Process for preparing a base oil having a reduced cloud point

Abstract

The present invention relates to a process for preparing a residual base oil from a hydrocarbon feed which is derived from a Fischer-Tropsch process, the process comprises the steps of: (a) providing a hydrocarbon feed which is derived from a Fischer-Tropsch process; (b) subjecting the hydrocarbon feed of step (a) to a hydrocracking/hydroisomerisation step to obtain an at least partially isomerised product; (c) separating at least part of the at least partially isomerised product as obtained in step (b) into one or more lower boiling fractions and a hydrowax residue fraction; (d) catalytic dewaxing of the hydrowax residue fraction of step (c) to obtain a highly isomerised product; (e) separating the highly isomerised product of step (d) into one or more light fractions and a isomerised residual fraction; (f) mixing of the isomerised residual fraction of step (e) with a diluent to obtain a diluted isomerised residual fraction; (g) cooling the diluted isomerised residual fraction of step (f) to a temperature between 0° C. and −60° C.; (i) subjecting the mixture of step (g) to a centrifuging step at a temperature between 0° C. and −60° C. to isolate the wax from the diluted isomerised residual fraction; (j) separating the diluent from the diluted isomerised residual fraction to obtain a residual base oil.

Claims

1. A process for preparing a residual base oil from a hydrocarbon feed which is derived from a Fischer-Tropsch process, the process comprising the steps of: (a) providing a hydrocarbon feed which is derived from a Fischer-Tropsch process; (b) subjecting the hydrocarbon feed of step (a) to a hydrocracking/hydroisomerisation step to obtain an at least partially isomerised product; (c) separating at least part of the at least partially isomerised product as obtained in step (b) into one or more lower boiling fractions and a hydrowax residue fraction; (d) catalytic dewaxing of the hydrowax residue fraction of step (c) to obtain a highly isomerised product; (e) separating the highly isomerised product of step (d) into one or more light fractions and an isomerised residual fraction; (f) mixing of the isomerised residual fraction of step (e) with a diluent to obtain a diluted isomerised residual fraction; (g) cooling the diluted isomerised residual fraction of step (f) to a temperature between 0° C. and −60° C.; (h) subjecting the mixture of step (g) to a centrifuging step at a temperature between 0° C. and −60° C. to isolate the wax from the diluted isomerised residual fraction; and (i) separating the diluent from the diluted isomerised residual fraction to obtain a residual base oil, wherein the residual base oil is haze-free at 0° C. and has a reduced cloud point compared to the cloud point of the base oil prior to the centrifugation step (h).

2. The process according to claim 1, wherein the diluent is added to the isomerised residual fraction in step (f) such that the ratio of diluent to isomerised residual fraction is of from 1:1 to 10:1.

3. The process according to claim 1, wherein the diluent of step (f) is a hydrocarbon stream which forms a single liquid phase with the liquid phase of the isomerised residual fraction.

4. The process according to claim 3, wherein the diluent of step (f) is selected from the group consisting of petroleum spirit, naphtha, kerosene, single component paraffin liquids in a carbon range of from 8 to 16 carbon atoms, and low boiling point polar compounds, wherein the low boiling point polar compounds have a boiling point in the range from 40 to 280° C. and consist of one or more of alcohols, ketones, ethers, and combinations thereof.

5. The process according to claim 3, wherein the diluent is selected from the group consisting of petroleum spirit and FT derived paraffinic naphtha fraction.

6. The process according to claim 1, wherein the diluted isomerised residual fraction in step (g) is cooled to a temperature in the range of from −5° C. to −50° C.

7. The process according to claim 1, wherein the diluent of step (i) is recycled to step (f).

8. The process according to claim 1, wherein the diluent is added to the isomerised residual fraction in step (f) such that the ratio of diluent to isomerised residual fraction is of from 1:1 to 3:1.

9. The process according to claim 1, wherein the diluent is added to the isomerised residual fraction in step (f) such that the ratio of diluent to isomerised residual fraction is of from 1:1 to 2:1.

10. The process according to claim 1, wherein the diluted isomerised residual fraction in step (g) is cooled to a temperature in the range of from −10° C. to −35° C.

Description

(1) FIG. 1 schematically shows a process scheme of the process scheme of a preferred embodiment of the process according to the present invention.

(2) For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line.

(3) The process scheme is generally referred to with reference numeral 1.

