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, the method comprising the steps of:

(a) performing a pre-fractionation step ( 2 ) as a layer crystallization (i) with a crude mixture comprising the at least one oil and the at least one wax or (ii) with a crude solvent mixture obtained by adding prior to the pre-fractionation step ( 2 ) at most 100% by weight of solvent relative to the weight of the crude mixture, wherein the pre-faction step ( 2 ) is sufficient to prepare a first fraction containing low waxy oil and a second fraction containing low oily wax,

(b) preforming a first crystallization step ( 12 ) which includes the further sub-steps of:

(b 1 ) performing a first suspension crystallization sub-step ( 14 ) with the first fraction containing low waxy oil to prepare a third fraction containing dewaxed oil and a fourth fraction; and

(b 2 ) after the first suspension crystallization sub-step ( 14 ), performing a second suspension crystallization sub-stage ( 14 ′) with a mixture of the fourth fraction obtained in the pre-fractionation stage of method sub-step (b 1 ) and the second fraction containing low oily wax obtained in step (a) to prepare a fifth fraction containing slack wax and a sixth fraction.

2. The method in accordance with claim 1 , wherein the pre-fractionation stage ( 2 ) comprises one or more layer crystallization sub-stages performed each with one or more static crystallizers.

3. The method in accordance with claim 1 , wherein the layer crystallization of the pre-fractionation stage ( 2 ) of method step (a) is carried out so that the first fraction obtained after crystallization comprises at most 70% by weight of the wax content of the crude mixture.

4. The method in accordance with claim 1 , wherein the method further comprises

(c) carrying out a second crystallization stage ( 36 ) comprising:

(c 1 ) carrying out at least one crystallization sub-stage ( 38 , 38 ′) with at least a part of the fifth fraction obtained in method step (b 2 ), wherein to the fifth fraction prior to the crystallization in method step (c 1 ) no solvent or at most 100% by weight of solvent relative to the weight of the fifth fraction are added, to prepare a seventh fraction containing deoiled light wax having an oil content of at most 5% by weight and having a kinematic viscosity of at most 7 cSt and an eighth fraction containing light soft wax having an oil content of more than 5% by weight and a kinematic viscosity of at most 7 cSt and

(c 2 ) optionally circulating at least a part of the eighth fraction into the second crystallization sub-stage ( 14 ′) of the first crystallization stage ( 12 ) of method step (b 2 ).

5. The method in accordance with claim 4 , wherein the method further comprises

(d) carrying out a third crystallization stage ( 43 ) comprising:

(d 1 ) carrying out at least one crystallization sub-stage ( 14 ″, 14 ″) with at least a part of the fifth fraction obtained in method step (b 2 ), wherein to the fifth fraction prior to the crystallization in method step (c 1 ) more than 100% by weight of solvent relative to the weight of the fifth fraction are added, to prepare a ninth fraction containing deoiled heavy wax having an oil content of at most 5% by weight and a kinematic viscosity of more than 7 cSt and a tenth fraction containing heavy soft wax having an oil content of more than 5% by weight and a kinematic viscosity of more than 7 cSt.

6. The method in accordance with claim 5 , wherein the crude mixture is mixed in any of method steps (a), (c 1 ) and (d 1 ) with a solvent selected from the group consisting of methyl ethyl ketone, methyl isobutyl ketone, acetone, benzene, toluene, dichloroethane, methylene dichloride, methanol, methyl tertiary butyl ether, N-methyl-pyrolidone and mixtures of two or more of the aforementioned solvents.

7. The method in accordance with claim 4 , wherein in the second crystallization stage ( 36 ) in method step (c) at least one layer crystallization sub-stage ( 38 , 38 ′) is carried out.

8. The method in accordance with claim 4 , wherein in the second crystallization stage ( 36 ) in method step (c) one to five crystallization sub-stages ( 38 , 38 ′) are carried out.

9. The method in accordance with claim 4 , wherein in method step (c 2 ) 10 to 100% of the eighth fraction are circulated into the second crystallization sub-stage ( 14 ′) of method step (b 2 ).

10. 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.

11. The method in accordance with claim 1 , wherein the first suspension crystallization sub-stage ( 14 ) of the first crystallization stage ( 12 ) in method step (b 1 ) and the second suspension crystallization sub-stage ( 14 ′) of the first crystallization stage ( 12 ) in method step (b 2 ) are carried out so that the third fraction containing dewaxed oil obtained in method step (b 1 ) comprise less than 5% by weight of wax and/or so that the fifth fraction containing slack wax obtained after method step (b 2 ) comprises less than 30% by weight of oil.