KR20150094620A - Method for oxidative dehydrogenation of n-butenes to butadiene - Google Patents

Abstract

A process for the oxidative dehydrogenation of n-butene to butadiene comprising two or more stages of preparation (i) and at least one regeneration step (ii) comprising the steps of: (i) reacting a n-butene- The mixture is mixed with an oxygen-containing gas and contacted with a multimetal oxide catalyst arranged in a fixed bed reactor at a temperature of 220 to 490 DEG C, comprising at least molybdenum, and one further metal, (Ii) in the regeneration step, the oxygen-containing recycle gas mixture is passed over the catalyst fixation layer at a temperature of from 200 to 450 DEG C to remove the carbon deposited on the catalyst by combustion, before the loss of conversion rate at a certain temperature is > 25% (Ii) between two preparation steps (i), and from 2 to 50% by weight of the carbon deposited on the catalyst in each regeneration step (ii) To It relates to a method comprising going.

Description

METHOD FOR OXIDATIVE DEHYDROGENATION OF N-BUTENES TO BUTADIENE < RTI ID = 0.0 >

The present invention relates to a process for the oxidative dehydrogenation of n-butene to butadiene.

Butadiene is an important basic chemical and is used, for example, in the manufacture of synthetic rubbers (butadiene homopolymers, styrene-butadiene rubbers or nitrile rubbers) or in the preparation of thermoplastic terpolymers (acrylonitrile-butadiene-styrene copolymers) . Butadiene is also converted (via 1,4-dichlorobutene and adiponitrile) to sulfolane, chloroprene and 1,4-hexamethylene diamine. In addition, vinylcyclohexene can be produced by dimerization of butadiene, which can be dehydrogenated to form styrene.

The butadiene can be prepared by thermal cracking (steam cracking) of saturated hydrocarbons, where naphtha is usually used as the raw material. Steam cracking of naphtha provides a hydrocarbon mixture of methane, ethane, ethene, acetylene, propane, propene, propyne, allene, butane, butene, butadiene, butyne, methylene, C ₅ -hydrocarbons and higher hydrocarbons.

Butadiene can also be obtained by oxidative dehydrogenation of n-butene (1-butene and / or 2-butene). Any mixture comprising n-butene can be used as the starting gas mixture for the oxidative dehydrogenation of n-butene to butadiene. For example, fractions obtained in the C ₄ fraction from naphtha crackers by removal of butadiene and isobutene, which contain n-butene (1-butene and / or 2-butene) as main constituents, can be used. Also, a gas mixture obtained by dimerization of ethylene, including 1-butene, cis-2-butene, trans-2-butene or mixtures thereof, can also be used as a starting gas. Also, a gaseous mixture obtained by flow catalytic cracking (FCC), including n-butene, can be used as a starting gas.

A gas mixture comprising n-butene and used as a starting gas in oxidative dehydrogenation of n-butene to butadiene can also be prepared by non-oxidative dehydrogenation of a gas mixture comprising n-butane.

WO2009 / 124945 discloses a coated catalyst for the oxidative dehydrogenation of 1-butene and / or 2-butene to butadiene, the coated catalyst comprising

(a) a support,

(b) (i) a catalytically active multimetal oxide comprising molybdenum and at least one additional metal and having the formula:

Mo ₁₂ Bi _a Cr _b X ¹ _c Fe _d X ² _e X ³ _f O _y

(Wherein,

X ¹ = Co and / or Ni,

X ² = Si and / or Al,

X ³ = Li, Na, K, Cs and / or Rb,

0.2? A? 1,

0? B? 2,

2? C? 10,

0.5? D? 10,

0? E? 10,

0? F? 0.5 and

y = number determined by the valence and abundance ratio of elements other than oxygen to achieve charge neutrality),

And (ii) at least one pore former

A shell

≪ / RTI >

WO 2010/137595 discloses a multimetal oxide catalyst for the oxidative dehydrogenation of alkenes to dienes comprising at least molybdenum, bismuth and cobalt and having the formula:

Mo _a Bi _b Co _c Ni _d Fe _e X _f Y _g Z _h Si _i O _j

X is at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), zinc (Zn), cerium (Ce) and samarium (Sm). Y is at least one element selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and thallium (Tl). Z is at least one element selected from the group consisting of boron (B), phosphorus (P), arsenic (As) and tungsten (W). aj is the atomic fraction of each element where a = 12, b = 0.5-7, c = 0-10, d = 0-10, where c + d = 1-10, 0-2, g = 0.04-2, h = 0-3 and I = 5-48. As an example, a catalyst having the composition Mo ₁₂ Bi ₅ Co _2.5 Ni _2.5 Fe _0.4 Na _0.35 B _0.2 K _0.08 Si ₂₄ in the form of pellets having a diameter of 5 mm and a height of 4 mm was oxidatively dehydrated into n-butene to butadiene Used for digestion.

In the oxidative dehydrogenation of n-butene to butadiene, precursors of carbonaceous materials such as styrene, anthraquinone and fluorenone can be formed, which can ultimately lead to the carbonization and deactivation of multi-metal oxide catalysts . The pressure drop on the catalyst bed may increase as a result of carbon-containing deposit formation. Regeneration can be performed by burning the carbon deposited on the multi-metal oxide catalyst at regular intervals using an oxygen-containing gas to restore the activity of the catalyst.

In JP 60-058928, at least a molybdenum, bismuth, iron, cobalt and / or zirconium oxide are formed by using an oxygen-containing gas mixture at a temperature of 300 to 700 ° C, preferably 350 to 650 ° C and an oxygen concentration of 0.1 to 5% Describes the regeneration of multi-metal oxide catalysts for the oxidative dehydrogenation of n-butene to butadiene, including antimony. A suitable inert gas, such as nitrogen, steam or air diluted with carbon dioxide, is introduced as the oxygen-containing gas mixture.

WO 2005/047226 discloses a multi-metal oxide catalyst for partial oxidation of acrolein to acrylic acid, comprising at least molybdenum and vanadium, by passing the oxygen-containing gas mixture over a multi-metal oxide catalyst at a temperature of 200 to 450 ° C. Is reproduced. As the oxygen-containing gas mixture, it is preferable to use lean air containing 3 to 10% by volume of oxygen. The gas mixture may contain steam in addition to oxygen and nitrogen.

It is an object of the present invention to provide a method for the oxidative dehydrogenation of n-butene to butadiene, which is very simple to regenerate a multi-metal oxide catalyst.

This object is achieved by an oxidative dehydrogenation of n-butene to butadiene, comprising at least two production steps (i) and at least one regeneration step (ii)

(i) mixing a starting gas mixture comprising n-butene with an oxygen-containing gas in a production step and, at a temperature of 220 to 490 DEG C in a fixed-bed reactor, comprising at least molybdenum and further metal, Contacting the multi-metal oxide catalyst,

Before the relative reduction in conversion at a given temperature is > 25%

(ii) regenerating the multimetal oxide catalyst by passing the oxygen-containing regeneration gas mixture over a fixed catalyst bed at a temperature of 200 to 450 DEG C to remove carbon deposited on the catalyst by combustion,

The regeneration step (ii) is carried out between two preparation steps (i)

And in each regeneration step (ii), 5 to 50% by weight of the carbon deposited on the catalyst is removed by combustion.

Surprisingly, it has been found that the activity of the multimetal oxide catalyst is essentially regenerated even if only less than 50% by weight of the carbon deposited on the catalyst is removed by combustion. At each regeneration step (ii), even if only 5% by weight of the deposited carbon is removed by combustion, the activity of the catalyst is greatly restored.

At each regeneration step, removing less than 50% by weight of the deposited carbon by burning can significantly shorten the regeneration time, which improves the economics of the process.

Preferably, from 5 to 50% by weight, particularly preferably from 10 to 35% by weight, in particular from 10 to 30% by weight, of the carbon deposited in the multimetal oxide catalyst is removed by combustion every regeneration step (ii).

Thus, the activity of the multimetal oxide catalyst is generally recovered to above 95%, preferably above 98%, especially above 99%, of the activity of the multimetal oxide catalyst at the start of the preceding preparation step (i).

The regeneration step (ii) is carried out when the relative reduction of the conversion rate at a certain temperature (i.e., based on the conversion rate at the beginning of each production step (i)) exceeds 25%. The regeneration step (ii) is preferably carried out before the relative reduction in the conversion rate at a certain temperature exceeds 15%, particularly preferably before the reduction in the conversion rate exceeds 10%. In general, the regeneration step (ii) is carried out only when the relative reduction in conversion at a given temperature is 2% or more.

Generally, the production step (i) has a period of from 5 to 5000 hours before reaching a relative reduction of not more than 25% conversion, based on the conversion rate at the beginning of this production step (i). The catalyst may experience up to 5,000 cycles of production and regeneration.

The amount of carbon that is deposited on the catalyst and removed by combustion can be determined by quantitative determination of the carbon oxides formed during each regeneration step (ii), for example, by on-line IR crystallization of the carbon oxides in offgas from regeneration . The total amount of carbon deposited on the catalyst is determined by removing all of the carbon by combustion using a mixture of 10 vol% oxygen, 80 vol% nitrogen, and 10 vol% steam at 400 캜 or higher. The temperature is selected so that no further formation of carbon oxides occurs even when the temperature is raised further. Alternatively, the amount of carbon deposited on the catalyst can be determined by measuring the carbon content of the sample taken in the catalyst.

