FI61199C - FOER FARING FOR FRAMING WITH AMOFA UTFAELLDA KISELSYRAPIGMENT - Google Patents

Description

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Patent- och ragittarstyralMn 'Arattkan utl »| d och utiJkrtften published 26.02.82 (32) (33) (31) Pyydetty matoikmu— Begird prtorltat 2U. 08.72 USA (US) 283-67 (71) J.M. Huber Corporation, Locust, New Jersey, USA (72) Satish Kumar Wason, Churchville, Maryland, Peter van der Heem,

Perryville, Maryland, Neil Bernard Jurinski, Churchville,

The present invention relates to synthetic, amorphous precipitated silica pigments and, more particularly, to a novel process for the preparation of synthetic, amorphous precipitated silica pigments. has improved physical and chemical properties.

As is known in the art, finely divided amorphous precipitated silica pigments and certain zeolite-type aluminosilicates can be prepared by acidifying an aqueous solution of silicate with an acid or an acid salt such as aluminum sulfate. Such products are commercially available and sold by J.M. Huber Corporation under the tradenames "Zeo", "Zeolex" and "Arogen". Typical examples of these products as well as methods for their preparation are disclosed in U.S. Panthers 2,739,073; 2,843,346 and 3,582,179.

In general, such known pigments are characterized and have the following properties: dense pore structure, high wet cake moisture content, high oil absorption, low corrugation resistance, high surface area and low seal density. Due to these properties such as high oil absorption, large surface area, etc., these pigments have been widely and successfully used as reinforcing pigments in rubber, in the manufacture of paper, in moisture regulators, etc. However, the high moisture content of the wet cake is disadvantageous in drying. and the filtration amounts increase, thus raising the total price of the final product. For example, in the conventional preparation of the silicic acid pigments defined above, the moisture content of the wet cake of the product (after filtration of the precipitated reaction mass) is approximately 82%; this means that only 18 parts of dry pigment can be recovered from 100 parts of a wet cake.

In this sense, a process has recently been developed for the production of quartz pigments with improved physical and chemical properties such as sparse pore structure, low wet cake moisture content, high wear resistance, low oil absorption and high seal densities. According to the teachings of the above application, the pigments are prepared by acidifying a solution of alkali metal silicate with acid until precipitation just begins. At this point, the reaction mass is aged for some time and then the addition of acid is continued until a precipitated product is obtained. According to an embodiment of the method shown, an adduct material such as aluminum is premixed with an acid to adjust the refractive index of the pigment so that it can be used in clear toothpaste preparations.

It is an object of the present invention to provide a further improved process for the preparation of amorphous, precipitated silica pigments for use in toothpastes having a low filter cake moisture content and low water retention and a generally unique balance of physical and chemical properties over conventional known precipitated pigments. In the process of the invention, an aqueous solution of sodium, potassium or lithium silicate is acidified with an acid to precipitate a pigment, and an alkali metal silicate solution is added to the reaction solution, and the precipitated pigment is recovered, and the invention is characterized in that the alkali metal silicate has a SiC 4, preferably 2.3-2.7, where X is sodium, potassium or lithium, the acid is first added exclusively to the aqueous solution until precipitation of the pigment just begins, and the addition of acid is continued from this point without interrupting the reaction while the alkali metal silicate solution is added until the pigment precipitates. the simultaneous addition rates of acid and silicate are adjusted so that the pH of the reaction mass

3,61199 remains constant between about 8.0 and 11.0 to give a pigment 2 having a surface area of about 50-200 m / g.

To illustrate the invention, reference is made to the following detailed description, which discloses particularly preferred methods and preparations for purposes of illustration.

