AU698799B2 - Organic tetravalent oxide sol and its use as additive for hydrocarbon compounds - Google Patents

Abstract

A new sol compsn. which comprises:- oxide particles of a tetravalent metal; an amphiphilic acid system, and a diluent in which the particles have a d90 no more than 200 nm, and the sol has at least one of the following characteristics:- the oxide particles are in the form of crystallite agglomerates (CeO2) which the crystallites have a d80 (pref. d90), measured by photometric counting (HR transmission electronic microscopy) of no more than 5nm, 90% of the agglomerates comprising 1-5 (pref. 1-3) crystallites. The amphiphilic system comprises at least one 11-50C acid and has at least one branching in the alpha-beta or gamma position to the acidic H. The use of the prods. as additives to gas oil fuels is also claimed.

Description

-1I- AUSTRAL IA PATENTS ACT 1990 QCOMP LERTER 2 PE R Q T T 0 AT T FOR A STANDARD r N -'NT ORIGINAL 9~*4 9 9 99 9* fr 9 96 99 9 .9 9 9 99"* 4 9999 99 49 9 99 9 94 4 69" 9.

9 99*9 9 999,9' 9 Name of Applicant: Actual Inventors: Address for Service: RHONE- POULENC CHIMIE Thierry CHOPIN, Pierre MACAUDIERE and Olivier TOURET SHELSTON WATERS 60 Margaret Street SYDNEY NSW 2000 Invention Title: "ORGANIC TETRAVALENT OXIDE SOL AND ITS USE AS ADDITIVE FOR HYDROCARBON COMPOUNDS" The following statement is a full description of this invention, including the best method of performing it known to us:-

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I 0 la ORGANIC TETRAVALENT OXIDE SOL AND ITS USE AS ADDITIVE FOR HYDROCARBON COMPOUNDS The subject of the present invention is a new tetravalent oxide sol and especially a new cerium sol.

It more particularly relates to organic sols of high stability and of controlled particle size.

Another subject of the present invention is a process for the use of these sols.

During studies carried out during the last four lustra, colloidal suspensions in organic medium of micrometric or submicronic particles have been "developed, the properties of these colloidal suspensions being similar to those of solutions. These colloidal suspensions are generally denoted by the term 15 "sols" by specialists in the field.

These sols had the property either of being stable with time and of coarse particle size (in general, dynamic diameter of the order of a micrometre and high viscosity) or of fine particle size but of low 20 stability: half life duration at most equal to one or two months, and of relatively low concentration.

However, to date, to the knowledge of the Applicant company, no one has managed to obtain these properties simultaneously.

Now, for certain uses, these properties are essential. More particularly for the reasons explained hereinbelow, the use as additive for fuels for internal combustion engines requires both the possibility of i a 3 ,i 1 .i il rT 1 2 existing in a high concentration and the necessity of having a low particle size and a very high stability.

The use as additive for diesel engines constitutes a good example of the constraints to which such a sol has to submit.

During the combustion of diesel oil in diesel engines,, the carbon-containing products have a tendency to form soots which are supposed to be harmful both to the environment and to the health. Techniques have been sought for a long time which make it possible to reduce the emission of these carbon-containing particles, r 'which will be denoted in the continuation of the description under the expression "soots".

This research is concomitant with the necessity of not 15 increasing the emission of carbon monoxide and of gases which are supposed to be toxic and mutagenic, such as nitrogen oxides.

A great many solutions have been proposed for reducing these carbon-containing emissions.

20 However, attention is increasingly being directed e towards fitting the exhaust circuits with a filter capable of stopping all, or a very high proportion (at least 80% by mass) of the carbon-containing particles generated by the combustion of the various fuels.

This technique is, however, limited by the storage capacity of the filter; it is necessary either to empty the filter or to burn off the soots contained therein.

This operation, known as regeneration, is extremely i:

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6 b i :r k *4 *r I expensive to provide and to implement. One of the most commonly proposed solutions is the combustion of these soots, which combustion is caused intermittently either by electrical heating or by the use of a fossil igniter fuel.

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

.0 A solution which would be satisfactory consists in introducing into the soots catalysts which make possible frequent self-ignition of the soots collected in the filter. To do this, it is necessary for these soots to have a self-ignition temperature which is 15 sufficiently low to be frequently reached during normal operation of the engine.

During the programme of research which has led to the present invention, it was proved that cerium could constitute a good element for reducing the self- 20 ignition temperature of the soots.

However, in order to be conveniently used and in order to correspond to provisions of a regulatory nature, it is provided that the additives must be introduced as required from a tank which must be able to be replaced only every 50,000 kilometres.

Under these conditions, the additives must be both very concentrated and sufficiently stable not to be detrimentally affected by the agitation conditions Ii 1' ~i ij o -4related to the operation of the vehicle and by the interval of several years between two replacements, This is why one of the aims of the present invention is to provide tetravalent oxide sols, and especially sols of tetravalent rare earths, which are both very concentrated and very stable.

This stability must apply not only when the sol is concentrated but also when the sol is diluted.

Another aim of the present invention is to provide a reactant which, after introduction into a diesel oil and then after combustion, gives good self-ignition of the soots.

According to a first aspect of the invention, there is provided organic sol containing: particles of tetravalent metal oxide, an amphiphilic acid system, a diluent, 15 wherein the particles of tetravalent metal oxide are in the form of agglomerates of Sa. !crystallites, in which crystallites the dso, measured by photometric counting (high resolution transmission electron microscopy) is not greater than 5 nanometres, 90% by Smass of the agglomerates containing from 1 to 5 crystallites.

According to a second aspect of the invention, there is provided a process for the preparation of an organic colloidal dispersion of a compound of cerium (IV) according to aV 44 the first aspect wherein it contains the following stages: a) subjecting an aqueous solution of cerium (IV) salts to thermohydrolysis so as to g precipitate a cerium dioxide; RA4 .T 1 786t.OO.DOC -4 1 a a

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a 9 a.l a ,:i -4ab) bringing a suspension of cerium dioxide resulting from stage into contact, simultaneously or consecutively, with an organic phase comprising an organic acid; and recovering the organic phase.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

The present invention relates to a sol containing: particles of tetravalent metal oxide, an amphiphilic acid system, a diluent, characterised in that the said particles have a d90 which is not greater than 200 nanometres and in that the sol has at least one of the following characteristics: the said particles of tetravalent metal oxide are in the form of agglomerates of 15 crystallites, advantageously of cerium dioxide, in which crystallites the dgo, advantageously the d9o, measured by photometric counting (high resolution transmission electron microscopy) is not greater than 5 nanometres, ninety per cent (by mass) of SDiJ r:2 1 t ,rr r; 4 L a

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1- the agglomerates containing from 1 to 5 and preferably from 1 to 3 crystallites, the said amphiphilic acid system contains at least one acid containing 11 to 50 carbon atoms having at least one branching a, 0, y or 6 to the atom carrying the acidic hydrogen.

It should here and now be made clear that the most outstanding sols are those which correspond to one of the conditions and at least partially to the other condition.

