US3401012A - Process for producing multivalent metal pyrophosphates - Google Patents

Description

United States Patent M t 3,401,012 PROCESS FOR PRODUCING MULTIVALENT METAL PYRQPHOSPHATES George D. Nelson, St. Louis, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Dec. 27, 1966, Ser. No. 604,599 11 Claims. (Cl. 23105) This invention relates to the production of multivalent metal pyrophosphates. More particularly it relates to a process for the production of high purity multivalent metal pyrophosphates using solid pyrophosphoric acid as a raw material.

Multivalent metal pyrophosphates have generally heretofore been prepared from the thermal dehydration of the appropriate oithoph-osphates. Multivalent metal orthophosphates, in many instances, are not readily available. It is believed that a process which would allow the production of various multivalent metal pyrophosphates directly from pyrophosphoric acid and a more readily available multivalent metal source would be an advancement in the art.

-In accordance with this invention, it has been found that high purity multivalent metal pyrophosphate can be produced by reacting pyrophosphoric acid and a multivalent metal source in an aqueous medium under controlled conditions of temperature and pH to thereby form a multivalent metal pyrophosphate precipitate. More particularly, it has been found that multivalent metal pyrophosphates can be produced by reacting pyrophosphoric acid and a multivalent metal source in an aqueous solution having a water content of at least about 85% by weight of the reaction medium and at temperatures of from about 17 C. to about 48 C., and at a pH from about 1.5 to about 7; and that an easy-tofilter, high purity multivalent metal pyrophosphate precipitates from the reaction mixture. It is to be noted as used herein multivalent metals means iron, cobalt, nickel, zinc, aluminum, tin, lead and copper.

Solid pyrophosphoric acid, H4P207, is a specific chemical compound having a P 0 content of 79.76% and is not to be confused with the syrupy liquid having 21 P 0 content of from 78% to about 82% which is sometimes known as liquid pyrophosphoric acid." The beforementioned liquid is a mixture of pyro, ortho, and polyphosphoric acids and is not suitable in the practice of this invention. Solid pyrophosphoric acid is known to exist in at least two forms-Form I crystalline material which melts at 54 C. and Form 11 crystalline material which melts at about 71 C. When heated to its melting temperature, solid pyrophosphoric acid undergoes a rearrangement to produce a mixture of pyro, ortho, and higher polyphosphoric acids. Although any form can be used in the practice of this invention, Form II is preferred since it is more thermally stable. Pyrophosphoric acid in an aqueous solution also hydrolyzes to form orthophosphoric acid. Such hydrolysis is more rapid at relatively high temperatures, that is, at temperatures above 50 C., therefore, temperatures below about 50 C. are to be used in the practice of this invention.

The other reactant used in the practice of this invention is a water-soluble multivalent metal source, that is, a multivalent metal source which is soluble to the extent of at least about 5% by weight in water at 25 C. The multivalent metal sources can include the salts of inorganic acids as well as the multivalent metal bases such as the multivalent metal oxides and hydroxides. When the multivalent metal salt-s are used, it is preferred to use salts of the inorganic acids such as the multivalent metal chlorides, carbonates, sulfates and nitrates and the multivalent metal salts of the lower al-kyl carboxylic acids (con- 3,401,012 Patented Sept. 10, 1968 taining from one to 4 carbon atoms). Illustrative of the foregoing salts that can be used are ferric chloride, ferric sulfate, zinc carbonate, cupric carbonate, cupric sulfate, lead acetate, lead sulfate, nickel sulfate, stannous chloride, nickel carbonate, cobalt nitrate, cobalt sulfate, iron formate, lead formate and Zinc butyrate.

In most instances, it is preferred to use the more common and relatively less expensive inorganic multivalent metal salts such as the chlorides, carbonates, and nitrates or the multivalent oxides and hydroxides, such as Zinc hydroxide, aluminum hydroxide, zinc oxide and ferric oxide.

In the process of this invention it is preferred to prepare a solution of pyrophosphoric acid by adding solid pyrophosphoric acid to water and maintaining the temperature of the resulfing solution at temperatures below 50 C. and preferably from about 0 to about 10 C. It has been found that when solutions prepared in the foregoing manner are used, the reaction conditions can be controlled much easier than if solid materials or more concentrated solutions are used. It is believed that in this manner both pH and the concentrations that are preferred can be maintained in a more suitable manner. However, solutions containing from about 5 to about 15% pyrophosphoric acid can be used if desired.

