Claims:We Claim:
1) A process for preparing, in a single vessel, simultaneously or sequentially, food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or a combination thereof the process comprising:
a) mixing a calcium compound for 2 to 12 minutes at 800 to 4000 rpm in a high-speed shear mixing vessel to micronise the calcium compound to a particle size of 2 to 150 microns; and
b) spraying the micronized calcium compound obtained in step (a) with an amount of 85% phosphoric acid which is stoichiometrically sufficient, relative to the amount of calcium compound in the vessel, to obtain the desired end-product while vigorously mixing the contents in the vessel at a speed of 400 to 4000 rpm for a reaction time of 2 to 10 minutes to enable the reaction to progress to completion yielding the end-product of food grade mono-calcium phosphate, di-calcium phosphate tri-calcium phosphate or a mixture thereof;
Provided that the temperature within the vessel in steps (a) and (b) does not exceed 70o Celsius.

2) The process as claimed in claim 1, wherein the calcium compound is selected from the group comprising calcium carbonate, calcium hydroxide and calcium oxide.

3) The process as claimed in claim 1, wherein the pH of phosphoric acid is not more than pH 2.
4) The process as claimed in claim 1, wherein the temperature in the vessel is prevented from exceeding 70o Celsius by controlling the rate of the reaction or surrounding the vessel by a water jacket.

5) The process as claimed in claim 1, wherein the exothermicity of the reaction is allowed to reduce the moisture content in the vessel resulting in anhydrous end-product.

6) The process as claimed in claim 1, wherein the rate of the reaction is controlled to prevent loss of moisture resulting in a hydrated end-product and, further, drying the end-product to obtain dried granules of the end-product.

7) The process as claimed in claim 1, wherein the rate of the reaction is controlled to prevent loss of moisture resulting in a hydrated end-product and, further, water of up to 10% by weight of the end-product is added into the vessel after completion of the reaction, followed by drying the end-product to obtain dried granules of the end-product.

8) A food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or a combination thereof prepared by the process of claim 1.

9) The food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or combination thereof as claimed in claim 8 optionally further comprising amino acids, enzymes, micronutrients, vitamins, growth promoters, minerals, proteins, colorants, starch, carbohydrates, baking ingredients and additives and antioxidants.

, Description:FIELD OF THE INVENTION
The present invention relates to a process for preparing food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or a combination thereof.

BACKGROUND OF THE INVENTION
Food grade calcium phosphate is produced by reaction of fine-grained mineral calcium compounds with phosphoric acid in the appropriate proportion. This process produces the calcium phosphate having the proportion of calcium to phosphorus which is desired.
Monocalcium phosphate produced by this process is normally employed in leavening agents used in baking systems. More specifically, monocalcium phosphate is used in baking powder and as a flavoring agent in soft drinks. If the calcium phosphate is tricalcium phosphate, it finds use as a flow promoter and anti-caking agent in table salts and beverage powders intended to be mixed with water to produce aqueous beverages. Another use of tricalcium phosphate is for incorporation into various powdered foods such as flour, corn meal and the like where it prevents reproduction of pests such as weevils in such foodstuffs during shipment or storage for long periods. Dicalcium phosphate is mainly used as a dietary supplement in prepared breakfast cereals, dog treats, enriched flour, and noodle products. It is also used as a tableting agent in some pharmaceutical preparations.

One of the challenges of preparing food grade calcium phosphates is the need for fine-grained high quality calcium compounds as a starting material which is expensive. Further, controlling the reaction conditions is challenging as the reaction is highly exothermic so controlling temperature, rate of the reaction and moisture content in the reactor become difficult. Also, in order to economise space, it would be ideal if various types of calcium phosphate i.e. monocalcium phosphate, dicalcium phosphate and tricalcium phosphate could all be prepared in the same reactor just by adjusting reaction conditions depending on which particular end-product is preferred.

SUMMARY OF THE INVENTION
According to an embodiment of the invention there is provided a process for preparing, in a single vessel, simultaneously or sequentially, food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or a combination thereof, the process comprising:
a) mixing a calcium compound for 2 to 12 minutes at 800 to 4000 rpm in a high-speed shear mixing vessel to micronise the calcium compound to a particle size of 2 to 150 microns; and
b) spraying the micronized calcium compound obtained in step (a) with an amount of 85% phosphoric acid which is stoichiometrically sufficient, relative to the amount of calcium compound in the vessel, to obtain the desired end-product while vigorously mixing the contents in the vessel at a speed of 400 to 4000 rpm for a reaction time of 2 to 10 minutes to enable the reaction to progress to completion yielding the end-product of food grade mono-calcium phosphate, di-calcium phosphate tri-calcium phosphate or a mixture thereof;
Provided that the temperature within the vessel in steps (a) and (b) does not exceed 70o Celsius.

According to another embodiment of the invention there is provided a food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or a combination thereof prepared by the above process.

