JP2016503073A - Process for producing 1,3-butadiene from n-butenes by oxidative dehydrogenation - Google Patents

Abstract

The present invention is a process for the production of butadiene from n-butenes, comprising the following steps: A) preparing a starting gas stream (a) containing n-butenes, B) said n-butenes Feeding the starting gas stream (a) and the oxygen-containing gas into at least one oxidative dehydrogenation zone and oxidative dehydrogenation of n-butenes to butadiene, butadiene, unreacted obtaining a product gas stream (b) containing n-butenes, water vapor, oxygen, low-boiling hydrocarbons, high-boiling subcomponents, optionally carbon oxides and optionally inert gases, Ca) said products Cooling the gas stream (b) by contact with an organic solvent as a coolant, Cb) at least one aqueous condensate by compressing the product gas stream (b) in at least one compression step A step (c1) and a gas stream (c2) containing butadiene, n-butenes, water vapor, oxygen, low-boiling hydrocarbons, optionally carbon oxides and optionally inert gases, D) said gas From stream (c2), C4 containing butadiene and n-butenes is obtained as gas stream (d2), a non-condensable, low-boiling gas component comprising oxygen, low-boiling hydrocarbons, optionally carbon oxides and optionally inert gases. Separation by absorption of hydrocarbons in the absorbent yields an absorbent stream loaded with C4 hydrocarbons and the gas stream (d2), and subsequently the C4 from the loaded absorbent stream. Desorbing hydrocarbons to obtain a C4 product gas stream (d1); E) the C4 product stream (d1) by extractive distillation using a selective solvent for butadiene by butadiene And a material stream (e1) containing a selective solvent and a material stream (e2) containing n-butenes, and F) a material stream (e1) containing the butadiene and the selective solvent. Distilling to obtain a material stream (f1) consisting essentially of the selective solvent and a material stream (f2) containing butadiene.

Description

  The present invention relates to a process for producing 1,3-butadiene from n-butenes by oxidative dehydrogenation (ODH).

  Butadiene is an important basic chemical, for example for the production of synthetic rubbers (butadiene-homopolymers, styrene-butadiene-rubbers or nitrile-rubbers) or thermoplastic terpolymers (acrylonitrile-butadiene-styrene- Copolymer). Butadiene reacts further to sulfolane, chloroprene and 1,4-hexamethylenediamine (via 1,4-dichlorobutene and adipic acid dinitrile). Dimerization of butadiene can further produce vinylcyclohexene, which can be dehydrogenated to styrene.

Butadiene can usually be produced by thermal cracking of saturated hydrocarbons (steam cracking), usually starting from naphtha as raw material. In naphtha steam cracking, methane, ethane, ethene, acetylene, propane, propene, propyne, allene, butanes, butenes, butadiene, butyne include methyl allene, hydrocarbon mixture consisting of C ₅ or higher hydrocarbons occurs .

Butadiene can also be obtained by oxidative dehydrogenation of n-butenes (1-butene and / or 2-butene). As the starting mixture for the oxidative dehydrogenation of n-butenes to butadiene (oxidative dehydrogenation, ODH), any mixture containing any n-butenes can be used. For example, n- butenes as main components obtained by the separation of the butadiene and isobutene from C ₄ fraction naphtha cracker The fractions containing the (1-butene and / or 2-butene) can be used. Furthermore, gas mixtures comprising 1-butene, cis-2-butene, trans-2-butene or mixtures thereof obtained by dimerization of ethylene can also be used as starting gas. Furthermore, as a starting gas, a gas mixture containing n-butenes obtained by fluid catalytic cracking (FCC) can be used.

  The oxidative dehydrogenation of butenes to butadiene is basically known.

  US 2012/0130137 A1 describes a process for the oxidative dehydrogenation of butenes to butadiene using, for example, catalysts containing molybdenum, bismuth and generally other metal oxides. For the sustained activity of such catalysts for oxidative dehydrogenation, a critical minimum of oxygen partial pressure in the gas atmosphere to avoid excessive reduction of the catalyst and thereby performance loss Is essential. For this reason and in general, it is not possible to work in an oxidative dehydrogenation reactor (ODH reactor) with a stoichiometric oxygen input or complete oxygen conversion. In US2012 / 0130137, for example, an oxygen content of 2.5 to 8% by volume in the starting gas is described.

  The need for oxygen excess for such catalyst systems is generally known and is reflected in the process conditions when using such catalysts. As a representative, the latest paper by Jung et al. (Catal. Surv. Asia 2009, 13, 78-93; DOI 10.1007 / s10563-009-9069-5 and Applied Catalysis A: General 2007, 317, 244-249; DOI 10.1016 / j.apcata.2006.10.021).

  However, the presence of oxygen in addition to butadiene in the aftertreatment section behind the ODH reactor stage of the process carried out under such oxygen excess is fundamentally dangerous. The formation and increase of organic peroxides should be investigated, especially in the liquid phase. These risks are discussed, for example, in D. S. Alexander (Industrial and Engineering Chemistry 1959, 51, 733-738).

  JP-A2011-006381 (Mitsubishi) describes the danger of peroxide formation in the post-treatment part of the process for producing conjugated alkadiene. For that solution, the addition of a polymerization inhibitor to the absorption solution for the process gas and the adjustment of the maximum peroxide content of 100 ppm by heating the absorption solution are described. However, it does not describe the avoidance or suppression of peroxides in the forward process steps. In particular, the cooling step by water quenching of the ODH reactor effluent should be regarded as important. Since the organic peroxides that are formed are hardly soluble in water, they may precipitate without being discharged with the aqueous purge stream and accumulate in the apparatus in solid or liquid form. At the same time, the temperature of the water quench is not high enough to assume that the peroxide formed is sufficiently high and can decompose continuously.

  In the catalytic oxidative dehydrogenation, high-boiling subcomponents such as maleic anhydride, phthalic anhydride, benzaldehyde, benzoic acid, ethylbenzene, styrene, fluorenone, anthraquinone and the like can be formed. Such deposits can hinder controlled work because they can lead to blockage and increased pressure loss in the reactor or in the post-treatment area behind the reactor. The high-boiling by-component deposits described above can also impair the function of the heat exchanger or can damage mobile devices such as compressors. Water vapor volatile compounds such as fluorenone can leach out of water operated quenching equipment and accumulate in the gas exhaust conduit behind it. As a result, there is also a risk that basically the solid deposit is post-connected in the part of the device, for example to the compressor, where damage is caused.

  US 2012/0130137 A1 paragraph [0122] also points out the problem of high-boiling by-products. In particular, mention may be made of phthalic anhydride, anthraquinone and fluorenone which are typically present in the product gas at a concentration of 0.001 to 0.10% by volume. In US 2012/0130137 A1 paragraphs [0124] to [0126], it is recommended that the hot reactor effluent gas be first cooled to 5-100 ° C., usually by direct contact with the cooling liquid (quenching tower). ing. Examples of the cooling liquid include water and an aqueous alkaline solution. The problem of clogging due to high boilers from the product gas in quenching or from polymerization products of high boiling by-products from the product gas is clearly stated. For this reason, it is preferable that by-products having a high boiling point are taken as little as possible from the reaction section to the cooling section (quenching).

