FR2768155A1 - COMPOSITION BASED ON AN ORGANIC SOIL OF TETRAVALENT OXIDE, AND AN ORGANIC ALKALINE OR ALKALINE-EARTH COMPOUND, ITS USE AS ADDITIVE OF HYDROCARBON COMPOUNDS - Google Patents

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 ORGANIC SOIL OF TETRAVALENT OXIDE
AND AN ORGANIC ALKALINE OR ALKALINE EARTH COMPOUND.

ITS USE AS AN ADDITIVE FOR HYDROCARBON COMPOUNDS
RHONE POULENÇ CHEMISTRY
The present invention relates to a composition based on an organic compound of alkali or alkaline earth and a tetravalent oxide sol, and in particular cerium.

 The present invention also relates to a method of using these compositions.

 It is known that during the combustion of diesel fuel in the diesel engine, the carbonaceous products tend to form soot. which are considered harmful for the environment as well as for health. It has long been sought for techniques which make it possible to reduce the emission of these carbonaceous particles, which will be referred to hereinafter as '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 all, or a very high proportion (at least 80% by weight) of the carbonaceous particles generated by the combustion of various fuels.

 This technique is however limited by the storage capacity of the filter, whether it is necessary to empty or burn the soot contained. This so-called regeneration operation is extremely expensive to plan and implement. One of the most commonly proposed solutions is the combustion of these soot, combustion which is caused intermittently either by electric heating, or by the use of a fossil igniter fuel.

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

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

 Cerium has been found to be a good element in reducing the soot auto-ignition temperature. However, the need has been felt to have a product which, after introduction into a diesel and then after combustion, gives a good self-ignition of soot at an even lower temperature.

 For this purpose, the composition of the invention is characterized in that it comprises an organic soil of tetravalent metal oxide particles and an organic compound of an alkali and / or an alkaline earth metal.

 The process for the preparation of the aforementioned composition is characterized in that an organic compound of an alkali or an alkaline earth metal is mixed with the organic soil.

 Tetravalent metal is more particularly cerium. More particularly, alkaline earth is strontium or calcium and alkali is sodium or potassium.

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

The organic compound of alkali or earth alkaline is an organometallic complex of the type described in the patent application WO 96/34074, the teaching of which is incorporated herein. It can be very particularly the complex defined in this application WO 96/34074 by the formula M (R) m.nL wherein M is alkaline or alkaline earth, R is the residue of an organic compound of RH formula in which H represents an active hydrogen atom reactive with the metal
M and attached either to a hetero atom selected 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 electro-attractor group , for example a hetero atom or a group consisting of or containing O, S or N, or an aromatic ring, for example phenyl, n is a number indicating the number of electro-donor organic molecules (Lewis bases) forming dative linkages with the metal cation in the complex, usually up to 5 in number, more preferably an integer of 1 to 4 and L is one or more electro-donor ligands (Lewis bases). R may comprise one or more functional groups capable of acting as an electro-donor organic ligand. The entire teaching of WO 96/34074 concerning the complex of formula above is incorporated herein by reference.

According to a particular embodiment, the aforementioned ground comprises particles of tetravalent metal oxide, an amphiphilic acid system and a diluent and it is further characterized in that said particles have a dg0 at most equal to 200 nanometers and has at least one of the following characteristics:
said tetravalent metal oxide particles are in the form of agglomerates of
crystallites, advantageously cerium dioxide, crystallites including dgg,
advantageously the dgo, measured by photometric counting (microscopy
transmission electronics) is at most equal to 5 nanometers,
ninety percent (by mass) of agglomerates with 1 to 5,
preferably 1 to 3 crystallites,
said amphiphilic acid system comprises at least one acid of 10 to 50 carbon atoms
carbon having at least one branching at alpha, beta, gamma or delta
the atom carrying the acidic hydrogen.

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

 It should be clarified now that the best performing soils are those that meet one of the conditions and at least partially the other.

 According to the implementation corresponding to the first term of the alternative, it is possible to be less restrictive on amphiphilic acids provided they are more restrictive on the particle size conditions. In the present description, the particle size characteristics often refer to dn type notation where n is a number from 1 to 99, this notation is well known in many technical fields, but is somewhat rarer in chemistry, so can it is useful to recall the meaning. This notation represents the particle size such that n% (by weight, or more exactly by weight, since the weight is not a quantity of material but a force) of the particles is less than or equal to said size.

 These more restrictive conditions and how to respond to them are explained below.

