Hydroisomerization treatment process for feeds from the fisher-t

Details Hydroisomerization treatment process for feeds from the fisher-t Hydroisomerization treatment process for feeds from the fisher-t

1996-07-05

1998-11-10

Shippen, Michael L.

Chemistry: fischer-tropsch processes; or purification or recover

Liquid phase fischer-tropsch reaction

518705, 585253, 585737, 208 18, 208 27, 208143, C07C 2700

Patent

active

058345221

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention concerns a hydroisomerisation treatment process for feeds from a Fischer-Tropsch process to produce lubricating oils.
In the Fischer-Tropsch process, synthesis gas (CO+H.sub.2) is catalytically transformed into oxygenated products and essentially linear hydrocarbons in the gaseous, liquid or solid state. These products are generally free of heteroatomic impurities such as sulphur, nitrogen or metals. They also contain practically no aromatics, naphthenes or, more generally, cyclic compounds. They can, however, contain a significant quantity of oxygenated products which, expressed as the weight of oxygen, is less than about 5%, and less than 10% by weight of unsaturated compounds (generally olefinic compounds). These compounds cannot be used as they are, in particular because of their cold behaviour properties which are not compatible with the normal uses of petroleum cuts. The pour point of a linear hydrocarbon containing 30 carbon atoms per molecule (boiling point about 450.degree. C., i.e., part of the oil cut), for example, is about +67.degree. C., while customs regulations require that a commercial oil must have a pour point of less than -90.degree. C. These hydrocarbons from the Fischer-Tropsch process must, therefore, be transformed into more valorisable products such as lubricating oils, after undergoing catalytic hydroisomerisation reactions.
All the catalysts which are currently used for hydroconversion are bifunctional, combining an acidic function with a hydrogenating function. The acidic function is provided by supports with large surface areas (generally 150 to 800 m.sup.2 .multidot.g.sup.1) with surface acidity, such as halogenated aluminas (in particular chlorinated or fluorinated), phosphorous-containing aluminas, combinations of boron oxides and aluminium, amorphous silica-aluminas and silica-aluminas. The hydrogenating function is provided either by one or more metals from group VIII of the periodic classification of the elements, such as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, or by combination of at least one metal from group VI such as chromium, molybdenum and tungsten with at least one metal from group VIII.
The balance between the acidic and hydrogenating functions is a fundamental parameter which governs the activity and selectivity of the catalyst. A weak acidic function and a strong hydrogenating function produces catalysts which are less active and selective as regards isomerisation while a strong acidic function and a weak hydrogenating function produces very active and selective catalysts as regards cracking. A third possibility is to use a strong acidic function and a strong hydrogenating function to obtain a very active but also very selective isomerisation catalyst. It is thus possible, by judicious choice of each of the functions, to adjust the activity/selectivity balance of the catalyst.


SUMMARY OF THE INVENTION

Our research on a number of silica-aluminas has led to the discovery that, surprisingly, the use of a catalyst containing neither halogen nor zeolite and comprising a particular silica-alumina can produce catalysts which are very active but also very selective as regards isomerisation of feeds as defined below.
More precisely, the catalyst of the invention is essentially constituted by 0.05-10% by weight of at least one precious metal from group VIII deposited on an amorphous silica-alumina support which contains 5-70% by weight of silica and has a BET specific surface area of 100-500 m.sup.2 /g, the catalyst having: defined above reduced by 3 nm and the average diameter as defined above increased by 3 nm, of more than 40% of the total pore volume,
In more detail, these characteristics are: patent is composed of silica SiO.sub.2 and alumina Al.sub.2 O.sub.3. The silica content, expressed as the percentage by weight, is between 5% and 70%, preferably between 20% and 60%, more preferably between 22% and 45%. This content can be accurately measured using X ray fluorescenc

REFERENCES:
patent: 3843509 (1974-10-01), Suto et al.
patent: 4648958 (1987-03-01), Ward
patent: 5151172 (1992-09-01), Kukes
patent: 5248409 (1993-09-01), Soled et al.

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