  JP-A 2011-001341 describes a two-stage cooling for a process for the oxidative dehydrogenation of alkenes to conjugated alkadienes. In that case, the product exhaust of the oxidative dehydrogenation is first adjusted to a temperature between 300 ° C. and 221 ° C. and then cooled again to a temperature between 99 ° C. and 21 ° C. In the paragraphs after paragraph [0066], it is preferable to use a heat exchanger for adjusting the temperature between 300 ° C. and 221 ° C., but in this case, a part of the high-boiling products derived from the product gas Can be precipitated in this heat exchanger. Therefore, JP-A 2011-001341 describes that the deposit is sometimes washed out from the heat exchanger with an organic solvent or an aqueous solvent. As the solvent, for example, an aromatic hydrocarbon such as toluene or xylene or an alkaline aqueous solvent such as an aqueous solution of sodium hydroxide is described. In order to avoid frequently stopping the process for cleaning the heat exchanger, JP-A2011-001341 is operated or cleaned in two parallel arrangements (so-called A / B method). A configuration with a heat exchanger is described.

  The object of the present invention is to provide a method for overcoming the above-mentioned drawbacks of the known methods. In particular, it is desirable to provide a method that avoids deposition by high-boiling organic by-components in equipment post-connected to oxidative dehydrogenation (ODH). Furthermore, it would be desirable to provide a method that avoids possible deposition of organic peroxides. Furthermore, the object of the present invention is to reduce the high load in the dissolved, emulsified or suspended form of wastewater with organic compounds and the generation of wastewater loaded with organic compounds.

The object is a method for producing butadiene from n-butenes, which comprises the following steps:
A) providing a starting gas stream (a) containing n-butenes;
B) A starting gas stream (a) containing said n-butenes and an oxygen-containing gas are fed into at least one oxidative dehydrogenation zone and oxidatively dehydrogenated from n-butenes to butadiene. This gives a product gas stream (b) containing butadiene, unreacted n-butenes, water vapor, oxygen, low-boiling hydrocarbons, high-boiling subcomponents, optionally carbon oxides and optionally inert gases. Steps,
Ca) cooling the product gas stream (b) by contact with an organic solvent;
Cb) compressing said product gas stream (b) in at least one compression step, so that at least one aqueous condensate stream (c1) and butadiene, n-butenes, water vapor, oxygen, low-boiling hydrocarbons, To obtain a gas stream (c2) containing carbon oxide and optionally an inert gas,
D) From the gas stream (c2), butadiene and n-butene are obtained as a gas stream (d2) from the gas stream (d2), which contains oxygen, low-boiling hydrocarbons, optionally carbon oxides and optionally inert gases. by separating by absorption in C ₄ in absorbent hydrocarbon containing class, and C ₄ absorbent stream loaded with hydrocarbons, the gas flow (d2) and were obtained and the load subsequently Desorbing said C ₄ hydrocarbons from an absorbent stream to obtain a C ₄ product gas stream (d1);
E) By subjecting the C ₄ product stream (d1) to extractive distillation using a selective solvent for butadiene, a material stream (e1) containing butadiene, a selective solvent, and a material stream (e2 containing n-butenes) ) And separating step,
F) distilling the material stream (e1) containing the butadiene and the selective solvent to obtain a material stream (f1) consisting essentially of the selective solvent and a material stream (f2) containing butadiene;
It is solved by the manufacturing method comprising:

  In step A), a starting gas stream containing n-butenes is prepared.

  According to the invention, an organic solvent is used in the cooling step Ca). These organic solvents generally have a higher solubility than water or alkaline aqueous solutions for high-boiling by-products that can lead to deposition and plugging in the plant part after the ODH reactor. Preferred organic solvents used as coolants are aromatic hydrocarbons, particularly preferably toluene, o-xylene, m-xylene, p-xylene or mixtures thereof.

  The following embodiments are preferred or particularly preferred variants of the method according to the invention.

  Said step Ca) is carried out in a plurality of steps Ca1) to Can), preferably in two steps and in two steps Ca1) and Ca2). In that case, it is particularly preferred that at least a part of the solvent is supplied as a coolant to the first step Ca1) after passing through the second step Ca2).

  Said step Cb) generally comprises at least one compression step Cba) and at least one cooling step Cbb). Preferably, in said at least one cooling step Cbb), the gas compressed in the compression step Cba) is contacted with a coolant. Particularly preferably, the cooling agent of the cooling step Cbb) contains the same organic solvent used as the cooling agent in step Ca). In one particularly preferred variant, at least a part of this coolant is fed as a coolant to step Ca) after at least one cooling step Cbb).

  Preferably, said step Cb) comprises a plurality of compression steps Cba1) to Cban) and a plurality of cooling steps Cbb1) to Cbbn), for example four compression steps Cba1) to Cba4) and four cooling steps Cbb1) to Cbb4). including.

Preferably step D) comprises steps Da) to Dc):
Da) absorbing C ₄ hydrocarbons containing butadiene and n-butenes in a high boiling absorbent to obtain an absorbent stream and a gas stream (d2) loaded with C ₄ hydrocarbons;
Db) removing oxygen from the C ₄ hydrocarbon loaded absorbent stream from step Da) by stripping with a non-condensable gas stream;
Dc) Desorbing C ₄ hydrocarbons from the loaded absorbent stream to obtain a C ₄ product gas stream (d1) consisting essentially of C ₄ hydrocarbons and containing less than 100 ppm oxygen. When,
including.

  Preferably the high boiling point absorbent used in step Da) is an aromatic hydrocarbon solvent, particularly preferably the aromatic hydrocarbon solvent used in step Ca), in particular toluene.

  A preferred embodiment of the method according to the invention is shown in FIGS. 1-3 and is described in detail below.

As the starting gas stream, pure n-butenes (1-butene and / or cis / trans-2-butene) may be used, but gas mixtures containing butenes may also be used. Such a gas mixture can be obtained, for example, by non-oxidative dehydrogenation of n-butane. Further, a fraction containing n-butenes (1-butene and cis- / trans-2-butene) as a main component obtained by separation of butadiene and isobutene from a naphtha cracked C ₄ fraction may be used. . Furthermore, a gas mixture obtained by dimerization of ethylene and containing pure 1-butene, cis-2-butene, trans-2-butene or mixtures thereof can also be used as starting gas. Furthermore, as a starting gas, a gas mixture containing n-butenes obtained by fluid catalytic cracking (FCC) can be used.

In one embodiment of the process according to the invention, a starting gas mixture containing n-butenes is obtained by non-oxidative dehydrogenation of n-butane. By combining non-oxidative catalytic dehydrogenation and oxidative dehydrogenation of the n-butenes formed, high yields of butadiene relative to the n-butane used can be obtained. In the non-oxidative catalytic dehydrogenation of n-butane, a gas mixture is obtained which contains secondary components in addition to butadiene, 1-butene, 2-butene and unreacted n-butane. Normal subcomponent hydrogen, steam, 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 dehydrogenation. Here, when dehydrogenation is carried out by supplying oxygen and additional hydrogen, the product gas mixture has a relatively high content of water vapor and carbon oxides. In the case of a working mode in which no oxygen is supplied, the product gas mixture of non-oxidative dehydrogenation has a relatively high content of hydrogen.

