PROCESS FOR PREPARING 1,3-BUTADIENE FROM N-BUTENES BY OXIDATIVE DEHYDROGENATION

Abstract

The invention relates to a process for preparing butadiene from n-butenes, comprising the steps of: A) providing an input gas stream a comprising n-butenes, B) feeding the input gas stream a comprising n-butenes and a gas containing at least oxygen into at least one oxidative dehydrogenation zone and oxidatively dehydrogenating n-butenes to butadiene, giving a product gas stream b comprising butadiene, unconverted n-butenes, water vapor, oxygen, low-boiling hydrocarbons and high-boiling secondary components, with or without carbon oxides and with or without inert gases; Ca) cooling the product gas stream b by contacting with a cooling medium in at least one cooling zone, the cooling medium being at least partly recycled and having an aqueous phase and an organic phase, Cb) compressing the cooled product gas stream b which may have been depleted of high-boiling secondary components in at least one compression stage, giving at least one aqueous condensate stream c1 and one gas stream c2 comprising butadiene, n-butenes, water vapor, oxygen and low-boiling hydrocarbons, with or without carbon oxides and with or without inert gases; D) removing uncondensable and low-boiling gas constituents comprising oxygen and low-boiling hydrocarbons, with or without carbon oxides and with or without inert gases, as gas stream d2 from the gas stream c2 by absorbing the C.sub.4 hydrocarbons comprising butadiene and n-butenes in an absorbent, giving an absorbent stream laden with C.sub.4 hydrocarbons and the gas stream d2, and then desorbing the C.sub.4 hydrocarbons from the laden absorbent stream, giving a C.sub.4 product gas stream d1, E) separating the C.sub.4 product stream d1 by extractive distillation with a butadiene-selective solvent into a stream e1 comprising butadiene and the selective solvent and a stream e2 comprising n-butenes; F) distilling the stream e1 comprising butadiene and the selective solvent into a stream f1 consisting essentially of the selective solvent and a stream f2 comprising butadiene, wherein stage Cb) comprises at least two compression stages Cba) and at least two cooling stages Cbb) configured in the form of quench columns, the cooling in the cooling stages being effected by direct contacting with a biphasic cooling medium having an aqueous phase and an organic phase.

Claims

1.-17. (canceled)

18. A process for preparing butadiene from n-butenes, comprising the steps of: A) providing an input gas stream a comprising n-butenes, B) feeding the input gas stream a comprising n-butenes and a gas containing at least oxygen into at least one oxidative dehydrogenation zone and oxidatively dehydrogenating n-butenes to butadiene, giving a product gas stream b comprising butadiene, unconverted n-butenes, water vapor, oxygen, low-boiling hydrocarbons and high-boiling secondary components, with or without carbon oxides and with or without inert gases; Ca) cooling the product gas stream b by contacting with a cooling medium in at least one cooling zone, the cooling medium being at least partly recycled and having an aqueous phase and an organic phase, Cb) compressing the cooled product gas stream b which may have been depleted of high-boiling secondary components in at least one compression stage, giving at least one aqueous condensate stream c1 and one gas stream c2 comprising butadiene, n-butenes, water vapor, oxygen and low-boiling hydrocarbons, with or without carbon oxides and with or without inert gases; D) removing uncondensable and low-boiling gas constituents comprising oxygen and low-boiling hydrocarbons, with or without carbon oxides and with or without inert gases, as gas stream d2 from the gas stream c2 by absorbing the C.sub.4 hydrocarbons comprising butadiene and n-butenes in an absorbent, giving an absorbent stream laden with C.sub.4 hydrocarbons and the gas stream d2, and then desorbing the C.sub.4 hydrocarbons from the laden absorbent stream, giving a C.sub.4 product gas stream d1, E) separating the C.sub.4 product stream d1 by extractive distillation with a butadiene-selective solvent into a stream e1 comprising butadiene and the selective solvent and a stream e2 comprising n-butenes; F) distilling the stream e1 comprising butadiene and the selective solvent into a stream f1 consisting essentially of the selective solvent and a stream f2 comprising butadiene, wherein stage Cb) comprises at least two compression stages Cba) and at least two cooling stages Cbb) configured in the form of quench columns, the cooling in the cooling stages being effected by direct contacting with a biphasic cooling medium having an aqueous phase and an organic phase formed from an organic solvent, wherein the organic solvent is selected from the group consisting of toluene, o-, m- and p-xylene, mesitylene, mono-, di- and triethylbenzene, mono-, di- and triisopropylbenzene and mixtures thereof, and wherein in the cooling stages Cbb), the mass ratio of the aqueous phase to the organic phase in the cooling medium when it is fed into the cooling zones prior to the contacting with the product gas stream is from 0.15:1 to 10:1.