(4) From a Fischer-Tropsch process reactor 2 a Fischer-Tropsch product stream 10 is obtained. This product is separated in a distillation column 3 into a fraction 20 boiling below a temperature in the range of 150 to 250° C. at atmospheric conditions and a fraction 30 boiling above a temperature in the range 250° C. at atmospheric conditions. The high boiling fraction 30 is fed to a hydrocracking/hydroisomerization reactor 4 wherein part of the components boiling above a temperature in the range of 250° C. are converted to product boiling below a temperature in the range of from 300 to 450° C. The partially isomerized effluent 40 of reactor 4 is distilled in a synthetic crude distillation column (SCD) 5 to recover a middle distillates fraction 50 and a atmospheric hydrowax residue fraction 60. Optionally, the effluent 60 is distilled in a high vacuum unit (HVU) to recover a waxy raffinate fraction 70 and a vacuum hydrowax residue fraction 80. The hydrowax residue 80 or 60 is fed to a catalytic dewaxing reactor 7 to obtain a highly isomerized product fraction 90. The effluent 90 of reactor 7 is distilled in a RDU redistillation unit 8 to recover a catalytic dewaxed gas oil fraction 100 and a hazy isomerized residual fraction 110. Fraction 110 is mixed with a diluent 120 to obtain a diluted isomerized residual fraction 130. Fraction 130 is cooled to a temperature between 0 and −60° C. (not shown). The cooled fraction 130 is subjected to a centrifuge unit 9 at a temperature between 0 and −60° C. to isolate a wax fraction 140 and a diluted residual base oil 150 from the diluted isomerized residual fraction 130. Fraction 150 is subjected to a flash column to separate the diluent 120 from the diluted residual base oil fraction to obtain a clear and bright base oil 160.

(5) The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES

Example 1

(6) From a Fischer Tropsch wax product, through a hydrocracking step (60 bar, 330-360° C.) and subsequent atmospheric and vacuum distillation a vacuum hydrowax residue was obtained (congealing point=103° C.). This vacuum hydrowax residue was subjected to a catalytic dewaxing step at 40 bara, WHSV=0.5 kg/l/hr, hydrogen to oil ratio 750 N1/kg, WABT=320° C. and subsequent batch atmospheric distillation followed by vacuum distillation. The isomerized residual fraction, with a density of D70/4=0.805, a kinematic viscosity according to ASTM D445 at 100° C. of 21.2 mm.sup.2/s, a pour point of PP=−24° C. and a cloud point of cp=42° C., was mixed with Petroleum Ether 40/60) in a ratio of 2 parts by weight of diluent to 1 part by weight of isomerized residual fraction. The diluted isomerized residual fraction was cooled to a temperature of −30° C. The cooled diluted isomerized residual fraction was exposed to a high rotation speed of 14000 RPM (equivalent to a Relative Centrifugal Force (RCF)=21000 g force) in a cooled laboratory centrifuge for a period of 10 minutes. Separation of microcrystalline wax and diluted residual base oil was obtained by decantation. The Petroleum Ether was flashed from the diluted residual base oil in a laboratory rotavap apparatus in a temperature range 90-140° C. and 300 mbar pressure. The base oil obtained was found to be clear and bright at a temperature of 0° C. for a period of 7 hours. The kinematic viscosity according to ASTM D445 at 100° C. of the base oil at a temperature of 100° C. was 18.9 mm.sup.2/s, a viscosity index of 153, a pour point was measured of pp=−42° C. and a cloud point of cp=−20° C. (see table 1).

Example 2

(7) In a second experiment according to the invention, the vacuum hydrowax residue used in experiment 1 was subjected to a dewaxing step operated at the same conditions that were applied in Example 1. Subsequently, the catalytic dewaxing unit effluent was distilled with a laboratory continuous atmospheric column in series with a short path distillation unit. The isomerized residual fraction, with a density of D70/4=0.805, a kinematic viscosity according to ASTM D445 at 100° C. of 21.3 mm.sup.2/s, a pour point of PP=−39° C. and a cloud point of cp=39° C., was mixed with Petroleum Ether 40/60) in a ratio of 2 parts by weight of diluent to 1 part by weight of isomerized residual fraction. The diluted isomerized residual fraction was cooled to a temperature of −60° C. The cooled diluted isomerized residual fraction was exposed to a lower rotation speed than in experiment 1 of 9157 RPM (equivalent to a Relative Centrifugal Force (RCF=9000 g force) in a laboratory centrifuge cooled to −20° C. for a period of 5 minutes. After this, the sample was cooled again to −60° C. and the centrifuge step of 5 minutes was repeated (at the same conditions as the first centrifuge step). Thereafter, separation of microcrystalline wax and diluted residual base oil was obtained by decantation. The Petroleum Ether was flashed from the diluted residual base oil in a laboratory rotavap apparatus in a temperature range 90-140° C. and 300 mbar pressure. The base oil obtained was found to be clear and bright at a temperature of 0° C. for a period of 7 hours, a kinematic viscosity according to ASTM D445 at 100° C. of the base oil at a temperature of 100° C. was 19.2 mm.sup.2/s, a cloud point of cp=−15° C. (see table 1).

