CA1189681A - Precipitated silicas and process for producing same - Google Patents
Precipitated silicas and process for producing sameInfo
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- CA1189681A CA1189681A CA000465709A CA465709A CA1189681A CA 1189681 A CA1189681 A CA 1189681A CA 000465709 A CA000465709 A CA 000465709A CA 465709 A CA465709 A CA 465709A CA 1189681 A CA1189681 A CA 1189681A
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Abstract
Abstract of the Disclosure Precipitated silicas having the following physicochemi-cal characteristic data:
according to Fig. 1 are produced by a process in which an original suspension of pre-cipitated silica produced according to German Auslegeschrift No.
1,467,019 is diluted and an alkali metal silicate solution, sul-phuric acid and water are simultaneously added, the pH value being kept constant between 7 and 9. The precipitated silicas are then filtered, washed, dried and micronized by means of a micronizer. Because of their abrasiveness the precipitated silicas can be used as polishing agents and abrasives and the micronized silicas may be used as polishing agents, abrasives and thickeners in toothpastes.
according to Fig. 1 are produced by a process in which an original suspension of pre-cipitated silica produced according to German Auslegeschrift No.
1,467,019 is diluted and an alkali metal silicate solution, sul-phuric acid and water are simultaneously added, the pH value being kept constant between 7 and 9. The precipitated silicas are then filtered, washed, dried and micronized by means of a micronizer. Because of their abrasiveness the precipitated silicas can be used as polishing agents and abrasives and the micronized silicas may be used as polishing agents, abrasives and thickeners in toothpastes.
Description
The present inventlon relates -to precipita~ed silicas and their production.
This application is a divisional application of copend-ing Canadian application No. 400,097 filed March 3, 1982.
A number of processes for producing low-structured pre-cipitated silicas are known. According to German Offenlegungss-chrift 2,344,31~ a prepolymerized sodium silicate solution is produced first by adding 5 to 10~ by weight of sodium sulphate to a sodium silicate solution and the silica is then precipitated by adding acid or a portion of the prepolymerized sodium silicate solution i5 adjusted with acid to a pH value between 6.5 and 11 and the silica is finally precipita-ted by simultaneously adding sodium silicate solution and acid at a constant pEI value. German Offenlegungsschrift No. 2,3~4,805 describes a process in which an alkali metal silicate begins to precipitate, whereupon the addition of acid in interrupted~ the reaction solution is aged for a period of up to Eour hours and simultaneous addition of acid and alkali metal silicate is then continued until the de-sired product is obtained.
German Offenlegungsschrift No. 2,446,038 describes a method in which at a p~l value of 9 and at a temperature of 65C
prepolymerized sodium silicate solution, to whlch 7~ by weight of electrolyte have been added, and a dilu-te (10 to 25% by weight) acid are fed into an electrolyte-containing solution of 3 to 15~
by weight of sodium sulphate. The pH is then adjusted -to a value below 5, followed hy aging at 77C for twen-ty minutes.
In German Offenlegungsschrift No. 2l522,~86 the produc-tion of a precipitated silica is described in which a portion (i.
e., 8 to 50~) of the entire alkali silicate solution is ini-tially used into which alkali metal silicate solution and acid flow sim-ultaneously until at the completion of the addition of alkali metal silicate and acid 20 to 500~ of the initial alkali metal silicate solution have been reacted. The pH is then lowered to a value below 6. Dilute (8 ~o 22~. by weight) sulphuric acid must be used.
AccordincJ to a further process dilute sodium silicate solution (density - 1.]52) and dilute hydrochloric acid (2N) are precipitated over a period of 2 hours on a 2o by ~eight dispersion at 80C and in the p~ range ~rom 7 to 7.5. The disper-sion is prepared from "light silica" (production not disclosed) and water. Th~reafter water is used for dilution. The silica thus obtained is distinguished by a very low powder density.
Althouqh the production methods cited above resul~ in low-structured silicas, these methods have certain disadvalltages which, on applying then on an industrial scale, render then relatively cumbersome and less economical as compared with conven-tional methods for ~roducin~ reinforcing silicas for rubber.
These disadvantaqes are:
(a) the introduction of an additional partial step for producing silica- or electrolyte-containing precipitation stocks-starting solutiolls, of electrolyte-containing precipitation reactants and (b) the distinct reduction of the space time yields in the pre-cipitation of these silicas due to the required introduction of an interruption interval (aginq step), due ~o the use o~ dilute reclction components and due to the longer precipitation times required.
Under the circumstances it is an operational require-ment to produce precipitated silicas having low structures in a simple, economical, optimized manner adapted to the opera-tional sequence of the productions of reinforcing fillers.
According to German Auslegeschrift No. 1,467,019 it is 3n known to precipitate amorphous precipitated silicas by simultan~
eously adding acid-and alkali metal silicate solutions to an alk-aline stock starting solution while observing certain process ~8~
conditions. Precipitated silicas o~tained by means of this pro-cess may be graded as substances having rela~ively high structures (relatively high oil a~sorption), relatively high specific surface areas, low powder densities and low solid contents of their filter cakes. ~ecause of their excellent dispersibility in rubber mix-tures they are preferred reinforcing fillers in the rubber indus-try, where they are in widespread use for the manufacture of rub-ber soles, tire treads and tec`hnical articles with or without the application of silanes. These types of precipitated silicas are constantly available as standard reinforcing fillers or as main products in any plant producing fillers. '~his also applies to the original precipitated suspension, which is stored as an inter-mediate product in large suspension storage tanks before they are passed to the filter presses for separating the electrolyte.
Surprisingly it has been ~ound that an original precipita-ted silica suspension produced according to German Auslegeschrift No. 1,467,019 can be used as an inexpensive starting product for obtainin~ precipitated silicas having low structure, hi~h hard--ness and this even in the case of ~reat fineness if speci~ic measures are followed in the subsequent modifica-tion and further proc~ssing. In this manner it is possible to avoicl ent,irely the op~rationally cumbersome, additional, frequently even unecomonical production of salt solutions for initially the precipitation, the economically absolutely intolerable redispersion of the dried precipitated silica powders to silica dispersions as the precipi-tation initial solution and the preparation of electrolyte-con tainin~ alkali metal silicate or acid sclutions and thus to simp-lify substantially the processes of the prior art and to reduce their costs. This also applies to the reduced space time yield since the process according to the present invention can be carried out without interruption intervals, ~ith relatively short precipi-tation times and concentrated reaction components.
3 ~
The present invention will be illustrated by way of the accompanying drawings, in which:-Fig. 1 is a particle size distribution curve of theprecipitated silica according to the present invention as deter-mined by the Coulter counter.
