Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/32—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen
  • C07C5/327—Formation of non-aromatic carbon-to-carbon double bonds only
  • C07C5/333—Catalytic processes
  • C07C5/3335—Catalytic processes with metals
  • C07C5/3337—Catalytic processes with metals of the platinum group
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C11/00—Aliphatic unsaturated hydrocarbons
  • C07C11/12—Alkadienes
  • C07C11/16—Alkadienes with four carbon atoms
  • C07C11/167—1, 3-Butadiene
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/02—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by hydrogenation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/02—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by hydrogenation
  • C07C5/03—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by hydrogenation of non-aromatic carbon-to-carbon double bonds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/04—Purification; Separation; Use of additives by distillation
  • C07C7/05—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds
  • C07C7/08—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds by extractive distillation

Definitions

• the invention relates to a process for the preparation of butadiene from n-butane.
• Butadiene is an important basic chemical and is used for example for the production of synthetic rubbers (butadiene homopolymers, styrene-butadiene rubber or nitrile rubber) or for the production of thermoplastic terpolymers (acrylonitrile-butadiene-styrene copolymers). Butadiene is further converted to sulfolane, chloroprene and 1,4-hexamethylenediamine (over 1,4-dichlorobutene and adiponitrile). By dimerization of butadiene, vinylcyclohexene can also be produced, which can be dehydrogenated to styrene.
• Butadiene can be prepared by thermal cracking (steam cracking) of saturated hydrocarbons, usually starting from naphtha as the raw material. Steam cracking of naphtha produces a hydrocarbon mixture of methane, ethane, ethene, acetylene, propane, propene, propyne, allenes, butenes, butadiene, butynes, methylalls, C 5 and higher hydrocarbons.
• the object of the invention is to provide a process for the preparation of butadiene from n-butane, incurred in the smallest possible extent coupling products.
• the object is achieved by a process for the preparation of butadiene from n-butane with the steps
• Carbon oxides and optionally water vapor is obtained; C) feeding the product gas stream b of the non-oxidative catalytic dehydrogenation and an oxygen-containing gas into at least one second dehydrogenation zone and oxidative dehydrogenation of n-butane, 1-butene and 2-butene, wherein a product gas stream c containing n-butane, 2-butene, Butadiene, low-boiling minor components, carbon oxides and water vapor is obtained, which has a higher content of butadiene than the product gas stream b;
• the inventive method is characterized by a particularly effective use of raw materials.
• losses of the raw material n-butane are minimized by recycling unreacted n-butane into the dehydrogenation.
• the coupling of non-oxidative catalytic dehydrogenation and oxidative dehydrogenation achieves a high butadiene yield.
• a feed gas stream a containing n-butane is provided.
• n-butane-rich gas mixtures such as liquefied petroleum gas (LPG) are assumed to be the raw material.
• LPG contains essentially saturated C 2 -C 5 hydrocarbons. It also contains methane and traces of C 6 + hydrocarbons.
• the composition of LPG can vary widely.
• the LPG used contains at least 10% by weight of butane.
• the n-butane-containing dehydrogenation feed gas stream is usually crude butane.
• it will be crude butane, which fulfills the specifications listed below (analogous to DE 102 45 585, quoting in volume fractions): Content of n-butane> 90 vol .-%, usually> 93 vol .-%, usually> 95 vol .-%; Content of isobutane ⁇ 1% by volume, usually ⁇ 0.5% by volume, generally ⁇ 0.3% by volume; Content of 1-butene ⁇ 1% by volume, usually ⁇ 0.5% by volume, generally ⁇ 0.3% by volume; Content of cis-butene ⁇ 1 vol .-%, usually ⁇ 0.5 vol .-%, usually ⁇ 0.3 vol .-%; Content of trans-butene ⁇ 1% by volume, usually ⁇ 0.5% by volume, generally ⁇ 0.3% by volume; Content of isobutene ⁇ 1% by volume, usually ⁇ 0.5% by volume, generally ⁇ 0.3% by volume;
• the provision of the n-butane-containing dehydrogenation feed gas stream comprises the steps
• A2 Separation of propane and optionally methane, ethane and C 5 + - hydrocarbons (mainly pentanes, besides hexanes, heptanes, benzene, toluene) from the LPG stream, wherein a stream containing butanes (n-butane and isobutane) is obtained .
• A3 Separation of isobutane from the butane-containing stream, wherein the n-butane-containing feed gas stream is obtained, and optionally isomerization of the separated isobutane to a n-butane / isobutane mixture and recycling the n-butane / isobutane mixture in the isobutane -
• the separation of propane and optionally methane, ethane and C 5 + hydrocarbons takes place, for example, in one or more conventional rectification columns.
• a first column low boilers methane, ethane, propane
• a second column high boilers C 5 + hydrocarbons
• a stream containing butanes is obtained, from which isobutane is separated off, for example in a customary rectification column.
• the remaining stream containing n-butane is used as feed gas stream for the subsequent butane dehydrogenation.
• the separated isobutane stream is preferably subjected to isomerization.
• the isobutane-containing stream is fed into an isomerization reactor.
• the isomerization of isobutane to n-butane can be carried out as described in GB-A 2,018,815. An n-butane / isobutane mixture is obtained, which is fed into the n-butane / isobutane separation column.
• the separated isobutane stream can also be supplied to a further use, for example, be used for the production of methacrylic acid, polyisobutene or methyl tert-butyl ether.
• n-butane-containing feed gas stream is fed to a dehydrogenation zone and subjected to non-oxidative catalytic dehydrogenation.
• n-butane is partially dehydrogenated in a dehydrogenation reactor on a dehydrogenating catalyst partially to 1-butene and 2-butene, wherein butadiene is formed.
• hydrogen and small amounts of methane, ethane, ethene, propane and propene fall on.
• carbon oxides (CO, CO 2 ) water and nitrogen may also be present in the product gas mixture of the non-oxidative catalytic n-butane dehydrogenation.
• unreacted n-butane is present in the product gas mixture.
• the non-oxidative catalytic n-butane dehydrogenation can be carried out with or without oxygen-containing gas as a co-feed.
• the non-oxidative catalytic n-butane dehydrogenation can in principle be carried out in all reactor types and procedures known from the prior art.
• a comparatively comprehensive description of dehydrogenation processes suitable according to the invention also contains "Catalytica® ® Studies Division, Oxidative Dehydrogenation and Alternative Dehydrogenation Processes" (Study Number 4192 OD, 1993, 430 Ferguson Drive, Mountain View, California, 94043-5272, USA).
• a suitable reactor form is the fixed bed tube or tube bundle reactor. These include the catalyst (dehydrogenation catalyst and, when working with oxygen as a co-feed, optionally special oxidation catalyst) as a fixed bed in a reaction tube or in a bundle of reaction tubes.
• the reaction tubes are usually heated indirectly by burning a gas, for example a hydrocarbon such as methane, in the space surrounding the reaction tubes. It is advantageous to apply this indirect form of heating only to the first about 20 to 30% of the length of the fixed bed and to heat the remaining bed length by the released in the context of indirect heating radiant heat to the required reaction temperature.
• Typical reaction tube internal diameters are about 10 to 15 cm.
• a typical Dehydrierrohrbündelreaktor comprises about 300 to 1000 reaction tubes.
• the temperature inside the reaction tube usually ranges from 300 to 700 ° C, preferably from 400 to 700 ° C.
• the working pressure is usually between 0.5 and 8 bar, often between 1 and 2 bar when using a low water vapor dilution (analogous to the Linde process for propane dehydrogenation), but also between 3 and 8 bar when using a high steam dilution (analogous to so-called “steam active reforming process” (STAR process) for the dehydrogenation of propane or butane by Phillips Petroleum Co., see US 4,902,849, US 4,996,387 and US 5,389,342.)
• Typical catalyst loadings (GHSV) are from 500 to 2000 h -1 on used hydrocarbon.
• the catalyst geometry can be, for example, spherical or cylindrical (hollow or full).