According to the implementation corresponding to the Sfirst alternative, it is possible to be less S restrictive as regards the amphiphilic acids on condition of being more restrictive as regards the particle size conditions. In the present description, the particle size characteristics often refer to notations of the dn type where n is a number from 1 to 4 ft 99. This notation is well known in many technical fields but, as it is somewhat rarer in chemistry, it 20 may therefore be useful to recall the meaning thereof.

JJ "This notation represents the particle size Such that n% (by weight, or more exactly by mass, since the weight is not an amount of matter but a force) of the particles is less than or equal to the said size.

These more restrictive conditions and the way of responding thereto are explained hereinbelow.

Advantageously 50% (statistical value) at least by mass of the agglomerates are monocrystalline, that is to say i j 1

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l _1 1 1 4L 4 D4 .4! 4,• 4 44e 44 44 44 4 6 that they consist only of a single crystallite (or at least appear to consist only of a single crystallite when the sol is examined by HRTEM (High Resolution Transmission Electron Microscopy)).

In addition, it is possible, by varying the technique and the hydrolysis conditions, to see to it that preferably 90%, by mass of the crystallites are of a size less than a value chosen in advance within the range 2 to 5 nanometres and preferably 3 to 4 nanometres.

The molar ratio of the said amphiphilic acid to the metal elements of the sol is advantageously not greater than 0.5, advantageously not greater than 0.4 and preferably not greater than 0.3. In this instance, the 15 molar ratio must be taken in the acceptation of a functional molar ratio (that is to say that mole of amphiphilic acid means the number of moles multiplied by the number n of useful acidic functional groups).

More precisely, the number of acid equivalents represents the number of molecules of acid 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 acidic functional groups in the case of a polyacid.

It is desirable, in the sol, for the residual cerium(III) content with respect to cerium(IV) to be as low as possible, generally less than 15% and ii k) Ii ~1 41 VW

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4 4 .4 44 4i4444 4 4 4 4 4 44*4i 44 .4 4 44 4 4.i 4) advantageously not greater than 1% and preferably not greater than 1/2%.

The sol advantageously has a concentration such that the cerium dioxide content (with its retinue of impurities) contained is between 20 and 60% and preferably 30 to 50% by mass.

The viscosity of the sol is determined by the flow time of the sol; this time is advantageously not more than one half-minute.

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

15 The impurities in the cerium which can accompany it into the sol are species arising from the cohydrolysis of metal cations with an acidic nature which usually accompany cerium (such as other rare-earth metals, actinides, and the like).

Metal cation with an acidic nature denotes a metal cation, most often corresponding to the highest oxidation state of the metal element in question, the hydroxide of which precipitates at low pH values, preferably at a pH of less than 4. The oxidation state is most often IV. Mention may be made, as acidic cations, of: cerium with the retinue of impurities usual in minerals or recycled products. In these crude mixtures, for them to be usable, the impurities in the i.il.

I F7"" :^I i IB and 2.0. I w r A 8 cerium represent no more than 1/10, advantageously 1/20 z.nd preferably 1/50 of the precipitable cations.

J i These limitations are limitations of the process but, within the preferred region, any degree of purity can be chosen.

Another aim of the present invention is to provide a process which makes it possible to manufacture colloidal dispersions of a cerium(IV) compound.

A process fcr the preparation of a colloidal dispersion of a compound of cerium(IV) and optionally of a metal i cation with an acidic nature in organic medium has now been found and it is this which constitutes one of the aims of the present invention, this process containing 15 the following stages: a) in subjecting an aqueous cerium-containing phase to a hydrolysis operation so as to to 4 precipitate a cerium dioxide (in the broad sense); b) in bringing a suspension of cerium dioxide resulting from Stage into contact, simultaneously or consecutively, with an organic phase comprising an organic acid and preferably an organic mixture or compound acting as solvent; c) and in then recovering the organic phase, which phase constitutes a sol.

It is advantageously possible, between Stage a) and Stage to separate the solid particles from the mother liquors, to optionally dry, preferably r 1

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9 by atomization, and then to repulp the solid particles in an aqueous phase, which will then be subjected to Stage Repulping is carried out so that the cerium dioxide content in the aqueous phase is between 100 and 400 g/l.

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

According to an advantageous implementation of the present invention, this drying is carried out by atomization, that is to say by spraying the mixture of I sols into a hot atmosphere (spray drying). Atomization can be carried out by means of any sprayer known per se, for example with a spray nozzle of the shower head *tI "t 15 or other type. It is also possible to use so-called rotary atomizers. For the various spraying techniques capable of being used in the present process, reference may be made especially to the standard work by Masters entitled "Spray Drying" (second edition, 1976, i 20 published by George Godwin London).

ll-,*lp It will be noted that it is also possible to implement the atomization/drying operation by means of a "flash" Sreactor, for example of the type developed by the 'Applicant company and described especially in French Patent Applications No. 2,257,326, 2,419,754 and 2,431,321. In this case, the treating gases (hot gases) are driven with a helical movement and flow in a vortex sink. The mixture to be dried is injected along a Lcf~ IUL~-. 1I X~I*IIIIII(L W L To: The Commissioner of Patents WODEN ACT 2606 File: 17861 1 Fee: $496,00 f trajectory which joins with the axis of symmetry of the helical trajectories of the said games, which makes it possible to completely transfer the amount of movement of the gases to the mixture to be treated. The gases thus in fact provide a double function: on the one hand, the spraying, that is to say the conversion of the initial mixture to fine droplets and, on the other hand, the drying of the droplets obtained. Moreover, the extremely low residence time (generally less than approximately 1/10 second) of the particles in the reactor has the advantage, inter alia, of limiting unlikely risks of overheating as a result of an excessively long contact with the hot gases. It should be noted here that this treatment of atomisation makes it possible to improve significantly the capacity of a sol thermohydrolysed at "low" temperature to form stable sols and even when the temperature of the gases is at least equal to 200 0 C (2 significant numbers), preferably between 200 and 3000C, to obtain results similar to those obtained by thermohydrolysis at "high" temperature (1500C), hence sols according to the .io present invention that are optimum.

.S :The temperature of the drying atmosphere can vary within wide limits, and it depends especially on the mean residence time which is desired or which can be imposed on the atomized product once in the said atmosphere. The drying conditions (temperatures and/or residence times) are generally determined Sconventionally so as at least to obtain a complete or virtually complete removal of the residual water contained in the product, that is to say, taken as a whole, until a constant weight is obtained for the latter.

Mention may be made, as water-soluble cerium compounds, of especially the salts of cerium(IV) Ouch 0 i i SHELSTON WATERS MARGARET STREET, SYDNEY, AUSTRALIA

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4"uf 4 .,i 44 4, 44 444 4 44"B as nitrates or ceric ammonium nitrates for example, which are particularly well suited in this instance.

