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

Abstract

The invention relates to a method for producing butadiene from n-butenes having the steps: A) providing a feed gas stream a comprising n-butenes; B) feeding the feed gas stream a comprising the n-butenes and an oxygen-comprising gas into at least one oxidative dehydrogenation zone and oxidatively dehydrogenating n-butenes to butadiene, wherein a product gas stream b comprising butadiene, unreacted n-butenes, steam, oxygen, low-boiling hydrocarbons, high-boiling minor components, possibly carbon oxides and possibly inert gases is obtained; Ca) cooling the product gas stream b by contacting it with a refrigerant and condensing at least a part of the high-boiling minor components; Cb) compressing the remaining product gas stream b in at least one compression stage, wherein at least one aqueous condensate stream c1 and a gas stream c2 comprising butadiene, n-butenes, steam, oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases are obtained; Da) separating off non-condensable and low-boiling gas components comprising oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases as gas stream d2 from the gas stream c2 by absorbing the C.sub.4 hydrocarbon-comprising butadiene and n-butenes in an absorbent, wherein an absorbent stream loaded with C.sub.4 hydrocarbons and the gas stream d2 are obtained, and Db) subsequent desorption of the C.sub.4 hydrocarbons from the loaded absorbent stream in a desorption column, wherein a C.sub.4 product gas stream d1 is obtained,
wherein a polymerization inhibitor is added in step Db) at the column head of the desorption column.

Claims

1.-10. (canceled)

11. A method for producing butadiene from n-butenes having the steps: A) providing a feed gas stream a comprising n-butenes; B) feeding the feed gas stream a comprising n-butenes and an oxygen-comprising gas into at least one oxidative dehydrogenation zone and oxidatively dehydrogenating n-butenes to butadiene, wherein a product gas stream b comprising butadiene, unreacted n-butenes, steam, oxygen, low-boiling hydrocarbons, high-boiling minor components, optionally carbon oxides and optionally inert gases is obtained; Ca) cooling the product gas stream b by contacting it with a refrigerant and condensing at least a part of the high-boiling minor components; Cb) compressing the remaining product gas stream b in at least one compression stage, wherein at least one aqueous condensate stream c1 and a gas stream c2 comprising butadiene, n-butenes, steam, oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases are obtained; Da) separating off non-condensable and low-boiling gas components comprising oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases as gas stream d2 from the gas stream c2 by absorbing the C.sub.4 hydrocarbon-comprising butadiene and n-butenes in an absorbent, wherein an absorbent stream loaded with C.sub.4 hydrocarbons and the gas stream d2 are obtained, and Db) subsequent desorption of the C.sub.4 hydrocarbons from the loaded absorbent stream in a desorption column, wherein a C.sub.4 product gas stream d1 is obtained, wherein a polymerization inhibitor is added in step Db) at the column head of the desorption column.

12. The method according to claim 11 further comprising: E) separating the C.sub.4 product stream d1 by extractive distillation using a solvent selective for butadiene into a material stream e1 comprising butadiene and the selective solvent, and a material stream e2 comprising n-butenes; F) distilling the material stream f2 comprising butadiene and the selective solvent into a material stream g1 substantially comprising the selective solvent, and a material stream g2 comprising butadiene.

13. The method according to claim 11, wherein the polymerization inhibitor is added at the top condenser of the desorption column.

14. The method according to claim 13, wherein the polymerization inhibitor is added in amounts such that the concentration of the polymerization inhibitor in the liquid condensate stream obtained at the top condenser is from 10 to 1500 ppm.

15. The method according to claim 11, wherein the polymerization inhibitor is selected from the group consisting of unsubstituted or substituted catechols and hydroquinones.

16. The method according to claim 14, wherein the polymerization inhibitor is a mixture of tert-butyl catechol and 4-methoxyphenol.

17. The method according to claim 11, wherein the oxygen-comprising gas fed in step B) comprises at least 90% by volume of oxygen.

18. The method according to claim 11, wherein the gas stream d2 that is separated off in step Da) is at least in part recirculated in step B).

19. The method according to claim 11, wherein the step Da) comprises the steps Da1), Da2) and Db): Da1) absorption of the C.sub.4 hydrocarbons comprising butadiene and n-butenes in a high-boiling absorbent, wherein an absorbent stream loaded with C.sub.4 hydrocarbons and the gas stream d2 are obtained, Da2) removal of oxygen from the absorbent stream of step Da) that is loaded with C.sub.4 hydrocarbons by stripping with a non-condensable gas stream, and Db) desorption of the C.sub.4 hydrocarbons from the loaded absorbent stream, wherein a C.sub.4 product gas stream d1 is obtained which comprises less than 100 ppm of oxygen.

20. The method according to claim 11, wherein the absorbent used in step Da) is an aromatic hydrocarbon solvent.

Description

COMPARATIVE EXAMPLE

[0127] On operation of the plant, polymeric deposits from a methacrolein-butadiene copolymer were found in the topmost column section of desorber column H after 10 days of operation.

[0128] In addition, polymeric deposits were also found in the C.sub.4 evaporator (N in FIG. 1). The polymer formation at this point was so dominant that the coiled tube evaporator of the plant became blocked.

