United States Patent:  6,054,411

Assignee:  Nippon Carbide Kogyo Kabushiki Kaisha (Tokyo, JP)

Filed:  July 13, 1999

Addition of a dicarboxylic acid such as adipic acid to a cyanamide aqueous solution brings about improvement in storage stability of the cyanamide aqueous solution.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cyanamide aqueous solution having improved storage stability.

The present invention provides a cyanamide aqueous solution containing a compound represented by formula (I), wherein said compound is present in an amount of 0.05 to 1.0% by weight based on the cyanamide aqueous solution exclusive of said compound.

HOOC(CH₂)_n COOH (I)

wherein n represents an integer of 0 to 5.

DETAILED DESCRIPTION OF THE INVENTION

The cyanamide aqueous solution which can be used in the present invention is prepared by, for example, starting with lime nitrogen, urea, etc. It is prepared by bubbling carbon dioxide gas through an aqueous solution of the starting material to precipitate calcium carbonate and removing the precipitate by filtration.

The cyanamide aqueous solution is not particularly limited in concentration. A cyanamide aqueous solution as prepared generally has a concentration of from about 20 to 80% by weight.

The dicarboxylic acid represented by formula (I), which is used as a stabilizer for a cyanamide aqueous solution, includes oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and pimelic acid. Of all, adipic acid is particularly preferred.

The amount of the dicarboxylic acid of formula (I) to be added ranges from 0.05 to 1.0 part by weight, preferably from 0.1 to 1.0 part by weight, still preferably from 0.1 to 0.5 part by weight, per 100 parts by weight of the cyanamide aqueous solution.

Where it is less than 0.05 part by weight, the storage stability tends to be insufficient. Addition of more than 1.0 part by weight also results in insufficient storage stability.

The dicarboxylic acid is usually incorporated into the cyanamide aqueous solution by mixing them with stirring. Where lime nitrogen is used as a starting material for the cyanamide aqueous solution, the dicarboxylic acid can be added to the preparation system in any stage of the preparation.

The storage stability of the dicarboxylic acid-containing cyanamide aqueous solution can further be enhanced by adjusting to a pH of 3 to 6, preferably 3 to 5. Suitable pH adjustors include inorganic acids, such as mineral acids, and organic acids, such as acetic acid.

Claim 1 of 2 Claims

1. A cyanamide aqueous solution containing adipic acid in an amount of 0.05 to 1.0% by weight based on the cyanamide aqueous solution exclusive of said adipic acid.

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