Patent GB-1233470-A (GB)
IPC: E04F13/08
Filed: 1968-12-11
Abstract: 1,233,470. Preparation of nitrilotriacetic acid and salts. W. R. GRACE & CO. 11 Dec., 1968 [12 Dec., 1967], No. 58947/68. Heading C2C. A process for the manufacture of nitrilotriacetic acid or an alkali metal nitrilotriacetate comprises: (1) forming a first reaction mixture by adding an aqueous formaldehyde solution (35-50% HCHO) to an ammoniated solution maintained at a temperature of 10-20‹ and formed by mixing aqueous ammonia (15-30% NH 3 ) with an aqueous solution of alkali metal cyanide (2 moles MCN per 150-200 millilitres water), there being used from 1 to 1.5 mole of ammonia and from 2À1 to 2.2 moles of formaldehyde per 2 moles of alkali metal cyanide; (2) forming a second reaction mixture by adding said first reaction mixture to an ammoniated solution which is at a temperature in the range 60-90‹ C. and at a pressure of 15-30 atmospheres gauge and which has been formed by adding anhydrous ammonia to an aqueous alkali metal hydroxide solution maintained in a first zone at a temperature of 20-30‹ C. in an amount sufficient to produce said pressure of 15-30 atmospheres gauge within said first zone when the temperature therein is increased to 60-90‹ C., the first reaction mixture being added to the ammoniated alkali metal hydroxide solution at a rate to provide about 2 equivalents of alkali metal cyanide reaction products present in said first reaction mixture per 0À3-1 mole of alkali metal hydroxide present in the ammoniated solution, the pressure within said pressurizable zone falling to about 5-10 atmospheres gauge during the addition of the first reaction mixture; (3) forming a third reaction mixture by heating the second reaction mixture in a pressurizable zone to about 105-110‹ C. for about 0À5-2 hours, venting said pressurizable zone when the pressure therein reaches about 15-30 atmospheres gauge, and boiling the mixture within the vented pressurizable zone until said mixture is substantially free of ammonia; (4) forming an aqueous solution of alkali metal nitrilotriacetate by adding to the third reaction mixture in the said second zone, which is vented and wherein the third reaction mixture is added and maintained at a temperature in the range 103-110‹ C.-a formaldehyde-cyanide solution formed by adding aqueous formaldehyde (35-50% HCHO) to an aqueous alkali metal cyanide solution (1 mole MCN per 100-200 ml. of water) maintained at 10-20‹ C. at a rate of 1À05-1À1 mole of formaldehyde per mol. of alkali metal cyanide, the formaldehyde-cyanide solution being added to the third reaction mixture at a rate to provide about 1 equivalent of alkali metal cyanide reaction products for each equivalent of alkali metal cyanide reaction products present in said third reaction mixture, and the temperature of the resulting mixture being maintained at about 103-110‹ C. until said resulting mixture within said second vented reaction zone is substantially free of ammonia; (5) lowering the pH of the aqueous solution of alkali metal nitrilotriacetate by addition of acid thereto, the acid being sulphuric, hydrochloric or phosphoric acid to give a pH in the range 7-10 when the desired product is nitrilotriacetic acid and the acid being nitrilotriacetic acid to give a pH of about 12 when the desired product is alkali metal nitrilotriacetate. (6) decolorizing the acidified nitrilotriacetate solution in step (5) by adding activated carbon thereto and agitating the mixture for 1-2 hours at a temperature in the range 80-100‹ C., and separating the decolorized alkali metal nitrilotriacetate from the carbon; and (7) when nitrilotriacetic acid is the desired product, adding sulphuric or hydrochloric acid to the decolorized solution obtained in step (6) thereby precipitating from said solution nitrilotriacetic acid which is separated and recovered. When preparing nitrilotriacetic acid there is preferably used 3-5 gms. of activated carbon per mole of alkali metal nitrilotriacetate in step (6). When the alkali metal salt is the desired product preferably 2-5 grams of activated carbon are added, per mole, and H 2 O 2 ; is added at the rate of 2-5 grams of 30% H 2 O 2  per mole of alkali metal nitrilotriacetate.