US20050192395A1 - Hydrophobic precipitated silica for defoamer formulations - Google Patents

Hydrophobic precipitated silica for defoamer formulations Download PDF

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US20050192395A1
US20050192395A1 US11/037,118 US3711805A US2005192395A1 US 20050192395 A1 US20050192395 A1 US 20050192395A1 US 3711805 A US3711805 A US 3711805A US 2005192395 A1 US2005192395 A1 US 2005192395A1
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precipitated silica
hydrophobicizer
silica
carried out
hydrophobic
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Christian Panz
Rene Allerdisse
Helga Obladen
Mario Loebbus
Anja Lukas
Roland Bergmann
Karl Meier
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Evonik Operations GmbH
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Degussa GmbH
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60P—VEHICLES ADAPTED FOR LOAD TRANSPORTATION OR TO TRANSPORT, TO CARRY, OR TO COMPRISE SPECIAL LOADS OR OBJECTS
    • B60P1/00—Vehicles predominantly for transporting loads and modified to facilitate loading, consolidating the load, or unloading
    • B60P1/04—Vehicles predominantly for transporting loads and modified to facilitate loading, consolidating the load, or unloading with a tipping movement of load-transporting element
    • B60P1/28—Tipping body constructions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D19/00—Degasification of liquids
    • B01D19/02—Foam dispersion or prevention
    • B01D19/04—Foam dispersion or prevention by addition of chemical substances
    • B01D19/0404—Foam dispersion or prevention by addition of chemical substances characterised by the nature of the chemical substance
    • B01D19/0409—Foam dispersion or prevention by addition of chemical substances characterised by the nature of the chemical substance compounds containing Si-atoms
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3009—Physical treatment, e.g. grinding; treatment with ultrasonic vibrations
    • C09C1/3018—Grinding
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3081—Treatment with organo-silicon compounds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/309—Combinations of treatments provided for in groups C09C1/3009 - C09C1/3081
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60P—VEHICLES ADAPTED FOR LOAD TRANSPORTATION OR TO TRANSPORT, TO CARRY, OR TO COMPRISE SPECIAL LOADS OR OBJECTS
    • B60P1/00—Vehicles predominantly for transporting loads and modified to facilitate loading, consolidating the load, or unloading
    • B60P1/04—Vehicles predominantly for transporting loads and modified to facilitate loading, consolidating the load, or unloading with a tipping movement of load-transporting element
    • B60P1/045—Levelling or stabilising systems for tippers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60Y—INDEXING SCHEME RELATING TO ASPECTS CROSS-CUTTING VEHICLE TECHNOLOGY
    • B60Y2200/00—Type of vehicle
    • B60Y2200/10—Road Vehicles
    • B60Y2200/14—Trucks; Load vehicles, Busses
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/11—Powder tap density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/19—Oil-absorption capacity, e.g. DBP values
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
    • Y10T428/2991—Coated
    • Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
    • Y10T428/2995—Silane, siloxane or silicone coating

Definitions

  • the present invention relates to hydrophobic precipitated silicas of high pH and low silanol group density, to a process for preparing them and to their use, such as in defoamers, fillers or carriers.
  • Hydrophobic precipitated silicas and processes for preparing them are known. Hydrophobicization is accomplished generally by populating the surface of a hydrophilic precipitated silica with suitable organic compounds. Examples of such hydrophobic or partly hydrophobic precipitated silicas are disclosed in patents EP 0 798 348, U.S. Pat. No. 4,377,493 and EP 1 281 735, EP 1 281 733 and EP 1 281 735 disclose hydrophobic precipitated silicas with a pH of 5-9, while WO 2003014020 discloses those having a pH of more than 9.5.
  • hydrophilic and hydrophobic precipitated silicas in defoamer formulations is likewise known (Pigments Technical Bulletin 42, DEGUSSA, 06/1986). Utility in defoamer formulations imposes exacting requirements on the precipitated silicas. Thus they ought to be readily and effectively dispersible into the defoamer formulation and ought to lead to a rapid knockdown time (response time), complete knockdown (immediate effect) and long holddown (service life). Knockdown describes the ability of the defoamer to reduce the height of the foam immediately following addition, down to a defined height of the foam. Holddown characterizes the service life of the defoamer, i.e., the duration of its activity.
  • the invention provides precipitated silicas having enhanced performance properties, particularly in defoamer formulations.
  • the invention also provides a process by which the precipitated silicas of the invention can be prepared.
  • the present invention provides hydrophobic alkaline precipitated silicas characterized by the following physicochemical parameters: BET ⁇ 110 m 2 /g CTAB ⁇ 150 m 2 /g BET/CTAB ratio ⁇ 3 Carbon content >3.1% pH >9
  • the invention further provides hydrophobic precipitated silicas which in addition to the abovementioned parameters, independently of one another, have one or more of the following physicochemical parameters: DBP ⁇ 230 g/(100 g) Modified Sears number ⁇ 6 ml/(5 g) Sears number/BET ratio ⁇ 0.05 ml/(5 m 2 ) Methanol wettability >50% Mean particle size d 50 ⁇ 14 ⁇ m Loss on ignition >3% Tapped density ⁇ 150 g/l
  • the present invention further provides a process by which the precipitated silicas of the invention can be prepared, comprising the following steps:
  • Steps e), f) and g) can be carried out at different points in time and in different sequence in the process of the invention.
  • the invention provides for the use of the precipitated silicas of the invention, particularly in defoamer formulations.
  • precipitated silicas particularly suitable for use in defoamer formulations are preferably of a nature such that they may insert themselves optimally at the interface between oil and water. This permits effective destruction of foam bubbles. It was found to be important for the surface of the precipitated silicas to combine a certain blend of hydrophilic and hydrophobic properties.