As briefly described above, conventional precipitated silicic acids are prepared by reacting an aqueous solution of silicate with an acid. The nature of the final silicic acid produced depends in part on the nature of the silicate solution used to make it. For example, it is generally accepted that commercially available sodium silicate solutions polymerize more or less depending on their silica / sodium oxide ratios (SiO 2 / NagO). For example, sodium metasilicate (molar ratio 1) is known to be predominantly monomeric in nature, while water glass (molar ratio 3 → 3) is both monomeric and polymeric in nature. Nevertheless, when the acid is added to the alkali metal silicate solution, the resulting reaction medium remains clear until a slight turbidity (called opal point) occurs. As the addition of acid continues, the silica or silica pigment begins to precipitate until the entire silicate solution has precipitated. In conventionally known methods, the pH of the reaction mass varies as the addition of acid is continued and is usually between about 5.5 and 6.5 at the end of the charge. At this point, the pulp is formed, washed and dried.

In accordance with the present invention, it has been found that if the acid is introduced into the silicate solution until the very first * 61199 opalescence is observed and the reaction or pigment precipitation is then continued at constant pH, the resulting pigments have unique physical and chemical properties which in fact depend on the pH used. -arvosta. As will be explained in more detail below, in addition to producing pigments with particularly advantageous properties (such as a lower wet cake moisture content, which allows for higher drying and filtration rates), it has been found that products with a large number of desirable properties can be prepared by varying pH. , where precipitation is performed after the first appearance of turbidity. More specifically, it has been found that “low pore structure” silicic acids having both large and small surface areas and a more uniform particle size can be prepared by the present invention.

In this regard, it may be noted that as used herein, the term “pore structure” refers to the ability of a silicic acid material to retain water in its wet cake and is thus also defined.

When silicas such as the conventional precipitated silicas mentioned above retain a large percentage of water, i. close to 75-85%, they are known and are referred to as dense pore structure p ^ j.-acids. Materials that retain less than 75% and preferably close to 50-70% water in their wet cake are referred to as low pore silica.

In the absence of more specific details in carrying out the invention, part of the total amount of alkali metal silicate used in the reaction is first fed to the reactor as a solution and the solution is heated to a temperature between about 37-121 ° C and preferably between about 66-79 ° C. In general, and unless specifically mentioned herein, reaction temperatures and rates as well as reagents, i. the concentrations of the silicate solution and the acid are the same as in the known processes for the preparation of precipitated silica pigments described above. However, in carrying out the invention, it has been found that particularly advantageous results are obtained if the concentration of the silicate solution is of the order of about 0.12 to 0.30 kg / l. The acidifying agent or acid, e.g. sulfuric acid, is next fed to the reactor until a slight turbidity (i.e. an opal point) occurs for the first time. At this time and without interrupting the reaction for a moment, a mixture of acid and the remaining silicate moieties (which can be added as separate streams or as an aqueous premix thereof) is added in such a way and at such a rate that the pH of the precipitating mass is constant until pigment precipitation is complete.

Although the amount of silicate initially fed to the reactor may be as small as a quarter of the total amount of silicate, it has been found that a more homogeneous product can be obtained when about half or two thirds of the total silicate is initially charged to the reactor and the rest of the silicate is added simultaneously with acid. at a substantially constant pH. As should be readily apparent to those skilled in the art, the precipitation pH can be varied by varying the amount or ratios of silicate and / or acid. If it is desired to obtain a sparse pore structure with a sparse, relatively large pmta, i.e. pigment above 100 m / g, the pH must be kept (after acidification to turbidity) higher than 10. The final pH of the batch must then be lowered to about 5.0-5.5. If it is desired to obtain a pigment with a sparse, small-area pore structure, the pH must be kept constant between about 8.0 and 9.5. After the pigment has precipitated and all the silicate has been added, the pH of the resulting slurry is lowered to about 6.5-7.0 by adding an excess of acid. However, this must be done slowly to maintain small surface properties.

In a further embodiment of the method, an adductive element such as aluminum, magnesium or the like is used to form a low-pore silicate, such as sodium aluminosilicate. In this embodiment, the acid is premixed with a solution of an adductive material such as aluminum (preferably in the form of a water-soluble salt such as aluminum sulfate, etc.) and the acid-metal salt mixture is then used to acidify the aqueous alkali metal silicate solution until precipitation just begins. At this point and in the same manner as above, the acid-metal salt / silicate is continued until the precipitation of the product is complete.