Ceric nitrate is preferably used. A solution of cerium(IV) 'salts can contain, without disadvantage, cerium in the cerous state but it is desirable for it to contain at least 85% of ceriun(IV). An aqueous ceric nitrate solution can, for example, be obtained by reaction of nitric acid with a ceric oxide hydrate prepared conventionally by reaction of a solution of a cerous salt, for example cerous carbonate, and of an aqueous ammonia solution in the presence of hydrogen peroxide. It is also possible, preferably, to use a ceric nitrate solution obtained according to the process for the electrolytic oxidation of a cerous 15 nitrate solution, as described in the document FR-A- 2,570,087, and which in this instance constitutes a starting material of choice.

It will be noted here that the aqueous solution of cerium(IV) salts can have a certain initial 20 free acidity, for example a normality varying between 0.1 and 4N. According to the present invention, it is possible both to use an initial solution of cerium(IV) salts actually having a certain free acidity as mentioned aboe and a solution which will have been neutralized beforehand more or less exhaustively by addition of alase, such as, for examplt,, an aqueous ammonia solution or alternatively a solution of alkali metal (sodium, potassium, and the like) hydroxide., but preferably an aqueous anmonia solution, so as to limit this acidity. it is then possible, in the latter case,

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4 14 I~ -1 0 0 c i I i, l -iw 1 .I I I 1 I I I o iO MF O 12 to define in a practical way a degree of neutralization of the initial cerium solution by the following equation: S n3 n2

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in which nl 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 for neutralizing the initial free acidity supplied by the aqueous cerium(IV) salt solution; and n3 represents the total number of moles of OH" ions supplied by addition of the base. When the "neutralization" variant is implemented, use is made in all the cases of an amount of base which must 15 necessarily be less than the amount of base which would Sr* be necessary to obtain complete precipitation of the hydroxide species Ce(OH) 4 In practice, the degrees of neutralization are thus restricted to values 1'20 not exceeding 1 and preferably still not exceeding The initial mixture thus being obtained, it is then heated, in accordance with the second stage of the process according to the invention (Stage The temperature at which the heat treatment also known as thermohydrolysis, is carried out can be between 80*C and the critical temperature of the reaction mixture, in particular between 80 and 350*C and preferably between 90 and 200°C.

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

When, as is preferred, the treatment temperature is chosen to be greater than the reflux temperature (at ordinary pressure) of the reaction mixture (that is to say generally greater than 100*C), for example chosen between 120 and most often between 150 and 350°C, the operation is then carried out in a closed chamber. The aqueous mixture containing the abovementioned species is introduced into this chamber (closed reactor more commonly known as an autoclave) and the necessary pressure then only results solely from the heating of the reaction mixture (autogenous I 4 t pressure). Under the temperature conditions given

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S• above, and in aqueous media, it is thus possible to i specify, by way of illustration, that the pressure in the closed reactor varies between a value greater than 1 bar (10 s Pa) and 200 bar (2 x 10 7 Pa) and preferably o between 5 bar (5 x 105 Pa) and 150 bar (1.5 x 10 7 Pa).

mm It is, of course, also possible to exert an external pressure which is then added to that resulting from the heating.

The heating can be carried out either under W o an air atmosphere or under an inert gas atmosphere, preferably nitrogen.

1 i y 1 1 1 f il (3 1 1 1 l 1 1 1 1 1 1 1 combustion engines requires both the possibility of 14 The duration of the treatment is not critical and can thus vary within wide limits, for example between 1 and 48 hours and preferably between 2 and 24 hours. The rise in temperature is likewise carried out at a rate which is not critical and it is thus possible to reach the set reaction temperature by heating the mixture, for example, between 30 minutes and 4 hours, these values being given entirely by way of indication.

On conclusion of the heating Stage a solid precipitate is recovered which can be separated from its mixture by any conventional solid/liquid separating technique such as, for example, elutriation, filtration, settling, draining or centrifuging.

It will be noted that it is, of course, possible to repeat a heating/precipitation stage as defined above one or a number of times, in an idential or nont identical way, by then implementing, for example, heat treatment cycles.

By way of indication, it is possible to use, as starting solution for the thermolysis, cerium(IV) SI solutions, in general of nitrate, corresponding to the following characteristics: I ,K 1 1 0 1 1 1 1 1 t 9 f 0 1 i 0 0 I j I I I to the 120 g/l and 100 g/l solubility limit Cerium content r 4C I

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4 II Acidity r not greater r between than 1 0.5 and Counterion any weakly oxygen- nitrate to the complexing containing and cerium anion non-complexing anion The characteristic of Stage of the 10 process of the invention is to produce an organic sol, an expression which denotes the dispersion of #4 4 4 optionally impure cerium dioxide (hereinafter cerium I4t,, dioxide will sometimes be denoted by the compound of the cation in organic medium, by transfer of the said cerium dioxide into an organic phase from an aqueous phase consisting of the ceric compound which is found in the colloidal form in an aqueous sol.

Aqueous sol denotes the colloidal dispersion of the compound of the cation in aqueous medium which constitutes the standard starting material of the Sprocess of the invention.

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54 .4r SrI cI 44 16 In order to satisfactorily carry out the process of the invention, it is desirable for the starting aqueous sol to satisfy the following requirements: a the proportion of metal in colloidal oxide (in the broad sense) form must be very high, advantageously 90%, preferably greater than or equal to 95% and, as a general rule, as high as possible a the concentration of colloidal oxide (in the broad sense) in the aqueous sol must be sufficient and preferably lie between 0.1 and 3 mol/litre, a the aqueous sol must have good thermal stability S properties and must not flocculate at the reaction temperature which is greater than 60 0 C and most 15 often varies between 80 and the boiling point (depending on the pressure).

SThe liquid organic medium used in the process of the invention can be an inert aliphatic or Scycloaliphatic hydrocarbon or their mixture such as, for example, mineral or petroleum spirits or mineral or petroleum ethers which can also contain aromatic components. The examples comprise 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 cuts of Solvesso type (registered trade mark of the Company Exxon), especially Solvesso 100 which essentially contains a o p hd r o h m rs a 20 fr eampl, mnera orpetrleu spiitsor mnerl o -C r i:l. ,c TR rr~mu~ZmFi~ mixture of methylethyl- and trimethylbenzene and Solvesso 150 which contains a mixture of alkylbenzenes, in particular of dimethylethylbenzene and of tetramethylbenzene.

Use may also be made of chlorinated hydrocarbons such as chloro- or dichlorobenzene and chlorotoluene, as well as of aliphatic and cycloaliphatic ethers such as diisopropyl ether or dibutyl ether and of aliphatic and cycloaliphatic ketones such as methyl isobutyl ketone, diisobutyl ketone or mesityl oxide.

Esters may be envisaged but they have the disadvantage that there is the risk of being hydrolysed. Mention may be made, as esters capable of being used, of those resulting from the acids mentioned in the present application with C1 to C8 alcohols and especially palmitates of secondary alcohols such as isopropanol.