  • the hydrophilic centers of the silica surface are controlled by adjusting the pH. The higher the pH of the end product, the more pronounced the hydrophilic centers on the silica surface. Hydrophilic centers, however, can come about at those sites on the surface of the precipitated silica where silanol groups were present prior to treatment with the basic component.
  • hydrophilic carriers can come about only at those sites on the surface of the silica where silanol groups were present prior to treatment with base.
  • hydrophilic carriers can come about only at those sites on the surface of the silica where silanol groups were present prior to treatment with base.
  • the precipitated silicas of the invention have a low silanol group density.
  • This silanol group density can be expressed by the Sears number/BET ratio.
  • the precipitated silicas of the invention preferably have by a high pH and a low silanol group density.
  • hydrophobic precipitated silicas with relatively long polysiloxane chains on the surfaces exhibit particularly good defoamer performance.
  • a measure which can be used to value this property is the ratio of BET to CTAB surface.
  • the precipitated silicas of the invention additionally feature a preferable particle size.
  • the particle size may play an important role, since the silica particles must on the one hand be sufficiently large to break the foam lamella but on the other hand must also be present in sufficient number.
  • hydrophobic precipitated silicas of the invention have not only high pH and low silanol group density, but also
  • the precipitated silicas of the invention have the following physicochemical parameters: BET ⁇ 110 m 2 /g CTAB ⁇ 150 m 2 /g BET/CTAB ratio ⁇ 3 Carbon content >3.1% pH >9.
  • DBP DBP ⁇ 230 g/(100 g) Modified Sears number ⁇ 6 ml/(5 g) Sears number/BET ratio ⁇ 0.05 ml/(5 m 2 ) Methanol wettability >50% Mean particle size d 50 ⁇ 14 ⁇ m Loss on ignition >3% Tapped density ⁇ 150 g/l
  • the precipitated silicas of the invention preferably have a BET of 30-110 m 2 /g, more preferably 40-80 m 2 /g, even more preferably 50-70 m 2 /g, a CTAB of 30-120 m 2 /g, more preferably 50-90 m 2 /g, even more preferably 60-80 m 2 /g, and a modified Sears number of 0.3-6.0 ml, more preferably 0.5-2.0 ml, even more preferably 0.8-1.4 ml.
  • the carbon content which is an important measure for assessing the hydrophobicity of a precipitated silica, is preferably 4-12%, more preferably 5-10% and with particular preference 6-10%.
  • the methanol wettability is preferably >60%.
  • a basic agent is added during the preparation of the precipitated silicas to adjust the pH of the dry silica.
  • the pH of the precipitated silica of the invention is preferably between 9-10.5, in particular between 9 and 10, more particularly 9.2-9.8.
  • Hydrophilic centers may come about on the silica surface at those sites where silanol groups were present prior to treatment with the basic agent.
  • the precipitated silica of the invention has a low silanol group density.
  • This silanol group density can be expressed by the Sears number/BET ratio.
  • the precipitated silicas of the invention can have a Sears number/BET ratio of ⁇ 0.04 ml/(5 m 2 ), preferably ⁇ 0.03 ml/(5 m 2 ), in one particular embodiment ⁇ 0.025 ml/(5 m 2 ).
  • the BET/CTAB ratio of the precipitated silicas of the invention is preferably ⁇ 1.5, more preferably ⁇ 1 and very preferably 0.5-0.99.
  • the mean particle size d 50 which is a property that is beneficial for effective and homogeneous incorporation into the defoamer formulation, is preferably ⁇ 10 ⁇ m, more preferably ⁇ 7.5 ⁇ m, very preferably ⁇ 6 ⁇ m and in particular ⁇ 5 ⁇ m.
  • the precipitated silicas of the invention may be prepared by a process comprising the steps of
  • the process of the invention may optionally include a step
  • Steps e), f) and g) may be carried out at different points in time in different sequence in the process of the invention.
  • the conditioned precipitated silica obtained after step g) can either be passed to step h) or mixed with a hydrophilic precipitated silica or precipitated silica dispersion or precipitated silica filtercake, dried if desired as per step d) and conditioned again if desired as per step g). This procedure is repeated until finally the hydrophobicized precipitated silica is passed to step h) and concluding milled in step i).
  • Step a) of the process of the invention preferably involves carrying out the steps of
  • the simultaneous addition of waterglass (a solution of a silicate e.g., sodium or potassium silicate) and acidifier in step ab) is made preferably such that the pH is held at a level of between 7 and 11, preferably 8 to 9.
  • the pH is measured at 60° C.
  • the temperature of the reaction solution is held in step ab) at a level of between 60 and 100° C., preferably between 65 and 95° C., more preferably between 70 and 90° C.
  • the addition of acidifier and waterglass is continued to a solids content of 40 to 70 g/l, preferably 45 to 65 g/l, more preferably 50 to 60 g/l and then stopped. This gives a precipitation time of 70 to 140 minutes, preferably 80 to 130 minutes.
  • step ac) the pH of the precipitation suspension is adjusted by adding an acidifier to a level of 2 to 8, preferably 2.5 to 4.0, more preferably 3 to 4.
  • the pH is measured at 60° C.
  • the waterglass used in step ab) has a modulus of 3 to 3.8, preferably 3.3 to 3.5, and a density of 1.1 to 1.39 g/ml, preferably 1.2 to 1.36 g/ml, more preferably 1.3-1.4 g/ml.
