Process for producing oils with a high viscosity index

Details Process for producing oils with a high viscosity index Process for producing oils with a high viscosity index

2000-08-24

2004-08-31

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

With subsequent treatment of products

C208S058000, C208S059000, C208S111010, C208S111300, C208S111350

Reexamination Certificate

active

06783661

ABSTRACT:

The present invention relates to a process for producing oils with high viscosity indices, more particularly oils with a viscosity index of more than about 100, from a feed containing constituents with boiling points of more than 300° C. The process is a sequence of operations enabling an oily residue to be recovered part of which is fractionated by thermal diffusion into different oils with different compositions and viscosity indices.
High performance engines require oils with ever higher viscosity indices. Specifications for indices are presently in the range 95 to 100.
International patent WO-A-97/18278 describes a process for producing a dewaxed lubricating oil, comprising at least one hydrocracking zone, at least one dewaxing zone and at least one hydrorefining zone. The hydrocarbon feed comprises gas oils from a first vacuum distillation, deasphalted raffinates or a mixture of two of such cuts. Cracked feeds can also be added to the initial feed but in quantities not exceeding 20% due to their high aromatics content and low hydrogen content.
U.S. Pat. No. 4,975,177 describes a process in three successive steps for producing a lubricant with a viscosity index of at least 130 and with a pour point of less than 5° F. (−15° C.), comprising a step for dewaxing a petroleum feed to form a paraffin-rich feed containing at least 50% by weight of paraffin and with a boiling point of more than 650° F. (343° C.), a step for catalytic dewaxing by isomerisation of the effluent obtained from step a) at high pressure in the presence of hydrogen and a catalyst containing a beta zeolite and a hydrodehydrogenating function, to isomerise the n-paraffins to iso-paraffins, and a selective dewaxing step in the presence of a catalyst based on zeolite with a constraint index of at least 8. The presence of hydrogen in the second step enables the activity of the catalyst to be maintained and encourages the different steps of the isomerisation mechanism. Isomerisation then entrains hydrogenation and dehydrogenation of the dewaxed feed.
The Applicant's French patent FR-A-2 600 669 describes a process for hydrocracking in three successive steps for the production of middle distillates (gasoline, kerosine, gas oil), which enables fractions to be recovered in accordance with their boiling points. Fractions with boiling points of less than 375° C. are recovered and those with boiling points of more than 375° C. are recycled. The present application is based on recovering oily fractions in accordance with their viscosity indices. Further, it can recover not only middle distillates but also a column bottoms product essentially containing oils with different compositions and viscosity indices.
The invention concerns the production of oils with high viscosity indices, preferably more than about 100, and more preferably more than about 140, by direct treatment of petroleum fractions. One advantage of the invention is the production of oils with different compositions. The refiner has the choice between recovering the oils or recycling them depending on the limiting viscosity index which has been fixed by him.
More particularly, the invention concerns a process for producing oils with a high viscosity index and is applicable to a feed containing constituents with boiling points of more than 300° C.
The feeds used in the present invention are petroleum fractions with a boiling point of more than 300° C., normally in the range about 300° C. to 650° C., preferably in the range about 350° C. to 550° C. These feeds are of a variety of origins. Non limiting examples of said feeds are those originating either from crude oil distillates or from effluents from conversion units, such as fluidised bed catalytic cracking units, hydrocracking or ebullated bed hydrotreatment.
These feeds principally contain aromatic, naphthenic and paraffinic compounds. They are characterized by defined kinematic viscosities defined using standards at 40° C. and 100° C. The kinematic viscosity at 40° C. is normally in the range about 40 to 500 square millimetres per second (mm
2
/s), usually in the range about 40 to 300 mm
2
/s, and the kinematic viscosity at 100° C. is generally in the range about 2 to 40 mm
2
/s, usually in the range about 5 to 15 mm
2
/s. The density of the feeds is normally in the range about 0.89 to 0.98, usually in the range about 0.91 to 0.97, at 15° C.
The process of the invention is a process for producing oils with a high viscosity index from a feed containing constituents with boiling points of more than 300° C. It comprises a step a) in which hydrogen is reacted with the feed or with a mixture of the feed with at least a fraction of a recycle stream from step c), in the presence of a catalyst comprising at least one amorphous non zeolitic matrix and at least one metal or compound of a metal from group VIII of the periodic table and/or at least one metal from group VIB, a step b) in which at least a portion of the effluent obtained from step a) is fractionated so as to separate at least one oil residue mainly comprising constituents with viscosity indices which are higher than that of the feed, and a step c) in which at least a portion of the oil residue obtained in step b) is fractionated by thermal diffusion into oil fractions with high viscosity indices. Said process can separate oils in accordance with their viscosity index.
In step a), the feed is converted into at least one effluent containing mainly kerosine, gasoline, gas oil and oils.
The catalyst for the first step can be in the form of beads, but it is usually in the form of extrudates. The hydrodehydrogenating function of said catalyst is ensured by the metal or compound of a metal selected from the group formed by metals from group VIII of the periodic table (in particular nickel and cobalt), and metals from group VIB (in particular molybdenum and tungsten). It is also possible to associate at least one metal from group VIII (nickel and/or cobalt) with at least one metal from group VIB (molybdenum and/or tungsten).
The total concentration of group VIII and VIB elements is expressed as the concentration of metal oxides. The concentration of group VIII metal oxides is normally in the range about 0.5% to 10% by weight, preferably in the range about 1% to 7% by weight. The concentration of group VIB metal oxides is normally in the range about 1% to about 30% by weight, preferably in the range about 5% to 20% by weight. The total concentration of group VIB and VIII metal oxides is normally in the range about 5% to 40% by weight, usually in the range about 7% to 30% by weight.
The ratio between the group VI metal (or metals) and the group VIII metal (or metals), expressed as the metal oxides, is generally about 20 to 1 by weight, usually about 10 to 2.
The matrix for the catalyst of step a) is normally selected from the group formed by alumina, silica, silica-aluminas, magnesia, clays and mixtures of at least two of these minerals. Preferably, a &ggr; or &eegr; alumina is used. The matrix can also contain oxides selected from the group formed by boron oxide, zirconia, titanium oxide and phosphorous pentoxide. The matrix is usually doped with phosphorous and possibly with boron. The presence of phosphorous in the catalyst firstly facilitates its preparation, in particular when impregnating nickel and molybdenum solutions, and secondly improves the acidity and hydrogenation activity of the catalyst. The concentration of phosphorous pentoxide P
2
O
5
is normally less than about 20% by weight, usually less than about 10% and more preferably less than about 1% by weight. The concentration of boron trioxide B
2
O
3
is normally less than about 10% by weight.
The hydrogen used in step a) of the process of the invention essentially acts to hydrogenate the aromatic compounds contained in the feed.
The catalyst for step a) encourages hydrogenation over cracking. It can open naphthenic rings and enables hydrogenation of aromatic compounds, to reduce the amount of condensed polycyclic aromatic hydrocarbons. This reduction results in a drop in the densit

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