 Advantageously, at least 50% (statistical value) of the agglomerates are monocrystalline, ie 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, it is possible, by modifying the technique and the hydrolysis conditions, to ensure that 80%, preferably 90% by mass, of the crystallites are smaller than a value chosen in advance in the range 2 to 5 nanometers, preferably 3 to 4 nanometers.

 Advantageously, the molar ratio between said amphiphilic acid and the metal elements of the soil is at most equal to 0.5; advantageously at 0.4; preferably at 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 n number of useful acid functions). More precisely, the number of acid equivalents represents the number of acid molecules when the acid used is monofunctional, and it is necessary to double or triple this number, in the case of diacids or triacids and, more generally, to multiply it by the number of acid functions in the case of a polyacid.

 It is desirable that, in the soil, the residual cerium II content with respect to cerium IV is as low as possible, in general less than 115%, advantageously at most equal to 1%, preferably to 1/2%.

 Advantageously, the sol has a concentration such that the content of cerium dioxide (with its attendant impurity) content is between 20 and 60%, preferably 30 to 50% by weight.

 The viscosity of the soil is determined by the flow time of the soil, this time is advantageously at most half a minute.

 Thus cerium, optionally with its impurities, is essentially in the form of agglomerates of metal oxide, optionally hydrated dioxide, which oxide agglomerate (s) is made liposoluble by means of an amphiphilic organic acid.

 The impurities of cerium that can accompany it in the soil are species derived from the co-hydrolysis of acidic metal cations usually accompanying cerium (such as other rare earths, actinides, etc.).

 By acidic metal cation is meant a metal cation, most often corresponding to the highest oxidation state of the metal element in question, and whose hydroxide precipitates at low pH values preferably at a pH below 4. The oxidation state is most often IV. As acidic cations, mention may be made of: cerium with the usual impurity procession in ores or recycled product. In these crude mixtures, to be usable, the impurities of the cerium represent at most 1/10, advantageously 1/20, preferably 1/50 of the precipitable cations.

 These limitations are process limitations but within the preferred zone any degree of purity can be chosen.

A process for preparing a colloidal dispersion of a cerium IV compound and optionally an acidic metal cation in an organic medium will now be described. This method comprises the following steps:
a) subjecting an aqueous ceric phase to a hydrolysis operation of
to precipitate a cerium dioxide (lato sensu)
(b) contact, simultaneously or consecutively, a suspension of
cerium dioxide from step (a) with an organic phase comprising a
organic acid and preferably an organic compound or mixture
role of solvent
c) then to recover the organic phase.

Which phase constitutes a soil.

 Advantageously, it is possible, between step a) and step b), to separate the solid particles from the mother liquors, optionally to dry them preferably by atomization, and then to plump the solid particles in the 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.

 The synthesis process of the compositions according to the invention will now be developed in more detail.

 According to an advantageous embodiment of the present invention, this drying is carried out by atomization, ie by spraying the soil mixture in a hot atmosphere (spray-drying). The atomization can be carried out using any sprayer known per se, for example by a spraying nozzle of the watering apple or other type. It is also possible to use so-called turbine atomizers. On the various spraying techniques that may be used in the present process, reference may be made in particular to the MASTERS basic work entitled 'SPRAY-DRYING' (second edition, 1976, Gerge Godwin-London editions).

It will be noted that the operation of drying atomizations can also be carried out by means of a flash reactor ", for example of the type developed by the
Applicant and described in particular in French Patent Applications Nos. 2,257,326, 2,419,754 and 2,431,321. In this case, the treating gases (hot gases) are driven by a helicoidal movement and flow into a well. The mixture to be dried is injected along a path coinciding with the axis of symmetry of the helicoidal trajectories of said gases, which makes it possible to perfectly transfer the amount of movement of the gases to the mixture to be treated, the gases thus ensuring a dual function: on the one hand the spraying, ie the transformation into fine droplets, of the initial mixture, and on the other hand the drying of the droplets obtained, Moreover, the extremely low residence time (generally less than 1/10 of about one second) particles in the reactor have the advantage, among other things, of limiting unlikely risks of overheating due to too long contact with the hot gases. atomization treatment significantly improves the ability of a thermohydrolysed soil at "low" temperature to form stable soils and even when the gas temperature is at least 200 C (2 significant figures), preferably between 200 and 300 "to obtain results similar to those obtained by thermohydrolysis at" high "temperature (1 50 C) and thus sols according to the present invention which are optimal.