• several (eg three) such tube bundle reactors can be operated in parallel in the first dehydrogenation zone.
• one or two of these reactors may optionally be in dehydrogenation operation, while in a second (third) reactor the catalyst feed is regenerated without having to suspend operation in the second dehydrogenation zone.
• Such a procedure is useful, for example, in the BASF Linde propane dehydrogenation process described in the literature.
• the dehydrogenation catalyst used in the STAR process is preferably promoters containing platinum on zinc (magnesium) spinel as a support (see, for example, US Pat. No. 5,073,662).
• the dehydrogenated propane is diluted with steam in the STAR process. Typical is a molar ratio of water vapor to propane in the range of 4 to 6.
• the reactor outlet pressure is often 3 to 8 bar and the reaction temperature is conveniently 480 to 620 0 C.
• Typical catalyst loading with propane are 200 to 4000 h "1 ( GHSV).
• the heterogeneously catalyzed, non-oxidative n-butane dehydrogenation can also be carried out in the moving bed in the process according to the invention.
• the catalyst moving bed can be housed in a radial flow reactor. In this, the catalyst moves slowly from top to bottom, while the reaction gas mixture flows radially. This procedure is used for example in the so-called UOP Oleflex dehydrogenation. Since the reactors are operated quasi adiabatically in this process, it is expedient to operate several reactors connected in series as a cascade (typically up to four). Within the cascade, a recycle stream containing n-butane may be supplied from the 2nd dehydrogenation zone. As a result, it is possible to avoid too great temperature differences of the reaction gas mixture at the reactor inlet and at the reactor outlet and nevertheless achieve good overall sales.
• the catalyst bed When the catalyst bed has left the moving bed reactor, it is fed to the regeneration and then reused.
• a dehydrogenation catalyst for example, a spherical dehydrogenation catalyst consisting essentially of platinum on a spherical alumina carrier can be used for this process.
• the hydrogen is added to dehydrogenating propane to avoid premature catalyst aging.
• the working pressure is typically 2 to 5 bar.
• the molar hydrogen to propane ratio is suitably 0.1 to 1.
• the reaction temperatures are preferably 550 to 650 0 C and the residence time of the catalyst in a reactor is about 2 to 10 h.
• the catalyst geometry may also be spherical, but also cylindrical (hollow or full) or otherwise geometrically designed.
• the non-oxidative catalytic n-butane dehydrogenation can also be carried out as described in Chem. Eng. Be. 1992 b, 47 (9-11) 2313, heterogeneously catalyzed in a fluidized bed.
• two fluidized beds are operated side by side, one of which is usually in the state of regeneration.
• the working pressure is typically 1 to 2 bar, the dehydrogenation temperature usually 550 to 600 0 C.
• the heat required for the dehydrogenation is thereby introduced into the reaction system by the dehydrogenation catalyst is preheated to the reaction temperature.
• an oxygen-containing co-feed By adding an oxygen-containing co-feed can be dispensed with the preheater, and the heat required directly in the reactor system by combustion of hydrogen and / or hydrocarbons in the presence of oxygen are generated.
• a hydrogen-containing co-feed may additionally be admixed.
• heterogeneously catalyzed n-butane dehydrogenation in a fluidized bed can also be carried out as described in Proceedings De Witt, Petrochem. Review, Houston, Texas, 1992. A, N1 described for propane.
• the heterogeneously catalyzed n-butane dehydrogenation can also be realized analogously to the process developed by ABB Lummus Crest (see Proceedings De Witt, Petrochem., Review, Houston, Texas, 1992, P1).
• the non-oxidative catalytic n-butane dehydrogenation can be carried out with or without oxygen-containing gas as a co-feed in a tray reactor.
• This contains one or more consecutive catalyst beds.
• the number of catalyst beds may be 1 to 20, advantageously 1 to 6, preferably 1 to 4 and in particular 1 to 3.
• the catalyst beds are preferably flowed through radially or axially from the reaction gas.
• such a tray reactor is operated with a fixed catalyst bed.
• the Fixed catalyst beds in a shaft furnace reactor arranged axially or in the annular gaps of concentrically arranged cylindrical gratings.
• a shaft furnace reactor corresponds to a horde.
• the implementation of the dehydrogenation in a single shaft furnace reactor corresponds to a preferred embodiment, wherein it is possible to work with an oxygen-containing co-feed.
• the dehydrogenation is carried out in a tray reactor with 3 catalyst beds.
• the reaction gas mixture in the tray reactor is subjected to intermediate heating on its way from one catalyst bed to the next catalyst bed, for example by passing over heated with hot gases heat exchanger surfaces or by passing through heated with hot fuel gases pipes.
• the non-oxidative catalytic n-butane dehydrogenation is carried out autothermally.
• oxygen is added to the reaction gas mixture of the n-butane dehydrogenation in at least one reaction zone and the hydrogen and / or hydrocarbon contained in the reaction gas mixture at least partially burned, whereby at least a portion of the required Dehydriertude in the at least one reaction zone is generated directly in the reaction gas mixture ,
• the amount of the oxygen-containing gas added to the reaction gas mixture is selected such that the amount of heat required for the dehydrogenation of the n-butane is produced by the combustion of hydrogen present in the reaction gas mixture and optionally of hydrocarbons present in the reaction gas mixture and / or of carbon present in the form of coke is produced.
• the total amount of oxygen fed, based on the total amount of butane is 0.001 to 0.5 mol / mol, preferably 0.005 to 0.2 mol / mol, particularly preferably 0.05 to 0.2 mol / mol.
• Oxygen can be used either as pure oxygen or as an oxygen-containing gas mixed with inert gases, for example in the form of air.
• Preferred oxygen-containing gas is air or oxygen-enriched air having an oxygen content of up to 50% by volume.
• the inert gases and the resulting combustion gases generally additionally dilute and thus promote the heterogeneously catalyzed dehydrogenation.
• the hydrogen burned to generate heat is the hydrogen formed in the catalytic n-butane dehydrogenation and, if appropriate, the hydrogen gas additionally added to the reaction gas mixture as hydrogen.
• the molar ratio H 2 IO 2 in the reaction gas mixture immediately after the supply of oxygen is 1 to 10, preferably 2 to 5 mol / mol. This applies to multi-stage reactors for each intermediate feed of oxygen-containing and possibly hydrogen-containing gas.
• the hydrogen combustion takes place catalytically.
• the dehydrogenation catalyst used generally also catalyzes the combustion of the hydrocarbons and of hydrogen with oxygen, so that in principle no special oxidation catalyst different from this one is required.
• the reaction is carried out in the presence of one or more oxidation catalysts which selectively catalyze the combustion of hydrogen to oxygen in the presence of hydrocarbons.
• the combustion of these hydrocarbons with oxygen to CO, CO 2 and water is therefore only to a minor extent.
• the dehydrogenation catalyst and the oxidation catalyst are present in different reaction zones.
• the oxidation catalyst may be present in only one, in several or in all reaction zones.
• the catalyst which selectively catalyzes the oxidation of hydrogen is disposed at the sites where higher oxygen partial pressures prevail than at other locations of the reactor, particularly near the oxygen-containing gas feed point.
• the feeding of oxygen-containing gas and / or hydrogen-containing gas can take place at one or more points of the reactor.
• an intermediate feed of oxygen-containing gas and of hydrogen-containing gas takes place before each tray of a tray reactor.
• the feed of oxygen-containing gas and optionally of hydrogen-containing gas takes place before each horde except the first Horde.
• behind each feed point is a layer of a specific oxidation catalyst, followed by a layer of the dehydrogenation catalyst.
• no special oxidation catalyst is present.
• the dehydrogenation temperature is generally 400 to 1100 0 C
• the pressure in the last catalyst bed of the tray reactor generally 0.2 to 5 bar, preferably 1 to 3 bar.
• the load (GHSV) is generally 500 up to 2000 h ⁇ 1 , in high-load mode also up to 100 000 h ⁇ 1 , preferably 4000 to 16 000 h "1 .
