FR3050195A1 - PROCESS FOR THE SYNTHESIS OF A MINERAL OXIDE USING A WATER-INSOLUBLE ORGANIC ACID - Google Patents

Abstract

A process for the synthesis of silica precipitated from an aqueous solution comprising a silicate ion and an alkaline cation, said process being characterized in that it comprises the precipitation of the silicate ion by a heavy organic acid having more than four carbon atoms. carbon

Description

PROCESS FOR THE SYNTHESIS OF A MINERAL OXIDE USING A WATER-INSOLUBLE ORGANIC ACID

FIELD OF THE INVENTION The invention relates to a process for the synthesis of precipitated silica.

BACKGROUND OF THE INVENTION

The synthesis of precipitated silica is a well-known industrial problem.

Current methods involve dissolution or alkaline melting of an ore to form a salt comprising a metal atom bonded to an oxygen atom of the water-soluble silicon oxide, followed by dissolution of the salt in water and precipitation by an acid. The precipitated silica is thus formed in an aqueous solution of an alkaline salt of the acid used.

For example, US 4590052 A by Y. Chevallier and J. C. Morawski for a procedure leading to precipitated silicas.

These processes have many disadvantages: • The oxide or hydroxide of precipitated silicon must be isolated by filtration and washing of the salt of the precipitation acid. • The process consumes a carbonate or an alkaline oxide or hydroxide in a large quantity. process consumes the precipitation acid • The process produces an aqueous effluent containing the precipitation salt the removal or discharge of which is a source of pollution

As a result, various means have been proposed for upgrading the salt, or for recycling and regenerating the acid and the carbonate, the oxide or the alkaline hydroxide. In particular, the use of carbon dioxide as a precipitation acid makes it possible to form an alkaline carbonate, the isolation of which by evaporation and drying from the mother liquors makes it possible to recycle to the alkaline melting. This saves material costs or proportional costs.

It has also been proposed to evaporate the filtration juices by multiple effect concentrators to isolate them in the solid state and market them.

These various processes have not found markets because of the high investment required for their implementation, difficult to make profitable.

It remains to find a simple and inexpensive solution to reduce the amount of reagents required to produce such mineral oxides.

A widespread application of such precipitated silica is its use as a filler in an elastomeric composition. In this respect, an important property of precipitated silica is its dispersibility.

BRIEF DESCRIPTION OF THE INVENTION

An object of the invention is to increase the dispersibility of the precipitated silica. The invention is a process for the synthesis of silica precipitated from an aqueous solution comprising a silicate ion and an alkaline cation, said process being characterized in that it comprises the precipitation of the silicate ion by a heavy organic acid comprising more than four carbon atoms.

Advantageously, such a process comprises at least one of the following steps: a bottom of a tank containing an aqueous solution of alkali silicate and a heavy organic acid is intimately contacted in a chemical reactor; A flow of an aqueous solution of alkali silicate and a flow rate of a heavy organic acid are added simultaneously to the reaction medium.

Advantageously, said heavy organic acid comprises more than six carbon atoms and preferably more than eight carbon atoms.

Advantageously said heavy organic acid is little or not soluble in water.

Advantageously, the alkaline salt of said heavy organic acid is soluble in water.

Advantageously, said heavy organic acid is a liquid ion exchanger.

Advantageously, the heavy organic acid is recovered from a solution of its alkaline salt by moving it from said alkaline salt by a stronger acid so as to recover the free heavy organic acid.

Advantageously, said solution is an aqueous solution.

Advantageously, said solution is an organic solution.

Advantageously, said recovery is carried out by crystallization, absorption, adsorption, ion exchange, filtration, membrane process, decantation or liquid-liquid extraction.

Advantageously, said recovery is carried out by reverse osmosis, ultrafiltration, microfiltration or nano filtration.

Advantageously, said recovery is carried out on the mother liquors of the precipitation of the silicate ion, after separating said waters from the precipitated silica by filtration and optionally washing the cake obtained. The invention is also a process for producing precipitated silica from an alkali silicate in aqueous solution, said aqueous solution thus comprising a silicate ion and an alkaline cation, said process being characterized in that it comprises the synthesis of silica precipitated by precipitation of the silicate ion by a heavy organic acid in the aqueous solution containing the alkaline cation, and extracting said alkaline cation from the aqueous solution with an organic solvent.

Advantageously, said organic solvent is a liquid ion exchanger

Advantageously, the synthesis of the precipitated silica comprises the following steps: a suspension of amorphous silica nanoparticles in the aqueous solution is produced; Said amorphous silica nanoparticles are coagulated or aggregated so as to form agglomerates and microscopic aggregates of silica nanoparticles; Said agglomerates and aggregates of silica nanoparticles are reinforced and stiffened by an additional deposition of silica on their surface.

Advantageously, the synthesis of the precipitated silica comprises a displacement of the alkaline salt of the silicic acid constituting the silicate in aqueous solution by a liquid cation exchanger so as to reduce the pH of said solution and to cause the separation of a solid phase of amorphous silica distinct from the aqueous phase.

Advantageously, said synthesis step is carried out using, as acid, a pure liquid cation exchanger, the alkaline salt of which passes into solution in the aqueous solution.

Advantageously, the liquid-liquid extraction step of the alkaline salt of the liquid ion exchanger is carried out by contacting an aqueous reaction medium containing the precipitated silica and an alkaline salt of the liquid cation exchanger, with a solvent of said alkaline salt.

Advantageously, the liquid-liquid extraction of the alkaline salt from the liquid ion exchanger is carried out after the synthesis of the precipitated silica.

Advantageously, the liquid-liquid extraction of the alkaline salt from the liquid ion exchanger is carried out at an intermediate stage of the synthesis of the precipitated silica.

Advantageously, the synthesis of the precipitated silica and the liquid-liquid extraction of the alkaline salt from the liquid ion exchanger are carried out simultaneously.

Advantageously, said joint implementation is carried out according to one of the following operating modes: a) a flow of aqueous silicate solution and a stream of the liquid cation exchanger solution in a solvent are contacted simultaneously by feeding them simultaneously; extracting the salified liquid cation exchanger, by co-introducing said streams directly into the reactor or into a material flow external to the reactor and feeding thereto; b) starting from an aqueous base containing an alkali silicate and possibly precipitated silica and putting it in contact with the liquid cation exchanger solution in the presence of an extraction solvent of the exchanger of salified liquid cation, this contacting can be done in the reactor or loop external to the reactor.

Advantageously, the methods for contacting said operating modes are used: during the step of synthesizing the soil so as to control the pH and the ionic strength of the reaction medium before or until the aggregation or precipitation of the silica; or • during the reinforcing or stiffening step of the aggregates.

Advantageously, the extraction solvent of the salified liquid cation exchanger is the liquid ion exchanger itself.

Advantageously, the liquid ion exchanger is chosen from at least one of the following molecules: organic esters of mono or bisubstituted phosphoric acid, long-chain carbon-containing carboxylic acids such as saturated or unsaturated C 6 fatty acids at C18, 2-ethylhexanoic acid, octanoic acid, nonanoic acid, so-called oxo acids, fatty acids substituted by fluoro, chlorine or bromine radicals. • Sulfuric esters of organic alcohols • Sulphonic derivatives of organic molecules

Advantageously, the alkaline cation is chosen from at least one of lithium, sodium and potassium cations.