 The temperature of the drying atmosphere can vary within wide limits, and depends in particular on the residence time required or that can be imposed on the atomized product once in said atmosphere. In general, the drying conditions (temperatures and / or residence time) are determined in a conventional manner so as to obtain at least a total or almost total elimination of the residual water contained in the product, that is to say, overall, until a constant weight is obtained for the latter.

 Examples of compounds which are soluble in cerium water are cerium IV salts such as cerium-ammonium nitrates or nitrates, which are particularly suitable here. Preferably, ceric nitrate is used. The solution of cerium IV salts may contain without difficulty cerium in the cerous state, but it is desirable that it contain 85% of cerium IV in castor oil. An aqueous solution of ceric nitrate may, for example, be obtained by reacting nitric acid with a hydrated ceric oxide prepared in a conventional manner by reacting a solution of a cerous salt, for example cerous carbonate, and of an ammonia solution in the presence of hydrogen peroxide. It is also preferable to use a solution of cracked nitrate obtained by the electrolytic oxidation process of a cerous nitrate solution as described in document FR-A-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 nature varying between 0.1 and 4 N. According to the present invention, it is as possible to implement an initial solution of cerium IV salts actually having a certain free acidity as mentioned above, a solution that has been previously neutralized more or less intensively by adding a base, such as for example an ammonia solution or d alkali hydroxides (sodium, potassium, etc.), 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 solution of cerium by the following equation
in which n1 represents the total number of moles of Ce IV present in the solution after neutralization; n2 represents the number of moles of OH ions actually necessary to neutralize the initial free acid provided by the aqueous solution of cerium IV salt; and n3 represents the total number of moles of OH ions added by the addition of the base. When the "neutralization" variant is used, in all cases a base quantity is used which must imperatively be less than the amount of base that would be necessary to obtain the total precipitation of the Ce (OH) 4 hydroxide species ( r = 4). In practice, it is thus limited to neutralization rates of not more than 1 and preferably not exceeding 0.5.

 The initial mixture is thus obtained, then, in accordance with the second step of the process according to the invention (step (a)), it is heated.

 The temperature at which the heat treatment (a), also called thermohydrolysis, is carried out may 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 conducted, depending on the temperature conditions selected, either under normal atmospheric pressure, or under pressure such as for example the saturated vapor pressure substantially corresponding to the temperature of the heat treatment.

When, as is preferred, the treatment temperature is chosen to be greater than the reflux temperature (under ordinary pressure) of the reaction mixture (that is to say generally greater than 10,000), for example chosen between 120, more often between 150 and 3500C, the operation is then conducted in a closed chamber. The aqueous mixture containing the aforementioned species is introduced into this chamber (closed reactor more commonly called autoclave), the necessary pressure then result only from the heating of the reaction medium (autogenous pressure). Under the conditions of the temperatures given above, and in aqueous media, it is thus possible to specify, by way of illustration, that the pressure in the closed reactor varies between a value greater than 1 Bar (105 Pa) and 200 Bar (2 107 Pa), preferably between 5 bar (5.
Pa) and 150 Bar (1.5107 Pa). It is of course also possible to exert an external pressure which is then added to that following the heating.

 The heating may be conducted either in an atmosphere of air or in 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. Similarly, the rise in temperature is carried out at a speed which is not critical, and it is thus possible to reach the reaction temperature set by heating the medium for example between 30 minutes and 4 hours, these values being given for all purposes. indicative fact.

At the end of step (a) of heating, 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.
Note that it is of course possible to repeat one or more times, identically or not, a heatingagelprecipitation step as defined above, then implementing for example cycles of heat treatments.

By way of indication, it is possible to use, as starting solution for thermolysis, solutions of cerium IV, generally nitrate, having the following characteristics:

<tb><SEP> Features <SEP> Possible <SEP> Preferred <SEP> Area <SEP> Preferred
<tb> Content <SEP> in <SEP> cerium <SEP> of <SEP> lg / l <SEP> to <SEP><SEP> limit <SEP> of <SEP> | <SEP> between <SEP> 40 <SEP> and <SEP> 120go1 <SEP> between <SEP> 60 <SEP> and <SEP> 1009 / l <SEP>
<tb><SEP> solubility
<tb> Acidity <SEP> r <SEP> at <SEP> plus <SEP> equals <SEP> at <SEP> 1 <SEP> r <SEP> included <SEP> between <SEP> 0.5 <SEP> and
<tb><SEP> -0.5
<tb> Against <SEP> ion <SEP> of <SEP> cerium <SEP> | <SEP> all <SEP> anion <SEP> weakly <SEP> anion <SEP> oxygenate <SEP> and <SEP> j <SEP> nitrate
<tb><SEP> complexing agent <SEP> no <SEP> complexing agent
<Tb>
The characteristic of step (b) of the process of the invention is to obtain an organic sol, an expression which refers to the dispersion of the cerium dioxide, possibly impure (hereinafter the cerium dioxide will sometimes be designated by the compound of the cation
Mn +), in organic medium, by transfer of said cerium dioxide in the organic phase, from an aqueous phase consisting of the ceric compound which is in colloidal form in an aqueous sol.

 The term "aqueous sol" refers to the colloidal dispersion of the compound of the cation M + + in an aqueous medium which constitutes the basic raw material of the process of the invention.

In order to satisfactorily carry out the process of the invention, it is desirable for the aqueous starting sol to satisfy the following requirements:
the metal content in the form of oxide (lato sensu) colloidal must be very
high, preferably 90%, preferably greater than or equal to 95% and
general rule as high as possible
the concentration of the aqueous sol in oxide (lato sensu) colloidal must be
sufficient and preferably between 0.1 and 3 moles / liter,
the aqueous sol must have good properties of thermal stability and
not flocculate at the reaction temperature which is greater than 60 ° C and varies
more often between 80 and boiling (variable depending on pressure).

The organic liquid medium used in the process of the invention may be an inert aliphatic or cycloaliphatic hydrocarbon where their mixture such as for example mineral spirits or petroleum, mineral ethers or petroleum may also contain aromatic components. Examples include hexane,
Heptane, octane, nonane, decane, cyclohexane, cyclopentane, cycloheptane and liquid naphthenes. Aromatic solvents such as benzene, toluene, ethylbenzene and xylenes are also suitable, as are petroleum cuts of the Solvesso type (trademark registered by the company EXXON), particularly the
Solvesso 100 which contains essentially a mixture of methylethyl and trimethylbenzene and Solvesso 150 which contains a mixture of alkylbenzenes in particular dimethylethylbenzene and tetramethylbenzene.

Chlorinated hydrocarbons such as chloro or dichlorobenzene and chlorotoluene can also be used as well as aliphatic and cycloaliphatic ethers such as diisopropyl ether, dibutyl ether and aliphatic and cycloaliphatic ketones such as methyl isobutyl ketone, isobutyl ketone,
Mesityl oxide.

 The esters can be envisaged, but they have the disadvantage of risking being hydrolysed. Esters which may be used are those derived from the acids mentioned in the present application with C 8 -C 8 alcohols and in particular the secondary alcohol palmitates such as isopropanol.

 The organic liquid or solvent system will be chosen by zonation of the solubilizing organic 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 amount of liquid or solvent obviously determines the final concentration. It is more economical and more convenient to prepare more concentrated dispersions which can be diluted later. during their employment.

 It is for this reason that the amount of solvent is not critical.

 It may be advantageous to add to the organic phase a promoter agent whose function is to accelerate the transfer of the colloids from the aqueous phase to the organic phase and to improve the stability of the organic soils retained. As promoters, it is possible to use the alcohol-functional compounds and more particularly linear or branched aliphatic alcohols having from 6 to 12 carbon atoms.

 Specific examples include 2-ethyl hexanol, decanol, dodecanol or a mixture of them.

 The proportion of said agent in the organic phase is not critical and may 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, however, is a little more constraining.

 The total number (average if the acid used is a> carbon mixture of the acids is preferably greater than 6, preferably 10, is also desirable to be less than about 60.

 If high concentrations of cerium, or the like are desired, it is desirable to select as short a acids as possible.

 These acids can be linear or branched. It is preferable, however, that the branches are either far from the carboxylic function or are few in number and carried by different carbons. The carboxylic acids that may be used for the present invention may be aryl, aliphatic or arylaliphatic acids.

They may carry other functions provided that these functions are stable in the environments where it is desired to use the cerium compounds according to the present invention.

 So that the soil remains usable at low temperature, below ambient, or even below zero degrees centigrade, it is preferable that the melting point of the acid, or of the acid mixture, is at most 50 Advantageously at room temperature, preferably at zero degree centigrade.