• a preferred catalyst which selectively catalyzes the combustion of hydrogen contains oxides and / or phosphates selected from the group consisting of the oxides and / or phosphates of germanium, tin, lead, arsenic, antimony or bismuth.
• Another preferred catalyst which catalyzes the combustion of hydrogen contains a noble metal of VIII. And / or I. Maury.
• the heterogeneously catalyzed partial dehydrogenation of n-butane requires comparatively high reaction temperatures.
• the achievable turnover is limited by the thermodynamic equilibrium.
• Typical reaction temperatures are from 300 to 800 ° C. or from 400 to 700 ° C.
• High temperatures and removal of the reaction product H 2 favor the equilibrium position in the sense of the target product.
• the conversion can be increased by lowering the partial pressure of the products.
• This can be achieved in a simple manner, for example by dehydration under reduced pressure and / or by admixing essentially inert diluent gases, such as, for example, water vapor, which is normally an inert gas for the dehydrogenation reaction.
• essentially inert diluent gases such as, for example, water vapor, which is normally an inert gas for the dehydrogenation reaction.
• a dilution with water vapor as a further advantage, as a rule, a reduced coking of the catalyst used, since the water vapor reacts with coke formed according to the principle of coal gasification.
• diluents for heterogeneously catalyzed butane dehydrogenation are, for example, CO, methane, ethane, CO 2 , nitrogen and noble gases such as He, Ne and Ar.
• the diluents mentioned are generally also suitable as diluents in the 2nd dehydrogenation zone.
• the molar ratio of water vapor to n-butane can be up to 30, more appropriate Way 0.1 to 2 and more favorably 0.5 to 1.
• the n-butane dehydrogenation can also be carried out (quasi) adiabatically.
• the reaction gas starting mixture is usually first heated to a temperature of 450 to 700 ° C (preferably from 550 to 65O 0 C), for example by direct firing of the reactor wall.
• the reaction gas mixture will then be cooled by about 30 ° C. to 200 ° C., depending on the conversion and dilution.
• a single shaft furnace reactor may be sufficient as a fixed bed reactor, which is flowed through by the reaction gas mixture axially and / or radially.
• this is a single closed reaction volume, for example a container whose inside diameter is 0.1 to 10 m, possibly also 0.5 to 5 m, and in which the fixed catalyst bed is placed on a carrier device (for example a grid). is applied.
• the catalyst-charged reaction volume which is substantially thermally insulated in adiabatic operation, is thereby flowed through axially by the hot, n-butane-containing reaction gas.
• the catalyst geometry can be both spherical and annular or strand-shaped. About introduced into the catalyst bed supply lines, the originating from the 2nd dehydrogenation n-butane recycle gas can be injected.
• the reactor may, for example, consist of two cylindrical grids located concentrically inside one another, and the catalyst bed may be arranged in its annular gap. In the adiabatic case, the jacket would, if necessary, again be thermally insulated.
• the aforementioned catalysts can be regenerated in a simple manner, for example, by dilute air at first at initial temperatures of from 300 to 600 ° C., often at 400 to 550 ° C., first in regeneration stages with nitrogen and / or water vapor the catalyst bed passes.
• the catalyst loading with regeneration gas can be, for example, 50 to 10,000 h -1 and the oxygen content of the regeneration gas 0.1 to 21% by volume in subsequent further regeneration stages, air can be used as regeneration gas under otherwise identical regeneration conditions
• the catalyst be regenerated with inert gas (for example N 2
• inert gas for example N 2
• pure hydrogen or hydrogen diluted with inert gas preferably water vapor
• the hydrogen content should be ⁇ 1% by volume).
• the heterogeneously catalyzed, non-oxidative n-butane dehydrogenation can be operated with comparatively low butane conversion ( ⁇ 15 mol%), in which case the high selectivity and catalyst lifetime are advantageous.
• the n-butane dehydrogenation should be operated at conversions> 15 mol%, more preferably> 30 mol%.
• the load of reaction gas may, for example, be 100 to 10,000 or 40,000 h -1 , for example 300 to 7000 h -1 or about 500 to 4000 h -1 .
• the fixed catalyst beds in a shaft furnace reactor are arranged axially or in the annular gaps of centrally arranged cylindrical gratings.
• reaction gas mixture undergoes intermediate heating on its way from one catalyst bed to the next catalyst bed, for example, by passing it over hot-surface heat exchanger surfaces (e.g., fins) or passing hot-gas-heated tubes in the tray reactor.
• hot-surface heat exchanger surfaces e.g., fins
• the tray reactor is otherwise operated adiabatically, it is sufficient for butane conversions ⁇ 30 mol%, especially when using the catalysts described in DE-A 199 37 107, in particular the exemplary embodiments, that is Reaction gas mixture preheated to a temperature of 450 to 550 ° C in the dehydrogenation reactor to lead and keep within the Horde reactor in this temperature range.
• the reaction gas mixture is expediently preheated to higher temperatures into the dehydrogenation reactor (these can be up to 700 ° C.) and kept within this elevated temperature range within the tray reactor.
• the oxygen feed is carried out so that the oxygen content of the reaction gas mixture, based on the amount of molecular hydrogen contained therein, 0.5 to 50, preferably 10 to 25 vol .-%.
• the resulting combustion gases generally additionally dilute and thus promote the heterogeneously catalyzed n-butane dehydrogenation.
• the isothermal nature of the heterogeneously catalyzed n-butane dehydrogenation can be further improved by placing in the rack reactor in the spaces between the
• Catalyst beds attaches closed internals. These internals contain suitable solids or liquids that are above a certain temperature evaporate or melt while consuming heat and condense where this temperature falls below, thereby releasing heat.
• gas mixture fed to the first dehydrogenation zone to that required for the heterogeneously catalyzed butane dehydrogenation in the first dehydrogenation zone
• an intermediate feed of oxygen-containing gas is optionally carried out before each horde of the tray reactor.
• the feed of oxygen-containing gas takes place before each horde except the first horde.
• Oxygen feed site a bed of specific, suitable for H 2 oxidation oxidation catalyst present, followed by a bed of
• Dehydrogenation catalyst If necessary, external molecular hydrogen (in pure form or diluted with inert gas) may additionally be added upstream of each horde. In a less preferred embodiment, the
• Catalyst beds also contain mixtures of dehydrogenation and H 2 oxidation catalysts.
• the dehydrogenation in the tray reactor is generally from 400 to 800 0 C, the pressure is generally 0.2 to 10 bar, preferably 0.5 to 4 bar and particularly preferably 1 to 3 bar.
• the total gas load (GHSV) is usually 500 to 10,000 h "1 , in high-load mode also up to 80000 h " 1 , regularly at 30,000 to 40,000 h "1 .
• dehydrogenation catalysts known in the art are suitable for the heterogeneously catalyzed n-butane dehydrogenation. These can be roughly divided into two groups. Namely, in those which are oxidic in nature (for example chromium oxide and / or alumina) and in those which contain at least one precious metal deposited on a usually oxidic support.
• the dehydrogenation catalysts used generally have a carrier and an active composition.
• the carrier is usually made of a heat-resistant oxide or mixed oxide.
• the dehydrogenation catalysts contain a metal oxide selected from the group consisting of zirconium dioxide, zinc oxide, alumina, silica, titania, magnesia, lanthana, ceria and mixtures thereof as a carrier.
• the mixtures may be physical mixtures or chemical mixed phases such as magnesium or zinc-aluminum oxide mixed oxides.
• Preferred supports are zirconia and / or silica, particularly preferred are mixtures of zirconia and silica.
• dehydrogenation catalysts comprising 0 to 99.9% by weight of zirconium dioxide, 0 to 60% by weight of alumina, silica and / or titanium dioxide and 0.1 to 10% by weight of at least one element of the first or second Main group (particularly preferably potassium and / or cesium), a third subgroup element, an element of the eighth subgroup of the Periodic Table of the Elements (particularly preferably platinum and / or palladium), lanthanum and / or tin, with the proviso that the sum % by weight gives 100% by weight.