Advantageously, the process produces, as effluent from the regeneration of the liquid ion exchanger, an aqueous saline solution of normality greater than 1, and preferably greater than 3.

Advantageously, the aqueous effluent resulting from the synthesis of the precipitated silica and the liquid-liquid extraction of the alkaline salt from the liquid ion exchanger is an aqueous effluent substantially free of amorphous solid silica and whose normality in sodium salt is less than 0.2 N, and preferably less than 0.01 N. The invention is also a process in which the precipitated silica has a BET specific surface area of between 50 and 350 m 2 / g, a CTAB surface of between 40 and and 320 m2 / g, and a pore volume greater than 0.7 cm3 / g. The invention is also a process in which the precipitated silica has a pore volume of between 0.7 cm3 / g and 12.0 cm3 / g, and even more preferably between 1.4 and 7.0 cm3 / g. The invention is also a process in which the precipitated silica comprises aggregates of nanometric elementary particles, the average size of said aggregates being between 30 and 80 nm. The invention is also a process in which the precipitated silica has a content of free alkaline cation fixed on the surface of less than 5% by weight, and preferably less than 0.5% by weight. The invention is also a process in which a suspension of 5% by weight in water of the precipitated silica has a pH below 8.5, and preferably between 6.0 and 7.5. The invention is also an elastomeric composition comprising an elastomeric matrix and a solid filler of precipitated silica obtained by the process according to the invention dispersed in said matrix. The invention is also an elastomeric composition in which solid particles of precipitated silica obtained by the process according to the invention are dispersed in an elastomeric matrix. The invention is also a process for producing silica precipitated from an alkaline silicate in aqueous solution, said aqueous solution thus comprising a silicate ion and an alkaline cation, characterized in that it comprises the following steps: alkali of the silicate is converted to an aqueous alkali halide solution by displacing an alkaline salt of an intermediate acid less strongly than the aqueous hydrogen halide; The amorphous silica is formed by precipitation of the silicate ion by the intermediate acid or by the hydrogen halide solution; The alkaline halide solution separated from the amorphous silica is electrolyzed so as to obtain an aqueous solution of alkaline hydroxide, and free halogen and hydrogen, or free halogen hydride or in aqueous solution .

Advantageously, the alkali silicate is regenerated by contact with a siliceous mineral raw material and with the aqueous solution of alkaline hydroxide obtained

Advantageously, said aqueous solution of the halogen hydride obtained is used to acidify said silicate directly or indirectly.

Advantageously, the alkaline cation is chosen from at least one of lithium, sodium and potassium cations.

Advantageously, the hydrogen halide is hydrochloric acid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a block diagram of an example of a first version of the method according to the invention.

FIG. 2 represents a block diagram of an example of a second version of the process according to the invention producing as valorizable secondary product sodium phosphate.

Figure 3 shows a block diagram of a precipitated silica manufacturing process.

FIG. 4 represents photographs of aggregates of silica precipitated according to the invention examined under the transmission electron microscope.

FIG. 5 represents a photograph of a precipitated silica aggregate obtained by a method according to the state of the art (document US 4590052 A by Y. Chevallier and J. C. Morawski) examined under the transmission electron microscope.

FIG. 6 represents a block diagram of an example of a third version of the process according to the invention integrating an electrolysis of sodium chloride.

DETAILED DESCRIPTION OF THE INVENTION

Solids known as precipitated silicas known in the state of the art are known in the form of dispersible dry powders in elastomers or they serve in particular as reinforcing fillers.

It is also used for many other uses, such as abrasives (toothpastes) etc.

These solids are distinguished from colloidal silicas or soils or silica aqua soils that exist only in the form of homogeneous liquid dispersions on a macroscopic scale stabilized at basic pH.

A precipitated silica consists of elemental silica nanoparticles aggregated into individualized rigid clusters. The cohesion of these clusters is ensured by silica bridges connecting the elementary particles.

These rigid bunches have diameters greater than 50 nm. This diameter may be greater than 100 micrometers.

These rigid clusters are bulky and have a significant pore volume, generally greater than 0.7 cm3 / g to ensure dispersibility.

The volume of these clusters allows their fine dispersion practically to the colloidal state in the elastomeric mixtures before crosslinking or vulcanization, by very highly shearing mechanical mixers (sold for example by Brabender). The invention is a synthetic process. silica precipitated from an aqueous solution comprising a silicate ion and an alkaline cation, said process being characterized by comprising precipitating the silicate ion with a heavy organic acid having more than four carbon atoms.

It turns out that the precipitated silicas produced by such a process are particularly easy to disperse in the elastomers and that their inclusion in the elastomeric mixture is facilitated.

This unpredictable discovery is an essential aspect of the invention.

Advantageously, such a process comprises at least one of the following steps: a bottom of a tank containing an aqueous solution of alkali silicate and a heavy organic acid is intimately contacted in a chemical reactor; A flow of an aqueous solution of alkali silicate and a flow rate of a heavy organic acid are added simultaneously to the reaction medium.

Advantageously, said heavy organic acid comprises more than six carbon atoms and preferably more than eight carbon atoms.

Advantageously said heavy organic acid is little or not soluble in water.

By being slightly soluble in water it will be understood that its solubility in an aqueous medium is less than 1% by weight, more preferably less than 0.2% by weight and even more preferably less than 0.01% by weight.

Advantageously, the alkaline salt of said heavy organic acid is soluble in water.

Advantageously, said heavy organic acid is a liquid ion exchanger.

Advantageously, the heavy organic acid is recovered from the aqueous solution of its alkaline salt by displacing its alkaline salt with an acid so as to recover the free acid.

Advantageously, said recovery is carried out by crystallization, absorption, adsorption, ion exchange, filtration, membrane process, decantation or liquid-liquid extraction.

Advantageously, said recovery is carried out by reverse osmosis, ultrafiltration, microfiltration or nano filtration.

Advantageously, said recovery is carried out on the mother liquors of the precipitation of the silicate ion, after separating said waters from the precipitated silica by filtration and optionally washing the cake obtained.

Advantageously, the heavy organic acid is recovered from the aqueous solution of its alkaline salt by displacing it from its alkaline salt with an acid so as to recover the free acid in the mixture resulting from the synthesis containing the precipitated silica.

Advantageously this latter recovery is by decantation of the acid or liquid liquid extraction.

Advantageously, said heavy organic acid is looped in the process.

According to a particularly advantageous embodiment of the invention the heavy organic acid is a liquid cation exchanger.

Advantageously, the alkaline salt of the liquid cation exchanger is completely soluble in an aqueous alkaline medium.

Advantageously, said production involves the following steps: a suspension of amorphous silica nanoparticles in water is carried out by neutralization of an aqueous solution of the alkali silicate by the liquid cation exchanger. The nanoparticles of amorphous silica in water are coagulated or aggregated so as to lead to agglomerates and aggregates of microscopic silica nanoparticles under the effect of an increase in the concentration of alkaline salt of the liquid cation exchanger in water • Agglomerates and aggregates of silica nanoparticles are reinforced and stiffened by an additional silica deposit on their surface.

Advantageously, the synthesis of the precipitated silica comprises a displacement of the alkaline salt of the silicic acid constituting the silicate in aqueous solution by a liquid cation exchanger so as to reduce the pH of said solution and to cause the separation of a solid phase of amorphous silica distinct from the aqueous phase.