  In step B), a starting gas stream containing n-butenes and an oxygen-containing gas are fed to at least one dehydrogenation zone (ODH reactor (1)) and the butenes contained in the gas mixture. Is oxidatively dehydrogenated to butadiene in the presence of an oxidative dehydrogenation catalyst.

  Catalysts suitable for oxidative dehydrogenation are generally based on Mo-Bi-O containing multi-metal oxide systems, generally additionally containing iron. In general, the catalyst system still contains additional components such as potassium, cesium, magnesium, zirconium, chromium, nickel, cobalt, cadmium, tin, lead, germanium, lanthanum, manganese, tungsten, phosphorus, cerium, aluminum. Or it contains components such as silicon. Ferrite containing iron has also been proposed as a catalyst.

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

Examples for multimetal oxides containing Mo-Bi-Fe-O are multimetal oxides containing Mo-Bi-Fe-Cr-O or containing Mo-Bi-Fe-Zr-O. is there. Preferred systems are, 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 2530959 (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 2530959 and DE-A 2447825 (Mo ₁₂ BiFe ₃ Co _4.5 Ni _2.5 W _0.5 K _0.1 O _x ).

Suitable multimetal oxides and the preparation of these oxides are further described in US Pat. No. 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 ). U.S. Pat. No. 4,336,409 (Mo ₁₂ BiNi ₆ Cd ₂ Cr ₃ P _0.5 O _x ), DE-A 2600128 (Mo ₁₂ BiNi _0.5 Cr ₃ P _0.5 Mg _7.5 K _0.1 O _x + SiO ₂ ) and DE-A 2440329 (Mo ₁₂ BiCo) _4.5 Ni _2.5 Cr ₃ P _0.5 K _0.1 O _x ).

Particularly preferred catalytically active multimetal oxides containing molybdenum and at least one further metal are of the general formula (Ia):
_{Mo 12 Bi a Fe b Co c} Ni d Cr e X 1 f X 2 g O y (Ia)
[Where:
X ¹ is Si, Mn and / or Al,
X ² is 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 of an element different from oxygen in (Ia) under charge neutral conditions].

A catalyst in which the catalytically active oxide material has only Co (d = 0) of the two types of metals Co and Ni is preferable. X ¹ is preferably Si and / or Mn, and X ² is preferably K, Na and / or Cs, particularly preferably X ² is K.

Said molecular oxygen-containing gas generally contains more than 10% by volume, preferably more than 15% by volume, even more preferably more than 20% by volume of molecular oxygen. It is preferably air. The upper limit of the molecular oxygen content is generally 50% by volume or less, preferably 30% by volume or less, and even more preferably 25% by volume or less. Furthermore, any inert gas may be contained in the gas containing molecular oxygen. Possible inert gases include nitrogen, argon, neon, helium, CO, CO ₂ and water. The amount of inert gas is generally 90% by volume or less for nitrogen, preferably 85% by volume or less, and even more preferably 80% by volume or less. In the case of components other than nitrogen, the amount is generally 10% by volume or less, preferably 1% by volume or less.

  For the implementation of the oxidative dehydrogenation by complete conversion of n-butenes, gas mixtures having a molar ratio of oxygen: n-butenes of at least 0.5 are preferred. It is preferred to work with an oxygen: n-butene ratio value of 0.55-10. To adjust this value, the starting material gas may be mixed with oxygen or an oxygen-containing gas, for example air, and optionally additional inert gas or water vapor. The resulting oxygen-containing gas mixture is then fed to oxidative dehydrogenation.

  The reaction temperature for oxidative dehydrogenation is generally controlled by a heat exchange medium present around the reaction tube. As such a liquid heat exchange medium, for example, a melt of salts such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate, and a melt of metals such as sodium and mercury and alloys of various metals are considered. However, ionic liquids or heat transfer oils can also be used. The temperature of the heat exchange medium is between 220 and 490 ° C, preferably between 300 and 450 ° C, particularly preferably between 350 and 420 ° C.

  Based on the exothermic reaction of the ongoing reaction, the temperature in a certain section inside the reactor may be higher than the temperature of the heat exchange medium during the reaction, so-called hot spots are formed. The position and height of the hot spot are determined by the reaction conditions, but they can also be adjusted by the dilution ratio of the catalyst layer or the flow rate of the mixed gas. The difference between the hot spot temperature and the temperature of the heat exchange medium is generally from 1 to 150 ° C., preferably from 10 to 100 ° C., particularly preferably from 20 to 80 ° C. The temperature at the end of the catalyst bed is generally 0-100 ° C., preferably 0.1-50 ° C., particularly preferably 1-25 ° C. higher than the temperature of the heat exchange medium.

  Said oxidative dehydrogenation can be carried out in any fixed bed reactor known from the prior art, for example in a shelf oven, a fixed bed tubular reactor or a fixed bed multitubular reactor, or in a plate heat exchange reactor. . A multitubular reactor is preferred.

  Preferably, the oxidative dehydrogenation is carried out in a fixed bed tubular reactor or a fixed bed multitubular reactor. The reaction tube is generally made of steel (as are the other elements of a multi-tube reactor). The wall thickness of the reaction tube is generally 1 to 3 mm. The inner diameter of the reaction tube is generally (uniformly) 10-50 mm, or 15-40 mm, often 20-30 mm. The number of reaction tubes accommodated in the multitubular reactor generally ranges from 1000, or 3000, or 5000 and preferably at least 10,000. Often, the number of reaction tubes housed in a multitubular reactor is 15000-30000, or -40000, or 50,000. The length of the reaction tube usually reaches several meters, and typically the reaction tube length ranges from 1 to 8 m, often from 2 to 7 m, often 2.5 to 6 m.

  Furthermore, the catalyst layer provided in the ODH reactor (1) may consist of one single layer or two or more layers. These layers may consist of pure catalyst or may be diluted with a material that does not react with components derived from the starting gas or the product gas of the reaction. Furthermore, the catalyst layer may comprise a solid material catalyst or a supported shell catalyst.

  The product gas stream (2) leaving the oxidative dehydrogenation contains, in addition to butadiene, generally still unreacted 1-butene and 2-butene, oxygen and water vapor. As a secondary component, the gas stream is further generally carbon monoxide, carbon dioxide, inert gas (mainly nitrogen), low-boiling hydrocarbons such as methane, ethane, ethene, propane and propene, butane and isobutane, optionally hydrogen. And optionally oxygen-containing hydrocarbons, so-called oxygenates. Examples of oxygenates include formaldehyde, furan, acetic acid, maleic anhydride, formic acid, methacrolein, methacrylic acid, crotonaldehyde, crotonic acid, propionic acid, acrylic acid, methyl vinyl ketone, styrene, benzaldehyde, benzoic acid, and phthalic anhydride. , Fluorenone, anthraquinone and butyraldehyde.

