Method for decommisioning and regenerating a reactor for the oxidative dehydrogenation of n-butenes

Patent metadata

Field	Value
Publication number	US-2020039901-A1
Application number	US-201816498693-A
Country	US
Kind code	A1
Filing date	Mar 26, 2018
Priority date	Mar 31, 2017
Publication date	Feb 6, 2020
Grant date	—

Abstract

The invention relates to a process for preparing butadiene from n-butenes in n reactors R 1 to Rn operated in parallel, wherein the process in the production phase of a reactor Rm in the n reactors comprises the steps:
A) provision of a feed gas stream a 1 m comprising n-butenes; B) feeding of the feed gas stream a 1 m comprising n-butenes, an oxygen-comprising gas stream a 2 m and a substream d 2 m of an oxygen-comprising total recycle gas stream d 2 into the oxidative dehydrogenation zone of the reactor and oxidative dehydrogenation of n-butenes to butadiene, giving a product gas substream bm comprising butadiene; C) combination of the product gas substream bm with further product gas substreams to form a total product gas stream b and cooling and compression of the total product gas stream b and condensation of at least part of the high-boiling secondary components, giving at least one aqueous condensate stream c 1 and a gas stream c 2 comprising butadiene; D) feeding of the gas stream c 2 into an absorption zone and separation of incondensable and low-boiling gas constituents as gas stream d from the gas stream c 2 by absorption of the C 4 -hydrocarbons in an absorption medium, giving an absorption medium stream d 1 loaded with C 4 -hydrocarbons and a recycle gas stream d 2 , and recirculation of a substream d 2 m of the total recycle gas stream d 2 into the reactor Rm, and during the regeneration phase of the reactor Rm further reactors are in the production phase and the regeneration phase of the reactor Rm comprises the steps in the order i) to v): i) reduction of the feed gas stream a 1 m comprising n-butenes and of the oxygen-comprising gas stream a 2 m and the feeding of an inert gas stream a 4 m into the reactor Rm; ii) further reduction of the feed gas stream a 1 m comprising n-butenes down to 0, reduction of the recycle gas substream d 2 m and increase of the inert gas stream a 4 m until the oxygen content in the reactor Rm is from 2 to 3% by volume; iii) regeneration of the catalyst by burning off carbon-comprising deposits at an oxygen content of from 2 to 3% by volume; iv) reduction of the inert gas stream a 4 m and increase of the recycle gas substream d 2 m until the oxygen content in the reactor Rm is from 4 to 10% by volume; v) reoxidation of the catalyst at an oxygen content of from 4 to 10% by volume.

First claim

1 . A process for preparing butadiene from n-butenes in n reactors R 1 to Rn operated in parallel, with each of the plurality of reactors operating in parallel going through a production phase and a regeneration phase, wherein the process in the production phase of a reactor Rm in the n reactors comprises the steps:
A) provision of a feed gas stream a 1 m comprising n-butenes;
B) feeding of the feed gas stream a 1 m comprising n-butenes, an oxygen-comprising gas stream a 2 m and a substream d 2 m of an oxygen-comprising total recycle gas stream d 2 into the oxidative dehydrogenation zone of the reactor and oxidative dehydrogenation of n-butenes to butadiene, giving a product gas substream bm comprising butadiene, unreacted n-butenes, water vapor, oxygen, low-boiling hydrocarbons, high-boiling secondary components, possibly carbon oxides and possibly inert gases;
C) combination of the product gas substream bm with further product gas substreams to form a total product gas stream b and cooling and compression of the total product gas stream b and condensation of at least part of the high-boiling secondary components, giving at least one aqueous condensate stream c 1 and a gas stream c 2 comprising butadiene, n-butenes, water vapor, oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases;
D) feeding of the gas stream c 2 into an absorption zone and separation of incondensable and low-boiling gas constituents comprising oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases as gas stream d from the gas stream c 2 by absorption of the C 4 -hydrocarbons comprising butadiene and n-butenes in an absorption medium, giving an absorption medium stream d 1 loaded with C 4 -hydrocarbons and a recycle gas stream d 2 , and recirculation, optionally after a purge gas stream p has been separated off, of a substream d 2 m of the total recycle gas stream d 2 into the reactor Rm,

wherein during the regeneration phase of the reactor Rm further reactors are in the production phase and the regeneration phase of the reactor Rm comprises the steps in the order i) to v):
i) reduction of the feed gas stream a 1 m comprising n-butenes and of the oxygen-comprising gas stream a 2 m and feeding of an inert gas stream a 4 m into the reactor Rm, with the total gas flow through the reactor Rm corresponding to from 55 to 75%, of the total gas flow through the reactor Rm during the production phase;
ii) further reduction of the feed gas stream a 1 m comprising n-butenes down to 0, reduction of the recycle gas substream d 2 m and increase of the inert gas stream a 4 m until the oxygen content in the reactor Rm is from 2 to 3% by volume, with the total gas flow through the reactor Rm corresponding to from 55 to 75% of the total gas flow through the reactor Rm during the production phase;
iii) regeneration of the catalyst by burning off carbon-comprising deposits at an oxygen content of from 2 to 3% by volume;
iv) reduction of the inert gas stream a 4 m and increase of the recycle gas substream d 2 m until the oxygen content in the reactor Rm is from 4 to 10% by volume, with the total gas flow through the reactor Rm corresponding to from 60 to 120% of the total gas flow during the production phase;
v) reoxidation of the catalyst at an oxygen content of from 4 to 10% by volume.