19. The process according to claim 18, wherein stage Cb) comprises at least three compression stages Cba) and at least three cooling stages Cbb).

20. The process according to claim 18, wherein one or more of the quench columns in the cooling stage Cbb) narrow conically in the bottom region, such that separation of the biphasic cooling medium into an aqueous phase and an organic phase is prevented.

21. The process according to claim 18, wherein a coolant having an aqueous phase and an organic phase is fed continuously or discontinuously into the compression stages Cba).

22. The process according to claim 21, wherein the coolant is fed into the intake line of at least one compressor of the compression stages Cba).

23. The process according to claim 21, wherein the coolant is fed into the housing of at least one compressor of the compression stages Cba).

24. The process according to claim 18, wherein stage Ca) is conducted in three stages Ca1), Ca2) and Ca3) in three cooling zones.

25. The process according to claim 18, wherein, in at least one of the stages Ca), the mass ratio of the aqueous phase to the organic phase in the cooling medium when it is fed into the cooling zones prior to the contacting with the product gas stream is from 0.013:1 to 100:1.

26. The process according to claim 25, wherein an organic solvent laden with high-boiling secondary components from the second stage Ca2) is conducted into the first stage Ca1), and an organic solvent less heavily laden with high-boiling secondary components from the third stage Ca3) is conducted into the second stage Ca2).

27. The process according to claim 25, wherein a fresh cooling medium as yet unladen with the high-boiling secondary components is fed into the third cooling stage Ca3) in single pass and in countercurrent into the cooling stage.

28. The process according to claim 25, wherein the diameter of the cooling stage Ca3) is less than the diameter of the cooling stages Ca1) and Ca2).

29. The process according to claim 25, wherein the first cooling stage Ca1) has a parallel and interchangeable configuration.

30. The process according to claim 18, wherein the cooling medium is fed into the cooling zones in the cooling stages Ca) and Cbb) through one or more nozzles.

31. The process according to claim 30, wherein a flow is generated in the nozzle(s), in which the Reynolds number Re of the two phases of the cooling medium is at least 100.

32. The process according to claim 18, wherein the biphasic cooling medium in the cooling stages Cbb) and the cooling stages Ca) comprise the same organic solvent.

33. The process according to claim 18, wherein step D) comprises steps Da) to Dc): Da) absorbing the C.sub.4 hydrocarbons comprising butadiene and n-butenes in a high-boiling absorbent, giving an absorbent stream laden with C.sub.4 hydrocarbons and the gas stream d2, Db) removing oxygen from the absorbent stream laden with C.sub.4 hydrocarbons from step Da) by stripping with an uncondensable gas stream, and Dc) desorbing the C.sub.4 hydrocarbons from the laden absorbent stream, giving a C.sub.4 product gas stream d1 comprising less than 100 ppm of oxygen.

34. The process according to claim 33, wherein the high-boiling absorbent used in step Da) is an aromatic hydrocarbon solvent.

Description

EXAMPLES

Comparative Example

[0189] In a commercial plant for production of about 130 000 t/a of 1,3-butadiene from n-butenes, the untreated gas is compressed from about 1.5 bar to about 10 bar using a three-stage turbo compressor with conventional stage coolers having a pressure drop of about 0.3 bar.

TABLE-US-00001 Compressor stage 1 2 3 Throughput kg/h 145718 142677 140759 Outlet temperature ° C. 104 106 107 Power kW 3005 3012 3003

[0190] The total power consumed by the compressor is 9020 kW.

Example

[0191] In a commercial plant for production of about 130 000 t/a of 1,3-butadiene from n-butenes, the untreated gas is compressed using a three-stage turbo compressor comprising the inventive quench columns as direct coolers with a pressure drop of about 0.03 bar. In addition, an amount of 1200 kg/h of water is injected into the housing of each individual compressor stage.

TABLE-US-00002 Compressor stage 1 2 3 Throughput kg/h 146918 143667 141818 Outlet temperature ° C. 80 81 82 Power kW 2716 2664 2691

[0192] The total power consumed by the compressor is 8071 kW.

[0193] These examples show the positive influence of the features of the present invention on the stage outlet temperatures and the compressor power. It should be noted that, according to operational experience from industrial plants, a reduction in the compressor outlet temperature by 10° C. already results in a reduction in the polymerization tendency/the fouling behavior in the parts of the equipment affected by half, and hence doubling of the service life of the compressor section.