Process for the preparation of coated granular sodium percarbonate, and product obtainable by the process
View Patent ↗The invention relates to a process for the preparation of coated granular sodium percarbonate having a low TAM value. The preparation is carried out by fluidized-bed spray granulation at a temperature T G in the range from 45 to 75° C., and the coating is effected by the spray application of an aqueous solution containing at least one coating component in a fluidized bed at a temperature T U in the range from 35 to 100° C. According to the invention, a) after the fluidized-bed spray granulation but before the coating, drying is carried out at T NT of greater than T G , or b) the fluidized-bed granulation is carried out in at least two steps at T G1 , T G2 . . . T Gn , T G2 or T Gn being higher than T G 1, and drying being unnecessary if ⅔ of the granulate have been formed at T G 1, or c) drying takes place not after the granulation but after the coating, at T UNT , T UNT being at least 20° C. higher than T G .
1. A process for the preparation of a coated granular sodium percarbonate, comprising:
(i) preparing granular sodium percarbonate by fluidized-bed spray granulation, wherein an aqueous sodium carbonate solution or suspension and an aqueous hydrogen peroxide solution are sprayed in a molar ratio of Na 2 CO 3 to H 2 O 2 in the range from 1:1.4 to 1:1.8 into a fluidized-bed comprising sodium percarbonate particles, at a fluidized-bed temperature T G in the range of from 45 to 75° C., and water is simultaneously evaporated off;
(ii) coating said granular sodium percarbonate by spray application, in a fluidised bed, of at least one aqueous solution comprising one or more coating components, with the simultaneous evaporation of water; and
(iii) drying said granular sodium percarbonate at a fluidized-bed temperature T NT in the range from greater than 75 to 95° C. that is higher than said fluidized-bed temperature T G , wherein said drying is carried out before the coating, or both before and after the coating.
2. The process as claimed in claim 1 , wherein said coating is carried out at a fluidized-bed temperature T U in the range from 35 to 100° C.
3. The process as claimed in claim 1 , wherein said fluidized-bed spray granulation is carried out in two fluidized-bed spray granulation steps, wherein a first fluidized-bed spray granulation step is carried out at said fluidized-bed temperature T G , a second fluidized-bed spray granulation step is carried out at a fluidized-bed temperature T GNT , and said fluidized-bed temperature T GNT is higher than said fluidized-bed temperature T G .
4. The process as claimed in claim 3 , wherein at least ⅚ of said granular sodium percarbonate is formed in said first fluidized-bed spray granulation step.
5. The process as claimed in claim 1 , wherein said fluidized-bed spray granulation is carried out in at least two fluidized-bed spray granulation steps, wherein a first fluidized-bed spray granulation step is carried out at a fluidized-bed temperature T G1 and one or more additional fluidized-bed spray granulation steps are carried out at fluidized-bed temperatures T Gn , wherein n is the number of said additional fluidized-bed spray granulation steps, and wherein said fluidized-bed temperatures T Gn are higher than said fluidized-bed temperature T G1 .
6. The process as claimed in claim 5 , wherein at least two thirds of said granular sodium percarbonate by mass is formed during a first fluidized-bed spray granulation step.
7. The process as claimed in claim 1 , wherein said fluidized-bed temperature T G is in the range of 55 to 75° C.
8. The process as claimed in claim 1 , wherein said granular percarbonate is dried with a dwell time of from 15 to 45 minutes.
9. The process as claimed in claim 1 , wherein the aqueous sodium carbonate solution or suspension and the aqueous hydrogen peroxide solution are sprayed in a molar ratio of Na 2 CO 3 and H 2 O 2 in the range of 1:1.5 to 1:1.6.
10. The process as claimed in claim 1 , wherein said fluidized-bed spray granulation and said drying are carried out in a flow trough which is divided into a plurality of chambers.
11. The process as claimed in claim 10 , wherein said coating and said drying of a coated granular sodium percarbonate are carried out in one or more downstream chambers of said flow trough or in a separate fluidised-bed reactor arranged downstream of said flow trough.
12. The process as claimed in claim 1 , wherein said granular sodium percarbonate, after drying, is coated with one or more layers of a coating material containing sodium sulfate to produce a coating on said granular sodium percarbonate, wherein said coating comprises an outermost coating layer containing sodium sulfate as principal component and a total amount of coating material of less than 10 wt. %, based on said coated granular sodium percarbonate.