  • the acidifier used in steps ab) and ac) may be a mineral acid, particularly sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid or carbonic acid, or carbon dioxide. Preference is given to sulfuric acid with a concentration of 1 mol/l to 18.76 mol/l and preferably from 7.0 to 18.8 mol/l. Preferably the same acidifiers are used in steps ab) and ac).
  • Step ac) may be followed if desired by a step
  • step b) the precipitation suspension is filtered and the filtercake is washed.
  • the filtering of the precipitation suspension, prepared beforehand, and the washing of the filtercake are performed by known methods, such as by filtration with a membrane filter press (Ullmann's Encyclopedia of Industrial Chemistry, 1992, 5th edition, vol. B1, page 10-1-10-59, incorporated herein by reference).
  • the filtercake is washed using preferably deionized water.
  • the filtercake obtained has a solids content of 13 to 25%, preferably 15 to 17%.
  • step c) the filtercake is liquefied, liquefying includes forming a suspension.
  • the filtercake is liquefied by adding water, preferably deionized water, and preferably with stirring.
  • step c) is carried out together with step e).
  • the filtercake is liquefied with the addition of water, preferably deionized water, and with stirring.
  • the suspension obtained has a solids content of 6 to 20%, preferably 6 to 17%, more preferably 6 to 11%.
  • the amount of shear energy introduced should only be just enough for liquefication.
  • step d The suspension obtained from the preceding process stages is dried in step d).
  • a wide variety of drying methods are known to the skilled worker for this purpose (Ullmann's Encyclopedia of Industrial Chemistry, 1992, 5th edition, vol. B 1, page 7-21-7-25 incorporated herein by reference). Drying by means of pneumatic conveying drier, spray dryer, rack dryer, belt dryer, rotary tube dryer, flash dryer, spin-flash dryer or nozzle tower has proven advantageous. Drying takes place with particular preference by spray dryer or nozzle tower.
  • step f) the moisture content of the precipitated silica can be adjusted in step d).
  • step c) If the liquefication of the filter cake in step c) takes place without the addition of a basic agent, then the basic component may be sprayed onto the precipitated silica after drying in a mixer (e.g., a low-shear plowshare mixer such as a Lödige mixer, for example). In this case, then, step e) takes place after step d).
  • the pH of the precipitated silica in this case is adjusted to a figure>7, preferably between 7 and 11, more preferably between 8 and 10.5 and in particular between 8.3 and 10.
  • step e) it is possible to use alkali metal hydroxides or carbonates, alkaline earth metal hydroxides or carbonates, alkali metal oxides, alkaline earth metal oxides, alkali metal silicates, alkaline earth metal silicates, ammonia and alkali metal aluminates or aqueous solutions or mixtures of said bases. Preference is given to using sodium and potassium hydroxide solutions.
  • Step f) of the process of the invention can be performed as wet or dry hydrophobicization.
  • Wet hydrophobicization means that the silicatic starting materials are aqueous silica suspensions or high-water-content silica filtercakes, which are populated with the corresponding hydrophobicizers, as described for example in DE 27 29 244 for precipitation suspensions with organohalosilanes.
  • Dry hydrophobicization means that the silicatic starting materials are silica powders having different moisture contents of 1 to 75%, which are coated with the corresponding hydrophobicizers.
  • a process of this kind is described for example in DE 26 28 975.
  • the teachings of DE 26 28 975 and DE 27 29 244 are expressly incorporated in this specification by reference, being considered part of the description of the present specification.
  • Step f) of the process of the invention can be carried out in the following versions or embodiments:
  • the hydrophobicizer is added to a precipitated silica having a water content of 1.0 to 80% by weight, preferably 2 to 50% by weight.
  • the water content can be adjusted in the course of drying in step d) or, if the basic agent (step e) is not added until after step d), by further drying or moistening if desired.
  • the following process sequences are possible: c)+e) ⁇ d) ⁇ f) or c) ⁇ e) ⁇ d) ⁇ f) or c) ⁇ d) ⁇ e) ⁇ f).
  • Step f) is carried out between steps a) and b).
  • the hydrophobicizer is added after the silicate has been precipitated with an acid, the addition taking place to the resultant dispersion of the precipitated silica.
  • a Rhein-Hütte mixer or a Kolthof mixing siren or an Ultra-Turrax it is possible to use, for example, a Rhein-Hütte mixer or a Kolthof mixing siren or an Ultra-Turrax. This version requires rapid filtration and accelerated drying (spin-flash dryer, spray dryer, nozzle tower) after the reaction.
  • the hydrophobicizer is added to a precipitated silica having a water content of 70 to 99% by weight during subsequent separation of the solid from the water.
  • the solids content can be raised by filtration, nozzle tower, spin-flash or any other accelerated drying. The higher the water content the more rapidly the increase in solids content ought to be performed in order to prevent separation.
  • the following process sequences are possible: c)+e) ⁇ f) and immediately ⁇ d) or c) ⁇ e) ⁇ f) and immediately ⁇ d) or c)+f) and immediately ⁇ e) and immediately ⁇ d) or c) ⁇ f) and immediately ⁇ e) and immediately ⁇ d) or c) ⁇ e)+f) and immediately ⁇ d).
  • Step f) takes place together with step d) or immediately before d).
  • the precipitated silica or hydrous silica can be passed, at the same time for example as the hydrophobicizer, to a spray dryer, nozzle tower dryer or spin-flash dryer.
  • the following process sequences are possible: c)+e) ⁇ f and then immediately ⁇ d), c) ⁇ d)+f) ⁇ e) or c)+e) ⁇ d)+f) or c) ⁇ e) ⁇ d)+f) or e)+f)+d).
