Method for the production of precipitated silica, comprising a membrane concentration step

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 1 PREPARATION PROCESS OF PRECIPITATED SILICA INCLUDING A MEMRANE CONCENTRATION STEP The present invention relates to an improved process for the preparation of precipitated silica.

It is known to use precipitated silicas as catalyst support, as absorbent of active materials (in particular liquid supports, for example used in food, such as vitamins (especially vitamin E), io choline chloride) , as a viscosity, texturizing or anti-caking agent, as an element for battery separators, as an additive for toothpaste, for paper.

Precipitated silicas can also be used as reinforcing filler in silicone matrices (for example for coating electrical cables) or in compositions based on polymer (s), natural (s) or synthetic (s), in particular d. 'elastomer (s), in particular diene, for example for shoe soles, floor coverings, gas barriers, flame retardant materials and also technical parts such as cable car rollers, gaskets for household appliances, gaskets for liquid or gas pipes, brake system gaskets, sheaths, cables and transmission belts.

Precipitated silica has been used in particular for a long time as a reinforcing white filler in elastomers, and in particular in tires.

The preparation of precipitated silica is generally carried out by precipitation reaction between a silicate, in particular an alkali metal silicate, and an acidifying agent, followed by a filtration separation step to obtain a filter cake and usually a step of washing said cake, then a possible step of disintegrating the filter cake and a step of drying, for example by atomization, of said cake.

In the context of the methods of the state of the art, the cake, generally after a disintegration operation, subjected to the atomization step, comprises a large amount of water.

The implementation of the atomization step therefore makes it possible in particular to evacuate this high quantity of water, which requires a large consumption of time and energy.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 2 Thus, one of the aims of the present invention consists in providing a process for preparing precipitated silica making it possible to limit energy expenditure, in particular in terms of drying.

One of the aims of the invention is in particular to provide an alternative to the known methods for preparing precipitated silica, which is economical and simple to implement.

One of the aims of the present invention preferably consists in providing a method making it possible to reduce the energy consumption during drying, in particular compared to the methods of the state of the art and this, in general, by at least about 10%, in particular. at least about 15%, for example at least about 20%.

One of the aims of the present invention preferably consists in providing a process making it possible to increase the productivity of the process for preparing precipitated silica, in particular at the level of the drying step, in particular in relation to the processes of the state of the art. technique, in general at least about 15%, in particular at least about 20%, for example at least about 25%.

The present invention therefore relates to a process for preparing precipitated silica comprising the reaction of a silicate with an acidifying agent to obtain a suspension of precipitated silica (Si), followed by a separation step to obtain a cake, by a step of disintegration of said cake to obtain a suspension of precipitated silica (S2) and of a step of drying this suspension, and wherein a membrane concentration step is performed between said disintegrating step and said drying step.

In particular, the method according to the present invention therefore comprises the following steps:

- at least one silicate is reacted (precipitation reaction) with at least one acidifying agent, so as to obtain a suspension of precipitated silica (Si), - a solid-liquid separation step, more particularly filtration, is carried out for to obtain a solid product, also designated "filter cake", - subjecting said filter cake to a disintegration operation, in order to obtain a suspension of precipitated silica (S2), - A step of membrane concentration of said suspension (S2) is then carried out, and - the product thus obtained is dried, preferably by atomization.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 3 The specific step of the method of the invention, taken in combination with the other steps of said method, consists of a membrane concentration step making it possible to remove a high quantity of water by mechanical means of the suspension (S3) obtained after disintegration.

Such an operation, combined with the other steps of the process, then makes it possible to increase the dry matter content of the product before the drying step.

The product which is then subjected to drying contains less water, which results in an energy saving for the subsequent drying step.

The implementation of the process according to the invention can make it possible to increase the productivity, in particular of the drying step, by at least approximately 15%, preferably by at least approximately 20%, for example by at least less about 25%, relative to the processes of the state of the art, advantageously while not degrading the properties of the precipitated silica obtained, in particular its dispersibility, in particular in elastomers.

The concentration step implemented involves membrane techniques.

It consists in particular in circulating the above-mentioned suspension (S2) through a membrane and in recovering the concentrate thus obtained.

These membrane techniques are well known to those skilled in the art.

According to one embodiment of the method of the invention, the membrane concentration step is carried out by tangential filtration.

This tangential filtration technique is also well known to those skilled in the art.

Thus, tangential filtration consists in passing a fluid, namely the aforementioned suspension (S2), tangentially to the surface of the filter. It is the pressure of the fluid that allows it to pass through the filter.

The particles, in this case, remain in the tangential circulation flow, and the clogging of the filter media thus takes place much less quickly.

According to one embodiment of the method of the invention, the membrane concentration step is carried out by standard or dynamic tangential filtration.

In the case of standard tangential filtration, the membrane used is fixed and it is therefore the fluid, namely here the suspension (S2), which circulates.

In the case of dynamic tangential filtration, the membrane is in motion.

These two tangential filtration techniques are well known to those skilled in the art.

