DESC:FIELD OF THE INVENTION:
The present invention relates to the production of ZnEDTA with improved physical and hygroscopic properties in a spray drying process.

BACKGROUND OF THE INVENTION:
Spray drying is a well-known technique used in fertilizer, food and pharmaceutical industries. Spray drying is a technology that transforms a material from liquid to a dried powder state by spraying the feed solution or suspension into a hot drying gas medium. Moreover, formation of dried particles from a liquid feed in a single processing step makes spray drying technology a unique and essential process.

Different techniques are used to produce the solids from a solution but each process suffers some issues. Smaller particles offers greater area of contact, which increases the solubility of the product. Smaller particles quickly dissolves in solvent. Better and quick solubility is desirable in case of water soluble fertilizers. Solubility enhancement of product is advantage of using this spray drying technology and it usually accompanies rapid drying of droplets to convert into amorphous form.

But at the same time if the particles are too small they do not possess the free flowing property and also they possess high hygroscopicity due to larger surface area. Normally spray dryers produce particles of size 50 microns average or below. Our attempt is to increase the particle size of 100 microns average.

Various spray drying parameters viz., feed rate, inlet temperature, feed solid content, atomizer disc speed (rpm) are optimized to improve the product quality. These parameters are captured in such a way that it gives a product within a pre-defined quality specification.

PRIOR ARTS:
European patent EP 1 910 250 B1 filed by McLaughlin et al applied on 6.04.2008 with a title” CHELATING AGENTS FOR MICRONUTRIENT FERTILISERS” discusses how chelating agents used in micro nutrient fertilizers production. In detail it describes the composition and method for improving the bio-availability of micronutrients using chelating agents. Our present invention is not related to the application process.

US patent US 2006/0084575 A1 filled by Frederick S. Sedun et al on Apr. 20, 2006 with title COMPOSITION AND METHOD FOR SELECTIVE HERBCDE discusses method of producing the stable herbicide formulation using chelates. Our current invention is not fit into this as we are not discussing any process related to herbicides.

WO 2007/006078 Al published on 18 January 2007 with a Title “CHELATING AGENTS FOR MICRONUTRIENT FERTILISERS’ describes the usage of chelating agents and chelated micronutrient application as fertilizer and availability of nutrient to plant. Our present invention is not related to the application process.

OBJECT OF THE INVENTION:

The main object of this invention is to produce ZnEDTA powder with improved physical properties in spray drying process.

One more object of this invention is to develop a process that can give uniform desired particle size of ZnEDTA powder of particle size 100 microns average in the spray drying process.

Another object of this invention is to develop a stable process that can produce less hygroscopic ZnEDTA powder.

DETAILED DESCRIPTION OF DRAWINGS:
Legend:
1. Reactor 11. Scrubber
2. Solution Transfer pump 12. Scrubber circulation pump
3. Feed tank 13. ID fan
4. Progressive cavity Screw pump 14. Stack
5. Atomizer disc 15. Reactants
6. Spray chamber 16.Demineralised water
7. Air filter 17. Steam to jacket of reactor
8. FD fan 18. Steam to air heater
9. Air Pre-heater 19. Hot air to spray chamber
10. Cyclone separator 20. Dust free air

DETAILED DESCRIPTION OF THE INVENTION:
Chelated compounds are more stable than non-chelated compounds. Therefore, metallic chelates are widely used in agriculture as micronutrient fertilizers to supply plants with Iron, Manganese, Zinc and Copper. The present invention relates to the production of ZnEDTA with improved physical properties in spray drying process. Spray drying is a proper art that is used for drying of several materials organic\inorganic. But ZnEDTA with improved physical properties does not exist in prior arts. Reactants are mixed in a batch. After ensuring the completion of reaction the solution is pumped to spray dryer feed tank. Physical and hygroscopic properties of material is influenced by the particle size of the product. Particle size is one of the key parameters which influence the flowablity also.

Referring to Fig.1 the reactants ( 15) Disodium EDTA and ZnO are added into steam jacketed reactor (1) where DM water (16) also is fed for the reaction to be conducted in aqueous media. Steam (17) is passed thro the jacket of the reactor to heat the inside solution. Reaction occurs at 70 to 80 deg C. Here the reaction is a neutralization reaction i.e. the completion of the reaction can be confirmed by checking PH of solution which reaches 6.0 to 6.5 Ph when the reaction is complete from the initial Di Sodium EDTA solution PH of 4.5.

The solution from the reactor is transferred with a solution transfer pump (2), which can be a centrifugal pump, to the spray dryer feed tank(3) and from there it is pumped to the spray dryer (6) with a progressive cavity screw pump (4) with a flow ranging from 800 to 1000 kg/h through centrifugal atomizer (5).

