The invention is concerned with a petroleum product and a process fop obtaining said petroleum product which may be used fop the formulation of a fuel fop an internal combustion engine, and the invention is also concerned with the product obtained by way of the process. The gas oils currently on the market which ape either in the form of motor fuels fop internal combustion engines with compression ignition (diesel type) of in the form of fuels ape most frequently products which have been refined and which contain about 0.3% sulphur (expressed by weight of sulphur). They ape usually obtained following a hydpodesulphuration treatment from a charge which can come from direct distillation of a crude petroleum of from a specific treatment of a crude petroleum (pyrolysis of distillation followed by pyrolysis of the fraction recovered during distillation, for example, of thermal cracking of catalytic cracking) usually containing at least 0.8% by weight of sulphur.
In some industrial countries, standards fop the content of sulphur have been set, or ape due to be set in the very neap future. These standards ape becoming increasingly strict, particularly in the case of gas oils which ape intended to be used as motor fuels. Thus, in France, particularly from 1995, the sulphur content of these gas oils will have to be at the most equal to 0.05% by weight (500 ppm) whilst the gas oils according to the standards in force have a sulphur content which can be as much as 0.3%.
Similarly, the gas oils used in France as fuels fop internal combustion engines must currently have a cetane index which is at least equal to 48, and gas oils used as fuels must have a cetane index which is at least equal to 40. Stricter standards ape to be expected in the neap future, particularly those concerning gas oils which ape used as engine fuels.
Moreover, given the diversity of charges to be treated (crudes of various origin, and viscoreduction-, coking-, hydpoconversion-, distillation- or catalytic cracking crudes) to produce the gas oil it is desirable to be able to offer the refiner a process which is flexible and which is capable of adapting the products formed to demand and to satisfy future requirements as far as sulphur and nitrogen levels, cetane index, colour and content of aromatics are concerned.
Finally, all existing processes such as hydrodesaromatisation or hydrocracking which enable petroleum products to be obtained which have a low sulphur content and which have a relatively high cetane index expend considerable amounts of hydrogen. By way of example, the process for hydrodesaromatisation of a direct distillation charge whose distillation intervals (ASTM D86) are 180.degree. C.&lt;T 5% &lt;300.degree. C., 260.degree. C.&lt;T 50%&lt;350, 350.degree. C.&lt;T 95%&lt;460.degree. C., expends 0.6 to 1.1% of hydrogen in relation to the charge, whilst the hydrocracking process requires more than 2% hydrogen in relation to its charge. Now, the hydrogen charge of the refinery which usually comes from the catalytic gas reforming unit tends to be inadequate in the light of the fact that gas oil standards are becoming increasingly strict, resulting in an increase in hydrotreatments.
Moreover, these existing processes result in a petroleum product being obtained whose cetane index does not exceed 63, this latter only being attained at the cost of hydrogenation of the aromatic hydrocarbons of the charge, which reaction uses up hydrogen. (see table).
It is therefore desirable to offer the refiner a process which will enable him to produce a petroleum product which satisfies the various standards which will be applicable in the very near future, and after 1995, as far as sulphur content is concerned.
The technological plan is illustrated by the following patents: U.S. Pat. No. 4,985,139, EP-A-0 215 496, GB-A-1 006 949 and GB-A-943 239.