According to a preferred embodiment of the method of the invention, the membrane concentration step is carried out by dynamic tangential filtration, in CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 4 particularly vibrating (for example at using the VSEP (Vibratory Shear Enhanced Processing) or rotary system.

According to one embodiment of the method of the invention, the membrane concentration step is carried out by rotary dynamic tangential filtration.

In the context of the process according to the invention, the tangential dynamic filtration technique with rotating discs is thus used, for example.

In this process, rotating ceramic discs then generate turbulence and a differential speed between the filter media and the suspension.

These turbulences prevent the formation of solid agglomerates on the surface of the membranes which can interfere with filtration.

This technology consists of removing water by mechanical means and not by evaporation, which ultimately reduces energy costs.

According to one embodiment of the process of the invention, the product obtained at the end of the membrane concentration step is a suspension (S3) of precipitated silica having a dry matter content (or dryness or solids content) greater than 24/0, preferably at least 26/0, by weight.

According to one embodiment of the process of the invention, the product obtained at the end of the membrane concentration step is a suspension (S3) of precipitated silica having a dry matter content of between 25 and 30% by weight.

According to one embodiment of the method of the invention, the membrane concentration step is carried out hot, and in particular at a temperature between 40 and 90 C.

The method according to the invention relates to a method for synthesizing precipitated silica, that is to say that a precipitation step is first implemented in which at least one acidifying agent is reacted with at least a silicate, without limitation to a particular type of precipitated silica.

The process according to the invention can be implemented in particular for the preparation of precipitated silicas as obtained according to the processes described for example in applications EP 0 520 862, EP 0 670 813, EP 0 670 814, EP 0 917 519. , WO 95/09127, WO 95/09128, WO 98/54090, WO 03/016215, WO 2009/112458 or WO 2012/010712.

The precipitation reaction by reaction of a silicate with an acidifying agent can be carried out in the process according to the present invention according to any method of preparation, in particular by adding an acidifying agent to a silicate base stock, or else by simultaneous addition, total or partial, of acidifying agent and silicate on a starter of water, or of silicate or of acidifying agent.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 The choice of the acidifying agent and of the silicate is made in a manner well known per se.

Generally used as acidifying agent a strong mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid, carbonic acid.

5 At the end of the precipitation step, an Si suspension (or slurry) of precipitated silica is obtained, to which various additives can optionally be added, which is then separated.

According to a particular embodiment of the invention, the separation step mentioned above consists of a solid-liquid separation step.

Preferably, it consists of a filtration step at the end of which a filtration cake is obtained, where appropriate followed by a step of washing said cake.

The filtration can be done by any suitable method, for example using a filter press or a belt filter or a rotary vacuum filter.

The cake obtained is then subjected to a crumbling step. The disintegration operation is a fluidization or liquefaction operation, in which the filter cake is made liquid, the precipitated silica being found in suspension.

In general, this operation makes it possible in particular to lower the viscosity of the suspension to be dried subsequently.

This operation can thus be carried out by subjecting the filter cake to a chemical action, for example by adding an aluminum compound such as sodium aluminate, and / or acid, preferably coupled to a mechanical action (for example by passing through a tank stirred continuously or through a colloidal type mill).

The suspension (in particular aqueous) S2 obtained after disintegration generally has a relatively low viscosity.

According to one embodiment, the method of the invention can comprise a crumbling step between the separation step and the disintegration step.

This optional step consists in crumbling the cake resulting from the separation step and makes it possible to reduce the particle size of said cake.

For example, this step can be carried out with a Gericke Nibleur, in which the cake is forced through a grid of diameter less than 20 mm, preferably of size between 2 and 14 mm.

This crumbling step can also be carried out by Wyssmont tools such as the "Rotocage Lumpbreaker", the "double Rotocage Lumpbreaker" or the "Triskelion Lumpbreaker".

The precipitated silica suspension S2 obtained in the disintegration step is subjected to the membrane concentration step as described above.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 6 The suspension of precipitated silica S3 resulting from the membrane concentration step is then dried.

This drying can be done by any means known per se.

According to a preferred embodiment of the process of the invention, the drying is carried out by atomization.

For this purpose, any suitable type of atomizer can be used, in particular an atomizer with turbines, nozzles, liquid pressure or two fluids.

Preferably, in the process according to the invention, the separation step is carried out by means of a filter (in particular rotary) under vacuum and the drying step is carried out using a nozzle atomizer. .

When the drying is carried out by means of a nozzle atomizer, the precipitated silica which can then be obtained is advantageously in the form of substantially spherical beads (microbeads), preferably of an average size of at least 80 m.

At the end of this drying, it is optionally possible to carry out a grinding step on the recovered product; the precipitated silica then obtained is generally in the form of a powder, preferably of average size between 5 and 70 m.

When the drying is carried out by means of a turbine atomizer, the precipitated silica which can then be obtained may be in the form of a powder, for example with an average size of between 5 and 70 m.

