EP1019462A1

EP1019462A1 - Composition based on an organic sol of tetravalent metal oxide and an organic alkaline-earth compound

Info

Publication number: EP1019462A1
Application number: EP98942782A
Authority: EP
Inventors: Thierry Birchem; Gilbert Blanchard
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1997-09-11
Filing date: 1998-08-25
Publication date: 2000-07-19
Also published as: AU9078898A; CN1275158A; NO20001237D0; JP2001515946A; WO1999013026A1; CA2303137A1; HUP0004601A2; KR20010030585A; BR9812072A; NO20001237L; FR2768155B1; FR2768155A1; HUP0004601A3

Abstract

The invention concerns a composition comprising an organic sol of particles of at least one tetravalent metal oxide, and at least an organic compound of at least one alkaline-earth. The composition may further contain at least an organic compound of at least an alkaline. The tetravalent metal is more particularly cerium. The invention also concerns the use of said composition as additive of hydrocarbon compounds.

Description

COMPOSITION BASED ON TETRAVALENT METAL DOXIDE ORGANIC SOL AND ORGANIC ALKALINE EARTH COMPOUND

The subject of the present invention is a composition based on at least one organic compound of at least one alkaline earth and of a sol of at least one oxide of at least one tetravalent metal.

The present invention also relates to a process for obtaining these compositions as well as their use.

It is known that when diesel fuel is burned in the diesel engine, carbon products tend to form soot, which is deemed to be harmful to the environment and to health. Techniques have been sought for a long time which make it possible to reduce the emission of these carbonaceous particles, which will be designated in the following description under the expression "soot".

This research is concomitant with the need not to increase the emission of carbon monoxide and gases known to be toxic and mutagenic, such as nitrogen oxides.

Many solutions have been proposed to reduce these carbon emissions.

However, we are moving more and more towards the adaptation in the exhaust circuits of a filter capable of stopping the whole; or a very high proportion (at least 80% by mass) of the carbonaceous particles generated by the combustion of the various fuels.

However, this technique is limited by the storage capacity of the filter, which must either be emptied or the soot contained in it must be burned. This so-called regeneration operation is extremely costly to plan and implement. One of the most commonly proposed solutions is the combustion of this soot, combustion caused intermittently either by electric heating or by the use of a fossil lighter fuel.

However, this technique has many drawbacks, not the least of which is the risk of thermal shock leading to a fracture or cracking of the ceramic filter, or a melting of the metal filter.

One solution which would be satisfactory consists in introducing into the soot catalysts which allow frequent self-ignition of the soot collected in the filter. For this, it is necessary that these soots have a sufficiently low auto-ignition temperature to be frequently reached during normal engine operation.

We realized that rare earths in general, and cerium in particular, could constitute a good element to reduce the temperature of auto-ignition of soot. However, the need was felt to have a product which, after introduction into diesel, then after combustion, gives good self-ignition of the soot at an even lower temperature.

For this purpose, the composition of the invention is characterized in that it comprises an organic sol of particles of at least one oxide of at least one tetravalent metal and at least one organic compound of at least one alkaline earth metal .

For the purposes of the invention, the term “sol” is intended to denote an organic colloidal suspension of particles of at least one oxide of at least one tetravalent metal.

The tetravalent metal can be chosen from rare earths which can form tetravalent metal oxides. By rare earth is meant the elements of the group constituted by yttrium and the elements of the periodic classification with atomic number between 57 and 71. The periodic classification of the elements to which reference is made is that published in the Supplement to the Chemical Bulletin de France n ° 1 (January 1966). As such, we can cite cerium, praseodymium, and terbium. In the particular case of rare earth mixtures, it is preferable that cerium is present. The tetravalent metal is more particularly cerium.

The alkaline earth can be chosen from magnesium, calcium, strontium, or barium. More particularly, the alkaline earth is calcium, or strontium.

According to a preferred variant of the invention, the composition comprises an organic sol of cerium oxide particles and at least one organic strontium compound.

The composition of the invention may, in addition, comprise at least one organic compound of at least one alkali.

The alkali will then be chosen from sodium, potassium, or cesium.

Also suitable in the context of the present invention, the compositions which comprise one or more organic compound (s) of one or more alkaline earth metals, and, if appropriate, one or more organic compound (s) ( s) one or more alkali.

The organic alkaline earth or alkaline compound is an organometallic complex of the type described in patent application WO 96/34074, the teaching of which on this subject is incorporated here.

It may very particularly be the complex defined in this application WO 96/34074 by the formula M (R) _m nL in which: ^a M is alkaline-earth and optionally alkaline,

^D R is the residue of an organic compound of formula RH in which H represents an active hydrogen atom reactive with the metal M and attached either to a heteroatom chosen from O, S and N in the organic group R, or to a carbon atom, this hetero atom or this carbon atom being located in the organic group R near an electron-attracting group, for example a hetero atom or a group consisting of or containing O, S or N, or an aromatic ring, for example phenyl, ^α n is a number indicating the number of organic electron-donor molecules

(Lewis bases) forming dative bonds with the metal cation in the complex, usually up to 5 in number, more particularly an integer from 1 to 4, and

^D L is one or more electron donor ligands (Lewis bases).