The organic liquid or solvent system will be chosen by taking into account the solubilizing organic acid used, the heating temperature and the final 20 application of the colloidal dispersion or solution. In certain cases, it is preferable to employ a mixture of solvents. The amount o liouid or solvent obviously determines the final conceitration. It is more economic and more convenient to prepare more concentrated dispersions which can be diluted later, at the time of their use. It is for this reason that the amount of solvent is not critical.

a It can be advantageous to add a promoter to the organic :s 1 low, T~r. 4 9 9 9 *9 9 9 99 9 9 9** 99 9 9 99 .9«9 *999 9 18 phase whose function is to accelerate transfer of the colloids from the aqueous phase to the organic phase and to improve the stability of the organic sols obtained. It is possible to use, as promoters, compounds containing an alcohol functional group and very particularly linear or branched aliphatic alcohols having from 6 to 12 carbon atoms.

Mention may be made, as specific examples, of 2-ethylhexanol, decanol, dodecanol or a mixture of them.

The proportion of the said promoter 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 highly suitable.

15 If the field of usable acids is very large, the total carbon ntunber in the molecule in order to obtain good dissolution is, however, rather more restrictive. The total (mean if the acid used is a mixture) carbon number of the acids .is advantageously 20" greaterthan 6 and preferably greater than 10 and it is also desirable for it to be less than approximately If high cerium, or equivalent, concentrations are desired, it is desirable to choose acids which are as short as possible.

These acids can be linear or branched. It is preferable, however, for the branchings to be either far from the carboxyl functional group or not very numerous and carried by different carbons. Carboxylic o it~ ua~u, i*r

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acids which can be used for the present invention can be arylic, aliphatic or arylaliphatic acids. They can carry other functional groups provided that these functional groups are stable in the media in which it is desired to use the cerium compounds according to the present invention.

In order for the sol to remain usable at low temperature, below room temperature or indeed below zero degree Centigrade, it is preferable for the melting point of the acid, or of the mixture of acids, to be not greater than 50°C, advantageously not greater than room temperature and preferably not greater than zero degrees Centigrade.

Thus, it is easily possible to use carboxylic 9 acids in which the carbon chain carries ketone functional .goups, such as pyruvic acids substituted a to the ketone functional group. These can also be a-halocarboxylic acids or a-hydroxycarboxylic acids.

The chain attached to the carboxyl group can carry unsaturations. However, in general, the tendency is to avoid too many double bonds because cerium catalyses crosslinking of the double bonds. The chain can be interrupted by ether or ester functional groups, provided that the lipophilicity of the chain carrying the carboxyl group is not excessively detrimentally affected. I It is thus possible to use aliphatic carboxylic acids, aliphatic sulphonic acids, aliphatic t a 0 .r 9.i 6 6 6* 4 *6 *6 a 4IS* -ftr r phosphonic acids, alkylarylsulphonic acids and alkylarylphosphonic acids having approximately from to approximately 40 carbon atoms, whether natural or synthetic. They can be used alone or as a mixture with one another.

Mention may be made, as paradigmatic examples, of the fatty acids of tallol, coconut oil, soybean oil, tallow oil or linseed oil, oleic acid, linoleic acid, stearic acid and its isomers, [lacuna] acid, pelargonic acid, capric acid, lauric acid, myristic acid, dodecylbenzenesulphonic acid, 2-ethylhexanoic acid, naphthenic acid, hexoic acid, toluenesulphonic acid, toluenephosphonic acid, laurylsulphonic acid, laurylphosphonic acid, 15 palmitylsulphonic aCid and palmitylphosphonic acid.

Oleic acid or alkylarylsulphonic acids are preferentially used.

The amount of amphiphilic organic acid used, expressed as number of moles of acid per mole of oxide (in the 20 broad sense), can vary within wide limits between 1/10 and 1 mol per mole of cerium dioxide. The upper limit does not have a critical nature but it is not necessary to use any more acid. The organic acid is preferentially 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 ratio by weight of the organic solvent to the '1

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ii t I organic acid is preferably chosen between 0.3 and The order of introduction of the various reactants is immaterial. The colloidal aqueous dispersion(s), the organic acid, the organic solvent and optionally the promoter can be mixed simultaneously. The organic acid, the organic solvent and optionally the promoter, which constitute the organic phase, can also be premixed.

The temperature of the reaction mixture is preferentially chosen within a range from 60*C to 150°C.

~In certain cases, due to the volatility of the organic solvent, there is reason to condense its vapours by cooling to a temperature below its boiling point. The operation is advantageously carried out at a temperature between 60 and 120°C and preferably between 90 and 110°C.

The reaction mixture is kept stirring throughout the heating, which can be from less than one hour to approximately one day and preferably between 2 hours .4 20 and half a day.

At the end of the abovementioned heating time, heating is halted. The presence of two phases is observed: an organic phase containing, in dispersion, the metal oxide/organic acid complex and a residual"aqueous S 25 phase.

The organic phase and the aqueous phase are then ,separated according to conventional separating techniques: settling, centrifuging, and the like.

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.4 4r 4, 4( 4 4( 4 4 4 4444 4 4 44 44 14: *4i 4 22 In accordance with the present invention, colloidal organic dispersions of metal oxide(s) are obtained in which the size of tie colloids can be very variable and can be controlled by varying certain parameters, especially the diameter of the starting colloidal aqueous dispersions, which depends on respecting the thermohydrolysis conditions.

For certain applications, it is possible to use the reaction mixture as 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, use is made of means well known to those skilled in the art, for example passing through a drying agent (including a hydrophobic membrane filter) or the addition of a third solvent which is inert with respect to the compound, which has a boiling point preferably less than 100°C and which forms an azeotrope with water, followed by distillation of the azeotrope obtained. Mention may be made, as third solvents suitable for the invention, of aliphatic hydrocarbons, such as hexane or heptane, cycloaliphatic or aromatic hydrocarbons, or alcohols such as, for example, ethanol, ethylene glycol, diethylene glycol, and the like.

It is preferrede in particular for applications as gazole additive, that the water content be equal to 1% at the most, advantageously I per thousand, preferably to 100 ppm.

The second alternative will now be examined, namely hifh constraint for the amphiphilic acids but lower for the basic essentials of the particles. It should be reminded that the best performances of the so! .sare obtained when a system of constraints is complemented at least partially by various constraints of the other system, SIt t w C: 4~I4 3 44 4 44 4E 4£ £4 I It it I 4 4 44 4 4 44 444 444-t 4 4.4 44 4* 4 4 64 t 44 4£ 4 4414 4 444444 4 Some constraints are mutual, therefore the detailed descriptions of the first part are only reviewed briefly in this second part, the sols complying with both types of constraints are the best.

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

When the system is a mixture of acids, the carbon number can be a fraction since it is then a mean and the constraints on the means are advantageously the same as those above for one of the, or the, constituent(s) of the said amphiphilic system. The minimum constraint is that the mean of the carbon atoms of the acids of the said amphiphilic system is at least equal to 10 carbon atoms. More specifically, the mean 15 of"the carbon atoms of the acids of the said amphiphilic system is advantageously from 11 to 25 and preferably from 15 to In order to obtain better results, especially when the chain length is low (less than 14 carbon atoms) and 20 when there is only one branching, and especially when it lies in a position y or 6 to the atom carrying the acidic hydrogen, it is very desirable for this branching to be at least two carbon atoms and advantageously three.