Advantageously, the precipitated silica is mainly composed of precipitated silica having a BET specific surface area of between 50 and 350 m 2 / g, a CTAB surface area of between 40 and 320 m 2 / g and a pore volume greater than 0.7 cm 3 / g. Advantageously, the dispersion of these agglomerates in an elastomeric matrix leads to a dispersion thereof greater than a Zvalue of 70 measured according to ASTM D7723-11.

Advantageously, the silicas obtained by the process according to the invention will make it possible to obtain a dispersion of the agglomerates in an elastomeric matrix greater than a Zvalue of 80 measured according to the ASTM D7723-11 standard, and preferably greater than a Zvalue of 90. .

Advantageously, the silicas obtained by the process according to the invention will make it possible to obtain a dispersion of the agglomerates in an elastomeric matrix greater than a Zvalue of 95 measured according to the ASTM D7723-11 standard, and preferably greater than a Zvalue of 98. .

A high Zvalue brings better mechanical characteristics and in particular a better resistance to abrasion of the vulcanizate.

Advantageously according to the invention the dispersion will be measured after ten minutes of mixing an elastomeric formulation in an internal mixer.

Advantageously according to the invention the dispersion will be measured by a dispergrader type apparatus marketed by the Alpha Technologies brand.

Advantageously according to the invention, the dispersion will be measured under the conditions described below in Example 4.

Advantageously, this precipitated silica has a water content measured by the loss on ignition in the air between room temperature and 105 ° C of between 2 and 25%.

Advantageously, this precipitated silica has a free alkaline cation content fixed on the silica surface of less than 5% by weight.

Advantageously, this precipitated silica has a content of free alkaline cation fixed on the surface of the silica of less than 5000 parts per million by weight (ppm), preferably less than 1000 ppm, and even more preferably less than 500 ppm.

As a result, the pH of the silica measured by a 5% suspension in water remains in an acceptable range for the drying and dispersing processes.

Advantageously, a suspension at 5% by weight in water of this precipitated silica has a pH of less than 8.5, and preferably between 6.0 and 7.5

Advantageously, this precipitated silica has the main impurity of sodium sulphate. Advantageously its content is less than 2.5% by weight, preferably less than 0.5% by weight, and even more preferably less than 0.2% by weight.

Advantageously, this precipitated silica will have a salified or free organic acid content of between 10 and 0.1%, and preferably between 5 and 0.5%.

Advantageously, for better dispersibility, the precipitated silica has a pore volume of between 0.7 cm 3 / g and 12.0 cm 3 / g, and even more advantageously between 1.4 and 7.0 cm 3 / g. In general, the larger the surface area of the precipitated silica, the higher the pore volume will tend to be.

A siliceous filler dispersed in an elastomeric mixture before crosslinking strongly adsorbs the various ingredients of an elastomeric mixture. In order to be able to crosslink it, ingredients such as polyethyleneglycol which block this surface are added to the mixture. These products are expensive and must be weighed against the reinforcing power.

The optimal compromise for using the precipitated silica as a reinforcing filler leads to the aforementioned specific surface range, BET specific surface area of the silica of between 50 and 350 m 2 / g, and CTAB surface area of between 40 and 320 m 2 / g .

Advantageously, the BET specific surface area of the precipitated silica will be between 50 and 300 m 2 / g and the CTAB surface area will be between 40 and 280 m 2 / g, and preferably the BET specific surface area of the silica will be between 70 and 250 m 2. / g and the CTAB surface will be between 40 and 240 m2 / g to have optimum performance as reinforcing filler in particular.

Even more advantageously, the BET specific surface area of the precipitated silica will be between 50 and 200 m 2 / g and the CTAB surface area will be between 40 and 190 m 2 / g. Most precipitated silicas on the market intended for use as filler in elastomers have surfaces of the order of 70 to 175 m2 / g. A conventional range further comprises a surface area silica of about 125 m 2 / g.

Advantageously, the microporosity of the precipitated silica will be low, and the CTAB surface will be close to the BET surface measured with nitrogen.

A precipitated silica dispersion in an elastomer is characterized by the average size of the resulting aggregates after the dispersion operation.

Advantageously, the precipitated silicas obtained by the process according to the invention will make it possible to obtain average sizes of aggregates between 30 nm and 100 nm, and more advantageously between 30 and 80 nm.

The average size of the aggregates will be measured by XDC (X Ray Disk Centrifugation).

In general, the alkali silicate solutions are ionized totally or partially in solvated cations and anions.

Advantageously, the aqueous solution of said alkali silicate used as synthesis intermediate or as raw material in the process has a concentration of said alkali silicate greater than 1 gram per liter, preferably greater than 3 gram per liter, still more preferably greater than 10 gram per liter. . Indeed lower concentrations would make the process uneconomical, from the point of view of the isolation of the final oxide or hydroxide for its use as a finished product or as a synthesis intermediate, both in proportional costs and in manufacturing investments due to concentration costs and the volume of installations.

Advantageously, the precipitated silica is obtained in the solid state as a commercial product.

Advantageously, the process according to the invention comprises a step of extracting the alkaline cation or its salified product by the liquid cation exchanger by a liquid cation exchanger.

Advantageously, the liquid liquid extraction step of the alkaline salt of the liquid cation exchanger will be carried out by contacting an aqueous reaction medium containing the precipitated silica and an alkaline salt of the liquid cation exchanger with a solvent. of this alkaline salt.

Advantageously this liquid liquid extraction step will be performed at the end of the synthesis process of the precipitated silica.

Advantageously, the extraction solvent of the salified liquid cation exchanger will be the liquid cation exchanger itself.

Advantageously, the step of extracting the alkaline cation by the liquid cation exchanger is conducted so as to obtain the precipitated silica in the form of a solid in aqueous suspension.

A liquid cation exchanger is an organic acid for extracting from an aqueous phase, by liquid-liquid extraction, metal cations in solution under specific operating conditions.

These operating conditions may be chosen pH or temperature conditions, or the presence of a third body as an organic solvent.

According to the invention, the liquid cation exchanger may advantageously be totally soluble in the aqueous phase under certain conditions and substantially immiscible in others.

In particular, an organic acid may be totally soluble in the aqueous phase in the form of its alkaline salt at basic pH and substantially immiscible in the same aqueous phase at a more acidic pH.

This will advantageously be the case of a pure used acid without additional solvent.

It may constitute a silicate neutralization acid at basic pH in a monophasic liquid medium.

It may constitute an extractant and therefore a liquid cation exchanger pH more acidic.

It is particularly advantageous to use such a scheme for its simplicity.

Advantageously, it will be considered that a liquid cation exchanger may consist of an organic acid with a number of carbons greater than four, preferably greater than 6, and even more preferably greater than 8. The extraction step can be carried out directly to the solution of the alkali silicate, so as to obtain a suspension of precipitated silica separated from a solution of the alkaline cation in the liquid cation exchanger.

In the case where the extraction step is carried out directly on the solution of the alkali silicate, the conjugated acid constituted by the precipitated or free silica must have a higher pKa than that of the liquid cation exchanger.

Advantageously, this pKa is greater by at least one unit and more advantageously by at least three units higher than the pKa of the liquid cation exchanger.

Advantageously, the liquid cation exchanger is regenerated in the process by counterextracting or regenerating the alkaline cation with a more potent acid than the liquid cation exchanger. Advantageously, this acid is in aqueous solution and makes it possible to obtain a solution of its alkaline salt in aqueous solution. Advantageously, this regeneration acid has a pKa lower than that of the liquid cation exchanger. Advantageously, this pKa is less than at least one unit and more preferably at least three units lower than the pKa of the liquid cation exchanger.