R can comprise one or more functional groups capable of acting as an organic electron-donor ligand. The entire teaching of WO 96/34074 concerning the complex of formula above is incorporated here by reference.

According to a particular embodiment, the abovementioned organic soil comprises: ^a particles of at least one oxide of at least one tetravalent metal, ^π an amphiphilic acid system, and ° a diluent, and it is further characterized by the fact that said particles have a dgo at most equal to 20 nanometers and it has at least one of the following characteristics:

• said particles of tetravalent metal oxide (s) are in the form of agglomerates of crystallites, the dgo of which, measured by photometric counting (high resolution transmission electron microscopy), is at most equal to 5 nanometers, 90% by mass of the agglomerates comprising from 1 to 5, preferably 1 to 3 crystallites,

• said amphiphilic acid system comprises at least one acid of 10 to 50 carbon atoms, having at least one branching in alpha, beta, gamma or delta of the atom carrying the acid hydrogen.

The aforementioned tetravalent metal oxide particles are advantageously cerium dioxide.

In the rest of the description, what will be described for the specific case of cerium, can also be applied to the other mixtures of rare earths mentioned above (in which cerium is always present).

The soil characteristics of this particular embodiment will be developed below.

In the present description, the particle size characteristics often refer to notations of the type d _n where n is a number from 1 to 99. This notation represents the size of the particles such that n% by weight of said particles has a size less than or equal at said size. For example, a 5 nanometer dgo means that 90% by weight of the particles have a size less than or equal to 5 nanometer. These more stringent conditions and how to respond to them are set out below.

Advantageously, at least 50% by mass of the agglomerates are monocrystalline, that is to say that they consist of only one crystallite (or at least appear to consist of only one crystallite when the the soil is examined by METHR (High Resolution Transmission Electron Microscopy).

In addition, by playing on the technique and the hydrolysis conditions, it can be ensured that 80%, preferably 90% by mass of the crystallites are of size in the range 2 to 5 nanometers. Advantageously, the molar ratio between said amphiphilic acid and the metallic elements of the soil is at most equal to 0.5, advantageously at most equal to 0.4, preferably at most equal to 0.3. Here the molar ratio must be taken in the acceptance of a functional molar ratio, that is to say that one counts as mole of amphiphilic acid, the number of mole multiplied by the number of useful acid functions. It is desirable that in the soil, the ratio between the cerium (III) content and the cerium (IV) content, be as low as possible, in general less than 1.5%, advantageously at most equal to 1% of preferably 0.5%.

Advantageously, the soil has a concentration such that the content of cerium dioxide contained is between 10 and 60%, preferably 30 to 50% by mass. Thus, the cerium is essentially in the form of a metal oxide agglomerate, optionally hydrated dioxide, which agglomerate of oxide (s) is made liposoluble by means of an amphiphilic organic acid.

In the soil, the cerium may possibly be accompanied by impurities. In the context of the present invention, the purity of the cerium is not critical. Soils of this type and their methods of preparation are known to those skilled in the art. However, as an example of preparation of a cerium-based soil, the following preparation process can be described.

This process comprises the following stages consisting of: a) subjecting an aqueous ceriferous phase to a hydrolysis operation so as to precipitate a cerium dioxide, b) bringing into contact, simultaneously or consecutively, a suspension of cerium dioxide obtained from step (a) with an organic phase comprising an organic acid and preferably an organic compound or mixture playing the role of solvent, then c) recovering the organic phase.

Which phase constitutes a soil.

The soil preparation process will now be developed in more detail. Advantageously, it is possible to proceed between step (a) and step (b), to a separation of the solid particles from the mother liquors, optionally to a drying preferably by atomization, then to repulp the solid particles in aqueous phase which will then be subject to step (b). The repulping is carried out so that the content of cerium dioxide in the aqueous phase is between 100 and 400 g / l.

According to an advantageous implementation of the present invention, advantageously the drying [between steps (a) and (b)] is carried out by atomization, that is to say by spraying the mixture of soils in a hot atmosphere (spray - drying). The atomization can be carried out by means of any sprayer known per se, for example by a spray nozzle of the sprinkler apple type or the like. One can also use so-called turbine atomizers. On the various spraying techniques likely to be used in the present process, reference may in particular be made to the basic work by MASTERS entitled "SPRAY-DRYING" (second edition, 1976, Editions Gerge Godwin - London).

