Process for manufacturing granules

Abstract

Process for manufacturing granules of at least one alkali metal salt of aminopolycarboxylic acid (A), comprising the steps of (a) providing an aqueous slurry of alkali metal salt of aminopolycarboxylic acid (A), (b) maintaining said aqueous slurry at a temperature in the range of from 50 to 90° C. over a period of time in the range of from 2 to 180 hours, (c) spray granulating said slurry with a gas inlet temperature of at least 150° C.

Claims

1. A process for manufacturing granules from an aqueous slurry of at least one alkali metal salt of aminopolycarboxylic acid (A) under agglomerating conditions, comprising: (a) providing an aqueous slurry of alkali metal salt of aminopolycarboxylic acid (A), (b) maintaining said aqueous slurry at a temperature in a range of from 50 to 90° C. over a period of time in a range of from 2 to 180 hours, and (c) spray granulating said slurry with a gas inlet temperature of at least 150° C. for an average residence time ranging from 2 minutes to 4 hours, to obtain granules of the at least one alkali metal salt of aminopolycarboxylic acid (A) having an average particle diameter (D50) in the range of from 0.4 mm to 2 mm.

2. The process according to claim 1, wherein said aqueous slurry provided in (a) has a concentration of (A) in a range of from 45 to 65% by weight.

3. The process according to claim 1, wherein the alkali metal salts of aminopolycarboxylic acids (A) are selected from alkali metal salts of methylglycine diacetic acid and glutamic acid diacetic acid.

4. The process according to claim 1, wherein the alkali metal salts of aminopolycarboxylic acids (A) are selected from sodium and potassium salts of methylglycine diacetic acid and glutamic acid diacetic acid, in each case fully neutralized.

5. The process according to claim 1, wherein the aqueous slurry in (b) is maintained at the temperature range with or without agitation.

6. The process according to claim 1, wherein the aqueous slurry in (b) is maintained at a temperature in a range of from 60 to 85° C.

7. The process according to claim 1, wherein the spray granulating of said slurry in (c) is performed by spraying said slurry on a fluidized bed of alkali metal salt of aminopolycarboxylic acid (A) particles.

8. The process according to claim 7, wherein the particles in the fluidized bed have an average diameter (D50) in a range of from 100 to 800 μm.

9. The process according to claim 1, wherein the aqueous slurry subjected to spray-granulation in (c) further comprises at least one additive selected from silica, silicates, and organic (co)polymers.

10. The process according to claim 1, wherein alkali metal salt of aminopolycarboxylic acid (A) is selected from compounds according to general formula (I)
[CH.sub.3—CH(COO)—N(CH.sub.2—COO).sub.2]M.sub.3-xH.sub.x  (I) wherein M is selected from alkali metal cations, same or different, and x is in a range of from zero to 1.0.

11. The process according to claim 1, wherein the slurry is spray granulated with a gas inlet temperature of at least 150° C. for an average residence time ranging from 30 minutes to 2 hours, .

12. The process according to claim 1, wherein the granules have an average particle diameter (D50) in the range of from 0.4 mm to 1.25 mm.

Description

EXAMPLE 1

(1) Step (a.1): an aqueous slurry of MGDA-Na.sub.3 (65% L-MGDA-Na.sub.3, 35% D-MGDA-Na.sub.3) was made by charging a vessel with 10.9 kg of a 40% by weight aqueous solution of MGDA-Na.sub.3 and heating it to 80° C. An amount of 4.1 kg MGDA-Na.sub.3 powder, amorphous, manufactured by non-agglomerative spray-drying, average particle diameter (D50) 15 μm, is added. After 30 minutes, an amount of 1.8 kg of water is added. An aqueous slurry is obtained.

(2) Step (b.1): the aqueous slurry obtained in accordance with step (a.1) is stirred for 3 hours at 80° C. An aged aqueous slurry is obtained.

(3) Step (c.1):

(4) A vessel containing a fluidized bed from 1 kg of solid MGDA-Na.sub.3 granule, initial average particle diameter 550 μm, is provided. The fluidization is accomplished by entering a so-called fluidization gas at the bottom of the vessel, said fluidization gas being air with an inlet temperature of 150° C.

(5) As soon as the bed temperature of at least 105° C. is reached, an amount of 2 kg/h of aged aqueous slurry according to step (b.1) is sprayed onto the fluidized bed with the help of a nozzle. The spraying—and thus atomizing—is accomplished with air with a gas inlet temperature of 150° C. Every 30 minutes an aliquot of granule is removed from the vessel, and classified by sieving. The fines—particle diameter of 350 μm or below—may be used as particulate solid for making more aqueous slurry according to step (a.1). The lumps—particle diameter more than 1.5 mm—may be milled and mixed with the fines before using them in step (a.1).

(6) A free-flowing granule of MGDA-Na.sub.3 is obtained that has excellent properties such as, but not limited to excellent percarbonate stability and low hygroscopicity. No hot spots are observed during processing. No sticky material is obtained.

EXAMPLE 2

(7) Basically, example 1 is repeated but with step (a.2) instead of step (a.1).

(8) Step (a.2): an aqueous slurry of racemic MGDA-Na.sub.3 was made by charging a vessel with 10.9 kg of a 40% by weight aqueous solution of MGDA-Na.sub.3 and heating it to 80° C. An amount of 4.1 kg MGDA-Na.sub.3 powder, crystalline, modification 1, manufactured by spray-granulation followed by milling, average particle diameter (D50) 65 μm, is added. After 30 minutes, an amount of 1.8 kg of water is added. An aqueous slurry is obtained.

(9) Step (b.2): the aqueous slurry obtained in accordance with step (a.2) is stirred for 3 hours at 80° C. An aged aqueous slurry is obtained.

(10) Step (c.2):

(11) The protocol of step (c.1) is followed but aged aqueous slurry according to step (b.2) is used.

(12) A free-flowing granule of MGDA-Na.sub.3 is obtained that has excellent properties such as, but not limited to excellent percarbonate stability and low hygroscopicity. No hot spots are observed during processing. No sticky material is obtained.

EXAMPLE 3

(13) Basically, example 1 is repeated but with step (a.3) instead of step (a.1).

(14) Step (a.3): an aqueous slurry of MGDA-Na.sub.3 (60% L-MGDA-Na.sub.3, 40% D-MGDA-Na.sub.3) was made by charging a vessel with 10.9 kg of a 40% by weight aqueous solution of MGDA-Na.sub.3 and heating it to 80° C. An amount of 4.1 kg MGDA-Na.sub.3 powder, crystalline, modification 2, manufactured by spray-granulation followed by milling, average particle diameter (D50) 50 μm is added. After 30 minutes, an amount of 1.8 kg of water is added. An aqueous slurry is obtained.

(15) Step (b.3): the aqueous slurry obtained in accordance with step (a.3) is stirred for 3 hours at 80° C. An aged aqueous slurry is obtained.

(16) Step (c.3):

(17) The protocol of step (c.1) is followed but aged aqueous slurry according to step (b.3) is used.

(18) A free-flowing granule of MGDA-Na.sub.3 is obtained that has excellent properties such as, but not limited to excellent percarbonate stability and low hygroscopicity. No hot spots are observed during processing. No sticky material is obtained.