As can be seen from the above, the starting materials or reagents used in this invention include alkali metal silicates, an acid and a water-soluble metal salt. As used herein, the phrase alkali metal silicates encompasses all common forms of silicates, such as, for example, metasilicates, disilicates, and water glass. Water-soluble potassium silicates and sodium silicates are particularly preferred. Due to the relatively low cost of sodium silicates, they are recommended. If sodium silicates are used, they are effective in all mixtures with a SiO 2 / NagO molar ratio of about 1-4. In this sense, commercially available sodium silicate solutions are more or less polymerized depending on their silica / sodium oxide ratios (SiO 2 / Na 2 O). For example, sodium metasilicate solution (molar ratio 1) is known to be predominantly monomeric in nature, while water glass (molar ratio 3 * 3) is both monomeric and 6,61199 polymeric in nature. As the silicic acid / sodium oxide molar ratio of sodium silicate increases, so does its silicate anionic polymer / monomer ratio. Although sodium silicates with a SiO 2 / Na 2 O molar ratio of 1 to 4 can be used, particularly advantageous results are obtained when the SiO 2 / Na 2 O ratio is between about 2.3 and 2.7.

Although the acidulant or acid is preferably a strong mineral acid such as sulfuric acid, nitric acid and hydrochloric acid, it is to be understood that other acids such as organic acids, e.g. acetic acid, formic acid or carbonic acid may be used. The adduct material may contain metals such as aluminum, zinc, magnesium and other alkaline earth metals such as calcium and barium.

However, as mentioned above, the adduct is preferably used in the form of a water-soluble salt of the metal, which should be miscible with the acid used for precipitation, i. it must not produce an insoluble product in the acid used for precipitation. For example, aluminum salts useful in the process of the invention include water-soluble salts of aluminum and strong acids such as aluminum sulfate, aluminum chloride, aluminum nitrate and ammonium alum. The acidulant or acid is preferably added as a dilute solution thereof. The recommended results are obtained if the acidic solution contains about 10-25% by weight of acid, based on the total weight of the solution. However, this may vary depending on the acid used, etc., as is known in the art.

The invention is further illustrated by the following examples. Although the examples are intended to illustrate the present invention, it is not intended to be limited thereto.

Example 1 132 L of a 0.15 kg / l silicate solution having a SiO 2 / Na 2 O molar ratio of 2.5 was added to the stirred reactor and the silicate solution was heated to 79 ° C. Sulfuric acid having a concentration of 11.4 # was added to the reactor at a rate of 3.18 l / min until a pH of 10.1 to 0.1 was reached. At this point, both acid and silicate were added simultaneously at 3.18 and 5.30 1 / min so that the pH remained constant at 10.1. The addition of silicate was stopped after 25 minutes. Excess acid was added and the charge was stopped at pH 5.0 and the charge was filtered, washed, dried and ground. The product of this p example had a surface area of 110 m / g and a wet cake moisture content of 70.

7 61 1 99

Example 2 In this experiment, 38 l of a 0.15 kg / l sodium silicate solution having a SiO 2 / Na 2 O molar ratio of 2.5 was added to the stirred reactor and the solution was heated to 79 ° C. Sulfuric acid at a concentration of 11.4% was added to the reactor at a rate of 0.45 l / min until the silica just started to precipitate. At this time, the pH of the reaction mixture was 10.1. At this point, both acid and silicate were added to the reactor simultaneously at 3.7 and 4.5 l / min. The pH of the reaction mass was kept constant at 9.0. The idea of keeping the charge at pH 9.0 was to make the silica particles grow to a larger size and to give the final product a less porous structure, a smaller surface area and a higher density than conventional silica. The precipitated mass was otherwise treated or purified in the same manner as in Example 1, except that the final pH was lowered to 6.0 by the gradual addition of excess acid. The product had an area of 53 m / g and a wet cake moisture- $ 64.