Advantageously, the liquid cation exchanger turns in a loop in the process between the regeneration and the precipitation. The liquid cation exchanger used for the present invention will be any organic substance that is liquid or in organic solution having a cation exchangeable exchangeable proton, and will be more advantageously included in the groups of phosphoric acids, carboxylic acids, and sulphonic acids.

These products will be used pure or in solution in an organic solvent or a mixture of organic solvents.

Advantageously they will be used pure in the liquid state.

Among the acids that can be used, particular mention will be made of: organic esters of mono or bis-substituted phosphoric acid such as di (2-ethylhexyl) phosphoric acid, linear or branched long-chain carboxylic acids such as saturated fatty acids or unsaturated C6 to C18 such as octanoic acid, nonanoic acid, decanoic acid, lauric acid, stearic acid, oleic acid, 2-ethylhexanoic acid, so-called oxo acids, fatty acids substituted with fluorine, chlorine or bromine radicals such as perbromooctanoic acid. • Organic esters of sulfuric acid such as dodecyl sulfate. • aromatic sulfonic acids such as dodecylbenzene sulfonate.

It should be noted that these molecules generally have a marked surfactant effect.

Of the alkaline cations of these salts, lithium, sodium and potassium are preferably listed in order of preference. Their extractibility by the liquid cation exchanger is generally increasing in this direction.

Rubidium and cesium cations can also be used.

Among the regeneration acids that may be used, the most common mineral acids, such as hydrofluoric, hydrochloric, hydrobromic, hydroiodic, hydrochloric, perchloric, sulfuric, nitric, phosphoric and carbonic acids, will be noted. It is also possible to use carboxylic or carbonic acids, sulphonic or alkylphosphoric acids, or any acid whose alkaline salt is recoverable.

Phosphoric, sulfuric, carbonic or hydrochloric acids are preferably chosen.

A process according to the invention advantageously comprises at least one step of extracting the alkaline cation by a liquid cation exchanger.

Advantageously, it comprises a second regeneration step of the liquid cation exchanger by performing a liquid-liquid counter-extraction of the alkaline cation with a more potent acid than the liquid cation exchanger, so as to form an alkaline salt of said acid. The step of extracting the alkaline cation is advantageously in a first liquid-liquid extraction step of the alkaline cation of its aqueous solution, the liquid cation exchanger displacing the silica of its alkali silicate.

According to a preferred embodiment of the invention, the alkaline salt of the liquid cation exchanger is advantageously collected in the form of its solution in an excess of liquid cation exchanger. The pure liquid cation exchanger itself serves as a solvent for extracting its alkaline salt.

Particularly favorable partition coefficients are thus obtained.

The partition coefficients obtained are easily greater than 2. They can be greater than 5 or even 10.

Advantageously, little liquid cation exchangers will be chosen which are either little or very little used in water in order to improve and make easier the recovery of the salt from these and the acid in use.

This water solubility in the process conditions will advantageously be less than 2000 parts per million by weight (ppm), more preferably less than 200 ppm, and still more preferably less than 20 ppm.

This operation is advantageously in a liquid iiquid extraction zone or in one or more decanter meiangers.

The liquid liquid extracting coionne should be able to treat precipitated aqueous suspensions of silica. We will opt for example for a coionne agitated (type Kuhni or RDC (Rotating Disk Contact en angiais). We can also choose a pulsed colony.

Without departing from the scope of the present invention, the salt of the liquid cation exchanger can be extracted with a solvent or a mixture of extracting solvents different from the pure liquid cation exchanger. In particular, it may be a mixture of the liquid cation exchanger and another solvent or mixture of solvents.

This solvent may be selected from the group consisting of esters, ethers and ketones and preferably aliphatic and aromatic derivatives thereof. With regard to the aliphatic esters, formates, acetates, propionates, butyrates, oxalates, phosphates and lactates (cyclohexyl acetate, furfuryl acetate, amyl acetate), aliphatic ketones can be used in particular. especially methyldiethyl ketone, methyl isobutyl ketone, methyi cyclohexanone, dimethyl cyciohexanone, aico (iso-butanol, pentanol, octanol, dodecanol, methylene cyanohexanol, 2-ethyl hexanol), carboxylic acids (octanoic acid, naphthenic acid). Other organic liquids can be used, such as tributyl phosphate, trioctyl phosphate, trioctylphosphine oxide, phosphonic acid esters, dimethyl phthalate, diethyl oxalate, aryl sulfonic acids, hydroxyoximes, and the like. derivatives of oximes, beta-diketones, alkylaryl sulfonamides, primary, secondary, tertiary, quaternary amines, etc .; Other types of useful solvents include aromatic solvents or benzene hydrocarbons such as xylene and toluene. The halogenated and especially chiorinated derivatives of these solvents can also be used for example chlorobenzene. In addition, another type of useful solvents is halogenated aliphatic carbides or halogenated hydrocarbons. It is possible to mention as potential candidates the halogenated ethylene carbides. Particularly in this case, mention may be made of dichlorethylene, trichlorethylene and tetrachlorethylene.

In particular, non-linear or branched aliphatic hydrocarbons will be used as petroleum fractions of the gasoline, gasoline, gasoline or light gasoline type. etc. ... or hydrocarbons such as hexanes, heptane, octane, decane, dodecanes, and their heavier counterparts.

Advantageously, solvents will be chosen which are not very or not flammable. These can be chlorinated solvents. These can be solvents whose flash point is sufficiently high as gas oil or kerosene.

Advantageously, the flash point of the solvent will be higher than the highest temperature prevailing in the process. This temperature may be a reaction temperature or a wall temperature in contact with the solvent or likely to be.

Advantageously, the flash point of the solvent will be greater than 110 ° C, preferably greater than 150 ° C, even more preferably greater than 170 ° C.

All the solvents described above can of course be used alone or in combination.

Advantageously, the partition coefficient K of the alkaline cation between the aqueous phase and the organic solvent of the liquid cation exchanger or its salt will be greater than 0.01, in favor of the organic phase, more preferably greater than 0.1, and still more preferably greater than 1.0 in favor of the latter. ρζ- Qchange Qa

The average molar concentration concentration of the cation in the liquid cation exchange is the molar volume concentration of the cation in the aqueous alkali salt solution of the oxide in question.

Advantageously, the volume ratio R of phase of the aqueous phase on the liquid cation exchanger phase brought into contact in the process will be greater than 1, preferably greater than 3, and even more preferably greater than 10.

Advantageously, the product R * K measured under the conditions of the most unfavorable concentrations and flow rates occurring in the process will be greater than 1, advantageously greater than 2, and more preferably greater than 4.

Indeed, it is known that during a multi-stage liquid liquid extraction, the partition coefficients and the volume flow rates vary according to the point considered along the extraction path.

Advantageously, the traces of liquid cation exchanger and its alkaline salt still present in the raffinate after extraction are themselves extracted, collected and recycled by an organic solvent acting by liquid-liquid extraction on said raffinate.

This process may include displacing the cation exchange salt present in the trace mother liquors with a relatively stronger acid at an adequate pH.

In particular sulfuric acid can be used at this stage, leaving only traces of sulphates in the final product. These as sodium sulphate are impurities commonly accepted and known by the user, as a pneumatician.