2 . The process according to claim 1 , wherein the oxygen:n-butenes ratio during step i) is from 0.7 to 1.0 times the ratio in the production phase.

3 . The process according to claim 1 , wherein the oxygen content in the reactor Rm is decreased to from 3 to 7% by volume during step i).

4 . The process according to claim 1 , wherein the gas stream a 1 m comprising n-butenes is reduced during step i) to from 25 to 50% of the gas flow during the production phase.

5 . The process according to claim 1 , wherein, during step ii), the gas stream a 1 m comprising n-butenes is reduced to from 12.5 to 25% of the gas flow during the production phase and the gas substream d 2 m is correspondingly reduced so that the oxygen:n-butenes ratio is from 0.7 to 1.0 times the ratio in the production phase, and the gas stream a 1 m comprising n-butenes is subsequently reduced to 0.

6 . The process according to claim 1 , wherein the step iii) is carried out over a time of from 5 to 60 minutes.

7 . The process according to claim 1 , wherein the step v) is carried out over a time of from 12 to 96 hours.

8 . The process according to claim 1 , wherein the ratio of oxygen to hydrocarbons in the production phase at an n-butenes content of from 50 to 100% by volume in the feed gas stream a 1 is from 1.3:1 to 1.65:1.

9 . The process according to claim 1 , wherein the pressure in the reactor Rm during the production and regeneration phase is from 1 to 5 bar.

10 . The process according to claim 1 , wherein the regeneration phase is followed by a start-up phase comprising the steps vi) to viii):
vi) optionally additional feeding of a stream of steam a 3 m into the dehydrogenation zone; vii) additional feeding-in of the feed gas stream a 1 m comprising butenes as a lower volume flow than in the production phase and increasing of this volume flow until at least 50% of the volume flow of the feed gas stream a 1 m in the production phase is reached, with the total gas flow through the reactor Rm corresponding to not more than 120% of the total gas flow during the production phase; viii) additional feeding-in, when at least 50% of the volume flow of the feed gas stream a 1 m comprising butenes in the production phase is reached, of the oxygen-comprising stream a 2 m at a lower volume flow than in the production phase, and increasing of the volume flows of the gas streams a 1 m and a 2 m until the volume flows in the production phase have been reached, with the total gas flow through the dehydrogenation zone corresponding to not more than 120% on the total gas flow during the production phase.

11 . The process according to claim 10 , wherein the total gas stream comprising the streams a 1 m , a 2 m , d 2 m and optionally a 3 m through the dehydrogenation zone during steps (vi), (vii) and (viii) remains essentially constant and corresponds to from 90 to 110% by volume of the total gas flow through the dehydrogenation zone during the production phase.

12 . The process according to either claim 10 , wherein the amount of steam in the dehydrogenation zone during steps vi), vii) and viii) is from 0.5 to 10% by volume.

13 . The process according to claim 10 , wherein the pressure in the reactor Rm during the start-up phase is from 1 to 5 bar.

14 . The process according to claim 1 , wherein step D) comprises the steps Da) and Db):
Da) separation of incondensable and low-boiling gas constituents comprising oxygen, low-boiling hydrocarbons, possibly carbon oxides and possibly inert gases as gas stream d 2 from the gas stream c 2 by absorption of the C 4 -hydrocarbons comprising butadiene and n-butenes in an absorption medium, giving an absorption medium stream d 1 loaded with C 4 -hydrocarbons and recycle gas stream d 2 , and Db) subsequent desorption of the C 4 -hydrocarbons from the loaded absorption medium stream d 1 , giving a C 4 product gas stream d 3 .

15 . The process according to claim 14 having the additional steps:
E) separation of the C 4 product stream d 3 by extractive distillation using a solvent which is selective for butadiene into a stream e 1 comprising butadiene and the selective solvent and a stream e 2 comprising n-butenes;
F) dist

Assignees

• Basf Se
• Linde Ag

Inventors

• Ungelenk Jan
• Hammen Oliver
• Walsdorff Christian
• Eckrich Rainer
• Boelt Heinz
• Toegel Christine
• Wenning Ulrike
• Reyneke Hendrik
• Wellenhofer Anton

Classifications

• C07C5/48 Primary

  with oxygen as an acceptor · CPC title

• C07C7/09

  by fractional condensation · CPC title

• C07C7/04

  by distillation · CPC title

• C07C11/167 Primary

  1, 3-Butadiene · CPC title

• C07C5/333

  Catalytic processes · CPC title