Catalysts suitable for oxydehydrogenation are generally based on Mo-Bi-O- containing multimetal oxide systems which generally contain iron. In general, the catalyst system may comprise additional catalyst components from Groups 1 to 15 of the Periodic Table, for example, potassium, cesium, magnesium, zirconium, chromium, nickel, cobalt, cadmium, tin, lead, germanium, lanthanum, manganese, Tungsten, phosphorus, cerium, aluminum or silicon. Iron-containing ferrites have also been proposed as catalysts.

In one preferred embodiment, the multi-metal oxide comprises cobalt and / or nickel. In a further preferred embodiment, the multimetal oxide comprises chromium. In a further preferred embodiment, the multimetal oxide comprises manganese.

In general, the catalytically active multimetal oxides comprising molybdenum and at least one additional metal have the formula (I)

(I)

Mo ₁₂ Bi _a Fe _b Co _c Ni _d Cr _e X ¹ _f X ² _g O _x

In the above equation, the variables have the following meanings:

X ¹ = W, Sn, Mn, La, Ce, Ge, Ti, Zr, Hf, Nb, P, Si, Sb, Al, Cd and / or Mg;

X ² = Li, Na, K, Cs and / or Rb;

a = 0.1 to 7, preferably 0.3 to 1.5;

b = 0 to 5, preferably 2 to 4;

c = 0 to 10, preferably 3 to 10;

d = 0 to 10;

e = 0 to 5, preferably 0.1 to 2;

f = 0 to 24, preferably 0.1 to 2;

g = 0 to 2, preferably 0.01 to 1; And

x = a number determined by the valency and abundance ratio of elements other than oxygen in the formula (I).

The catalyst may be an all-active catalyst or a coated catalyst. When the catalyst is a coated catalyst, the catalyst has a support (a), and a shell (b) comprising molybdenum and a catalytically active multimetal oxide comprising at least one additional metal.

Suitable support materials for the coated catalysts are, for example, porous or preferably nonporous aluminum oxide, silicon dioxide, zirconium dioxide, silicon carbide or silicates such as magnesium silicate or aluminum silicate (for example from CeramTec) Grade C 220 stearate). The material of the support is chemically inert.

The support material may be porous or non-porous. The support material is preferably non-porous (based on the volume of the support, the total volume of pores is preferably < = 1% by volume).

An essentially nonporous spherical stearate with a rough surface and a diameter of from 1 to 8 mm, preferably from 2 to 6 mm, particularly preferably from 2 to 3 or from 4 to 5 mm (for example Type C from Celamtec 220 < / RTI > stearate) support is particularly preferred. However, it is also possible, as a support, to use a cylinder consisting of a support material and having a length of 2 to 10 mm and an outer diameter of 4 to 10 mm. In the case of a ring as a support, the wall thickness is usually 1 to 4 mm. The preferred annular-shaped support has a length of 2 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. In particular, a ring having a geometry of 7 mm x 3 mm x 4 mm (outer diameter x length x inner diameter) is also suitable as a support. The layer thickness of the shell (b) of the multi-metal oxide composition comprising molybdenum and at least one further metal is generally from 5 to 1000 mu m. Preferably 10 to 800 占 퐉, particularly preferably 50 to 600 占 퐉, very particularly preferably 80 to 500 占 퐉. The layer thickness of the shell (b) composed of a multi-metal oxide composition comprising molybdenum and at least one further metal is generally from 5 to 1000 mu m. Preferably 10 to 800 占 퐉, particularly preferably 50 to 600 占 퐉, very particularly preferably 80 to 500 占 퐉.

Examples of Mo-Bi-Fe-O- containing multimetal oxides are Mo-Bi-Fe-Cr-O- or Mo-Bi-Fe-Zr-O- The preferred system, for _{example, US 4,547,615 (Mo 12 BiFe 0.1} Ni 8 ZrCr 3 K 0.2 O x and _{Mo 12 BiFe 0. 1 Ni 8} AlCr 3 K 0. 2 O x), US 4,424,141 (Mo 12 BiFe 3 Co _{4.5 Ni 2.5 P 0.5 K 0.1 O} x + SiO 2), DE-A 25 30 959 (Mo 12 BiFe 3 Co 4. 5 Ni 2. 5 Cr 0 .5 K 0. 1 O x, Mo 13.75 BiFe 3 Co 4.5 _{Ni 2.5 Ge 0.5 K 0.8 O x} , Mo 12 BiFe 3 Co 4. 5 Ni 2. 5 Mn 0 .5 K 0. 1 O x , and _{Mo 12 BiFe 3 Co 4.5 Ni 2.5} La 0.5 K 0.1 O x), US 3,911,039 _{(Mo 12 BiFe 3 Co 4.} 5 Ni 2. 5 Sn 0 .5 K 0. 1 O x), DE-A 25 30 959 and DE-A 24 47 825 (Mo 12 BiFe 3 Co 4.5 Ni 2.5 W 0.5 K _0.1 O _x ).

Suitable multi-metal oxides and their preparation are also _{US 4,423,281 (Mo 12 BiNi 8 Pb} 0.5 Cr 3 K 0.2 O x and _{Mo 12 Bi b Ni 7 Al 3} Cr 0 .5 K 0. 5 O x), US 4,336,409 (Mo 12 _{BiNi 6 Cd 2 Cr 3 P 0.5} O x), DE-A 26 00 128 (Mo 12 BiNi 0. 5 Cr 3 P 0. 5 Mg 7 .5 K 0. 1 O x + SiO 2) and DE-A 24 40 329 (Mo ₁₂ BiCo _4.5 Ni _2.5 Cr ₃ P _0.5 K _0.1 O _x ).

Particularly preferred catalytically active multimetal oxides comprising molybdenum and at least one further metal have the formula (Ia)

<Formula Ia>

Mo ₁₂ Bi _a Fe _b Co _c Ni _d Cr _e X ¹ _f X ² _g O _y

In this formula,

X ¹ = Si, Mn and / or Al,

X ² = Li, Na, K, Cs and / or Rb,

0.2? A? 1,

0.5? B? 10,

0? C? 10,

0? D? 10,

2? C + d? 10

0? E? 2,

0? F? 10

0? G? 0.5

y = Is a number determined by the valence and abundance ratio of elements other than oxygen in formula (Ia) to achieve charge neutrality.

Catalysts in which the catalytically active oxide composition comprises only Co among the two metal Co and Ni (d = 0) are preferred. X ¹ is preferably Si and / or Mn, X ² is preferably K, Na and / or Cs, and X ² is particularly preferably K.

In the formula (Ia), the stoichiometric coefficient a is preferably 0.4? A? 1, particularly preferably 0.4? A? 0.95. The value of the variable b is preferably in the range of 1? B? 5, particularly preferably in the range of 2? B? 4. The sum of the stoichiometric coefficients c + d is preferably in the range of 4? C + d? 8, particularly preferably in the range of 6? C + d? 8. The stoichiometric coefficient e is preferably in the range of 0.1? E? 2, particularly preferably in the range of 0.2? E? 1. The stoichiometric coefficient g is advantageously? 0. 0.01? G? 0.5 is preferable, and 0.05? G? 0.2 is particularly preferable.

The value of the stoichiometric coefficient y of oxygen is derived from the valence and abundance ratio of the cations so as to maintain charge neutrality. Coated catalysts according to the present invention having a catalytically active oxide composition having a Co / Ni molar ratio of at least 2: 1, preferably at least 3: 1, particularly preferably at least 4: 1, are advantageous. It is best to have only Co.

The coated catalyst is prepared by applying a layer comprising a multimetal oxide comprising molybdenum and at least one additional metal to the support by means of a binder and drying and calcining the coated support.

The finely divided multimetal oxides comprising molybdenum and at least one further metal which can be used according to the invention are in principle prepared by preparing a close dry mixture of the starting compounds of the elemental constituents of the catalytically active oxide composition, Lt; RTI ID = 0.0 &gt; 150 C &lt; / RTI &gt;

Preparation of multi-metal oxide catalysts

To prepare a suitable finely divided multimetal oxide composition, the starting compounds known for the elemental constituents other than oxygen of the desired multimetal oxide composition are used as the starting material at the respective stoichiometric ratios, from which very close, preferably, A finely divided dry mixture is prepared, and then this dry mixture is subjected to heat treatment. The source may be an oxide or a compound that can be converted to an oxide by heating in the presence of at least oxygen. Thus, in addition to the oxides, halides, nitrates, formates, oxalates, acetates, carbonates or hydroxides can be used as starting compounds.

Further suitable starting compounds for molybdenum are their oxo compounds (molybdenum salts) or acids derived therefrom.

Suitable starting compounds of Bi, Cr, Fe and Co are, in particular, the nitrates thereof.

Intimate mixing of the starting compounds may in principle be carried out in dry form or in the form of an aqueous solution or suspension.