  The product gas stream (2) at the reactor outlet is characterized by a temperature close to that at the end of the catalyst bed. The product gas stream is then brought to a temperature of 150 to 400 ° C., preferably to a temperature of 160 to 300 ° C., particularly preferably to a temperature of 170 to 250 ° C. In order to keep the temperature in the desired range, it is possible to insulate the conduit through which the product gas stream flows or to use a heat exchanger. The heat exchanger system is optional as long as the system can be used to maintain the product gas temperature at a desired level. Examples of heat exchangers include spiral heat exchangers, plate heat exchangers, double tube heat exchangers, multi-tube heat exchangers, kettle-type spiral heat exchangers, and kettle-type jacket heat exchangers And liquid-liquid contact heat exchangers, pneumatic heat exchangers, direct contact heat exchangers and ribbed tube heat exchangers. While the product gas temperature is adjusted to the desired temperature, some of the high-boiling byproducts contained in the product gas may precipitate, and therefore the heat exchanger system is preferably It is desirable to have two or more heat exchangers. If two or more heat exchangers planned in that case are arranged in parallel and thus it is possible to separate the cooling of the product gas obtained in the heat exchanger, the The amount of high-boiling byproducts that accumulates in the heat exchanger is reduced, thus increasing the operating time of the heat exchanger. As an alternative to the above method, the two or more heat exchangers planned may be arranged in parallel. The product gas is supplied to one or more heat exchangers but not to all heat exchangers, and the heat exchanger is replaced with another heat exchanger after a predetermined operating time. The In this way, cooling can be continued, a part of the heat of reaction can be recovered, and in parallel, high-boiling by-products deposited on one of the heat exchangers can be removed. As said organic solvent, as long as the said high boiling point by-product can be melt | dissolved, the solvent can be used. Examples are aqueous solutions of aromatic hydrocarbon solvents such as toluene and xylene and alkaline aqueous solvents such as sodium hydroxide.

  Subsequently, most of the high-boiling subcomponents and water are separated from the product gas stream (2) by cooling and compression. According to the invention, the cooling is performed by contact with an organic solvent. This step is also referred to below as quenching. This rapid cooling may consist of only one step ((3) in FIG. 1) or multiple steps (eg (3), (7) in FIG. 1). Said product gas stream (2) is therefore brought into direct contact with the organic solvent as coolant (4) and is thereby cooled. As coolant, organic solvents, preferably aromatic hydrocarbons, particularly preferably toluene, o-xylene, m-xylene, p-xylene or mixtures thereof are used according to the invention.

  Two-stage quenching (including steps (3) and (7) according to FIG. 1) is preferred. Step Ca) thus comprises two cooling steps Ca1) and Ca2) in which the product gas stream (b) is contacted with an organic solvent.

  Generally, the product gas (2) has a temperature of 100-440 ° C. before quenching (3), depending on the presence of heat exchangers and the temperature level. The product gas is contacted with a coolant comprising an organic solvent in the first quenching step (3). In this case, the coolant may be introduced through a nozzle in order to achieve as efficient a homogeneous mixing with the product gas as possible. For the same purpose, the quenching step may incorporate internal structures, such as other nozzles, through which the product gas and coolant pass. The inlet to the coolant quench is designed to minimize clogging due to deposition in the region of the coolant inlet.

  In general, the product gas (2) is cooled to 5 to 180 ° C., preferably 30 to 130 ° C., and even more preferably 60 to 110 ° C. in the first quenching step (3). The temperature of the coolant (4) at the inlet is generally 25 to 200 ° C, preferably 40 to 120 ° C, particularly preferably 50 to 90 ° C. The pressure in the first quenching step (3) is not particularly limited, but is generally 0.01 to 4 barg, preferably 0.1 to 2 barg, particularly preferably 0.2 to 1 barg. If higher amounts of high boiling by-products are present in the product gas, they can easily lead to polymerization of the high boiling by-products and solid deposition, which are caused in this process section by the high boiling by-products. . Generally, the rapid cooling step (3) is configured as a cooling tower. The coolant (4) used in the cooling tower is often circulated in the quenching cycle. The coolant circulation rate (liters per hour) is generally 0.0001-5 l / g, preferably 0.001-1 l / g, particularly preferably 0.002-0, relative to the mass flow rate of butadiene (grams per hour). .2 l / g.

  The temperature of the coolant (4) at the bottom may generally be 27-210 ° C, preferably 45-130 ° C, particularly preferably 55-95 ° C. Since the amount of load due to subcomponents of the coolant (4) increases with time, a part of the loaded coolant is withdrawn from the circulation as a purge flow (4a) and the unloaded coolant (4b) is added. The circulation amount can be kept constant. The ratio between the outflow amount and the supply amount depends on the steam load of the product gas and the product gas temperature at the end of the first quenching step.

  Depending on the temperature, pressure and water content of the product gas (2), water condensation can occur in the first quench step (3). In this case, an additional aqueous phase (5) can be formed which can additionally contain water-soluble auxiliary components. This aqueous phase can then be withdrawn at the bottom of the quenching step (3). The aqueous phase can also be separated in an additional phase separator. This phase separator may be present, for example, in a quench cycle. The aqueous phase can be withdrawn or at least partially returned to quenching. The coolant (4) can also be withdrawn, or at least partially returned to quenching.

  On the other hand, the phase separator may be present, for example, in the purge stream (4a). The aqueous phase can be withdrawn or at least partially returned to quenching. The coolant (4) can be returned at least partially to quenching. Depending on the homogeneous mixing of the aqueous and organic phases in the quench, especially at the bottom, in this case the aqueous content in the return of the quench cycle may be several hundred ppm by volume, possibly several percent by volume. Or the quench cycle may consist largely of an aqueous phase.

  An operation in which no water phase is formed in the first quenching step (3) is preferred.

  The product gas stream (6), which is cooled and optionally reduced in secondary components, can now be fed to the second quenching step (7). In this step, the gas stream can now again be contacted with the coolant (8).

  As coolant (8), according to the invention, organic solvents, preferably aromatic hydrocarbon solvents, particularly preferably toluene, o-xylene, m-xylene, p-xylene and mixtures thereof are used.

  Generally, the product gas is cooled to 5-100 ° C, preferably 15-85 ° C, and even more preferably 30-70 ° C, up to the gas outlet of the second quench step (7). The coolant may be supplied countercurrent to the product gas. In this case, the temperature of the coolant (8) at the coolant inlet may be 5 to 100 ° C., preferably 15 to 85 ° C., particularly preferably 30 to 70 ° C. The pressure in the second quenching step (7) is not particularly limited, but is generally 0.01 to 4 barg, preferably 0.1 to 2 barg, particularly preferably 0.2 to 1 barg. The second quench step (7) is preferably configured as a cooling tower. The coolant (8) used in the cooling tower is often circulated in the quenching cycle. The circulating flow rate of the coolant (8) (liters per hour) is generally 0.0001 to 5 l / g, preferably 0.001 to 1 l / g, particularly preferably 0.001 to the mass flow rate of butadiene (grams per hour). It may be 002 to 0.2 l / g.