 Thus, it is easy to use carboxylic acids whose carbon chain carries ketonic functions such as the pyruvic acids substituted in alpha for the ketone function. It can also be alpha-halo carboxylic acids or alpha hydroxycarboxylic acids.

 The chain attached to the carboxylic group may carry unsaturations.

 However, in general, it tends to avoid too many double bonds because cerium catalyzes the crosslinking of double bonds. The chain can be interrupted by ether or ester functions provided that the lipophilicity of the carrier chain of the carboxylic group is not greatly impaired.

 Thus, aliphatic carboxylic acids, aliphatic sulfonic acids, aliphatic phosphonic acids, alkylarylsulfonic acids and alkylarylphosphonic acids having from about 10 to about 40 carbon atoms, whether natural or synthetic, can be used. They can be used alone or mixed together.

 As paradigmatic examples, mention may be made of tall oil fatty acids, coconut oil, soy, tallow, linseed oil, oleic acid, linoleic acid, stearic acid and its derivatives. isomers, acid, pelargonic acid, capric acid, lauric acid, myristic acid, dodecylbenzenesulfonic acid, 2-ethylhexanoic acid, naphthenic acid, hexoic acid, toluenesulphonic acid, toluenephosphonic acid, laurylsulfonic acid, laurylphosphonic acid, palmitylsulfonic acid and palmitylphosphonic acid. Preferably, oleic acid or alkylaryl sulfonic acids are used.

 The quantity of amphiphilic organic acid used, expressed as the number of moles of acid per mole of oxide (lato sensu), can vary within wide limits between 1/10 and 1 mole per mole of cerium dioxide. The upper limit is not critical, but it is not necessary to use more acid. Preferably, the organic acid is used in a proportion of 1/5 to 4/5 mol 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 of the organic solvent to the organic acid is preferably from 0.3 to 2.0.

 The order of introduction of the different reagents is indifferent. Simultaneous mixing of the colloidal aqueous dispersion (s), the organic acid, the organic solvent and optionally the promoter can be carried out simultaneously. It is also possible to premix the organic acid, the organic solvent and optionally the promoter which constitutes the organic phase.

 The temperature of the reaction medium is preferably chosen in a range from 60 ° C 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, the reaction is carried out at a temperature of between 60 and 1200 ° C., preferably between 90 and 110 ° C.

 The reaction mixture is stirred for the duration of the heating which may be less than an hour to a day, preferably between 2 hours and half a day.

 At the end of the aforementioned 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 standard separation techniques: decantation, centrifugation, etc.

 According to the present invention, organic colloidal dispersions of metal oxide (s) are obtained whose colloid size can be very variable and can be controlled by adjusting certain parameters, in particular the diameter of the initial colloidal aqueous dispersions which depends on the respect of the conditions of thermohydrolysis.

For some applications it is possible to use the reaction mixture as it is but sometimes it is desirable to remove water which may represent 1 to 3% by weight of the organic phase. For this purpose, the means well known to those skilled in the art are used, for example a passage on a drying agent (including a hydrophobic membrane filter) or the addition of a third solvent which is inert with respect to the composed of Mn +, having a boiling point, preferably less than 100 ° C., and forming an azeotrope with water and then distilling off the azeotrope obtained. As third solvents suitable for the invention, mention may be made of aliphatic hydrocarbons, such as hexane,
Heptane, cycloaliphatic hydrocarbons: aromatic, or alcohols such as, for example, ethanol, ethylene glycol, diethylene glycol etc.

 It is preferable, particularly for applications as a diesel fuel adjuvant, that the water content is at most equal to 149, advantageously 1 per thousand, preferably 100 ppm.

 We will now examine the second term of the alternative, ie strong stress for the amphiphilic acids, but weaker for the bulk of the particles.

 It should be remembered that the best soil performances are obtained when a system of constraints is completed at least partially by various constraints of the other system. Some of the constraints are common, so the descriptions detailed in the first part are only briefly covered in this second part. soils that meet both types of constraints are the best.

 The preferred range is from 15 to 25 carbon atoms for the acids of said amphiphilic system.

 When the system is a mixture of acids the carbon number can be fractional since it is then an average and the constraints on the average are advantageously the same as those above for one of, or the component (s) of said amphiphilic system. The minimum stress is that the average of the carbon atoms of the acids of said amphiphilic system is at least equal to 10 carbon atoms. More specifically, the average of the carbon atoms of the acids of said amphiphilic system is advantageously from 11 to 25, preferably from 15 to 25.