The product dried (for example by a turbine atomizer) or ground as indicated above may optionally be subjected to an agglomeration step, which consists for example of direct compression, wet granulation (that is to say, ie with the use of a binder such as water, silica suspension, etc.), extrusion or, preferably, dry compaction.

When the latter technique is implemented, it may prove to be appropriate, before proceeding with the compaction, to deaerate (an operation also called predensification or degassing) the powdery products so as to eliminate the air included in them and ensure more regular compaction.

The precipitated silica that can be obtained at the end of this agglomeration step is generally in the form of granules, in particular of a size of at least 1 mm, for example between 1 and 10 mm, in particular depending on the size. axis of their greatest dimension.

The following examples illustrate the invention without, however, limiting its scope.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 7 EXAMPLES Example 1 The precipitated silica suspension used (S2) is a slurry (slurry) of Z1165MP silica, resulting from a filtration step and then from a step of disintegrating the cake obtained in the filtration step, having the following characteristics:

Temperature: 50 C pH: 6.0 - 6.5 Humidity: 77% A part (S'2) of the suspension S2 is dried directly by atomization.

The other part of the S2 suspension is subjected to a membrane concentration step on a DCF 152 / 0.14 (Kmpt) filtration unit, developing a filtering surface of 0.14 m2 and using membranes made of A1203 (Kerafol) with a diameter of pores of 200 nm.

The transmembrane pressure is set at 0.8 bar and backwashes at 0.4 bar are performed every 4 seconds.

The permeate flow rate is 25 Uh / m2.

The S3 concentrated slurry obtained is at 26% dry extract.

The slurry S3 at 26% dry extract is then atomized, as in the case of the S'2 part of the suspension S2.

There is thus a gain in energy consumption of 15% compared to the direct drying of the S'2 slurry and an associated productivity gain of 18/0.

The particle sizes of the slurries before and after membrane concentration are given in the following table.

Suspension% particles <0.5 lm (*) in the S'2 suspension 65% S3 65% (*) The percentage of particles with a diameter of less than 0.5 lm is measured by particle size distribution by sedimentation carried out on the Sedigraph device 5100 (Micromeretics) from the percentage of particles CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 8 less than 0.5 m.

The suspension analyzed by this technique is diluted to 4.6% by weight in purified water and it is stirred weakly.

The suspension obtained is then sieved using a 250 μm sieve and the analysis is carried out by taking a measurement range between 0.3 and 85 m.

These data show that the mechanical actions undergone by the slurry (or slurry) of silica S2 (to obtain the slurry S3) do not modify its fine particle content.

Example 2 The precipitated silica suspension used (S2) is a slurry (slurry) of Z1165MP silica, resulting from a filtration step then from a step of disintegrating the cake obtained in the filtration step, having the following characteristics:

Temperature: 50 C pH: 6.0 - 6.5 Humidity: 77% A part (S'2) of the suspension S2 is dried directly by atomization.

The other part of the suspension S2 is subjected to a membrane concentration step on an SSDF CRD-01 filtration unit (Novoflow).

This unit contains a stack of 3 discs 152 mm in diameter made up of Kerafol A1203 membranes with a pore diameter of 200 nm), i.e. a filtering surface area of ​​0.1 m2.

A transmembrane pressure of 1 bar is applied.

An S3 slurry at 27.5% dry extract is obtained with a permeate flow rate of 18 Uh / m2.

The slurry S3 at 27.5% dry extract is then atomized, as in the case of the S'2 part of the suspension S2.

There is thus a gain in energy consumption of 22% compared to the direct drying of the S'2 slurry and an associated gain in productivity of 27%.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 9 The particle sizes of the slurries before and after membrane concentration are given in the following table.

Suspension% particles <0.5 lm (*) in the S'2 suspension 59% S3 62% (*) measurement carried out as in example 1 These data show that the mechanical actions undergone by the slurry (or slurry) of silica S2 (to obtain the slurry S3) do not appreciably modify its fine particle content.

Example 3 The precipitated silica suspension used (S2) is a slurry (slurry) of Z1165MP silica, resulting from a filtration step then from a step of disintegrating the cake obtained in the filtration step, having the following characteristics:

Temperature: 50 C pH: 6.0 - 6.5 Humidity: 84% A part (5'2) of the suspension S2 is dried directly by atomization.

The other part of the suspension S2 is subjected to a membrane concentration step on a Carbosep tangential filtration unit equipped with a Carbosep M9 membrane having a cut-off threshold of 300 kD.

The recirculation flow rate is set at 800 Uh and the average transmembrane pressure is 2 bars.

The S3 concentrated slurry obtained is at 26% dry extract, with an average permeate flow rate of 100 L / h / m2.

The slurry S3 at 26% dry extract is then atomized, as in the case of part 5′2 of the suspension S2.

There is thus a gain in energy consumption of 46% compared to the direct drying of the slurry 52 and an associated gain in productivity of 84/0.

CA 02867569 2014-09-08 WO 2013/139934 PCT / EP2013 / 055978 The method according to the invention comprising a membrane concentration step therefore makes it possible to save energy and increase the productivity during drying.