Oligomerisation process

1. A process for the preparation of alpha-olefin oligomers, comprising contacting an olefinic feedstock comprising C 5 to C 20 alpha-olefins with a liquid complex catalyst to produce alpha-olefin oligomers, the liquid complex catalyst comprising:

(i) at least one metal halide salt of the formula MX 3 , wherein M is selected from aluminium and gallium, and each X is independently selected from chlorine, bromine and iodine; and

(ii) at least one Lewis basic donor ligand containing a donor atom selected from oxygen, sulphur, nitrogen, phosphorus, arsenic and selenium, wherein the at least one Lewis basic donor ligand is selected from compounds having a formula selected from R 1 —C(O)—R 1 , R 1 —S(O)—R 1 , R 2 NH—C(O)—NHR 2 , R 2 NH—C(S)—NHR 2 , R 1 —C(O)—NR 2 2 , (R 3 ) 3 P(O) and R 1 —CN wherein:

each R 1 independently represents a C 1 to C 10 alkyl group;

R 2 is selected from hydrogen or a C 1 to C 10 alkyl group; and

R 3 represents a C 4 to C 40 alkyl group;

wherein any of R 1 , R 2 and R 3 may optionally be substituted by one or more fluorine atoms;

wherein a molar ratio of the at least one metal halide salt to the at least one Lewis basic donor ligand is in the range of from 1:1 to 4:1, and wherein a ratio of carbon-14 to carbon-12 in the olefinic feedstock is at least 0.5×10 −13 ; and

wherein said contacting produces a product comprising a fraction which comprises alpha-olefin dimers, trimers, and tetramers, wherein the product predominantly comprises said fraction.

2. The process according to claim 1 , wherein M represents aluminium.

3. The process according to claim 2 , wherein the molar ratio of the at least one metal halide salt to the at least one Lewis basic donor ligand is in the range of from 1:1 to 2:1.

4. The process according to claim 2 , wherein the molar ratio of the at least one metal halide salt to the at least one Lewis basic donor ligand is in the range of from about 55:45 to about 65:35.

5. The process according to claim 2 , wherein the molar ratio of the at least one metal halide salt to the at least one Lewis basic donor ligand is about 3:2.

6. The process according to claim 1 , wherein X represents bromine or chlorine.

7. The process according to claim 6 , wherein MX 3 represents AlCl 3 .

8. The process according to claim 1 , wherein the at least one Lewis basic donor ligand is selected from ligands containing a donor atom selected from oxygen, sulphur, nitrogen and phosphorus.

9. The process according to claim 8 , wherein the at least one Lewis basic donor ligand is selected from the group of compounds consisting of ketones, sulfoxides, phosphine-oxides, ureas, esters, amides, ethers, thioketones, thioureas, thioamides, thioethers, amines, nitriles and phosphines.

10. The process according to claim 1 , wherein the at least one Lewis basic donor ligand is selected from urea, N,N′-dimethylurea, N,N′-dimethylthiourea, acetamide, dimethylacetamide, acetone, dimethylsulfoxide and trioctylphosphine oxide.

11. The process according to claim 1 , wherein the olefinic feedstock comprises at least 50 wt % of one or more C 5 to C 20 alpha-olefins.

12. The process according to claim 1 , wherein the olefinic feedstock comprises at least 30 wt % C 8 to C 14 alpha-olefins.

13. The process according to claim 12 , wherein the olefinic feedstock comprises at least 30 wt % C 10 to C 12 alpha-olefins.

14. The process according to claim 13 , wherein the olefinic feedstock comprises at least 30 wt % 1-decene or 1-dodecene.

15. The process according to claim 1 , wherein the olefinic feedstock comprises at least 30 wt % C 16 to C 18 alpha-olefins.

16. The process according to claim 15 , wherein the olefinic feedstock comprises at least 30 wt % 1-hexadecene or 1-octadecene.

17. The process according to claim 1 , wherein the olefinic feedstock comprises up to 20 wt % paraffins.

18. The process according to claim 1 , wherein the ratio of carbon-14 to carbon-12 in the olefinic feedstock is at least 0.6×10 −13 .

19. The process according to claim 1 , wherein the olefinic feedstock is contacted with the liquid complex catalyst at a temperature of from 0 to 160° C.

20. The process according to claim 1 , wherein the olefinic feedstock is contacted with from 0.01 to 5 wt % of the liquid complex catalyst based on a total weight of the liquid complex catalyst and olefinic feedstock.

21. The process according to claim 1 , wherein the olefinic feedstock comprises at least 50 wt % of one or more C 6 to C 18 alpha-olefins.