It will be noted that it is also possible to implement the spray-drying operation by means of a "flash" reactor, for example of the type developed by the Applicant and described in particular in French patent applications number 2 257 326, 2 419 754 and 2 431 321. In this case, the treating gases (hot gases) are driven in a helical movement and flow in a vortex well. The mixture to be dried is injected along a trajectory coincident with the axis of symmetry of the helical trajectories of said gases, which allows the momentum of the gases to be transferred perfectly to the mixture to be treated. The gases thus in fact perform a double function: on the one hand the spraying, that is to say the transformation into fine droplets, of the initial mixture, and on the other hand the drying of the droplets obtained. Furthermore, the extremely short residence time (generally less than about 1/10 of a second) of the particles in the reactor has the advantage, among other things, of limiting improbable risks of overheating as a result of too long contact with the hot gases. It should be noted here that this atomization treatment makes it possible to significantly improve the ability of a thermohydrolysed soil at "low" temperatures to form stable soils and even when the temperature of the gases is at least equal to 200 ° C., preferably between 200 and 300 ° C, to obtain results similar to those obtained by thermohydrolysis at "high" temperature (150 ° C), and therefore soils according to the present invention which are optimal.

The temperature of the drying atmosphere can vary within wide limits, and it depends in particular on the average residence time that is desired or that can be imposed on the atomized product once in said atmosphere. In a general way, the drying conditions (temperatures and / or residence time) are conventionally determined so as to at least obtain a total or almost total elimination of the residual water contained in the product, that is to say, overall, up to obtaining a constant weight for the latter. The solid particles will then be repulped in the aqueous phase.

Mention may in particular be made, as water-soluble compounds of cerium, of cerium (IV) salts such as nitrates or cerium ammonium nitrates, for example, which are particularly suitable here. Preferably, ceric nitrate is used.

The cerium (IV) salt solution can contain cerium in cerous state without disadvantage, but it is desirable that it contains at least 85% of cerium (IV). An aqueous solution of ceric nitrate can for example be obtained by reaction of nitric acid with a hydrated ceric oxide prepared in a conventional manner by reaction of a solution of a cerous salt, for example cerous carbonate, and an ammonia solution in the presence of hydrogen peroxide. It is also possible, preferably, to use a ceric nitrate solution obtained according to the electrolytic oxidation process of a cerous nitrate solution as described in document FR 2 570 087, which constitutes here a raw material of choice.

It will be noted here that the aqueous solution of cerium (IV) salts may have a certain initial free acidity, for example a normality varying between 0.1 and 4 N. According to the present invention, it is as much possible to use a solution initial of cerium (IV) salts actually having a certain free acidity as mentioned above, than a solution which will have been previously neutralized in a more or less extensive manner by adding a base, such as for example a solution of ammonia or alternatively alkali hydroxides, in particular sodium or potassium, but preferably an ammonia solution, so as to limit this acidity. We can then, in the latter case, define in a practical way a neutralization rate (r) of the initial cerium solution by the following equation: r = n3 -n2 ni

in which ni represents the total number of moles of Ce (IV) present in the solution after neutralization; n2 represents the total number of moles of OH ions "effectively necessary to neutralize the initial free acidity provided by the aqueous solution of cerium (IV) salt; and n3 represents the total number of moles of OH ions" provided by l 'addition of the base. When the "neutralization" variant is implemented, a quantity of base is used in all cases which must imperatively be less than the quantity of base which would be necessary to obtain the total precipitation of the hydroxide species Ce (OH) (r = 4). In practice, this is limited to neutralization rates not exceeding 1, and preferably not exceeding 0.5.

The following operation consists in carrying out a hydrolysis so as to precipitate a cerium dioxide. Cerium dioxide is precipitated by heat treatment, also called thermohydrolysis.

The temperature at which the thermohydrolysis is carried out can be between 80 ° C. and the critical temperature of the reaction medium, in particular between 80 and 350 ° C., preferably between 90 and 200 ° C.

This treatment can be carried out, depending on the temperature conditions adopted, either under normal atmospheric pressure or under pressure such as for example the saturated vapor pressure corresponding substantially to the temperature of the heat treatment.

When, as is preferred, the treatment temperature is chosen to be higher than the reflux temperature (under ordinary pressure) of the reaction mixture (that is to say generally greater than 10 ° C.), for example chosen from 120, more often between 150 and 350 ° C, the operation is then carried out in a closed enclosure which is more particularly a closed reactor more commonly called an autoclave. The aqueous mixture containing the aforementioned species is introduced into this enclosure, the necessary pressure results only from the heating of the reaction medium (autogenous pressure). Under the temperature conditions given above, and in aqueous media, it can thus be specified, by way of illustration, that the pressure in the closed reactor varies between a value greater than 1 Bar (10 ⁵ Pa) and 200 Bar (20.10 ⁷ Pa), preferably between 5 Bar

(5.10 ⁵ Pa) and 150 Bar (1, 5.10 ⁷ Pa). It is of course also possible to exert an external pressure which is then added to that following the heating. The heating can be carried out either under an atmosphere of air, or under an atmosphere of inert gas, preferably nitrogen.