The pyrophosphoric acid can be added to an aqueous solution or slurry of a multivalent metal source with the water concentration of the resulting medium at from about 84% to about by weight. If preferred, however, the two solutions can be added simultaneously to water at reaction temperatures, pHs and concentrations. Furthermore, if desired, the multivalent metal source can be added to the pyrophosphoric acid, however, pH control is more difiicult to control at the: preferred range, that is, from about 3 to about 5 at early stages of addition of the multivalent metal source because the pH of the pyroph-osphoric acid solution is below about 2.

In most instances, it is necessary to control the pH of the reaction medium by the addition of a basic material, such as ammonium hydroxide, sodium hydroxide or by a basic salt such as sodium carbonate, potassium carbonate and the like. The pH is preferably controlled between about 3 and about 6 during the reaction for most of the multivalent pyrophosphates. In some instances, however, it is necessary to adjust the pH to a value above 6 in order to obtain satisfactory precipitation from a solution. In most instances, it is necessary to have a pH value above about 3 at the completion of the reaction for the pyrophosphates to precipitate readily from the solution. At pH values much below about 1.5, orthophosphates tend to form and at pH values above about 7, mixed salts containing various other cations tend to be formed thereby contaminating the product.

The temperature of the reaction medium should be controlled at temperatures below :about 50 C. to avoid excessive hydrolysis of the pyrophosphoric acid. Preferably the temperature of the reaction medium should be from about 17 C. to about 48 C. Although temperatures below 17 C., that is as low as about 5 C. can be used, however, it is necessary in most instances to provide some means of cooling such as a brine system to obtain these lower temperatures, therefore, it is since these lower temperatures do not achieve any additional beneficial results normally they will not be used.

The water concentration in the reaction medium should be at least about 84% by weight of the total reaction medium to enable adequate control of the process. Although there is no essential maximum water concentration in order to achieve the benefits of this invention, it is generally preferred to use a water concentration below about 95% in order to avoid problems relating to disposal of an excessive amount of water. Although, if desired, water concentrations greater than 95% can be used (such as 97 99%) and the water can be recovered and recycled. Water concentrations of less than about 84% can result in the contamination by compounds which Would be water soluble at the higher water concentrations, therefore, are to be avoided. Thus, in most instances, it is preferred to maintain a Water concentration in the reaction medium of from about 87% to about 95%.

The multivalent metal pyrophosphates that are produced by the process of this invention have extremely high purities. The main reason for the high purities of these materials is because of the relatively insoluble nature of the multivalent metal pyrophosphates as compared to other salts which may be formed in the reaction medium. This process, therefore, enables the production of salts having a multivalent metal pyrophosphate content of at least about 90% by weight. These high purity compounds can be produced even if the pyrophosphoric acid has an assay which is relatively low or even if alkali metal ions or ammonium ions are present, since the other salts which can be formed in the reaction medium are soluble within the concentrations of water that are present; therefore, they will not crystallize from the reaction medium to cause contamination of the pyrophosphates unless the pH or temperature is allowed to exceed the range as specified herein.

The yields that are achieved in the practice of this invention are relatively high, that is, above about 90%, based upon the amount of multivalent pyrophosphate that is produced from the pyrophosphoric :acid reactant.

Recovery of the pyrophosphates is achieved by filtration, centrifugation and the like. It is generally preferred to separate the multivalent metal pyrophosphates from the reaction medium by filtration, followed by a Water solution wash to remove any of the materials which are contained in the aqueous portion of the cake. This can be done with water which will remove any of the trace amounts of materials which are present in the cake. Similarly a centrifuge with a wash cycle provides an adequate means of recovery of the multivalent pyrophosphates produced by the process of this invention. In some instances, if the presence of the other salts which are present in the reaction medium would not be detrimental, it is possible to separate the multivalent pyrophosphates by allowing the multivalent metal pyrophosphates to settle from the reaction medium and then decanting the liquid portion from the solid pyrophosphates. In these instances, however, it must be noted that the aqueous material which is contained in the solids contains other compounds that are soluble in the water, therefore, lower purity pyrophosphates are recovered in this manner. However, the solid pyrophosphate can be subjected to a water wash which will dissolve these compounds thereby yielding a high purity multivalent metal pyrophosphate.