The aqueous suspension may be prepared, for example, by combining an aqueous solution containing the molybdenum and the remaining metal. Alkali metal or alkaline earth metal may be present in both solutions. Precipitation is effected by combining the solutions, which leads to the formation of a suspension. The temperature of the precipitation may be above room temperature, preferably between 30 ° C and 95 ° C, particularly preferably between 35 ° C and 80 ° C. The suspension can then be aged for a certain period of time at elevated temperatures. The time period of aging is generally in the range of 0 to 24 hours, preferably 0 to 12 hours, particularly preferably 0 to 8 hours. The temperature during the aging is generally in the range of 20 占 폚 to 99 占 폚, preferably 30 占 폚 to 90 占 폚, particularly preferably 35 占 폚 to 80 占 폚. The suspension is generally mixed by agitation during precipitation and aging. The pH of the mixed solution or suspension is generally in the range of pH 1 to pH 12, preferably pH 2 to pH 11, particularly preferably pH 3 to pH 10.

Removal of water produces a solid representing a tight mixture of added metal components. The drying step is generally carried out by evaporation, spray drying or freeze-drying. The drying is preferably carried out by spray drying. For this purpose, the suspension is atomized by a spray head, usually at a temperature of 120 ° C to 300 ° C at elevated temperature, and the dried product is collected at a temperature of> 60 ° C. The residual moisture content determined by drying of the spray-dried powder at 120 占 폚 is generally less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 12% by weight.

For the preparation of the pre-active catalyst, in a further step, the spray-dried powder is converted into a shaped body. Possible molding aids (lubricants) are, for example, water, boron trifluoride or graphite. Typically ≤10% by weight, generally ≤6% by weight, often ≤4% by weight, of the molding aid is added, based on the composition to be molded to provide the molded catalyst precursor. The amount added is generally > 0.5 wt%. A preferred lubricant is graphite.

The heat treatment of the shaped catalyst precursor is generally carried out at a temperature in excess of 350 [deg.] C. However, it does not exceed a temperature of typically 650 ° C during the course of the heat treatment. According to the present invention, the temperature in the heat treatment advantageously does not exceed 600 캜, preferably does not exceed 550 캜, and particularly preferably does not exceed 500 캜. In addition, the temperature during the heat treatment of the shaped catalyst precursor is preferably above 380 ° C, advantageously above 400 ° C, particularly advantageously above 420 ° C, very particularly preferably above 440 ° C. The heat treatment can also be divided into a plurality of steps over time. For example, it is possible to first carry out the heat treatment at a temperature of 150 to 350 DEG C, preferably 220 to 280 DEG C, and subsequently carry out the heat treatment at a temperature of 400 to 600 DEG C, preferably 430 to 550 DEG C It is possible. The heat treatment of the shaped catalyst precursor typically takes a lot of time (usually over 5 hours). The total duration of heat treatment is often extended beyond 10 hours. Does not exceed the treatment time of generally 45 hours or 35 hours in the heat treatment of the shaped catalyst precursor. The total processing time is usually less than 30 hours. The heat treatment of the shaped catalyst precursor preferably does not exceed a temperature of 500 DEG C and the treatment time at temperature window &gt; 400 DEG C is preferably extended to 5 to 30 hours.

The heat treatment (calcination) of the shaped catalyst precursor can be carried out under an inert gas or under an oxidizing atmosphere such as air or in a reducing atmosphere (for example in a mixture of inert gas, NH ₃ , CO and / or H ₂ or methane) have. It goes without saying that the heat treatment may also be carried out under reduced pressure. The heat treatment of the shaped catalyst precursor may in principle be carried out in a wide variety of furnace types, for example in a heatable convection chamber, a tray furnace, a rotary tubular furnace, a belt calciner or a shaft furnace. The heat treatment of the shaped catalyst precursor is preferably carried out in a belt calcining apparatus as recommended in DE-A 10046957 and WO 02/24620. Thermal treatment of the formed catalyst precursor at less than 350 < 0 &gt; C generally involves thermal decomposition of the source of the elemental constituents of the desired catalyst contained in the shaped catalyst precursor. This decomposition phase frequently occurs during heating to a temperature of &lt; 350 [deg.] C in the process of the present invention.

The catalytically active metal oxide composition obtained after calcination may subsequently be converted to a fine powder by milling, for the preparation of the coated catalyst, which is then applied to the outer surface of the support with the aid of a liquid binder. The fineness of the catalytically active oxide composition applied to the surface of the support will correspond to the desired shell thickness.

Suitable support materials for the preparation of the coated catalyst are porous or preferably nonporous aluminum oxide, silicon dioxide, zirconium dioxide, silicon carbide or silicates such as magnesium silicate or aluminum silicate (e.g., a grade C 220 stearate from Celamtec Tight). The material of the support is chemically inert.

The support material may be porous or non-porous. The support material is preferably non-porous (based on the volume of the support, the total volume of pores is preferably &lt; = 1% by volume).

Preferred hollow cylinders as a support have a length of 2 to 10 mm and an outer diameter of 4 to 10 mm. Further, the wall thickness is preferably 1 to 4 mm. Particularly preferred ring-shaped supports 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. An example of a support is a ring having a geometry of 7 mm x 3 mm x 4 mm (outer diameter x length x inner diameter).

The layer thickness D of the multi-metal oxide composition comprising molybdenum and at least one further metal is generally between 5 and 1000 mu m. Preferably 10 to 800 占 퐉, particularly preferably 50 to 600 占 퐉, very particularly preferably 80 to 500 占 퐉.

The application of the multimetal oxides containing molybdenum and at least one further metal to the surface of the support can be carried out in a manner corresponding to the process described in the prior art, for example in US-A 2006/0205978 and EP A 0 714 700. &lt; / RTI &gt;

In general, the finely divided metal oxide composition is applied to the surface of the support or to the surface of the first layer with the aid of a liquid binder. Possible liquid binders are, for example, water, organic solvents, or solutions of organic materials (e.g. organic solvents) in or in organic solvents.

Solutions containing 20 to 95% by weight of water and 5 to 80% by weight of organic compounds as liquid binders are particularly advantageously used. The organic content in the liquid binder described above is preferably 10 to 50% by weight, particularly preferably 10 to 30% by weight.

In general, organic binders or binder components with a boiling point or sublimation temperature at atmospheric pressure (1 atm) of &gt; 100 [deg.] C, preferably &gt; The boiling point or sublimation point of such organic binder or binder component at atmospheric pressure is at the same time very particularly preferably less than the maximum calcination temperature used during the preparation of the molybdenum-containing finely divided multimetal oxide. This maximum calcination temperature is generally ≤ 600 ° C, often ≤ 500 ° C.

Examples of organic binders which may be mentioned are mono- or polyhydric organic alcohols such as, for example, ethylene glycol, 1,4-butanediol, 1,6-hexanediol or glycerol, mono- or polybasic organic carboxylic acids such as propionic acid , Oxalic acid, malonic acid, glutaric acid or maleic acid, aminoalcohols such as ethanolamine or diethanolamine, and mono- or polyunsaturated organic amides such as formamide. Examples of suitable organic binder promoters which are soluble in water, in an organic liquid or in a mixture of water and an organic liquid are monosaccharides and oligosaccharides such as glucose, fructose, sucrose and / or lactose.

A particularly preferred liquid binder is a solution comprising from 20 to 95% by weight of water and from 5 to 80% by weight of glycerol. The proportion of glycerol in these aqueous solutions is preferably 5 to 50% by weight, particularly preferably 8 to 35% by weight.

The application of molybdenum-containing finely divided multimetal oxides can be carried out by mixing the finely divided composition of molybdenum-containing multimetal oxides with a liquid binder, as described in DE-A 1642921, DE-A 2106796 and DE-A 2626887 Dispersing the resulting suspension and spraying it onto a stirred and optionally a hot support. After spraying is complete, the moisture content of the resulting coated catalyst can be reduced by passing hot air over the catalyst, as described in DE-A 2909670.

In order to produce a suitable pore structure of the catalyst and to improve the material transport properties, it is possible to use finely divided multi-component systems applied to the support with a pore former such as malonic acid, melamine, nonylphenol ethoxylate, stearic acid, glucose, starch, fumaric acid and succinic acid, May be added to the metal oxide. The catalyst preferably does not contain any pore formers.

However, the support is preferably first wetted with a liquid binder and the finely divided composition of the multimetal oxide is subsequently applied to the surface of the wetted support by a binder, and the wetted support is rolled into the finely divided composition. In order to achieve the desired layer thickness, the above-described method is preferably repeated several times, i. E. The support with the first coat is again wetted and then coated by contact with dry finely divided compositions.

In order to carry out the process on an industrial scale, it is advisable to use the process described in DE-A 2909671, preferably using the binder recommended in EP-A 714700. In other words, the support to be coated is introduced into a rotatable container (for example a rotary plate or a coating drum) which is preferably inclined (the inclination angle is generally between 30 and 90 DEG C).