Comparative Example 3

(8) In a comparative experiment, the vacuum hydrowax residue used in experiment 1 was subjected to a dewaxing step operated at the same conditions that were applied in Example 1. In a third experiment not according to the invention Subsequently, the catalytic dewaxing unit effluent was distilled with a laboratory continuous atmospheric column in series with a short path distillation unit, as in example 2. The isomerized residual fraction, with a density of D70/4=0.805, a kinematic viscosity according to ASTM D445 at 100° C. of 21.3 mm2/s, a pour point of PP=−39° C. and a cloud point of cp=39° C., was mixed with Petroleum Ether (40/60) in a ratio of 2 parts by weight of diluent to 1 part by weight of isomerized residual fraction. The diluted isomerized residual fraction was cooled to a temperature of −20° C. In order to separate the microcrystalline wax and diluted residual base oil, the cooled diluted isomerized residual fraction was filtered with a stack of Whatmann filter papers (41/42/41) in a laboratory batch filtration device that was maintained at temperature of −20° C. The Whatmann filter 41 has been specified with a pore size from 20 to 25 μm and the Whatmann filter 42 with a pore size of 2.5 μm. The Petroleum Ether was flashed from the diluted residual base oil in a laboratory rotavap apparatus in a temperature range 90-140° C. and 300 mbar pressure. The base oil obtained was found to be hazy at a temperature of 0° C., a kinematic viscosity according to ASTM D445 at 100° C. of the base oil at a temperature of 100° C. was 21.0 mm2/s, a cloud point of cp=+26° C. (see table 1).

Comparative Example 4

(9) In a comparative fourth experiment not according to the invention, the vacuum hydrowax residue used in experiment 1 was subjected to a dewaxing step operated at the same conditions that were applied in Example 1. Subsequently, the catalytic dewaxing unit effluent was distilled with a laboratory continuous atmospheric column in series with a short path distillation unit as in example 2. The isomerized residual fraction, with a density of D70/4=0.805, a kinematic viscosity according to ASTM D445 at 100° C. of 21.3 mm2/s, a pour point of PP=−39° C. and a cloud point of cp=39° C., was mixed with heptane in a ratio of 4 parts by weight of diluent to 1 part by weight of isomerized residual fraction. The diluted isomerized residual fraction was cooled to a temperature of −25° C. In order to separate the microcrystalline wax and diluted residual base oil, the cooled diluted isomerized residual fraction was filtered with a stack of Whattmann filter papers (41/42/41) in a laboratory batch filtration device that was maintained at temperature of −25° C. The Whatmann filter 41 has been specified with a pore size from 20 to 25 μm and the Whatmann filter 42 with a pore size of 2.5 μm. The heptane was flashed from the diluted residual base oil in a laboratory rotavap apparatus in a temperature range 90-140° C. and 300 mbar pressure. The base oil obtained was found to be hazy at a temperature of 0° C., a kinematic viscosity according to ASTM D445 at 100° C. of the base oil at a temperature of 100° C. was 20.6 mm2/s, a cloud point of cp=+19° C. (see table 1).

(10) TABLE-US-00001 TABLE 1 Comparative Comparative Properties base oil Example 1 Example 2 Example 3 Example 4 Kinematic viscosity 18.9 19.2 21.0 20.6 at 100° C. (cSt) Pour point (° C.) −42 −42 −30 −30 Cloud point (° C.) −20 −15 +26 +19 Appearance at 0° C. Clear and Clear and hazy hazy bright bright

Discussion

(11) Examples 1 and 2 show that in both experiments using the centrifuging step a clear and bright Fischer-Tropsch derived residual base oil is obtained. In addition, the cloud points of the base oils in Example 1 and 2 have been reduced significantly compared to the cloud points before the centrifugation step. Also the kinematic viscosity at 100° C. of the clear and bright base oil is comparable to the isomerized residual fraction which indicates that the centrifuging method does not influence the kinematic viscosity of the base oil.

(12) Comparative examples 3 and 4 show that in both experiments using a filtration step a hazy Fischer Tropsch derived residual base oil is obtained. In addition, the cloud points of the base oils in comparative Examples 3 and 4 have only been reduced moderately compared to the cloud points before the filtration step. In both cases, cloud point remains far above zero ° C.