Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/124—Preparation of adsorbing porous silica not in gel form and not finely divided, i.e. silicon skeletons, by acidic treatment of siliceous materials
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
  • C01B33/187—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates
  • C01B33/193—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates of aqueous solutions of silicates

Definitions

• the present invention relates to an improved process for the preparation of precipitated silica.
• precipitated silicas as a catalyst support, as an absorbent of active substances (in particular liquid carriers, for example used in foodstuffs, such as vitamins (vitamin E in particular), choline chloride), as a viscosifying, texturizing or anti-caking agent, as an element for battery separators, as an additive for toothpaste, for paper.
• active substances in particular liquid carriers, for example used in foodstuffs, such as vitamins (vitamin E in particular), choline chloride
• a viscosifying, texturizing or anti-caking agent as an element for battery separators, as an additive for toothpaste, for paper.
• precipitated silicas as reinforcing filler in silicone matrices (for example for coating electrical cables) or in compositions based on polymer (s), natural or synthetic, in particular elastomer (s), especially diene, for example for shoe soles, floor coverings, gas barriers, fire-retardant materials and also technical parts such as ropeway rollers, appliance seals, liquid or gas line joints, brake system seals, ducts, cables and transmission belts.
• Precipitated silica has in particular been used for a long time as reinforcing white filler in elastomers, and in particular in tires.
• the precipitated silica preparation 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 drying step, for example by atomization, said cake.
• one of the aims of the present invention is to provide a process for the preparation of precipitated silica which makes it possible to limit energy expenditure, particularly in terms of drying.
• One of the aims of the present invention is to provide a method for preparing precipitated silica that can limit the drying times.
• One of the aims of the invention is in particular to provide an alternative to the known preparation processes of precipitated silica, which is economical and simple to implement.
• One of the aims of the present invention consists preferentially in providing a method making it possible to reduce the energy consumption during drying, in particular with respect to the methods of the state of the art, and this, in general, of at least about 15%, in particular at least about 20%, for example at least about 25%.
• One of the aims of the present invention is preferably to provide a method for increasing the productivity of the process for the preparation of precipitated silica, in particular at the level of the drying step, in particular with respect to the processes of the state of the in general at least about 20%, in particular at least about 25%, for example at least about 30%.
• the present invention therefore relates to a process for preparing precipitated silica comprising reacting a silicate with an acidifying agent to obtain a suspension of precipitated silica, followed by a separation step to obtain a cake and a drying step of said cake, and wherein a step of compacting said cake at a pressure greater than 10 bar is performed between the separation step and the drying step.
• the method according to the present invention thus comprises the following steps:
• a solid-liquid separation step is carried out, more particularly filtration, to obtain a solid product, also referred to as a "filter cake",
• said filter cake is subjected to a compacting step at a pressure greater than 10 bar
• the specific step of the process of the invention taken in combination with the other steps of said process, consists of a compacting step at a pressure high, to remove a significant amount of water cake obtained after the precipitation and separation steps.
• Such a high pressure compacting operation combined with the other process steps, 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 method according to the invention makes it possible, in particular at the level of the drying step, to reduce the energy consumption, and to increase the productivity, in general, by at least about 20%, preferably by at least about 25%, for example at least about 30%, especially at least about 35%, in comparison with the processes of the state of the art, advantageously while not degrading the properties of the precipitated silica obtained, especially its dispersibility, in particular in elastomers.
• the compacting stage of the filter cake makes it possible in particular to remove water.
• the more compact the filter cake the more water is removed and therefore the dry matter content of said cake is increased.
• the compaction step is carried out at a pressure greater than 10 bar, preferably at a pressure of at least 20 bar.
• the compacting step is carried out at a pressure greater than 10 bar and less than 60 bar, preferably between 15 and 45 bar, in particular between 20 and 45 bar, in particular between 20 and 35 bar.
• this step is carried out at a compacting pressure of between 20 and 30 bar.