The concentration of liquid cation exchanger in the final product can thus be limited to less than 1000 parts per million by weight (ppm), or even less than 100 ppm, or even less than 10 ppm.

The second step or step of regeneration of the liquid cation exchanger is advantageously by liquid-liquid extraction of the cation present in the organic extract from the first step by contact with an aqueous solution of the regeneration acid. This operation is advantageously in a liquid liquid extraction column such as a plate column, or in one or more settling mixers. It can also be done in a centrifugal decanter. The alkaline salt of the regeneration acid can be obtained directly in concentrated aqueous solution or even in the crystallized state.

The alkaline salt of the regeneration acid can at this point simply be upgraded after a possible concentration in a single or multiple concentrator effect that may involve a mechanical vapor recompression, and / or a crystallization step, filtration and drying. This can in particular be the case of a phosphate or a sodium sulphate.

It is possible to include in the process a third dissociation step of the alkaline salt finally obtained at the end of the regeneration step.

This step may in particular consist of either: • an electrolysis of the aqueous solution of this salt so as to obtain an alkaline hydroxide solution and optionally the regeneration acid. In this case, the regeneration acid is advantageously hydrochloric acid. The alkaline solution can be used and recycled in the process to effect the etching of an ore and to obtain an alkaline silicate, • an isolation of the formed salt and its recycling in an attack step of a mineral such as an alkaline melting at high temperature to obtain the alkali silicate.

Advantageously, this third step comprises the following steps: the alkaline cation of the silicate is converted into an aqueous alkaline halide solution by displacing an alkaline salt of an intermediate acid that is less strong than the aqueous hydrogen halide; The amorphous silica is formed by precipitation of the silicate ion by the intermediate acid or by the hydrogen halide solution; The alkaline halide solution separated from the amorphous silica is electrolyzed so as to obtain an aqueous solution of alkaline hydroxide, and free halogen and hydrogen, or free halogen hydride or in aqueous solution

This displacement of an alkaline salt of a heavy organic acid that is less intense than the aqueous hydrogen halide is advantageously carried out on a solution of the heavy organic acid salt obtained at the end of the silica precipitation step. .

Advantageously, this solution consists of an organic solution of this salt obtained by liquid liquid extraction thereof in the mother liquors of the precipitation.

Advantageously, the alkali silicate is regenerated by contact with a siliceous mineral raw material and with the aqueous solution of alkaline hydroxide obtained

Advantageously, said aqueous halogen hydride solution obtained is used to indirectly acidify said silicate by displacing an alkaline salt of a lower heavy organic precipitation acid than the aqueous hydrogen halide.

Advantageously, the alkaline cation is chosen from at least one of lithium, sodium and potassium cations.

Advantageously, the halogen is chlorine.

Processes are thus obtained using only well-known, inexpensive operations such as liquid extraction, without expensive intermediates. Any type of acid and alkaline cation can be valorized, independently of the acid used for the precipitation or displacement of the silica without any pollution thereof. This advantageously allows the use of regeneration acids otherwise prohibited for their side effects, such as hydrochloric acid whose corrosion effects in the final oxide are well known and prohibit its use in the tire in contact with the metal carcasses.

This also makes it possible to obtain intermediates precipitated silica suspensions easier to isolate by filtration because no longer requiring washing, and final products purer, very pure or extremely pure.

The residual alkali salt concentration may preferably be less than 0.5% by weight in the final product, advantageously less than 0.2%, or even less than 0.05%.

This also eliminates the release of alkaline salt solutions into the environment, and is therefore a green or ecological process.

The precipitation process of the silica is advantageously carried out in several successive stages.

In a first step, a suspension of silica nanoparticles, or sol, is produced by neutralization of an alkali silicate solution by the liquid cation exchanger.

The nanoparticles are then coagulated or aggregated with stirring, by increasing the ionic strength of the solution under the effect of an increase in the concentration of the alkali salt solution of the liquid cation exchanger, resulting in flocs or clusters or clusters of microscopic silica nanoparticles precursors of the final clusters of precipitated silica.

These aggregates are then reinforced and stiffened by additional deposition of silica on their surface, particularly at the contact points between nanoparticles due to the nanoscale negative radius of curvature occurring at this junction point (a phenomenon similar to Ostwald slip).

This stiffening allows the solid to withstand subsequent filtration and washing operations, and especially the drying step in which the capillary tensions associated with the evaporation of water subject the floc, aggregate or cluster to the forces of considerable shrinkage likely to cause its implosion and compacting. A compacted flock would be indispersible in an elastomer or it would cause the appearance of hard points sources of unacceptable mechanical weakness.

Advantageously, the amount of silica deposited during the reinforcement represents more than 20% of the weight of the final material, and still more advantageously more than 50% of the weight of the final material.

The material is then neutralized, filtered, washed and dried.

Figure 3 schematizes these different operations.

More particularly, the reaction stage of a process according to the invention will advantageously be carried out as follows.

A diluted sodium silicate stock having 1 to 15% solids, and more preferably 2 to 7% solids is heated to the reaction temperature. This is advantageously greater than 60 ° C. and advantageously between 75 and 95 ° C. At this bottom of the tank is gradually added a flow rate of liquid cation exchanger. This addition typically lasts between 30 minutes and 2 hours 30 minutes, for example, and can be interrupted by breaks and matures.

During this stage a soil is formed and the silica precipitate consisting of aggregates or clusters of soil particles appears. At the end of the addition, the sodium was substantially neutralized by the liquid cation exchanger.

The pH is adjusted for example between 7.5 and 9.5. In this stage, the liquid cation exchanger is advantageously used pure undiluted so as to dissolve completely in the aqueous medium in the form of its sodium salt.

This avoids the formation of a biphasic liquid liquid medium.

In the medium obtained, a dilute sodium silicate flow rate and a pure liquid cation exchanger flow rate are added simultaneously, generally at constant pH, slowly enough so that the silicic acid produced is deposited on the surface of the aggregates present in the aqueous medium of the precipitation reactor. At the end of this last step, the precipitated silica is formed.

Variable specific surfaces of the final product can be obtained by playing in particular on the initial dilution of the sodium silicate foot.

Greater dilution increases the surface area.

In the case of such a process, a liquid liquid extraction of the sodium salt of the liquid cation exchanger takes place after the reaction step described above.

According to another version of the process, the liquid liquid extraction step of the salified liquid cation exchanger takes place partially or totally during the reaction step of synthesis of the precipitated silica.

This liquid liquid extraction step can be carried out in various ways without departing from the scope of the present invention.

For example: a / it will be advantageously put in contact in the reactor by simultaneously feeding the silicate solution and the liquid cation exchanger solution in the presence of an extraction solvent of the salified liquid cation exchanger, by cointroduction in the reactor or in an external loop. This loop may comprise a settling tank for stopping the organic phase before introduction into the reactor. b / it may advantageously from a base stock containing an alkali silicate and put it in contact with the liquid cation exchange solution in the presence of an extraction solvent of the salified liquid cation exchanger. This contacting can be done in the reactor or loop external to the reactor. The liquid phases are separated sequentially batchwise, semi-batchwise or continuously. This continuous separation can take place by overflow or in an external loop on a mixer settler or decanter alone. c / it will be possible to realize a combination of these operating modes a and b

The contacting processes described by one of the procedures a, b and c described above may advantageously take place: during the step of synthesis of the soil so as to control the pH and the ionic strength of the reaction medium before or until aggregation or precipitation of the silica. During the reinforcing or stiffening step of the aggregates.