The temperature required to cause the removal of the adhesion promoter is less than the maximum calcination temperature for the catalyst, typically 200 ° C to 600 ° C. The catalyst is preferably heated to a temperature in the range from 240 캜 to 500 캜, particularly preferably from 260 캜 to 400 캜. The time until the adhesion promoter is removed may be several hours. To remove the adhesion promoter, the catalyst is generally heated to the aforementioned temperature for 0.5 to 24 hours. The time is preferably in the range of 1.5 to 8 hours, particularly preferably in the range of 2 to 6 hours. The flow of gas around the catalyst can accelerate the removal of the adhesion promoter. The gas is preferably air or nitrogen, particularly preferably air. Removal of the adhesion promoter can be carried out, for example, in an oven in which the gas flows or in a suitable drying apparatus, for example a belt dryer.

Oxidative dehydrogenation (oxydehydrogenation, ODH)

In a plurality of production cycles (i), the oxidative dehydrogenation of n-butene to butadiene is carried out by mixing the starting gas mixture comprising n-butene with an oxygen-containing gas and optionally further inert gases or vapors, Lt; RTI ID = 0.0 &gt; 220 C &lt; / RTI &gt; to &lt; RTI ID = 0.0 &gt; 490 C. &lt; / RTI &gt;

The reaction temperature of oxydehydrogenation is generally controlled by the heat transfer medium located around the reaction tube. As such liquid heat transfer media, for example, melts of salts such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate and also melts of metals such as sodium, mercury and alloys of various metals can be used. However, ionic liquids or heat transfer oils can also be used. The temperature of the heat transfer medium is in the range of 220 to 490 캜, preferably 300 to 450 캜, particularly preferably 350 to 420 캜.

Due to the exothermic nature of the reaction taking place, the temperature may be higher than the temperature of the heat transfer medium in a particular section of the interior of the reactor during the reaction, forming a hot spot. The location and size of the hot spots are determined by the reaction conditions, but may also be controlled by the dilution rate of the catalyst bed or by passage of the mixed gas.

Oxy-dehydrogenation can be carried out in any fixed bed reactor known in the prior art, for example a tray oven, a fixed bed tubular reactor or a multitubular reactor or a plate heat exchanger reactor. A multi-tubular reactor is preferred.

Further, the catalyst layer provided in the reactor may be a single zone or two or more zones. These zones can be made of pure catalyst or can be diluted with a starting gas or a material that does not react with the components of the product gas formed by the reaction. The catalyst zone may also consist of a pre-activated catalyst or a supported coated catalyst.

As a starting gas, a gas mixture containing pure n-butene (1-butene and / or cis- / trans-2-butene) as well as butene can be used. Such a mixture can be obtained, for example, by non-oxidative dehydrogenation of n-butane. It is also possible to use the fractions obtained in the C ₄ fraction obtained from the cracking of naphtha by the removal of butadiene and isobutene, which contain n-butene (1-butene and / or 2-butene) as main constituents. Also as the starting gas, a gas mixture comprising pure 1-butene, cis-2-butene, trans-2-butene or mixtures thereof and obtained by dimerization of ethylene can also be used. As starting gas, a gas mixture comprising n-butene and obtained by flow catalytic cracking (FCC) may also be used.

In one embodiment of the process of the present invention, the starting gas mixture comprising n-butene is obtained by non-oxidative dehydrogenation of n-butane. Based on the n-butane used, the high yield of butadiene can be obtained by coupling the non-oxidizing catalyst dehydrogenation and the oxidative dehydrogenation of the n-butene formed. The non-oxidative catalytic dehydrogenation of n-butane provides a gas mixture comprising butadiene, 1-butene, 2-butene and unreacted n-butane and also secondary components. Common secondary constituents are hydrogen, water vapor, nitrogen, CO and CO ₂ , methane, ethane, ethene, propane and propene. The composition of the gas mixture leaving the first dehydrogenation zone can vary greatly depending on the mode of operation of the dehydrogenation. Thus, when dehydrogenation is carried out by the introduction of oxygen and additional hydrogen, the product gas mixture has a relatively high amount of water vapor and carbon oxides. In an operating mode without the introduction of oxygen, the product gas mixture from non-oxidative dehydrogenation has a relatively high content of hydrogen.

The product gas stream from non-oxidative dehydrogenation of n-butane typically contains from 0.1 to 15% by volume of butadiene, from 1 to 15% by volume of 1-butene, from 1 to 25% by volume of 2-butene (cis / (Methane, ethane, ethene, propane and propene), from 0.1 to 40% by volume of hydrogen, from 0 to 10% by volume of water, and from 20 to 70% by volume of n-butane, from 1 to 70% by volume of water vapor, from 0 to 10% by volume of low boiling point hydrocarbons 0 to 70% by volume of nitrogen and 0 to 5% by volume of carbon oxides. The product gas stream from the non-oxidizing dehydrogenation can be fed to the oxidative dehydrogenation without further post-treatment.

In addition, any impurities may be present in the starting gas for the oxydehydrogenation in an amount that does not interfere with the effectiveness of the present invention. Impurities that may be mentioned in the preparation of butadiene from n-butene (1-butene and cis- / trans-2-butene) include saturated and unsaturated, branched and unbranched hydrocarbons such as methane, ethane, ethene, acetylene, Propane, propene, propyne, n-butane, isobutane, isobutene, n-pentane and also dienes such as 1,2-butadiene. The amount of impurities is generally 70% or less, preferably 30% or less, more preferably 10% or less, particularly preferably 1% or less. The concentration of linear monoolefins (n-butene and higher homologues) having four or more carbon atoms in the starting gas is not limited in any particular way; It is generally 35.00-99.99 vol%, preferably 71.00-99.0 vol%, even more preferably 75.00-95.0 vol%.

To perform oxidative dehydrogenation with complete conversion of butene, a gas mixture having an oxygen: n-butene molar ratio of at least 0.5 is needed. It is preferable to work in an oxygen: n-butene ratio of 0.55 to 10. To set this value, the starting gas may be mixed with oxygen or an oxygen-containing gas, such as air, and optionally an inert gas or vapor. The oxygen-containing gas mixture obtained is then fed into oxy dehydrogenation.

The gas comprising molecular oxygen is generally a gas comprising greater than 10% by volume, preferably greater than 15% by volume, more preferably greater than 20% by volume of molecular oxygen and particularly preferably air. The upper limit for the content of molecular oxygen is generally not more than 50% by volume, preferably not more than 30% by volume, more preferably not more than 25% by volume. In addition, any inert gas may be present in the gas containing molecular oxygen in an amount that does not interfere with the effectiveness of the present invention. As possible inert gases, nitrogen, argon, neon, helium, CO, CO ₂ and water can be mentioned. The amount of inert gas is generally not more than 90% by volume, preferably not more than 85% by volume, more preferably not more than 80% by volume in the case of nitrogen. In the case of constituents other than nitrogen, they are generally present in an amount of up to 10% by volume, preferably up to 1% by volume. If this amount becomes too large, it becomes much more difficult to provide the required reaction with oxygen.

In addition, an inert gas such as nitrogen and also water (as water vapor) can be included with the gas comprising a mixed gas composed of a starting gas and molecular oxygen. Nitrogen exists to set the oxygen concentration and to prevent the formation of explosive gas mixtures, and the same applies to water vapor. Water vapor is also present to control the carbonization of the catalyst and to remove the heat of the reaction. Water (as water vapor) and nitrogen are preferably mixed into the gaseous mixture and introduced into the reactor. When water vapor is introduced into the reactor, a ratio of 0.2-5.0 (dead skin), preferably 0.5-4, even more preferably 0.8-2.5, is preferably introduced, based on the introduced amount of the above-mentioned starting gas . When nitrogen gas is introduced into the reactor, a ratio of 0.1-8.0 (dead skin), preferably 0.5-5.0, more preferably 0.8-3.0, based on the introduced amount of the above-described starting gas is preferably introduced do.

The proportion of the starting gas containing hydrocarbons in the mixed gas is generally at least 4.0 vol%, preferably at least 6.0 vol%, even more preferably at least 8.0 vol%. On the other hand, the upper limit is 20% by volume or less, preferably 16.0% by volume or less, and more preferably 13.0% by volume or less. To safely avoid the formation of an explosive gas mixture, before obtaining a mixed gas, nitrogen gas is first introduced into the starting gas or into the gas containing molecular oxygen, and the gas containing the starting gas and the molecular oxygen is mixed to form a mixed gas And then this mixed gas is preferably introduced.

During stable operation, the residence time in the reactor is not limited in any particular manner in the present invention, but the lower limit is generally at least 0.3 s, preferably at least 0.7 s, even more preferably at least 1.0 s. The upper limit is 5.0 s or less, preferably 3.5 s or less, more preferably 2.5 s or less. The ratio of the amount of the mixed gas throughput for the catalyst amount in the reactor is 500-8000 h ^-1, preferably 800-4000 h ^-1, more preferably from 1200-3500 h ^{- 1.} (Expressed in units of g _butene / (g _catalyst * time)) of butene on the catalyst during stable operation is generally in the range of 0.1-5.0 h ^-1 , preferably 0.2-3.0 h ^-1 , even more preferably 0.25 -1.0 h ^{- 1} . The volume and mass of the catalyst are based on the complete catalyst consisting of the support and the active composition.

