TITLE OF THE INVENTION:
"The process for producing high grade Calcium Hypochlorite" FIELD OF INVENTION:
The present invention is related to the manufacture of Calcium Hypochlorite with high purity by an improved continuous process. It also relates to the product obtained by applying the said process.
BACKGROUND:
A variety of processes were being adopted for manufacturing Calcium Hypochlorite from lime and alkalies (e.g., sodium hydroxide); Out of which very less number of processes were directed towards producing the best quality Calcium Hypochlorite which is free from contaminants and diluents at the lowest possible cost. There were some other processes which were designed to reduce waste materials resulting from the process.
For example, IN Pat No. 159346 describes a process for manufacturing of hydrated Calcium Hypochlorite which consists the preparation of aqueous slurry of calcium hydroxide and subjecting the slurry to single step chlorination. The chlorinated slurry thus obtained was fed to filtration by means of centrifugation. In Patent Number - 159346, Lime stone was used for obtaining Calcium Oxide which results in the contamination of the product. During the reaction with Lime Stone impurities like Silica and Calcium Carbonate were generated which need to be removed by way of screening.
U.S. Pat. No. 4,364,917 describes a continuous process for preparing slurry of calcium hypochlorite wherein a solution of sodium hydroxide was fed to one end of an elongated tubular reactor. The calcium hydroxide slurry and chlorine gas were introduced through a large number of injection sites along the length of the reactor. The red-ox potential of the reaction mixture at any injection site must not be inferior to that at the immediately
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preceding site and must be in the range 900 to 950 mV at the exit end of the reactor. The process in Patent Number - US 4,364,917, occurs in a single reactor which would be difficult to maintain different temperatures.
In particular, it has been found that readily separable crystals of sodium chloride and calcium hypochlorite can be formed by diluting (a) an aqueous slurry of sodium hydroxide, lime, and bleach mother liquor (an aqueous solution substantially saturated with sodium chloride and calcium hypochlorite) with (b) aqueous salt solution saturated with calcium ion and sodium chloride, and chlorinating thus obtained aqueous admixture in the presence of a seed bed of sodium chloride crystals and neutral calcium hypochlorite crystals at temperatures at which the loss of calcium hypochlorite by accelerated decomposition is avoided. Calcium hypochlorite particles and the larger sodium chloride crystals produced by the aforesaid process are readily separable and bleach mother liquor can be recycled.
Sodium Chloride will be formed as a by product during the manufacture of Calcium Hypochlorite. None of the conventional processes have explained how the removal of Sodium Chloride should be done effectively. Some prior have tried to provide methods like hydraulic (sluggish in nature) method through which Solid Sodium Chloride can be removed but even with that method the removal was not so effective.
The product produced by adopting any of the conventional processes will contain less amount of free available chlorine. Not even one conventional process provided for an economical and a stable method through which Calcium Hypochlorite can be manufactured with 65%-70% of free available chlorine. Most of the conventional processes does not provide for the effective removal of impurities from the product. The moisture content in the product is also relatively low.
OBJECT OF THE INVENTION:
The present invention aims at overcoming the aforementioned disadvantages by providing a process which enables the production of good quality calcium hypochlorite to be obtained with a good yield by reducing the process complications.
The Principal object of the present invention is to manufacture Calcium Hypochlorite with large amount of available chlorine. The Calcium Hypochlorite manufactured by the present process consists approximately 65%-70% of available chlorine in it.
Another object of the present invention is to develop process, less sensitive to operational upsets for which the prior art methods did not provide any solution. This could be achieved only by higher operational margins for process parameters and equipments.
The present process have included cake washing as one of the principal steps which resulted in effective removal of impurities and an obvious improvement in the quality. This step also helps in maintaining the required moisture levels in the final product.
SUMMERY OF INVENTION:
The present invention discusses a process where Calcium Hypochlorite is manufactured with 65%-70% of free available chlorine. This specific method was not known so far.
The main emphasis of the present invention is to bring a new and useful method that can minimize all the difficulties that are associated with the conventional processes. The manufacturing process herein consists the preparation of MOL (Milk of lime) as an initial step which gets chlorinated to produce dibasic Calcium Hypochlorite slurry. The slurry thus obtained is made to react with Caustic Soda and Chlorine gas simultaneously. Then the slurry is further chlorinated to increase the amount of free available chlorine.
The above chlorinated slurry is filtered by a drum filter to separate Mother Liquor. The cake obtained is fed to dryer. The dried material is sieved to get uniform sized granules. The undersized granules and powder generated in the bag house will be converted to Bulk Density Granules.