The tin pyrophosphate is useful as a butter in certain I dentrifice compositions. Pyrophosphates such as the cobalt, copper, nickel and iron pyrophosphate are generally useful as catalysts in oxidation reactions in gasoline purification. Moreover, many of the pyrophosphates produced by the process of this invention are useful in electrical plating baths.

To more specifically illustrate the process of this invention, the following non-limiting specific examples are presented. All parts, proportions and presentations are by weight unless otherwise indicated.

EXAMPLE I About 358 parts of zinc oxide are slurried in about 4,000 parts of water. About 356 parts of crystalline pyrophosphoric acid (79.6% P are dissolved in about 3,000 parts of water at 0 to C. The aqueous solution of pyrophosphoric .acid prepared above is fed into a stirred vessel containing the zinc oxide slurry at about C. and at a rate of to parts per minute. The temperature of the reaction medium is held at from about 23 C. to about 38 C. A pH of from about 3.0 to about 3.7 is maintained throughout the reaction by the addition of a 2% solution of sodium hydroxide. Stirring is discontinued and about 5,300 parts of liquid are then decanted from a solid precipitate. The precipitate is washed with water on a filter and air dried. A ZnO content of the precipitate of about 40.0% is determined by the ammonium orthophosphatepyrophosphate gravimetric method as described in Willard and Furman, Elementary Quantitative Analysis, 3rd ed., D. Van Nostrand Company, New York (1940).

A P 0 content of about 36.6% of a sample of the product is determined by the method of Van Wazer et al. described in Analytical Chemistry, 26, 1755 (1954), after ion exchange separation of the metal ions by a cationic exchange resin.

Ignition loss measurements determines the molecular bound water content of a sample of the Product to be 23.2% H O.

The following analyses of P species present as ortho, end and middle groups are obtained by the method described in Analytical Chemistry, 26, 1755, supra.

Percent of phosphorus species Ortho Ends 99.1 Middles 0.0

EXAMPLE ll About 178 parts of crystalline pyrophosphoric acid are dissolved in about 3200 parts of water at a temperature of from about 0 to 10 C. The temperature of this aqueous solution of pyrophosphoric acid is maintained at below 10 C. until it is added at the rate of about parts per minute to a stirred reaction vessel equipped with cooling coils containing about 2000 parts of water at about 40 C. About 2600 parts of cupric carbonate and about 3000 parts of water at a temperature of about 25 C. are added simultaneously with the pyrophosphoric acid solution. The temperature of the reaction medium while the materials are being added is maintained at about 25-33 C. by circulating brine at about 15 C. through the cooling coils. The pH is maintained at about 2.4 to 3.3 by the addition of ammonium hydroxide. After all of the acid and cupric carbonate solution are added, the pH is adjusted to about 5.0 by the addition of a 10% solution of sodium hydroxide.

A granular precipitate is formed which is easily separated from the liquid solution phase by filtration.

Using the electrolytic analytical method as described in Kolthoff and Sandell, Textbook of Quantitative Analysis, rev. ed. (1946), McMillan Company, New York, for determining the CuO content and the previous methods described in Example I for the remaining analyses the following analyses a-re obtained on samples of the granular material.

Percent CuO 43.8 P 0 38.2 P as ortho 0.0 P as ends 94.0 P as middles 6.0 Loss on ignition 19.7

From these analyses it is apparent that the material produced is CU2P2O74H2O.

EXAMPLE III About 314 parts of crystalline pyrophosp'horic acid are dissolved in about 4000 parts of water. The temperature of this aqueous solution of pyrophosphoric acid is maintained at below 10 C. until it is added at the rate of about 50 parts per minute to a stirred reaction vessel equipped with cooling coils containing about 454 parts of ferric oxide and about 4,000 parts of water at a temperature of about 25 C. The temperature of the reaction medium while the pyrophosphoric acid is being added is maintained at about 23-24 C. by circulating brine at about 15 C; through. the cooling coils and by agitating the reaction medium. The pH of the reaction medium is maintained at from about 2.3 to about 3.3 by the addition of a sodium hydroxide solution. After all of the acid is added, the pH is adjusted to about 6.0 by adding ammonium hydroxide.