In order to explain the nomenclature of the positions, examples of di(2-ethylhexyl) hydrogen phosphate and of 2-ethyloctanoic, acid will be found below 24 Position (H func- a-(atom) p-(atom) y-(atom) -(atom) -(atom) tional group) HO -PO(OCH 17 -O -CH 2 -CH(CAs) -CH 2 (C3H 7 HO -CO -CH(C, 2 H) CH 2

CH

2 CaH(C 3

H

7 It is preferable for the longest linear part to be at least 6 and preferably 8 carbons.

It is advantageous for the pK, of at least one of the acids to be not greater than 5 and preferably not 9, greater than It is also advantageous for the side chain(s) of the branched acids to contain at least two carbon atoms and preferably three carbon atoms.

15 It is preferable, especially when the acids are carboxylic acids, for the amphiphilic acid system to be a mixture of acids.

In this case, the conditions regarding the branching must apply to at least half, advantageously two thirds and preferably four fifths, by moles, of the i constituent acids of the said amphiphilic acid(s) system.

Mention may be made, among the acids giving very good results, of acids containing phosphorus, such as i 25 phosphoric acids, especially diesters of phosphoric acid, phosphohic acids and their monoesters, and phosphinic acids.

Mention should be made, among carboxylic acids giving

A

'4 9 )Q 4: 44 r* 4 9 4 good results, of the constituent acids of the mixture of acids known under the name of isostearic acid. The acidic system is advantageously isostearic acid itself.

The starting melting point of the amphiphilic acid(s) system is advantageously less than 50 0 C, more advantageously less than or equal to 206C and preferably not greater than 0°C.

For good stability and for good extraction, it is desirable for the molar ratio of the extractant to the tetravalent metal, preferably cerium, to be between 0.1 and 0.6 and preferably between 0.2 and 0.4. This ratio increases when the size of the particles decreases.

In order to obtain particularly stable sols, as it has 'een shown that the presence of coarse particles harmed the long-term stability of the sols according to the present invention, or even of the sols produced from more conventional acids, it is preferable for not more than advantageously not more than 1% and preferably not more than 0.5% by mass of the tetravalent metal oxide particles to be not greater than 0.1 micrometre, advantageously not greater than 0.05 micrometre and preferably not greater than 0.02 micrometre.

Any diluent leading to a stable sol comes within the cgntext of this invention.

The sols according to the present invention can be used for many implementations. According to the desired use, a compromise should be chosen by taking into account the technical data below; for synthesis and stability, i:i" i i *U i ar" r -:-Ill-i i 99 9999( 1 0 19 069 :too*# 994

I

9t to 4 t I 91y (*9 99 £~t 9 49 9 26 it is desirable to avoid highly non-polar hydrocarbons, such as, for example, non-cyclic aliphatic hydrocarbons. Diluents having a polar functional group, such as esters or ethers, give good results but, for certain uses, possibly should be avoided as far as possible. Mixing diluents can introduce 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 sol is used to form a dilute sol in a diesel oil. The starting sol is generally very concentrated, which limits the latitude of those skilled in the art. Moreover, for reasons of compatibility with diesel oil and its many additives, 15 the diluents preferably then have little polarity. As constituent components of a diluent, aromatic or aliphatic compounds are preferable to compounds having a polar functional group, such as, for example, ester or ether functional groups.

It is preferable for the diluents to have a kauributanol value (measured according to ASTM standard D II 33) of less than 105 and advantageously of less than For use as a charged additive, it is preferable for the melting point of the diluents, or mixtures of diluents, to be low and to correspond to the melting point constraints described in the present document with respect to the amphiphilic acid system.

o j j i i r

I

r r icrc tt'~ 1 *r* ~Y iu il-' ~-U~-YYYLY~li~-- _i.ll-yl I1W1 .9 9i *i a 49 ai lIa I 4494 *i .9 9 il a a 9 27 It is also preferable for these diluents to have a solubility in water which is very low, preferably less than 5% by mass, preferably not more than 1% and more preferentially at most equal to 0.5% by mass.

Correspondingly, it is also preferable for the water to be soluble to not more than preferably to not more than 1% and more preferentially to not more than in the diluent.

Mention may be made, among the preferred diluents, of aromatic hydrocarbon compounds and their mixtures, as well as aliphatic compounds and their mixtures containing less than 50%, preferably 25% or more preferentially 1% of aromatic compounds.

The tetravalent metal oxides can contain relatively low 15 proportions of metals having other valencies. In general, the proportion of addition elements, or of impurities, which is contained in the tetravalent metal particles does not exceed 10% by mass and more generally 5% by mass.

20 The tetravalent metal content of the sol according to the invention is advantageously not greater than 2/3 by mass and preferably between 30 and 40% (mass). For use as an additive in charged diesel, it is preferable for the content not to fall below 1/6 and preferably 1/5.

The organic sols according to the present invention are generally prepared in a known way by heating an aqueous sol containing the said tetravalent metal oxide in the presence of the said diluent and of the said I f -u.iJ* 1 amphiphilic acid system.

According to one of the particularly advantageous characteristics of the invention, care should be taken that there is no excessively coarse particle in the aqueous sol and thus in the final sol.

Removal of the particles of coarsest sizes can be carried out by any technique which makes it possible to selectively remove the coarsest particles. This removal can be carried out on the aqueous sol, on the organic sol or on both.

I',t t However, it is preferable that at least one separation takes place 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 is possible to range up to centrifugations corresponding to 50,000 G; the limit is only a limit of a technological nature.

2a It should be noted that centrifugation prior to the 20 stage of forming the organic sol, often known as the extraction stage, promotes the latter.

The aqueous sols are advantageously prepared by hydrolysis, preferably by thermohydrolysis. Mention may be made, among the techniques which can be used for the present invention, of the techniques disclosed in'the European Patent Publication published under the number 97563 on behalf of the Applicant company. Mention may also be made of the European Patent Application i4; t n ii~ IC1-(

*I

29 published under the number 206907.

The said sols obtained according to the invention have a concentration of cerium(IV) compound which can be very high since it can range up to 3.5M to 4M of CeO,. It is observed that the extraction yield of cerium in the organic phase is very good since it can reach 90 to By quasi-elastic light scattering, the presence is revealed of colloids having a hydrodynamic diameter which varies with the conditions of preparation and S" which is less than 100 A (that is to say than the t r detection limit of current devices).

0' The organic sols thus developed have excellent stability. No settlement is observed after several months.

V tC According to one of the preferred characteristics of the present invention, the sol is such that, adjusted Sto a concentration of cerium metal contained of t, tthe viscosity of the sol at 25°C is not greater than 20 20 mPa-s, advantageously not greater than 15 mPa-s and preferably not greater than 10 mPa s.

It is also preferred that the counter anions of the cerium solution from which the sol originates be only present in the various sols according to the present invention in proportion at the most equal to 0.1, advantageously to 0.05, preferably to 0.03 equivalents per 100 g of cerium dioxide. This constraint is mainly valid for the superficial layer of crystallites, layer of pentatomic thickness.

