Production of lubricant base oils

Details Production of lubricant base oils Production of lubricant base oils

1998-12-01

2001-11-13

Myers, Helane E. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

With subsequent treatment of products

C208S027000, C208S108000, C208S950000

Reexamination Certificate

active

06315891

ABSTRACT:

THIS INVENTION relates to the production of lubricant base oils. It relates in particular to a process for producing a waxy product suitable for the production of lubricant base oils, and to a process for treating a waxy product to produce a dewaxed product suitable for use as a lubricant base oil.
According to a first aspect of the invention, there is provided a process for producing a waxy product, which process comprises hydrotreating a feedstock comprising a Fischer-Tropsch wax and a petroleum-based waxy distillate, to produce a range of hydrogenated products; and recovering a waxy product from the range of hydrogenated products.
By ‘Fischer-Tropsch wax’ is meant a wax obtained by the so-called Fischer-Tropsch process. The Fischer-Tropsch process includes converting a synthesis gas comprising mainly hydrogen and carbon monoxide, to hydrocarbons. The conversion is effected by contacting the synthesis gas with a Fischer-Tropsch catalyst, normally an iron or cobalt based catalyst, in a fixed bed or a slurry bed reactor under either low or high temperature Fischer-Tropsch operating conditions. In this manner, a mixture of hydrocarbons having different boiling ranges, is obtained. The Fischer-Tropsch wax is then recovered, eg by means of distillation, from this hydrocarbon mixture. The Fischer-Tropsch wax typically has a composition wherein about 80% by volume thereof has a boiling point higher than 550° C. atmospheric equivalent temperature (‘AET’). Thus, for example, the Fischer-Tropsch wax may have an ASTM D2887 gas chromatography simulated distillation range in accordance with Table 1.
TABLE 1
Fischer-Tropsch wax (simulated distillation
according to ASTM D2887)
% off (by volume)
° C.
Initial boiling
430
point
10
510
30
570
50
610
The term ‘petroleum-based waxy distillate’ is known in the art. It thus means a waxy distillate obtained by physically separating a suitable crude oil using atmospheric and vacuum distillation. Suitable crude oils are so-called ‘lube crudes’. Typically, the crude oil can be a Middle East crude oil, a North Sea crude oil, or an African crude oil. Thus, for example, the petroleum-based waxy distillate may have an ASTM D2887 gas chromatography simulated distillation range in accordance with Table 2.
TABLE 2
Petroleum-based waxy distillate (simulated
distillation according to ASTM D2887)
% off (by volume)
° C.
Initial boiling
255
point
10
344
30
397
50
432
70
463
90
511
Final boiling point
579
The volumetric proportion of Fischer-Tropsch wax to petroleum-based waxy distillate in the feedstock may be between 5:95 and 50:50, preferably between 5:95 and 20:80.
The hydrotreatment may include hydrocracking the feedstock in a hydrocracking stage. The hydrocracking may be effected at a temperature of 300° C. to 410° C., preferably 350° C. to 400° C.; a pressure of 120-160 bar(g); a hydrogen partial pressure of 20-200 bar(g), preferably 100-175 bar(g); a hydrogen to liquid ratio of 200-2000:1 m
n
3
, and a liquid hourly space velocity (‘LHSV’) of 0,2-2 h
−1
.
The recovery of the waxy product from the range of hydrogenated products produced may include distilling, in a distillation stage, the range of hydrogenated products to obtain, as a bottoms fraction, the waxy product. Thus, typically, the products obtained from the distillation stage may be in accordance with Table 3.
TABLE 3
Distillatian Stage
Carbon range
Mass %
C
1
-C
4
 1-3
C
5
-C
6
 4-6
C
7
-C
15
20-30
C
15
-C
28
35-40
C
28
C
40
15-25
C
>40
 5-15
The bottoms fraction, ie the C
>40
fraction, is thus the waxy product.
The bottoms fraction or waxy product from the distillation stage may then be subjected to dewaxing, eg solvent dewaxing, in a dewaxing stage, to recover a dewaxed product.
