METHOD FOR OPERATING A DEHYDROGENATION REACTOR FOR THE DEHYDROGENATION OF HYDROCARBONS

Abstract

The invention relates to a method for operating a dehydrogenation reactor for the dehydrogenation of hydrocarbons is provided wherein the dehydrogenation reactor comprises a potassium promoted iron oxide catalyst, the hydrocarbons being dehydrogenated in contact with the catalyst and carbon dioxide is introduced during a) start-up of the reactor, b) shut-down of the reactor, and c) steaming procedures, wherein the carbon dioxide is introduced in conjunction with steam in at least one method step.

Claims

1-16. (canceled)

17. A method for operating a dehydrogenation reactor for the dehydrogenation of hydrocarbons wherein the dehydrogenation reactor comprises a potassium promoted iron oxide catalyst the hydrocarbons being dehydrogenated in contact with the catalyst, characterized in that carbon dioxide is introduced during a. start-up of the reactor, b. shut-down of the reactor, and c. steaming procedures, characterized in that the method comprises the following steps during start-up (a): i. heating the reactor to a first temperature by a recirculating gas stream comprising nitrogen, ii. heating the reactor to a second temperature by introducing steam, and optionally continuing nitrogen recirculation along with the steam, iii. optionally, checking for leaks, and iv. heating the reactor to a third temperature and stopping carbon dioxide introduction before introducing the hydrocarbon, wherein the carbon dioxide is introduced in step i) via the recirculating nitrogen gas stream and in steps ii) and iv) via the steam and optional recirculating nitrogen, the method comprises the following steps during shut-down (b): i. stopping the introduction of hydrocarbons into the reactor, the reactor being at a third temperature, ii. cooling the reactor to a first temperature using a coolant gas comprising steam and optionally adding nitrogen and recirculating the nitrogen along with the steam, iii. cooling the reactor to a fourth temperature using a recirculating coolant gas comprising nitrogen, wherein the carbon dioxide is introduced in step ii) via the coolant gas comprising steam and optional recirculating nitrogen and in step iii) via the coolant gas comprising nitrogen, the method comprises the following steps during steaming procedures (c) beginning from normal operation: i. stopping the introduction of hydrocarbons into the reactor, the reactor being at a third temperature ii. adjusting the reactor to and holding at a fifth temperature with steam and optionally adding nitrogen and recirculating the nitrogen, iii. adjusting the temperature to a third temperature and stopping the introduction of carbon dioxide before introducing the hydrocarbon, wherein the carbon dioxide is introduced in steps ii) and iii) via the steam and optional recirculating nitrogen, wherein the concentration of carbon dioxide in the steam is from 0.1 to 20% by volume and the concentration of carbon dioxide in the nitrogen gas is from 2 to 50% by volume.

18. The method of claim 17, characterized in that carbon dioxide recirculation is practiced.

19. The method of claim 17, characterized in that steaming-procedures are incorporated into a start-up comprising the following steps: i. heating the reactor to a first temperature by a recirculating gas stream comprising nitrogen, ii. heating to and holding at a fifth temperature with steam and optionally recirculating the nitrogen, iii. adjusting the temperature to a third temperature and stopping the introduction of carbon dioxide before introducing the hydrocarbon, wherein the carbon dioxide is introduced in step i) via the recirculating nitrogen gas stream and in steps ii) and iii) via the steam and optional recirculating nitrogen.

20. The method of claim 17, characterized in that the fifth temperature is maintained for a time of 30 minutes to 4 hours.

21. The method of claim 17, characterized in that the first temperature is in the range of from 260 C. to 370 C.

22. The method of claim 17, characterized in that the second temperature is in the range of from 480 C. to 590 C.

23. The method of claim 17, characterized in that the third temperature is in the range of from 540 C. to 650 C.

24. The method of claim 17, characterized in that the fourth temperature is in the range of from 20 C. to 50 C.

25. The method of claim 17, characterized in that the fifth temperature is in the range of from 540 C. to 650 C.

26. The method of claim 17, characterized in that the concentration of carbon dioxide in the nitrogen gas is from 0.1 to 100% by volume.

27. The method of claim 17, characterized in that the catalyst is an iron based dehydrogenation catalyst comprising from 40 to 90% by weight iron and from 5 to 30% by weight potassium.

28. The method of claim 17, characterized in that the hydrocarbon is selected from the group of alkylbenzenes such as ethylbenzene, methylethylbenzenes, diethylbenzene and alkanes such as propane, butane and linear alkanes through C9 to C15.