According to the present invention there are provided a precipitated silicas which have -the following physical data:
micronizer BET surface area according to DI~ 66131 sq m/g 15-110 tamped powder density according to DIN 53194 g/l 90-650 Cu abrasion in a 10%
glycerine dispersionmg 5--30 bright reference value A
according to DIN 55921 % 90-96 particle size distribu-tion curve as determined by the Coulter counter according to Fig. 1 "ALPINE retained o~ sieve"
> 63~m % by weight <0.1 viscosity in a 30~
glycerine- and water dispersion ~
(Brookfield RTV Sp5)mPas 60,000 The high tamped powder densities, which are three times the value for the tamped powder densities of conventional pre-cipitated silicas for reinforcing rubber permanen-tly reduces the expenditure for packing rnatrial, emptying, transport and storage.
When incorporating the precipitated silicas the relatively small processing volumes are appreciated by the consumer.
The high, precisely ad~ustable Cu-abrasion value permits its use as an abrasive and polishing agent. Surprisingly it has been found that the abrasiveness does no-t permanently decrease, as is usual, with increasing fine division of one and the same basic silica material so that the combined property abrasiveness and high degree of fineness make this silica a valuable filler ;~8~
for toothpastes. The maintained abrasion effect with simultan-eously high degree of fineness thus permits the use of micronizers (air or steam jet mills) which, because of the substantially - ~a -$~
mutual grain pulverization, avoids wall abrasion in the grinding mill due to the principle of substantially mutual grain pulveri-zation and thus results in briyh~er, purer final products as com-pared with the products produced by the mills provided with mech-anical impact tools.
The unique combination of abrasive and thickening effect is particularly interesting for the use o~ the precipi~ated silica according to the present invention as a cleaning agent in tooth-pastes. This combined property which has been observed only in the micronized, finely divided variant enables the cosmetics in-dustry to manage with a single silica component and in most cases with smaller amounts.
The present invention also provides a process for pro-ducing the precipitated silicas according to the present invention which have the following physicochemical characteristic data:
micronizer BET surface area according to DIN 66131 sq m/g 15-110 tamped powder density 20 according to DIN 53194 g/l 90-650 Cu abrasion in a 10~
glycerine dispersionmg 5 30 bright reference value A
acco~ding to DIN 55921 ~ 90 96 particle size distribu-tion curve as determined by the Coulter counter according to Fig. 1 ''ALPINF retained on sieve"
>63~m ~ by weight <0.1 viscosity in a 30%
glycerine-water dispersi~n (1:1) (Brookield RTV Sp5) mPas 60 000 In the process an original precipitated sili~a, pro-duced bY precipitatin~ the silica in an alkali metal silicate solution having a concentration of approximately 5 to 25g of SiO2 per litre of solution with an acidic alkali metal silicate solu-tion having specific solution concentrations and specific feed rates while maintaining a ~recipitation temperature between 80 and 90C in the reacti.on medium the viscosity of the reaction medium being kept uniformly low during a period of at least 30 of the total precipitation time, the pH value being maintained between 10 and 12 and the addition of ~he reactants being termina-ted only when the viscosity, after passing through a maximum, has decreased to a value of less than 100% of the initial viscosity, is diluted with hot water to a content of precipitated silica of 10 to 30 g per litre and a sodium sulphate content of 6 to 20 ~
of Na2SO4 per litre, heated to a temperature of 85 to 95C, the pH is adjusted with sulphuric acid to a value of 7 to 9 and while keeping this pH value constant by the simultaneous addi~ion of alkali metal silicate solution, sulphuric acid and, as required, hot water a precipitated silica concentration of 40 ~o 80 g is 20 obtained over a precipitation time of 15 to 180 minutes, the suspension is acidified with concentrated sulphuric acid to a p~l value below 7, the precipitated silica is separated from the sus-pension by a filter press, washed, dried and micronized by a micronizer.
In a preferred embodiment an original precipitated silica suspension, which according to German Auslegeschrlft No. 1,467,019 is intensively sheared during its production phase, is used.
This is always advantageous in cases when particularly high powder densities and hi~h Cu-abrasion values are to be attained. In a particular embodiment of the present invention the shearing op-e.ration can be carried out according to German Patent No. 1,767, 332.
The alkali me~al silicate solutions used may have a weight ratio of SiO2:Na2O = 2 to 4. In a preferred embodiment of the present invention the alkali metal silicate solution can have a concentration of 8.0~ by weiyht of Na2O and 26.8% by weight of SiO2. This corresponds to a weight ratio of SiO2:Na2O - 3.46.
In the simultaneous addition of alkali metal silicate solution, sulphuric acid and, as required, hot water 0.5 to lO
litres of alkali metal silicate solution having a density of 1.353, a weight ratio of SiO2:Na2O = 3.46 may be added per lO
litres of precipitated silica suspension per hour as well as 0.5 to l litre oE a 96% sulphuric acid per hour and up to lO litres of hot water per hour.
The concentration of the sulphuric acid used may be up to 96% hy weight. In a preferred embodiment the concentration of the sulphuric acid may be up to 50% by weight.
The process for producing the precipitated silica has the following advanta~es:
(a) the high content of solids in the filter cake of up to 50~
by weight reduces the energy requirements of the drying process and thus the drying costs to approximately 25% of the values for `t.h~ reinforcing silicas used in the rubber sector, (b) the high content of s~lids in the filter cake of up to 50%
doubles the capacity of the filter press, (c) the relatively low specific surface area of the precipitated silica having a lower structure results in distinctly reduced washing times and thus in savings of wash water and in additional capacity of the filter press, and (d) there exists the possibility of adjusting the physicochemical characteristic data of the silica accordin~ to the present inven~
tion in a controlled manner.
The precipitated silica according to the present inven-tion and the process for producing same are explained and describ-ed in greater detail by means of the following Examples:Example 1 ~Comparison Example~
This Example describes the production of a precipitated silica according to the German Auslegeschrift No. 1,467,019.
73 litres of hot water and 5.25 litres of sodium sili-cate solution (density:1.353 g/ml weight ratio of .SiO2:Na2O =
3.46) are heated to 85C in a rubberized 120-litre precipitator with stirring. During the next 90 minutes while s-tirring and maintaining the temperature of 85C 11 l~h of sodium silicate solution (density = 1.353 g/!ml, weight ratio of SiO~:Na2O - 3.46) and 0.965 l/h of a concentrated 96~ sulphuric acid are simultan-eously dosed into this alkaline precipitation solution.
The precipitated silica suspension is then adjusted with a concentrated 96% sulphuric acid to a pH value of 8.5. This is done by feedin~ acid in for several minutes at a rate of 1.25 litres per hour. The precipitated silica thus obtained has a solids content of approximately 85 g per litre. Its Na2SO4 con-tent is approximately 55 g per litre. It is used as A so-called "original precipitated silica suspension" for producing the pre-cipitated silicas according to the present invention as describedin the Examples hereafter.