  • spin-flash drying step c) is optional and therefore may also be omitted entirely.
  • the filtercake can be mixed before drying with the basic agent and the hydrophobicizer and then dried, i.e., e)+f) ⁇ d).
  • dry precipitated silica is mixed with the hydrophobicizer in for example a Gericke or Lödige mixer.
  • the following process sequences are possible: c)+e) ⁇ d) ⁇ f) or c) ⁇ e) ⁇ d) ⁇ f) or c) ⁇ d) ⁇ f) ⁇ e).
  • the mixing of dried precipitated silica with the hydrophobicizer is also possible in the course of the milling (step i)) in the mill.
  • steps a) and b) are carried out first in all the versions.
  • Step c) then follows. Where two process steps are connected by a “+” sign (e.g., c)+e)), this means that the two process steps are carried out together. Where, on the other hand, the process steps are joined by an “ ⁇ ” (e.g., c) ⁇ e)), this means that the process steps are carried out in succession.
  • the final process step indicated in each case is followed by the process steps referred to in the general process description with the letters h) and i) and if desired g). In the case of version 2 step b) is followed by steps c)-i), with g) being optional.
  • step f) is carried out such that the hydrophobicizer is mixed with an already alkalified precipitated silica and versions wherein the hydrophobicizer is added before or at the same time as step e), i.e., the alkalifier is added.
  • the hydrophobicizer is added to the pulverulent, already alkalified precipitated silica.
  • Version 1 is particularly preferred. With very particular preference version 1 is carried out such that steps are carried out in the order c)+e) ⁇ d) ⁇ f) or c) ⁇ e) ⁇ d) ⁇ f) or c) ⁇ d) ⁇ e) ⁇ f).
  • organopolysiloxane derivatives may be used; it is, however, also possible to use other silicon compounds which react to give organopolysiloxanes under the chosen reaction conditions (for example, dichlorodimethylsilane in an aqueous environment).
  • R may be alkyl and/or aryl radicals, which may be substituted by functional groups such as the hydroxyl group, the amino group, polyethers such as ethylene oxide and propylene oxide, and halide groups such as fluoride.
  • R may also contain groups such as hydroxyl, amino, halide, alkoxy, alkenyl, alkynyl and aryl groups, and groups containing sulfur.
  • X may include reactive groups such as hydroxy, silanol, amino, mercapto, halide, alkoxy, alkenyl and hydride groups.
  • R is preferably rep methyl.
  • organopolysiloxane derivatives Because of the presence of certain functional groups in organopolysiloxane derivatives it is possible for salts or low molecular mass substances such as NH 3 , amines, alcohols, etc. to be formed, which can lead to disruptive impurities.
  • An important exception here is constituted by silanol-functionalized polysiloxanes, since the only impurity formed in that case is water, which is easy to remove under the chosen operating conditions.
  • the hydrophobicizer may comprise a methyl-terminated polydimethylsiloxane, in particular one having a viscosity of 5-100 mPa.s, 10-100 mPa.s, 30-100 mpa.s, preferably 40-60 mpa.s.
  • a suitable polysiloxane oil is DOW CORNING (R) 200 FLUID 50 CS.
  • Step g) is carried out with mixtures of the precipitated silica and the hydrophobicizer or with precipitated silicas already coated with the hydrophobicizer. It involves a heat treatment of the precipitated silica mixed or coated with hydrophobicizer, at a temperature of from 10 to 150° C., preferably from 100 to 150° C., more preferably at 105° C. to 110C. Step g) is carried out until a material has been formed which is wettable by water but for which silica and silicone oil no longer separate from one another on introduction into water. Accordingly the conditioning in step g) generally takes place for a period of 0.5 to 72 hours, preferably 0.5 to 2 hours. One preferred embodiment conditions at 100 to 150° C. for 0.5 to 2 hours.
  • step g) is followed immediately by step h) then a methanol wettability >20% is preferred. If, however, step g) is not carried out directly before step h) then the methanol wettability should be ⁇ 20%.
  • step g) is carried out after step d), it being possible if desired for steps e) and f) or else only e) or only f) to take place between steps d) and g).
  • the following embodiments are preferred: c)+e) ⁇ d) ⁇ f) ⁇ g) or c) ⁇ e) ⁇ d) ⁇ f) ⁇ g) or c) ⁇ d) ⁇ e) ⁇ f) ⁇ g) or c)+e) ⁇ f) ⁇ d) ⁇ g) or c) ⁇ e) ⁇ f) ⁇ d) ⁇ g) or c)+f) ⁇ e) ⁇ d) ⁇ g) or c) ⁇ f) ⁇ e) ⁇ d) ⁇ g) or c) ⁇ e)+f) ⁇ d) ⁇ g).
  • the conditioning time in step g) is 0.5 to 72 hours, preferably 0.5 to 12 hours, more preferably 0.5 to 2 hours.
  • the post-conditioning, partially hydrophobicized silica has a methanol wettability of 20% or more.
  • Step f) of the process of the invention can be carried out, in a version 6, by mixing an already conditioned precipitated silica after step g) with a hydrophilic precipitated silica.
  • a masterbatch i.e., a conditioned precipitated silica, obtained according to process steps a) to g), in accordance with one of the abovementioned embodiments and then to mix said masterbatch with a (hydrophilic) or water-containing precipitated silica.
  • a base silica according to step d) or e) is coated in a mass ratio of hydrophobicizer to precipitated silica of 3:1 to 1:5, preferably 1:1 to 1:3, with a hydrophobicizer, e.g., silicone oil, e.g., DOW CORNING (R) 200 FLUID 50 CS (dimethylpolysiloxane 50 mPa.s, terminated with trimethylsilyl groups, carbon content about 33%) (step f)).