  Depending on the temperature, pressure and water content of the product gas (6), water condensation may occur in the second quench step (7). In this case, an additional aqueous phase (9) can be formed which can additionally contain water-soluble auxiliary components. This aqueous phase can then be withdrawn at the bottom of the quenching step (7). The aqueous phase can also be separated in an additional phase separator. This phase separator may be present, for example, in a quench cycle. The aqueous phase can be withdrawn or at least partially returned to quenching. The coolant (8) can also be returned at least partially to quenching. In this case, the water content in the return of the quench cycle is small.

  On the other hand, the phase separator may be present, for example, in the purge stream (8a). The aqueous phase can be withdrawn or at least partially returned to quenching. The coolant (8) can be at least partially returned to the quench. Depending on the homogeneous mixing of the aqueous and organic phases in the quench, especially at the bottom, in this case the aqueous content in the return of the quench cycle may be several hundred ppm by volume, possibly several percent by volume. Or the quench cycle may consist largely of an aqueous phase.

  The temperature of the coolant (8) at the bottom may generally be 20-210 ° C, preferably 35-120 ° C, particularly preferably 45-85 ° C. Since the load amount due to the subcomponent of the coolant (8) increases with time, a part of the loaded coolant is withdrawn from the circulation as a purge flow (8a), and the unloaded coolant (8b) is added. The circulation amount can be kept constant.

In order to achieve the best possible contact between the product gas and the coolant, internal structures may be present in the second quench step (8). Such internal structures include, for example, bubble cap trays, centrifuge trays, and / or sieve trays, regular packings, such as sheet packings having a specific surface area of 100 to 1000 m < ² > / m < ³ >, e.g. Mellapak (R) ) Including a tower having 250 Y, as well as a packed tower.

  The solvent circulations of the two quenching steps may be separated from each other or connected to each other. Here, for example, stream (8a) may be fed into stream (4b) or replaced with stream (4b). The desired temperature of these circulating streams can be adjusted with a suitable heat exchanger.

  In a preferred embodiment of the invention, therefore, the cooling step Ca) is carried out in two stages, wherein the solvent of the second step Ca2) loaded with the subcomponents goes to the first step Ca1). Sent. The solvent removed from the second step Ca2) contains fewer subcomponents than the solvent removed from the first step Ca1).

  In order to minimize entrainment of liquid components from the quench into the waste gas conduit, structural measures may be taken, for example a demister may be installed. Furthermore, high-boiling substances that are not separated from the product gas during quenching can be removed from the product gas by further structural measures such as further gas cleaning.

  Used in n-butane, 1-butene, 2-butenes, butadiene, optionally oxygen, hydrogen, steam, small amounts of methane, ethane, ethene, propane and propene, isobutane, carbon oxides, inert gases and quenching A gas stream (10) containing part of the solvent is obtained. Furthermore, in this gas flow (10), a trace amount of high-boiling components that have not been quantitatively separated during quenching may remain.

  Subsequently, the gas stream (b) from the cooling step Ca) with reduced high-boiling subcomponents is cooled in at least one compression step Cba) in step Cb) and preferably in at least one cooling step Cbb). It is cooled by contacting with an organic solvent.

  The product gas stream (10) from the solvent quench ((3) or preferably (3) and (7)) is compressed in at least one compression step (11) and then further cooled in the cooling device (13). In this case, at least one condensate stream (15) containing water is produced. Further, the solvent used in the solvent quench is condensed to form a separate phase (14). Contains butadiene, 1-butene, 2-butenes, oxygen, steam, and optionally low boiling hydrocarbons such as methane, ethane, ethene, propane and propene, butane and isobutane, optionally carbon oxides and optionally inert gases Gas stream (16) remains. Furthermore, this product gas stream may still contain trace amounts of high boiling components.

The compression and cooling of the gas stream (10) can be performed in one stage or in multiple stages (n stages). In general, the total compression is from a pressure in the range of 1.0 to 4.0 bar (absolute pressure) to a pressure in the range of 3.5 to 20 bar (absolute pressure). Each compression step is followed by a cooling step in which the gas stream is cooled to a temperature in the range of 15-60 ° C. Thus, the condensate stream may contain multiple streams in multi-stage compression. The condensed stream mainly consists of water (aqueous phase (15)) and a solvent (organic phase (14)) used in quenching. Both streams (aqueous and organic phase), Other small scale, may contain secondary components such as low boilers, C ₄ hydrocarbons, oxygenates and carbon oxides.

  In order to cool the stream (12) and / or to remove other subcomponents from the stream (12), the condensed quenching solvent (14) is cooled in a heat exchanger and cooled. It can be returned to the device (13) as an agent. Since the amount of load due to the subcomponent of the coolant (14) increases with time, a part of the loaded coolant (14a) is extracted from the circulation, and the coolant (14b) is added by adding an unloaded solvent (14b). The circulation amount of can be kept constant.

  The solvent (14b) added as a coolant is therefore preferably likewise composed of an aromatic hydrocarbon solvent used as a quenching solvent.

Said condensate stream (14a) can be returned to the quench circulation (4b) and / or (8b). Thereby, the C ₄ component absorbed in the condensate stream (14a) is brought back into the gas stream, thereby increasing the yield.

  Suitable compressors are, for example, turbo compressors, rotary piston compressors and reciprocating piston compressors. The compressor can be driven using, for example, an electric motor, an expander, a gas turbine or a steam turbine. Typical compression ratios per compressor step (discharge pressure: suction pressure) are between 1.5 and 3.0, depending on the type of construction. The cooling of the compressed gas is carried out using a heat exchanger rinsed with an organic solvent or an organic quenching step, which can be configured, for example, as a multi-tube heat exchanger, a spiral heat exchanger or a plate heat exchanger. Done. As the coolant, cooling water or heat transfer oil is used in the heat exchanger. In addition, air cooling using a blower is preferably used.

  Butadiene, n-butenes, oxygen, low-boiling hydrocarbons (methane, ethane, ethene, propane, propene, n-butane, isobutane), optionally steam, optionally carbon oxides and optionally inert gases and sometimes traces A gas stream (16) containing the following secondary components is fed as a starting stream for further purification.

In step D), non-condensable, low-boiling gas components, including oxygen, low-boiling hydrocarbons (methane, ethane, ethene, propane, propene), carbon oxides and inert gases, As (19) separated from the process gas stream (16) by absorption of C ₄ hydrocarbons in a high boiling absorbent (28 and / or 30) and subsequent desorption of C ₄ hydrocarbons. Preferably, step D) comprises steps Da) to Dc) as represented in FIG.
Da) Absorbant and gas streams (19) loaded with C ₄ hydrocarbons by absorbing C ₄ hydrocarbons containing butadiene and n-butenes in high boiling absorbents (28 and / or 30) A step that yields
The C ₄ to absorbent stream loaded with hydrocarbons from the db) Step Da), can not condense by removing oxygen by stripping with a gas stream (18), C ₄ loaded absorption medium in hydrocarbon A step in which a stream (20) is obtained;
Dc) desorbing C ₄ hydrocarbons from the loaded absorbent stream to obtain a C ₄ product gas stream (31) consisting essentially of C ₄ hydrocarbons;
including.