29. The method of claim 18, characterized in that steaming-procedures are incorporated into a start-up comprising the following steps: iv. heating the reactor to a first temperature by a recirculating gas stream comprising nitrogen, v. heating to and holding at a fifth temperature with steam and optionally recirculating the nitrogen, vi. adjusting the temperature to a third temperature and stopping the introduction of carbon dioxide before introducing the hydrocarbon, wherein the carbon dioxide is introduced in step i) via the recirculating nitrogen gas stream and in steps ii) and iii) via the steam and optional recirculating nitrogen.

30. The method of claim 18, characterized in that the fifth temperature is maintained for a time of 30 minutes to 4 hours.

31. The method of claim 18, characterized in that: the first temperature is in the range of from 260 C. to 370 C., the second temperature is in the range of from 480 C. to 590 C., the third temperature is in the range of from 540 C. to 650 C., the fourth temperature is in the range of from 20 C. to 50 C., or the fifth temperature is in the range of from 540 C. to 650 C.

32. The method of claim 18, characterized in that the concentration of carbon dioxide in the nitrogen gas is from 0.1 to 100% by volume.

33. The method of claim 18 characterized in that the catalyst is an iron based dehydrogenation catalyst comprising from 40 to 90% by weight iron and from 5 to 30% by weight potassium.

34. The method of claim 18, characterized in that the hydrocarbon is selected from the group of alkylbenzenes such as ethylbenzene, methylethylbenzenes, diethylbenzene and alkanes such as propane, butane and linear alkanes through C9 to C15.

Description

[0072] An embodiment of the present invention will now be described further, by way of example, with reference to the accompanying drawing, in which:

[0073] FIG. 1 shows a schematic flow diagram depicting the steam, nitrogen and carbon dioxide flow through a system comprising two reactors.

[0074] The gas flow through a system comprising two reactor vessels is schematically depicted in FIG. 1. Steam can be introduced into the system by a steam source line 20, nitrogen by a nitrogen source line 22 and carbon dioxide can be introduced by a carbon dioxide source line 24. The gases are mixed using a mixer 14 before the gas is led into a heater 28. The heater may be a steam superheating furnace. The heated gas is then fed into the first reactor vessel 10. In the embodiment shown in FIG. 1, the effluent of the first reactor vessel 10 is first led through a re-heating device 30 before the gas stream is introduced into the second reactor vessel 12.

[0075] The effluent is then passed to a condensing heat exchanger 32. Water is condensed inside the condensing heat exchanger 32 and leaves the system through line 34. Nitrogen and carbon dioxide are led to a compressor 16 through recirculation line 26 and are then fed back into the mixer 14.

[0076] In normal dehydrogenation operation, hydrocarbons can be introduced into the system via a hydrocarbon source line 18 and are removed through line 36 after the effluent has passed through the heat exchanger 32.

[0077] In further embodiments of the invention, different configurations are possible, e.g. a different number of reactor vessels may be used or several reactor vessels could be used in a parallel configuration.

[0078] The following example, the FIGURE and the claims further illustrate the invention.

EXAMPLE 1

[0079] During the start-up of the reactor, air is purged from the equipment with nitrogen, then nitrogen and carbon dioxide are introduced. To make up for losses to flare, nitrogen and carbon dioxide continue to be added so that flow rates of about 60,000 lb/hr including the recycled nitrogen and carbon dioxide can be maintained through the reactors while heating to 315.5 C. (600 F). After passing through heat exchangers, a compressor recirculates the gas back to the mixers. The CO.sub.2 concentration in the reactor effluent is 10 vol %.

[0080] After reaching the first temperature of 315.5 C. (600 F), steam is introduced into the mixer along with recirculated nitrogen and carbon dioxide while heating to 537.8 C. (1000 F). The total flow rates to the reactors are 100,000 lb/hr steam, 15,240 lb/hr of nitrogen, and 1,091 lb/hr of carbon dioxide. Through the recirculation line, 15,000 lb/hr of nitrogen and 1000 lb/hr of carbon dioxide are fed back into the mixer. About 240 lb/hr nitrogen and 182 lb/hr of carbon dioxide are also added to the mixer to make up for losses to condensate and flare.

[0081] The reactor is heated further. When the third temperature is reached, the introduction of carbon dioxide is stopped. The reactor can then be used for the dehydrogenation of hydrocarbons.