  • the powder thus formed is subsequently conditioned for half an hour at a temperature of more than 100° C., preferably from 100 to 150° C., more preferably from 105 to 110° C. Conditioning (step g) is continued until a material has formed which is wettable by water (methanol wettability ⁇ 20%) but for which silica and silicone oil can no longer be separated from one another on introduction into water.
  • This masterbatch is subsequently mixed with a (hydrophilic) or water-containing precipitated silica (e.g., filtercake after step b) or silica dispersion after one of steps a) or c) or c)+e) or c) ⁇ e)).
  • a (hydrophilic) or water-containing precipitated silica e.g., filtercake after step b) or silica dispersion after one of steps a) or c) or c)+e) or c) ⁇ e)
  • the water content of the hydrophilic precipitated silica may vary within the ranges already stated.
  • Mixing the masterbatch with aqueous silica dispersions produces stable mixtures for which the hydrophobicizer—silicone oil for example—no longer separates from the silica.
  • the overall mixture typically includes 1 part by weight of hydrophobicizer, about 4-8 parts by weight of precipitated silica and 20-60 parts by weight of water.
  • a masterbatch (50% silica and 50% silicone oil) is mixed thoroughly with about 10-16 times the amount of filtercake (solids content about 20%) and about 10-20 times the amount of additional water.
  • the advantage of this procedure is that the water-wettable masterbatch (which may contain up to 75% of hydrophobic organopolysiloxane) can be dispersed very finely and stably, directly in the silica suspension, without the use of emulsifiers or surfactants being necessary.
  • the organopolysiloxane-containing silica thus obtained can be conditioned (step g)). These steps can be carried out individually, where appropriate with milling beforehand. Milling ought not, however, to be carried out prior to coating f). It is also possible to carry out two or more of these versions—that is, identical or different versions—in succession.
  • hydrophobicizers may be compounds of low volatility, an important part in the predistribution of the hydrophobicizers on the silica surface is played by capillary forces and diffusion events at the liquid/solid phase boundary.
  • Heat treatment i.e., process step h
  • step i takes place in accordance with known methods, e.g., impact classifier mills or jet classifier mills (Ullmann's Encyclopedia of Industrial Chemistry, 1992, 5th edition, vol. B1, page 5-20-5-39, page 17-1-17-17, incorporated herein by reference).
  • the precipitated silica of the invention can be milled to the desired ultimate fineness on a variety of mills such as, for example, an impact mill, air jet mill or opposed-jet mill. Classifying may take place during or after milling.
  • hydrophobic precipitated silicas of the invention are milled to a mean particle size d 50 of ⁇ 14 ⁇ m, preferably ⁇ 10 ⁇ m, more preferably ⁇ 7.5 ⁇ m, very preferably ⁇ 6 ⁇ m and in particular ⁇ 5 ⁇ m.
  • the precipitated silicas of the invention are used preferably in defoamer formulations for preventing excessive foaming.
  • the silicas of the invention can additionally be used in all applications in which silicas are commonly used, such as, for example, as a reinforcing filler in silicone rubber, in HTV silicone rubber as a lightening additive in peroxidically crosslinking systems, as a flow assistant, in battery separators, as an antiblocking agent, as a flatting agent in inks and paints, as a vehicle for—for example—agricultural products and foodstuffs, in coatings, in printing inks, in fire-extinguishing powders, in plastics, in the nonimpact printing sector, in paper stock, in the personal care sector, and in specialty applications.
  • silicas are commonly used, such as, for example, as a reinforcing filler in silicone rubber, in HTV silicone rubber as a lightening additive in peroxidically crosslinking systems, as a flow assistant, in battery separators, as an antiblocking agent, as a flatting agent in inks and paints, as a vehicle for—for example—a
  • the physicochemical data of the precipitated silicas of the invention are determined using the following methods:
  • the specific nitrogen surface area (referred to below as BET surface area) of the pulverulent, spherical or granular silica is determined in accordance with ISO 5794-1/Annex D (incorporated herein by reference) using an Areameter (Ströhlein, JUWE).
  • the method is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the “external” surface of the silica, in a method based on ASTM 3765 (incorporated herein by reference) or NFT 45-007 (section 5.12.1.3 (incorporated herein by reference)).
  • CTAB N-hexadecyl-N,N,N-trimethylammonium bromide
  • CTAB is adsorbed in aqueous solution with stirring and ultrasound treatment.
  • unadsorbed CTAB is determined by back-titration with SDSS (dioctylsodium sulfosuccinate solution, Aerosol OT solution) using a titroprocessor, the endpoint being given by the maximum turbidity of the solution and determined using a phototrode.
  • SDSS dioctylsodium sulfosuccinate solution, Aerosol OT solution
  • the temperature throughout all of the operations conducted is 23-25° C., to prevent crystallization of CTAB.
  • the back-titration is based on the following reaction equation: ( C 20 ⁇ H 37 ⁇ O 4 ) ⁇ SO 3 ⁇ Na + BrN ⁇ ( CH 3 ) 3 ⁇ ( C 16 ⁇ H 33 ) -> ( C 20 ⁇ H 37 ⁇ O 4 ) ⁇ SO 3 ⁇ N ⁇ ( CH 3 ) 3 ⁇ ( C 16 ⁇ H 33 ) + NaBr ⁇ ⁇ ⁇ SDSS ⁇ ⁇ CTAB
  • SDSS 0.00423 mol/l in deionized water
  • the consumption of SDSS solution for titrating 5 ml of CTAB solution should be checked 1 ⁇ daily before each series of measurements. This is done by setting the phototrode, before beginning the titration, at 1000 ⁇ 20 mV (corresponding to a transparency of 100%).