FIG. 1 represents a block diagram of an example of a first version of the method according to the invention. A flow of siliceous sand 1 is brought into contact (A) with a concentrated solution of sodium hydroxide 2 so as to form sodium silicate in aqueous solution 3.

The silicate, after any dilution, is contacted (B) with a heavy organic acid such as 2-ethyl hexanoic acid 4, so as to precipitate the silica. The sodium salt of the organic acid goes into solution. This solution is brought into contact, after filtration and washing (C) of the precipitated silica 9, of sulfuric acid in solution 7 (Step D). In this way, the organic phase 4 composed of the insoluble heavy organic acid separated by decantation of the mother liquors, which is purified and regenerated, is reworked in step (B) and an aqueous solution of sodium sulphate. Advantageously, the sillice will be dried in a flash dryer as an atomizer with very short residence times. Indeed, the salt of the organic carboxylic acid has a tendency to dissociate volatile free acid and surface silanols of silica salified with sodium. These surface silicate ions produce an increase in the pH of an aqueous suspension of the final silica. Alternatively an excess of free organic acid will be added in order to saturate the drying gas and prevent this drift.

FIG. 2 represents a block diagram of an example of a second version of the method according to the invention.

A flow of siliceous sand 11 and sodium carbonate 12 are brought into contact (F) carried at high temperature and dissolved in water so as to form sodium silicate in aqueous solution 13.

The silicate, after any dilution, is brought into contact (G) with a liquid cation exchanger 14 such as di-2-ethylhexyl phosphoric acid, or 2-ethyl hexanoic acid, in large excess. The sodium salt of the liquid cation exchanger passes into organic solution and is separated in the form of a liquid organic solution 15. This solution is brought into contact (E) with phosphoric acid in solution 11 so as to form the phase organic composition composed of the purified and regenerated liquid cation exchanger which returns to step (G), and an aqueous solution of concentrated sodium phosphate which can be used as a chemical intermediate. The final silica suspension 18 optionally filtered and washed 19 (step H) is substantially free of its sodium salt.

FIG. 6 represents a block diagram of an example of a third version of the method according to the invention. A flow of siliceous sand 1 is brought into contact (A) with a concentrated solution of sodium hydroxide 2 so as to form sodium silicate in aqueous solution 3.

The silicate, after any dilution, is contacted (B) with a liquid ion exchanger 4 such as di-2-ethylhexyl phosphoric acid, or 2-ethyl hexanoic acid. The sodium salt of the liquid ion exchanger finally goes into organic solution and is separated in the form of a liquid organic solution 5. This solution is brought into contact (C) with hydrochloric acid in solution 7 so to form the organic phase 4 composed of the purified and regenerated liquid ion exchanger which returns to step (B), and an aqueous solution of concentrated sodium chloride 6 containing 15 to 25% of dry extract which starts in step ( D). Step (D) consists of electrolyzing the solution 6 and regenerating a sodium hydroxide solution 2 containing 10 to 20% by weight of dry extract which starts again in stage (A). Hydrochloric acid 7 produced by electrolysis (directly in the membrane process by introducing hydrogen gas at the chlorine release cell, or indirectly by the combustion of a mixture of chlorine and hydrogen and absorption of the acid formed in an aqueous phase, such as the weak sodium chloride solution containing 5 to 15% of dry extract resulting from the electrolysis) goes back to the stage of regeneration of the ionic ion exchanger (C ).

Advantageously to protect the electrolysis process and to avoid the formation of organic impurities which could accumulate in the process loop, deep elimination of the liquid ion exchanger contained in the sodium chloride solution will be carried out 6 before the next step D and after step C.

This purification can be done by liquid liquid extraction with an organic solvent such as an insoluble hydrocarbon fraction. The liquid ion exchanger is recovered by washing the extract with sodium hydroxide and reinjected into the process.

It may also be done for example by passing the brine 6 on a weak or strong anion exchange resin and fixing the liquid ion exchanger on it. The resin is regenerated after use and the liquid ion exchanger is recovered and recycled.

It can also be done for example by passing brine 6 on an adsorbent such as activated carbon and absorption of the liquid ion exchanger on it. The coal is regenerated after use with water vapor and the liquid ion exchanger is recovered and recycled. In general, it will be preferred to operate the purification process on an acidified brine 6 so as to move the entire liquid ion exchanger of its alkaline salt. Step (E) is a step of purifying the silica solution or suspension 8 from step (B). It may for example be constituted by a liquid extraction liquid at pH 2 by petrol. The liquid ion exchanger is recovered by washing the petroleum spirit extract with sodium hydroxide and reinjected into the process.

The final solution or suspension 9 is substantially free of sodium salt.

Example 1

Precipitation is carried out in a stainless steel reactor with a volume of 1.0 liter, having a stirring system consisting of a so-called three-bladed turbine of 60 mm diameter and having a double envelope for temperature control. 305.5 milliliters of distilled water are then introduced under stirring at room temperature, followed by 50 milliliters of aqueous sodium silicate solution with a weight ratio of SiO 2 / Na 2 O of 3.25 and containing 370 g of SiO 2 per liter.

The resulting mixture is heated to 90 ° C in about 30 minutes. The precipitation reaction of the silica is then carried out, the temperature being maintained at 90 ° C in about 30 minutes, and the stirring speed being set at 350 rpm.

0.358 ml / min of 2-ethyl hexanoic acid is added to the stirred solution by a metering pump. After 37 minutes of reaction, the precipitate is well formed. The addition of acid is stopped and a ripening step is conducted for 15 minutes. After this period of time, the addition of the acid is resumed at the same flow rate for 37 minutes. The final pH is 8.33. After this period, ie 89 minutes after the beginning of the reaction, a simultaneous addition of 2-ethyl hexanoic acid at a flow rate of 0.176 ml / min and a freshly prepared aqueous solution of sodium silicate is carried out. sodium with a weight ratio of SiO 2 / Na 2 O of 3.25 and containing 55 g of SiO 2 per liter, this solution being introduced at a flow rate of 2.05 ml per minute. Simultaneous introduction of acid and silicate solution is continued for 40 minutes, and the pH of the reaction medium is 8.3 ± 0.2 at 90 ° C.

After this period of 40 minutes for the simultaneous addition of acid and silicate, the addition of silicate is stopped, and the addition of acid is continued until a pH of 6.5 is reached.

The resulting slurry was transferred to a 1L jacketed thermostated glass reactor equipped with Mixel 3-bladed propeller stirring and a bottom valve, and maintained at 90 ° C. 250 milliliter of ethyl 2-hexanoic acid at 90 ° C are added under just sufficient stirring to carry out the homogeneous suspension of the two liquid phases. After stirring for 5 minutes, the two phases are left to decant for ten minutes, and the lower aqueous phase is withdrawn. The organic phase is then withdrawn in turn.

The aqueous suspension obtained is reintroduced into the reactor and reextracted with 250 milliliters of pure 2-ethylhexanoic acid as previously. The extraction operation is performed three times.

The residual silica suspension is then adjusted to pH 3.5 with sulfuric acid at 70 g / L pure acid in distilled water in the 1 liter reactor. 250 milliliters of octane are added with stirring so as to extract the 2-ethyl hexanoic acid residues in solution and in suspension. The mixture is decanted and separated.

