Method of manufacturing hydrocarbons

1. A method for manufacturing hydrocarbons by operating a Fischer-Tropsch reactor comprising a fixed bed of reduced Fischer-Tropsch catalyst that comprises cobalt as catalytically active metal, said method comprising the steps of:

a) supplying an initial gaseous feed stream comprising carbon monoxide and hydrogen to the reactor;

b) converting carbon monoxide and hydrogen supplied with the initial gaseous feed stream to the reactor into hydrocarbons at an initial reaction temperature;

c) obtaining an initial hydrocarbon stream from the Fischer-Tropsch reactor;

d) adding to a further gaseous feed stream a nitrogen-containing compound selected from the group consisting of ammonia, HCN, NO, amines, nitriles, and a heterocyclic compound containing at least one nitrogen atom as a ring member of a heterocyclic ring and combinations thereof, such that the nitrogen-containing compound is present in the further gaseous feed stream in a concentration of up to 10 ppmV;

e) obtaining, during and/or after addition of the nitrogen-containing compound, a further hydrocarbon stream from the Fischer-Tropsch reactor having a second C41+ concentration which is less than an initial C41+ concentration in the initial hydrocarbon stream; and

wherein the second C41+ concentration is at least 5% less than the initial C41+ concentration of the initial hydrocarbon stream.

2. A method according to claim 1 , wherein the second C41+ concentration is at least 10% less than the initial C41+ concentration.

3. A method according to claim 1 , wherein the nitrogen-containing compound is present in the further gaseous feed stream in a concentration in the range of 0.05 to 10 ppmV.

4. A method according to claim 1 , wherein the method further comprises the steps of:

f) determining the concentration of hydrocarbons having a chain length of at least 41 carbons (C41+) in the further hydrocarbon stream obtained in step e), being the further C41+ concentration;

g) increasing, decreasing or maintaining the amount of the nitrogen-containing compound added to the further gaseous feed stream, based on concentration of hydrocarbons having a chain length of at least 41 carbons (C41+) in the further hydrocarbon stream obtained in step f).

5. A method according to claim 4 , wherein steps f) and g) are repeated until the concentration of the further C41+ hydrocarbons is at least 5% less than that of the initial C41+ concentration.

6. 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.

7. A method according to claim 1 , wherein the nitrogen-containing compound is ammonia.

8. A method according to claim 1 , wherein the initial reaction temperature is in the range of 200 to 230° C.

9. A method according to claim 1 , wherein the second C41+ concentration is less than 30 w % based on the total weight of the hydrocarbon stream obtained in step e).

10. A method according to claim 1 wherein the initial C41+ concentration is at least 40 w % based on the weight of the initial hydrocarbon stream obtained in step c).

11. A method according to claim 1 wherein the second C41+ concentration is at least 15% less than the initial C41+ fraction.

12. A method according to claim 1 , further comprising the step of determining the concentration of hydrocarbons having a chain length of at least 41 carbons (C41+) in the initial hydrocarbon stream obtained in step c), being the initial C41+ concentration.

13. A method according to claim 1 , wherein the initial reaction temperature is in the range of 205 to 220° C.