DETAILED DESCRIPTION OF THE INVENTION:
The initial step in the preparation of Calcium Hypochlorite is preparation of MOL (Milk of Lime). The MOL in the present process is prepared by admixing hydrated lime and slaked quick lime. The prepared MOL is maintained with minimum amount of Calcium Carbonate. This MOL is partly chlorinated to produce Dibasic Calcium Hypochlorite. This entire reaction so far happens in Reactor which is surrounded by a Jacket through which chilling medium is circulated so as to maintain the suitable temperature.
The whole mass from the 1st Reactor is fed to reactor where it gets mixed with Sodium Hydroxide and Chlorine gas simultaneously. A reaction takes place between Sodium Hydroxide and Chlorine gas, resulting in the production of Sodium Hypochlorite. The Sodium Hypochlorite thus obtained is finally converted into Calcium Hypochlorite by reacting with Calcium Chloride that is generated in Reactor.
The slurry from the 2nd reactor is made to enter 3rd Reactor wherein further chlorination of the product takes place. The further chlorination of the product results in the increase of free available chlorine concentration. The un-reacted Calcium Hydroxide (Ingredient in Reactor) is converted into Calcium Hypochlorite and Calcium Chloride. Thus generated calcium chloride is again converted into calcium hypochlorite and sodium chloride.
So the final product in the 3'^'' Reactor contains an admixture of both liquid phase and solid phase. The liquid phase is a saturated solution of Calcium Hypochlorite and Sodium Chloride and other soluble impurities. The solid phase consists of calcium hypochlorite, sodium chloride, calcium hydroxide and other insoluble residues.
The overall mass of the 3rd Reactor is subjected to wet sieving method to separate Sodium Chloride Crystals. The slurry is being sent to a slurry tank which is provided with an agitator to complete expected reaction and to get homogeneous slurry.
The slurry from the slurry tank is pumped on to the drum filter where the remained sodium chloride portion is removed as wet drain salt and the major part of the liquid gets separated as Mother Liquor. All the solid particles that are present in the slurry will be collected, separated and recovered as a wet cake. Then the wet cake is washed thoroughly to remove the impurities and to attain the desired purity.
The cleaned cake is conveyed to mixer granulator wherein a suitable powder is added to attain the good granulation and also to control the moisture content at a desired level. Thus obtained powder is taken through a grating machine in order to break the lumps formed. The grated powder is allowed to enter the dryer for drying. The dried powder is transported pneumatically to a vibrating screen to get the desired granular size. The desired size granules are collected and packed as normal material, the rejected Material is again converted into bulk density granules.
EXAMPLE:
MANUFACTURE OF 01.000 M.T. OF CALCIUM HYPOCHLORITE OF 68% - 70% AVAILABLE CHLORINE:
Milk of lime containing 660 Kg. of Calcium Hydroxide is fed to reactor; 600 Kg. of Sodium Hydroxide is fed in the reactor and 1200 Kg. of chlorine is fed into all the three reactors together. This 1200 Kgs. of Chlorine is distributed among the three reactors at their respective Stoichiometric requirements. About 2.8 M.T. of mother liquor is separated from drum filter. The temperature profiles in the process are as follow.
Reactor 1 - 15° C to 25° C Reactor2- 15°Cto30°C Reactor 3 - 20° C - 35 ° C.

CLAIMS:
We Claim
1. A process for producing high grade Calcium Hypochlorite, comprising the basic steps of;
a. Preparing a MOL (Milk of Lime)
b. Chlorinating the MOL to produce Dibasic Calcium Hypochlorite slurry
c. Addition of Caustic Soda and Chlorine gas to Dibasic Calcium Hypochlorite slurry
d. Further chlorinating the slurry.
e. Filtration of the slurry to obtain Filter cake
f. Washing of Filter Cake
g. Drying of Filter cake and Sieving
2. The MOL according to Claim 1 (a) is prepared by mixing hydrated lime and slaked quick lime.
3. The steps claimed in Claim 1 (b), 1 (c) and 1 (d), are carried in a series of reactors that are maintained at a temperature of 150 C to 30® C.
4. The filtration as claimed in Claim 1 (e) is carried by Wet Sieving and Drum Filter.
5. The washing according to claim 1(f), is carried out to remove the impurities at a substantial level.
6. The drying according to claim 1(g) is carried by a dryer.
7. The process as claimed in Claim 1, and substantially as described here in.