Process for oligomerizing olefins with streams having a reduced olefin content

1. A process for oligomerizing C2- to C8-olefins in at least three reaction stages connected in series, each reaction stage comprising at least one reactor and at least one distillation column, wherein the process comprises:

(a) providing a starting mixture comprising C2- to C8-olefins, and dividing the starting mixture into first feed stream and second feed stream, wherein the first feed stream is fed as feed stream to the first reaction stage and the second feed stream is added to the feed stream to at least one of the downstream reaction stages, in which the olefin content is less than 50% by weight;

(b) a first reaction stage: oligomerizing, using an oligomerization catalyst, the olefins in the feed stream to the first reaction stage in at least one reactor and separating oligomers formed as bottom product in a downstream distillation column, wherein an overhead product formed in the distillation column is at least partially fed as feed stream to the second reaction stage;

(c) a second reaction stage: oligomerizing, using an oligomerization catalyst, the olefins in the feed stream to the second reaction stage in at least one reactor and separating oligomers formed as bottom product in a distillation column, wherein an overhead product formed in the distillation column is at least partially fed as feed stream to the third reaction stage; and

(d) a third reaction stage: oligomerizing, using an oligomerization catalyst, the olefins in the feed stream to the third reaction stage in at least one reactor and separating oligomers formed in this case as bottom product in a distillation column;

wherein the at least one reactor in the last reaction stage is operated adiabatically, but the reactors in the preceding reaction stages are cooled using a cooling medium; and

wherein each oligomerization catalyst used in the reactors of the individual reaction stages comprises a nickel compound on an aluminosilicate support material and which comprises less than 0.5% by weight titanium dioxide and zirconium dioxide in an overall composition of each of the oligomerization catalysts.

2. The process according to claim 1 , wherein, based on a cooling power of 100% for the at least one reactor in the first reaction stage, the cooling power in the reactor(s) of the subsequent reaction stages is less than 100% but is 0% only in the last reaction stage.

3. The process according to claim 1 , wherein heat absorbed by the cooling medium is used to heat one or more of the feed streams to the individual reaction stages.

4. The process according to claim 3 , wherein the one or more feed streams to the individual reaction stages are heated to a temperature of >50° C.

5. The process according to claim 1 , wherein the oligomerization in each of the reaction stages present is carried out at a temperature in the range of 50 to 200° C.

6. The process according to claim 5 , wherein the temperature is in the range of 60 to 130° C.

7. The process according to claim 1 , wherein the pressure in the oligomerization of each of the reaction stages present is 10 to 70 bar.

8. The process according to claim 7 , wherein the pressure is 20 to 55 bar.

9. The process according to claim 1 , wherein the oligomerization catalyst in the reactors of the individual reaction stages has a composition of

15 to 40% by weight NiO,

5 to 30% by weight Al 2 O 3 ,

55 to 80% by weight SiO 2 and

0.01 to 2.5% by weight of an alkali metal oxide.

10. The process for oligomerization according to claim 1 ,

wherein (d) is:

(d) third reaction stage: oligomerizing, using the oligomerization catalyst, the olefins in the feed stream to the third reaction stage in at least one reactor and separating oligomers formed as bottom product in a distillation column, wherein an overhead product formed in the distillation column is at least partially fed as feed stream to the fourth reaction stage; and

wherein said process further comprises:

(e) fourth reaction stage: oligomerizing, using an oligomerization catalyst, the olefins in the feed stream to the fourth reaction stage in at least one reactor and separating oligomers formed as bottom product in a distillation column.

11. The process for oligomerization according to claim 10 ,

wherein (e) is:

(e) fourth reaction stage: oligomerizing, using the oligomerization catalyst, the olefins in the feed stream to the fourth reaction stage in at least one reactor and separating oligomers formed as bottom product in a distillation column, wherein the overhead product formed in the distillation column is at least partially fed as feed stream to the fifth reaction stage; and

wherein said process further comprises:

(f) fifth reaction stage: oligomerizing, using the oligomerization catalyst, of the olefins in the feed stream to the fifth reaction stage in at least one reactor and separating oligomers formed as bottom product in a distillation column.

12. The process according to claim 1 , wherein the overhead product of the distillation column of the last reaction stage is partially or fully recycled to the at least one reactor in the last reaction stage and/or is partially or fully discharged from the process.