Example 3 In this example, 18.9 L of a 0.15 kg / L sodium silicate solution having a SiO 2 / Na 2 O molar ratio of 2.5 was added to the stirred reactor and the silicate was heated to 79 ° C. Acid at a concentration of 10.5% was added to the silicate until turbidity or slight precipitation occurred in the reactor. At this point, 18.9 L of silicate and 11.4 L of acid were added simultaneously at 0.76 and 0.45 L / min and the batch was finalized to pH 6.0, filtered, washed, dried and ground.

Example 4

The procedure of Example 3 was repeated except that 22.7 L of silicate was added to the reactor and the remaining 15.1 L was added with acid. Example 5

The general procedure of Example 4 was repeated except that 26.4 L of silicate was added to the reactor and the remaining 11.3 L was added simultaneously with the acid. The batch was treated in the same manner as in Example 4.

Example 6

The procedure of Example 2 was repeated except that the precipitation pH was adjusted to 9.9 to 0.1. The batch was finalized and purified as in Example 2.

Example 7

The procedure of Example 1 was repeated except that the final pH was adjusted to 3.2. It was found that even with a lower pH of 8 61199, products with a larger surface area are obtained.

Example 8

The general procedures of Examples 1-7 were repeated in a series of experiments except that the precipitation pH was varied between about 6.5-11.0. The results of these experiments were essentially the same as in Examples 1-7 except that it was found that products with predetermined properties and characteristics could be obtained. All manufactured products had lower wet cake moisture contents than conventional products and were all less than 75%. · Increasing the precipitation pH also increased the surface area of the product.

Example 9

The general procedure of Examples 1-8 was repeated except that sulfuric acid was replaced with nitric acid, hydrochloric acid, acetic acid and formic acid. The results were essentially the same as in Examples 1-8.

Example 10

The general procedures of Examples 1-9 were repeated in a series of experiments except that the 2,5-silicate of Examples 1-9 was replaced with aqueous solutions of sodium silicates with molar ratios (SiO 2 / Na 2 O) between 1-4. The results were essentially the same as above except that the wet cake was found to have a lower moisture content than when 2,5-silicate was used. In addition, the surface area was found to be substantially smaller when silicate having a molar ratio of 2.5 was used.

Example 11 In this example, a silica pigment was prepared according to the prior art. There, the entire silicate solution was acidified with acid (pH not constant) until precipitation was complete. The wet cake had a moisture content of 85% and the product was not as homogeneous as the product of the invention.

Claims (6)

9 61199 A process for preparing amorphous, precipitated silica pigments for use in toothpastes having a low moisture content and low water retention in a filter cake, in which an aqueous solution of sodium, potassium or lithium silicate is acidified with acid to precipitate the pigment and an alkali metal that an aqueous solution of an alkali metal silicate having a molar ratio of SiO 2 / X 2 O of about 1 to 4, preferably 2.3 to 2.7, wherein X is sodium, potassium or lithium, is first supplemented exclusively with acid until precipitation of the pigment has just begun, and continuing from this point without interrupting the reaction while adding the alkali metal silicate solution until complete precipitation of the pigment has occurred and the simultaneous rates of addition of acid and silicate are adjusted so that the pH of the reaction mass remains constant between about 8.0-11.0 to give a pigment with a surface area of is about 50- 200 m2 / g. Process according to Claim 1, characterized in that the recovered pigment is dried and comminuted. Process according to Claim 1 or 2, characterized in that sulfuric acid, nitric acid or hydrochloric acid is used as the acid. Process according to one of the preceding claims, characterized in that an additive which is a water-soluble aluminum, calcium, zinc or magnesium salt is added with the acid. 1. A method for the production of amorphous pigments containing a mixture of sodium and potassium-free sodium compounds in the reaction process for the addition of alkali metal silicates, and for the addition of pigments in the oil, the transfer of the water to the alkali metal silicates with molar silica SiO2 / X20 of ca 1-4, heating 2.3-2.7, colors X and sodium, potassium or lithium, free from pigment and lilac, pigments utilized by pigments