For this purpose, in the absorption step (17), the gas stream (16) is contacted with an inert absorbent and C ₄ hydrocarbons are absorbed into the inert absorbent, in which case C An absorbent loaded with ₄ hydrocarbons and an exhaust gas (19) containing other gas components are obtained. In the desorption step, the C ₄ hydrocarbons are released again from the high boiling absorbent.

The absorption step may be carried out in any suitable absorption tower known to those skilled in the art. The absorption can be done by simply passing the product gas stream through the absorbent. However, the absorption can also take place in the tower or in a rotary absorber. In that case, it is possible to work in cocurrent, countercurrent or crossflow. The absorption is preferably carried out in countercurrent. Suitable absorption towers are, for example, plate towers with bubble cap trays, centrifugal trays and / or sieve trays, ordered packings, for example sheet packings with a specific surface area of 100 to 1000 m ² / m ³ , such as Mellapak® Includes towers with 250 Y, as well as packed towers. However, there are also trickle towers and spray towers, graphite block absorbers, surface absorbers such as thick and thin film absorbers and rotating columns, Tellerwaescher, Kreuzschleierwaescher and rotary scrubbers. Be considered.

  In one embodiment, a gas stream (16) containing butadiene, n-butenes and a low boiling gas component that cannot be condensed is fed in the lower region of the absorption tower. In the upper region of the absorption tower, a high-boiling absorbent (28 and / or 30) is charged.

Inert absorbent used in the absorption step is generally a non-polar solvent having a high boiling point, in which, obviously C ₄ hydrocarbon mixture to be separated than the gas component to be other separation It is a highly soluble solvent. Suitable absorbents are relatively non-polar organic solvents, for example C ₈ aliphatic -C ₁₈ - alkanes or aromatic hydrocarbons such medium oil fractions from paraffin distillation, ethers with toluene or bulky groups, Or it is a mixture of the said solvent, In this case, the polar solvent, for example, 1, 2- dimethyl phthalate, may be added to the said solvent. Suitable absorbents, further, C ₁ -C ₈ linear benzoic acid and phthalic acid - esters of alkanols, and the heat transfer oil described above, for example biphenyl and diphenyl ether, in their chlorine derivatives and triarylalkenes is there. A suitable absorbent is a mixture of biphenyl and diphenyl ether, preferably in an azeotropic composition, for example the commercially available Diphyl®. Often the solvent mixture contains dimethyl phthalate in an amount of 0.1 to 25% by weight.

  In a preferred embodiment in the absorption step Da), the same solvent as in the cooling step Ca) is used.

  Preferred absorbents are solvents having a solubility capacity for organic peroxides of at least 1000 ppm (mg active oxygen per kg of solvent). In a preferred embodiment, toluene is used as the absorbing solvent.

Essentially oxygen, low-boiling hydrocarbons (methane, ethane, ethene, propane, propene), optionally C ₄ hydrocarbons (butane, butenes, butadiene), optionally inert at the top of the absorption tower (17) An exhaust gas stream (19) containing gas, optionally carbon oxide and optionally further water vapor is withdrawn. This material stream can be partially fed to the ODH reactor. Thereby, for example, the input stream of the ODH reactor can be adjusted to the desired C ₄ hydrocarbon content.

  At the top of the absorption tower, in a further tower, the remainder of the oxygen dissolved in the absorbent by flushing with gas (18) is discharged. The residual oxygen fraction is desirably so low that the stream (31) leaving the desorption tower containing butane, butene and butadiene no longer contains only a maximum of 100 ppm oxygen.

The stripping of oxygen in step Db) can be carried out in any suitable column known to those skilled in the art. The stripping can be done by simply passing a non-condensable gas, preferably an inert gas such as nitrogen, through the loaded absorbent solution. Stripped-off C ₄ hydrocarbons are backwashed into the absorbing solution at the top of the absorber (17) by returning the gas stream to the absorber. This can be done either by laying the stripper tower piping or by directly attaching the stripper tower below the absorption tower. Since the pressure in the stripper tower part and the absorption tower part is the same according to the present invention, the direct connection can be made. Suitable stripper columns are, for example, plate columns with bubble cap trays, centrifuge trays and / or sieve trays, regular packings, for example sheet packings with a specific surface area of 100 to 1000 m ² / m ³ , such as Mellapak® Includes towers with 250 Y, as well as packed towers. However, trickle and spray towers as well as rotating columns, plate scrubbers, cross veil scrubbers and rotary scrubbers are also contemplated. A suitable gas is, for example, nitrogen or methane.

C ₄ loaded with hydrocarbon absorbent stream (20) comprises water. This water is separated from the absorbent as stream (22) in the decanter (21), so that a stream (23) is obtained which already contains only water dissolved in the absorbent.

The fully water-removed absorbent stream (23) loaded with C ₄ hydrocarbons can be heated in a heat exchanger and subsequently introduced into the desorption tower (25) as stream (24). In one variant, the desorption step Dc) is performed by flash evaporation and / or heating of the loaded absorbent. A preferred variant is the use of a reboiler at the bottom of the desorption tower (25).

The absorbent (27) regenerated in the desorption step can be cooled in a heat exchanger and returned to the absorption step (17) as a stream (28). Low boilers such as ethane or propane and high boiling components such as benzaldehyde, maleic anhydride and phthalic anhydride present in the process gas stream may accumulate in the circulating stream. In order to limit its accumulation, a purge stream (29) can be withdrawn. This purge stream, alone or in combination with streams (14a) and / or (8b) and / or (4b), is a low boiler (36) according to the prior art in a distillation column (35) (FIG. 3). And regenerated absorbent (30) and / or regenerated coolant (4b and / or 8b and / or 14b) (FIGS. 2 and 3) and high boilers (37). it can. Preferably, the stream (14b and / or 8b and / or 4b) is fed directly in order to backwash C ₄ hydrocarbons still dissolved in the stream (29) into the process gas stream. can do. If stream (29) is separated in distillation column (35), streams (36) and (37) are, for example, burned and thus available as energy. Of course, said stream (14a and / or 8a and / or 4a) may be washed in distillation column (35) without stream (29) and returned to the process.

Mainly n- butane, C ₄ product gas stream comprising n- butenes and butadiene (31) is generally 20 to 80% by volume of butadiene, 0 to 80 vol% n- butane, 1 of 0 vol% -Butene and 0-50 volume% 2-butenes are contained so that the whole quantity may be 100 volume%. In addition, a small amount of isobutane may be included.

A portion of the condensed desorption tower top discharge containing primarily C ₄ hydrocarbons is returned to the top of the tower as stream (34) to enhance the separation capacity of the tower.

The liquid C ₄ product stream (stream 32) or the gaseous C ₄ product stream (stream 33) leaving the condenser is subsequently subjected to extractive distillation with a selective solvent for butadiene in step E) and butadiene and A material stream containing a selective solvent and a material stream containing n-butenes are separated.