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

To clarify the nomenclatures of the positions, the examples of 2-ethylhexyl acid phosphate and 2-ethyl-2-octanoic acid are given below.

<tb><SEP> position <SEP> alpha <SEP><SEP> beta <SEP> gamma <SEP> \ <SEP> delta
<tb> (function SEP> H) SEP>SEP>SEP>SEP>SEP>SEP> - <SEP> (atom) <SEP> - <SEP> (atom) <SEP>
<tb><SEP> HO <SEP> -P (C8H <SEP> 7) <SEP> -0 <SEP>: <SEP> -CH2 <SEP> -CH (C2H5) <SEP> -CH2 (C3H7)
<tb><SEP> HO <SEP><SEP><SEP> -CO <SEP> | <SEP> -CH (C2H5) <SEP> CH2 <SEP> | <SEP> CH2 <SEP> | <SEP> CH2 (C3H7)
<Tb>
It is preferred that the longest linear portion be at least 6, preferably 8 carbons.

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

 It is also advantageous if the side chain (s) of the branched acids comprise at least two atoms, preferably three carbon atoms.

 It is preferable, especially when the acids are carboxylic acids, that the amphiphilic acid system is a mixture of acids.

 In this case the conditions on the branching must operate on at least half, advantageously two thirds, preferably four fifths by mole of the constituent acids of said system of amphiphilic acid (s).

 Among the acids giving very good results, mention may be made of phosphorus-containing acids, such as phosphoric acids, in particular diesters of phosphoric acid, phosphonic acids, and their mono esters, and phosphinic acids.

 Among the carboxylic acids giving good results, it is appropriate to mention the constituent acids of the mixture of acids known as isostearic acid. The acid system is advantageously isostearic acid itself.

 The starting melting point of the amphiphilic acid (s) system is advantageously less than 50 ° C, more preferably less than or equal to 20 ° C, preferably not more than 0 ° C.

 For a good stability and for a good extraction it is desirable that the molar ratio between the extractant and the tetravalent metal, preferably cerium, is between 0.1 and 0.6, preferably between 0.2 and 0, 4. This report believes when particle size decreases.

To obtain particularly stable soils, as it has been shown that the presence of coarse particles is detrimental to the long-term stability of soils according to the present invention, or even soils made from more conventional acids, it is preferable that at most 5%, advantageously at most 1%, preferably at most 0.5% by weight of the tetravalent metal oxide particles, at most equal to 0.1 micrometer, advantageously at 0.05 micrometer, preferably at most 0.02 micrometer
Any diluent leading to stable soil is within the scope of this invention.

 The floors according to the present invention can be used in many ways. Depending on the desired implementation, a compromise should be chosen taking into account the technical data below; for synthesis and stability it is desirable to avoid highly apolar hydrocarbons, such as non-cyclic aliphatic hydrocarbons. diluents, such as esters or ethers, having a polar function give good results, but for some uses may be to avoid as far as possible. the mixture of diluents can provide a solution by offsetting the non-polarity of certain diluents by the addition of polar compounds, generally solvents.

 According to a particularly advantageous embodiment of the present invention, the soil is used to form a soil diluted in a diesel fuel. the initial soil is generally very concentrated, which limits the latitude of the skilled person. Moreover, for reasons of compatibility with diesel fuel and its numerous additives, the diluents are then preferably not very polar. As constituent elements 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 preferred that the diluents have a Kauri Butanol number (measured according to ASTM D 1133) less than 105, preferably less than 90.

 For use as an on-board additive it is preferred that the melting point of the diluents, or mixtures of diluents, be low and meet the melting point constraints described in this Title about the amphiphilic acid system.

 It is also preferable that these diluents have a very low solubility in water, preferably less than 5% by weight, preferably at most 1%, more preferably at most 0.5% by weight.

 In a symmetrical manner, it is also preferable that the water is soluble to not more than 5%, preferably not more than 1%, more preferably not more than 0.5% in the diluent.

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

 The tetravalent metal oxides may contain relatively small proportions of metals having other valences. In general, the proportion of addition elements. or impurities, contained in the tetravalent metal particles, does not exceed 10% by weight, more generally 5% by weight.

 The tetravalent metal content of the soil according to the invention is advantageously at most 2/3 by weight, preferably between 30 and 40% (by weight). For use in additive for onboard diesel, it is preferable that the content does not go below 1/6, preferably 1/5.

