METHOD FOR PRODUCING BUTADIENE BY OXIDATIVELY DEHYDROGENATING N-BUTENES

Abstract

A) provision of a feed gas stream a comprising n-butenes;

B) introduction of the feed gas stream a comprising n-butenes and an oxygen-comprising gas into a dehydrogenation reactor and oxidative dehydrogenation of n-butenes to butadiene;

C) cooling and compression of the product gas stream b in at least one cooling stage comprising a quenching column and in a compression stage comprising a compressor, with the product gas stream b being brought into contact with at least one circulated coolant;

D) separation of incondensable and low-boiling gas constituents as gas stream d2 from the gas stream c2 by absorption of the C.sub.4-hydrocarbons in at least one circulated absorption medium;

E) separation of the C.sub.4 product stream d1 by extractive distillation using a solvent which is selective for butadiene into a stream e1 comprising butadiene and the selective solvent and a stream e2 comprising n-butenes;

F) distillation of the stream e1 comprising butadiene and the selective solvent to give a stream f1 consisting essentially of the selective solvent and a stream f2 comprising butadiene;

wherein the measures (i) to (iii) below are carried out (i) avoidance of formation of explosive gas mixtures by monitoring of the oxygen concentration in the oxygen-comprising gas streams fed into the dehydrogenation zone and control of the mass flows of oxygen-comprising gas streams and gas streams comprising hydrocarbons in such a way that no explosive gas mixtures can be formed; (ii) interruption of the introduction of the oxygen-comprising gas mixture into the dehydrogenation zone when a limit value for the oxygen concentration in the dehydrogenation gas mixture is exceeded; (iii) carrying out of the steps A) to F) in apparatuses which are configured so as to be explosion-protected, where liquid-conveying pipes are configured so as to be explosion-protected and gas conduits are configured so as to be detonation-protected.

Claims

1.-15. (canceled)

16. A process for preparing butadiene from n-butenes, which comprises the following steps: A) providing a feed gas stream a comprising n-butenes; B) introducing the feed gas stream and an oxygen-comprising gas into at least one dehydrogenation zone comprising a dehydrogenation reactor and oxidative dehydrogenation of n-butenes to butadiene, giving a product gas stream b comprising butadiene, unreacted n-butenes, water vapor, oxygen, low-boiling hydrocarbons, optionally carbon oxides and optionally inert gases; C) cooling and compressing the product gas stream b in at least one cooling stage comprising at least one quenching column and in at least one compression stage comprising at least one compressor and optionally one or more intermediate cooling units between the compressors, with the product gas stream b being brought into contact with at least one circulated coolant to give at least one condensate stream c1 comprising water and a gas stream c2 comprising butadiene, n-butenes, water vapor, oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases; D) separating incondensable and low-boiling gas constituents comprising oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases as gas stream d2 from the gas stream c2 by absorption of the C4-hydrocarbons comprising butadiene medium stream loaded with C4-hydrocarbons and the gas stream d2, and subsequent desorption of the C4-hydrocarbons from the loaded absorption medium stream to give a C4 product gas stream d1; E) separating the C4 product stream d1 by extractive distillation using a solvent which is selective for butadiene 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 to give a stream f1 consisting essentially of the selective solvent and a stream f2 comprising butadiene; wherein the steps (i) to (iii) below are carried out: (i) avoidance of formation of explosive gas mixtures by monitoring of the oxygen concentration in the oxygen-comprising gas streams fed into 5 the dehydrogenation zone and control of the mass flows of oxygen comprising gas streams and gas streams comprising hydrocarbons in such a way that no explosive gas mixtures can be formed; (ii) interruption of the introduction of the oxygen-comprising gas mixture into the dehydrogenation zone when a limit value for the oxygen concentration in the dehydrogenation gas mixture is exceeded; (iii) carrying out of the steps A) to F) in apparatuses which are configured so as to be explosion-protected, where liquid-conveying pipes are configured so as to be explosion-protected and gas conduits are configured so as to be detonation-protected.

17. The process according to claim 16, wherein one or more of the following apparatuses are designed so as to be explosion-protected: the dehydrogenation reactor used in step B); the quenching column used in step C); the compressors used in step C); the intermediate coolers used in step C); the distillation column used in step F); or the decanter used in the solvent regeneration unit.

18. The process according to claim 16, wherein the intermediate coolers used in step C) are configured as direct coolers.

19. The process according to claim 16, wherein distillation columns used in steps D), E) and/or F) are configured as tray columns having gastight column trays.

20. The process according to claim 16, wherein gas feed lines into the distillation columns used in steps D), E) and/or F) dip into the liquid.

21. The process according to claim 16, wherein gas conduits and gas-conveying apparatuses have such a ratio of length:diameter that detonation is ruled out.

22. The process according to claim 21, wherein the ratio of length:diameter is not more than 50:1.

23. The process according to claim 16, wherein the cooling stage Ca) is carried out in two cooling stages Ca1) and Ca2) and both cooling stages are designed as direct cooling units.

24. The process according to claim 23, wherein at least part of the coolant which has passed through the second cooling stage Ca2) is fed as coolant to the first cooling stage Ca1).

25. The process according to claim 23, wherein the stage Cb) generally comprises at least one compression stage Cba) and at least one cooling stage Cbb), where the gas which has been compressed in the compression stage Cba) is brought into contact with a coolant in the at least one cooling stage Cbb).