Extractive distillation can be performed, for example, in “Erdoel und Kohle-Erdgas-Petrochemie”, Vol. 34 (8), pp. 343-346 or “Ullmanns Enzyklopaedie”. der Technischen Chemie), Vol. 9, 4th Edition 1975, pages 1-18. For this purpose, the C ₄ product gas stream is contacted in the extraction zone with an extractant, preferably an N-methylpyrrolidone (NMP) / water mixture. The extraction zone is generally configured in the form of a washing tower containing trays, packings or packing as internal structures. The washing tower generally has 30 to 70 theoretical separation stages, whereby a sufficiently good separation action is achieved. Preferably, the washing tower has a backwash zone at the top of the tower. This backwash zone is used to recover the extractant contained in the gas phase by a liquid hydrocarbon reflux whose top fraction has been previously condensed. Weight ratio C ₄ product gas stream of the extractant in the feed of the extraction zone is generally 10: 1 to 20: 1. Extractive distillation is preferably at a bottom temperature in the range of 100-250 ° C., in particular at a temperature in the range of 110-210 ° C., at a top temperature in the range of 10-100 ° C., in particular at a temperature in the range of 20-70 ° C. And working at pressures in the range of 1-15 bar, in particular in the range of 3-8 bar. The extractive distillation column preferably has 5 to 70 theoretical separation stages.

  Suitable extractants include 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). In general, alkyl-substituted lower aliphatic acid amides or N-alkyl-substituted cyclic acid amides are used. In particular, dimethylformamide, acetonitrile, furfural and especially NMP are preferred.

  However, a mixture of this extractant with each other, for example a mixture of NMP and acetonitrile, this extractant with a cosolvent and / or t-butyl ether, such as methyl-t-butyl ether, ethyl-t-butyl ether, propyl-t-butyl ether, n It is also possible to use a mixture with -or iso-butyl-t-butyl ether. Particularly suitable are NMP, preferably NMP in aqueous solution, preferably NMP having 0-20% by weight water, particularly preferably NMP having 7-10% by weight water, in particular 8.3% by weight. NMP with water.

The top product stream of the extractive distillation column contains mainly butane and butenes and a small amount of butadiene, which is withdrawn in gaseous or liquid form. In general, a stream consisting primarily of n-butane and 2-butene has up to 100% by volume of n-butane, 0-50% by volume of 2-butene, and 0-3% by volume of further components such as isobutane, Contains isobutene, propane, propene and C ₅ ⁺ hydrocarbons.

Stream composed of the predominantly n- butane and 2-butene is entirely the or part may be supplied to the C ₄ feed ODH reactor. The butene isomer of this return stream consists primarily of 2-butenes, and since 2-butenes are generally oxidatively dehydrogenated to butadiene more slowly than 1-butene, this return stream is Prior to feeding to the reactor, it may be catalytically isomerized. Thereby, the isomer distribution can be adjusted according to the isomer distribution in thermodynamic equilibrium.

  In step F), the material stream containing butadiene and the selective solvent is separated by distillation into a material stream consisting essentially of the selective solvent and a material stream containing butadiene.

  The material stream obtained at the bottom of the extractive distillation column generally contains extractant, water, butadiene and low proportions of butenes and butane, which are fed to the distillation column. In this distillation column, butadiene can be obtained via the top of the column or as a side extract. At the bottom of the distillation column, a material stream containing an extractant and possibly water is produced, wherein the composition of the material stream containing the extractant and water corresponds to the same composition that is added to the extraction. To do. The material stream containing the extractant and water is preferably returned to extractive distillation.

  When butadiene is obtained via the side outlet, the extraction solution thus withdrawn is transferred to a desorption zone where the butadiene is once again desorbed from the extraction solution and backwashed. The desorption zone may for example be configured in the form of a washing tower having a backwash zone having 2 to 30 theoretical plates, preferably 5 to 20 theoretical plates, and optionally 4 theoretical plates, for example. . This backwash zone is used to recover the extractant contained in the gas phase by a liquid hydrocarbon reflux whose top fraction has been previously condensed. As an internal structure, a packing, a tray or a filling body is provided. Said distillation is preferably carried out at a bottom temperature in the range from 100 to 300 ° C., in particular in the range from 150 to 200 ° C. and at a top temperature in the range from 0 to 70 ° C., in particular in the range from 10 to 50 ° C. The pressure in the distillation column is then preferably in the range from 1 to 10 bar. Generally, in the desorption zone, there will be a reduced pressure and / or elevated temperature for the extraction zone.

  The useful product stream obtained at the top of the column generally contains 90-100% by volume butadiene, 0-10% by volume 2-butene and 0-10% by volume n-butane and isobutane. For further purification of butadiene, further distillation can be carried out according to the prior art.

2 shows a preferred embodiment of the method according to the invention. 2 shows a preferred embodiment of the method according to the invention. 2 shows a preferred embodiment of the method according to the invention.

Example The example, the toluene phase, even in a quench step and the compression step, describes the use also used in C ₄ absorption. Thereby, excellent penetration of a series of high-boiling subcomponents is already caused by quenching, and deposition behind the quench is suppressed. In addition, the second quench section purge stream, the compressor intercooler purge stream, and the C ₄ absorption / desorption purge stream are returned to the circulation stream located further forward in the process to discharge Loss of C ₄ hydrocarbons dissolved in the purified toluene is minimized.

  From the ODH reactor (1), process gas (2) is prepared at a temperature of 210 ° C., a pressure of 1.3 bar and the composition shown in Table 1. This gas stream is cooled in the quenching section (3) to a temperature of 60 ° C. by a toluene circulating stream having a temperature of 35 ° C. and having the composition shown in stream 1 in Table 1 as stream (4). In that case, a series of subcomponents are eluted from the gas stream and the composition of the process gas stream changes to the concentration indicated for stream (6). The mass ratio of the circulating stream (4) to the process gas (2) and the purge stream (4a) is 1 to 0.2 to 0.0033. Stream (4b) comprises on the one hand a purge stream (8a) (second quench step) and on the other hand a replenishment stream consisting of fresh toluene.

In the second quench step (7), the gas stream (6) is further cooled to 40 ° C. by means of a further toluene circulation stream (8) which enters the quench at 35 ° C. at the top of the column. The resulting gas stream (10) has the composition shown in Table 1, while the mass ratio between streams (6) and (8) is 1 to 5.6 and the purge stream ( 8a) is withdrawn at a rate of 2% of stream (8) and introduced into the first quenching section. Said stream (8b) consists of a purge stream (29), 0.2% of which is C ₄ absorbed, and 51.6% of streams (14a, 14a ′, 14a ″ and 14a ′ ″) (compressor The heat exchanger purge stream behind steps 1-4), 48.2% of which is fresh toluene.

  The gas stream (10) is compressed to 10 bar (absolute pressure) in a four-stage compressor with an intercooler as illustrated in FIG. The purge streams (14a, 14a ', 14a "and 14a") are all fed to stream (8b).