The precipitated silica suspension is then acidified with a concentrated 96% sulphuric acid to a pH value of 3.5, whereupon the precipitated silica is separated from the suspension by means of a laboratory filter press. The filter cake is then washed with water, dried at a temperature of 110 to 120C and ground in a laboratory pinned disc mill. The physicochemical data have been compiled in the following Table I.
Example 2 The "original precipitated silica suspension" of Exampl~
1 is diluted with water until the precipitated silica content is 20 g per litre and the Na2SO4 content is 13 g per li~re.
~ 8 ]0.5 litres of this suspension are heated to 85~C in a rubberized 30-litre precipitator while stirrin~. While maintain-inq this temperature and a pH ~Talue of 8.5 for 30 minutes in sodium tetrasilicate solution (8,0% of Na2O and 26.8% of SiO2, density 1.353 g~ml, weight ratio of SiO2:Na2O = 3.46) at a rate of 92.4 ml per minute, a 50~ sulphuric acid at a rate of 19.6 ml per minute and water at a rate of 185.4 ml per minute are simul-taneously added to the precipitated silica suspension. Su~sequent-ly the precipitated silica suspension is adjusted with a 50%
sulphuric acid to a pH value of approximately 3.5. On terminating the precipitation time the precipitated silica content is 64 g per litre.
The silica thus obtained is separated from ~he suspen-sion by means of a laboratory filter press. The filter cake is washed with water until it is low in salt, whereupon it is dried at 110 to 120C and ground in a laboratory pinned disc mill. The characteristic data have been compiled in the following Table I.
Example 3 The procedure is the same as that in Example 2, but the amount of the simultaneously dosed components sodium tetrasilicate, sulphuric acid and water is halved. As compared with Example 2, the tamped powder densi.ty is practically doubled by this measure wh.ile the abrasiveness drops distinctly. The precipitated silica content o~ the suspension is 49 g per litre. The characteristic data have been compiled in the following Table I.
Example 4 The procedure is the same as that in Example 3, but the precipitation time is extended from 30 to 60 minutes. The pre-cipitated silica content is 64 g pex litre. As compared with theprecipitated silic~ obtained in the Examples 2 and 3 the tamped powder densit~ is distinctly higher. This also ~pplies to the _ 9 _ Cu abrasion~ The characteristic data have been compiled in the following Table I.
Example 5 The procedure of Example 4 is followed bu~ the precipi-tation time is raised ~rom 60 to 120 munutes and the amounts of the sumultan-eously dos0d compone~ts sodi~ tetr~ te, sulphuric acid and water are halved. The dosaqes are sodium tetracilica~e 23.1 ml per minutes, sulphuric acid 4.9 ml per minute and water 46.35 ml per minute. The precipi tated silica content is 64 g per litre. The tamped powder density and the abrasion values are even hiqher. The characteristic data have been compiled in the following Table I.
Example 6 The procedure of Example 4 is followed but with the diffenence that the "original precipitated silica suspension" o~f Example 1 is diluted only to a precipitated silica content of 30 g per litre and an Na2SO~ content of approximately 20 g per litre.
10.5 litres of this suspension are used for the further precipi-tation~ The precipitated silica content obtained is 71 g per litr~. The tamped powder density and the abrasion slightly de-crease as compared with the data for the precipitated silica ac-cording to ~xample 4. The characteristic data have been compiled in the following Table I.
Example 7 The procedure of Example 4 is followed but with the diffexence that the so-called "original precipitated silica suspension" of Example 1 is diluted with additional water to a precipitated silica content of 13 g per litre and an Na2SO4 con-tent of 8.5 g per litre. However, the addition of 92.7 ml of water per minute during the precipitation is dispensed with.
A content of precipitated silica of 64 g per litre is obtained.
The characteristic data o~ this precipitated silica have been compiled in the following Table I~
Example 8 The procedure of Example 7 is followed but with the dif-ference that the precipitation is carried out at 95C and the precipitation time is reduced from 60 to 45 minutes. A precipi-tated silica content of 52 g per litre is obtained. The charac-teristic data of the precipitated silica obtained have been com-piled in the following Table I.
Example 9 First an "original precipitated silica suspension"
according to Example 1 is produced, it has a content of 80 g of precipitated silica per litre and of approximately 52 g of Na2SO4 per litre as well as a pH value of 8.5. However, during the entire precipitation time of 90 minutes the suspension is in-tensively sheared by means of a rotary pump, which recirculates the content of the cup several times. Detailed data on the ap-paratus equipment and the shear conditions can be found in German Patent No. 1.767,332, particularly in column 8, line 31 to 68.
The original silica suspension produced in this manner is adjusted with water to a precipitated silica content of 20 g per litre and an Na2SO4 con-tent of 13 g per litre. 10.5 litres of this suspension serve Eor the subsequent precipitation, which is carried out according to Example 3.
The resulting content of precipitated silica is 49 g per litre. The characteristic data of the precipitated silica have been compiled in the following Table I and show that the abrasion values and the tamped powder density of the precipitated silica are substantially increased by the measure of shearing as com-pared with the corresponding values of a precipitated silica produced from a non-sheared original precipitated silica suspen-sion.
Example 10 The p~ocedure o~ ~xample 9 is followed but with the ~ 11 --~8~ ;3~
single difference ~hat the precipitation time is extended from 30 to 60 minutes. ~ precipitated silica content of 64 g per litre results~ An appreciable increase of both the abrasion value (by 92%) and the tamped powder density (by 24%) is attained once more.
Example 11 The large-scale industrial production of the precipitated silica according to the present invention is explained hereafter:
In a wooden 70 cu m precipitating vat provided with a paddle mixer the formula of Example 1 adapted to the relative sizes is used and an original precipitated silica suspension having a pH value of 8.5 and a content of precipitated silica of approximately 85 q per litre and a content of Na2SO4 of approxi-mately 55 g per litre is first produced. 8 cu m of this supension are then left in this wooden 70-cu m vat and mixed with 26 cu m of hot water to a precipitation solution containing approximately 20 g of precipitated silica per litre and approximately 13 g of Ma2SO4 per litre and heated to 85C. While keeping the tempera-ture and the pH value of 8.5 constant 8.8 cu m of sodium silicate solution (density 1.353 g/ml, modulus of SiO2:Na2O = 3.46), 0.90 cu m of a concentrated 96% sulphuric acid and 19.0 cu m of hot water are simultaneously fed into the precipitation solution for 45 minutes. After completed precipitation the suspension is ad-justed with a concentrated 96% sulphuric acid to a pH value of 3.5 within a few minutes. The resulting content of precipitated silica is approximately 64 g per litre.
For further processing the precipitated silica is sep-arated from the suspension by means of a filter press, washed, dried in a shelf dryer and micronized in a bowl mill. The charac-teristic data of the precipitated slilica obtained are listed in the following Table I.
