METHOD FOR THE ACTIVATION OR REJUVENATION OF A CATALYST

Abstract

A method is disclosed for rejuvenation a cobalt Fischer Tropsch catalyst used in a Fischer Tropsch process operating in recycle mode. The method permits the use of specific inert gases to adjust the mole weight of the gas so that the recycle compressor designed for normal steady state operation can also be used in the method. Hydrogen from a membrane permeate stream is added to the reactor loop at a temperature between 300 F and 400 F and the carbon oxides are reacted out to purify the hydrogen. This stream is continuously recycled and the temperature is raised to between 425 F and 500 F and held at the final temperature for between 4 hours and 48 hours. The cobalt Fischer Tropsch catalyst is effectively rejuvenated in-situ by the method.

Claims

1. A method to activate or rejuvenate a cobalt Fischer Tropsch catalyst used in a Fischer Tropsch process, the method comprising: A) purging a Fischer Tropsch reactor loop with a feed gas, argon, or a mixture thereof; B) adding permeate hydrogen from a hydrogen membrane to the Fischer Tropsch reactor loop to between 10% and 80% while recycling the loop with little or no purge, at a temperature below 300 F in the Fischer Tropsch reactor; C) raising the temperature in the Fischer Tropsch reactor to between 300 F and 400 F to hydrogenate carbon oxides from the permeate hydrogen, thus making methane and other heavier hydrocarbons, resulting in a circulating gas comprising hydrogen and relatively inert hydrocarbon gases or argon, that is substantially depleted of carbon oxides; and D) raising the temperature of the Fischer Tropsch reactor to between 425 F and 500 F and holding for between 4 hours and 48 hours while recycling the hydrogen-containing gas with little or no purge.

2. The method of claim 1 wherein the feed gas is methane, natural gas, associated gas, coal seam gas, landfill gas, biogas, or a combination thereof.

4. The method of claim 1 wherein the Fischer Tropsch reactor loop comprises a recycle compressor and where the recycle compressor of the Fischer Tropsch reactor loop is a driver for recycling the gases.

5. The method of claim 1 wherein the Fischer Tropsch reactor is a fixed bed reactor.

6. The method of claim 1 wherein the method occurs at an elevated pressure above 10 bar.

7. The method of claim 1 wherein the rejuvenation occurs at an elevated pressure above 20 bar.

8. The method of claim 1 wherein the method operates at a gas flow rate equal to or greater than the flow rate used during normal synthesis operation.

9. The method of claim 1 wherein the method operates at a gas flow rate above 500 GHSV.

10. The method of claim 1 wherein the method operates at a gas flow rate above 1,000 GHSV.

11. The method of claim 1 wherein the gas is circulated with a compressor.

12. The method of claim 11 where the compressor is a centrifugal compressor.

13. The method of claim 1 wherein 90% or more of the carbon oxides are converted to methane or higher hydrocarbons in step C.

14. The method of claim 1 wherein the cobalt catalyst is rejuvenated in-situ.

15. The method of claim 1 wherein the hydrogen of step (B) is from a PSA system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0018] The methods discussed herein are merely illustrative of specific manners in which to make and use this invention and are not to be interpreted as limiting in scope.

[0019] While the method has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the construction and the arrangement of the devices and components without departing from the spirit and scope of this disclosure. It is understood that the method is not limited to the embodiments set forth herein for purposes of exemplification.

[0020] In general, in a first aspect, the invention relates to a method to rejuvenate a cobalt Fischer Tropsch catalyst used for the production of heavy hydrocarbon products from synthesis gas.

[0021] As noted above, it is an object of the present invention to use a rejuvenation method to recover activity of a partially deactivated cobalt Fischer Tropsch catalyst with minimal additional equipment and cost. For a Fischer Tropsch reactor that is designed to operate in a recycle mode, it is therefore desirable to use the existing equipment such as the recycle compressor, hydrogen membrane, and product knockout drums to rejuvenate the catalyst. Since the Fischer Tropsch recycle process may be designed for a relatively low pressure drop and high flow, a centrifugal compressor is a likely choice for the system. Centrifugal compressors must be designed for the operating pressure and gas conditions. While a centrifugal compressor is the preferred choice of the present invention, any type of compressor known to one skilled in the art may be used and still be within the scope of the invention.