DETAILED DESCRIPTION OF THE INVENTION
For the preparation of food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or a combination thereof according to the invention, the calcium compound used as a starting material can be selected from the group comprising calcium carbonate, calcium hydroxide and calcium oxide. Frictional energy in the mixing vessel is used to break up the calcium compound into a fine particle size. So even if the starting material is not an expensive fine-grained calcium compound, the frictional energy of the mixing vessel reduces particle size of the calcium compound thereby increasing the surface area of the calcium compound before the reaction. As the calcium compound particles are broken down into finer particle sizes which flow around in the mixing vessel in step (a) of the process of the invention, spraying of phosphoric acid in step (b) helps to settle the dust and the reaction takes places at the particle level i.e. there is particulate interaction where the particles of calcium compound instantaneously react with the spray droplets of phosphoric acid which results in a faster and more efficient process.
Several factors influence which type of calcium phosphate will be produced in the vessel. By adjusting the reaction conditions such as rate of the reaction, reaction time, moisture content and temperature of the reaction, along with adding the stoichiometrically appropriate amount of phosphoric acid for the desired end-product, one can obtain the desired type of calcium phosphate. Since the reaction is exothermic and there is simultaneous release of CO2, the rate and temperature of reaction are controlled by moisture content in the reaction, concentration of reactants and rate of addition of reactants. Also, the high shear creates a draft to take away the heat, gases and moisture released during the reaction thereby preventing excessive build-up of heat inside the mixing vessel. Moisture content of the final product is usually 0.2 to 2%. The introduction of phosphoric acid as a spray into the mixing vessel and controlling the said spray affects the rate of the reaction, the reaction time and even the temperature of the reaction and moisture content. If the reaction is not controlled, due to the exothermicity of the reaction, the temperature inside the vessel increases thereby reducing the moisture content in the vessel. The spinning motion of the vessel also increases heat within the vessel which acts to reduce moisture content in the vessel.
Preferably the pH of phosphoric acid is not more than pH 2. The temperature in the vessel can be prevented from exceeding 70o Celsius by controlling the rate of the reaction which in turn can be done by controlling the exothermicity of the reaction by stopping, pausing or reducing the force of spraying the phosphoric acid and thereby altering the availability of the phosphoric acid reactant. Alternatively, or in combination, the temperature of the vessel can also be maintained by surrounding the vessel by a water jacket. In one embodiment, the exothermicity of the reaction is allowed to reduce the moisture content in the vessel resulting in anhydrous end-product. Once the reaction is over, water is added in controlled sequence to granulate the product with the desired particle size distribution as per the end-application requirement.
In another embodiment of the invention, the rate of the reaction is controlled to prevent loss of moisture resulting in a hydrated end-product and, further, drying the end-product to obtain dried granules of the end-product. Alternatively, the rate of the reaction is controlled to prevent loss of moisture resulting in a hydrated end-product and, further, water of up to 10% by weight of the end-product is added into the vessel after completion of the reaction, followed by drying the end-product to obtain dried granules of the end-product. Along with water a suitable food grade binder acceptable for the particular end-application may or may not be used to make the product specific or additives may be added to make the product homogeneous as per end-application requirement. These could be flavours, colorants, enzymes, vitamins, minerals etc specific for a particular application i.e. depending on end-usage.
If the temperature within the vessel is controlled, less water needs to be added to obtain the granules as the moisture content in the vessel would not have been lost. However, if the reaction rate has been allowed to proceed without control, then the high temperature inside the vessel would have caused loss of moisture and hence more water would be needed to wet the surface of the end-product particles to enable binding on the surface to form granules.
The food grade mono-calcium phosphate, di-calcium phosphate, tri-calcium phosphate or combination may optionally further comprise amino acids, enzymes, micronutrients, vitamins, growth promoters, minerals, proteins, antioxidants, baking ingredients and additives, colorants or other fillers such as carbohydrates, starch etc as per the end-usage/application and customer needs.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof:

Example 1: Preparation of mono-calcium phosphate anhydrous
4.36 kg CaCO3 was added to the mixing vessel (reactor) with high shearing and mixing capability. The shearing was carried out for 3 to 5 mins at a rotor rpm of 4000 rpm (rotor speed can be controlled and time duration can be varied) with the pan moving in counter clock wise (opposite direction) to central rotor at a fixed rpm of 20. To this 9.24 kg of 85% food grade phosphoric acid was slowly sprayed into the reactor within 5 to 6 minutes. Then 10 ml pyrophosphate solution was diluted to 30 ml with water and added as a stabilizer i.e. sprayed in 1 minute post addition of phosphoric acid. Rotation was continued at 400 rpm till material was dry ensuring that temperature did not exceed 70oC throughout the process. Product as fine amorphous powder was obtained which met the standard specification for food grade mono-calcium phosphate anhydrous.
In a repeated experiment, instead of isolating the fine amorphous powder after completion of the reaction, 100 to 150 ml of water was sprayed slowly as the vessel was rotated at 400 rpm for 2 to 3 mins to agglomerate the powder to granular morphology.

Example 2: Preparation of di-calcium phosphate anhydrous
6.3 kg CaCO3 was added to the mixing vessel (reactor) with high shearing and mixing capability. The shearing was carried out for 2 to 3 minutes at a rotor rpm of 4000 rpm (rotor speed can be controlled to different rates and time duration can be varied) with the pan moving in counter clock wise (opposite direction) to central rotor at a fixed rpm of 20. To this 6.35 kg of 85% food grade phosphoric acid and 3 kg water was simultaneously sprayed into the reactor within 5 to 6 minutes. Post reactant dosage, 10 ml diluted of pyrophosphate solution diluted to 30 ml with water was sprayed within 1 minute as a stabilizer. Use of this stabilizer is optional. Rotation was continued at 400 rpm till a dry amorphous powder was obtained. The product was found to meet food grade di-calcium phosphate anhydrous specifications.
In a repeated experiment, instead of isolating the dry amorphous powder, 100 to 150 ml of water was sprayed onto the powder at 400 rpm for 2 to 3 mins to agglomerate the powder to granular morphology with desired particle size distribution.

The above examples are non-limiting. The invention is defined by the claims that follow.