The duration of the treatment is not critical, and can thus vary within wide limits, for example between 1 and 48 hours, preferably between 2 and 24 hours.

Likewise, the temperature rise takes place at a speed which is not critical, and the fixed reaction temperature can be reached by heating the medium for example between 30 minutes and 4 hours, these values being given entirely indicative.

At the end of the thermohydrolysis step [step (a)], a solid precipitate is recovered which can be separated from its medium by any conventional solid-liquid separation technique such as, for example, elutriation, filtration, decantation, spinning or centrifugation.

It will be noted that it is of course possible to repeat one or more times, identical or not, a heating (thermohydrolysis) / precipitation step as shown below. above defined, then using for example heat treatment cycles.

As an indication, cerium (IV) solutions, generally nitrate, which meet the following characteristics can be used as the starting solution for thermolysis.

The characteristic of stage (b) of the process of the invention is to obtain an organic sol, expression which designates the dispersion of the cerium dioxide, possibly impure, in organic medium, by transferring said cerium dioxide in organic phase, from an aqueous phase constituted by the ceric compound which is in colloidal form in an aqueous soil. The term “aqueous sol” denotes the colloidal dispersion of cerium dioxide in an aqueous medium which constitutes the basic raw material of step (b).

In order to carry out the process of the invention satisfactorily, it is desirable that the aqueous starting soil satisfies the following requirements: "the level of metal (s) in the form of colloidal oxide (s) must be very high, advantageously 90%, preferably greater than or equal to 95%, and as a rule as high as possible;

• the concentration of the aqueous soil in colloidal oxide must be sufficient and preferably be between 0.1 and 3 moles / liter; • the aqueous soil must have good thermal stability properties and not flocculate at the reaction temperature which is above 60 ° C and most often varies between 80 ° C and boiling (variable depending on pressure).

The organic liquid medium used in step (b) of the process can be an inert aliphatic, cycloaliphatic hydrocarbon, where their mixture, such as for example mineral or petroleum spirits, mineral or petroleum ethers which may also contain aromatic components. Mention may be made, by way of indication, of hexane, heptane, octane, nonane, decane, cyclohexane, cyclopentane, cycloheptane and liquid naphthenes. Aromatic solvents such as benzene, toluene, ethylbenzene and xylenes are also suitable as well as petroleum fractions of the ISOPAR or SOLVESSO type (trademarks registered by the company EXXON), in particular SOLVESSO 100 which essentially contains a mixture of methylethyl and trimethylbenzene, and SOLVESSO 150 which contains a mixture of alkylbenzenes in particular of dimethylethylbenzene and tetramethylbenzene.

It is also possible to use chlorinated hydrocarbons such as chloro or dichlorobenzene, chlorotoluene, as well as aliphalic and cycloaliphatic ethers such as diisopropyl ether, dibutyl ether and aliphatic and cycloaliphatic ketones such as methylisobutylketone , diisobutylketone, mesityl oxide.

Esters can be considered, but they have the disadvantage of risking being hydrolyzed. Mention may be made, as esters capable of being used, of those obtained from the acids cited in the present application with C1 to C8 alcohols and in particular secondary alcohol palmitates such as isopropanol.

The organic liquid or solvent system will be chosen taking into account the organic solubilizing acid used, the heating temperature and the final application of the colloidal solution or dispersion. In some cases it is better to use a mixture of solvents. The quantity of liquid or solvents obviously determines the final concentration. It is more economical and more convenient to prepare more concentrated dispersions which can be diluted later during use. It is for this reason that the amount of solvent is not critical. It may be advantageous to add a promoter to the organic phase, the function of which is to accelerate the transfer of colloids from the aqueous phase to the organic phase and to improve the stability of the organic soils obtained. As promoters, it is possible to use the compounds with an alcohol function, and very particularly linear or branched aliphatic alcohols having from 6 to 12 carbon atoms. As specific examples, mention may be made of 2-ethyl hexanol, decanol, dodecanol, or their mixture.

The proportion of said agent in the organic phase is not critical and can vary within wide limits.

However, a proportion of between 2 and 15% by weight is generally suitable.

If the field of usable acids is very large, the total number of carbon in the molecule to obtain good dissolution is a little more restrictive.

The total number (average if the acid used is a mixture) of carbon acids is advantageously greater than 6 preferably 10, it is also desirable that it is less than about 60.

If high concentrations of cerium or equivalent are desired, it is desirable to choose acids that are as short as possible. These acids can be linear or branched. It is preferable, however, for the branches to be either far from the carboxylic function, or few in number and carried by different carbons. The carboxylic acids which can be used for the present invention can be aryl, aliphatic or arylaliphatic acids. They can carry other functions provided that these functions are stable in the media where it is desired to use the cerium compounds according to the present invention.

To keep the soil usable at low temperature, below ambient, or even below 0 ° C, it is preferable that the melting point of the acid, or of the acid mixture, is at most equal to 50 ° C advantageously at room temperature, preferably at 0 ° C.