• the dehydrogenation catalysts are in the form of catalyst strands (diameter typically 1 to 10 mm, preferably 1 to 5 to 5 mm, length typically 1 to 20 mm, preferably 3 to 10 mm), tablets (preferably of similar dimensions as the strands) and / or catalyst rings (outer diameter and length typically 2 to 30 mm, for example 2 to 10 mm, wall thickness expediently 1 to 10 mm, for example 1 to 5 mm or 1 to 3 mm) before.
• the dehydrogenation catalysts (for example those described in DE-A 199 37 107) catalyze both the dehydrogenation of n-butane and the combustion of molecular hydrogen.
• the active composition of the dehydrogenation catalysts generally contain one or more elements of VIII. Subgroup, preferably platinum and / or palladium, more preferably platinum. In addition, the dehydrogenation catalysts have one or more elements of the I. and / or II. Main group, preferably potassium and / or cesium. Furthermore, the dehydrogenation catalysts may contain one or more elements of the IM. Subgroup including the lanthanides and actinides, preferably lanthanum and / or cerium. Finally, the dehydrogenation catalysts may contain one or more elements of III. and / or IV. Main group, preferably one or more elements from the group consisting of boron, gallium, silicon, germanium, tin and lead, particularly preferably tin.
• the dehydrogenation catalyst contains at least one element of subgroup VIII, at least one element of main group I and / or II, at least one element of IM. and / or IV. main group and at least one element of IM.
• Subgroup including the lanthanides and actinides.
• all dehydrogenation catalysts can be used which are described in WO 99/46039, US Pat. No. 4,788,371, EP-A 705,136, WO 99/29420, US Pat. No. 5,220,091, US Pat. No. 5,430,220, US Pat. No. 5,877,369, EP 0 117 146, DE-A 199 37 106 DE-A 199 37 105 and DE-A 199 37 107 are disclosed.
• Particularly preferred catalysts for the above-described variants of the autothermal n-butane dehydrogenation are the catalysts according to Examples 1, 2, 3 and 4 of DE-A 199 37 107.
• Characteristic of the heterogeneously catalyzed, non-oxidative dehydrogenation of n-butane is that it is endothermic. That is, the heat energy required for the adjustment of the required reaction temperature and the heat energy required for the reaction must either be supplied to the starting gas mixture in advance and / or in the course of the heterogeneously catalyzed dehydrogenation. Optionally, the required heat of reaction is removed from the reaction gas mixture itself.
• n-butane-containing reaction gas mixture can be diluted with water vapor.
• Depositing carbon is partially or completely converted under these conditions according to the principle of coal gasification.
• Another way to remove deposited carbon compounds from the catalyst surface is to charge the dehydrogenation catalyst from time to time at elevated temperature with an oxygen-containing gas (conveniently in the absence of hydrocarbons) and thereby burn off the deposited carbon.
• an oxygen-containing gas inveniently in the absence of hydrocarbons
• a substantial suppression of the formation of carbon deposits on the catalyst is also possible by adding molecular hydrogen to the n-butane to be dehydrogenated before bringing it into contact with the dehydrogenation catalyst.
• the dehydrogenating n-butane may also be added to a mixture of water vapor and molecular hydrogen. Addition of molecular hydrogen also minimizes the formation of allenes (1,2-butadiene, propadiene), butynes, propyne, and acetylene as by-products.
• the non-oxidative n-butane dehydrogenation is preferably carried out in the presence of water vapor.
• the added water vapor serves as a heat carrier and supports the gasification of organic deposits on the catalysts, whereby the coking of the catalysts counteracted and the service life of the catalysts is increased.
• the organic deposits are converted into carbon monoxide, carbon dioxide and possibly water.
• the dehydrogenation catalyst can be regenerated in a manner known per se.
• steam can be added to the reaction gas mixture or, from time to time, an oxygen-containing gas can be passed over the catalyst bed at elevated temperature and the deposited carbon burned off. Dilution with water vapor shifts the equilibrium to the products of dehydration.
• the catalyst is reduced after regeneration with a hydrogen-containing gas.
• n-butane dehydrogenation a gas mixture is obtained which, in addition to butadiene 1-butene, 2-butene and unreacted n-butane, contains minor constituents. Common secondary constituents are hydrogen, water vapor, nitrogen, CO and CO 2 , methane, ethane, ethene, propane and propene.
• the composition of the gaseous mixture leaving the first dehydrogenation zone can vary widely depending on the mode of dehydrogenation.
• the product gas mixture has a comparatively high content of water vapor and carbon oxides.
• the product gas mixture of the non-oxidative dehydrogenation a comparatively high content of hydrogen.
• the product gas stream b of the non-oxidative autothermal n-butane dehydrogenation typically contains 0.1 to 15% by volume of butadiene, 1 to 20% by volume of 1-butene, 1 to 35% by volume of 2-butene (cis / trans-2-butene), 20 to 80% by volume of n-butane, 1 to 70% by volume of steam, 0 to 10% by volume of low-boiling hydrocarbons (methane, ethane, ethene, propane and propene), 0, 1 to 40% by volume of hydrogen, 0 to 70% by volume of nitrogen and 0 to 15% by volume of carbon oxides.
• the product gas stream b leaving the first dehydrogenation zone is preferably separated into two substreams, wherein only one of the two substreams is subjected to the further process parts C to F and the second substream can be returned to the first dehydrogenation zone.
• a corresponding procedure is described in DE-A 102 11 275.
• the non-oxidative catalytic dehydrogenation according to the invention is followed by an oxidative dehydrogenation (oxydehydrogenation) as process part C.
• oxidative dehydrogenation oxydehydrogenation
• 1-butene and 2-butene are dehydrogenated to 1,3-butadiene, with 1-butene generally reacting almost completely.
• a gas mixture which has a molar oxygen: n-butenes ratio of at least 0.5. Preference is given to working at an oxygen: n-butenes ratio of 0.55 to 50.
• the product gas mixture originating from the non-oxidative catalytic dehydrogenation is generally mixed with oxygen or an oxygen-containing gas, for example air. The resulting oxygen-containing gas mixture is then fed to the oxydehydrogenation.
• Suitable processes are described, for example, in WO-A 2004007408, DE 10361822, DE 10361823 and DE 10361824.
• a 10211275 processes for the preparation of acrolein or acrylic acid from propane or propene and suitable reactors and catalysts are described, as they can be used in an analogous manner for the production of butadiene.
• the feed gas mixture fed to the second dehydrogenation zone has the following composition, see also WO-A 04/07408, DE-A 102 45 585 and DE-A 102 46 119.
• the load (Nl / I'h) of the oxidation catalyst with reaction gas is frequently 1500 to 2500 h -1 or up to 4000 h -1 .
• the load with butenes may be 50 or 80 to 200 or 300 and more Nl / lh.
• the catalysts which are particularly suitable for the oxydehydrogenation are generally based on a Mo-Bi-O-containing multimetal oxide system, which as a rule also contains iron.
• the catalyst system contains further additional components from the 1st to 15th group of the Periodic Table, such as potassium, magnesium, zirconium, chromium, nickel, cobalt, cadmium, tin, lead, germanium, lanthanum, manganese, tungsten, phosphorus, Cerium, aluminum or silicon.
• Suitable catalysts for the oxydehydrogenation are disclosed in DE-A 44 31 957, the non-prepublished German patent application DE 102004025445 and DE-A 44 31 949. This applies in particular to those of the general formula I in the two abovementioned publications. Particularly advantageous catalysts for oxydehydrogenation are disclosed in DE-A 103 25 488, DE-A 103 25 487, DE-A 103 53 954, DE-A 103 44 149, DE-A 103 51 269, DE-A 103 50 812 DE-A 103 50 822.