 Organic sols, according to the present invention, are generally prepared in known manner by heating an aqueous sol containing said tetravalent metal oxide, in the presence of said diluent and said amphiphilic acid system.

 According to a particularly advantageous feature of the invention it should be ensured that there is no too coarse particle in the aqueous soil and thus in the final soil.

 The removal of the coarsest size particles can be done by any technique to selectively remove the coarser particles. This elimination can be done on the aqueous soil, on the organic soil or on both.

 However, it is preferred that there be at least one separation on the aqueous sol. The preferred technique is centrifugation.

 A centrifugation of the aqueous sol corresponding to 1000 to 10,000 G for one hour generally gives good results. However, it can go up to centrifugations corresponding to 50 000 G, the limit is only a technological limit.

 It should be noted that the centrifugation prior to the constitution step of the organic soil, often called extraction step, favors the latter.

 The aqueous sols are advantageously produced by hydrolysis, preferably by thermohydrolysis. Among the techniques usable 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 applicant. European patent application published under number 206907 can also be mentioned.

Said soils obtained according to the invention have a concentration of cerium IV compound which can be very high since it can be up to 3.5 M to 4 M of
CeO 2.

 It is found that the extraction yield of cerium in the organic phase is very good since it can reach 90 to 95%.

 By quasi-elastic light scattering, the presence of colloids having a variable hydrodynamic diameter with the conditions of preparation and less than 100 Å (that is to say the detection of the current apparatus) is demonstrated.

 The organic so produced soils have excellent stability. Decantation is not observed after several months.

 According to one of the preferred features of the present invention, the sol is such that, adjusted to a 30% concentration of cerium metal, the viscosity of the sol at 25 ° C. is at most 20 mPa · S, advantageously at 15 mPa. .S, preferably at 10 mPa.S.

 It is also preferable that the anions of the cerium source solution of the soil, are no longer present in the various soils of the present invention at a content at most equal to 0.1; preferably at 0.05, preferably at 0.03 equivalents per 100 grams of cerium dioxide. this constraint is especially valid for the superficial couohe of cryStallites, layer of pentaatomic thickness. this viscosity can be measured by Contraves brand "low shear" by varying the speed gradient from 0.01 to 1.

 The organic soils thus obtained can be diluted to obtain concentrations of 10 to 500, preferably 50 to 200 ppm. The diluent is advantageously a fuel for internal combustion engine preferably diesel; The invention therefore also targets soils whose organic phase is essentially composed of diesel and its additives.

 The invention also relates to the use of organic sols prepared according to the invention as siccatives in the paint and varnish industry in order to accelerate the drying of unsaturated oils and as combustion aids in fuels or liquid fuels of energy generators. such as internal combustion engines, oil burners or jet engines. The sols according to the invention can also be used in cosmetics.

EXAMPLES
Reagents:
Unless otherwise stated, the reagents used in the examples are:
- a preeneutralized ceric nitrate at r = + 0.5 (see European patent in the name of
applicant published under No 153227)
an extractant of oleic acid, which can be replaced without modification
with 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 gas oil.

General procedure:
The procedure of the examples is as follows:
the first step consists in the synthesis of the precursor which is an aqueous sol
of CeO2 colloids whose size (TEM) is between 3 and 5 nm.

 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 in CeO 2.

 Autoclaving is carried out at 1600 ° C. for 4 hours, with a rise in temperature in 1 hour. Stirring is maintained throughout the operation.

 After autoclaving, the product is decanted and then separated (filtered and drained) from the mother liquors. It is then redispersed in water, which makes it possible to obtain a stable aqueous sol. The concentration of this soil is 150 g / l.

Example
Reagents
a preneutralized ceric citrate at r = + 0.5 and at a concentration of 80 g / l in cerium
an extracting agent for oleic acid,
First step back:
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 in CeO 2.

 The au: oclavage is performed at 160 C for 4 hours, with a rise in temperature in 1 hour.

 The agftation is maintained throughout the operation.

 The solution obtained is filtered on sintered n.

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

 In a flask, a metered quantity of aqueous CeO 2 sol is added, to which is added the organic mixture which is such that the molar ratio of oleic acid / enum is 0.3 and the SOLVESSO 150 / oleic acid ratio is 3.75.

In the example considered, this leads to use
- 24.8 g of CeO2 (ie 0.1651 sol at 150 g / l),
- 12.2 g of oleic acid,
- 45.7 9 of SOLVESSO 150.

 The mixture is then heated at 100 ° C under reflux for about 10 hours.