  • the titration vessel is closed with a lid and stirred using an Ultra Turrax T 25 stirrer (stirrer shaft KV-18G, 18 mm diameter) at 18 000 rpm for not more than 1 minute until wetting is complete.
  • the titration vessel is screwed onto the titroprocessor DL 70 and the pH of the suspension is adjusted with KOH (0.1 mol/l) to a figure of 9 ⁇ 0.05. If the pH is already greater than 9 no pH correction is performed, so as not to alter the surface.
  • the suspension is sonicated for 4 minutes in the titration vessel in an ultrasound bath (Bandelin, Sonorex RK 106 S, 35 kHz) at 25° C. It is followed immediately by pressure filtration through a membrane filter under a nitrogen pressure of 1.2 bar. The initial fraction of 5 ml is discarded.
  • CTAB CTAB ⁇ ⁇ (without ⁇ ⁇ moisture ⁇ ⁇ correction ) ⁇ ⁇ in ⁇ ⁇ m 2 ⁇ / ⁇ g * 100 100 - moisture ⁇ ⁇ content ⁇ ⁇ in ⁇ ⁇ %
  • the moisture content of the silica is determined in accordance with the below-described method of “Determination of Moisture Content or Loss on Drying”.
  • the carbon content in silicas is determined using the C-mat 500 (Ströhlein Instruments).
  • the samples are heat treated at about 1350° C. and the carbon is oxidized to CO 2 by a stream of oxygen.
  • the CO 2 is measured in an infrared cell.
  • the silica samples are measured.
  • the initial mass is 0.04-0.05 g.
  • the porcelain boat is covered with a porcelain lid. In the event of deviations >0.005% a greater number of measurements are carried out and the average is calculated.
  • the C-mat 500 is operated in accordance with the operating instructions from Ströhlein Instruments.
  • the method serves for determining the pH of an aqueous suspension of silicas at 20° C.
  • the pH meter Knick, type 766 pH meter Calimatic with temperature sensor
  • the pH electrode Schott N7680 combination electrode
  • the calibration function is to be chosen such that the two buffer solutions used include the expected pH of the sample (buffer solutions of pH 4.00 and 7.00, pH 7.00 and pH 9.00 and, where appropriate, pH 7.00 and 12.00).
  • the suspension is made up to the 100 ml mark using 50.0 ml of analytical-grade methanol and 50.0 ml of deionized water.
  • the suspension is shaken in the sealed vessel for 5 minutes using a shaker machine (Gerhardt, model LS10, 55 W, level 7) at 20° C.
  • the pH is measured directly thereafter.
  • the electrode is rinsed first with deionized water and then with a portion of the suspension, and then is immersed into the suspension.
  • a magnetic stirrer bar is then added to the suspension, and the pH measurement is carried out at constant stirring speed with a slight vortex being formed in the suspension. After exactly 5 minutes the pH is read off on the display.
  • DBP number which is a measure of the absorbency of the precipitated silica, is determined by a method based on standard DIN 53601 (incorporated herein by reference), as follows:
  • dibutyl phthalate is added dropwise to the mixture at a rate of 4 ml/min at room temperature by means of the Brabender T 90/50 Dosimat. Its incorporation by mixing takes place with only a small amount of force, and is monitored by means of the digital display. Toward the end of the determination the mixture becomes pasty, which is indicated by a sharp increase in the required force.
  • a display reading of 600 digits (torque of 0.6 Nm) an electrical contact shuts off both the kneader and the DBP feed.
  • the synchronous motor for the DBP feed is coupled to a digital counter, so that the consumption of DBP in ml can be read off.
  • DBP V * D * 100 E * g 100 ⁇ ⁇ g + K
  • DBP DBP absorption in g/100 g
  • the DBP absorption is defined for the anhydrous, dried silica.
  • the correction value K for calculating the DBP absorption. This value can be determined using the correction table below: for example, silica having a water content of 5.8% would mean an addition of 33 g/(100 g) for the DBP absorption.
  • the moisture content of the silica is determined in accordance with the below-described method of “determination of moisture content or loss on drying”.
  • the determination method is based on the following chemical reactions, where “Si”—OH is intended to symbolize a silanol group of the silica: “ Si”—OH+NaCl “Si”—ONa+HCl HCl+KOH KCl+H 2 O.
  • 10.00 g of a pulverulent, spherical or granular silica with a moisture content of 5 ⁇ 1% are comminuted for 60 seconds using an IKA universal mill M 20 (550 W; 20 000 rpm). It may be necessary to adjust the moisture content of the starting material by drying at 105° C. in a drying oven or by uniform moistening, and to repeat the comminution. 2.50 g of the silica thus treated are weighed out at room temperature into a 250 ml titration vessel and 60.0 ml of analytical-grade methanol are added.
  • the pH meter (Knick, type: 766 pH meter Calimatic with temperature sensor) and the pH electrode (Schott N7680 combination electrode) are calibrated at room temperature using buffer solutions (pH 7.00 and 9.00).
  • the pH meter is used first to measure the initial pH of the suspension at 25° C., and then depending on the result the pH is adjusted to 6.00 using potassium hydroxide solution (0.1 mol/l) or hydrochloric acid solution (0.1 mol/l).
  • the consumption of KOH or HCl solution in ml to reach pH 6.00 corresponds to V 1 ′.
  • V 1 ′ and V 2 ′ are first standardized to the theoretical sample weight of 1 g and expanded by a factor of 5, giving V 1 and the Sears number V 2 in the units ml/(5 g).