A granular precipitate is formed and about one hour after all of the pyrophosphoric acid solution has been added, the agitation is stopped and the granular material is separated from the liquid solution phase by filtration.

Using the KMnO volumetric method as described in Willard-and Furman, Elementary Quantitative Analysis, 3rd ed. (1940), D. Van Nostrand Company, New York, the Fe O content of the material is determined. Other analytical determinations are made in accordance with the techniques described in Example I. From these analyses, the material produced is determined to be Fe (P O -20H O.

EXAMPLE IV About 178 parts of crystalline pyrophosphoric acid are dissolved in about 3,000 parts of water at a temperature of about 10 C. The temperature of this aqueous solution of pyrophosphoric acid is maintained at below 10 C. until-it is added at the rate of about 100 parts per minute to a stirred reaction vessel equipped with cooling coils containing about 2,000 parts of Water. A solution prepared by adding about 450 parts of stannous chloride dihydrate to about 5,000 parts of Water at a temperature of 25 C. is added simultaneously with the acid to the water in the react-ion vessel. The temperature of the reaction medium while the pyrophosphoric acid and the stannous chloride solution are being added, is maintained at about 21 C. by circulating brine at about C. through the cooling coils and by agitation. The pH of the reaction medium is maintained at about 4.5 by the addition of sodium hydroxide, until all of each solution is added. About 10 minutes after the solutions are added, the reaction medium is adjusted to a pH of about 7.0, with a 10% solution of ammonium hydroxide. A granular precipitate is formed and the agitation is discontinued. The granular material is separated from the liquid solution phase by filtration.

Using the analytical techniques as in Example I, the material is determined to be essentially anhydrous and has the formula, SIIgPzOq.

EXAMPLE V About 106 parts of crystalline pyrophosphoric acid are dissolved in about 2,000 parts of water at a temperature of from about 0 to 10 C. The temperature of this aqueous solution of pyrophosphoric acid is maintained at below 10 C. until it is added at the rate of about 100 parts per minute to a stirred reaction vessel equipped with cool ing coils containing about 454 parts of lead acetate and about 4,000 parts of water at a temperature of about 25 C. The temperature of the reaction medium while the pyrophosphoric acid is being added, is maintained at about 25-35 C. by circulating brine at about 15 C. through the cooling coils and by agitation. A pH of about 1.7 to about 4.2 is maintained during the addition of the acid by the addition of the 10% solution of sodium hydroxide. -In about hour, after all of the pyrophosphoric acid is added, the agitation is discontinued and a granular material separates from the liquid phase.

Using the analytical techniques as in Example I, the material is determined to be essentially anhydrous and has the formula Pb2'P207. An X-ray diffraction pattern on a sample of the material is identical to the Pb P O prepared by thermal dehydration and reported at J. Am. Ceram, Soc. 43, 452 (1960).

6 EXAMPLE VI About 530 parts of crystalline pyrophosphoric acid are dissolved in about 4,000 parts of Water at a temperature of 10 C. The temperature of this aqueous solution of pyrophopshoric acid is maintained at below 15 C. until it is added at the rate of about parts per minute to a stirred reaction vessel equipped with cooling coils containing about 340 parts of aluminum hydroxide and about 5,000 parts of Water at a temperature of about 25 C. The temperature of the reaction medium while the pyrophosphoric acid is being added is maintained at about 33-48 C. by circulating water through the cooling coils and by agitation. The pH of the reaction medium is maintained at about 2.2 to about 2.4 by the addition of minor amounts of a 10% solution of ammonium hydroxide until all of the pyrophosphoric acid is added. Additional ammonium hydroxide is then added to adjust the pH to about 6.0.,

A granular material is formed and the agitation is discontinued and the material is separated from the aqueous solution phase by decanting off the aqueous solution phase.

Using the MP0; gravimetric method for determining A1 0 and by using the other methods as described in Example I, the following analyses are obtained on samples of the crystalline material.

From these analyses it is apparent that the material is Al (P O -20H O. Since no X-ray diffraction pattern could be obtained, the material is believed to be largely amorphous.

