FORM 2
THE PATENTS ACT, 1970
(Act 39 of 1970)
COMPLETE SPECIFICATION
(See Section 10)
Title: "An improved crystallization process for manufacturing Sodium Percarbonate Powder'*
Name: M/s. Gujarat Alkalies and Chemicals Limited.
Address: P.O. Petrochemicals - 391 346,
Dist: Vadodara, Gujarat - India.
Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to be performed.

Title of the Present Invention
An improved crystallization process for manufacturing Sodium Percarbonate Powder
Field of the Present Invention
The present invention relates to manufacturing of Sodium Percarbonate powder using crystallization process. More particularly, the present invention relates to manufacturing of Sodium Percarbonate powder using stabilizers and reaction of Hydrogen Peroxide with Sodium Carbonate in presence of water and a salting out agent.
Background of the Present Invention
Known methods of manufacturing Sodium Percarbonate include Crystallization, Spray process, and Dry process. Sodium Percarbonate inherently has low storage stability, especially, in presence of various components in cleaning formulations and in warm and moist conditions. Stabilizing Sodium Percarbonate against loss of oxygen is important and essential.
Common methods of stabilization of Sodium Percarbonate are to coat Sodium Percarbonate particles with stabilizing components. Coating may be carried out using various chemicals as per needs and requirements of different applications. Sodium Percarbonate can be in powder or granulated form depending upon the manufacturing method adopted and the application of the product.
Methods for manufacturing stabilized Sodium Percarbonate by coating are disclosed in some patents. For example, DE 4,306,399 discloses a method to coat Sodium Percarbonate by spraying wet Sodium Percarbonate with an aqueous solution or suspension containing Sodium Perborate.
CN 101066752 discloses use of stabilizers such as EDTA and l-Hydroxyethyl-1,1-Disodium Diphosphate in reaction of Sodium Carbonate with Hydrogen Peroxide solution and Sodium Chloride.
CN 101270232 discloses preparation of Sodium Percarbonate granules using internal stabilizers.
The present invention provides an improved crystallization process wherein the Sodium Percarbonate manufactured in accordance with the present invention remains stable for atleast 90 days in powder form and the manufacturing process as per the

present invention does not require any coating, thereby eliminating the coating step from the process. Hence, the present invention provides economic significance as the process of coating is eliminated.
The process of manufacturing Sodium Percarbonate in accordance with the present invention is an improved process as most of the process steps like addition, reaction, crystallization/salting out are carried out in the same reactor. The process does not make use of any external stabilizer for imparting stability in the final product. Sodium Percarbonate manufactured in accordance with the present invention has characteristics such as high active oxygen content in the range of 13.5 - 14.5%, high stability and excellent dissolution rate.
Summary of the Present Invention
The present invention relates to an improved crystallization process for preparing Sodium Percarbonate powder with high stability and excellent water solubility. The process involves the reaction of Hydrogen Peroxide with Sodium Carbonate in presence of unique combination of three internal stabilizers comprising of Sodium Meta Silicate Nanohydrate, Magnesium Sulphate Heptahydrate & Ethylene Diamine Terra Acetic Acid (EDTA) - Disodium Salt and water as reaction media and Sodium Chloride as salting out agent. The product thus crystallized is centrifuged, dried, pulverized and sieved. The mother liquor obtained after centrifuging is recycled in the process.
The manufacturing process as per the present invention uses a unique combination of internal stabilizers not disclosed in prior art. Thus, the present invention shows a technical advance in the process by using a unique combination of the three internal stabilizers never used earlier in such processes. It is the use of these three internal stabilizers in the manner disclosed that permits elimination of the coating step which otherwise would be required in order to produce stabilized Sodium Percarbonate. Sodium Percarbonate produced in accordance with the present invention has comparable stability with the coated product.
The manufacturing process in accordance with the present invention is eco-friendly, as the mother liquor obtained after centrifuging is recycled without the generation of any effluents.
Sodium Percarbonate Powder manufactured in accordance with the present invention has excellent water solubility and high stability.