Regeneration of multi-metal oxide catalysts

According to the present invention, a regeneration step (ii) is performed between each two manufacturing steps (i). The regeneration step (ii) is carried out before the reduction in conversion at a given temperature exceeds 25%. The regeneration cycle (ii) is carried out by passing the oxygen-containing regeneration gas mixture over the fixed catalyst bed at a temperature of from 200 to 450 ° C, so that the carbon deposited on the multimetal oxide catalyst is removed by combustion. According to the invention, 5 to 50% by weight of the carbon deposited on the catalyst is removed by combustion every regeneration cycle (ii).

The oxygen-containing regeneration gas mixture used in the regeneration step (i) generally comprises an oxygen-containing gas and further inert gases, vapors and / or hydrocarbons. Generally, it contains 0.5 to 22% by volume, preferably 1 to 20% by volume, especially 2 to 18% by volume of oxygen.

The preferred oxygen-containing gas present in the regeneration gas mixture is air. In order to produce an oxygen-containing regeneration gas mixture, an inert gas, a vapor and / or a hydrocarbon may optionally be further mixed into the oxygen-containing gas. As possible inert gases, mention may be made of nitrogen, argon, neon, helium, CO and CO ₂ . The amount of inert gas is generally not more than 90% by volume, preferably not more than 85% by volume, more preferably not more than 80% by volume in the case of nitrogen. In the case of constituents other than nitrogen, they are generally present in an amount of up to 10% by volume, preferably up to 1% by volume. The amount of oxygen-containing gas is selected such that the volume ratio of molecular oxygen in the regeneration gas mixture at the start of regeneration is from 0 to 50%, preferably from 0.5 to 22%, more preferably from 1 to 10%. The ratio of molecular oxygen can be increased during the course of regeneration.

The steam may also be included in the oxygen-containing regeneration gas mixture. Nitrogen is present to set the oxygen concentration and the same applies to steam. Vapor may also be present as a moderate oxidant for removing the heat of the reaction and for the removal of carbon-containing deposits. It is preferred to mix the water (as the vapor) and nitrogen into the regeneration gas mixture and introduce the latter into the reactor. When introducing the steam into the reactor at the beginning of regeneration, it is preferable to introduce a volume ratio of 0 to 50%, preferably 0.5 to 22%, even more preferably 1 to 10%. The ratio of steam can be increased during the course of regeneration. The amount of nitrogen is selected such that the volume ratio of molecular nitrogen in the regeneration gas mixture at the start of regeneration is 20 to 99%, preferably 50 to 98%, more preferably 70 to 96%. The ratio of nitrogen can be lowered during the course of regeneration.

The regeneration gas mixture may also contain hydrocarbons. They may be added to or mixed with an inert gas. The volume ratio of hydrocarbons in the oxygen-containing regeneration gas mixture is generally less than 50%, preferably less than 10%, more preferably less than 2%. The hydrocarbons may be selected from the group consisting of saturated and unsaturated, branched and unbranched hydrocarbons such as methane, ethane, ethene, acetylene, propane, propene, propyne, n-butane, isobutane, n-butene, isobutene, It may also include dienes such as 1,3-butadiene and 1,2-butadiene. In particular, they comprise hydrocarbons which are unreactive in the presence of catalyst under regeneration conditions in the presence of oxygen.

During stable operation, the residence time of the regeneration gas mixture in the reactor during regeneration is not subject to any particular limitation, but the lower limit is generally at least 0.3 s, preferably at least 0.7 s, even more preferably at least 1.0 s. The upper limit is 7.0 s or less, preferably 5.0 s or less, even more preferably 3.5 s or less. A ^first-flow rate of the mixed gas to the catalyst volume of the inside of the reactor is from 500 to 8000 h ^-1, preferably 600 to 4000 h. The temperature of the heat transfer medium is in the range of 220 to 490 캜, preferably 300 to 450 캜, particularly preferably 350 to 420 캜. All of the above and below mentioned temperatures in the production step (i) and the regeneration step (ii) relate to the temperature of the heat transfer medium at the inlet of the heat transfer medium on the reactor.

The temperature in the regeneration cycle (ii) is preferably at most 20 ° C higher than the temperature in the production cycle (i), particularly preferably at most 10 ° C higher. The temperature in the production cycle (i) is preferably above 350 ° C, particularly preferably above 360 ° C, in particular above 365 ° C and below 420 ° C. The temperature referred to is the temperature of the heat transfer medium at the inlet of the heat transfer medium on the reactor.

Product gas Of the stream  After treatment

The product gas stream leaving the oxidative dehydrogenation of the preparation stage contains butadiene and generally also unreacted n-butane and isobutane, 2-butene and water vapor. Containing hydrocarbons generally known as carbon monoxide, carbon dioxide, oxygen, nitrogen, methane, ethane, ethene, propane and propene, possibly hydrogen and also as oxygenates. Generally, only a small proportion of 1-butene and isobutene is included.

The product gas stream leaving the oxidative dehydrogenation may contain, for example, from 1 to 40 vol% butadiene, from 20 to 80 vol% n-butane, from 0 to 5 vol% isobutane, from 0.5 to 40 vol% 0 to 5% by volume of 1-butene, 0 to 70% by volume of water vapor, 0 to 10% by volume of low boiling hydrocarbons (methane, ethane, ethene, propane and propene) 30 vol% oxygen, 0-70 vol% nitrogen, 0-10 vol% carbon oxides, and 0-10 vol% oxygenate. The oxigenate may be selected from the group consisting of formaldehyde, furan, acetic acid, maleic anhydride, formic acid, methacrolein, methacrylic acid, crotonaldehyde, crotonic acid, propionic acid, acrylic acid, methyl vinyl ketone, styrene, benzaldehyde, Phthalic anhydride, fluorenone, anthraquinone and butyraldehyde.

Some of the oxygenate may be further oligomerized and dehydrogenated at the catalyst surface and in the aftertreatment to form deposits comprising carbon, hydrogen and oxygen, hereinafter referred to as carbonaceous materials. These deposits are undesirable since they can lead to interruption of cleaning and regeneration during operation of the process. Typical precursors of carbonaceous materials include styrene, fluorenone, and anthraquinone.

The product gas stream at the reactor outlet has a temperature close to the temperature at the end of the catalyst bed. The product gas stream is then brought to a temperature of from 150 to 400 ° C, preferably from 160 to 300 ° C, particularly preferably from 170 to 250 ° C. Although it is possible to isolate the line through which the product gas stream passes to maintain the temperature in the desired range, it is desirable to use a heat exchanger. The heat exchanger system may have any type as long as the temperature of the product gas can be maintained at a desired level by the system. Examples of heat exchangers include spiral heat exchangers, plate heat exchangers, double tubular heat exchangers, multiple tubular heat exchangers, boiler spiral heat exchangers, boiler jacket heat exchangers, liquid-liquid contact heat exchangers, air heat exchangers, A heat exchanger and also a finned tubular heat exchanger can be mentioned. The heat exchanger system should preferably have two or more heat exchangers, since a portion of the high boiling point byproducts contained in the product gas may be precipitated while the temperature of the product gas is set to the desired temperature. If the two or more heat exchangers provided are arranged in parallel so that the divided cooling of the obtained product gas is made possible in the heat exchanger, the amount of high boiling point by-products deposited in the heat exchanger is reduced and the operating time of the heat exchanger can be prolonged . As an alternative to the above-described method, the two or more heat exchangers provided may be arranged in parallel. The product gas may be supplied to one or more but not all heat exchangers and these heat exchangers may be alternated by other heat exchangers after a certain period of operation. In this way, cooling can be continued and a portion of the heat of reaction can be recovered while at the same time removing the high boiling point byproducts deposited in one of the heat exchangers. As the above-mentioned organic solvent, any non-limiting solvent, for example, an aromatic hydrocarbon solvent such as toluene, xylene, etc., or an aqueous solution of an aqueous alkaline solvent such as sodium hydroxide may be used so long as it can dissolve the high boiling point by- .

If the product gas stream contains only trace amounts of oxygen, a process step of removing residual oxygen from the product gas stream may be performed. The residual oxygen can intervene as long as it can cause the formation of butadiene peroxide in subsequent processing steps and can act as an initiator of the polymerization reaction. Unstabilized 1,3-butadiene can form dangerous butadiene peroxide in the presence of oxygen. The peroxide is a viscous liquid. Its density is higher than that of butadiene. They are also only slightly soluble in liquid 1,3-butadiene, so they settle at the bottom of the storage container. Despite its relatively low chemical reactivity, peroxides are highly unstable compounds that can spontaneously decompose at temperatures in the range of 85-110 ° C. An extraordinary danger is the high impact sensitivity of the peroxide that explodes due to the explosive power of the explosive. The risk of polymer formation exists especially where butadiene is separated by distillation and where it can lead to deposits of polymer ("popcorn" formation) in the column. The removal of oxygen is preferably carried out immediately after the oxidative dehydrogenation. Generally, a catalytic combustion step in which oxygen reacts with hydrogen added in this step in the presence of a catalyst is carried out for this purpose. This reduces the oxygen content to a small amount.