Thus, according to a second aspect of the invention, there is provided a process for treating a waxy product, which process comprises dewaxing, in a dewaxing stage, the waxy product obtained from the process according to the first aspect of the invention, to obtain a dewaxed product suitable for use as a lubricant base oil.
The dewaxing may comprise solvent dewaxing of the waxy product.
Preferred solvent combinations for dewaxing lube feedstocks such as waxy distillates, waxy raffinates, waxy hydrocracker residues and the corresponding distillate fractions are a methyl ethyl ketone/toluene (‘MEK/T’) and a dichloro-ethene/methylene chloride (‘Di/Me’). This MEK/T or Di/Me can be used for dewaxing the waxy product; however, MEK/T is preferred.
The mass proportion of dichloroethene to methylenechloride in the MEK/T solvent is between 40:60 and 60:40, and may, for example, be about 50:50. The mass proportion of waxy product to solvent may be between 1:2 and 1:12, preferably between 1:3 and 1:10.
The dewaxing may comprise mixing the waxy product in liquid form with the MEK/T solvent; cooling the mixture to a sub-ambient dewaxing temperature, with solid wax crystals forming, and with the dewaxing temperature depending on the pour point which is required for the dewaxed product or the lubricant base oil; and separating, in a separation stage, the wax crystals from a mother liquor comprising dewaxed oil as the dewaxed product and spent solvent. The separation stage may, in particular, comprise a filter stage having at least one filter, eg a rotary filter, with the mother liquor or main filtrate thus passing through the filter and the solid wax crystals remaining as a wax cake on the filter. The process may include washing, in a washing step, the wax cake with fresh MEK/T mixture as a wash solvent, to obtain solvent free slack wax and spent solvent. The process may include recovering the spent solvent from the washing step and from the main filtrate, and recirculating or re-using the recovered solvent within the dewaxing stage. The recovery of the spent solvent may be effected by means of multistage distillation and stripping.
In the washing step, sufficient wash solvent may be used so that the mass proportion of waxy product initially used to wash solvent is between 1:1 and 1:2.
The dewaxing temperature may be between −5° C. and −32° C., for example between −12° C. and −27° C. The dewaxing temperature as set out hereinbefore, dependent on the pour point which is required for the resultant or corresponding lubricant base oil. For example, to produce a base oil with a pour point of −9° C., the corresponding dewaxing temperature is higher than the dewaxing temperature required to achieve a pour point of −18° C.
The dewaxed product thus obtained is suitable for use as a lubricant base oil, and the Applicant has surprisingly found that the lubricant base oil has a viscosity index (‘VI’) of 145 or higher, so that it is suitable for use as a super high viscosity index (‘SHVI’) lubricant base oil.
The invention naturally extends to a waxy product when produced by the process according to the first aspect of the invention, and to a dewaxed product, when produced by the process according to the second aspect of the invention.
According to a third aspect of the invention, there is provided a lubricant base oil which comprises a dewaxed product, as hereinbefore described.
According to a fourth aspect of the invention, there is provided a lubricant base oil which comprises a dewaxed waxy product obtained from the hydrotreatment of a feedstock comprising a Fischer-Tropsch wax and a petroleum based waxy distillate.
The lubricant base oil may thus have a VI of 145 or higher.
The invention will now be described by way of example with reference to the accompanying flow diagram of a process according to the invention for producing a dewaxed product, and with reference to the subsequent non-limiting example.
In the drawing, reference numeral
10
generally indicates a process according to the invention for producing a dewaxed product.
The process
10
includes a crude oil flow line
12
leading into an atmospheric distillation stage
14
comprising an atmospheric crude distillation tower. An atmospheric residue flow line
16
leads from the stage
14
to a vacuum distillation stage
1

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