Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2001-12-20
2003-11-11
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S089000, C208S085000, C208S143000, C208S210000, C208S213000, C208S2160PP, C208S217000, C208S25100H, C208S25400R
Reexamination Certificate
active
06645371
ABSTRACT:
The present invention relates to hydrotreatment (HDT) of hydrocarbon fractions to produce hydrocarbon fractions with a low sulphur, nitrogen and aromatic compound content particularly for use in the field of fuel for internal combustion engines. Such hydrocarbon fractions include jet fuel, diesel fuel and kerosine. In this field, the invention is or particular application during processes for transforming a middle distillate, more particularly a gas oil cut with a view to producing dearomatised and desulphurised high cetane index fuel. The invention can also be applied to hydrotreating heavier products, alone or as a mixture with diluents, for example hydrocarbon fractions from atmospheric or vacuum distillation in the context of hydrodemetallisation (HDM), hydrodesulphurisation (HDS) or hydrodenitrogenation (HDN) reactions.
The present process can be carried out both to improve the characteristics of the finished product as regards the specifications required to achieve the quality of the products and the pollution standards (sulphur and aromatic compound content in particular) and to prepare feeds for refinery units for transforming or converting (visbreaking, cokefaction or catalytic cracking for a vacuum distillate, isomerisation or reforming for a naphtha, for example) using catalysts that are sensitive to impurities (for example sulphur for metal catalysts, nitrogen for acidic catalysts and metals in general).
In the context of desulphurising and dearomatising gas oil cuts, current legislation in the majority of industrialised countries requires that the fuel used in said engines contains a quantity of sulphur that is less than about 500 parts per million (ppm). In the vast majority of those states, there are currently no standards imposing a maximum aromatic compound and nitrogen content. However, a number of states, such as Sweden and California, envisage limiting the aromatics content to a value of less than 20% by volume, or even less than 10% by volume and some experts believe that this content could be limited to 5% by volume. In Sweden in particular, some classes of diesel fuel already have to satisfy very strict specifications. In that state, class II diesel fuel must not contain more than 50 ppm of sulphur and no more than 10% by volume of aromatic compounds, and class I fuel no more than 10 ppm of sulphur and 5% by volume of aromatic compounds. In Sweden, class III diesel fuel must currently contain less than 500 ppm of sulphur and less than 25% by volume of aromatic compounds. Similar limits are also in force for the sale of that type of fuel in California.
Meanwhile, motorists in a number of states are pressing for legislation to force oil suppliers to produce and sell a fuel with a cetane index with a minimum value. Current French legislation requires a minimum cetane index of 51, but in the near future this may be at least 53 (as is already the case for class I fuel in Sweden) and probably at least 55, most probably in the range 55 to 65.
Many specialists seriously predict the possibility of a future standard imposing a nitrogen content of less than about 200 ppm, for example, and perhaps less than 100 ppm. A low nitrogen content produces a more stable product and is generally desirable both from the vendor's and the manufacturer's viewpoint.
On the other hand, the heavy residual cuts from atmospheric distillation or vacuum distillation contain organometallic compounds in asphaltenes in which metals are found (nickel, vanadium, etc.). These poison the catalysts used when catalytically converting hydrocarbon cuts from vacuum distillation. While no standard has been imposed as regards the metals content in automobile fuels (apart from the lead content in gasoline), eliminating metals by hydrotreatment has proved to be vital.
In general, then, the development of reliable, effective processes for reducing the contents of both aromatic compounds, sulphur and nitrogen as well as metals is necessary. In its broadest sense, the process of the present invention concerns any process in which a fixed bed is used in a reactor during a catalytic process and in which a liquid feed and a gaseous reactant are injected into the reactor either side of the bed and flow in the bed as a counter-current. More particularly, the process is applicable to the hydrotreatment of petroleum cuts. The disadvantages and advantages of the different prior art processes in this area and the technical solutions proposed have recently been described by S. T. Sie (Fuel Processing Technology, 61, 149-171 (1999)).
The principal constraint linked to that type of device (fixed bed, counter-current of reactant fluids) is the possible existence of a flooding phenomenon, limiting the possible flow rate of each of the phases that may traverse the catalytic bed. Then, with the high gas pressures usually required when hydrotreating, there is a risk that the liquid phase will be entrained in the gas phase flowing as a counter-current. To limit risks of flooding, a counter-current flow can therefore only reasonably be envisaged if pressure drops in the catalytic bed are limited. A small catalyst size is known to entrain a large pressure drop. In order to increase the range of possible flow rates, an increase in the conventional supported catalyst particle dimensions generally adopted for fixed beds (0.5 to 10 mm) appears to be necessary, a priori. However, a larger grain size causes a reduction in catalytic activity in the reaction bed because of limited intra-particle diffusion of the feed in large particles.
The present invention aims to provide a process that can limit pressure drops linked to the use of a counter-current flow of fluids in a fixed bed reactor during a catalytic hydrotreatment process while retaining acceptable catalytic activity in the mixture of particles used.
In accordance with the invention, it has also been discovered that it is possible to limit hydrodynamic problems linked to pressure drops in the catalytic bed (flooding) and problems of the chemical reaction kinetics (catalyst size and activity) by dissociating the two.
In other words, one aim of the invention is to retain a reasonable catalytic activity in the bed while minimising pressure drops.
By way of non limiting example, the remainder of the description of the present invention uses hydrotreatment processes that can produce a product with improved characteristics as regards cetane index and thermal stability as an example, also aromatic compound content, olefin content, sulphur content and nitrogen content from conventional straight run gas oil cuts or products from another conversion process (cokefaction, visbreaking, residue hydroconversion, etc.).
Conventionally, the process layout for a hydrorefining unit is relatively simple. Firstly, the feed is mixed with a hydrogen-rich gas then heated to the reaction temperature (by heat exchanger or an oven). It then passes into a reactor in which hydrotreatment is carried out. After separation, the mixture obtained from the reactor produces:
a gas rich in H
2
S, nitrogen and impurities;
light products resulting from decomposition of impurities, nitrogen and sulphur elimination and leading to the destruction of numerous molecules and to the production of lighter fractions;
a hydrorefined product with the same volatility as the feed, but with improved characteristics.
However, to obtain a residual sulphur content of the order of 5 ppm by weight and a diaromatics content of less than 2% by weight, the following constraining conditions are imposed:
the reaction temperature must be sufficient to activate the reaction. However, the increase in reaction temperature is limited by coke formation. It is generally in the range 340° C. to 370° C.;
the hydrogen pressure must be high (of the order of 60 bars at 350° C. for gas oil HDS and more than 80 bars for gas oil HDA at the same temperature) to displace the reactions in a favourable direction, minimise radical side reactions (leading, for example, to thermal cracking and/or to polymerisation and condensation of polynuclear a
Carpot Laurence
Chapus Thierry
Morel Frederic
Rocher Philippe
Vuillemot Daniel
Arnold Jr. James
Griffin Walter D.
Institut Francais Du Petrole
Millen White Zelano & Branigan P.C.
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