817 can also be used. This applies in particular to the exemplary embodiments listed in these documents. Especially when they are designed as hollow cylinder full catalysts as described in EP-A 575 897.
• the multimetal oxide catalyst ACF-2 from Nippon Shokubai containing Bi, Mo and Fe can also be used in the propene oxidation stage.
• acrolein in the aforementioned propene oxidation stage, no pure acrolein is obtained, but rather a mixture from whose secondary components the acrolein can be separated in a manner known per se.
• the acrolein so separated can be used as an intermediate for the synthesis of various end products.
• it can also be used for gas phase catalytic oxidation for the production of acrylic acid.
• the reaction gases containing the acrolein in the propene oxidation zone are transferred to this further oxidation zone without removal of secondary components. If necessary, they undergo intermediate cooling beforehand.
• This further oxidation zone can also advantageously be implemented in a separate multi-contact tube fixed-bed reactor, as described, for example, in DE-A 44 31 949, DE-A 44 42 346, DE-A 1 97 36 105 or EP-A 731 082.
• the volume (Nl) ratio is 1: (1 to 3): (> 0 to 20): (3 to 30), preferably of 1: (1 to 3): (0.5 to 10): (7 to 18) worked.
• molecular oxygen to the acrolein-containing product gas mixture from the propene oxidation zone before it is introduced into the acrolein oxidation zone.
• This can be in the form of air, in the form of nitrogen-depleted air or in the form of pure oxygen.
• additional dilution gases known essentially as indifferent, can be added at this point as desired.
• the reaction temperature is expediently chosen to be from 200 ° C. to 300 ° C., preferably from 220 to 290 ° C.
• the reaction pressure is usually 0.5 to 5 bar, preferably 1 to 3 bar.
• the total space load is preferably 1000 to 2500 Nl / l / h.
• Suitable catalysts for this oxidation stage are e.g. those of the general formula I or I 'from DE-A 44 42 346.
• the multi-metal oxide catalysts of DE-A 1 97 36 105 in particular the exemplary embodiments mentioned in this document, can also be used.
• the multimetal oxide catalyst ACS-4 from Nippon Shokubai comprising Bi, Mo and Fe can also be used in the acrolein oxidation stage.
• the various reaction zones described above can also be implemented in a single reactor, as described, for example, in DE-A 19807079.
• the catalysts required for catalytic oxide dehydrogenation and the subsequent propene / acrolein oxidation can be implemented, for example, within one and the same reaction tube as two or three successive catalyst beds (three successive reaction zones).
• the oxide dehydrogenation catalyst bed can be replaced, for example, by an empty section in the reaction tube as the corresponding reaction zone in the aforementioned arrangement.
• the individual catalyst beds and the empty section can be operated at one and the same temperature or with a temperature-structured (multi-zone) reactor at different temperatures.
• the gas mixture leaving the acrolein oxidation zone naturally does not consist of pure acrylic acid, but of a gas mixture containing the latter, from which acrylic acid can be separated in a manner known per se.
• the various known variants of acrylic acid separation are e.g. summarized in DE-A 1 96 00 955.
• the acrolein could also be separated from the reaction gas mixture leaving the propene oxidation zone.
• a common feature of the separation process is that the desired product is separated from the reaction gas mixture of the acrolein oxidation stage either by absorption with a solvent (cf. also DE-A 43 08 087) or by absorption with water and / or by partial condensation (this the resulting absorbate or condensate is then worked up by distillation (optionally with the addition of an azeotropic entrainer) and / or crystallization, and essentially pure acrylic acid or pure acrolein is thus obtained).
• the dividing line is drawn in such a way that a residual gas stream that is essentially free of acrylic acid and / or acrolein and largely of H0 (generally the H0 volume fraction of the residual gas flow is> 10% by volume) is produced, the main components of which are N and unreacted propane.
• the residual gas stream can e.g. small amounts of
• Contain gases such as carbon oxides (CO, C0), noble gases, 0, H 2 0 and unreacted propene.
• the separation of at least part of the nitrogen contained therein, which is required according to the invention before the further use of the aforementioned residual gas flow as circulating gas, can e.g. be carried out in a simple manner by distillation (it is of course possible to carry out the nitrogen separation only in the case of a partial amount of the residual gas stream, for example 50 to 70%).
• fractional distillation preferably a fractional pressure distillation at low temperatures.
• the pressure to be applied can e.g. 10 to 100 bar.
• Packing columns, tray columns or packing columns can be used as rectification columns.
• Tray columns are suitable for those with dual flow trays, bubble trays or valve trays.
• the return ratio can be, for example, 1 to 10.
• Other possibilities for nitrogen separation are, for example, pressure swing absorption, pressure washing and pressure extraction.