• Suitable catalysts and their preparation are described, for example, in US Pat. No. 4,423,281 (M ⁇ i 2 BiNi 8 Pb 0 , 5 Cr 3 Ko, 2 O x and M ⁇ i 2 Bi b Ni 7 Al 3 Cro, 5 Ko, 5 O x ), US Pat. No. 4,336,409 (MOi 2 BiNi 6 Cd 2 Cr 3 Po 15 O x ), DE-A 26 00 128 (M ⁇ i 2 BiNio, 5 Cr 3 Po, 5 Mg7, 5 Ko, iO ⁇ + SiO 2 ) and DE-A 24 40 329 ( MOi 2 BiCo 415 Ni 215 Cr 3 Po 15 K O jO x ).
• multimetal oxide active compounds of the general formula I of DE-A 199 55 176 are particularly suitable.
• Also suitable for this oxidation step are the Mo, Bi and Fe-containing multimetal oxide catalysts described in DE-A 100 46 957, DE-A 100 63 162, DE-C 33 38 380, DE-A 199 02 562, EP-A 15 565, DE-C 23 80 765, EP-A 807 465, EP-A 27 9374, DE-A 33 00 044, EP-A 575 897, US-A 4438217, DE-A 198 55 913, WO 98/24746 DE-A 197 46 210 (of the general formula II), JP-A 91/294239, EP-A 293 224 and EP-A 700 714 are disclosed.
• the hollow cylinders preferably have the following dimensions: 5.5 mm ⁇ 3 mm ⁇ 3.5 mm, or 5 mm ⁇ 2 mm ⁇ 2 mm, or 5 mm ⁇ 3 mm ⁇ 2 mm, or 6 mm ⁇ 3 mm ⁇ 3 mm , or 7 mm x 3 mm x 4 mm (each outer diameter x height x inner diameter).
• Other suitable catalyst geometries are strands (eg 7.7 mm in length and 7 mm in diameter, or 6.4 mm in length and 5.7 mm
• a variety of suitable for the oxydehydrogenation of n-butenes to butadiene Multimetalloxidgenmassen can be classified under the general formula IV, Mo 12 Bi a Fe b X 1 c X 2 d X 3 ⁇ X 4 , On (IV) 1
• X 2 thallium, an alkali metal and / or an alkaline earth metal
• X 3 zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and / or tungsten,
• X 4 silicon, aluminum, titanium and / or zirconium
• active compounds of the general formula IV can be prepared in a simple manner by, starting from suitable sources of their elements, a very intimate, preferably finely divided, the elemental composition corresponding dry mixture and this calcined at temperatures of 350 to 650 0 C.
• the calcination can be carried out both under inert gas and under an oxidizing atmosphere such as air (or a mixture of inert gas and oxygen) or under reducing atmosphere (eg a mixture of inert gas, NH 3 , CO and / or H 2 ).
• the calcination time may be several minutes to a few hours and usually decreases with increasing temperature.
• Suitable sources of the elemental constituents of the multimetal oxide active compositions IV are oxides or compounds which can be converted into oxides by heating, at least in the presence of oxygen.
• suitable starting compounds are, in particular, halides, nitrates, formates, oxalates, citrates, acetates, carbonates, amine complexes, ammonium salts and / or hydroxides.
• the intimate mixing of the starting compounds for the preparation of multimetal oxide active materials IV can be carried out in a dry or in a wet state.
• the starting compounds are expediently used as finely divided powders and subjected to calcination after mixing and optionally compacting.
• the intimate mixing takes place in the wet state.
• the starting compounds are mixed together in the form of an aqueous solution and / or suspension.
• Particularly intimate dry mixtures are then obtained in the described mixing process, if only from dissolved in
• Solvent is preferably used water. Subsequently, the resulting aqueous mass is dried, the drying process preferably by
• the multimetal oxide of the general formula IV can be used in the oxidative dehydrogenation shaped both in powder form and to certain catalyst geometries, wherein the shaping before or after the final
• Calcination can be done. For example, from the powder form of the active composition or its uncalcined or partially calcined precursor composition
• Stearic acid as a lubricant and / or molding aids and reinforcing agents such
• Microfibers of glass, asbestos, silicon carbide or potassium titanate can be added.
• Suitable Vollkatalysatorgeometrien are eg solid cylinder or hollow cylinder with an outer diameter and a length of 2 to 10 mm.
• a wall thickness of 1 to 3 mm is appropriate.
• the full catalyst may also have spherical geometry, wherein the ball diameter may be 2 to 10 mm.
• a particularly favorable hollow cylinder geometry has the dimensions 5 mm ⁇ 3 mm ⁇ 2 mm (outer diameter ⁇ length ⁇ inner diameter), in particular in the case of solid catalysts.
• the shaping of the pulverulent active composition or its pulverulent, not yet or only partially calcined precursor composition can also be effected by application to preformed, inert catalyst supports.
• the coating of the carrier bodies for the preparation of coated catalysts is usually carried out in a suitable rotatable container, e.g. in DE-A 29 09 671, EP-A 293 859 or EP-A 714 700.
• the powder to be applied is moistened to coat the carrier body and after application, e.g. by means of hot air, dried again.
• the layer thickness of the powder mass applied to the carrier body is suitably in the range from 10 to 1000 .mu.m, preferably from
• carrier materials it is possible to use customary porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates, such as magnesium silicate or aluminum silicate. They are essentially inert.
• the carrier bodies may be regularly or irregularly shaped, with regularly shaped carrier bodies having a marked surface roughness, e.g. Spheres or hollow cylinders are preferred. Suitable is the use of substantially non-porous, surface-rough, spherical steatite supports whose diameter is 1 to 10 mm or 1 to 8 mm, preferably 4 to 5 mm.
• the wall thickness is usually from 1 to 4 mm.
• Preferably used annular carrier bodies have a length of 2 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm.
• Particularly suitable according to the invention are rings of the geometry 7 mm ⁇ 3 mm ⁇ 4 mm (outer diameter ⁇ length ⁇ inner diameter) as the carrier body.
• the fineness of the catalytically active oxide materials to be applied to the surface of the support body is adapted to the desired shell thickness, see also EP-A 714 700.
• multimetal oxide active compositions to be used for the oxydehydrogenation of n-butenes to butadiene are compounds of the general formula V
• Y 1 only bismuth or bismuth and at least one of the elements tellurium, antimony, tin and copper,
• Y 2 molybdenum or molybdenum and tungsten
• Y 3 an alkali metal, thallium and / or samarium
• Y 4 an alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and / or mercury
• Y 5 iron or iron and at least one of the elements chromium and cerium
• Y 6 phosphorus, arsenic, boron and / or antimony
• Y 7 a rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and / or uranium,
• a ' 0.01 to 8
• b' 0.1 to 30,
• c ' 0 to 4
• d' 0 to 20
• e ' 0.001 to 20
• f 0 to 6
• x', y ' numbers determined by the valency and frequency of the non-oxygen elements in V
• p, q numbers whose ratio p / q is 0.1 to 10 .
• Particularly advantageous multimetal oxide compositions V are those in which Y 1 is only bismuth.
• Y 1 is only bismuth.
• those of the formula VI those of the formula VI,
• Z 2 molybdenum or molybdenum and tungsten
• Z 4 thallium, an alkali metal and / or an alkaline earth metal
• Z 5 phosphorus, arsenic, boron, antimony, tin, cerium and / or lead,
• Z 6 silicon, aluminum, titanium and / or zirconium
• Z 7 copper, silver and / or gold
• inert support materials come i.a. also as inert materials for dilution and / or delimitation of the corresponding fixed catalyst beds from each other, or as a protective and / or the gas mixture auftropicende infill into consideration.
• the oxydehydrogenation is carried out generally at a temperature of 220 to 490 ° C and preferably from 250 to 450 0 C. It chooses a reactor inlet pressure that is sufficient, existing in the system and the subsequent workup
• This reactor inlet pressure is usually 0.005 to 1 MPa gauge, preferably 0.01 to 0.5 MPa gauge. Naturally, the gas pressure applied in the inlet area of the reactor largely drops over the entire catalyst bed.