The resulting gas stream (16 ′ ″) (starting stream of the heat exchanger (13 ′ ″) after the fourth compression step) has a temperature of 35 ° C. and the composition shown in Table 1. This stream is fed into the absorption column (17) by means of an absorbent stream (28) which enters the column at 10 bar (absolute pressure) at the top of the column and countercurrently at 35 ° C. ₄ Separated into an absorbent stream loaded with hydrocarbons. The loaded absorbent stream is deoxygenated by a stream of nitrogen (18) having a temperature of 35 ° C. until the gas stream (33) exiting the desorption tower has only 10 ppm oxygen. The mass ratio between streams (16 ′ ″) and (28) is 1 to 2.48, and the mass ratio between streams (28) and (18) is 1 to 0.006. is there. A stream (22) containing mainly water is withdrawn from the stream (20). Its flow is a proportion of 0.002% of the flow (20) and its exact composition is shown in Table 2.

  The resulting stream (23) is warmed to 120 ° C. and introduced as stream (24) into a desorption column (25) having a top pressure of 5.5 bar (absolute pressure). The mass flow ratio between stream (26) and stream (27) having a temperature of 175 ° C. is 1 to 100. The mass flow ratio between the overhead streams (31) and (34) is 1 to 0.56, and the product stream (33) has the composition shown in Table 2 and the above extraction Guided again to distillation. Stream (32) does not come out in this example.

Table 1

Table 2

Example 2:
This example describes the use of mesitylene in a quench step. Thereby, excellent penetration of a series of high-boiling subcomponents is already caused by quenching, and deposition behind the quench is suppressed.

  From the ODH reactor (1), a process gas (2) is prepared at a temperature of 190 ° C., a pressure of 1.3 bar and the composition shown in Table 3. This gas stream is cooled to a temperature of 71 ° C. in the quench section (3) by a mesitylene / water circulation stream (4) having a phase ratio of 8: 1 (mesitylene: water) and a temperature of 35 ° C. In that case, a series of subcomponents are eluted from the gas stream and the composition of the process gas stream changes to the concentration indicated for stream (6). The mass ratio of the circulating stream (4) to the process gas (2) and the purge stream (4a) is 1 to 0.1 to 0.01. Stream (4b) consists on the one hand of a purge stream (8a) (second quench step) and on the other hand a replenishment stream of fresh mesitylene / water with a phase ratio of 5: 2 (mesitylene: water).

  In the second quench step (7), the gas stream (6) is further cooled to 54 ° C. by means of a further mesitylene recycle stream (8) entering the quench at 35 ° C. at the top of the column. The resulting gas stream (10) exhibits a reduction in the secondary components shown in Table 4, while the mass ratio between streams (6) and (8) is 1 to 3.8 and purge Stream (8a) is withdrawn at a rate of 4.25% of stream (8) and introduced into the first quench section. Stream (8b) is 100% composed of fresh mesitylene. In particular, it was observed that the hardly volatile substances as well as the substances present as solids upon quenching at the process conditions are greatly reduced from the process gas (2).

Table 3

Table 4

  1 ODH reactor, 2 process gas, 3 quench step, 4 coolant, 4a purge flow, 4b flow, 5 water phase, 6 gas flow, 7 quench step, 8 coolant, 8a purge flow, 8b flow, 9 water phase , 10 gas stream, 11 compression step, 12 stream, 13 cooling device, 14 coolant, 14a loaded refrigerant, 14b unloaded coolant, 15 condensate stream, 16 gas stream, 17 absorber tower, 18 gas stream , 19 gas stream, 20 absorbent stream, 21 decanter, 22 stream, 23 stream, 24 stream, 25 desorption tower, 26 stream, 27 absorbent, 28 stream, 29 purge stream, 30 absorbent, 31 product gas stream, 32 streams, 33 product streams, 34 streams, 35 distillation towers, 36 streams, 37 streams

Claims (12)

A method for producing butadiene from n-butenes comprising the following steps:
A) providing a starting gas stream (a) containing n-butenes;
B) A starting gas stream (a) containing said n-butenes and an oxygen-containing gas are fed into at least one oxidative dehydrogenation zone and oxidatively dehydrogenated from n-butenes to butadiene. This gives a product gas stream (b) containing butadiene, unreacted n-butenes, water vapor, oxygen, low-boiling hydrocarbons, high-boiling subcomponents, optionally carbon oxides and optionally inert gases. Steps,
Ca) cooling the product gas stream (b) by contact with an organic solvent as a coolant;
Cb) compressing said product gas stream (b) in at least one compression step, so that at least one aqueous condensate stream (c1) and butadiene, n-butenes, water vapor, oxygen, low-boiling hydrocarbons, To obtain a gas stream (c2) containing carbon oxide and optionally an inert gas,
D) From the gas stream (c2), butadiene and n-butene are obtained as a gas stream (d2) from the gas stream (d2), which contains oxygen, low-boiling hydrocarbons, optionally carbon oxides and optionally inert gases. by separating by absorption in C ₄ in absorbent hydrocarbon containing class, and C ₄ absorbent stream loaded with hydrocarbons, the gas flow (d2) and were obtained and the load subsequently Desorbing said C ₄ hydrocarbons from an absorbent stream to obtain a C ₄ product gas stream (d1);
E) By subjecting the C ₄ product stream (d1) to extractive distillation using a selective solvent for butadiene, a material stream (e1) containing butadiene, a selective solvent, and a material stream (e2 containing n-butenes) ) And separating step,
F) distilling the material stream (e1) containing the butadiene and the selective solvent to obtain a material stream (f1) consisting essentially of the selective solvent and a material stream (f2) containing butadiene;
The said manufacturing method which has these.   The process according to claim 1, characterized in that the solvent used in step Ca) is selected from toluene, o-xylene, m-xylene and p-xylene and mixtures thereof.   The method according to claim 1 or 2, characterized in that the step Ca) is performed in multiple stages.   Method according to claim 3, characterized in that said step Ca) is carried out in two steps Ca1) and Ca2).   The method according to claim 4, characterized in that at least a part of the solvent is supplied as a coolant to the first step Ca1) after passing through a second cooling step Ca2).   6. A method according to any one of claims 1 to 5, characterized in that said step Cb) comprises at least one compression step Cba) and at least one cooling step Cbb).   The method of claim 6, wherein in the at least one cooling step, the gas compressed in the compression step is contacted with a coolant.   8. The method according to claim 7, characterized in that the cooling agent in the cooling step Cbb) contains the same organic solvent used as the cooling agent in the step Ca).   9. The method according to claim 8, characterized in that at least a part of the coolant is supplied as a coolant to step Ca) after passing through at least one cooling step Cbb).   10. A method according to any one of claims 5 to 9, characterized in that said step Cb) comprises a plurality of compression steps Cba1) to Cban) and cooling steps Cbb1) to Cbbn). Said step D) comprises the following steps Da) to Dc):
Da) absorbing C ₄ hydrocarbons containing butadiene and n-butenes in a high boiling absorbent to obtain an absorbent stream and a gas stream (d2) loaded with C ₄ hydrocarbons;
Db) removing oxygen from the C ₄ hydrocarbon loaded absorbent stream from step Da) by stripping with a non-condensable gas stream;
Dc) desorbing C ₄ hydrocarbons from the loaded absorbent stream to obtain a C ₄ product gas stream (d1) containing less than 100 ppm oxygen;
10. The method according to any one of claims 1 to 9, characterized by comprising:   The process according to claim 10, characterized in that the high-boiling absorbent used in step Da) is an aromatic hydrocarbon solvent.

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