Detailed Description of the Present Invention
The present invention deals with the manufacturing of the sodium percarbonate powder by an improved crystallization process using a unique combination of internal stabilizers Magnesium Sulphate Heptahydrate, Sodium Metasilicate Nanohydrate & Disodium salt of EDTA. The combination of this use of internal stabilizers results in longer shelf life of sodium percarbonate powder. The process does not make use of any external stabilizer and the reaction conditions are very mild including the drying of the product. The process is eco friendly as the mother liquor is repeatedly recycled in the process, with no effluent as such generated.
Equipments required: A 250 Ltr. SS 316 reactor system fitted with mechanical stirrer, digital temperature indicator, addition funnel, solid addition port is taken for carrying out the reaction.
Chemicals required: Quantities of Sodium Carbonate, D M Water, Sodium Chloride solution used as salting out agent, composite internal stabilizers - mixture of Magnesium Sulphate Heptahydrate, Sodium Metasilicate Nanohydrate & Disodium salt of EDTA and 50% Hydrogen Peroxide.
The best mode of performing the present invention comprises the following steps:
Step l:
Desired quantity of Sodium Carbonate, Sodium Chloride, three internal stabilizers-mixture of Magnesium Sulphate Heptahydrate, Sodium Metasilicate Nanohydrate & Disodium salt of EDTA are taken in the reactor and the contents are stirred and cooled down to 10 - 15°C which is followed by the slow addition of 50% Hydrogen Peroxide preferably at the same temperature. The reaction including the addition of Hydrogen Peroxide gets completed in 10 - 30 hrs.
Sodium Chloride is used in this process as a salting out agent. The strength of sodium chloride solution used is 25% and the quantity used is also unique. The weight ratio of the components is an essential part of the process. Hence, the weight ratio of the sodium carbonate and the salting out agent used is kept in the range of 2.5:1. The weight ratio of the sodium carbonate and the combination of the three internal stabilizers is kept in ratio of 62.5:1 to 100:1. The optimum molar ratio of sodium carbonate and hydrogen peroxide varies from 1:1.50 to 1:2.25.
Step 2:
Once the addition of Hydrogen Peroxide is completed the contents in the reactor are
further stirred and then centrifuging is carried out using a rubber line basket type of
centrifuge.

Step3:
Simultaneously, the mother liquor is collected and kept in a storage tank for using and recycling the same in the subsequent batches, without generation of any effluent, making the process eco-friendly.
Step4:
After centrifuging the contents a wet cake is obtained which is dried using air
circulating dryer at 50 - 65°C for 2-5hrs.
Step5:
After the drying the product is further pulverized and sieved obtaining a powder form
of Sodium Percarbonate having excellent water solubility and high stability.
Sodium percarbonate obtained through the above mentioned process has active oxygen content -13.5 - 14.5%, bulk density - 0.5 - 0.9 gm per cc, pH of 1% solution: 10.6 - 10.7, solubility in water (gpl at 20° C ): 120 - 130, Dissolution rate (2gpl at 15° C): 99% in 25 -30 second, particle size 90 - 95% < 75 micron. The final sodium percarbonate powder is stable for at least 90 days.
The present invention will be described in terms of specific examples and examples should be considered as illustrative of the invention and not as limiting the same. The examples described herein will substantiate our claims
Example: 1
10 kg Sodium Carbonate, 30 Lit DM water, 15.50 kg NaCl solution (25%), along with the composite internal stabilizers - 55gms magnesium sulphate heptahydrate, 55gms sodium meta silicate nanohydrate and 50gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 - 11° C followed by the slow addition of 9.62 kg. 50% Hydrogen Peroxide in 19 hrs keeping the temperature of the reaction in between 12 ± 2° C. The contents are further stirred for 6 hrs at the same temperature followed by the centrifugation of the mixture at 30°C to separate the product. The Mother liquor obtained (54.18 kg.) is recycled in the subsequent batches. The wet product is dried in air circulating dryer at 60° C for 4 hrs. The dry product (9.10 kg.) obtained is further pulverized and sieved.
The product shows active oxygen - 14.47 wt %, bulk density 0.637 gms per cc, pH of 1% solution : 10.67, solubility in water : 120 gpl at 20° C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.