Thus it is easy to use carboxylic acids whose carbon chain carries ketone functions such as pyruvic acids substituted in alpha of the ketone function. It can also be alpha-halo carboxylic acids or alpha-hydroxy carboxylic acids. The chain attached to the carboxylic group can carry unsaturations.

However, in general there is a tendency to avoid too many double bonds because cerium catalyzes the crosslinking of the double bonds. The chain can be interrupted by ether or ester functions provided that the lipophilicity of the chain carrying the carboxylic group is not too much altered. Thus, it is possible to use aliphatic carboxylic acids, aliphatic sulfonic acids, aliphatic phosphonic acids, alkylarylsulfonic acids, and alkylarylphosphonic acids having about 10 to about 40 carbon atoms, whether natural or synthetic. They can be used alone or mixed with each other. By way of example, mention may be made of tall oil fatty acids, coconut oil, soybean, tallow, linseed oil, oleic acid, linoleic acid, stearic acid and its isomers , pelargonic acid, capric acid, lauric acid, myristic acid, dodecylbenzenesulfonic acid, 2-ethylhexanoic acid, naphthenic acid, hexoic acid, toluenesulfonic acid , toluene-phosphonic acid, lauryl-sulfonic acid, Iauryl-phosphonic acid, palmityl-sulfonic acid, and palmityl-phosphonic acid. Preferably, oleic acid or alkylarylsulfonic acids are used.

The amount of amphiphilic organic acid used, expressed as the number of moles of acid per mole of oxide, can vary within wide limits between 1/10 and 1 mole of cerium dioxide. The upper bound is not critical, but there is no need to use more acid. Preferably, the organic acid is used in an amount of 1/5 to 4/5 mole per mole of cerium dioxide. In the organic phase, the proportion between the organic solvent and the organic acid is not critical. The weight ratio between the organic solvent and the organic acid is preferably chosen between 0.3 and 2.0.

The order of introduction of the different reagents is indifferent. It is possible to carry out the simultaneous mixing of the colloidal aqueous dispersion (s), of the organic acid, of the organic solvent, and optionally of the promoter agent. It is also possible to make the premix of the organic acid, of the organic solvent and optionally of the promoter agent which constitute the organic phase.

The temperature of the reaction medium is preferably chosen in a range from 60 to 150 ° C.

In some cases, due to the volatility of the organic solvent, it is necessary to condense its vapors by cooling to a temperature below its boiling point.

Advantageously, one works at a temperature between 60 and 120 ° C., preferably between 90 and 110 ° C.

The reaction mixture is kept under stirring for the entire duration of the heating, which can be from less than an hour to around one day, preferably between 2 hours and half a day.

At the end of the above heating time, the heating is stopped. The presence of two phases is noted: an organic phase containing in dispersion, the metal oxide - organic acid complex and a residual aqueous phase.

The organic phase and the aqueous phase are then separated according to conventional separation techniques: decantation, centrifugation, etc.

In accordance with the present invention, organic colloidal dispersions of metal oxides are obtained, the size of the colloids of which can be very variable and can be controlled by varying certain parameters, in particular the diameter of the starting colloidal aqueous dispersions in step (b), which depends on compliance with the thermohydrolysis conditions in step (a).

For certain applications, it is possible to use the reaction mixture as it is, but sometimes it is desirable to remove the water, which can represent from 1 to 3% by weight of the organic phase. To this end, means well known to those skilled in the art are used, for example passing over a drying agent (including a hydrophobic membrane filter) or the addition of a third solvent which is inert with respect to cerium dioxide, preferably having a boiling point below 100 ° C and forming an azeotrope with water and then distillation of the azeotrope obtained. As third solvents suitable for the invention, there may be mentioned aliphatic hydrocarbons, such as hexane, heptane, cycloaliphatic hydrocarbons: aromatic, or alcohols such as, for example, ethanol, ethylene glycol , diethylene giycol etc. It is preferable, in particular for applications as an adjuvant for diesel, that the water content is at most equal to 1%, advantageously 1000 ppm, preferably 100 ppm.

We will now examine the amphiphilic acid system.

As already mentioned, the amphiphilic acid system comprises at least one acid of 10 to 50 carbon atoms, having at least one branching in alpha, beta, gamma or delta of the atom carrying the acid hydrogen.

Advantageously, the amphilphile acid system comprises at least one acid of 11 to 25 carbon atoms. The preferred range is 15 to 25 carbon atoms for the acids of said amphiphilic system.

For best results, especially when the chain length is short (less than 14 carbon atoms), when the branch is unique and especially when it is located in the gamma or delta position of the atom carrying acid hydrogen , it is very desirable that this branching be at least two carbon atoms, advantageously three.

To explain the nomenclature of the positions below, we will find the examples of di (2-ethylhexyl) acid phosphate and 2-ethyl octanoic acid

It is preferred that the longest linear part is at least 6, preferably 8 carbon atoms.