• the pressure may be about 25 bar.
• this compaction step it is generally preferable to perform this compaction step at a pressure of at most 45 bar, in particular at most 35 bar. Indeed, at too high pressures, the cake of Filtration may be degraded and therefore not lead to precipitated silica particles of satisfactory quality.
• the compaction step may optionally be performed on the same filter as that used during the filtration step.
• the filtration step, the optional washing step and the compaction step may in certain cases consist of a single separation step including filtration, a possible washing (with water for example) and a strong final compaction on a filter equipped with a compaction means, such as a filter press.
• the duration of the compacting step at the indicated pressure is at least 200 seconds, preferably between 300 and 600 seconds.
• the product obtained at the end of the compacting step has a solids content (or dryness or solids content) of at least 25% by weight, in particular between 25 and 40% by weight. weight, for example between 25 and 35% by weight.
• the product obtained at the end of the compacting step has a solids content of at least 28% by weight, in particular between 28 and 35% by weight, for example between 28 and 32%. in weight.
• This level of solids may be at least 29%, especially at least 30%, by weight, and in particular between 29 and 35% by weight, for example between 29 and 32% by weight.
• the process according to the invention relates to a process for the synthesis of precipitated silica, that is to say that a precipitation stage is first implemented in which at least one acidifying agent is reacted with at least one acidifying agent.
• silicate without limitation to a particular type of precipitated silica.
• the process according to the invention can be used 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 and EP 0 917 519. , WO 95/09127, WO 95/09128, WO 98/54090, WO 03/016215, WO 2009/1 12458 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 stockstock, or by simultaneous total or partial addition of acidifying agent and silicate on a base of water, or silicate or acidifying agent.
• the choice of acidifying agent and silicate is in a manner well known per se.
• the acidifying agent used is 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.
• the separation step mentioned above consists of a solid-liquid separation step.
• it consists of a filtration step, at the end of which a filter cake is obtained, optionally followed by a washing step of said cake.
• the filtration may be carried out by any suitable method, for example by means of a filter press or a belt filter or a vacuum rotary filter.
• the resulting cake is then subjected to the compacting step described above. It is advantageously carried out by washing on a filter equipped with a compacting means, at the pressure mentioned above. It can be carried out at the end of filtration, after or towards the end of a possible washing step, for example on a filter press by swelling of the membranes of the membranous trays.
• the cake obtained at the end of the compacting step is then subjected to a drying step.
• the drying technique implemented during the drying step of the process of the present invention is not an atomization method.
• a ring-dryer can be used.
• the drying can be carried out by means of superheated steam, in particular in a fluidized bed or in a ring dryer.
• the process according to the invention does not comprise a disintegration step, in particular between the compaction step (or the optional delamination step as indicated below) and the drying step.
• This embodiment thus comprises direct drying of the cake, without passing through an intermediate disintegration step, and, in general, the drying step of the corresponding process according to the invention is then not carried out by atomization.
• the process according to the invention may comprise a step of disintegrating the cake obtained at the end of the step of compaction (or of the optional slicing step as indicated below).
• the disintegration operation is a fluidification or liquefaction operation, in which the cake is made liquid, the precipitated silica being in suspension.
• this operation makes it possible in particular to lower the viscosity of the suspension to be dried later.
• This operation can thus be carried out by subjecting the 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 continuously stirred tank or in a colloid mill).
• the drying step is then generally carried out by atomization.
• any type of suitable atomizer may be used, especially a turbine atomizer, preferably a nozzle atomizer, liquid pressure or two fluids. More particularly, the precipitated silica that can then be obtained is in the form of substantially spherical beads (microbeads), preferably of average size of at least 80 ⁇ .
• the method of the invention may comprise a step of lopping between the compaction step and the drying step (or the possible disintegration step).
• This optional step consists in crumbling the cake resulting from the compaction step and makes it possible to reduce the particle size of said cake.