After cooling, the organic phase is separated from the aqueous phase and then filtered on a hydrophobic filter.

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

 This gives a soil stability measured greater than 4 months (sample duration), the concentration of CeO2 is 29.1% (mass), and the colloid size (measured by MET) is between 3 and 5nm .

EXAMPLE 2 Mixture of an organic cerium sol and a strontium salt according to the invention
A strontium salt of the polyisobutylene succinic anhydride of molecular weight 420 Sr-PlBSA 420 is repaired, as described in Examples 13 and 14 of the OCTEL patent WO 96/34074.

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

EXAMPLE 3
Mixture of an organic soil of cenum and a salt of strontium according to the invention
The procedure is as in Example 2 using the organic cerium sol and the Sr-PI BSA 420 salt in the following proportions: 75 mol% of cerium and 25 mol% of Sr.

Performance. measurement of the soot ignition temperature
We proceed as follows
A carbon black known to be reproductively produced (reference ELFTEX 125 n ° 137 from CABOT) was selected for these properties in terms of particle size and specific surface area. 60 nm and 30 m2 / g are of the same order of magnitude as the carbon particles emitted at the outlet of a diesel engine exhaust.This carbon black is impregnated with the additive so as to obtain a final content of 15% by weight. weight (metal equivalent.
Sr). This content is representative of what can be obtained in the particles emitted at the exhaust of a diesel engine when an additive is used in diesel fuel. The impregnation is carried out in the same manner as the catalysts supported by the so-called dry impregnation technique. Carbon black and the desired amount of additive are intimately mixed in a glass vessel until a homogeneous paste is obtained. Then, the whole is dried overnight at 95 ° C. The monitoring in Thermo Gravimetric Analysis (ATG) of the combustion in the 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 as all the more active as the corresponding temperature of the beginning of combustion of the carbon during the ATG will be low.A test carried out with the non-impregnated carbon black of additive The ATG is carried out with a charge of 20 to 25 mg of carbon black, in an air flow rate of 3.5 Nl / h and with a temperature programming between room temperature and 900 "C at a rate of of 100C / min.

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

<tb><SEP> Additives <SEP> T <SEP> inliammation <SEP>(0C><SEP>
<tb><SEP> without <SEP> 580
<tb><SEP> This <SEP> (exem <SEP><SEP> 1) <SEP> 305
<tb> This <SEP> -Sr <SEP> (example <SEP> 2) <SEP><SEP> 230 <SEP>
<tb><SEP> Ce-Sr <SEP> (example <SEP> 3) <SEP> 210
<Tb>
The results obtained show unambiguously that the soot ignition temperature is lowered significantly when the carbon particles are impregnated with an additive consisting of the mixture of an organic cerium sol and a strontium salt.

Claims (9)

 an organic compound of an alkaline and / or alkaline earth metal.  an organic soil of tetravalent metal oxide particles,  CLAIMS 1. Composition characterized in that it comprises 2. Composition according to claim 1, characterized in that the tetravalent metal is cerium. 3. Composition according to claim 1 or 2, characterized in that the alkaline earth is strontium or calcium and alkali sodium or potassium. 4. Composition according to one of the preceding claims, characterized in that the soil comprises:  tetravalent metal oxide particles,  an amphiphilic acid system,  - a diluent. and in that said particles have a dg0 at most equal to 200 nanometers and the sol has at least one of the following characteristics: said particles of tetravalent metal oxide are in the form of agglomerates of  crystallites, advantageously cerium dioxide, crystallites including dgg,  advantageously the dgo, measured by photometric counting (microscopy  electronic high-resolution transmission) is at most equal to 5 nanometers,  ninety percent (by mass) of agglomerates with 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 alpha, beta, gamma or delta of the acid hydrogen bearing atom. 5. Composition according to one of the preceding claims, characterized in that the diluent consists essentially of diesel and its additives. 6. Composition according to one of the preceding claims, characterized in that the tetravalent / alkaline and / or alkaline earth metal and tetravalent metal atomic proportion is at least 50%, more particularly at least 70%. 7. Fuel for an internal combustion engine, characterized in that it is obtained by mixing a conventional fuel with a composition according to one of the preceding claims. 8. Use of the compositions according to claims 1 to 6 as diesel propellant adjuvant. 9. Process for the preparation of a composition according to one of claims 1 to 6, characterized in that an organic compound of an alkali or an alkaline earth is mixed with the organic soil.