It is advantageous for the pKa of at least one of the acids to be at least 5, preferably 4.5.

It is also advantageous for the side chain (s) of the branched acids to contain at least two atoms, preferably three carbon atoms. It is preferable, in particular when the acids are carboxylic acids, that the amphiphilic acid system is a mixture of acids.

In this case the conditions on ia branching must act on at least half, advantageously two thirds, preferably four fifths by mole of the constituent acids of said amphiphilic acid system. Among the acids which give very good results, mention may be made of acids containing phosphorus, such as phosphoric acids, in particular the diesters of phosphonic acid, and their monoesters, and phosphinic acids. Among the carboxylic acids which give good results, mention should be made of the constituent acids of the mixture of acids known under the name of isostearic acid. The acid system is advantageously isostearic acid itself.

The starting melting point of the amphiphilic acid system (s) is advantageously less than 50 ° C, more advantageously less than or equal to 20 ° C, preferably at most equal to 0 ° C.

For good stability and for good extraction, it is desirable that the molar ratio between the extractant and the tetravalent metal (s), preferably cerium, be between 1, 1 and 0.6, preferably between 0.2 and 0.4. This ratio increases when the particle size decreases.

To obtain particularly stable soils, it is preferable that at most 5%, advantageously at most 1%, preferably at most 0.5% by mass of the particles of metal oxide (s) tetravait (s) , or at most equal to 100 nm, advantageously 50 nanometers, preferably 20 nanometers. Any diluent leading to a stable soil is within the scope of this invention.

The floors according to the present invention can be used according to numerous implementations. Depending on the desired implementation, a compromise should be chosen taking into account the following technical data:

for synthesis and stability, it is desirable to avoid very non-polar hydrocarbons, such as, for example, non-cyclic aliphatic hydrocarbons,

- diluents, such as esters or ethers, having a polar function give good results, but for certain uses may be avoided as far as possible.

The mixture of diluents can provide a solution by compensating for the non-polarity of certain diluents by the addition of polar compounds, generally solvents. According to a particularly advantageous implementation of the present invention, the soil is used to form a soil diluted in diesel. The initial soil is generally very concentrated.

Furthermore, for reasons of compatibility with diesel, and its numerous additives, the diluents are preferably not very polar. As a constituent of a diluent, the aromatic or aliphatic compounds are preferable to the compounds having a polar function, such as for example the ester or ether functions.

It is preferable that the diluents have a Kauri Butanol index (measured according to standard ASTM D 11 33) less than 105, advantageously less than 90.

For use as an on-board additive, it is preferable that the melting point of the diluents, or mixture of diluents, be low and meet the melting point constraints described in this title with regard to the amphiphilic acid system. . It is also preferable that these diluents have a very low solubility in water, preferably less than 5% by mass, preferably at most 1%, more preferably at most equal to 0.5% by mass.

Symmetrically, it is also preferable for the water to be soluble at most 5%, preferably at most 1%, more preferably at most 0.5% in the diluent.

Among the preferred diluents, there are mentioned aromatic hydrocarbon compounds and their mixtures, as well as aliphatic compounds and their mixture containing less than 50%, preferably 25%, or more preferably 1% of aromatic compounds.

The oxides of tetravalent metal (s) may contain relatively small proportions of metals having other valencies. In general, the proportion of addition elements, or impurities, contained in the particles of tetravalent metal (s), does not exceed 10% by mass, more particularly 5% by mass. The content of tetravalent metal (s) in the soil according to the invention is advantageously at most equal 2/3 by mass, preferably between 30 and 40% by mass. For the use as an additive for on-board diesel, it is preferable that the content of the sink does not drop below 1/6, preferably 1/5.

The organic soils according to the present invention are generally prepared in a known manner by heating an aqueous soil containing the said tetravalent metal oxide (s), in the presence of said diluent. and said amphiphilic acid system.

According to one of the particularly advantageous characteristics of the invention, care should be taken to ensure that there are no excessively coarse particles in the aqueous soil and therefore in the final soil. The coarsest-sized particles can be removed by any technique which makes it possible to selectively remove the coarsest particles. This elimination can be carried out on aqueous soil, on organic soil, or both.

However, it is preferred that there is at least one separation on the aqueous soil.

The preferred technique is centrifugation. Centrifuging the aqueous soil corresponding to 1000 to 10,000 G for one hour generally gives good results. One can, however, go as far as centrifugations corresponding to 50,000 G.

It should be noted that the centrifugation prior to the organic soil constitution stage, often called the extraction stage, promotes the latter. The aqueous soils are advantageously produced by hydrolysis, preferably by thermohydrolysis. Among the techniques which can be used for the present invention, mention may be made of the techniques disclosed in the European patent application published under the number 97563 in the name of the Claimant. Mention may also be made of the European patent application published under the number 206907.