• this step can be carried out with a Gericke Nimer, 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 performed by Wyssmont tools such as "Rotocage Lumpbreaker", “Double Rotocage Lumpbreaker” or "Triskelion Lumpbreaker”.
• the precipitated silica obtained at the end of the drying step is in the form of granules (for example substantially cylindrical ) or powder.
• the drying step may optionally proceed to a grinding step on the recovered product.
• the dried product especially when it is in powder form, or ground may optionally be subjected to an agglomeration step, which consists for example of a direct compression, wet granulation (ie say with use of a binder such as water, silica suspension ...), a extrusion or, preferably, dry compaction.
• agglomeration step which consists for example of a direct compression, wet granulation (ie say with use of a binder such as water, silica suspension ...), a extrusion or, preferably, dry compaction.
• agglomeration step which consists for example of a direct compression, wet granulation (ie say with use of a binder such as water, silica suspension ...), a extrusion or, preferably, dry compaction.
• deaerate operation also called pre-densification or degassing
• the precipitated silica that can be obtained at the end of this agglomeration step is generally in the form of granules
• the precipitated silica obtained by the process according to the invention when in the form of granules, especially at the end of the drying step, these have a size of at least 1 mm, in particular between 1 and 10 mm, for example between 1 and 8 mm, especially along the axis of their largest dimension, and preferably a particle size less than 75 ⁇ less than 5% by weight.
• the precipitated silica obtained by the process according to the invention is in powder form, it generally has an average size of between 5 and 60 ⁇ .
• the precipitated silica suspension used (S) is a silica slurry (slurry) Z1 165MP, resulting from a precipitation reaction, having the following characteristics:
• the silica suspension S is filtered and washed on a filter press and then subjected to compacting at a pressure of 8 bar on the same filter.
• the resulting silica cake has a solids content of 23.5% by weight.
• the silica cake is then swept by a passage in a starter (Gericke) equipped with an 8 mm grid.
• the swept silica cake is then fed into a "Ring Dryer” dryer (ring dryer GEA Barr Rosin) by a conveyor belt at 8 kg / h.
• the inlet temperature of the dryer is set at 305 ° C and the outlet temperature at 130 ° C.
• the output product is precipitated silica in the form of a moisture powder equal to 6.4%.
• the precipitated silica obtained has a porous distribution such as its porous volume ratio V 2 / V 1 (pore volume consisting of pores with diameters of between 175 and 275 ⁇ / pore volume consisting of pores with diameters less than or equal to 400 ⁇ , porous volumes being measured by mercury porosimetry, the pore diameters being calculated by the Washburn relationship with a theta contact angle equal to 130 ° and a gamma surface tension equal to 484 Dynes / cm or N / m (Micromeritics Autopore IV porosimeter) 9500)) is 54%.
• V 2 / V 1 porous volume ratio
• V 1 porous volume consisting of pores with diameters of between 175 and 275 ⁇ / pore volume consisting of pores with diameters less than or equal to 400 ⁇
• porous volumes being measured by mercury porosimetry, the pore diameters being calculated by the Washburn relationship with a theta contact angle equal to 130 ° and a gamma surface tension equal
• the silica cake obtained has a solids content of 30% by weight.
• the silica cake is then swept by a passage in a starter (Gericke) equipped with an 8 mm grid.
• the sponge silica cake is then fed into a Ring Dryer (GEA Barr Rosin) using a conveyor belt at 9 kg / h.
• the inlet temperature of the dryer is fixed at 300 ' ⁇ and the outlet temperature at 131' ⁇ .
• the output product is precipitated silica in the form of a moisture powder of 7.1%.
• the precipitated silica In addition to having a pore volume ratio V2 / V1 (56%) close to that of the precipitated silica obtained in Example 1, the precipitated silica also has a dispersibility similar to the latter.
• the method according to the invention here comprising a compacting step at a pressure of 25 bar makes it possible to save energy and increase productivity during drying.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Silicon Compounds (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)

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