• the amount of nitrogen to be separated according to the invention can be 5%, or 10%, or 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90% or 95 to 100%.
• the nitrogen from the residual gas stream on its own, but together with other components of the residual gas stream to be recycled which are not very desirable in the context of a continuous implementation of the process according to the invention.
• These components will primarily be the carbon oxides CO and C0 as well as unreacted oxygen and ethylene and methane.
• only a part of the aforementioned constituents can be separated off together with the nitrogen.
• the process according to the invention is preferably carried out in such a way that at the point in time at which the product gas mixture leaves the last reaction zone, at least 70%, preferably at least 80%, of the total molecular oxygen supplied to the different reaction zones has been converted.
• reaction gas starting mixture 98.7 mol / h of reaction gas starting mixture, compressed to a pressure of 2.5 bar and heated to a temperature of 430.degree.
• a 6.8 m long reaction tube made of V2A steel (2.5 mm wall thickness; 2.6 cm inside diameter) was charged with the aforementioned reaction gas starting mixture, which was cooled over its entire length to a temperature of 430 ° C. using a salt bath.
• the inlet pressure was 2.5 bar, the outlet pressure was 1.9 bar.
• reaction gas starting mixture composed below:
• the reaction gas starting mixture was brought to 200 ° C. and used to feed the subsequent acrolein oxidation tube.
• This reaction tube (V2A steel; length: 3.80 m, 2.0 mm wall thickness; 2.6 cm inner diameter) was initially in the outflow direction over a length of 50 cm with a bed of steatite balls (diameter: 4-5 mm) loaded.
• a bed of the multimetal oxide catalyst according to Example b, SI of DE-A 4442346 followed on a contact tube length of 2.70 m.
• the entire length of the reaction tube was kept at 270 ° C. with a salt bath and charged with the reaction gas starting mixture described above.
• the inlet pressure was 1.9 bar and the outlet pressure was 1.7 bar.
• the product mixture leaving the reaction tube in an amount of 106.0 mol / h had the following composition:
• the hot reaction gas leaving the acrolein oxidation stage was extracted from 57.4% by weight in a venturi scrubber (quench apparatus) by direct contact with quench liquid (140-150 ° C.) injected through slots in the narrowest cross-section of the venturi tube.
• quench liquid 140-150 ° C.
• Diphenyl ether, 20.7% by weight of diphenyl and 20% by weight of o-dimethyl phthalate cooled to a temperature of about 175 ° C.
• the drop-like liquid portion of the quench liquid was separated from the gas phase consisting of reaction gas and evaporated quench liquid in a downstream droplet separator (storage container with gas pipe led away at the top) and returned in a circuit I to the venturi scrubber.
• a partial stream of the recycled quench liquid was subjected to a solvent distillation, the quench liquid being distilled over and high-boiling secondary components which were burned up remaining.
• the distilled quench liquid was fed to the outlet of the absorption column described below.
• the gas phase which had a temperature of approximately 175 ° C., was fed into the lower part of a packed column (3 m high; double jacket made of glass; inner diameter 50 mm; three packed zones with lengths (from bottom to top) 90 cm, 90 cm and 50 cm ; the packing zones were thermostatted from bottom to top as follows: 90 ° C, 60 ° C, 20 ° C; the penultimate and the last packing zone were separated by a chimney tray; the packing units were stainless steel metal helices with a helix diameter of 5 mm and one Helix length of 5 mm; immediately above the middle one
• the absorbent was fed to the packing zone) and the countercurrent of 2400 g / h of the mixture, likewise composed of 57.4% by weight of diphenyl ether, 20.7% by weight of diphenyl and 20% by weight of o-dimethyl phthalate, with a temperature from 50 ° C abandoned absorbent suspended.
• the outlet of the absorption column which in addition to acrylic acid also has low-boiling by-products such as Contained acrolein and acetic acid was indirectly heated in a heat exchanger to 100 ° C and placed on the top of a desorption column, which was also designed as a packed column with a length of 2 m (double jacket made of glass; 50 mm inner diameter; packing: stainless steel helices with a spiral diameter of 5 mm and a helix length of 5 mm; a packing zone of length 1 m; thermostatted to 120 ° C).
• the components with a lower boiling point than acrylic acid such as acrolein and acetic acid, were largely removed from the acrylic acid / absorbent mixture by stripping with 9.1 mol / h propane (countercurrent; feed temperature 120 ° C.).
• the loaded propane (stripping gas) leaving the desorption column was recirculated and combined with the hot reaction gas of the acrolein oxidation stage before it entered the venturi quench.