13. A process for the preparation of a coated granular sodium percarbonate, comprising:
(i) preparing granular sodium percarbonate by fluidized-bed spray granulation, wherein an aqueous sodium carbonate solution or suspension and an aqueous hydrogen peroxide solution are sprayed in a molar ratio of Na 2 CO 3 to H 2 O 2 in the range from 1:1.4 to 1:1.8 into a fluidized-bed comprising sodium percarbonate particles, at a fluidized-bed temperature T G in the range of from 45 to 75° C., and water is simultaneously evaporated off;
(ii) coating said granular sodium percarbonate by spray application, in a fluidised bed, of at least one aqueous solution comprising one or more coating components, with the simultaneous evaporation of water; and
(iii) drying said granular sodium percarbonate at a fluidized-bed temperature T NT in the range from greater than 75 to 95° C. that is higher than said fluidized-bed temperature T G , wherein said drying is carried out before coating, or both before and after coating,
wherein said fluidized-bed temperature T NT is from 10 to 30° C. greater than T G .
14. The process as claimed in claim 13 , wherein said coating is carried out at a fluidized-bed temperature T U in the range from 35 to 100° C.
15. The process as claimed in claim 14 , wherein said fluidized-bed temperature T U is in the range from 40 to 90° C.
16. The process as claimed in claim 13 , wherein said fluidized-bed spray granulation is carried out in at least two fluidized-bed spray granulation steps, wherein a first fluidized-bed spray granulation step is carried out at a fluidized-bed temperature T G1 , and one or more additional fluidized-bed spray granulation steps are carried out at fluidized-bed temperatures T Gn , wherein n is the number of said additional fluidized-bed spray granulation steps, and wherein said fluidized-bed temperatures T Gn are higher than said fluidized-bed temperature T G1 , and at least two thirds of said granular sodium percarbonate by mass is formed during a first fluidized-bed spray granulation step.
17. The process as claimed in claim 13 , wherein said fluidized-bed temperature T G is in the range of 55 to 75° C.
18. The process as claimed in claim 13 , wherein said granular percarbonate is dried with a dwell time of from 15 to 45 minutes.
19. A process for the preparation of a coated granular sodium percarbonate, comprising:
(i) preparing granular sodium percarbonate by fluidized-bed spray granulation, wherein an aqueous sodium carbonate solution or suspension and an aqueous hydrogen peroxide solution are sprayed in a molar ratio of Na 2 CO 3 to H 2 O 2 in the range from 1:1.4 to 1:1.8 into a fluidized-bed comprising sodium percarbonate particles, at a fluidized-bed temperature T G in the range of from 45 to 75° C., and water is simultaneously evaporated off;
(ii) coating said granular sodium percarbonate by spray application, in a fluidised bed, of at least one aqueous solution comprising one or more coating components, with the simultaneous evaporation of water; and
(iii) drying said granular sodium percarbonate at a fluidized-bed temperature T NT in the range from greater than 75 to 95° C. that is higher than said fluidized-bed temperature T G , wherein said drying is carried out before coating, or both before and after coating,
wherein said aqueous hydrogen peroxide solution comprises a magnesium salt in an amount equivalent to 100 to 1000 ppm Mg 2+ in said coated granular sodium percarbonate.
20. The process as claimed in claim 19 , wherein said coating is carried out at a fluidized-bed temperature T U in the range from 35 to 100° C.
21. The process as claimed in claim 20 , wherein said fluidized-bed temperature T U is in the range from 40 to 90° C.
22. The process as claimed in claim 19 , wherein said fluidized-bed spray granulation is carried out in at least two fluidized-bed spray granulation steps, wherein a first fluidized-bed spray granulation step is carried out at a fluidized-bed temperature T G1 , and one or more additional fluidized-bed spray granulation steps are carried out at fluidized-bed temperatures T Gn , wherein n is the number of said additional fluidized-bed spray granulation steps temperatures T Gn are higher than said fluidized-bed temperature T G1 , and at least two thirds of said granular sodium percarbonate by mass is formed during a first fluidized-bed spray granulation step.
23. The process as claimed in claim 19 , wherein said fluidized-bed temperature T G is in the range of 55 to 75° C.
24. The process as claimed in claim 19 , wherein said granular percarbonate is dried with a dwell time of from 15 to 45 minutes.