Example 12 The apparatus corresponds to that of Example 11. As described therein, an "original precipitated silica suspensio~"
having a pH value of 8,5 and a content of precipitated silica of approximately 85 g per litre and a content of Na2SO4 of approxi mately 55 g per litre is first produced.
10 cu m of this suspension are then left in a 70 cu m wooden vat, mixed with 27 cu m of hot water to yield a precipi-tation solution containing approximately 23 g of precipitated silica per litre and 15 g of Na2SO4 per litre and is heated to 85C. At this temperature and while maintaining a pH value of 8.5 to 9.0, 9.6 cu m of sodium silicate solution (density: 1.353 g/ml, weight ratio of SiO2:Na2O = 3.46), 0.94 cu m of a concen-trated 96% sulphuric acid and 20~0 cu m of hot water are simultan-eoulsy dosed into the suspension for a period of 80 minutes.
After completed precipitation the suspension is adjusted with a concentrated 96% sulphuric acid to a pH value of 3.5. The content of precipitated silica is 64 g per litre.
For further processing the precipitated silica it is separated from the suspension by means of a filter press, washed, dried in a shelf dryer and micronized with steam in a Jet-o-mizer, type 0808. The ~rinding capacity is 50 kg per hour at a grinding pressure of 8.5 bars. The characteristic data of the precipitated silica obtained have been compiled in the following Table I.
E~ample 13 The procedure of Example 11 is followed. The only dif-ference is the different kind of grinding by means of a microni~er using a steam jet and the conditions of Example 12 Example 14 The procedure of Exa~ple 12 is followed, but the precipi-tation time is extended from 80 to 110 minutes. The dosed quanti-ties of concentrated sulphuric acid, hot water and sodium silicate solution are correspondingl~ adapted. On completed precipitation the content of precipi~ated silica is 64 g per litre. The condi-tions of micronizing with s~eam are also changed, i.e.~ grinding capacity 630 kg per hour, grinding pressure 11 bars ~ he physicochemical characteristic data of the precipi~
tated silicas produced according to the Examples 1 to 14 are evi-dent from the following Table I. The data of E~ample 1 are those of a comparison example according to the prior art, describing the production of a precipitated silica ha~ing insufficient abra-sion properties and a low tamped powder densityO The physico-chemical data of the precipitated silicas obtained according tothe Examples 2 to 10 represent products of laboratory processes while the data of the Examples 11 to 14 represent the physical data of the precipitated silicas produced under plant conditions.
The physical data specific surface area, tamped powder density and bright reference value A are determined by means of DIN methods.
The measurement of the Cu abrasion and the determination of the ALPINE retained on sieve >63~m are described hereafter.
Determination of the Cu Abrasion in 10~ Glycerine Dispersion a) Production of the Glycerine Dispersion 153 q of anhydrous glycerine (DAB7; S=1.26) are weighed into a 250-ml polyethylene beaker. 17 g of precipitated silica are carefully intermixed with a spatula. The mixture is subsequ-ently homo~enized with a vane stirrer (diameter 5.2 cm) Eor 12 minutes at 1500 r.p.m.
b) Carrying out the Abrasion Measurement The abrasion measurement is carried out in an abrasion tester, which is known from the following publications: 1) P
Pfrenqle, Fette, ~eifen, ~nstrichmittel, 63 (5) (1961) pages 445 to 451 "Abrasion and Reinigungskraft von Putzkorpern in Zahnpasten";
~) A ~ , F. DAN~ arfu~erie and ~o~metik 59 (2) (~-978) pages 37 to 45 "Anwendunqstechnische~ru'fung von Zahnpas-~en". For this purpose each of the six troug~ls of the tester is coated with 20 ml of the homogeneous dispersion. The ahrasion caused by six surface -ground nylon brushes on six surface-ground Cu sheets (electroly-tic copper) in fiye hours with 50 000 double strokes is determined by differential weighing. In the computation of the abrasiveness average values are determined from ~he values obtained. The abrasion (abrasiveness) is defined in mg of Cu.
Determination of the Residue on Sieve with the ALPINE Air Jet Sieve In order to determine the residue on sieve, the precipi-tated silica is passed through a 500~ sieve to destroy possibly present exhaust air knots, whereupon 10 g of the screened material are put on a specific air jet sieve and screened at 200 mm water column negative pressure. Precipitated silica particles deposited of the plexiglass cover of the sieve are knocked off by a number of knocks on the knob of the sieve cover. The screening is com-pleted when the residue remains constant, which usually is evident from the fluid appearance. To be on the safe side, screening is continued for another minute. In the case of material having particle portions < 500~ the sample is no~ passed through a sieve first, but is put directly on the air jet sieve. If ag~lomerates fonm, the scre~nin~ process is briefly interrupted and the agglo~erates are destroyed with a brush und~er sli~ht pressure. After the screening process, the residue retained on sieve is carefully knocked o~f from ~he air jet sieve a~ h~1 back.
Computation ~ The residue retained on sieve is defined in percent in conjunction with the width of mesh of the sieve.
Apparatus: ALPINE air jet sieve, laboratory type S 200 air jet sieve having a sieve weave according to DIN 4 188.
Testing of the rheological efficiency of abrasive silicas in a 30% glycerine-water dispersion (mixture 1:1) Brookfield RTV
Sp5.
1. Sample Mixture 60 ~ of silica 70 g of anhvdrous silica D~B7;
densitv 1.26 mg/l 70 q of distilled water 200 q of 30 ~ dispersion relative to silica.
This application is a divisional application of copend-ing Canadian application No. 400,097 filed March 3, 1982.
A number of processes for producing low-structured pre-cipitated silicas are known. According to German Offenlegungss-chrift 2,344,31~ a prepolymerized sodium silicate solution is produced first by adding 5 to 10~ by weight of sodium sulphate to a sodium silicate solution and the silica is then precipitated by adding acid or a portion of the prepolymerized sodium silicate solution i5 adjusted with acid to a pH value between 6.5 and 11 and the silica is finally precipita-ted by simultaneously adding sodium silicate solution and acid at a constant pEI value. German Offenlegungsschrift No. 2,3~4,805 describes a process in which an alkali metal silicate begins to precipitate, whereupon the addition of acid in interrupted~ the reaction solution is aged for a period of up to Eour hours and simultaneous addition of acid and alkali metal silicate is then continued until the de-sired product is obtained.
German Offenlegungsschrift No. 2,446,038 describes a method in which at a p~l value of 9 and at a temperature of 65C
prepolymerized sodium silicate solution, to whlch 7~ by weight of electrolyte have been added, and a dilu-te (10 to 25% by weight) acid are fed into an electrolyte-containing solution of 3 to 15~
by weight of sodium sulphate. The pH is then adjusted -to a value below 5, followed hy aging at 77C for twen-ty minutes.