The product gas from the O ₂ removal step is then brought to the same temperature level as described for the downstream region of the ODH reactor. Cooling of the compressed gas is performed, for example, by a heat exchanger, which can be configured as a multistage heat exchanger, a spiral heat exchanger or a plate heat exchanger. The heat removed here is preferably used for heat accumulation in the process.

Most of the high boiling point secondary component and water can subsequently be separated from the product gas stream by cooling. This separation is preferably carried out in quenching. Such quenching may comprise one or more steps. It is preferable to use a method of bringing the product gas directly into contact with the cooling medium and cooling it. While the cooling medium is not subject to any particular limitation, it is preferred to use water or an alkaline aqueous solution. This is a gas stream in which n-butane, 1-butene, 2-butene, butadiene, possibly oxygen, hydrogen, water vapor and small amounts of methane, ethane, ethene, propane and propene, isobutene, carbon oxides and inert gases remain . Also, trace amounts of high boiling point components that were not quantitatively removed from quenching may remain in the product gas stream.

The product gas stream from the quench is subsequently compressed in one or more compression stages and subsequently cooled so that one or more condensate streams containing water are condensed and condensed into n-butane, 1-butene, 2-butene , Butadiene, possibly hydrogen, water vapor and a gaseous stream comprising methane, ethane, ethene, propane and propene, isobutene, carbon oxides and inert gases, possibly oxygen and hydrogen, in minor amounts. Compression can be done in one or more steps. Overall, the gas stream is compressed at a pressure in the range of 1.0 to 4.0 bar (absolute) to a pressure in the range of 3.5 to 20 bar (absolute). After each compression step, a cooling step is carried out to cool the gas stream to a temperature in the range of 15 to 60 占 폚. Whereby the condensate stream may also include multiple streams in the case of multistage compression. The condensate stream generally contains at least 80 wt.%, Preferably at least 90 wt.% Water and further comprises a small amount of low boiling materials, C4-hydrocarbons, oxygenates and carbon oxides.

Suitable compressions are, for example, turbo compressors, rotary piston compressors and reciprocating piston compressors. The compressor can be driven, for example, by an electric motor, an expander or a gas turbine or a steam turbine. The typical compression ratio (outlet pressure: inlet pressure) per compressor stage ranges from 1.5 to 3.0, depending on the configuration. Cooling of the compressed gas is performed, for example, by a heat exchanger, which can be configured as a multistage heat exchanger, a spiral heat exchanger or a plate heat exchanger. The coolant used in the heat exchanger is a cooling water or heat transfer oil. It is also desirable to use air cooling with a blower.

A stream comprising butadiene, butene, butane, an inert gas and possibly carbon oxides, oxygen, hydrogen and low boiling hydrocarbons (methane, ethane, ethene, propane, propene) and small amounts of oxygenate, .

The separation of the low boiling secondary components from the product gas stream can be effected by conventional separation methods such as distillation, rectification, membrane treatment, absorption or adsorption.

To separate any hydrogen contained in the product gas stream, the product gas mixture may optionally pass through a membrane, which is only permeable to molecular hydrogen, and generally constituted as a tube, after cooling, for example in a heat exchanger. The molecular hydrogen separated in this manner can be used for hydrogenation, if necessary, at least partially, if necessary, or otherwise handed over, for example, to produce electrical energy in a fuel cell.

The carbon dioxide contained in the product gas stream can be separated by a CO ₂ gas scrub. Carbon dioxide scrubbing can be performed after a separate combustion step in which the carbon monoxide is selectively oxidized to carbon dioxide.

(Methane, ethane, ethene, propane, propene) and an inert gas, such as possibly nitrogen, can be used as the adsorbing / desorbing agent in a preferred embodiment of the process, are separated by a high-boiling absorption medium in a desorption cycle, C ₄ - to provide an essentially C ₄ product gas stream consisting of a hydrocarbon. Generally, the C ₄ product gas stream comprises at least 80 vol%, preferably at least 90 vol%, particularly preferably at least 95 vol% C ₄ -hydrocarbons, essentially n-butane, 2-butene and butadiene .

For this purpose, the product gas stream is contacted with an inert adsorption medium in the absorption step, after the preliminary removal of water, and the C ₄ -hydrocarbons are absorbed in the inert adsorption medium to form a C ₄ -hydrocarbon-loaded absorption medium and the remaining gas constituents To provide tailgas. In the desorption step, the C ₄ -hydrocarbons are released from the absorption medium again.

The absorption step may be carried out in any suitable absorption column known to those skilled in the art. Absorption can be carried out simply by passing the product gas stream through the absorption medium. However, it can also be carried out in a column or in a rotary absorber. Absorption can be performed by co-current, counter current or cross flow. The absorption is preferably carried out in countercurrent. Suitable absorption columns include, for example, tray columns with bubble cap trays, centrifuge trays and / or sieve trays, structural packing, sheet metal packing with a specific surface area of, for example, 100 to 1000 m 2 / m 3, A column with Pack (Mellapak) 250 Y, and a column with random packing. However, it is also possible to use dripping tops and spray towers, graphite block absorbers, surface absorbers such as thick film absorbers and thin film absorbers and also rotating columns, plate scrubbers, cross-spray scrubbers and rotary scrubbers.

In one embodiment, a stream comprising butadiene, butene, butane and / or nitrogen and possibly oxygen, hydrogen and / or carbon dioxide is fed to the lower region of the absorption column. In the upper region of the absorption column, a stream comprising solvent and optionally water is introduced.

The inert absorbing medium used in the absorption step is generally a high boiling point non-polar solvent having a solubility which is considerably greater than the solubility of the remaining gas constituents in which the C ₄ -hydrocarbon mixture to be separated is to be separated. Suitable absorbent medium is a relatively non-polar organic solvent, for example an aliphatic C ₈ -C ₁₈ - alkanes or aromatic hydrocarbons, such as five days middle fractions from paraffin distillation, toluene or having a bulky ether, or a mixture of these solvents; Polar solvents such as 1,2-dimethyl phthalate may be added to these. Further suitable absorption media are esters of phthalic acid with benzoic acid esters and straight chain C ₁ -C ₈ -alkanols and also heat transfer oils such as biphenyl and diphenyl ethers, chlorinated derivatives thereof and also triarylalkenes. A suitable absorbent medium is preferably an azeotropic composition having, biphenyl and a mixture of diphenyl ether, for example, ^® commercially available dipil (Diphyl). This solvent mixture often contains dimethyl phthalate in an amount of 0.1 to 25% by weight.

Suitable absorption media are fractions obtained from octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane and octadecane or refinery streams and include the abovementioned linear alkanes as main components do.

In a preferred embodiment, an alkane mixture such as tetradecane (industrial C14-C17 fraction) is used as the solvent for absorption.

At the top of the absorption column there may be introduced essentially inert gases, carbon oxides, possibly butane, butenes such as 2-butene and butadiene, possibly oxygen, hydrogen and low boiling hydrocarbons (e.g. methane, ethane, Pen) and water vapor. This stream can be fed in part into the ODH reactor or the O ₂ elimination reactor. This allows, for example, the feed stream to be sent into the ODH reactor so that it can be adjusted to the desired C ₄ -hydrocarbon content.

The C ₄ -hydrocarbon loaded solvent stream is introduced into the desorption column. According to the present invention, all of the columns known to those skilled in the art are suitable for this purpose. In one method variant, the desorption step is carried out by reduced pressure and / or heating of the loaded solvent. A preferred method variant is the introduction of fresh vapor to the bottom of the desorber and / or the introduction of stripping vapors. The solvent that has greatly reduced in C ₄ -hydrocarbons can be fed to the phase separation as a mixture with the condensed vapor (water), so that the water is separated from the solvent. All devices known to those skilled in the art are suitable for this purpose. It is also possible to use water separated from the solvent for the production of the stripping vapor.

From 70 to 100% by weight of solvent and from 0 to 30% by weight of water, particularly preferably from 80 to 100% by weight of solvent and from 0 to 20% by weight of water, in particular from 85 to 95% by weight of solvent and from 5 to 15% Of water is preferably used. The absorbing medium that has been regenerated in the desorption step is recycled to the absorption step.

The separation is generally not completely perfect and consequently, depending on the type of separation, small amounts or only minor amounts of additional gaseous constituents, especially high boiling point hydrocarbons, can be present in the C ₄ product gas stream. The reduction of the volumetric flow induced by the separation also reduces the burden on subsequent processing steps.

C ₄ product gas streams consisting essentially of n-butane, butenes such as 2-butene and butadiene generally contain 20 to 80% by volume of butadiene, 20 to 80% by volume of n-butane, 0 to 10% Butene and 0 to 50% by volume of 2-butene, the total amount being 100% by volume in total. A small amount of isobutane may also be included.

The C ₄ product gas stream may subsequently be separated into a stream consisting essentially of n-butane and 2-butene and a stream consisting of butadiene by extractive distillation. The stream consisting essentially of n-butane and 2-butene can be recycled, in whole or in part, to the C ₄ feed to the ODH reactor. Since the butene isomer in this recycle stream consists essentially of 2-butene and this 2-butene is more oxidatively dehydrogenated to butadiene than 1-butene in general, the isomerization of the catalyst to the recycle stream prior to introduction into the ODH reactor Process can be carried out. In this catalytic process, an isomer distribution corresponding to the isomer distribution in thermodynamic equilibrium can be established.