  • Hydrophobic silicas and silicates can be made water-wettable by adding methanol. This is done by means of methanol/water mixtures of different concentration. In this way it is possible to draw conclusions concerning the degree of hydrophobicization of the silicas or silicates.
  • each hydrophobic silica or silicate is weighed out into 6 centrifuge tubes each with a capacity of 15 ml, and to each of the tubes there are added 8 ml of a methanol/water mixture of ascending methanol concentration.
  • the methanol concentration of the mixtures is guided by the anticipated methanol wettability.
  • the centrifuge tubes are tightly closed and then shaken vigorously (10 up-and-down movements).
  • the tubes are then centrifuged at 2500 rpm for 5 minutes.
  • the wetted fractions form a sediment whose volume can be read off on the scale on the centrifuge tubes.
  • the sediment volumes are plotted against the methanol/water mixture concentration on a graph.
  • the individual measurement points produce a curve (x axis: percentage fraction of methanol in the methanol/water mixtures, y axis: height of sediment) whose position and slope characterizes the degree of hydrophobicization of the precipitated silica.
  • x axis percentage fraction of methanol in the methanol/water mixtures
  • y axis height of sediment
  • the application of laser diffraction for the determination of particle sizes is based on the phenomenon whereby particles scatter monochromatic light with a different intensity pattern in all directions. This scattering is dependent on the particle size. The smaller the particles the greater the scattering angles.
  • the laser diffraction instrument LS 230 (COULTER) and the liquid module (small volume module plus, 120 ml, COULTER) are warmed up for 2 h and the module is rinsed three times with ethanol. An offset measurement and an adjustment are made by the instrument automatically each hour.
  • the pump speed is set at 50%.
  • a background measurement is carried out automatically before each measurement.
  • a single-use pipette is rinsed three times with the suspension before each sampling. About 2 ml of the suspension are taken up with the pipette and 1-3 drops are metered immediately into the liquid module of the instrument. The remainder in the single-use pipette is introduced back into the glass beaker. Following the addition there is a waiting time until the laser diffraction instrument indicates constant concentration. Suspension is added until a light absorption figure of 8 to 12% is reached and the instrument reports “OK”. The measurement is made at room temperature with the evaluation model of the above-determined .rfd file.
  • the software calculates the particle size distribution on the basis of the volume distribution, taking into account the Mie theory and the optical model parameters (.rfd file).
  • the solids content of the precipitated suspension is determined gravimetrically by filtering the sample.
  • V suspension 100.0 ml of the homogenized precipitation suspension (V suspension ) are measured off at room temperature using a measuring cylinder.
  • the sample is filtered through a circular filter (TYPE 572 from SCHLEICHER & SCHUELL) in a porcelain suction filter unit, but is not sucked dry, so as to prevent cracking of the filter cake.
  • the filtercake is washed with 100.0 ml of deionized water.
  • the washed filtercake is filtered completely, transferred to a tared porcelain dish and dried to a constant weight in a drying oven at 105 ⁇ 2° C.
  • the weight of the dried silica (msample) is determined.
  • the moisture content or loss on drying (LD) of silicas is determined by a method based on ISO 787-2 (incorporated herein by reference) after 2-hour drying at 105° C. This loss on drying is accounted for predominantly by aqueous moisture.
  • the weighing boat is weighed to an accuracy of 0.1 mg on a precision balance, in order to determine the final weight A.
  • the loss on ignition of silica at 1000° C. is determined in a method based on DIN EN ISO 3262-1 (incorporated herein by reference). At this temperature physically and chemically bound water and other volatile constituents escape.
  • the moisture content (LD) of the sample investigated is determined by the afore-described method “determination of moisture content or loss on drying” in a method based on DIN EN ISO 787-2 (incorporated herein by reference).
  • 0.5 g of the pulverulent, spherical or granular silica are weighed out to an accuracy of 0.1 mg into a tared porcelain crucible purified by calcining beforehand (initial mass E).
  • the sample is heated in a muffle furnace at 1000 ⁇ 50° C. for 2 h.
  • the porcelain crucible is subsequently cooled to room temperature in a desiccator with silica gel as drying agent.
  • the final mass A is determined gravimetrically.
  • A denotes final mass in g
  • E denotes initial mass in g
  • LD denotes loss on drying, in %.
  • the tapped density is determined in a method based on DIN EN ISO 787-11 (incorporated herein by reference).
  • a defined amount of a sample which has not been sieved beforehand is introduced into a graduated glass cylinder and subjected to a fixed number of jolts by means of a jolting volumeter. In the course of jolting the sample undergoes compaction.
  • the result of the analysis conducted is the tapped density.
  • the measurements are carried out on a jolting volumeter with counter from Engelsmann, Ludwigshafen, type STAV 2003.
  • the suspension was filtered and washed sufficiently with deionized water.
  • the resulting solids content of the filtercake is 15-17%.
  • the filtercake With deionized water introduced initially, and with gentle stirring, the filtercake is liquefied so as to give a silica suspension with a solids content of 6-11%. This suspension was then adjusted to a pH of 9 using NaOH solution (50% by weight). Immediately thereafter the suspension was spray dried (drier exit temperature: 130° C.). After the spray drying operation the precipitated silica was sprayed uniformly in a mixer (M5R, L ⁇ DIGE) with silicone oil (dimethylpolysiloxane, methyl-terminated, 50 mpa.s, e.g., DOW CORNING (R) 200 FLUID 50 CS, carbon content about 33%) with stirring and was heat treated in a muffle furnace at 200° C. for 3 h. The dried precipitated silica was milled using an impact classifier mill (50 ZPS, HOSOKAWA-ALPINE).