Example: 2
10 kg. Sodium Carbonate, 30 Lit DM water, 15.50 kg. NaCl solution (25%), along with the composite internal stabilizers - 35 gms magnesium sulphate heptahydrate, 35 gms sodium meta silicate nanohydrate and 30 gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 - 11° C followed by the slow addition of 14.45 kg. 50% Hydrogen Peroxide in 8 hrs keeping the temperature of the reaction in between 12 ± 2° C. The contents are further stirred for 6 hrs at the same temperature followed by the centrifugation of mixture at 35°C to separate the product. The Mother liquor obtained (55.24 kg.) is recycled in the subsequent batches. The wet product is dried in air circulating dryer at 60° C for 3.5 hrs. The dry product (11.84 kg) obtained is further pulverized and sieved.
The product shows active oxygen - 13.94 Wt%, bulk density 0.63 gms per cc, pH of 1% solution : 10.65, solubility in water : 120 gpl at 20° C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.
Example: 3
10 kg. Sodium Carbonate, 26.72 Lit DM water, 15.84 kg. NaCl solution (25%), along with the composite internal stabilizers - 55 gms magnesium sulphate heptahydrate, 55 gms sodium meta silicate nanohydrate and 50 gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 - 11° C followed by the slow addition of 9.63 kg. 50% Hydrogen Peroxide in 6 hrs keeping the temperature of the reaction in between 11 ± 1° C. The contents are further stirred for 6 hrs at the same temperature followed by the centrifugation of mixture at 28°C to separate the product. The Mother liquor obtained (51.84 kg.) is recycled in the subsequent batches. The wet product is dried in air circulating dryer at 55° C for 5 hrs. The dry product (8.66 kg) obtained is further pulverized and sieved.
The product shows active oxygen - 13.55 wt%, bulk density 0.63 gms per cc, pH of 1% solution : 10.64, solubility in water : 120 gpl at 20° C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.
Example: 4
30 kg. Sodium Carbonate 90 Lit DM water, 46.58 kgs NaCl solution (25%), along with the composite internal stabilizers - 165 gms magnesium sulphate heptahydrate, 165 gms sodium meta silicate nanohydrate and 150 gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 -11° C followed by

the slow addition of 28.86 kg. 50% Hydrogen Peroxide in 14 hrs keeping the temperature of the reaction in between 11 ± 1° C. The contents are further stirred for 6 hrs at the same temperature followed by the centrifugation of mixture at 28°C to separate the product. The Mother liquor obtained (160.78 kg.) is recycled in the subsequent batches. The wet product is dried in air circulating dryer at 60° C for 5 hrs. The dry product (30.25 kg.) obtained is further pulverized and sieved.
The product shows active oxygen - 14.37 wt%, bulk density 0.53 gms per cc, pH of 1% solution : 10.67, solubility in water : 120 gpl at 20° C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.
Example: 5
30 kg. Sodium Carbonate, 90 Lit DM water, 47.49 kg. NaCl solution (25%), along with the composite internal stabilizers - 165 gms magnesium sulphate heptahydrate, 165 gms sodium meta silicate nanohydrate and 150 gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 -11° C followed by the slow addition of 28.86 kg. 50% Hydrogen Peroxide in 5 hrs keeping the temperature of the reaction in between 11 ± 1° C. The contents are further stirred for 5 hrs at the same temperature followed by the centrifugation of mixture at 27°C to separate the product. The Mother liquor obtained (161.20 kg) is recycled in the subsequent batches. The wet product is dried in air circulating dryer at 60° C for 5 hrs. The dry product (30.51 kg) obtained is further pulverized and sieved.
The product shows active oxygen - 13.99 wt%, bulk density 0.66 gms per cc, pH of 1% solution : 10.67, solubility in water : 120 gpl at 20°C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.
Example: 6
7.34 kg. Sodium Carbonate, 46.64 kg. Mother liquor of earlier batches containing 5.60% Sodium Carbonate & 7.80% Sodium Chloride, 1.35 kg. NaCl solution (25%), along with the composite internal stabilizers - 55gms magnesium sulphate heptahydrate, 55gms sodium meta silicate nanohydrate and 50gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 - 11° C followed by the slow addition of 9.620 kgs of 50% Hydrogen Peroxide in 19 hrs keeping the temperature of the reaction in between 12 ± 2° C. The contents are further stirred for 6 hrs at the same temperature followed by the centrifugation of mixture at 30°C to separate the product. The Mother liquor (53.60 Kg.) is further