Said soils obtained according to the invention have a concentration of cerium (IV) compound which can be very high since it can range up to 3.5 M to 4 M of CeO ₂ . It is found that the yield of extraction of cerium in the organic phase is very good since it can reach 90 to 95%.

The organic soils thus produced have excellent stability. No settling is observed after several months.

According to one of the preferred characteristics of the present invention, the self is such that, adjusted to a concentration of cerium metal content of 30%, the viscosity of the soil to

25 ° C is at most equal to 20 mPa.s, advantageously 15 mPa.s, preferably 10 mPa.s. This viscosity can be measured by Contraves brand low shear by varying the speed gradient from 0.01 to 1 s ^-1 .

It is also preferable that the counter anions of the soil source cerium solution are no longer present in the various soils according to the present invention except at a content at most equal to 0.1, advantageously 0.05, preferably at 0.03 equivalents per 100 grams of cerium dioxide.

The organic soils thus obtained can be diluted to obtain concentrations of 10 to 500 ppm, preferably from 50 to 200 ppm of metal (s) tetravalent (s).

The diluent is advantageously a fuel for an internal combustion engine, preferably diesel. Thus, the invention also relates to soils whose organic phase consists essentially of diesel and its additives.

Another object of the present invention is the process for preparing the above-mentioned composition. This preparation process is characterized in that at least one organic compound of at least one alkaline earth is mixed and, where appropriate, at least one organic compound of at least one alkaline, with the abovementioned organic self. .

Generally, the atomic proportion of metal (s) tetravalent (s) / sum of elements metal (s) tetravalent (s), alkaline earth, and possibly alkaline, is at least 50%, more particularly at least 70% .

The invention also relates to the use of said compositions. The compositions of the invention can be used as driers in the paint and varnish industry in order to accelerate the drying of unsaturated oils. They can also be used as combustion additives in fuels or liquid fuels of energy generators such as internal combustion engines, oil burners, or jet propellers. The compositions of the invention are more particularly suitable as an adjuvant for diesel oils for a diesel engine.

Concrete but non-limiting examples will now be given.

Reagent EXAMPLES:

Unless otherwise provided, the reagents used in the examples are:

- a pre-neutralized ceric nitrate at r = + 0.5 (cf. European patent in the name of the Applicant published under the number 153227)

- an oleic acid extracting agent, which can be replaced without modification by olein (70% oleic acid + 30% linoleic acid)

- a solvent, SOLVESSO 150, which is not specific and can be replaced by ISOPAR L, hexane or even diesel. General operating mode:

The procedure for the examples is as follows:

- The first step consists in the synthesis of the precursor which is an aqueous sol of CeO ₂ colloids whose size (TEM) is between 3 and 5 mm.

The ceric nitrate solution at r = + 0.5 is placed in an autoclave covered with tantalum. The concentration of the solution used is 60 g / l expressed as CeO ₂ .

Autoclaving is carried out at 180 ° C for 4 hours, with a temperature rise in 1 hour. Agitation is maintained throughout the operation.

After autoclaving, the product is decanted and then separated (filtered and wrung) from the mother liquors. It is then redispersed in water, which makes it possible to obtain a stable aqueous soil.

The concentration of this soil of 150 g / l.

Example 1

Reagents: - a pre-neutralized ceric nitrate at r = + 0.5 and at a concentration of 60 g / l of cerium.

- an oleic acid extracting agent, First step:

The ceric nitrate solution at r = + 0.5 is placed in an autoclave covered with tantalum. The concentration of the solution used is 80 g / l expressed as CeO ₂ .

Autoclaving is carried out at 180 ° C for 4 hours, with a temperature rise in 1 hour.

Agitation is maintained throughout the operation. The solution obtained is filtered through a No. 4 frit.

The product is then redispersed in water, which makes it possible to obtain a stable aqueous soil. The concentration of this soil is 150 g / l. Second step: The second step of the preparation is the transfer of colloids from the aqueous phase to the organic phase.

In a flask, a metered amount of aqueous sol of CeO _{2 is placed} , to which the organic mixture is added which is such that the molar ratio oleic acid / cerium is 0.3 and the ratio SOLVESSO 150 / oleic acid is 3 , 75. In the example considered, this leads to using:

- 24.8 g of CeO ₂ (i.e. 0.165 I of soil at 150 g / l),

-12.2 g of oleic acid,

- 45.7 g of SOLVESSO 150.

The mixture is then heated to 100 ° C. at reflux for approximately 10 hours. After cooling, the organic phase is separated from the aqueous phase and then filtered through a hydrophobic filter.

The exact soil title is then measured by calcination (dry extract after 6 hours at 950 ° C).

This gives a soil with measured stability greater than 4 months (duration of the sample), whose CeO ₂ concentration is 29.1% (mass), and whose colloid size (measured by TEM) is between 3 and 5 nm.