• the oxydehydrogenation of n-butenes to butadiene may be carried out with the described catalysts e.g. be carried out in a one-zone Dahlutton fixed bed reactor, as described in DE-A 44 31 957.
• oxygen is generally used. If N 2 is chosen as the inert diluent gas, the use of air or oxygen-enriched air as the source of oxygen proves to be particularly advantageous.
• n-butene oxygen: inert gases (including water vapor) volume (NI) ratio of 1: (1, 0 to 3.0) :( 5 to 25), preferably 1: (1, 7 to 2 , 3) :( 10 to 15) worked.
• the reaction pressure is usually in the range of 1 to 3 bar and the total space load is preferably 1500 to 4000 or 6000 Nl / I'h or more.
• the load, based on n-butenes, is typically 90 to 200 Nl / l-h or to 300 Nl / l-h or more.
• the single-zone multiple contact tube fixed bed reactor is supplied with the feed gas mixture from above.
• a heat exchange agent is expediently a molten salt, preferably consisting of 60 wt .-% potassium nitrate (KNO 3 ) and 40 wt .-% sodium nitrite (NaNO 2 ), or from 53 wt .-% potassium nitrate (KNO 3 ), 40 wt .-% Sodium nitrite (NaNO 2 ) and 7 wt .-% sodium nitrate (NaNO 3 ) used.
• KNO 3 potassium nitrate
• NaNO 2 sodium nitrite
• NaNO 3 7 wt .-% sodium nitrate
• section C is undiluted.
• the aforementioned feed variant is particularly useful if as catalysts such as in Example 3 of WO-A 04/07408, Example 1 of DE-A 100 46 957 or according to Example 3 of DE-A 100 46 957 and as an inert material rings of steatite with Geometry 7mm x 7mm x 4mm (outside diameter x height x inside diameter) can be used.
• catalysts such as in Example 3 of WO-A 04/07408, Example 1 of DE-A 100 46 957 or according to Example 3 of DE-A 100 46 957 and as an inert material rings of steatite with Geometry 7mm x 7mm x 4mm (outside diameter x height x inside diameter) can be used.
• Geometry 7mm x 7mm x 4mm outer diameter x height x inside diameter
• the oxydehydrogenation of n-butenes to butadiene can also be carried out with the catalysts described in a two-zone multiple contact tube fixed bed reactor, as described in DE-A 199 10 506.
• the conversion of the n-butenes obtained with a single pass is normally at values> 85 mol%, or> 90 mol% or> 95 mol%.
• the salt bath temperature of multiple contact tube reactors for the oxydehydrogenation of n-butenes to butadiene is generally from 300 to 400 0 C.
• the heat exchange means normally (preferably molten salts) in such amounts through the multiple contact tube fixed-bed reactors out that the difference between its input and their starting temperature is usually ⁇ 5 ° C.
• the oxydehydrogenation can be carried out by first passing a reaction gas mixture over the catalyst bed containing no oxygen.
• the oxygen required for the oxydehydrogenation is provided as lattice oxygen.
• an oxygen-containing gas e.g., air, oxygen-enriched air, or deoxygenated air
• the catalyst bed is regenerated to subsequently be available again for an oxygen-free reaction gas mixture.
• plate heat exchange reactors with salt and / or boiling cooling as e.g. in DE-A 19 929 487 and DE-A 19 952 964, or fluidized-bed reactors are used.
• first and the second dehydrogenation zone in the process according to the invention can also be configured as described in WO-A 04007408, DE-A 19 837 517, US Pat.
• the external temperature control in the two dehydrogenation zones if appropriate in multi-zone reactor systems, is customarily adapted to the specific reaction gas mixture composition and catalyst feed in a manner known per se.
• An excess of molecular oxygen usually has an advantageous effect on the kinetics of the dehydrogenation. Since, in contrast to the ratios in the first dehydrogenation zone (non-oxidative dehydrogenation), the hydrogenation of the n-butenes to butadiene undergoes kinetic control, in the second dehydrogenation zone (oxydehydrogenation) also worked with a molar excess of n-butenes against molecular oxygen become. In this case, the excess n-butenes also play the role of a diluent gas.
• both pure molecular oxygen and inert gas such as CO 2 , CO, noble gases, N 2 and / or saturated hydrocarbons become more dilute molecular Oxygen into consideration.
• air will be used as the source of oxygen at least to meet a partial demand for molecular oxygen.
• a pressure regulating device in the simplest case a throttle device, for example a throttle valve or also a swirl regulator
• a suitable point e.g. also partially permeable apertured apertures whose holes can be successively partially or completely closed.
• Typical pressure increases (which can be carried out continuously in accordance with the deactivation in progress, but also discontinuously) can amount to up to 3000 mbar and more over the course of the operating time.
• the product gas stream c leaving the oxidative dehydrogenation contains, in addition to butadiene and unreacted n-butane, 2-butene and water vapor. As minor constituents it generally contains carbon monoxide, carbon dioxide, oxygen, nitrogen, methane, ethane, ethene, propane and propene, optionally hydrogen and oxygen-containing hydrocarbons, so-called oxygenates. In general, it contains only small amounts of 1-butene.
• Oxygenates include, for example, lower aldehydes, lower alkane carboxylic acids (e.g., acetic, formic, and propionic acids), as well as maleic anhydride, benzaldehyde, aromatic carboxylic acids, and aromatic carboxylic acid anhydrides (e.g., phthalic anhydride and benzoic acid).
• lower aldehydes lower alkane carboxylic acids (e.g., acetic, formic, and propionic acids)
• maleic anhydride e.g., benzaldehyde
• aromatic carboxylic acids e.g., phthalic anhydride and benzoic acid
• the product gas stream leaving the oxidative dehydrogenation comprises c 1 to 50% by volume of butadiene, 20 to 80% by volume of n-butane, 0.5 to 40% by volume of 2-butene, 0 to 20% by volume.
• % Nitrogen 0 to 10% by volume of carbon oxides and 0 to 10% by volume of oxygenates.
• Oxygenates may be, for example, furan, acetic acid, maleic anhydride, formic acid or butyraldehyde.
• the low-boiling minor constituents other than the C 4 hydrocarbons are at least partly, but preferably in the range from Essentially completely separated from the product gas stream of n-butane dehydrogenation, wherein a C 4 -Shgasstrom d is obtained.
• first water is separated from the product gas stream c in the process part D.
• the separation of water can be carried out, for example, by condensation by cooling and / or compressing the product gas stream c and can be carried out in one or more cooling and / or compression stages.
• the separation of the low-boiling secondary constituents from the product gas stream can be carried out by customary separation processes such as distillation, rectification, membrane process, absorption or adsorption.
• the product gas mixture optionally after cooling, for example, in an indirect heat exchanger, are passed through a usually formed as a tube membrane, which is permeable only for molecular hydrogen.
• the thus separated molecular hydrogen can, if necessary, at least partially used in the dehydrogenation or else be supplied to another utilization, for example, be used for generating electrical energy in fuel cells.
• the carbon dioxide contained in the product gas stream c can be separated by CO 2 gas scrubbing.
• the carbon dioxide gas scrubber may be preceded by a separate combustion stage in which carbon monoxide is selectively oxidized to carbon dioxide.
• the gas stream c is compressed in at least one first compression stage and then cooled, wherein at least one condensate stream comprising water condenses out and a gas stream c 'containing n-butane, n-butenes, butadiene, hydrogen, water vapor, optionally carbon oxides and optionally inert gases remains.
• the compression can be done in one or more stages. Overall, is compressed from a pressure in the range of 1.0 to 4.0 bar to a pressure in the range of 3.5 to 20 bar. After each compression stage is followed by a cooling step, in which the gas stream is cooled to a temperature in the range of 15 to 60 0 C.
• the aqueous condensate stream may thus also comprise a plurality of streams in the case of multistage compression.