In German Offenlegungsschrift No. 2l522,~86 the produc-tion of a precipitated silica is described in which a portion (i.
e., 8 to 50~) of the entire alkali silicate solution is ini-tially used into which alkali metal silicate solution and acid flow sim-ultaneously until at the completion of the addition of alkali metal silicate and acid 20 to 500~ of the initial alkali metal silicate solution have been reacted. The pH is then lowered to a value below 6. Dilute (8 ~o 22~. by weight) sulphuric acid must be used.
AccordincJ to a further process dilute sodium silicate solution (density - 1.]52) and dilute hydrochloric acid (2N) are precipitated over a period of 2 hours on a 2o by ~eight dispersion at 80C and in the p~ range ~rom 7 to 7.5. The disper-sion is prepared from "light silica" (production not disclosed) and water. Th~reafter water is used for dilution. The silica thus obtained is distinguished by a very low powder density.
Althouqh the production methods cited above resul~ in low-structured silicas, these methods have certain disadvalltages which, on applying then on an industrial scale, render then relatively cumbersome and less economical as compared with conven-tional methods for ~roducin~ reinforcing silicas for rubber.
These disadvantaqes are:
(a) the introduction of an additional partial step for producing silica- or electrolyte-containing precipitation stocks-starting solutiolls, of electrolyte-containing precipitation reactants and (b) the distinct reduction of the space time yields in the pre-cipitation of these silicas due to the required introduction of an interruption interval (aginq step), due ~o the use o~ dilute reclction components and due to the longer precipitation times required.
Under the circumstances it is an operational require-ment to produce precipitated silicas having low structures in a simple, economical, optimized manner adapted to the opera-tional sequence of the productions of reinforcing fillers.
According to German Auslegeschrift No. 1,467,019 it is 3n known to precipitate amorphous precipitated silicas by simultan~
eously adding acid-and alkali metal silicate solutions to an alk-aline stock starting solution while observing certain process ~8~
conditions. Precipitated silicas o~tained by means of this pro-cess may be graded as substances having rela~ively high structures (relatively high oil a~sorption), relatively high specific surface areas, low powder densities and low solid contents of their filter cakes. ~ecause of their excellent dispersibility in rubber mix-tures they are preferred reinforcing fillers in the rubber indus-try, where they are in widespread use for the manufacture of rub-ber soles, tire treads and tec`hnical articles with or without the application of silanes. These types of precipitated silicas are constantly available as standard reinforcing fillers or as main products in any plant producing fillers. '~his also applies to the original precipitated suspension, which is stored as an inter-mediate product in large suspension storage tanks before they are passed to the filter presses for separating the electrolyte.
Surprisingly it has been ~ound that an original precipita-ted silica suspension produced according to German Auslegeschrift No. 1,467,019 can be used as an inexpensive starting product for obtainin~ precipitated silicas having low structure, hi~h hard--ness and this even in the case of ~reat fineness if speci~ic measures are followed in the subsequent modifica-tion and further proc~ssing. In this manner it is possible to avoicl ent,irely the op~rationally cumbersome, additional, frequently even unecomonical production of salt solutions for initially the precipitation, the economically absolutely intolerable redispersion of the dried precipitated silica powders to silica dispersions as the precipi-tation initial solution and the preparation of electrolyte-con tainin~ alkali metal silicate or acid sclutions and thus to simp-lify substantially the processes of the prior art and to reduce their costs. This also applies to the reduced space time yield since the process according to the present invention can be carried out without interruption intervals, ~ith relatively short precipi-tation times and concentrated reaction components.
3 ~
The present invention will be illustrated by way of the accompanying drawings, in which:-Fig. 1 is a particle size distribution curve of theprecipitated silica according to the present invention as deter-mined by the Coulter counter.
According to the present invention there are provided a precipitated silicas which have -the following physical data:
micronizer BET surface area according to DI~ 66131 sq m/g 15-110 tamped powder density according to DIN 53194 g/l 90-650 Cu abrasion in a 10%
glycerine dispersionmg 5--30 bright reference value A
according to DIN 55921 % 90-96 particle size distribu-tion curve as determined by the Coulter counter according to Fig. 1 "ALPINE retained o~ sieve"
> 63~m % by weight <0.1 viscosity in a 30~
glycerine- and water dispersion ~
(Brookfield RTV Sp5)mPas 60,000 The high tamped powder densities, which are three times the value for the tamped powder densities of conventional pre-cipitated silicas for reinforcing rubber permanen-tly reduces the expenditure for packing rnatrial, emptying, transport and storage.
When incorporating the precipitated silicas the relatively small processing volumes are appreciated by the consumer.
The high, precisely ad~ustable Cu-abrasion value permits its use as an abrasive and polishing agent. Surprisingly it has been found that the abrasiveness does no-t permanently decrease, as is usual, with increasing fine division of one and the same basic silica material so that the combined property abrasiveness and high degree of fineness make this silica a valuable filler ;~8~
for toothpastes. The maintained abrasion effect with simultan-eously high degree of fineness thus permits the use of micronizers (air or steam jet mills) which, because of the substantially - ~a -$~
mutual grain pulverization, avoids wall abrasion in the grinding mill due to the principle of substantially mutual grain pulveri-zation and thus results in briyh~er, purer final products as com-pared with the products produced by the mills provided with mech-anical impact tools.
The unique combination of abrasive and thickening effect is particularly interesting for the use o~ the precipi~ated silica according to the present invention as a cleaning agent in tooth-pastes. This combined property which has been observed only in the micronized, finely divided variant enables the cosmetics in-dustry to manage with a single silica component and in most cases with smaller amounts.
The present invention also provides a process for pro-ducing the precipitated silicas according to the present invention which have the following physicochemical characteristic data:
micronizer BET surface area according to DIN 66131 sq m/g 15-110 tamped powder density 20 according to DIN 53194 g/l 90-650 Cu abrasion in a 10~
glycerine dispersionmg 5 30 bright reference value A
acco~ding to DIN 55921 ~ 90 96 particle size distribu-tion curve as determined by the Coulter counter according to Fig. 1 ''ALPINF retained on sieve"
>63~m ~ by weight <0.1 viscosity in a 30%
glycerine-water dispersi~n (1:1) (Brookield RTV Sp5) mPas 60 000 In the process an original precipitated sili~a, pro-duced bY precipitatin~ the silica in an alkali metal silicate solution having a concentration of approximately 5 to 25g of SiO2 per litre of solution with an acidic alkali metal silicate solu-tion having specific solution concentrations and specific feed rates while maintaining a ~recipitation temperature between 80 and 90C in the reacti.on medium the viscosity of the reaction medium being kept uniformly low during a period of at least 30 of the total precipitation time, the pH value being maintained between 10 and 12 and the addition of ~he reactants being termina-ted only when the viscosity, after passing through a maximum, has decreased to a value of less than 100% of the initial viscosity, is diluted with hot water to a content of precipitated silica of 10 to 30 g per litre and a sodium sulphate content of 6 to 20 ~
of Na2SO4 per litre, heated to a temperature of 85 to 95C, the pH is adjusted with sulphuric acid to a value of 7 to 9 and while keeping this pH value constant by the simultaneous addi~ion of alkali metal silicate solution, sulphuric acid and, as required, hot water a precipitated silica concentration of 40 ~o 80 g is 20 obtained over a precipitation time of 15 to 180 minutes, the suspension is acidified with concentrated sulphuric acid to a p~l value below 7, the precipitated silica is separated from the sus-pension by a filter press, washed, dried and micronized by a micronizer.