EXAMPLE VII About 178 parts of crystalline pyrophosphoric acid are dissolved in about 2,000 parts of water at a temperature of about 5 C. The temperature of this aqueous solution of pyrophosphoric acid is maintained at below 10 C. until it is added at the rate of about 10 0 parts per minute to a stirred reaction vessel equipped with cooling coils containing about 2,000 parts of water at above 25 C. About 290 parts of nickel carbonate are added to about 2,000 parts of water at a temperature of about 25 C. and the solution is fed simultaneously with the pyrophosphoric acid to the water in the reaction vessel. The temperature of the reaction medium while the solutions are being added is maintained at about 40 C. by circulating water through the cooling coils and by agitating the reaction mixture. The pH is maintained at about 3.5 to about 4.3 with the addition of ammonium hydroxide. After all of the solutions are added, the pH is raised to about 6.0 with sodium hydroxide.

A granular material is formed and is separated from the liquid solution phase by filtration.

Using the analytical techniques as in Example II, the following analyses are obtained on samples of the crystalline material.

From these analyses it is apparent that the material is NigPgOq SHZO.

EXAMPLE VIII About 178 parts of crystalline pyrophosphoric acid are dissolved in about 3,000 parts of water at a temperature of about C. The temperature of this aqueous solution of pyrophosphoric acid is maintained at below 10 C. until it is added at the rate of about 100 parts per minute to a reaction vessel equipped with cooling coils and a stirrer and which contains about 562 parts of cobalt sulfate and about 4,500 parts of water at a temperature of about 45 C. The temperature of the reaction medium while the pyrophosphoric' acid is being added is maintained at about 40 C. by circulating brine at about C. through the cooling coils and by maintaining agitation of the reaction medium. The pH is held at about 4.0 by the addition of ammonium hydroxide until all of the pyrophosphoric acid is added, after which it is raised to about 5.7.

A granular material is formed and about one hour after all of the pyrophosphoric acid solution has been added,

the agitation is discontinued, and the granular material is separated from the liquid solution phase by filtration.

Using the analytical techniques as in Example II, the following analyses are obtained on samples of the crystalline material.

From these analyses the material is determined to be 002F207 8H2O.

What is claimed is:

1. A process for producing metal pyrophosphates comprising reacting pyrophosphoric acid and a metal source selected from the group consisting of iron, zinc, lead,

Iil)

copper, cobalt, aluminum, nickel and tin in an aqueous medium containing at least about 84 weight percent of water, at a temperature below about C. and at a pH from about 1.5 to about 7 to thereby form a metal pyrophosphate precipitate selected from the group consisting of iron, zinc, lead, copper, cobalt, aluminum, nickel and tin and recovering said metal pyrophosphate.

2. A process according to claim 1 wherein said pH is from about 2 to about 6.

3. A process according to ciaim 1 wherein said metal source is selected from the group consisting of water soluble metal hydroxides, oxides, salts of inorganic acids, salts of lower alkyl acids and mixtures thereof.

4. A process according to claim 3 wherein said metal is copper.

5. A process according to claim 3 where said metal is zinc.

6. A process according to claim 3 wherein said metal is iron.

7. A process according to claim 3 wherein said metal is nickel.

8. A process according to claim 3 wherein said metal is tin.

9. A process according to claim 3 wherein said metal is aluminum.

10. A process according to claim 3 wherein said metal is lead.

11. A process according to claim 3 wherein said metal is cobalt.

No references cited.

OSCAR R. VERTIZ, Primary Examiner.

L. A. MARSH, Assistant Examiner.

Claims (1)

1. A PROCESS FOR PRODUCING METAL PYROPHOSPHATES COMPRISING REACTING PYROPHOSPHORIC ACID AND A METAL SOURCE SELECTED FROM THE GROUP CONSISTING OF IRON, ZINC, LEAD, COPPER, COBALT, ALUMINUM, NICKEL AND TIN IN AN AQUEOUS MEDIUM CONTAINING AT LEAST ABOUT 84 WEIGHT PERCENT OF WATER, AT A TEMPERATURE BELOW ABOUT 50*C. AND AT A PH FROM ABOUT 1.5 TO ABOUT 7 TO THEREBY FORM A METAL PYROPHOSPHATE PRECIPITATE SELECTED FROM THE GROUP CONSISTING OF IRON, ZINC, LEAD, COPPER, COBALT, ALUMINUM, NICKEL AND TIN AND RECOVERING SAID METAL PYROPHOSPHATE.