• the gas stream c ' generally consists essentially of C 4 hydrocarbons (essentially n-butane, 2-butene and butadiene), hydrogen, carbon dioxide and water vapor.
• the stream c ' may still contain low boilers, inert gases (nitrogen) and carbon oxides as further secondary components.
• the aqueous condensate stream is generally at least 80 wt .-%, preferably at least 90 wt .-% of water and also contains minor amounts of low boilers, C 4 hydrocarbons, oxygenates and carbon dioxide.
• Suitable compressors are, for example, turbo, rotary piston and reciprocating compressors. The compressors can be driven, for example, with an electric motor, an expander or a gas or steam turbine. Typical compression ratios (outlet pressure: inlet pressure) per compressor stage are between 1, 5 and 3.0, depending on the design.
• the cooling of the compressed gas takes place with heat exchangers, which can be designed, for example, as a tube bundle, spiral or plate heat exchanger.
• heat exchangers which can be designed, for example, as a tube bundle, spiral or plate heat exchanger.
• coolant cooling water or heat transfer oils are used in the heat exchangers.
• air cooling is preferably used using blowers.
• the non-condensable or low-boiling gas components such as hydrogen, oxygen, carbon oxides, the low-boiling hydrocarbons (methane, ethane, ethene, propane, propene) and optionally nitrogen in an absorption / desorption cycle by means of a separated high-boiling absorbent, wherein a C 4 product gas stream d is obtained, which consists essentially of the C 4 - hydrocarbons.
• the C 4 product gas stream d is at least 80% by volume, preferably at least 90% by volume, particularly preferably at least 95% by volume, of the C 4 hydrocarbons.
• the stream d consists of n-butane, 2-butene and butadiene.
• the product gas stream c is brought into contact with an inert absorbent after prior removal of water, and the C 4 hydrocarbons are absorbed in the inert absorbent, whereby absorption medium laden with C 4 hydrocarbons and an offgas containing the remaining gas constituents are obtained.
• the C 4 hydrocarbons are released from the absorbent again.
• Inert absorbent used in the absorption stage are generally high-boiling nonpolar solvents in which the C 4 - hydrocarbon mixture to be separated has a significantly higher solubility than the other gas constituents.
• the absorption can be carried out by simply passing the product gas stream c through the absorbent. But it can also be done in columns or in rotational absorbers. It can be used in cocurrent, countercurrent or cross flow.
• Suitable absorption columns are, for example, tray columns with bell, centrifugal and / or sieve trays, columns with structured packings, for example sheet metal packings with a specific surface area of 100 to 1000 m 2 / m 3 as Mellapak ® 250 Y, and packed columns.
• trickle and spray towers, graphite block absorbers, surface absorbers such as thick-layer and thin-layer absorbers as well as rotary columns, rags, cross-flow scrubbers and rotary scrubbers are also suitable.
• Suitable absorbents are comparatively non-polar organic solvents, for example C 5 -C 8 -alkenoalkenes, or aromatic hydrocarbons, such as the paraffin distillation, naphtha or bulky group ethers, or mixtures of these solvents, these being a polar solvent such as 1, 2 Dimethyl phthalate may be added.
• Suitable absorbents are furthermore esters of benzoic acid and phthalic acid with straight-chain C 1 -C 8 -alkanols, such as n-butyl benzoate,
• Methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, and so-called heat transfer oils such as biphenyl and diphenyl ether, their chlorinated derivatives and triaryl alkenes.
• a suitable absorbent is a mixture of biphenyl and diphenyl ether, preferably in the azeotropic composition, for example, the commercially available Diphyl ®. Frequently, this solvent mixture contains dimethyl phthalate in an amount of 0.1 to 25 wt .-%.
• Suitable absorbents are also pentanes, hexanes, heptanes, octanes, nonanes, decanes, undecanes, dodecanes, tridecanes, tetradecanes, pentadecanes, hexadecanes, heptadecanes and octadecanes or fractions obtained from refinery streams which contain as main components said linear alkanes.
• Suitable solvents are also butyrolactone, nitriles such as acetonitrile, propionitrile, methoxypropionitrile, ketones such as acetone, furfural, N-alkyl-substituted lower aliphatic acid amides such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-formylmorpholine, N-alkyl-substituted cyclic acid amides (lactams) such as N-alkyl.
• Alkylpyrrolidones especially N-methylpyrrolidone (NMP).
• the loaded absorbent is heated and / or expanded to a lower pressure.
• the desorption may also be by stripping or in a combination of relaxation, heating and stripping in one or more process steps.
• the absorbent regenerated in the desorption stage is returned to the absorption stage.
• the desorption step is carried out by relaxation and / or heating of the loaded desorbent.
• the desorption is carried out in two stages, wherein in the first stage the desorption takes place exclusively by expansion and heating.
• the absorbent which, after this first stage, still has a considerable residual charge of C 4 -hydrocarbons, is subjected to a second desorption stage, in which the remaining C 4 -hydrocarbons are removed by combining expansion and heating and stripping.
• Suitable stripping gases are water vapor, air, nitrogen, carbon oxides or flue gases. Is stripped with steam, so the desorption is followed by a phase separation, in which an aqueous phase and the organic absorbent phase are obtained.
• the aqueous phase can be re-evaporated and reused as stripping medium.
• the regenerated absorbent from the second desorption stage is returned to the absorption stage.
• the exhaust gas of the second desorption stage can be recycled to the first or second dehydrogenation stage.
• the separation D is generally not completely complete, so that in the C 4 -PrO- duktgasstrom - depending on the nature of the separation - still small amounts or even traces of other gas components, in particular the low-boiling hydrocarbons, may be present.
• volume flow reduction also caused by the separation D relieves the subsequent process steps.
• the exhaust gas containing the remaining gas constituents, which also contains oxygen, can be used, for example, for the regeneration of the catalyst bed in the first or second dehydrogenation zone.
• the C 4 -PrO duktgasstrom d consisting essentially of n-butane, 2-butene and butadiene generally contains 20 to 80% by volume of butadiene, 20 to 80% by volume of n-butane, 0 to 50% by volume. % 2-butene and 0 to 20% by volume of 1-butene.
• the product gas stream c or d may still contain small amounts of oxygen. If the product gas stream c or d contains more than just slight traces of oxygen, a process stage for removing residual oxygen from the product gas stream c or d is generally carried out.
• the residual oxygen may have a disturbing effect insofar as it is used in downstream process steps as an initiator for Polymerization reactions can act. This danger is particularly present in the distillative removal of butadiene (step E)) and can lead to deposits of polymers (formation of so-called "popcorn") in the extractive distillation column Thereby, the oxygen removal is preferably carried out immediately after the oxidative dehydrogenation.
• a catalytic combustion stage is carried out in which oxygen is reacted with the hydrogen contained in the gas stream c, c 'or d in the presence of a catalyst the absorption / desorption step, that is carried out only in the gas stream d, hydrogen must be added to the gas stream d.
• Platinum and tin are advantageously used in a weight ratio of 1: 4 to 1: 0.2, preferably in a ratio of 1: 2 to 1: 0.5, in particular in a ratio of approximately 1: 1.
• the catalyst contains 0.05 to 0.09 wt .-% platinum and 0.05 to 0.09 wt .-% tin based on the total weight of the catalyst.
• the alumina catalyst contains only platinum and tin.
• the catalyst support of ⁇ -aluminum oxide advantageously has a BET surface area of 0.5 to 15 m 2 / g, preferably 2 to 14 m 2 / g, in particular 7 to 11 m 2 / g.
• the carrier used is preferably a shaped body. Preferred geometries are, for example, tablets, ring tablets, spheres, cylinders, star strands or gear-shaped strands with diameters of 1 to 10 mm, preferably 2 to 6 mm. Particularly preferred are balls or cylinders, in particular cylinders.
• Altematiwerfahren for removing residual oxygen from the product gas stream c, c 'or d include contacting the product gas stream with a mixture of metal oxides, which contains copper in the oxidation state 0 in a reduced form.