In a preferred embodiment an original precipitated silica suspension, which according to German Auslegeschrlft No. 1,467,019 is intensively sheared during its production phase, is used.
This is always advantageous in cases when particularly high powder densities and hi~h Cu-abrasion values are to be attained. In a particular embodiment of the present invention the shearing op-e.ration can be carried out according to German Patent No. 1,767, 332.
The alkali me~al silicate solutions used may have a weight ratio of SiO2:Na2O = 2 to 4. In a preferred embodiment of the present invention the alkali metal silicate solution can have a concentration of 8.0~ by weiyht of Na2O and 26.8% by weight of SiO2. This corresponds to a weight ratio of SiO2:Na2O - 3.46.
In the simultaneous addition of alkali metal silicate solution, sulphuric acid and, as required, hot water 0.5 to lO
litres of alkali metal silicate solution having a density of 1.353, a weight ratio of SiO2:Na2O = 3.46 may be added per lO
litres of precipitated silica suspension per hour as well as 0.5 to l litre oE a 96% sulphuric acid per hour and up to lO litres of hot water per hour.
The concentration of the sulphuric acid used may be up to 96% hy weight. In a preferred embodiment the concentration of the sulphuric acid may be up to 50% by weight.
The process for producing the precipitated silica has the following advanta~es:
(a) the high content of solids in the filter cake of up to 50~
by weight reduces the energy requirements of the drying process and thus the drying costs to approximately 25% of the values for `t.h~ reinforcing silicas used in the rubber sector, (b) the high content of s~lids in the filter cake of up to 50%
doubles the capacity of the filter press, (c) the relatively low specific surface area of the precipitated silica having a lower structure results in distinctly reduced washing times and thus in savings of wash water and in additional capacity of the filter press, and (d) there exists the possibility of adjusting the physicochemical characteristic data of the silica accordin~ to the present inven~
tion in a controlled manner.
The precipitated silica according to the present inven-tion and the process for producing same are explained and describ-ed in greater detail by means of the following Examples:Example 1 ~Comparison Example~
This Example describes the production of a precipitated silica according to the German Auslegeschrift No. 1,467,019.
73 litres of hot water and 5.25 litres of sodium sili-cate solution (density:1.353 g/ml weight ratio of .SiO2:Na2O =
3.46) are heated to 85C in a rubberized 120-litre precipitator with stirring. During the next 90 minutes while s-tirring and maintaining the temperature of 85C 11 l~h of sodium silicate solution (density = 1.353 g/!ml, weight ratio of SiO~:Na2O - 3.46) and 0.965 l/h of a concentrated 96~ sulphuric acid are simultan-eously dosed into this alkaline precipitation solution.
The precipitated silica suspension is then adjusted with a concentrated 96% sulphuric acid to a pH value of 8.5. This is done by feedin~ acid in for several minutes at a rate of 1.25 litres per hour. The precipitated silica thus obtained has a solids content of approximately 85 g per litre. Its Na2SO4 con-tent is approximately 55 g per litre. It is used as A so-called "original precipitated silica suspension" for producing the pre-cipitated silicas according to the present invention as describedin the Examples hereafter.
The precipitated silica suspension is then acidified with a concentrated 96% sulphuric acid to a pH value of 3.5, whereupon the precipitated silica is separated from the suspension by means of a laboratory filter press. The filter cake is then washed with water, dried at a temperature of 110 to 120C and ground in a laboratory pinned disc mill. The physicochemical data have been compiled in the following Table I.
Example 2 The "original precipitated silica suspension" of Exampl~
1 is diluted with water until the precipitated silica content is 20 g per litre and the Na2SO4 content is 13 g per li~re.
~ 8 ]0.5 litres of this suspension are heated to 85~C in a rubberized 30-litre precipitator while stirrin~. While maintain-inq this temperature and a pH ~Talue of 8.5 for 30 minutes in sodium tetrasilicate solution (8,0% of Na2O and 26.8% of SiO2, density 1.353 g~ml, weight ratio of SiO2:Na2O = 3.46) at a rate of 92.4 ml per minute, a 50~ sulphuric acid at a rate of 19.6 ml per minute and water at a rate of 185.4 ml per minute are simul-taneously added to the precipitated silica suspension. Su~sequent-ly the precipitated silica suspension is adjusted with a 50%
sulphuric acid to a pH value of approximately 3.5. On terminating the precipitation time the precipitated silica content is 64 g per litre.
The silica thus obtained is separated from ~he suspen-sion by means of a laboratory filter press. The filter cake is washed with water until it is low in salt, whereupon it is dried at 110 to 120C and ground in a laboratory pinned disc mill. The characteristic data have been compiled in the following Table I.
Example 3 The procedure is the same as that in Example 2, but the amount of the simultaneously dosed components sodium tetrasilicate, sulphuric acid and water is halved. As compared with Example 2, the tamped powder densi.ty is practically doubled by this measure wh.ile the abrasiveness drops distinctly. The precipitated silica content o~ the suspension is 49 g per litre. The characteristic data have been compiled in the following Table I.
Example 4 The procedure is the same as that in Example 3, but the precipitation time is extended from 30 to 60 minutes. The pre-cipitated silica content is 64 g pex litre. As compared with theprecipitated silic~ obtained in the Examples 2 and 3 the tamped powder densit~ is distinctly higher. This also ~pplies to the _ 9 _ Cu abrasion~ The characteristic data have been compiled in the following Table I.
Example 5 The procedure of Example 4 is followed bu~ the precipi-tation time is raised ~rom 60 to 120 munutes and the amounts of the sumultan-eously dos0d compone~ts sodi~ tetr~ te, sulphuric acid and water are halved. The dosaqes are sodium tetracilica~e 23.1 ml per minutes, sulphuric acid 4.9 ml per minute and water 46.35 ml per minute. The precipi tated silica content is 64 g per litre. The tamped powder density and the abrasion values are even hiqher. The characteristic data have been compiled in the following Table I.
Example 6 The procedure of Example 4 is followed but with the diffenence that the "original precipitated silica suspension" o~f Example 1 is diluted only to a precipitated silica content of 30 g per litre and an Na2SO~ content of approximately 20 g per litre.