This viscosity can be measured by low shear, Contraves trade mark, by varying the rate gradient from 0.01 to 1.

A

43

L

r r-...atQ rarr~l r Uit V i V

(C

It It I ail

I

The organic sols thus obtained can be diluted in order to obtain concentrations of 10 to 500 and preferably of 50 to 200 ppm. The diluent is advantageously a fuel for an internal combustion engine, preferably a diesel engine; the invention is thus also targeted at sols in which the organic phase consists essentially of diesel oil and of its additives.

The invention also relates to the use of the organic sols prepared according to the invention as driers in the paints and varnishes industry with a view to accelerating drying of unsaturated oils and as combustion adjuvants in liquid motor fuels or fuels for power generators such as internal combustion engines, oil burners or jet engines. The sols according to the 15 invention can also be used in cosmetics.

EXAMPLES OF THE FIRST ALTERNATIVE Reactants: Except if it is otherwise arranged, the reactants used in the examples are: 20 a ceric nitrate preneutralized to r 0.5 (cf.

European Patent on behalf of the Applicant company, published under the No. 153,227) 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 oil.

General procedure of the examples: Except when this is otherwise specified hereinbelow, the procedure of the examples is the following: ,i L J: jl h t, *set

C

it t 4 4 t

'C

I

S

31 the first stage consists of the synthesis of the precursor which is an aqueous sol of CeO, colloids in which the size (TEM) is between 3 and 5 nm.

The ceric nitrate solution with r 0.5 is placed in a covered tantalum autoclave. The concentration of the solution used is 80 g/l, expressed as CeO 2 Autoclaving is carried out at 160°C for 4 hours with a temperature rise over 1 hour. Stirring is maintained throughout the operation.

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

15 Example 1 Reactants: a ceric nitrate preneutralized to r 0.5 and at a cerium concentration of 80 g/l, an oleic acid extracting agent.

First stage: The Cerelec solution with r 0.5 is placed in a covered tantalum autoclave. The concentration of the solution used is 80 g/l, expressed as CeO 2 Autoclaving is carried out at 160°C for 4 hours with a temperature rise over 1 hour.

Stirring is maintained throughout the operation.

The solution obtained is filtered on sintered 1 Ar i

A

32 glass, no. 4.

The product is then redispersed in water, which makes it possible obtain a stable aqueous sol.

The concentration of this sol is 150 g/l.

The second stage of the preparation is the transfer of the colloids from the aqueous phase to the organic phase.

A quantitatively determined amount of CeO, aqueous sol is placed in a round-bottom flask to which S 10 is added the organic mixture which is such that the oleic acid/cerium molar ratio is 0.3 and the Solvesso 150/oleic acid ratio is 3.75.

In the example under consideration, this leads to the use of: 15 24.8 g of CeO 2 0.165 1 of sol at a concentration of 150 g/1), 12.2 g of oleic acid, 45.7 g of Solvesso 150.

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

The exact assay of the sol is then measured by calcination (solids content after 6 hours at 950°C).

A sol is thus obtained with a measured stability greater than 4 months (duration of the sample), the CeO 2 concentration of which is 29.1% (mass) and the colloid size of which (measured by TEM) is Li

K/

A, -46- 33 between 3 and 5 nm.

Example 2 The procedure used is similar to that of Example 1. The proportions of the various reactants are adjusted so as to obtain a stable sol with a particle size of 3 to 5 nm, the characteristics of which are: CeO 2 content of 47% (mass), oleic acid/cerium ratio of 0.25.

Example 3 10 This time a procedure is used which is similar to that of Example 1 as regards transfer into the organic phase but which differs therefrom in the preparation stage of the aqueous precursor.

aThe red ceric nitrate solution is thermohydrolysed under standard conditions (concentration of 80 g/l, temperature of 100 0

C,

r After separating from the mother liquors, the It thermohydrolysis hydrate is repulped in water and then dried by atomization (bichi atomizer, attack temperature 240 0 C, outlet temperature 120 0

C).

After this drying stage, the product remains perfectly dispersible. It is used for preparing the aqueous CeO 2 sol which is used as precursor in the transfer to the organic phase.

2 The saol synthesized according to thisproduct is perfectly stable, the colloid size (TEM) is between 3 and 5 rm (Figure 3, sample 9238) and its Ce, content i 39 (cncntatino 0 /)tmertr f 0°, Ik 7 -47t 4 t0C t t t.

Assessment of the viscosity of the organic sols by measuring the flow time of 1 ml of sol through a 1 ml Prolabo pipette (brand name: Blau Brand, Swift precision (precision 1 ml 0.006) Cerium sol Cerium Oleic/Ce Time in dioxide seconds content Precursor hydro- 30% 0.20 35.6 lysed at 100 0

C

Precursor hydro- 30% (28.1) 0.30 41.2.

lysed at 100*C Precursor hydro- 40% 0.20 17.4 lysed at 150 0

C

Precursor hydro- 40% (34.7) 0.30 22.3 lysed at 150*C Precursor hydra- 40% 0.30 26.3 lysed at 150*C Precursor hydra- 40% (39.7) 0.20 22.6 lysed at 160*C Sal of Example 40% isastearlc 21 No. 4 (known 0.30 viscosity= mPa-s) The hydrolysis temperature, the olein/cerium ratio and the true CeO 2 level all influence the P viscosity at the same time.

EXAMPLES OF THE SECOND ALTERNATIVE

GENERALITIES

The synthesis of the organic cerium sol takes place in two stages: the synthesis of a cerium hydrate which is redispersible to form an aqueous cerium sol and then transfer of the sol into the organic phase.

SYNTHESIS OF THE AQUEOUS SOL It concerns a conventional synthesis by t.f. 10 thermohydrolysis of a cerium(IV) nitrate solution containing 80 g/1 of cerium oxide preneutralized with St aqueous ammonia to obtain a ratio R close to 0.5. The cerium oxide concentration is in the region of 80 g/1. After four hours of thermohydrolysis at t t 4 15 150°C in an autoclave, the precipitate of ceri'im hydrate type is recovered by filtration.

The hydrate is then resusp nded by repulping in water.

A fraction of the product is dispersed in the sol form, the remainder forming a moderately stable suspension. A concentration of 160 g/1 is generally targeted. The pH of the solution is acidic (less than pH 1).

A second type of precursor can also be used.

The cerium(IV) solution, still preneutralized at R 0.5, is this time thermohydrolysed at 100°C for four hours. After filtering the hydrate, the precipitate is taken up again in water to form a sol which is dried by at6mization (Bichi or LEA). The dried hydrate is finally redissolved to form a stable sol at 36 a concentration of 160 g/l.

TRANSFER OF THE SOL INTO THE ORGANIC PHASE Transfer of the so). into the organic phase is obtained using an extracting agent diluted in an organic solvent. The molar ratio of the extractant to the cerium is set at 0.3 for a total amount of cerium of the order of 40%, as CeO 2 32.5% as cerium metal), in the final organic phase.

