GB1358068A - Continuous manufacture of alkali metal salts of amino polyacetic acids - Google Patents

Abstract

1358068 Amino polyacetic acids BADISCHE ANILIN- & SODA-FABBIK AG 6 Oct 1971 [7 Oct 1970] 46435/71 Heading C2C [Also in Division G1] Alkali metal salts of amino polyacetic acid<SP>s</SP> are prepared from formaldehyde and an alkali metal cyanide or from formaldehyde, a non- aromatic diamine or triamine and an alkali metal cyanide in aqueous solution at elevated temperature in at least two reaction zones conheated in cascade, the formaldehyde solution and (where used) the stoichiometric amount of a solution of the amine being passed to the first zone or zones and the alkali metal cyanide solution being simultaneously metered thereto under the control of a potentiometric cell or cells such that the alkali metal cyanide concentration in the first zone or zones, as determined by the potentiometric cell or cells, assumes a nearly constant value, this being chosen so that the alkali metal cyanide concentration in the final reaction zone (which may also be determined by a potentiometric cell) is not more than 100 p.p.m. The potentiometric cell may comprise a noble metal electrode, e.g. of gold or silver, dipping into the solution whose cyanide concentration is to be measured and/or controlled, and connected to a reference, e.g. calomel, electrode in contact with the solution by way of a diaphragm. The resulting p.d. may be measured to determine the cyanide concentration, or used to control a metering device, e.g. a magnetic valve pre-set to operate at a given p.d., for the fed cyanide solution. With CH 2 O and alkali metal cyanide the product is a salt of nitrilotriacetic acid; with amines the product is a salt of the corresponding aminoacetic acid; specified amines are 1,2- and 1,3-propylenediamine, ethylenediamine, hexamethylenediamine, 1,2-diaminocyclohexane, piperazine and diethylenetriamine. Byproduct ammonia is preferably removed, e.g. by passage of an inert gas.