10.5 litres of this suspension are used for the further precipi-tation~ The precipitated silica content obtained is 71 g per litr~. The tamped powder density and the abrasion slightly de-crease as compared with the data for the precipitated silica ac-cording to ~xample 4. The characteristic data have been compiled in the following Table I.
Example 7 The procedure of Example 4 is followed but with the diffexence that the so-called "original precipitated silica suspension" of Example 1 is diluted with additional water to a precipitated silica content of 13 g per litre and an Na2SO4 con-tent of 8.5 g per litre. However, the addition of 92.7 ml of water per minute during the precipitation is dispensed with.
A content of precipitated silica of 64 g per litre is obtained.
The characteristic data o~ this precipitated silica have been compiled in the following Table I~
Example 8 The procedure of Example 7 is followed but with the dif-ference that the precipitation is carried out at 95C and the precipitation time is reduced from 60 to 45 minutes. A precipi-tated silica content of 52 g per litre is obtained. The charac-teristic data of the precipitated silica obtained have been com-piled in the following Table I.
Example 9 First an "original precipitated silica suspension"
according to Example 1 is produced, it has a content of 80 g of precipitated silica per litre and of approximately 52 g of Na2SO4 per litre as well as a pH value of 8.5. However, during the entire precipitation time of 90 minutes the suspension is in-tensively sheared by means of a rotary pump, which recirculates the content of the cup several times. Detailed data on the ap-paratus equipment and the shear conditions can be found in German Patent No. 1.767,332, particularly in column 8, line 31 to 68.
The original silica suspension produced in this manner is adjusted with water to a precipitated silica content of 20 g per litre and an Na2SO4 con-tent of 13 g per litre. 10.5 litres of this suspension serve Eor the subsequent precipitation, which is carried out according to Example 3.
The resulting content of precipitated silica is 49 g per litre. The characteristic data of the precipitated silica have been compiled in the following Table I and show that the abrasion values and the tamped powder density of the precipitated silica are substantially increased by the measure of shearing as com-pared with the corresponding values of a precipitated silica produced from a non-sheared original precipitated silica suspen-sion.
Example 10 The p~ocedure o~ ~xample 9 is followed but with the ~ 11 --~8~ ;3~
single difference ~hat the precipitation time is extended from 30 to 60 minutes. ~ precipitated silica content of 64 g per litre results~ An appreciable increase of both the abrasion value (by 92%) and the tamped powder density (by 24%) is attained once more.
Example 11 The large-scale industrial production of the precipitated silica according to the present invention is explained hereafter:
In a wooden 70 cu m precipitating vat provided with a paddle mixer the formula of Example 1 adapted to the relative sizes is used and an original precipitated silica suspension having a pH value of 8.5 and a content of precipitated silica of approximately 85 q per litre and a content of Na2SO4 of approxi-mately 55 g per litre is first produced. 8 cu m of this supension are then left in this wooden 70-cu m vat and mixed with 26 cu m of hot water to a precipitation solution containing approximately 20 g of precipitated silica per litre and approximately 13 g of Ma2SO4 per litre and heated to 85C. While keeping the tempera-ture and the pH value of 8.5 constant 8.8 cu m of sodium silicate solution (density 1.353 g/ml, modulus of SiO2:Na2O = 3.46), 0.90 cu m of a concentrated 96% sulphuric acid and 19.0 cu m of hot water are simultaneously fed into the precipitation solution for 45 minutes. After completed precipitation the suspension is ad-justed with a concentrated 96% sulphuric acid to a pH value of 3.5 within a few minutes. The resulting content of precipitated silica is approximately 64 g per litre.
For further processing the precipitated silica is sep-arated from the suspension by means of a filter press, washed, dried in a shelf dryer and micronized in a bowl mill. The charac-teristic data of the precipitated slilica obtained are listed in the following Table I.
Example 12 The apparatus corresponds to that of Example 11. As described therein, an "original precipitated silica suspensio~"
having a pH value of 8,5 and a content of precipitated silica of approximately 85 g per litre and a content of Na2SO4 of approxi mately 55 g per litre is first produced.
10 cu m of this suspension are then left in a 70 cu m wooden vat, mixed with 27 cu m of hot water to yield a precipi-tation solution containing approximately 23 g of precipitated silica per litre and 15 g of Na2SO4 per litre and is heated to 85C. At this temperature and while maintaining a pH value of 8.5 to 9.0, 9.6 cu m of sodium silicate solution (density: 1.353 g/ml, weight ratio of SiO2:Na2O = 3.46), 0.94 cu m of a concen-trated 96% sulphuric acid and 20~0 cu m of hot water are simultan-eoulsy dosed into the suspension for a period of 80 minutes.
After completed precipitation the suspension is adjusted with a concentrated 96% sulphuric acid to a pH value of 3.5. The content of precipitated silica is 64 g per litre.
For further processing the precipitated silica it is separated from the suspension by means of a filter press, washed, dried in a shelf dryer and micronized with steam in a Jet-o-mizer, type 0808. The ~rinding capacity is 50 kg per hour at a grinding pressure of 8.5 bars. The characteristic data of the precipitated silica obtained have been compiled in the following Table I.
E~ample 13 The procedure of Example 11 is followed. The only dif-ference is the different kind of grinding by means of a microni~er using a steam jet and the conditions of Example 12 Example 14 The procedure of Exa~ple 12 is followed, but the precipi-tation time is extended from 80 to 110 minutes. The dosed quanti-ties of concentrated sulphuric acid, hot water and sodium silicate solution are correspondingl~ adapted. On completed precipitation the content of precipi~ated silica is 64 g per litre. The condi-tions of micronizing with s~eam are also changed, i.e.~ grinding capacity 630 kg per hour, grinding pressure 11 bars ~ he physicochemical characteristic data of the precipi~
tated silicas produced according to the Examples 1 to 14 are evi-dent from the following Table I. The data of E~ample 1 are those of a comparison example according to the prior art, describing the production of a precipitated silica ha~ing insufficient abra-sion properties and a low tamped powder densityO The physico-chemical data of the precipitated silicas obtained according tothe Examples 2 to 10 represent products of laboratory processes while the data of the Examples 11 to 14 represent the physical data of the precipitated silicas produced under plant conditions.
The physical data specific surface area, tamped powder density and bright reference value A are determined by means of DIN methods.
The measurement of the Cu abrasion and the determination of the ALPINE retained on sieve >63~m are described hereafter.
