Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
2000-05-04
2004-11-09
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S058000, C208S059000, C208S089000
Reexamination Certificate
active
06814856
ABSTRACT:
The present invention relates to the field of fuels for internal combustion engines. More particularly, it relates to the production of a fuel for a compression ignition engine, and to the fuel obtained therefrom.
Whether from straight run distillation of a crude petroleum or from a conversion process such as catalytic cracking, gas oil cuts still contain non negligible quantities of aromatic compounds, nitrogen-containing compounds and sulphur-containing compounds. Current legislation in the majority of industrialised countries requires that a fuel for use in engines must contain less than 500 parts per million (ppm) of sulphur. In the vast majority of those countries, there are currently no regulations imposing a maximum aromatic compound and nitrogen content. However, a number of countries or states, for example Sweden and California, envisage limiting the quantity of aromatic compounds to a value of less than 20% by weight, or even to less than 10%, and some experts think that that limit should be 5%. In Sweden in particular, some classes of diesel fuel already have to satisfy very strict regulations. Thus in that country, class II diesel fuel must not contain more than 50 ppm of sulphur and more than 10% by weight of aromatic compounds, and class I fuel must not contain more than 10 ppm of sulphur and 5% by weight of aromatic compounds. Currently in Sweden, class III diesel fuel must contain less than 500 ppm of sulphur and less than 25% by weight of aromatic compounds. Similar limits have to be satisfied to sell that type of fuel in California.
Meanwhile, motorists in a number of countries are pressing for legislation to require oilmen to produce and sell a fuel with a minimum cetane number of constantly improving quality. Current European legislation requires a minimum cetane number of 49 which from the year 2000 will rise to 51, probably at least 53 and more probably in the range 55 to 70.
Further, the same European regulations predict a tightening of the regulations regarding the density, the 95% point, sulphur content and polyaromatics content.
A number of specialists seriously envisage the possibility of a future standard imposing a nitrogen content of less than about 200 ppm, for example, and even less than 100 ppm by weight. A low nitrogen content results in a better product stability and is generally desired both by the vendor of the product and by the manufacturer.
It is thus necessary to develop a reliable and effective process which enables a product to be produced which has improved characteristics both as regards the cetane number and the aromatic compound content, sulphur content and nitrogen content. The gas oil cuts originate either from straight run crude oil distillation, or from catalytic cracking: i.e., light distillate cuts (LCO, Light Cycle Oil), heavy fraction cuts (HCO, Heavy Cycle Oil), or from another conversion process (cokefaction, visbreaking, residue hydroconversion, etc.), or from gas oils from the distillation of aromatic or naphthenoaromatic Hamaca, Zuata, or El Pao type crude oil. The production of an effluent which is directly and integrally upgradeable as a very high quality fuel cut is particularly important.
Conventional processes can improve the cetane number to an extent which satisfies current cetane number regulations for the majority of feeds. However, with gas oil cuts originating from a catalytic cracking type conversion process or in the case of particularly severe specifications, this increase reaches a limit which cannot be exceeded using the conventional sequences of such processes.
Further, a well known advantage of these catalysts is that a prolonged service life is possible without observing any deactivation.
The prior art describes processes for hydrogenating petroleum cuts which are particularly rich in aromatic compounds which use a catalyst, for example U.S. Pat. No. 5,037,532 or the publication “Proceedings of the 14
th
World Petroleum Congress, 1994, p. 19-26” which describe processes which lead to the production of hydrocarbon cuts, and increase in the cetane number is obtained by intense hydrogenation of the aromatic compounds.
We have now sought to produce fuels with a cetane number of the same order as those obtained by conventional hydrogenation processes or higher but without having recourse to hydrogenation which is too intense.
The present invention is distinguished over the prior art in that it combines hydrocracking with hydrogenation.
Such a combination has already been described for the treatment of heavy feeds, for example in French patent FR-A-2 600 669.
In that patent, the treated feed contains at least 50% by weight of constituents boiling above 375° C. and the aim of the process is to convert at least 70% by volume of those heavy constituents to constituents with a boiling point of less than 375° C.
At the end of the process, at least one cut is produced with a boiling point below 375° C. (gasoline, gas oil) and a heavy cut is produced with a boiling point of at least 375° C. which can be recycled to improve conversion. The light compounds are, of course, separated out (residual H
2
, C
1
-C
4
, H
2
S, NH
3
. . . ).
Thus this process comprising a hydrotreatment step followed by a hydrocracking step uses a zeolitic catalyst converts a heavy cut to a gas oil (250-375° C.) and a gasoline (150-250° C.) with the highest yield possible.
The Applicant has been able to establish that, compared with the prior art hydrogenation to treat gas oil cuts, the process of the invention, combining hydrogenation and hydrocracking, breaks the conventional cetane limits encountered in conventional hydrogenation processes and more substantially reduces the 95% ASTM point (the point corresponding to the boiling point of 95% of the cut).
More precisely, the invention provides a process for converting a gas oil cut into a high cetane number fuel which is dearomatised, desulphurised and has good cold properties, the process comprising the following steps:
a) at least one first step termed hydrogenation in which said gas oil cut is passed, in the presence of hydrogen, over a catalyst comprising an amorphous mineral support, at least one metal or compound of a metal from group VIB of the periodic table (Handbook of Chemistry and Physics, 76
th
Edition, 1995-1996) in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 40%, at least one non noble metal or compound of an non noble metal from group VIII of the periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.01% to 30%, and of phosphorous or at least one compound of phosphorous in a quantity, expressed as the weight of phosphorous pentoxide with respect to the weight of the support, of about 0.001% to 20%; and
b) at least one second step, termed hydrocracking, in which the hydrogenated product from the first step is passed, in the presence of hydrogen, over a catalyst comprising a mineral support which is partly zeolitic, at least one metal or compound of a metal from group VIB of the periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 40% and at least one non noble metal or compound of a non noble metal from group VIII in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.01% to 20%, the light compounds then being separated from the hydrocracking effluent. This two-step process essentially comprises substantial or managed hydrogenation of the aromatic compounds—depending on the amount of aromatic compounds which are to be in the final product, then hydrocracking intended to open the naphthenes produced in the first step, to form paraffins.
These feeds are treated in hydrogen in the presence of catalysts, this treatment enabling the aromatic compounds present in the feed to be hydrogenated; it can also simultaneously carry out is hydrodesulphurisation and hydrodenitrogenation.
In the process of the present invention
Aussillous Marcel
Billion Alain
Briot Patrick
Gueret Christophe
Kasztelan Slavik
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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