Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
2000-05-01
2003-08-05
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S062000, C208S027000, C585S310000, C585S734000, C585S736000, C585S737000
Reexamination Certificate
active
06602402
ABSTRACT:
The present invention relates to an improved process for producing very high quality base stock, i.e., with a high viscosity index (VI), good stability to UV and a low pour point, from hydrocarbon feeds (preferably from hydrocarbon feeds from the Fischer-Tropsch process or from hydrocracking residues), optionally with simultaneous production of very high quality middle distillates (in particular gas oils and kerosine,), i.e., with a low pour point and a high cetane index.
PRIOR ART
High quality lubricants are fundamentally important to proper operation of modern machines, automobiles and trucks.
Such lubricants are usually obtained by a succession of refining steps which can improve the properties of a petroleum cut. In particular, treating heavy petroleum fraction with large quantities of linear or slightly branched paraffins is necessary to obtain good quality base stock in the best possible yields, using an operation aimed at eliminating linear or very slightly branched paraffins from feeds which are then used as base stock.
High molecular weight paraffins which are linear or very slightly branched which are present in the oils result in high pour points and thus in coagulation for low temperature applications. In order to reduce the pour points, such linear paraffins which are not or are only very slightly branched must be completely or partially eliminated.
A further means is catalytic treatment in the presence or absence of hydrogen and because of their form selectivity, zeolites are among the most widely used catalysts.
Zeolite based catalysts such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 have been described for use in such processes.
All catalysts currently used in hydroisomerisation are bifunctional, combining an acid function with a hydrogenating function. The acid function is provided by supports with large surface areas (in general 150 to 180 m
2
/g) with a superficial acidity, such as halogenated aluminas (chlorinated or fluorinated in particular), phosphorous-containing aluminas, combinations of oxides of boron and aluminium, amorphous silica-aluminas and aluminosilicates. The hydrogenating function is provided either by one or more metals from group VIII of the periodic table such as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, or by combining at least one group VI metal such as chromium, molybdenum or tungsten and at least one group VIII metal.
The balance between the two functions, acid and hydrogenating, is the fundamental parameter which governs the activity and selectivity of the catalyst. A weak acid function and a strong hydrogenating function produces catalysts with low activity which are selective as regards isomerisation, while a strong acid function and a weak hydrogenating function produces catalysts which are highly active and selective as regards cracking. A third possibility is to use a strong acid function and a strong hydrogenating function to obtain a highly active catalyst which is also highly selective as regards isomerisation. Thus by careful choice of each of the functions, the activity/selectivity balance of the catalyst can be adjusted.
In the process of the invention the Applicant proposes jointly producing very good quality middle distillates, base stock with a VI and a pour point at least equal to those obtained with a hydrorefining and/or hydrocracking process.
SUBJECT MATTER OF THE INVENTION
The Applicant's research has been concentrated on developing an improved process for producing very high quality lubricating oils and high quality middle distillates from hydrocarbon feeds, preferably from hydrocarbon feeds from the Fischer-Tropsch process or from hydrocracking residues.
The present invention thus relates to a sequence of processes for joint production of very high quality base stock and very high quality middle distillates (in particular gas oils) from petroleum cuts. The oils obtained have a high viscosity index (VI), low volatility, good UV stability and a low pour point.
More precisely, the invention provides a process for producing oils from a hydrocarbon feed (of which at least 20% by volume preferably has a boiling point of at least 340° C.), said process comprising the following steps in succession:
(a) converting the feed with simultaneous hydroisomerisation of at least a portion of the n-paraffins of the feed, said feed having a sulphur content of less than 1000 ppm by weight, a nitrogen content of less than 200 ppm by weight, a metals content of less than 50 ppm by weight, an oxygen content of at most 0.2% by weight (preferably said step being carried out at a temperature of 200-500° C., at a pressure of 2-25 MPa, with a space velocity of 0.1-10 h
−1
, in the presence of hydrogen, at a ratio generally in the range 100-2000 l. H
2
/l of feed), in the presence of a catalyst containing at least one noble metal deposited on an amorphous acidic support, the dispersion of the noble metal being less than 20%,
(b) catalytic dewaxing of at least a portion of the effluent from step a), (preferably carried out at a temperature of 200-500° C., at a pressure of 1-25 MPa, with an hourly space velocity of 0.05-50 h
−1
, in the presence of 50-2000 liters of hydrogen/liter of effluent entering step b)), in the presence of a catalyst comprising at least one hydrodehydrogenating element and at least one molecular sieve.
Thus step a) is optionally preceded by a hydrotreatment step generally carried out at a temperature of 200-450° C., at a pressure of 2 to 25 MPa, at a space velocity of 0.1-6 h
−1
, in the presence of hydrogen in a hydrogen/hydrocarbon volume ratio of 100-2000 l/l, and in the presence of an amorphous catalyst comprising at least one group VIII metal and at least one group VIB metal.
All of the effluent from step a) can be sent to step b).
Step a) is optionally followed by separating the light gases from the effluent obtained at the end of step a).
Preferably, the effluent from the conversion-hydroisomerisation treatment undergoes a distillation step (preferably atmospheric) to separate compounds with a boiling point of less than 340° C. (gas, gasoline, kerosine, gas oil) from products with an initial boiling point of more than at least 340° C. and which form the residue. Thus in general, at least one middle distillate fraction with a pour point of at most −20° C. and a cetane index of at least 50 is separated.
Catalytic dewaxing step b) is thus applicable to at least the residue from the distillation step which contains compounds with a boiling point of more than at least 340° C. In a further implementation of the invention, the effluent from step a) is not distilled before carrying out step b). At most, at least a portion of the light gases are separated (by flash) and it then undergoes catalytic dewaxing.
Preferably, step b) is carried out using a catalyst containing at least one molecular sieve wherein the microporous system has at least one principal channel type with a pore opening containing 9 or 10 T atoms, T being selected from the group formed by Si, Al, P, B, Ti, Fe, Ga, alternating with an equal number of oxygen atoms, the distance between two accessible pore openings containing 9 or 10 T atoms being equal to 0.75 mm at most, and said sieve having a 2-methylnonane/5-methylnonane ratio of more than 5 in the n-decane test.
Advantageously, the effluent from the dewaxing treatment undergoes a distillation step advantageously comprising atmospheric distillation and vacuum distillation so as to separate at least one oil fraction with a boiling point of more than 340° C. It usually has a pour point of less than −10° C., and a VI of more than 95, with a viscosity of at least 3 cSt (i.e., 3 mm
2
/s) at 100° C. This distillation step is essential when there is no distillation step between steps a) and b).
Advantageously, the effluent from the dewaxing treatment, which has optionally been distilled, undergoes a hydrofinishing treatment.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention comprises the following step
Benazzi Eric
Cseri Tivadar
Gueret Christophe
Kasztelan Slavik
Marchal-George Nathalie
Griffin Walter D.
Institut Francais du Pe'trole
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