• the non-absorbed gas mixture leaving the second packing zone upward in the absorption column was cooled further in the third packing zone in order to separate off the easily condensable part of the secondary components contained therein, for example water and acetic acid, by condensation.
• This condensate is called acid water.
• part of the acid water above the third packing zone of the absorption column was returned to the absorption column at a temperature of 20 ° C.
• the sour water was removed from the chimney floor below the uppermost packing zone.
• the reflux ratio was 200.
• the amount of acid water continuously taken off was 22.8 mol / h.
• acrylic acid In addition to 94.5% by weight of water, it also contained 2.8% by weight of acrylic acid. This can be recovered if necessary as described in DE-A 1 96 00 955.
• the gas stream ultimately leaving the absorption column formed the residual gas stream.
• the bottom liquid of the desorption column was fed on the 8th tray from below to a tray column containing 57 dual flow trays (inside diameter: 50 mm; length 3.8 m; top pressure: 100 mbar; bottom pressure: 280 mbar: bottom temperature: 195 ° C) a pressure loss resistor was attached to the 9th floor;) and rectified in the same.
• 5.3 mol of crude acrylic acid were taken off from the bottom of the 48th bottom from the bottom via a side draw. The purity of the crude acrylic acid removed was> 98% by weight.
• Phenothiazine was added to the reflux at the top of the rectification column as a polymerization inhibitor, in such amounts that the side draw contained 300 ppm of phenothiazine (DE-A 1 96 00 955 shows a schematic representation of the process for working up the reaction gas of the acrolein oxidation stage; in addition the processing method is also shown in DE-A 4308087).
• the residual gas stream leaving the absorption column had the following composition:
• the bottom liquid continuously withdrawn was 71.9 mol / h. It was converted into the vapor phase and, as described at the outset, recirculated to the catalytic propylene oxide hydrogenation.
• the yield of acrylic acid was 58.4 mol% and the selectivity of acrylic acid formation was 62.2 mol%.
• cycle gas can also be used for stripping instead of propane.
• propane can be e.g. feed directly to the oxydehydrogenation stage.
• reaction gas starting mixture 173.1 mol / h, compressed to a pressure of 1.8 bar and heated to a temperature of 430.degree.
• a 3.8 long reaction tube made of V2A steel 2.0 mm wall thickness; 2.6 cm inside diameter was charged with the aforementioned reaction gas starting mixture, which has been salt bath cooled to a temperature of 430 ° C along its entire length.
• a reaction tube (V2A steel; length 3.80 m; 2.0 mm wall thickness, 2.6 cm inside diameter) was initially charged in the outflow direction over a length of 50 cm with a bed of steatite balls (diameter: 4-5 mm) . On a contact tube length of 3.0 m, a bed of the
• the entire length of the reaction tube was kept at 350 ° C. with a salt bath and charged with 202.6 mol / h of the aforementioned reaction gas outlet mixture (which had a temperature of 200 ° C.).
• the outlet pressure was 2.0 bar.
• This reaction tube (V2A steel; length: 3.80 m, 2.0 mm
• the entire length of the reaction tube was kept at 270 ° C. with a salt bath and charged with the reaction gas starting mixture described above.
• the inlet pressure was 1.9 bar and the outlet pressure was 1.7 bar.
• the product mixture leaving the reaction tube in an amount of 203.1 mol / h had the following composition:
• the acrylic acid formed was removed from the hot reaction gas leaving the acrolein oxidation stage in a manner corresponding to that in A a). 17.4 mol / h of propane were used for stripping.
• the amount of acid water removed was 43.6 mol / h. It contained 94.2% by weight of water and 3.1% by weight of acrylic acid.
• the amount of crude acrylic acid removed in the rectification column via side draw was 10.2 mol / h.
• the residual gas stream leaving the absorption column had the following composition:
• cycle gas can also be used for stripping instead of propane.
• propane can be e.g. feed directly to the oxydehydrogenation stage.
• the yield of acrylic acid was 58.5 mol%.
• the selectivity of the acrylic acid formation was 62.4 mol% and the total oxygen conversion was 87.9 mol. -%.
• reaction gas starting mixture 98.3 mol / h of reaction gas starting mixture, compressed to a pressure of 1.8 bar and heated to a temperature of 430.degree.
• reaction starting mixture an empty reaction tube made of V2A steel
• the product mixture (107.0 mol / h) leaving the reaction tube had the following composition:
• a reaction tube (V2A steel; length 3.80 m; 2.0 mm wall thickness, 2.6 cm inner diameter) was initially in the outflow direction over a length of 50 cm with a bed of steatite balls (diameter: 4-5 mm ) loaded.