• a mixture of metal oxides which contains copper in the oxidation state 0 in a reduced form.
• such a mixture generally still contains aluminum oxides and zinc oxides, wherein the copper content is usually up to 10 wt .-%.
• other methods of removing traces of oxygen can be used. Examples are the separation by means of molecular sieves using membranes, or by contacting with a NaNO 2 solution.
• the C 4 product gas stream d is separated by means of extractive distillation into a stream e 1 consisting essentially of n-butane and 2-butene and a product stream e 2 consisting essentially of butadiene.
• the stream e1 consisting essentially of n-butane and 2-butene is at least partially recycled to the first dehydrogenation stage.
• Extractive distillation may be carried out as described in Petroleum and Coal Natural Gas Petrochemistry, Vol. 34 (8), pp. 343-346 or Ullmanns Enzyklopadie der Technischen Chemie, Vol. 9, 4th edition 1975, pages 1-18.
• the C 4 product gas stream d is brought into contact with an extraction agent, preferably an N-methylpyrrolidone (NMP) / water mixture, in an extraction zone.
• NMP N-methylpyrrolidone
• the extraction zone is generally carried out in the form of a wash column which contains trays, fillers or packings as internals. This generally has 30 to 70 theoretical plates, so that a sufficiently good release effect is achieved.
• the wash column has a backwash zone in the column head. This backwash zone serves to recover the extractant contained in the gas phase by means of liquid hydrocarbon reflux, to which the top fraction is condensed beforehand. As a liquid hydrocarbon reflux and the process to be supplied fresh butane can be used. Typical temperatures at the top of the column are between 30 and 60 ° C.
• the mass ratio of extractant to C 4 product gas stream d in the feed of the extraction zone is generally from 10: 1 to 20: 1.
• Suitable extractants are butyrolactone, nitriles such as acetonitrile, propionitrile, methoxypropionitrile, ketones such as acetone, furfural, N-alkyl-substituted lower aliphatic acid amides such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-formylmorpholine, N-alkyl-substituted cyclic acid amides (lactams) such as N-alkylpyrrolidones , in particular N-methylpyrrolidone (NMP).
• NMP N-methylpyrrolidone
• alkyl-substituted lower aliphatic acid amides or N-alkyl substituted cyclic acid amides are used.
• Particularly advantageous are dimethylformamide, acetonitrile, furfural and in particular NMP.
• mixtures of these extractants with each other for.
• mixtures of these extractants with cosolvents and / or tert-butyl ether for.
• methyl tert-butyl ether ethyl tert-butyl ether, propyl tert-butyl ether, n- or iso-butyl tert-butyl ether
• NMP preferably in aqueous solution, preferably with 0 to 20 wt .-% water, more preferably with 7 to 10 wt .-% water, in particular with 8.3 wt .-% water.
• the extractive distillation column is a gaseous, consisting essentially of n-butane and 2-butene stream e1, which is generally withdrawn via the top of the column, and obtained as Soabzugsstrom a mixture of extractant and butadiene. From this mixture butadiene can be subsequently obtained as a pure product.
• the bottom withdrawing stream is the extractant, which still contains butadiene and optionally secondary components (impurities).
• the bottom draw stream is recycled, optionally after carrying out further purification steps, back into the extractive distillation.
• the stream e1 consisting essentially of n-butane and 2-butene contains from 50 to 100% by volume of n-butane, from 0 to 50% by volume of 2-butene and from 0 to 3% by volume of further constituents, such as isobutane , Isobutene, propane, propene and C 5 + hydrocarbons.
• the stream e1 is at least partially recycled to the first De hydrogenation.
• the extractive distillation, isolation of the pure butadiene and purification of the extractant can be carried out as follows: the side draw stream of the extractive distillation column of extractant and butadiene, which also contains impurities (acetylene, propyne, 1, 2-butadiene), is fed into a wash column, which is charged with fresh extractant. Crude butadiene, which contains, for example, 98% by weight of butadiene, is withdrawn from the column top of the wash column. The bottom draw stream is enriched with acetylene and is recycled to the extractive distillation.
• the crude butadiene may contain as impurities propyne and 1,2-butadiene.
• the crude butadiene is fed to a first purifying distillation column and a butadiene stream enriched with propyne is separated off at the top.
• the bottom draw stream which is essentially propyne-free, but still contains traces of 1, 2-butadiene, is fed to a second pure distillation column, in which a substantially 1, 2-butadiene-free pure butadiene stream having a purity of, for example, at least 99, 6 wt .-% as top draw stream or side draw stream in the enrichment section of the column and a 1,2-butadiene-enriched bottom draw stream can be obtained.
• the extractant is partially or completely discharged as a bottom draw stream from the extractive distillation and regenerated as follows:
• the extraction solution is transferred to a desorption zone with respect to the extraction zone reduced pressure and / or elevated temperature, wherein from the extraction solution butadiene and existing acetylene traces be desorbed.
• the desorption zone can be designed, for example, in the form of a wash column which has 5 to 15, preferably 8 to 10 theoretical stages and a backwash zone with, for example, 4 theoretical stages.
• This backwashing zone is used to recover the extraction agent contained in the gas phase by means of liquid hydrocarbon reflux, to which the top fraction is condensed beforehand, or by adding water.
• internals packings, trays or packing are provided.
• the pressure at the top of the column is, for example, 1.5 bar.
• the temperature in the bottom of the column is for example 130 to 150 ° C.
• a substantially acetylene-free extractant is obtained, which is recycled to the extractive distillation column.
• the top draw stream of the wash column is returned to the bottom of the extractive distillation column.
• the bottom draw stream of the wash column is returned to the top of the extractive distillation column.
• the desorption zone can also be operated at the same pressure as the extractive distillation.
• the desired product stream e2 as obtained, for example, as the top draw stream of the second pure distillation column, can contain up to 100% by volume of butadiene.
• the invention is further illustrated by the following example.
• An n-butane containing feed gas stream (4) obtained by combining a fresh gas stream (1) and a recycle stream (15) is fed to the first autothermally operated n-butane non-oxidative catalytic dehydrogenation (BDH) stage (20) ,
• BDH non-oxidative catalytic dehydrogenation
• the hydrogen formed in the dehydrogenation is selectively burned, to which combustion air is supplied as stream (2).
• water vapor (3) is added.
• a dehydrogenation gas mixture (5) which, after leaving the non-oxidative n-butane dehydrogenation stage (20), is obtained.
• ODH oxidative n-butane dehydrogenation
• the exit gas (7) of the ODH is compressed in two stages with intermediate cooling.
• the aqueous condensate (8) produced during the intermediate cooling is discharged from the process.
• an organic, C 4 - hydrocarbons-containing phase can be separated and fed back to the first dehydrogenation.
• the compressed, butadiene-containing gas (9) is fed to an absorption stage (23), which is operated with tetradecane as an absorbent.
• an absorbent stream (11) loaded with the C 4 hydrocarbons and an inert gas stream (10) discharged from the process are obtained.
• a butadiene, n-butane and 2-butene-containing stream (13) is separated in the desorption column (24), wherein the absorbent (12) is recovered. This is stripped in a stripping column (25) with air (18) to remove residues of C 4 hydrocarbons.
• the gaseous top draw stream (19) of the stripping column (25) consisting of air and C 4 hydrocarbons is fed to the ODH (21).
• the stream (17) of the regenerated absorbent is supplemented by fresh absorbent (17a) and returned to the absorption stage (23).
• the stream (13) is compressed and fed to a reactor (26) in which the residual oxygen remaining in the stream (13) is catalytically converted to water with hydrogen (13a).
• the substantially oxygen-free C 4 -hydrocarbon stream (14) is used in an extractive distillation stage (27) using aqueous N-methylpyrrolidone Solution in a butadiene-containing product stream (16) and a n-butane-containing recycle stream (15), which is recycled to the BDH, separated.

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