The residual silica suspension is filtered. The wet cake is dried. The physicochemical characteristics of the silica obtained are as follows:

CTAB surface 139 m2 / g; BET surface 143 m2 / g;

FIG. 4 represents a photograph of the precipitated silica aggregate obtained by this method examined under the transmission electron microscope.

It can be seen that the agglomerates have a much more open structure than that obtained by a conventional method (FIG. 5).

This helps to understand the cause of their higher dispersibility in elastomers.

The volume of 2-ethyl hexanoic acid resulting from the extraction is brought into contact with sulfuric acid at 20% by weight in distilled water while stirring in the 1-liter reactor until a pH of 2.0 is obtained. in the aqueous phase. The aqueous phase of brine is withdrawn and separated from the regenerated organic phase which can return to the process and serve for a new batch.

The organic octane phase containing traces of 2-ethyl hexanoic acid is identically regenerated by contacting with stirring an aqueous sodium hydroxide solution so as to recover ethyl hexanoic acid in the form of an aqueous solution of its sodium salt. This can then be acidified to decant the pure acid.

Example 2

Precipitation is carried out in a stainless steel reactor with a volume of 1.0 liter, having a stirring system consisting of a so-called three-bladed turbine of 60 mm diameter and having a double envelope for temperature control. 305.5 milliliters of distilled water are then introduced under stirring at room temperature, followed by 50 milliliters of aqueous sodium silicate solution with a weight ratio of SiO 2 / Na 2 O of 3.25 and containing 370 g of SiO 2 per liter.

The resulting mixture is heated to 90 ° C in about 30 minutes. The precipitation reaction of the silica is then carried out, the temperature being maintained at 90 ° C in about 30 minutes, and the stirring speed being set at 350 rpm.

0.394 ml / min of the nonanoic or pelargonic acid is added to the solution with stirring by a metering pump. After 37 minutes of reaction, the precipitate is well formed. The addition of acid is stopped and a ripening step is conducted for 15 minutes. After this period of time, the addition of the acid is resumed at the same flow rate for 37 minutes. The final Ph is 8.33. After this period, ie 89 minutes after the beginning of the reaction, a simultaneous addition of nonanoic acid at a flow rate of 0.194 ml / min and a freshly prepared aqueous solution of sodium silicate with a ratio by weight of SiO 2 / Na 2 O of 3.25 and containing 55 g of SiO 2 per liter, this solution being introduced with a flow rate of 2.05 ml per minute. Simultaneous introduction of acid and silicate solution is continued for 40 minutes, and the pH of the reaction medium is 8.3 ± 0.2 at 90 ° C.

After this period of 40 minutes for the simultaneous addition of acid and silicate, the addition of silicate is stopped, and the addition of acid is continued until a pH of 6.5 is reached.

The resulting slurry was transferred to a 1L jacketed thermostated glass reactor equipped with Mixel 3-blade propeller stirring and a bottom valve, and maintained at 90 ° C. 250 milliliters of nonanoic acid at 90 ° C. are added with stirring just sufficient to carry out the homogeneous suspension of the two liquid phases. After stirring for 5 minutes, the two phases are left to decant for ten minutes, and the lower aqueous phase is withdrawn. The organic phase is then withdrawn in turn.

The aqueous suspension obtained is reintroduced into the reactor and reextracted with 250 milliliters of pure nonanoic acid as previously. The extraction operation is performed three times.

The residual silica suspension is then adjusted to pH 3.5 with sulfuric acid at 70 g / L pure acid in distilled water in the 1 liter reactor. 250 milliliters of octane are added with stirring so as to extract the nonanoic acid residues in solution and in suspension. The mixture is decanted and separated.

The residual silica suspension is filtered. The wet cake is dried. The physicochemical characteristics of the silica obtained are as follows:

CTAB surface area 142 m2 / g; BEI area 148 m2 / g;

The volume of nonanoic acid resulting from the extraction is brought into contact with sulfuric acid at 20% by weight in distilled water while stirring in the 1 liter reactor until a pH of 2.0 is obtained in the aqueous phase. . The aqueous phase of brine is withdrawn and separated from the regenerated organic phase which can return to the process and serve for a new batch.

The organic octane phase containing traces of nonanoic acid is identically regenerated by contacting with stirring an aqueous sodium hydroxide solution so as to recover the nonanoic acid in the form of an aqueous solution of its sodium salt. This can then be acidified to decant the pure acid.

Example 3

Precipitation is carried out in a stainless steel reactor with a volume of 1.0 liter, having a stirring system consisting of a so-called three-bladed turbine of 60 mm diameter and having a double envelope for temperature control. 305.5 milliliters of distilled water and then 25 milliliters of aqueous sodium silicate solution with a weight ratio of SiO 2 / Na 2 O of 3.25 and containing 370 g of SiO 2 per liter are introduced with stirring at ambient temperature.

The resulting mixture is heated to 90 ° C in about 30 minutes. The precipitation reaction of the silica is then carried out, the temperature being maintained at 90 ° C in about 30 minutes, and the stirring speed being set at 350 rpm.

0.179 ml / min of 2-ethyl hexanoic acid is added to the solution with stirring by a metering pump. After 47 minutes of reaction, the precipitate is well formed. The addition of acid is stopped and a ripening step is conducted for 15 minutes. After this period of time, the addition of the acid is resumed at the same flow rate for 27 minutes. The final pH is 8.02. After this period, that is to say 89 minutes after the beginning of the reaction, a simultaneous addition of 2-ethyl hexanoic acid at a rate of 0.088 ml / min and a freshly prepared aqueous solution of sodium silicate is carried out. sodium with a weight ratio of SiO 2 / Na 2 O of 3.25 and containing 55 g of SiO 2 per liter, this solution being introduced at a flow rate of 1.02 ml per minute. Simultaneous introduction of acid and silicate solution is continued for 40 minutes, and the pH of the reaction medium is 7.9 ± 0.2 at 90 ° C.

After this period of 40 minutes for the simultaneous addition of acid and silicate, the addition of silicate is stopped, and the addition of acid is continued until a pH of 6.5 is reached.

The resulting slurry was transferred to a 1L jacketed thermostated glass reactor equipped with Mixel 3-bladed propeller stirring and a bottom valve, and maintained at 90 ° C. 250 milliliters of ethyl 2-hexanoic acid at 90 ° C. are added with stirring just sufficient to carry out the homogeneous suspension of the two liquid phases. After stirring for 5 minutes, the two phases are left to decant for ten minutes, and the lower aqueous phase is withdrawn. The organic phase is then withdrawn in turn.

The aqueous suspension obtained is reintroduced into the reactor and reextracted with 250 milliliters of pure 2-ethylhexanoic acid as previously. The extraction operation is performed three times.

The residual silica suspension is then adjusted to pH 3.5 with sulfuric acid at 70 g / L pure acid in distilled water in the 1 liter reactor. 250 milliliters of octane are added with stirring so as to extract the 2-ethyl hexanoic acid residues in solution and in suspension. The mixture is decanted and separated.

The residual silica suspension is filtered. The wet cake is dried. The physicochemical characteristics of the silica obtained are as follows:

CTAB surface 218 m2 / g; BEI surface area 225 m2 / g;

The volume of 2-ethyl hexanoic acid resulting from the extraction is brought into contact with sulfuric acid at 20% by weight in distilled water while stirring in the 1-liter reactor until a pH of 2.0 is obtained. in the aqueous phase. The aqueous phase of brine is withdrawn and separated from the regenerated organic phase which can return to the process and serve for a new batch.

