Method for Start-up And Operation Of A Fischer-Tropsch Reactor

Abstract

The invention relates to a method for start-up and operation of a Fischer-Tropsch reactor comprising the steps of: (a) providing a reactor with a fixed bed of reduced Fischer-Tropsch catalyst that comprises cobalt as catalytically active metal; (b) supplying a gaseous feed stream comprising carbon monoxide and hydrogen to the reactor, wherein the gaseous feed stream comprises a nitrogen-containing compound other than molecular nitrogen in an initial concentration, wherein the initial concentration in the range of from 10 to 350 ppbv based on the volume of the gaseous feed stream; (c) converting carbon monoxide and hydrogen supplied with the gaseous feed stream to the reactor into hydrocarbons at a reaction temperature and at a set reactor productivity, whilst maintaining the initial concentration of the nitrogen-containing compound and maintaining the set reactor productivity during a first time period by adjusting the reaction temperature; (d) decreasing the concentration of the nitrogen- containing compound to a second concentration in the range of from 0 to 20 ppbv, wherein the second concentration is at least 5 ppbv below the initial concentration, preferably at least 20 ppbv below the initial concentration, and maintaining the reactor productivity by adjusting the reaction temperature.

Claims

1. A method for start-up and operation of a Fischer-Tropsch reactor comprising the steps of: (a) providing a reactor with a fixed bed of reduced Fischer-Tropsch catalyst that comprises cobalt as catalytically active metal; (b) supplying a gaseous feed stream comprising carbon monoxide and hydrogen to the reactor, wherein the gaseous feed stream comprises a nitrogen-containing compound other than molecular nitrogen in an initial concentration, wherein the initial concentration in the range of from 10 to 350 ppbv based on the volume of the gaseous feed stream; (c) converting carbon monoxide and hydrogen supplied with the gaseous feed stream to the reactor into hydrocarbons at a reaction temperature and at a set reactor productivity, whilst maintaining the initial concentration of the nitrogen-containing compound and maintaining the set reactor productivity during a first time period by adjusting the reaction temperature; (d) decreasing the concentration of the nitrogen-containing compound to a second concentration in the range of from 0 to 20 ppbv, wherein the second concentration is at least 5 ppbv below the initial concentration, and maintaining the reactor productivity by adjusting the reaction temperature.

2. A method according to claim 1, wherein the catalyst is a fresh catalyst

3. A method according to claim 1, wherein the nitrogen-containing compound is a compound selected from the group consisting of ammonia, HCN, NO, an amine and combinations or two or more thereof.

4. A method according to claim 3, wherein the nitrogen-containing compound is ammonia.

5. A method according to claim 1, wherein the initial concentration of the nitrogen-containing compound in the gaseous feed is in the range of from 20 to 150 ppbv, preferably of from 30 to 50 ppbv.

6. A method according claim 1, wherein the first time period is in the range of from 50 to 5,000 hours.

7. A method according claim 1, wherein the reactor is provided with a fixed bed of reduced catalyst in step (a) by reducing a fixed bed of catalyst precursor in the reactor.

8. A method according to claim 7, wherein the fixed bed of catalyst precursor is reduced by contacting the catalyst precursor with a hydrogen-containing gas comprising nitrogen or ammonia at a reduction temperature and pressure.

9. A method according to claim 8, wherein the hydrogen-containing gas comprises in the range of from 1 to 60 vol % nitrogen.

10. A method according to claim 8, wherein the hydrogen-containing gas comprises in the range of from 2 to 1000 ppmv ammonia.

11. A method according claim 1, wherein the catalyst does not comprise a noble metal.

Description

EXAMPLES

Example 1 (Invention)

[0049] A gaseous feed stream comprising 50 ppbv nitrogen-containing compounds (HCN and ammonia) was supplied to a reactor tube comprising reduced cobalt-based Fischer-Tropsch catalyst, at an inlet pressure of 60 bar (absolute). The gaseous feed was composed of fresh synthesis gas (50%) and synthesis gas recycled from the reactor tube (50%). The synthesis gas comprised 75% decontaminated synthesis gas with a concentration of HCN and ammonia in the range of from 2 to 10 ppbv and 25% of synthesis gas from a steam methane reforming unit with a concentration of HCN and ammonia of approximately 800 ppbv. The recycled synthesis gas was free of HCN and ammonia.

[0050] The reaction temperature needed for a space time yield (STY) of 200 g/l.h was 202? C. During 865 runhours, the gaseous feed stream was kept the same and the gas hourly space velocity and the space time yield was maintained at 200 g/l.h by gradually increasing the reaction temperature. Then the fresh synthesis gas was changed to 100% decontaminated synthesis gas with a concentration of HCN and ammonia of 10 ppbv. Again the space time yield was maintained at 200 g/l.h and the reaction temperature adjusted. Immediately upon changing the gaseous feed stream, the reaction temperature had to be decreased by 3? C. to keep the space time yield at 200 g/l.h. Thereafter, the reaction temperature had to be gradually increased to compensate for loss in catalyst activity. The inlet pressure was 60 bar (absolute) during the entire experiment.

[0051] At 1,800 runhours from the start of the reactor, the experiment was stopped and the intrinsic activity of the catalyst was determined.

Example 2 (Comparative)

[0052] The experiment of Example 1 was repeated but now the fresh synthesis gas was 100% decontaminated synthesis gas from the start of the experiment. As in experiment 1, the reactor productivity (STY) was maintained at a value of 200 g/l.h during the experiment and the reaction temperature was adjusted. The inlet pressure was 60 bar (absolute).

[0053] The initial reaction temperature needed to set the reactor productivity (STY) at a value of 200 g/l.h was 199? C. During the experiment the reaction temperature had to be gradually increased to maintain STY at 200 g/l.h. After 1,800 runhours, the experiment was stopped and the intrinsic activity of the catalyst was determined.

[0054] The intrinsic activity of the catalyst used in experiment 1 was 26% higher than the intrinsic activity of the catalyst used in comparative experiment 2. This shows that the method according to the invention results in improved catalyst stability compared to a process wherein less than 10 ppbv N-containing compound is present in the gaseous feed stream during start-up and the initial operation phase of the reactor.