26. The process according to claim 25, wherein the coolant of the cooling stage Cbb) is the same organic solvent which is used as coolant in the cooling stage Ca) and at least part of this coolant is, after passing through the at least one cooling stage Cbb), fed as coolant to the cooling stage Ca).

27. The process according to claim 23, wherein the circulated coolant is mesitylene.

28. The process according to claim 16, wherein step D) comprises the steps Da) to Dc): Da) absorption of the C.sub.4-hydrocarbons comprising butadiene and n-butenes in an absorption medium to give an absorption medium stream loaded with C.sub.4-hydrocarbons and the gas stream d2, Db) removal of oxygen from the absorption medium stream loaded with C.sub.4-hydrocarbons from step Da) by stripping with an incondensable gas stream and Dc) desorption of the C.sub.4-hydrocarbons from the loaded absorption medium stream to give a C.sub.4 product gas stream d1.

29. An apparatus for carrying out the process for preparing butadiene from n-butenes according to claim 16, which comprises: A) feed line for providing a feed gas stream a comprising n-butenes; B) feed lines for introducing the feed gas stream a comprising n-butenes and an oxygen-comprising gas into at least one dehydrogenation zone, dehydrogenation zone comprising a dehydrogenation reactor for the oxidative dehydrogenation of n-butenes to butadiene, giving a product gas stream b comprising butadiene, unreacted n-butenes, water vapor, oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases; C) feed line for introducing the product gas stream b into a cooling stage and at least one cooling stage comprising at least one quenching column and at least one compression stage comprising at least one compressor and optionally one or more intermediate coolers between the compressors, where the product gas stream b is brought into contact with at least one circulated coolant to give at least one condensate stream c1 comprising water and a gas stream c2 comprising butadiene, n-butenes, water vapor, oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases; D) facility for separating off incondensable and low-boiling gas constituents comprising oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases as gas stream d2 from the gas stream c2 by absorption of the C.sub.4-hydrocarbons comprising butadiene and n-butenes in at least one circulated absorption medium, giving at least one absorption medium stream loaded with C.sub.4-hydrocarbons and the gas stream d2, and facility for subsequent desorption of the C.sub.4-hydrocarbons from the loaded absorption medium stream to give a C.sub.4 product gas stream d1; E) extractive distillation column for separating the C.sub.4 product stream d1 by extractive distillation using a solvent which is selective for butadiene into a stream e1 comprising butadiene and the selective solvent and a stream e2 comprising n-butenes; F) distillation column for distillation of the stream e1 comprising butadiene and the selective solvent to give a stream f1 consisting essentially of the selective solvent and a butadiene-comprising stream f2; wherein one or more of the apparatuses used for carrying out steps A) to F) are configured so as to be explosion-protected, liquid-conveying pipes are configured so as to be explosion-protected and gas conduits are configured so as to be detonation-protected.

30. The apparatus according to claim 29, wherein one or more of the following apparatuses are designed so as to be explosion-protected: the dehydrogenation reactor used in step B); the quenching column used in step C); the compressors used in step C); the intermediate coolers used in step C); the distillation column used in step F); the decanter used in the solvent regeneration unit.

Description

EXAMPLE

[0162] A commercial plant for producing 1,3-butadiene from n-butenes comprises, inter alia, [0163] reactors for catalytic oxidative dehydrogenation [0164] a quenching column for cooling the product gas stream [0165] compressors for compressing the product gas stream [0166] an absorption column for separating off the inert gas constituents as overhead product from the C4 fraction as bottom product

[0167] In order to ensure a satisfactory catalyst operating life, the reactors are operated using an oxygen excess of 6% by volume at the reactor outlet. The streams at the entry into the reactors (n-butenes, air, steam, nitrogen) are equipped with certified quantity measurements and ratio regulation. The condensation of water vapor comprised in the product gas in the quenching column increases the oxygen concentration in the overhead product from the absorption column to above 7% by volume. Apparatuses affected in the plant sections mentioned are designed so as to be explosion-protected and the connecting pipes are designed so as to be detonation-protected. As additional safety element, a certified oxygen measurement is installed in the overhead product from the absorption column, by means of which the oxygen concentration in the system can be monitored continuously. Possible measuring principles for these analytical instruments are laser measurements or paramagnetic measurements or a combination of the two measuring principles.

[0168] The safety concept according to the invention allows the design and safe operation of commercial plants for the oxidative dehydrogenation of butenes to butadiene, in particular in processes in which an excess of oxygen at the outlet of the oxidation reactor is necessary.

[0169] FIG. 4 shows

[0170] a) reactor in the reactor section having an explosion-protected design

[0171] b) quenching column in the quenching section having an explosion-protected design

[0172] c) solvent regeneration unit having an explosion-protected design

[0173] d) intermediate cooler using mesitylene as coolant in the compression section as direct cooler having an explosion-protected design

[0174] e) compression stages (compressors) in the compression section having an explosion-protected design

[0175] f) butadiene column in the butadiene isolation section having an explosion-protected design

[0176] g) explosion-protected gas conduits

[0177] h) detonation-protected gas conduits

[0178] i) explosion-protected liquid conduits

[0179] In all column, the gas feed lines dip into the liquid.

[0180] All pipes for liquids to and from the columns have an explosion-protected design in order to prevent mechanical overloading of the pipes conveying liquid in the event of an explosion in a vessel.

[0181] All gas pipes between the sections have a detonation-protected design.