Example 1

[0129] The polymers found have been with high probability formed via a free-radical mechanism. As a countermeasure, a free-radical trap was added to the condenser at the top of the desorber column. By selection of this point of addition, both the condenser and the downstream components were protected from polymers by the free-radical trap. Said free-radical trap distributed itself via the C.sub.4 reflux stream 30 into the desorber column and protects the upper column sections which are not protected by an inhibition of the absorbent conducted in circulation. In addition, it also flows together with the stream 28 into the C.sub.4 evaporator and also there prevents the formation of polymers. In experiments in the miniplant system with the fluxes tabulated hereinafter, it has been found that fault-free operation was achieved by these measures.

[0130] The composition of the individual material streams is shown in table 1.

TABLE-US-00001 TABLE 1 Stream: 12 16 17 18 19 20 21 21a 21b Temperature C. 54.1 32.4 52.9 35.0 60.0 148.0 30.0 30.0 30.0 Pressure bar 10.0 10.0 10.0 10.0 5.5 5.5 10.3 10.2 10.1 Mass flow rate kg/h 9.5 8.3 22.0 0.3 22.0 22.8 22.8 2.3 20.1 BUTANE % by weight 3.34 0.53 1.26 0.00 1.26 0.01 0.01 0.00 0.01 I-BUTANE 0.74 0.10 0.28 0.00 0.28 0.00 0.00 0.00 0.00 1-BUTENE 0.02 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 C-2-BUTENE 0.58 0.01 0.25 0.00 0.25 0.00 0.00 0.00 0.01 T-2-BUTENE 1.36 0.02 0.59 0.00 0.59 0.01 0.01 0.00 0.01 1.3-BUTADIENE 9.65 0.40 4.10 0.00 4.10 0.05 0.05 0.00 0.06 Water 0.87 0.30 0.38 0.00 0.38 10.52 10.52 99.42 0.04 ACROLEIN 0.17 0.13 0.68 0.00 0.68 0.67 0.67 0.23 0.72 ACETALDEHYDE 0.13 0.01 0.07 0.00 0.7 0.02 0.02 0.03 0.02 Methacrolein 0.28 0.25 1.01 0.00 1.01 0.98 0.98 0.18 1.08 Mesitylene 0.54 0.21 90.97 0.00 90.97 87.56 87.56 0.01 97.89 Stabilizer 0.0000 0.0000 0.0096 0.0000 0.0096 0.0165 0.0165 0.0654 0.0104 CO.sub.2 0.94 1.07 0.01 0.00 0.01 0.00 0.00 0.00 0.00 CO 0.19 0.22 0.00 0.00 0.00 0.00 0.00 0.00 0.00 N.sub.2 74.78 89.56 0.15 100.00 0.15 0.00 0.00 0.00 0.00 O.sub.2 6.16 7.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Others 0.26 0.08 0.23 0.00 0.23 0.15 0.15 0.07 0.16 Stream: 22 23 24 25 26 27 27a 28 29 30 Temperature C. 30 157 35 30 35 50 30 17 17 17 Pressure bar 10.2 5.6165 10.2 10.1 10 5.5 5.4 5.3 5.4 5.3 Mass flow rate kg/h 0.15 2.33 0.07 0.30 0.24 3.39 0.001 1.42 0.08 1.90 BUTANE % by weight 0.00 0.00 0.00 0.01 0.00 18.68 0.00 18.86 10.46 18.86 I-BUTANE 0.00 0.00 0.00 0.00 0.00 4.20 0.00 4.21 3.48 4.21 1-BUTENE 0.00 0.00 0.00 0.00 0.00 0.12 0.00 0.12 0.07 0.12 C-2-BUTENE 0.00 0.00 0.00 0.01 0.00 3.69 0.00 3.74 1.61 3.74 T-2-BUTENE 0.00 0.00 0.00 0.01 0.00 8.69 0.00 8.79 4.10 8.79 1.3-BUTADIENE 0.00 0.00 0.00 0.06 0.00 60.29 0.00 60.83 35.80 60.83 Water 99.42 99.43 100.00 0.04 0.00 0.74 10.00 0.75 0.16 0.75 ACROLEIN 0.23 0.23 0.00 0.72 0.00 0.19 0.00 0.20 0.01 0.20 ACETALDEHYDE 0.03 0.03 0.00 0.02 0.00 0.80 0.00 0.80 0.71 0.80 Methacrolein 0.18 0.18 0.00 1.08 0.00 0.20 0.00 0.21 0.01 0.21 Mesitylene 0.01 0.01 0.00 97.89 100.00 0.01 0.00 0.01 0.00 0.01 Stabilizer 0.0654 0.0486 0.0000 0.0104 0.0000 0.0000 90.0000 0.0271 0.0000 0.0271 CO.sub.2 0.00 0.00 0.00 0.00 0.00 0.06 0.00 0.04 1.03 0.04 CO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 N.sub.2 0.00 0.00 0.00 0.00 0.00 1.03 0.00 0.08 42.19 0.08 O.sub.2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 others 0.07 0.07 0.00 0.16 0.00 1.30 0.00 1.32 0.35 1.32