  • an impact classifier mill 50 ZPS, HOSOKAWA-ALPINE
  • the resulting product has the following physicochemical parameters: BET 56 m 2 /g Carbon content 7.9% pH 9.7 Mod. Sears number 1.2 ml/(5 g) Sears/BET ratio 0.021 ml/(5 m 2 ) DBP 175 g/100 g CTAB 66 m 2 /g BET/CTAB ratio 0.85 Methanol wettability 65% Mean particle size d 50 6.4 ⁇ m (3 min US/20 W) Loss on ignition 17.7% Tapped density 127 g/l
  • precipitated silicas were investigated for their suitability in defoamer formulations.
  • the properties of precipitated silicas were investigated using model formulations which cover a wide range of the fields of application and formulations that are used industrially.
  • a basic prerequisite for an effective formulation is an efficient dispersion step of the highly dispersed precipitated silica in selected oils.
  • the task here is to distribute the precipitated silica as homogeneously as possible in the oil phase without destroying it through excessive shearing forces.
  • This defoamer test is particularly suitable for depicting foaming systems in motion.
  • Test detergent consisting of: Sodium dodecylbenzenesulfonate (Maranil ® Paste A 55, 11.67% Cognis Dtl. GmbH & Co. KG, datasheet revision No. 9-01.2000) Fatty alcohol C16-C18 with about 5 mol of EO 1.21% (Dehydol ® TA 5, Cognis Dtl. GmbH & Co. KG, datasheet revision No. 3-01.1998) Fatty alcohol C12-C18 with about 7 mol of EO 7.24% (Dehydol ® LT 7, Cognis Dtl. GmbH & Co. KG, datasheet revision No.
  • test detergent all of the raw materials in powder form were charged to a standard commercial mixer, e.g., a Lödige mixer.
  • the liquid raw materials were sprayed onto the powder materials with stirring. After all of the liquid raw materials were sprayed on it was necessary to continue mixing for about 10 minutes in order to achieve a homogeneous distribution.
  • the pump test apparatus is depicted diagrammatically in FIG. 1 . It consists of a jacketed glass vessel ( 1 ), a temperature-conditioned oil bath, a gear pump ( 2 ) and a foam height detection system employing photoelectric cells ( 3 a and 3 b ).
  • a wash liquor was prepared by stirring 6 g of the test detergent into 994 g of water. This liquor is adjusted to a pH of 13 by adding sodium hydroxide solution.
  • test defoamer dispersion ((0.07 ml in the case of mineral oil dispersions and 0.01 ml in the case of silicone oil dispersions) was added all at once to the foam solution, using a microliter pipette, and the development of the foam height was recorded as a function of time.
  • the schematic course of the plot is depicted in FIG. 3 .
  • the foam rises to ( 5 ).
  • the defoamer formulation is injected ( 6 ).
  • the foam collapses in on itself.
  • the remaining foam height emerges as a function of the quality of the defoamer formulation.
  • the ability of the defoamer to reduce the foam height immediately following addition, down to a defined foam height, is described by the knockdown parameter ( 7 ). This is defined as the difference between the foam height at the moment when the defoamer formulation is added and the minimal remaining foam height.
  • the time which elapses between addition of the defoamer formulation and attainment of the lowest foam height is referred to as the knockdown time ( 8 ).
  • the action of the defoamer formulation subsides again with a differing rate according to its quality.
  • the foam height rises again to ( 9 ).
  • the time which elapses between the moment when the minimum foam height is reached, following the addition of the defoamer formulation, and the time at which a foam height of 200 mm is regained is characterized by the hold down ( 10 ) parameter.
  • the hold down is therefore a measure of the service life of the defoamer, i.e., the duration of its activity. Defoamer formulations where the foam height is not reduced to below 200 mm are not assigned a hold down.
  • the extent of foam formation/amount of foam was regulated by factors including the flow rate, nozzle shape, etc.
  • An advantage of this test method is that a variety of aqueous, thermally conditioned foam solutions can be tested as test solutions under dynamic conditions closely resembling those prevailing in practice. Additionally the defoamer is monitored over a defined period of time. It is possible to state whether the defoamer and hence the silica present therein exhibits an action but also to state how quickly the action begins, how great it is, and how long it lasts. The subsidence of the action of defoamers is a known phenomenon which is accelerated further by extreme conditions (high temperature, high alkalinity, high shearing forces). Since all of these conditions can be mimicked it is possible to say what silica in combination with an oil under real-life conditions exhibits the best defoaming properties.
  • Both a mineral oil dispersion and a silicone oil dispersion were produced from the product from example 1 and were investigated for defoaming action.
  • Both a mineral oil dispersion and a silicone oil dispersion were produced from the hydrophobic precipitated silica Sipernat D10 (DEGUSSA AG), as comparative example 1.
  • Comparative example 2 involves a hydrophobic precipitated silica from patent EP 1 281 735 (incorporated herein by reference), example 2. Both a mineral oil dispersion and a 25 silicone oil dispersion were prepared from this precipitated silica and were investigated for defoaming action.
  • Example 1 BET m 2 /g 56 110 96 CTAB m 2 /g 66 78 41 BET/CTAB ratio — 0.85 1.41 2.34 Carbon content % 7.9 2.9 3.9 pH — 9.7 9.9 7.9 DBP g/100 g 175 210 207 Mod.
  • German application 102004005411.8 filed on Feb. 3, 2004 is incorporated herein by reference in its entirety.
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US8614256B2 (en) 2013-12-24
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CA2495735A1 (en) 2005-08-03
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