• the entire length of the reaction tube was kept at 350 ° C. with a salt bath and charged with 120.0 mol / h of the aforementioned reaction gas starting mixture (which had a temperature of 200 ° C.) and was compressed to a pressure of 1.8 bar.
• the outlet pressure was 1.6 bar.
• This reaction tube (V2A steel; length: 3.80 m, 2.0 mm wall thickness; 2.6 cm inner diameter) was initially in the outflow direction over a length of 50 cm with a bed of steatite balls (diameter: 4-5 mm) loaded.
• a bed of the multimetal oxide catalyst according to Example b, SI of DE-A 4442346 followed on a contact tube length of 2.70 m.
• the entire length of the reaction tube was kept at 270 ° C. with a salt bath and charged with the reaction gas starting mixture described above.
• the inlet pressure was 1.5 bar and the outlet pressure was 1.3 bar.
• the product mixture leaving the reaction tube in an amount of 120.3 mol / h had the following composition:
• the acrylic acid formed was removed from the hot reaction gas leaving the acrolein oxidation stage in a manner corresponding to that in Aa). 12.1 mol / h of propane were used for stripping.
• the amount of acid water removed was 25.8 mol / h. It contained 94.4% by weight of water and 2.9% by weight of acrylic acid.
• the amount of crude acrylic acid removed in the rectification column via side draw was 6.2 mol / h.
• the residual gas stream leaving the absorption column had the following composition:
• cycle gas can also be used for stripping instead of propane.
• propane can, for example, be fed directly to the oxide dehydrogenation stage.
• the yield of acrylic acid was 51.4 mol%.
• the selectivity of the acrylic acid formation was 52.9 mol% and the total oxygen conversion was 87.3 mol. -%.
• 2.0 mol / s 0 are required for the production of 1 mol / s acrylic acid by oxydehydrogenation of propane and subsequent gas phase oxidation of propene (under the conditions mentioned above).
• the starting material for the recovery of 2.0 mol / s 0 is air (78 vol.% N 2 , 21 vol.% 0 and 1 vol.% Residual gases), the composition of which for the sake of simplicity is 80 vol.% N and 20 vol .-% 0 2 should be assumed. Ideal behavior should also be assumed.
• the air is cooled from 1 bar to -194 ° C. while maintaining the pressure and, as a liquid in the boiling state, is poured into the middle part of a liquid at 1 bar operated adiabatic rectification column to over
• the minimum reflux ratio at the top of the column (v m i n ) is defined as the ratio of the proportion of the amount of N in gaseous form at the top of the rectification column per unit of time, which, in order to achieve the separation task after condensation, must at least be returned to the rectification column to the proportion which is withdrawn .
• m is calculated v i n to 0.4. That is, in order to be able to remove 8 mol / s pure N 2 at the top of the column, 3.2 mol / s N must be returned to the column.
• the liquid withdrawn at the bottom of the column is heated to 20 ° C. at 1 bar, mixed with 2 mol / s propane (20 ° C., 1 bar), heated to 500 ° C. while maintaining the pressure from 1 bar and oxidized (either catalytically and / or homogeneous) and then oxidized by gas phase catalysis.
• the reaction gas mixture consisting of 1 mol / s propene, 2 mol / s H0 and 1.0 mol / s acrylic acid is then cooled to 20 ° C.
• 10 mol / s air (a mixture of 2.0 mol / s 0 2 and 8.0 mol / s N) is assumed, which have a temperature of 20 ° C. and a Has a pressure of 1 bar. This is separated in a first rectification column.
• the rectificative separation takes place as in a), but in pure nitrogen (top product) and a mixture of 80% by volume 0 2 and 20% by volume N 2 (bottom product).
• the boiling temperature of a mixture of 80 vol.% 0 and 20 vol.% N is for one
• the mixture of 2.0 mol / s 0 and 0.5 mol / s N thus obtained is heated from 1 bar to 20 ° C. while maintaining the pressure and at 2.0 mol / s of propane, which is likewise at a pressure of 1 bar mixed.
• the mixture is heated to 500 ° C. while maintaining pressure and catalytically and / or homogeneously oxidehydrogenated under these conditions and then oxidized by gas-phase catalysis.
• the resulting reaction product mixture is cooled from 1 bar to 20 ° C. while maintaining the pressure, the water of reaction and the acrylic acid completely condensing out as a result of the high boiling temperature difference.
• the remaining, 20 ° C and 1 bar mixture of 1.0 mol / s propane and 0.5 mol / s N 2 is cooled while maintaining pressure (-185 ° C) so that it boils liquid in the middle part of a second 1 bar adiabatically operated rectification column can be conducted in order to be separated overhead into pure nitrogen and as bottom liquid into pure propane.

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• 1998
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