The aqueous sol described above is brought 10 into contact with the organic phase and then, with slow stirring, the solution is progressively brought to 100 0 C (reflux of water).

The synthesis takes place in two separate

I

phases: Exchange: the organic lphase, initially lighter than the aqueous s becomes progressively cloudy. Exchange seems to take place very quickly *and the orc-anic phase, becoming more dense, then passe's to the bottom of the reactor. When the two phases have a similar density, a significant emulsion forms and it is then advisable not to stir the .eactor too vigorously, in order to limit the phenomenon.

At the end of the exchange, the aqueous phase becomes clear again whereas the organic phase remains cloudy. The duration of this phase varies from 2 to 4 hours depending on the nature of the precursors., *Maturation: once exchange is complete, a phaiue 4 4,

I

I

I'l t 4 .4 *too*: known as maturation takes place during which the organic phase releases the nitrates and water molecules entrained by the hydrate aggregates during transfer. The organic phase progressively becomes clear and it is observed that nitrous vapours are being given off. Finally, a stable, perfectly clear organic sol which is black in colour with red glints is obtained. The maturation phase is of variable length but, under the conditions followed, is seldom less than 6 hours.

In the laboratory, the sol is recovered by filtration on a hydrophobic filter and then centrifuged to remove possible agglomerates responsible for slight deposition of certain products with time.

Example 4: extraction with ISOSTEARIC ACID, 150 0 C sol Synthesis of the aqueous sol: 415 ml of a cerium(IV) nitrate solution (1.4 mol/l, 0.58 mol/l of free acid, d 1.433) are neutralized with 835 ml of a 0.64 mol/l aqueous anumonia solution at the rate of 0.5 OH'/Ce/h, so as finally to obtain a solution containing 80 g/l of Ce0 2 preneutralized to R COH']/[Ce] The solution is then placed in an autoclave, brought to a temperature of 150 0 C over one hour and then left at 150*C for four hours. After cooling, the hydrate obtained is filtered (sintered glass 4) and the oxide content determined by loss on ignition at 900°C.

g of cerium oxide in hydrate form are taken up again in 250 ml of water so as to obtain an aqueous sol with 4 SMention should be made, among carboxylic acids giving t 38 a concentration of 160 g/l.

Synthesis of the organic sol: in order to form 100 g of sol, 19.9 g of isostearic acid (ISA) are diluted in 40.1 g of Solvesso (aromatic petroleum cut), so as finally to obtain an ISA/Ce molar ratio of 0.3 and a final CeO 2 concentration in the organic phase of The organic phase is brought into contact with the aqueous phase with gentle stirring and the mixture is then brought to reflux (100-103 0 C) for 15 h.

0 10 The organic phase, after separation by settling, is filtered on a hydrophobic filter and then optionally centrifuged at 4500 rev/min.

The sol obtained, with a cerium oxide concentration of 40% by mass, has a clear black colour S* 15 with red glints. It is perfectly stable.

Change of viscosity as a function of time The viscosity is measured by low shear, Contraves trademark, by varying the rate gradient from 0.01 to 1. In all cases, the viscosity of the additive is independent of the rate gradient. Measurement is carried out in a sol at 25 0 C with a metal content of The following table gives the change in the Sviscosity as a function of time for the sol thus 25 prepared.

A.,

4 t I 1 4 44 t 4444 4t41~ 4 f4 E~ 44 4 44 4 4.

4 t It 444'

I

41' 4 IIl 4 4454 44 Is 4 II 4

II

II

4.

Ills

I

I

544955

S

Duration of ageing Viscosity of the additive in (dlays) mPa-s (uncertainty of 3. rPa-s) closed flask open flask 0 150 (temperature of -18 0

C)

0 10 68 11 311 118 10 11 165 10.5 11.7 292 9.5 12.8 10 330 9 13 Example 5 (comparative): extraction with OLEIC ACID, 150*C Sol A preparation is carried out as in Example 1 except as regards the organic phase consisting of 19.7 g of oleic acid (OAp extractant) and 40.3 g of Solvesso (diluent).

Thie sol obtained is less stable since it allows a slight deposit to appear of a few days in the bottom of the flask (deposit containing especially cerium oxide).

gNpple 6 extraction with ISOSTEARIC ACD 1000C sol Synthesis of the agueous Sol: 415 ml of a cerium(IV) nitrate solution (1.4 mol/l, 0.58 mol/l of free acid, Otta cc A l I 4 %Ltt 44444 d 1.433) are neutralized with 835 ml of 0.64 mol/l aqueous ammonia solution at the rate of 0.5 OH-/Ce/h, so as finally to obtain a solution containing 80 g/l of CeO 2 preneutralized to R [OH'I/[CeJ The solution is then brought to reflux for 4 h and the hydrate obtained is then filtered. It is resuspended at 150 g/l in water and then atomized on a Bchi (800 ml/h, inlet temperature: 240 0 C, outlet temperature: 130°C).

Finally, the hydrate is dissolved at 160 g/l before being extracted with an organic phase under the same operating conditions as for Example 1.

The sol obtained, which is black in colour but not clear, is not very stable insofar as a yellow deposit appears after a few hours.

If the organic sol is centrifuged at 4500 rev/min for one hour, the sol is then significantly more stable insofar as the deposit had not appeared after several days.

Example 7: extraction with ISOSTEARIC ACID, centrifuged 100*C sol Taken as a whole, the reaction is carried out 7W in the same way as for Example 3, except that the aqueous sol is centrifuged at 4500 rev/min for one hour in order to remove the particles of greater than 60 nm probably poorly dissociated during the synthesis.

The organic sol obtained after extraction is then much more stable than that of Example 3, especially insofar

I

J ZA~ It

I

4, 4,4, r I I 4"t r, 44 C 4* 4, #41 4, I as no deposition was observed after several weeks of storage.

The change in the viscosity is the same as that of Example No. [lacuna], to within the uncertainty of the measurement.

Example 8 (comparative): extraction with 2ethylhexanoic acid, 150°C sol The preparation is carried out as in Example 1, except that the 'traction is carried out 10 with an organic phase conp;,-ing 10 g of 2-ethylhexanoic acid and 50 g of Solvesso.

After extracting for more than 25 h, a cloudy organic sol is obtained, the stability of which does not exceed a few days (deposition of particles in the bottom of the flask).

Example 1 (comparative): extraction with 3,5,5trimethylhexanoic acid The preparation is carried out as in Example 1, except that extraction is carried out with an organic phase consisting of 11 g of 3,5,5trimethylhexanoic acid and 49 g of Solvesso.

After extracting for several hours, a yellow putty is formed in the bottom of the round-bottom flask.

Synthesis of the sol is not possible with this type of extractant unsubstituted a to the carboxylic acid" group.

This example, by comparison with the above comparative example, shows that when a pure acid is used and that 7, l hi it i m, I I 42 when the closest branching to the acidic functional group is both methyl and y to the H functional group (compare the table above), the results are significantly less favourable.

f ii tIkC

I

r.