Extractive distillation, for example, the literature ( "Erdoel und Kohle - Erdgas - Petrochemie", Volume 34 (8), pages 343 to 346), or ( "Ullmanns Enzyklopaedie der Technischen Chemie" , Volume 9, 4 th edition 1975, pages 1 to 18). For this purpose, the C ₄ product gas stream is contacted with an extractant, preferably N-methylpyrrolidone (NMP) / water mixture, in the extraction zone. The extraction zone is generally in the form of a scrubbing column comprising trays, random packing elements or alignment packings as internal structures. It has generally 30 to 70 theoretical stages to achieve a sufficiently good separation action. The scrubbing column preferably has a backwash zone at the top of the column. This backwash zone serves to recover the extractant contained in the gas phase by a liquid hydrocarbon runback, and the overhead fraction is pre-condensed for that purpose. The mass ratio of the extractant to the C ₄ product gas stream in the feed of the extraction zone is generally from 10: 1 to 20: 1. The extractive distillation is preferably carried out at a temperature in the range from 100 to 250 ° C, in particular in the range from 110 to 210 ° C at the bottom, at a temperature in the range from 10 to 100 ° C in the upper part, especially in the range from 20 to 70 ° C, At a pressure in the range of 3 to 8 bar. The extractive distillation column preferably has from 5 to 70 theoretical stages.

Suitable extraction agents include butyrolactone, nitriles such as acetonitrile, propionitrile, methoxypropionitrile, ketones such as acetone, furfural, N-alkyl-substituted lower aliphatic acid amides such as dimethylformamide, diethyl Alkylamines such as formamide, dimethylacetamide, diethylacetamide, N-formyl-morpholine, N-alkyl-substituted cyclic acid amides (lactams) such as N-alkylpyrrolidones, especially N-methylpyrrolidone )to be. Alkyl-substituted lower aliphatic acid amides or N-alkyl-substituted cyclic acid amides are generally used. Dimethylformamide, acetonitrile, furfural and especially NMP are particularly advantageous.

However, these extracting agents, for example mixtures of NMP and acetonitrile with each other, with these extracting agents and / or tertiary butyl ethers, such as methyl tert-butyl ether, ethyl tert-butyl ether, A mixture of butyl ether, n-butyl tert-butyl ether or isobutyl tert-butyl ether can also be used. Particularly suitable extractants are preferably NMP in aqueous solution, preferably comprising from 0 to 20% by weight of water, particularly preferably from 7 to 10% by weight of water, in particular 8.3% by weight of water.

The overhead product stream from the extractive distillation column contains essentially butane and butene and small amounts of butadiene and is taken off in gaseous or liquid form. Generally, streams consisting essentially of n-butane and 2-butene contain 50 to 100% by volume of n-butane, 0 to 50% by volume of 2-butene and 0 to 3% by volume of additional constituents such as isobutane , Isobutene, propane, propene and C ₅ ⁺ -hydrocarbons.

At the bottom of the extractive distillation column, a stream is obtained containing the extractant, water, butadiene and a minor proportion of butene and butane and fed into the distillation column. Among them, butadiene is obtained as a top or side outlet stream. A stream comprising an extractant and water, having a composition of a stream comprising an extractant and water corresponding to the composition introduced into the extraction, is obtained at the bottom of the distillation column. The stream comprising the extractant and water is preferably recycled to the extractive distillation.

The extractant solution is transferred to the desorption zone where the butadiene is desorbed from the extraction solution. The desorption zone may be configured in the form of a scrubbing column having, for example, 2 to 30, preferably 5, 5 theoretical stages and optionally a backwash zone having, for example, four theoretical stages . This backwash zone serves to recover the extractant contained in the gas phase by the liquid hydrocarbon runbag, and the overhead fraction is pre-condensed for that purpose. An alignment packing, tray or random packing is provided as an internal structure. The distillation is preferably carried out at a temperature in the range from 100 to 300 ° C at the bottom, in particular in the range from 150 to 200 ° C, and at a temperature in the range from 0 to 70 ° C, in particular from 10 to 50 ° C in the upper part. The pressure in the distillation column is preferably in the range of 1 to 10 bar. Generally, in the desorption zone, lower pressure and / or higher temperature prevails over the extraction zone.

The desired product stream obtained at the top of the column generally comprises 90 to 100% by volume of butadiene, 0 to 10% by volume of 2-butene and 0 to 10% by volume of n-butane and isobutane. To further purify the butadiene, additional distillation can be performed as described in the prior art.

The following examples illustrate the invention.

The parameter conversion ratio X and the selectivity S calculated in the embodiment were determined as follows:

(XXX _in ) is the molar amount of component XXX at the reactor inlet, moles (XXX _out ) is the molar amount of component XXX at the reactor outlet and butene is 1-butene, cis-2-butene, Butene and isobutene.

<Examples>

Catalyst preparation

Example  One

Two solutions A and B were prepared.

Solution A:

3200 g of water was placed in a 10 L stainless steel port. While stirring with an anchor stirrer, 5.2 g of KOH solution (32 wt% KOH) was added to the initially charged water. The solution was heated to 60 &lt; 0 &gt; C. Then 1066 g of ammonium chilled molybdodecanoate solution ((NH ₄ ) ₆ Mo ₇ O ₂₄ * 4 H ₂ 0, 54 wt% Mo) was added in small portions over a period of 10 minutes. The resulting suspension was stirred for another 10 minutes.

Solution B:

1771 g of a cobalt (II) nitrate solution (12.3 wt% of Co) was placed in a 5 L stainless steel pot and heated to 60 캜 with stirring (anchor stirrer). Subsequently, 645 g of iron (III) nitrate solution (13.7% by weight of Fe) was added in small portions at a time over a period of 10 minutes while maintaining the temperature. The formed solution was stirred for another 10 minutes. Subsequently, 619 g of bismuth nitrate solution (10.7% by weight of Bi) was added while maintaining the above temperature. After stirring for an additional 10 minutes, 109 g of chromium (III) nitrate was added in small portions as a solid and the resulting dark red solution was stirred for another 10 minutes.

Solution B was pumped to Solution A over a period of 15 minutes by a peristaltic pump while maintaining a temperature of 60 占 폚. During and after the addition, the mixture was stirred by means of a high-speed mixer (Ultra-Turrax). After the addition was complete, the mixture was stirred for another 5 minutes. Then 93.8 g of SiO ₂ suspension (Ludox; about 49% of SiO ₂ , Grace) was added and the mixture was stirred for another 5 minutes.

The resulting suspension was spray dried over a period of 1.5 hours in a spray dryer (spray head No. FOA1, rotation speed: 25,000 rpm) from NIRO. During this time the temperature of the initial charge was maintained at 60 占 폚. The gas inlet temperature of the spray dryer was 300 캜, and the gas outlet temperature was 110 캜. The powder obtained had a particle size (d ₅₀ ) of less than 40 μm.

The obtained powder was mixed with 1% by weight of graphite, compressed twice under a pressure of 9 bar, and crushed by a sieve having a mesh opening of 0.8 mm. The crushed material was again mixed with 2% by weight of graphite and the mixture was pressed by a Kilian S100 tablet press to provide a 5 x 3 x 2 mm (outer diameter x length x inner diameter) ring.

The resulting catalyst precursor was calcined batchwise (500 g) in a convection furnace (Type K, 750/2 S, 55 l internal volume) from Heraeus, Germany. For this purpose I used the following program:

- heated to 130 ° C in 72 minutes, maintained for 72 minutes

- heated to 190 ° C in 36 minutes, held for 72 minutes

- Heating at 220 ° C in 36 minutes, holding for 72 minutes

- heated to 265 ° C in 36 minutes, maintained for 72 minutes

- heated to 380 ° C in 93 minutes, held for 187 minutes

- heated to 430 ° C in 93 minutes, held for 187 minutes

- heated to 490 ℃ in 93 minutes, maintained for 467 minutes

After calcination, the calculated stoichiometry Mo ₁₂ Co ₇ Fe ₃ Bi _{0 .6} K _{0 .08} Cr _{0 . 5} Si _{1 .} A catalyst with ₆ O _x was obtained.

Example  2

The calcined ring obtained in Example 1 was pulverized into powder.

The support (a stitite ring having dimensions of 5 x 3 x 2 mm (outer diameter x height x inner diameter)) was coated with this precursor composition. For this purpose, 1054 g of the support was placed in a coating drum (2 L internal volume, inclination angle of the central drum axis = 30 DEG for the horizontal line). The drum was set to the number of revolutions (25 rpm). About 60 ml of a liquid binder (1: 3 mixture of glycerol: water) was sprayed onto the support over a period of about 30 minutes by an atomizer nozzle operated by compressed air (spraying air: 500 standard l / h). The nozzle was installed in the upper half of the rolling-down section of the drum so as to wet the support to be conveyed. 191 g of the fine powdery precursor composition of the milling catalyst was introduced into the drum by means of a powder screw, at which point the powder was added in a rolling-down section but below the spray cone. Powder was metered in so as to obtain uniform distribution of powder on the surface. After the coating was completed, the resulting coated catalyst consisting of the precursor composition and the support was dried in a drying oven at 300 캜 for 4 hours.

