Fuel and related compositions – Liquid fuels – Heterocyclic carbon compound containing a hetero ring having...
44347, 44386, 44398, 44554, C10L 122
The present invention relates to a new additive composition which improves the cold operability of middle distillates to temperatures ranging beyond -20.degree. C., and more particularly for diesel fuels and domestic fuel oils.
This cold operability corresponds to a limiting temperature at which middle distillates can be employed without any problem of blocking. It is intermediate between the cloud point temperature (AFNOR NFT 60105 or ASTMD 2500-66), characteristic of the onset of crystallization of waxes in the distillate and the flow point of the latter (AFNOR NFT 60105 or ASTMD 97-66).
It is well known that the crystallization of waxes is a factor limiting the use of middle distillates. It is also important to prepare diesel fuels adapted to the temperatures at which they will be employed in motor vehicles, that is to say to the surrounding climate. A cold operability of fuels at -10.degree. C. is generally sufficient in many industrialized countries. However, in other countries, such as the Scandinavian countries, Canada and the countries of North Asia, fuel utilization temperatures well below -20.degree. C. can be expected. The same applies in the case of domestic fuel oils stored outside for private houses and buildings.
This adaptation of the cold operability of diesel fuels is important, especially when engines are being started cold. If waxes have crystallized at the bottom of the fuel tank they can be drawn into the engine on starting and can block in particular the filters and prefilters arranged before the combustion chamber. Similarly in the case of the storage of domestic fuel oils, the waxes precipitate at the bottom of a tank and can be drawn in and can obstruct the conduits leading to the boiler. It is obvious that the presence of solids, such as wax crystals; prevents the normal circulation of the middle distillate.
To improve their circulation either in the engine or towards the boilers, a number of types of additives have come to light.
In a first step, the oil industry concentrated on the development of additives promoting the filterability of fuels at low temperature. The role of these additives, called CFPP (cold filter-plugging point) additives, is to limit the size of the wax crystals formed. Additives of this type, known very extensively to the person skilled in the art, are at present systematically added to middle distillates.
However, these additives, while controlling the size of the wax crystals, cannot prevent the sedimentation of the crystals formed, that is to say their agglomeration, especially in the fuel tank of diesel vehicles when standing or in storage tanks for domestic fuel oils.
Accordingly, in a second step, the oil industry made efforts to develop antisedimentation additives, that is to say dispersants, which keep the wax crystals in suspension in the middle dispersants, which prevents them from depositing and agglomerating together. The Applicant Company has developed especially such an additive described in French Patent Application FR-A-92 15358 of 17 Dec. 1992.
Nevertheless, the joint action of the CFPP and antisedimentation additives has not made it possible to improve the cold operability of all middle distillates produced in refining in the case of all the known crude oils.
This is why the oil industry has introduced a third type of additives with a view to lowering the cold operability temperature of middle distillates, whatever they be, beyond -20.degree. C., even if their cloud point temperature is higher than -20.degree. C.
The present invention is aimed at a new additive composition enabling the cold operability temperature of middle distillates to be lowered and maintained, even after storage, at temperatures beyond -20.degree.C., including especially an additive of the third type which has the effect of maintaining a good dispersion of the wax crystals in the middle distillate.
The subject of the present invention is therefore and additive composition following the cold operability temperature of the distillates beyond -20.degree. C., characterize
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