[0022] To keep the method simple and the cost low, operating conditions of the rejuvenation method will preferably be set so that the same compressor used in normal operation of the Fischer Tropsch loop can be used for the rejuvenation method. Normally the recycle compressor will operate with a mole weight in the range of approximately 10 to 30. The recycle gas in normal Fischer Tropsch operation may consist of unreacted hydrogen and carbon monoxide and system inert gases, which may include nitrogen, carbon dioxide, and light hydrocarbons. If the feed gas being processed is a biogas, it may contain large amounts of carbon dioxide, which will make the recycle gas stream mole weight higher. If the feed gas is natural gas, methane will build up as the inert gas and the mole weight will be lower. In all cases, the mole weight of the normal recycle stream is much higher than that of hydrogen, which is the gas needed in the rejuvenation method. Since hydrogen has a mole weight of 2, it will not be possible to use the existing process recycle compressor to operate the rejuvenation method without substantially changing the composition of the gas. An inert gas must be added to the hydrogen used in the rejuvenation method to increase the mole weight of the gas so that the process compressor can be used for both operations. Without the addition of an inert gas, the only other options are to provide a separate compressor for recycle or operate the method on a once-through basis, which is not practical. While the method can be practiced with a very high concentration of hydrogen, it is desirable to dilute the hydrogen. This dilute system still has adequate hydrogen since the method is operated above 10 bar, preferably above 20 bar, up to the normal operating pressure of the Fischer Tropsch reaction, which could be up to 60 bar or more. At these pressures, the hydrogen partial pressure is high and it will therefore be adequate for the rejuvenation method. In a preferred embodiment of the process the hydrogen is diluted to between 20% and 50% hydrogen concentration. By definition this is an in-situ rejuvenation, as the catalyst is fully rejuvenated in the reactor and returned to service with minimal downtime.

Experimental

[0023] A long continuous run was carried out to demonstrate the effectiveness of the rejuvenation method of the present invention for recovering activity of a partially deactivated cobalt Fischer Tropsch catalyst. For the run a ½ inch internal diameter micro reactor was packed with a mixture of 22.5 cc of inert ceramic material and 7.5 cc of cobalt Fischer Tropsch catalyst made according to U.S. Pat. No. 9,358,526. The catalyst was initially activated using a ROR activation process described in U.S. Pat. No. 10,434,506. The experiments were done using bottled syngas with a H2:CO ratio of 1.6 and containing approximately 34% nitrogen as a diluent and internal standard for analysis. Operating conditions are listed in Table 1 below. The catalyst relative performance is described using a kinetic factor Kt. The initial Kt of the catalyst was around 3.0, while the Kt was 2.77 at 50 hours on stream and 2.45 at 150 hours on stream. After 2,200 hours of steady operation, the catalyst Kt was down to 1.54 or about 55% of its fresh 50 hour rate.

[0024] After 2,200 hours of operation, the reaction was stopped and a rejuvenation was performed according to the present invention. A hydrogen containing stream comprising 95% hydrogen and a 5% mix of CO and CO2 in roughly equivalent amounts was diluted with 50% methane and passed through the catalyst at temperatures between 300 F and 400 F for several hours, demonstrating substantial conversion of both the CO and CO2. After this, the hydrogen stream was diluted by adding methane to the hydrogen stream to a concentration of 75% methane and 25% hydrogen. The temperature was raised to 475F and held for 24 hours. The catalyst was put back on stream at conditions substantially equivalent to run 1. This operation is referred to in Table 1 as run 2 and demonstrates essentially full recovery of activity.

TABLE-US-00001 TABLE 1 Fischer Tropsch catalyst performance before and after rejuvenation Run Tempera- Pressure Flow Hours on Activity number ture (F.) (psig) (GHSV) stream (Hr) Kt Run 1 380 500 4000 50 2.77 Run 1 380 500 3250 150 2.45 Run 1 380 500 2750 2200 1.54 Run 2 365 500 2750 50 2.45 Run 2 375 500 2750 150 2.49

[0025] It is not required that the flowrate of the compressor during a rejuvenation operation be the same as the flowrate in the normal Fischer Tropsch synthesis mode. It is preferable that the flowrate be equal to or higher than the flow during normal synthesis operation. The pressure drop will naturally go down in the rejuvenation mode since no liquid products are being produced during the operation of the rejuvenation method which are normally produced in the synthesis mode. Addition of one or more inert gases selected from argon, and one or more feed gases, or combinations can be used to set the mole weight of the gases used in the method of the present invention to stay within the limits of the recycle compressor designed for the normal Fischer Tropsch synthesis operation. If light hydrocarbons heavier than propane are used, they may have to be heated to keep them in the vapor phase, which can become self-limiting.

[0026] The present invention is directed at a method to rejuvenate a cobalt Fischer Tropsch catalyst used in a Fischer Tropsch process comprising: [0027] A) purging the Fischer Tropsch reactor loop with a feed gas, argon, or a mixture thereof; [0028] B) adding permeate hydrogen from a hydrogen membrane to the Fischer Tropsch reactor loop to between 10% and 80%, preferably from 20% to 50%, while recycling the loop with little or no purge, at a temperature below 300 F in the Fischer Tropsch reactor; [0029] C) raising the temperature in the Fischer Tropsch reactor to between 300 F and 400 F to hydrogenate carbon oxides from the permeate gas, thus making methane and other heavier hydrocarbons, resulting in a circulating gas comprising hydrogen and relatively inert hydrocarbon gases or argon, that is substantially depleted of carbon oxides; [0030] D) raising the temperature of the Fischer Tropsch reactor to between 425 F and 500 F and holding for between 4 hours and 48 hours while recycling the hydrogen containing gas with little or no purge.

[0031] When the rejuvenation method is completed, the temperature may be reduced to a safe operating temperature to start the Fischer Tropsch process.

[0032] Whereas, the devices and methods have been described in relation to the claims, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.