recycled in the subsequent batches. The wet product is dried in air circulating dryer at 60° C for 4 hrs. The dry product (8.80 kg.) is further pulverized and sieved.
The product shows active oxygen - 14.43 wt%, bulk density 0.64 gms per cc, pH of 1% solution : 10.66, solubility in water : 120 gpl at 20° C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.
Example: 7
23.25 kgs Sodium Carbonate 134 kg. Mother Liquor of earlier batches containing 5.00% Sodium Carbonate & 7.18% Sodium Chloride, 9.28 kgs NaCl solution (25%), along with the composite internal stabilizers - 165 gms magnesium sulphate heptahydrate, 165 gms sodium meta silicate nanohydrate and 150 gms EDTA Disodium Salt are taken in a reactor. The contents are stirred and cooled down to 10 -11° C followed by the slow addition of 28.86 kg, 50% Hydrogen Peroxide in 14 hrs keeping the temperature of the reaction in between 12 ± 1° C. The contents are further stirred for 6 hrs at the same temperature followed by the centrifugation of mixture at 25°C to separate the product, The Mother liquor (161 Kg.) is further recycled in the subsequent batches. The wet product is dried in air circulating dryer at 60° C for 5 hrs. The dry product (30.35 kg.) is further pulverized and sieved.
The product shows active oxygen - 14.45 wt%, bulk density 0.539 gms per cc, pH of 1% solution : 10.68, solubility in water : 120 gpl at 20° C, dissolution rate : 2 gpl at 15° C in 30 seconds, total heavy metal content (as Pb) < 15 ppm, particle size distribution 90 - 95% < 75 micron and excellent stability for at least 90 days.

We Claim:
1. An improved crystallization process for manufacturing Sodium Percarbonate
Powder comprising
the step of reacting Sodium Carbonate with Hydrogen Peroxide in
presence of three internal stabilizers—Ethylene Diamine Tetra Acetic
Acid-Disodium salt, Magnesium Sulphate Heptahydrate, Sodium Meta
Silicate Nanohydrate and salting out agent—Sodium Chloride;
the step of centrifuging the contents;
the step of drying Sodium Percarbonate;
the step of pulverizing Sodium Percarbonate; and
the step of sieving of Sodium Percarbonate.
2. A process as per claim 1 wherein the Sodium Percarbonate Powder manufactured is stable for at least 90 days.
3. A process as per claim 1 wherein the Sodium Percarbonate Powder manufactured has 13.5-14.5% active Oxygen content.
4. A process as per claim 1 wherein the Sodium Percarbonate Powder manufactured has solubility of 120 -130 gpl in water at 20° C.
5. A process as per claim 1 wherein the Sodium Percarbonate Powder manufactured has dissolution rate of 99% in 25-30 seconds.
6. A process as per claim I wherein the reaction is carried out at a temperature range of 10-15° C.
7. A process as per claim 1 wherein the weight ratio of Sodium Carbonate and me three internal stabilizers is kept in the range 62.5:1 to 100:1.
8. A process as per claim 1 wherein the weight ratio of Sodium Carbonate and the salting agent is kept at 2.5:1.
9. A process as per claim 1 wherein the drying of Sodium Percarbonate is carried out at 50-65° C in air-circulating dryer for 2-5 hours.