A .r

IA

Claims (4)

1. 2. The organic sol according to claim 1 wherein the amphiphilic acid system contains at least one containing 1 to 50 carbon atoms having at least one branching a, 13, y, 8 to the atom carrying the acidic hydrogen. St 3. The organic sol according to claim 1 or 2 wherein the tetravalent metal oxide is r t cerium dioxide. t
2. 4. The organic sol according to any one of claims 1 to 3 wherein the d 90 is not greater S* r than 5 nanometres. The organic sol according to any one of claims 1 to 4 wherein 90% by mass of the agglomerates contain from 1 to 3 crystallites. O vi 6, Organic sol according to any one of claims 1 to 5 wherein 50% (statistical value) at S, 20 least by mass of the agglomerates are monocrystalline.
3. 7. Organic sol according to any one of claims 1 to 6 wherein 80% by mass of the I *t.S crystallites are of a size less than a value chosen in advance within the range 2 to i nanometres, 1
4. 17861-idDOC fr S S. 5, S S I S 4~ C 44 8. Organic sol according to claim 7 wherein 90% by mass of the crystallites are of a size less than a value chosen in advance within the range 2 to 5 nanometres. 9. Organic sol according to claim 7 or 8 wherein the value chosen in advance is 3 to 4 nanometres. 10. Organic sol according to any one of claims i to 9, wherein the molar ratio of the amphiphilic acid to the metal elements of the sol is not greater than 11. Organic sol according to any one of claims 1 to 10, wherein the residual cerium (III) content with respect to cerium (IV) is as low as possible. 12. Organic sol according to claim 11 wherein. the residual cerium (111) content is less to than 13. Organic sol according to claim 11 or 12 wherein the residual cerium (III) content is not greater than 1% 14. Organic sol according to any one of claims 11 to 13 wherein the residual cerium content is not greater than 1/2%. t5 15. Organic sol according to any one of claims i to 14, wherein the metal oxide is cerium dioxide and its content (with its retinue of impurities) contained is between and 16. Organic sol according to claim 15 wherein the cerium dioxide content is 30 to by mass. 17. Organic sol according to any one of claims I to 16, wherein the viscosity of the sol is such that not more than one half-minute is necessary for it to flow one ml. 18S. Organic sol according to any one of claims i to 14 and 17, wherein it has a concentration of 10 to 500 ppm. Mz 9 Organic sal accord ing to, claim 18 wherein it has a concentration of 50 to 200 ppm. I CQ G'6 It K A 99 4 9 49t 9 **9491 4 99 96 69 9 9. 9 99 9 .9 6 9e*696 9 Organic sol according to any one of claims 1 to 19, wherein the organic phase consists essentially of diesel oil and of its additives. 21. Organic sol according to any one of claims 1 to 20, wherein the amlphiphilic acid system is a mixture of acids. 22. Organic sol according to any one of claims i to 21, wherein the mean carbon number of the acids of the amphiphilic acid system is at least equal to 23. Organic sol according to claim 22 wherein the mean carbon number is between and 24. Organic sol according to any one of claims ito 23, wherein at least one of the acids of the amphiphilic acid system has a small p not greater than Organic sot according to claim 24 wherein the pK, is not greater than 26. Organic sol according to any one of claims 2 to 25, wherein the side chain(s) of the acids having at least one branching contain at least 2 carbon atoms. 27. Organic sol according to claim 26 wherein the side chain(s) having at least one 15 branching chain contain at least 3 carbon atoms. 28. Organic sol according to any one of claims 1ito 27, wherein the amphiphilic acid system contains isostearic acid. 29, Organic sol according to any one of claims i to 28, wherein the amaphiphilic acid system is a diester of phosphoric acid. 30. Organic sol according to any one of claims 1 to 29, wherein the starting melting point of the amiphiphilic acid system is not greater than 501C. 31. Organic sot according to claim 30 wherein the starting melting point is not greater than 20 0 C. lto 4k1 to** I, 'V 46 32. Organic sol according to claim 30 or 31, wherein the starting melting point is not greater than 0 0 C. 33. Organic sol according to any one of claims 1 to 32, wherein the tetravalent oxide particles have not more than by mass of them, in which the size is greater than 0.1 micrometre. 34. Organic sol according to claim 33, wherein the tetravalent oxide particles have not more than 1% by mass of them of size greater than 0.1 micrometre. Organic sol according to claim 33 or 34 wherein the tetravalent oxide particles have not more than 0.5% by mass of them of size greater than 0.1 micrometre. 36. Organic sol according to any one of claims 33 to 35, wherein the size is not greater than 0.05 micrometre. 37. Organic sol according to any one of claims 33 to 36 wherein the size is greater than 0.02 micrometre. 38. Organic sol according to any one of claims 1 to 37, wherein the diluent contains not more than 50% of aromatic hydrocarbon. 39. Organic sol according to claim 38, wherein the diluent contains not more than of aromatic hydrocarbon. Fuel for an internal combustion engine, obtained by mixing a conventional fuel with an organic sol according to any of claims 1 to 39. 41. Use of the organic sols according to any of claims 1 to 39 as adjuvant in diesel oils for diesel engines. 42. A process for the preparation of an organic colloidal dispersion of a compound of L t i I II~i D te II II- IIr i r i+tC- ;ir-r *yc* F' i-- "i r iii 1 'I1 i -47- cerium (IV) according to any one of the preceding claims, wherein it contains the following stages: a) subjecting an aqueous solution of cerium (IV) salts to thermohydrolysis operation so as to precipitate a cerium dioxide; b) bringing a suspension of cerium dioxide resulting from stage into contact, simultaneously or consecutively, with an organic phase comprising an organic acid; and recovering the organic phase. 43. A process according to claim 42, wherein the suspension is brought into contact with an organic phase comprising an organic mixture or compound acting as solvent. 44. Process according to claim 42 or 43, wherein the temperature at which the thermohydrolysis is carried out is between 80°C and the critical temperature of the reaction mixture. 45. A process according to any one of claims 42 to 44, wherein the organic mixture 15 which acts as solvent contains diesel oil. 46. An organic sol as claimed in claim 1, substantially as herein described with reference to any of the examples but excluding any comparative Examples. 47. A process for the preparation of an organic colloidal dispersion as claimed in claim 42, substantially as herein described with reference to any of the Examples but excluding 20 any comparative Examples. DATED this 1st day of October 1998 RHONE-POULENC CHIMIE 4 t 4? 4 ru 4 (4i I- 4'' )tC I 4 j i i i i i SAttorney: RUTH M. CLARKSON SR Fellow Institute of Patent Attorneys of Australia K of BALDWIN SHELSTON WATERS S17861-o.DOC I ABSTRACT The subject of the present invention is a sol 4. ,tta S C i I. tr I Ct ii C 41 IO 'III containing: a tetravalent metal oxide, 5 an amphiphilic acid system, a diluent. This sol is defined in that the said amphiphilic acid system contains at least one acid containing 11 to 50 carbon atoms having at least one 10 branching a, P, y or 5 to the atom carrying the acidic hydrogen. Application to protecting the environment. 'I 4 9 .1