Process for the oligomerization of olefins with control of the oligomer content in the hydrocarbon streams to be oligomerized

1. A process for oligomerization of C 3 - to C 5 -olefins, comprising:

oligomerizing a feed mixture comprising the C 3 - to C 5 -olefins in at least one reaction stage and in the presence of a heterogeneous oligomerization catalyst comprising

a nickel compound, and

a support material, comprising

an aluminum oxide, a silicon dioxide, or an aluminosilicate,

wherein one reaction stage in each case comprises

at least one reactor in which the oligomerization is carried out forming an oligomerizate, and

at least one distillation column in which the oligomers formed during the oligomerization are at least partially separated from a residual oligomenzate,

wherein at least a portion of the residual oligomerizate from which the oligomers have been separated is recycled to one or more reactor(s) of the at least one reaction stage, and a content of oligomers in a feed to one or more reactor(s) of the at least one reaction stage, which comprises the recycled residual oligomerizate and a fresh feed of the feed mixture, is less than 0.4% by weight, based on a total composition of the feed,

wherein a content of oligomers is monitored during ongoing operation.

2. The process according to claim 1 , wherein the content of oligomers in the feed to one or more reactor(s) of the at least one reaction stage is ≤0.2% by weight, based on the total composition of the feed.

3. The process according to claim 1 , wherein the oligomerization is carried out in at least two reaction stages, wherein the oligomers formed in the reactor or in the reactors of the first reaction stage are separated from the residual oligomerizate in the distillation column of the first reaction stage, and wherein the residual oligomerizate is fed partly to the reactor(s) of the same reaction stage and partly to the reactor(s) of the next reaction stage.

4. The process according to claim 1 , wherein the support material of the oligomerization catalyst comprises the aluminosilicate.

5. The process according to claim 4 , wherein the support material of the oligomerization catalyst consists of the aluminosilicate.

6. The process according to claim 4 , wherein the heterogeneous oligomerization catalyst 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.

7. The process according to claim 1 , wherein the oligomerization catalyst has a specific surface area, calculated according to BET, of 150 to 700 m 2 /g.

8. 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.

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

10. The process according to claim 1 , wherein the process is a process for oligomerizing C 4 -olefins.

11. The process according to claim 1 , wherein the oligomerization in each of the at least one reaction stages is carried out in a liquid phase.

12. The process according to claim 1 , wherein a degree of dimerization after the oligomerization is at least 60% based on a converted reactant.

13. The process according to claim 1 , wherein weight hourly space velocity (WHSV) during the oligomerization is from 1 g of reactant per g of catalyst and per h: 1 h −1 to 190 h −1 .

14. The process according to claim 8 , wherein the temperature is in the range of 60 to 130° C.

15. The process according to claim 9 , wherein the pressure is from 20 to 55 bar.