Process for preparing fatty acid zinc salts

Details Process for preparing fatty acid zinc salts Process for preparing fatty acid zinc salts

2003-02-05

2004-02-10

Carr, Deborah D. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Fatty compounds having an acid moiety which contains the...

Reexamination Certificate

active

06689894

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing fatty acid zinc salts in high yield by reaction of zinc oxide, fatty acids, and a catalyst, preferably in the presence of a surfactant, in water at a relatively low reaction temperature.
2. Description of Related Art
Metal soaps, such as zinc soaps (i.e., fatty acid zinc salts), have been used as anti-blocking and anti-caking agents, lubricant and mold release agents, thickening agents, waterproofing agents, and the like. They generally possess many of the desirable properties of the fatty acids from which zinc salts are manufactured.
Various processes, including precipitation and fusion processes, to produce metal soaps for industrial uses are known in the art.
U.S. Pat. No. 3,803,188 discloses that metallic soaps of Group II of the Periodic Table can be prepared by dispersing a metal oxide in a higher fatty acid and mixing therewith 3.5 to 40 mole equivalents of water based on the fatty acid. Surfactants are said to be useful catalysts for the reaction.
Precipitation processes produce metallic soaps by reaction of an aqueous solution of a water-soluble metal salt and a fatty acid alkali metal salt, whereupon the metal soap precipitates out of the solution. These precipitation processes are expensive owing to the large amount of water-soluble inorganic salt by-produced causing water pollution problems, and the requirement of time consuming filtering, washing, and drying steps to isolate a purified metal soap from the aqueous product mixture.
In fusion processes, metal soaps are produced by reaction of a metal oxide, hydroxide, carbonate, or acetate with a molten fatty acid at a high temperature. These fusion processes have disadvantages that limit their use. For example, most commercial fusion processes use expensive high temperature equipment and complex handling procedures, and need long reaction times for a complete reaction. They usually yield large lumps of discolored metal soaps that must be ground to a desired particle size, often causing serious air pollution problems.
U.S. Pat. No. 4,307,027 discloses metallic salts of higher molecular weight fatty acids that are produced in a continuous process by feeding fatty acid and base into a plug flow reactor to maintain a residence time of about 2 to about 60 minutes at a temperature of about 75° F. to about 280° F. to obtain a metallic salt, then grinding the metallic salt in a hammer mill to obtain coarse particles and then grinding the coarse particles in a jet mill to obtain fine particles of the metallic salt. Optionally, the fatty acid and base may be fed initially into a stirred-tank reactor to maintain a residence time of about 10 to about 80 minutes at a temperature of from about 115° F. to about 300° F. to initiate metallic salt reaction before feeding the metallic salt reaction mixture into the plug flow reactor.
U.S. Pat. No. 4,316,852 discloses metallic soaps, particularly zinc soaps that are produced from a reaction mixture initially comprising a metal oxide or hydroxide, for example, zinc oxide, water and a glyceryl ester, particularly a triglyceride, the ester and said metal oxide or hydroxide being present in at least approximately stoichiometric amounts. The reaction mixture is agitated and the reactants are reacted in the agitated mixture to produce a metallic soap and glycerine, at a temperature at which the metallic soap is molten, in the presence of an excess of water effective to dissolve the glycerine formed in the reaction mixture such that reaction between by-product glycerine and the product metallic soap is substantially hindered. Eventually, the reaction mixture is allowed to separate into an aqueous layer and a molten layer of product metallic soap under a pressure such that the aqueous layer is essentially quiescent, and the molten metallic soap layer is dissociated from the aqueous layer. In this way, it is said, metallic soaps of high purity can be obtained.
U.S. Pat. No. 5,164,523 describes a fusion process for the rapid production of a granular metal soap that passes a mixture of metal (e.g., zinc) oxide, one or more molten fatty acids and a catalyst through a heated reactor to form molten metallic soap which is then ejected through a spray nozzle in a cooling tower to form a granular soap product. Use of a spiral tubular reactor with a rapid heating coil is disclosed. The reaction is conducted under pressure to maintain water generated by the reaction in the liquid state. Flashing of the reaction water in the cooling tower aids in cooling and formation of fine granules.
Other processes for preparing metal soaps are known wherein a mixture containing a metal oxide, hydroxide, or carbonate, an organic acid or fatty acid, optionally in the presence of a catalyst, such as water, is subjected to vigorous agitation or grinding at a temperature below the melting point of the organic acid and the metal soap. The products prepared in this manner after drying are light-colored, finely divided powders. However, the metal soap formation reaction often takes place slowly in these processes resulting in products having high levels of unreacted organic acid or fatty acid.
U.S. Pat. No. 3,476,786 discloses that finely divided water insoluble metallic salts of higher fatty acids can be produced by grinding solid fatty acids with particular solid metals, metal oxides, metal hydroxides, metal carbonates or mixtures thereof in the presence of a catalyst and in the absence of water.
U.S. Pat. No. 4,060,535 discloses that metal salts of organic acids can be produced rapidly and efficiently by subjecting a reaction mixture that contains a metal oxide, hydroxide, or carbonate, an organic acid that has a melting point above 20° C., and a small amount of water to vigorous agitation in an apparatus having attrition and shearing action at a temperature that is below the melting point of the organic acid and below the melting point of the metal salt that is being produced until substantially all of the organic acid has reacted.
U.S. Pat. No. 4,294,771 discloses a method for producing metal soaps by reacting aliphatic carboxylic acids with metal oxides, metal hydroxides and/or metal carbonates, wherein the metal soaps are directly obtained in the form of granulates without requiring an additional granulating step.
U.S. Pat. No. 4,473,504 discloses a method of producing large granules of metallic soap by reacting a water-insoluble metal carbonate and fatty acid.
It is an object of the present invention to provide a low temperature process for producing good quality fatty acid zinc salts in high yield.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a low temperature process for rapidly and efficiently preparing fatty acid zinc salts. The process comprises adding a fatty acid in its liquid state to an aqueous slurry of zinc oxide and a catalyst, preferably in the presence of a surfactant, and reacting the mixture at a temperature of from about 60° C. to about 75° C. for about 5 to about 120 minutes or until substantially all of the fatty acid has reacted.
The catalyst is present in the reaction mixture at a level from about 0.01 weight percent to about 0.2 weight percent. Fatty acids that can be employed in the practice of this invention include monocarboxylic acids having from about 8 to about 30 carbon atoms. The surfactant is used at an amount of about 0.05% to about 2% by weight of the whole reaction mixture. An advantage of the present invention is that fatty acid zinc salts having good quality and physical forms suitable for direct use are produced rapidly and economically.
More particularly, the present invention is directed to a process for preparing fatty acid zinc salts comprising the steps of:
stirring a slurry mixture comprising zinc oxide, at least one catalyst, and water at a temperature in the range of from about 55° C. to about 65° C.;
adding at least one fatty acid in its liquid state to said stirred slurry mixture; and
reacting the fatty acid with the zinc

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