Example 2

Mixture of an organic cerium sol and a strontium salt according to the invention A strontium salt of polyisobutylene succinic anhydride of molecular weight 420 Sr-PIBSA 420 is prepared, as described in Examples 13 and 14 of the patent

WO 96/34074 from the company OCTEL.

Then an organic cerium sol described in Example 1 is mixed with the r-PIBSA 420 salt in the following proportions: 90 mol% of cerium and 10 mol% of Sr.

Example 3

Mixture of an organic cerium sol and a strontium salt according to the invention, the procedure is as in Example 2, using the organic cerium sol and the Sr-PIBSA 420 salt in the following proportions: 75 % molar of cerium and 25% molar of Sr. Performance: measurement of the ignition temperature of soot

We proceed as follows:

A carbon black which we know can be produced productively (ref.

ELFTEX 125 n ° 137 from) was selected for these properties in terms of particle size and specific surface. These 60 nm and 30 m ² / g respectively are of the same order of magnitude as the carbonaceous particles emitted at the outlet of an exhaust from a diesel engine.

This carbon black is impregnated with an additive so as to obtain a final content of 15% by weight of metal equivalent (Ce + Sr). This content is representative of what can be obtained in the particles emitted from the exhaust of a diesel engine, during the use of an additive in diesel fuel. The impregnation is carried out in the same way as the supported catalysts are prepared by the technique known as dry impregnation.

Carbon black and the desired amount of additive are thoroughly mixed in a glass container until a homogeneous paste is obtained. Then, the whole is dried overnight at 95 ° C. Monitoring in Thermo Gravimetric Analysis (ATG) of the combustion in air of this impregnated carbon black makes it possible to highlight the greater or lesser catalytic effect thus generated by the presence of the additive. The additive will be considered to be all the more active as the corresponding temperature of the start of combustion of carbon during the ATG will be low.

A test carried out with carbon black not impregnated with an additive serves as a reference. ATG is performed with a load of 20 to 25 mg of carbon black, in an air flow of 3.5 Nl / h and with a temperature programming between room temperature and 900 ° C at a rate of 10 ° C / min.

For the mixtures prepared according to Examples 1 to 3, the ignition temperatures are collated in the table below:

Results by ATG:

The results obtained show without ambiguity that the ignition temperature of the soot is significantly lowered when the carbon particles are impregnated with an additive consisting of the mixture of an organic sol of cerium and a strontium salt.

Claims

1. Composition characterized in that it comprises an organic sol of particles of at least one oxide of at least one tetravalent metal and at least one organic compound of at least one alkaline earth metal.

2. Composition according to claim 1, characterized in that the tetravalent metal is cerium, praseodymium, terbium; in the particular case of rare earth mixtures, it is preferable that cerium is present.

3. Composition according to one of claims 1 or 2, characterized in that the tetravalent metal is cerium.

4. Composition according to any one of claims 1 to 3, characterized in that the alkaline earth is magnesium, calcium, strontium or barium.

5. Composition according to any one of claims 1 to 4, characterized in that it comprises an organic sol of cerium oxide particles and at least one organic strontium compound.

6. Composition according to any one of claims 1 to 5, characterized in that it comprises at least one organic compound of at least one alkali.

7. Composition according to any one of claims 1 to 6, characterized in that the alkali is chosen from sodium, potassium, and cesium.

8. Composition according to any one of the preceding claims, characterized in that the soil comprises:

° particles of at least one oxide of at least one tetravalent metal, ° an amphiphilic acid system, and ^α a diluent, and it is further characterized by the fact that said particles have a dgo at most equal to 20 nanometers and it has at least one of the following characteristics:

• said tetravalent metal oxide (s) particles (s) are in the form of agglomerates of crystallites, the dgo of which, measured by photometric counting (high resolution transmission electron microscopy), is at most equal to 5 nanometers, 90% by mass of the agglomerates comprising from 1 to 5, preferably 1 to 3 crystallites, • said amphiphilic acid system comprises at least one acid of 10 to 50 carbon atoms, having at least one branching in alpha, beta, gamma or delta of the atom carrying the acid hydrogen.

9. Composition according to claim 8, characterized in that the tetravalent metal oxide particles are cerium dioxide.

10. Composition according to any one of the preceding claims, characterized in that the diluent consists essentially of diesel and its additives.

11. Composition according to any one of the preceding claims, characterized in that the atomic proportion of metal (aux) tetravalent (s) / sum of the metal elements (aux) tetravalent (s), alkaline-earth, and optionally alkaline, is d '' at least 50%, more particularly at least 70%.

12. Process for preparing a composition according to one of claims 1 to 11, characterized in that at least one organic compound of at least one alkaline earth is mixed, and if necessary at least one compound organic of at least one alkaline, with organic soil.

13. Fuel for an internal combustion engine, characterized in that it is obtained by mixing with a conventional fuel a composition according to any one of claims 1 to 11.

14. Use of the compositions according to any one of claims 1 to 11 as an adjuvant for diesel fuel for a diesel engine.