Method and apparatus for purifying a mixture comprising oil and wax

1. A method for fractionating a crude mixture comprising at least one oil and at least one wax, which comprises the following steps:

(a) mixing the crude mixture with a solvent to obtain a crude solvent-mixture,

(b) carrying out at least one crystallization stage with the solvent-mixture obtained in step (a) to prepare a first fraction containing dewaxed oil and a second fraction containing slack wax,

(c) carrying out at least one crystallization stage with the second fraction obtained in step (b) in a layer crystallizer, wherein to the second fraction prior to the crystallization in step (c) no solvent or at most 100% by weight of solvent relative to the weight of the second fraction are added, to prepare a third fraction containing hard wax having an oil content of at most 1.5% by weight and a fourth fraction containing soft wax having an oil content of more than 1.5% by weight and

(d) circulating at least a part of the fourth fraction into at least one of the at least one crystallization stage of step (b).

2. The method in accordance with claim 1 , wherein the crude mixture includes 60 to 99% by weight of oil and 1 to 40% by weight of wax.

3. The method in accordance with claim 1 , wherein the crude mixture includes, based on the total weight of wax, at least 50% by weight of light wax having a viscosity at 100° C. of at most 7 cSt.

4. The method in accordance with claim 1 , wherein the crude mixture is mixed in step (a) with a solvent selected from the group consisting of methyl ethyl ketone, methyl isobutyl ketone, acetone, benzene, toluene, dichloromethane, dichloroethane, methylene dichloride, methanol, methyl tertiary butyl ether, N-methyl-pyrolidone and mixtures of two or more of the aforementioned solvents.

5. The method in accordance with claim 4 , wherein the solvent is a mixture of methyl ethyl ketone and toluene or a mixture of dichloroethane and methylene dichloride.

6. The method in accordance with claim 1 , wherein in step (b) at least one suspension crystallization stage is carried out.

7. The method in accordance with claim 1 , wherein in step (b) one to five crystallization stages are carried out.

8. The method in accordance with claim 1 , wherein to the second fraction obtained in step (b), prior to the crystallization in step (c), at most 100% by weight of solvent relative to the weight of the second fraction is added.

9. The method in accordance with claim 1 , wherein in step (c) at least one static crystallization stage is carried out.

10. The method in accordance with claim 1 , wherein in step (c) one to five crystallization stages are carried out.

11. The method in accordance with claim 1 , wherein in step (d) 10 to 100% of the fourth fraction are circulated into the at least one crystallization stage of step (b).

12. A plant for fractionating a crude mixture comprising at least one oil and at least one wax, in particular for carrying out a method in accordance with claim 1 , wherein the plant comprises:

i) a source of a crude mixture,

ii) a first crystallization section comprising two to ten suspension crystallizers,

iii) a second crystallization section comprising at least one layer crystallizer, and

iv) a circulation line connecting the outlet of the at least one layer crystallizer iii) and an inlet of the at least one suspension crystallizer ii).

13. The plant in accordance with claim 12 , wherein the first crystallization section ii) comprises two to five suspension crystallizers, and the second crystallization section iii) comprises one to thirty layer crystallizers.

14. The plant in accordance with claim 12 , wherein the first crystallization section comprises a line for feeding solvent into the at least one suspension crystallizer.