<Dehydration experiment>

The dehydrogenation experiments were carried out in a selective reactor. The sorting reactor was a salt bath reactor having a length of 120 cm and an inner diameter of 14.9 mm, and had a temperature sensor sheath with an outer diameter of 3.17 mm. Multiple temperature sensor elements with seven measurement points were placed in the temperature sensor sheath. The bottom four measurement points had a gap of 10 cm and the top four measurement points had a gap of 5 cm.

Butane and raffinate II or 1-butene were metered in liquid form through a Coriolis flow meter at about 10 bar, mixed in a static mixer and depressurized and vaporized into a subsequently heated vaporizer section. This gas was then mixed with nitrogen and introduced into a preheater with a statorite layer. Water was metered in liquid form and vaporized in a stream of air at the vaporizer coil. The air / steam mixture was combined with the N ₂ / raffinate II / butane mixture in the lower region of the preheater. The fully mixed feed gas was then fed into the reactor, at which time the on-line GC analytical stream could be withdrawn. The analytical stream was likewise withdrawn from the product gas leaving the reactor and analyzed to determine the volume ratio of CO and CO ₂ by on-line GC measurement or by an IR analyzer. After the bifurcation for the analytical line, there was a pressure regulating valve to set the pressure level in the reactor.

Example  3

A 6 cm long after-layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm was placed on the catalyst support grid at the lower end of the screening reactor. Then 44 g of the catalyst obtained in Example 1 were mixed well with 88 g of the stearate ring having the same geometry and introduced into the reactor (146 ml layer volume, 88 cm layer height). Following the catalyst layer was a 7 cm long reserve layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm.

200 &lt; / RTI &gt; standard l / h of reaction gas having a composition of 8% 1-butene, 2% butane, 7.5% oxygen, 15% water and 67.5% The reactor was operated. The product gas was analyzed by GC. Conversion rate and selectivity data are shown in Table 1.

Then a mixture of 10% by volume of oxygen, 80% by volume of nitrogen and 10% by volume of steam was passed over the catalyst for 20 hours and heated to 400 DEG C during the course. The formed carbon oxides were recorded by an IR measuring instrument. The amount of carbon removed by combustion is also shown in Table 1.

Example 4

A 6 cm long after-layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm was placed on the catalyst support grid at the lower end of the screening reactor. 120 g of the catalyst obtained in Example 2 were then introduced into the reactor (18 g of active composition, 113 ml layer volume, 68 cm layer height). Following the catalyst layer was a 7 cm long reserve layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm.

Using a reaction gas of 200 standard l / h having a composition of 8 vol% 1-butene, 2 vol% butane, 7.5 vol% oxygen, 15 vol% steam and 67.5 vol% nitrogen, The reactor was operated at temperature for 50 hours. The product gas was analyzed by GC. Conversion rate and selectivity data are shown in Table 1.

Then a mixture of 10% by volume of oxygen, 80% by volume of nitrogen and 10% by volume of steam was passed over the catalyst for 20 hours and heated to 400 DEG C during the course. The formed carbon oxides were recorded by an IR measuring instrument. The amount of carbon removed by combustion is also shown in Table 1.

The original conversion rate was substantially restored by removing the carbonaceous deposits by combustion.

Example  5

A 6 cm long after-layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm was placed on the catalyst support grid at the lower end of the screening reactor. 120 g of the catalyst obtained in Example 2 were then introduced into the reactor (18 g of active composition, 113 ml layer volume, 68 cm layer height). Following the catalyst layer was a 7 cm long reserve layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm.

At a bath temperature of 384 [deg.] C using a reaction gas of 200 standard l / h having a composition of 8 vol% butene, 2 vol% butane, 7.5 vol% oxygen, 15 vol% steam and 67.5 vol% The reactor was operated for 20 hours (per manufacturing step). The product gas was analyzed by GC. The conversion rate and selectivity data are shown in Table 2.

After each stage of the preparation, a mixture of 10 vol% oxygen, 80 vol% nitrogen and 10 vol% steam was passed over the catalyst at the same temperature (regeneration step). The formed carbon oxides were recorded by an IR measuring instrument. The amount of carbon removed by combustion is also shown in Table 2. The preparation and regeneration steps (combustion-elimination operation) of the five cycles are shown in Table 2.

After the cycle, the catalyst was operated for an additional 20 hours using the gas described above. The reactor was then flushed with a gas having a composition of 10% by volume of oxygen, 10% by volume of steam and 10% by volume of nitrogen, while simultaneously raising the temperature to 400 DEG C to determine the total amount of carbon removed by combustion. The amount of carbon removed by combustion is shown in Table 2.

Example  6

A 6 cm long after-layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm was placed on the catalyst support grid at the lower end of the screening reactor. Then 44 g of the catalyst obtained in Example 1 were mixed well with 88 g of the stearate ring having the same geometry and introduced into the reactor (146 ml layer volume, 88 cm layer height). Following the catalyst layer was a 7 cm long reserve layer containing 16 g of stearate balls with a diameter of 3.5-4.5 mm.

Using a reaction gas of 200 standard l / h having a composition of 8 vol% butene, 2 vol% butane, 7.5 vol% oxygen, 15 vol% steam and 67.5 vol% nitrogen, The reactor was operated for 20 hours (per manufacturing step). The product gas was analyzed by GC. Conversion rate and selectivity data are shown in Table 3.

After each preparation step, a mixture of 10% by volume of oxygen, 80% by volume of nitrogen and 10% by volume of water was passed over the catalyst for 30 minutes at the same temperature (regeneration step). The formed carbon oxides were recorded by an IR measuring instrument. The amount of carbon removed by combustion is also shown in Table 3. The preparation and regeneration steps (combustion-elimination operation) of the five cycles are shown in Table 3.

After the cycle, the catalyst was operated for an additional 20 hours using the gas described above. The reactor was then flushed with a gas having a composition of 10% by volume of oxygen, 10% by volume of steam and 90% by volume of nitrogen, while simultaneously raising the temperature to 400 DEG C to determine the total amount of carbon removed by combustion. The amount of carbon removed by combustion is shown in Table 3.

In the amount removed by less than 5% of the total carbon deposited, the activity was no longer recovered to a satisfactory level.

Claims (8)

A process for the oxidative dehydrogenation of n-butene to butadiene, comprising at least two production steps (i) and at least one regeneration step (ii)
(i) in one production step, the starting gas mixture comprising n-butene is mixed with an oxygen-containing gas and, at a temperature of from 220 to 490 DEG C in a fixed-bed reactor, at least molybdenum and further metal, Contacting with a multi-metal oxide catalyst arranged in a catalyst bed,
Before the relative reduction in conversion at a given temperature is > 25%
(ii) regenerating the multimetal oxide catalyst by passing the oxygen-containing regeneration gas mixture over a fixed catalyst bed at a temperature of 200 to 450 DEG C to remove carbon deposited on the catalyst by combustion,
The regeneration step (ii) is carried out between two preparation steps (i)
In each regeneration step (ii), from 2 to 50% by weight of the carbon deposited in the catalyst is removed by combustion. 2. The process of claim 1, wherein the oxygen-containing regeneration gas mixture comprises from 0.5 to 22 vol% oxygen. The process of any preceding claim, wherein the oxygen-containing recycle gas mixture comprises 0 to 30% by volume of steam. 4. The process according to any one of claims 1 to 3, wherein the temperature in the production step (i) is from 350 to 410 占 폚. The process according to any one of claims 1 to 4, wherein the temperature in the regeneration step (ii) is 0 to 20 ° C higher than the temperature in the production step (i). 6. The process according to any one of claims 1 to 5, wherein, during the regeneration step (ii), 10 to 35% by weight of the carbon deposited on the catalyst is removed by combustion. 6. The process according to any one of claims 1 to 5, wherein, during the regeneration step (ii), 10 to 25% by weight of the carbon deposited on the catalyst is removed by combustion. 8. A process according to any one of claims 1 to 7, wherein the multimetal oxide comprising molybdenum and at least one further metal has the formula (I)
(I)
Mo ₁₂ Bi _a Fe _b Co _c Ni _d Cr _e X ¹ _f X ² _g O _x
In the above equation, the variables have the following meanings:
X ¹ = W, Sn, Mn, La, Ce, Ge, Ti, Zr, Hf, Nb, P, Si, Sb, Al, Cd and / or Mg;
X ² = Li, Na, K, Cs and / or Rb;
a = 0.1 to 7, preferably 0.3 to 1.5;
b = 0 to 5, preferably 2 to 4;
c = 0 to 10, preferably 3 to 10;
d = 0 to 10;
e = 0 to 5, preferably 0.1 to 2;
f = 0 to 24, preferably 0.1 to 2;
g = 0 to 2, preferably 0.01 to 1; And
x = a number determined by the valency and abundance ratio of elements other than oxygen in the formula (I).