The organic octane phase containing traces of 2-ethyl hexanoic acid is identically regenerated by contacting with stirring an aqueous sodium hydroxide solution so as to recover ethyl hexanoic acid in the form of an aqueous solution of its sodium salt. This can then be acidified to decant the pure acid.

Example 4

This example is intended to illustrate the application to the reinforcement of elastomers.

A precipitated silica with a BE.sub.2 surface reference of 155 m2 / g (for example Zeosil silica 1165 MP Solvay) is used. The above products are used in a mixture having the formulation below.

Parts by weight Rubber SBR 1509 100,00 Silica 50,00

Polyethylene glycol MW = 4000 3.00 Stearic acid 3.00 Zinc oxide 3.00

Benzothiazyl disulfide accelerator VULCAFOR MBTSe 0.75 Accelerator diorthotolyl guanidine VULCAFOR 1.50 Antioxygen (PERMANAX ODe) 2.00 Sulfur 2.25

The mixing is carried out by an internal mixer with a mixing time of ten minutes. The temperature at the end of the mixing is 160 ° C.

The dispersion of the agglomerates measured on the raw mixture at the dispergrader (Alpha Technologies) and calculated according to the D7723-11 standard is 75% (Zvalue 75).

The following rheological properties are then appreciated: 1 - Mechanical properties

MONSANTO Rheometer (ASTM D 2084): Measurement of the rheological properties of the mixture during vulcanization. CM - Maximum torque after complete crosslinking.

Cm = Minimum torque: Consistency of the unvulcanized mixture ("raw mix") at the temperature of the AC test (E Couples): In relation to the degree of crosslinking. 2 - Static properties

They are measured according to the standards

a) ASTM D 2240-75 Shore A Hardness b) ASTM D 1054-55 Rebound 3 - Dynamic Properties ASTM D 623-67 Goodrich Flexometer.

This apparatus makes it possible to subject a vulcanizer to alternating deformations and to determine its resistance to fatigue and internal heating. a) AT: A between the temperature at the heart of the test tube c and the temperature of the chamber (internal heating). b) Test conditions load 106 N, deflection 22.2 Z, frequency 21.4 Hz chamber temperature = 500 C.

The results are summarized below

Apparent density of the product: 0,25

Mechanical properties:

Torque: 64 Shore Hardness A: 68 Bounce Z: 25

Rubber heating #Tc OC: 109 Example 5

This example is intended to illustrate the application to the strengthening of elastomers compared to the previous test.

A precipitated silica made according to Example 1 of BET surface area of 142 m2 / is prepared by the process according to the invention. This product is used in a mixture having the formulation below.

Parts by weight Rubber SBR 1509 100,00 Silica 50,00

Polyethylene glycol MW = 4000 3.00 Stearic acid 3.00 Zinc oxide 3.00

Benzothiazyl disulfide accelerator VULCAFOR MBTSe 0.75 Accelerator diorthotolyl guanidine VULCAFOR 1.50 Antioxygen (PERMANAX ODe) 2.00 Sulfur 2.25

The mixing is carried out by an internal mixer with a mixing time of ten minutes. The temperature at the end of the mixing is 155 ° C.

The dispersion of the agglomerates measured on the raw mixture with the dispergrader (Alpha Technologies) and calculated according to the D7723-11 standard is 85% (Zvalue of 85).

The following rheological properties are then appreciated: 1 - Mechanical properties

MONSANTO Rheometer (ASTM D 2084): Measurement of rheological properties of the mixture during vulcanization. CM - Maximal torque after complete crosslinking,

Cm = Minimum torque: Consistency of the unvulcanized mixture ("raw mix") at the temperature of the AC test (E Couples): In relation to the degree of crosslinking. 2 - Static properties

They are measured according to the standards

a) ASTM D 2240-75 Shore A Hardness b) ASTM D 1054-55 Rebound 3 - Dynamic Properties ASTM D 623-67 Goodrich Flexometer.

This apparatus makes it possible to subject a vulcanizer to alternating deformations and to determine its resistance to fatigue and internal heating. a) AT: A between the temperature at the heart of the test tube c and the temperature of the chamber (internal heating). b) Test conditions load 106 N, deflection 22.2 Z, frequency 21.4 Hz chamber temperature = 500 C.

The results are summarized below

Apparent density of the product: 0.18

Mechanical properties:

Torque: 65 Shore Hardness A: 63 Bounce Z: 25

Warming rubber #Tc OC: 103

In this specification, the BET surface area will be considered as measured by nitrogen adsorption.

This surface is determined according to the method of BRUNAUER-EMMET-TELLER described in the Journal of the American Chemical Society vol 60 p 309 February 1938.

The CTAB specific surface area will be considered in this specification as measured according to ASTM D6845-12.

This CTAB surface is the external surface determined by absorption of trimethyl ammonium bromide.

In addition, another characteristic of precipitated silicas is their porosity. It is specified here and for the whole description that the porous volumes given are measured by mercury porosimetry, the pore diameters being calculated by the WASHBURN relationship with a theta contact angle = 130 and a gamma surface tension = 484 Dynes / cm. The porosity measurements are made on products dried at 150 ° C. under a pressure of 1 Pa.

Claims (10)

A process for the synthesis of silica precipitated from an aqueous solution comprising a silicate ion and an alkaline cation, said process being characterized in that it comprises the precipitation of the silicate ion by a heavy organic acid comprising more than four carbon atoms. The process according to claim 1, wherein said heavy organic acid is little or not soluble in water. 3. Method according to one of claims 1 or 2, wherein the heavy organic acid is recovered from a solution of its alkaline salt by moving it from said alkaline salt by a stronger acid so as to recover the acid. free heavy organic. . 4. The method of claim 3, wherein said recovery is performed on the mother liquors of the precipitation of the silicate ion, after separating said waters of the precipitated silica by filtration and optionally washed cake obtained. 5. Method according to one of claims 1 or 2, wherein said heavy organic acid is a liquid ion exchanger. 6. Process for producing precipitated silica according to claim 5 from an alkali silicate in aqueous solution, said aqueous solution thus comprising a silicate ion and an alkaline cation, said process being characterized in that it comprises the synthesis of silica. precipitated by precipitation of the silicate ion by a heavy organic acid in the aqueous solution containing the alkaline cation, and extracting said alkaline cation from the aqueous solution by a liquid cation exchanger 7. Process for producing precipitated silica according to claim 6, characterized in that the extraction solvent of the salified liquid cation exchanger is the liquid ion exchanger itself. 8. Process for producing precipitated silica according to one of claims 1 to 7, characterized in that it comprises the following steps: the alkaline cation of the silicate is converted into an aqueous solution of alkaline halide by displacement of a salt alkali of an intermediate acid less strong than the aqueous hydrogen halide; the amorphous silica is formed by precipitation of the silicate ion by the intermediate acid or by the hydrogen halide solution; the alkaline halide solution separated from the amorphous silica is electrolyzed so as to obtain an aqueous solution of alkaline hydroxide, and free halogen and hydrogen, or free halogen hydride or in aqueous solution; 9. An elastomeric composition comprising an elastomeric matrix and a solid filler of precipitated silica obtained by the method according to one of claims 1 to 8 dispersed in said matrix. 10. A process for producing an elastomeric composition in which solid particles of precipitated silica obtained by the process according to one of claims 1 to 8 are dispersed in an elastomeric matrix.