Determination of the Cu Abrasion in 10~ Glycerine Dispersion a) Production of the Glycerine Dispersion 153 q of anhydrous glycerine (DAB7; S=1.26) are weighed into a 250-ml polyethylene beaker. 17 g of precipitated silica are carefully intermixed with a spatula. The mixture is subsequ-ently homo~enized with a vane stirrer (diameter 5.2 cm) Eor 12 minutes at 1500 r.p.m.
b) Carrying out the Abrasion Measurement The abrasion measurement is carried out in an abrasion tester, which is known from the following publications: 1) P
Pfrenqle, Fette, ~eifen, ~nstrichmittel, 63 (5) (1961) pages 445 to 451 "Abrasion and Reinigungskraft von Putzkorpern in Zahnpasten";
~) A ~ , F. DAN~ arfu~erie and ~o~metik 59 (2) (~-978) pages 37 to 45 "Anwendunqstechnische~ru'fung von Zahnpas-~en". For this purpose each of the six troug~ls of the tester is coated with 20 ml of the homogeneous dispersion. The ahrasion caused by six surface -ground nylon brushes on six surface-ground Cu sheets (electroly-tic copper) in fiye hours with 50 000 double strokes is determined by differential weighing. In the computation of the abrasiveness average values are determined from ~he values obtained. The abrasion (abrasiveness) is defined in mg of Cu.
Determination of the Residue on Sieve with the ALPINE Air Jet Sieve In order to determine the residue on sieve, the precipi-tated silica is passed through a 500~ sieve to destroy possibly present exhaust air knots, whereupon 10 g of the screened material are put on a specific air jet sieve and screened at 200 mm water column negative pressure. Precipitated silica particles deposited of the plexiglass cover of the sieve are knocked off by a number of knocks on the knob of the sieve cover. The screening is com-pleted when the residue remains constant, which usually is evident from the fluid appearance. To be on the safe side, screening is continued for another minute. In the case of material having particle portions < 500~ the sample is no~ passed through a sieve first, but is put directly on the air jet sieve. If ag~lomerates fonm, the scre~nin~ process is briefly interrupted and the agglo~erates are destroyed with a brush und~er sli~ht pressure. After the screening process, the residue retained on sieve is carefully knocked o~f from ~he air jet sieve a~ h~1 back.
Computation ~ The residue retained on sieve is defined in percent in conjunction with the width of mesh of the sieve.
Apparatus: ALPINE air jet sieve, laboratory type S 200 air jet sieve having a sieve weave according to DIN 4 188.
Testing of the rheological efficiency of abrasive silicas in a 30% glycerine-water dispersion (mixture 1:1) Brookfield RTV
Sp5.
1. Sample Mixture 60 ~ of silica 70 g of anhvdrous silica D~B7;
densitv 1.26 mg/l 70 q of distilled water 200 q of 30 ~ dispersion relative to silica.
2. Carrying out the Test The abrasive silicas were s~irred by hand in a 400-ml ~eaker (wide shape) into the glycerine-water mixture with a glass rod (1 minute) and allowed to stand for 24 hours, whereupon the viscosity was measured.
3. Measurement The measurement of the viscosi~y is carried out in the same beaker with a Brookfield Viscosimeter RTV spindle 5 at var ious r.p.m.
4. Computation Read scale value x factor = viscosity in mPas.
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Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A precipitated silica, having the following phy-sicochemical characteristic data:
according to Fig.1
according to Fig.1
2. A process for producing a precipitated silica having the following physicochemical characteristic data:
according to Fig.1 in which an original precipitated silica suspension, produced by precipitating the silica from an alkali silicate solution having a concentration of approximately 5 to 25 g of SiO2 per litre with an acidic alkali metal silicate solution having specific solution concentrations and specific feed rates while maintaining a pre-cipitation temperature between 80 and 90°C in the reaction medium, the viscosity of the reaction medium being kept uniformly low during a period of at least 30% of the total precipitation time, the pH value being kept between 10 and 12 and the addition of the reactants being terminated only when the viscosity, after passing through a maximum, has decreased to a value of less than 100% of the initial viscosity, is diluted with hot water to a content of precipitated silica of 10 to 30 g per litre and a sodium sul-phate content of 6 to 20 g of Na2SO4 per litre, heated to 85-95°C, the pH is adjusted with sulphuric acid to a value of 7 to 9 and while keeping this pH value constant by simultaneously adding alkali metal silicate solution, sulphuric acid and, as required hot water, a precipitated silica concentration of 40 to 80 g per litre is obtained over a precipitation time of 15 to 180 minutes, the suspension is acidified with concentrated sulphuric acid to a pH value below 7, the precipitated silica is separated from the suspension by a filter press, washed, dried and micronized by a micronizer.
according to Fig.1 in which an original precipitated silica suspension, produced by precipitating the silica from an alkali silicate solution having a concentration of approximately 5 to 25 g of SiO2 per litre with an acidic alkali metal silicate solution having specific solution concentrations and specific feed rates while maintaining a pre-cipitation temperature between 80 and 90°C in the reaction medium, the viscosity of the reaction medium being kept uniformly low during a period of at least 30% of the total precipitation time, the pH value being kept between 10 and 12 and the addition of the reactants being terminated only when the viscosity, after passing through a maximum, has decreased to a value of less than 100% of the initial viscosity, is diluted with hot water to a content of precipitated silica of 10 to 30 g per litre and a sodium sul-phate content of 6 to 20 g of Na2SO4 per litre, heated to 85-95°C, the pH is adjusted with sulphuric acid to a value of 7 to 9 and while keeping this pH value constant by simultaneously adding alkali metal silicate solution, sulphuric acid and, as required hot water, a precipitated silica concentration of 40 to 80 g per litre is obtained over a precipitation time of 15 to 180 minutes, the suspension is acidified with concentrated sulphuric acid to a pH value below 7, the precipitated silica is separated from the suspension by a filter press, washed, dried and micronized by a micronizer.
3. A process according to claim 2, in which the original precipitated silica suspension is intensively sheared during the entire period of its production up to the time of its dilution with hot water.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3114493.4 | 1981-04-10 | ||
| DE19813114493 DE3114493A1 (en) | 1981-04-10 | 1981-04-10 | "FELLING SILICONES AND METHOD FOR THE PRODUCTION THEREOF" |
| CA000400097A CA1183672A (en) | 1981-04-10 | 1982-03-31 | Precipitated silicas and process for producing same |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000400097A Division CA1183672A (en) | 1981-04-10 | 1982-03-31 | Precipitated silicas and process for producing same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1189681A true CA1189681A (en) | 1985-07-02 |
Family
ID=25669640
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000465709A Expired CA1189681A (en) | 1981-04-10 | 1984-10-17 | Precipitated silicas and process for producing same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1189681A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4956167A (en) * | 1986-02-28 | 1990-09-11 | Unilever Patent Holdings B.V. | Silicas |
-
1984
- 1984-10-17 CA CA000465709A patent/CA1189681A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4956167A (en) * | 1986-02-28 | 1990-09-11 | Unilever Patent Holdings B.V. | Silicas |
| US5447704A (en) * | 1986-02-28 | 1995-09-05 | Unilever Patent Holdings B.V. | Amorphous silica |
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