Ambient air is drawn through air filter (7) by a force draft fan (8) and heated to desired temperature in air pre-heater (9) to supply hot air (19) to spray dryer. Steam(18) at controlled rate is supplied to air pre heater to obtain the required temperature of air.

Atomized feed solution gets dried when it comes in contact with hot air supplied by FD fan through air distributor.

One Induced draft fan (13) is used to maintain the constant draft across the spray dryer. It eliminates the sudden flush out of the powder and increases the residence time of the particle in the spray dryer (6) during a contentious run. Powder that is formed in spray chamber comes out along with hot air which will be separated in cyclone separator (10).

Exhaust air is scrubbed with water in a scrubber (11) to avoid the carryover of product with exhaust air. Scrubber is provided with a circulation pump(12) for the scrubber liquor. Dust free air (20) from scrubber is let out through the stack (14). This type of spray drying based, single-step particle processing method, is mainly useful to formulate the final product in powder form of tiny particles.
A number of experiments are conducted to control the physical and hygroscopic properties of the ZnEDTA powder coming out from the spray dryer.
Before conducting the experiments we correlated the feed concentration as % of solids with specific gravity of the solution by varying the concentration and measuring the SPG in laboratory and recorded the data as below.

Sno Percentage solids Specific gravity with hydrometer
1 0.00% 1.000
2 4.76% 1.028
3 9.09% 1.053
4 13.04% 1.076
5 16.67% 1.102
6 20.00% 1.030
7 23.08% 1.151
8 25.93% 1.175
9 28.57% 1.195
10 31.03% 1.202
11 33.33% 1.204
12 35.48% 1.220
13 37.50% 1.237
14 39.39% 1.252
15 41.18% 1.266
16 42.86% 1.280
17 44.44% 1.296
18 45.95% 1.309
19 47.37% 1.310
20 48.72% 1.315
21 50.00% 1.321

Experiment 1:
Here we studied the stability of the product at different particle sizes with respect to hygroscopicity. Material produced in lab scale is sieved and different size particles are examined on the glass slide under micro scope.

25 micron size particles taken on a glass slide observed under microscope in 10X lens. It is found wet as shown in the Fig.2.

50 micron size particles taken on a glass slide observed under microscope in 10X lens. It is also found wet and it sticking to the glass slide as shown in the Fig.3.

100 micron size particles taken on a glass slide observed under microscope in 10X lens. It is found dry comparatively as shown in the Fig.4.

It is concluded that the bigger particles are dry, compared to the smaller ones. So we need to improve the particle size to produce ZnEDTA powder with good physical properties.

Different approaches are there to achieve the particle size of spray dried product. Selection of methods depends on the type of dryer, Atomizer, air flow distribution inside the spray chamber.

Many parameters like Feed Concentration, Feed temperature, Pressure, Atomizer Speed, Atomizer diameter, Atomizer nozzle size, No of nozzles, Draft inside the Spray chamber and chamber inlet temperature control the physical and hygroscopic properties of the dried powder.

The above parameter have been devided into two groups Viz. fixed and variable parameters. Some parameters are fixed at one level and others are varied during the experiments.

Fixed parameters: Vairable Parameters:
1. Atomizer Dia = 0.21 m 1. Feed concentration : % solids
2. Atomizer nozzle dia = 0.015m 2. Atomizer speed . RPM
3. No of Nozzles = 24. 3. Feed flow rate .Kg\hr
4. Draft inside the chamber = -30 mmwc.
5. Feed temperature = 65deg C.
6. Feed solution pressure = 0.5Ksc
7. Chamber inlet air temperature = 210 Deg C
8. Chamber inlet air flow = 15000 m3/hr.

We designed a set of experiments to study the effect of these variables on particle size of dried ZnEDTA powder in step by step process. i.e varrying one parameter at a time.

Experiment :2

Reactants are mixed in reactor as per the stochoemetric requirement. After ensuring the completion of the reaction, the solution is fed to the spray dryer.
We fixed the atomizer speed 12000 RPM and altered the feed flow (Kg/hr).Below graph indicates the comparison between the particle size obtained by running at two concentrations of the solution. Average particle size increased as the feed flow increased to 1050 Kg/hr.

Experiment :3

We fixed feed flow at 1050 Kg/hr solution to the sparay dryer. Below plot indicates the effect of atomizer speed on particle size of ZnEDTA powder.

Particle size improved with decreasing the atomizer RPM. But at a lower rpm conditions we observed some part of solution getting poured down from the atomizer disc instead getting sprayed, this is called weeping.

Experiment:4

We optimized the atomizer speed at which it can atomize 1050Kg/hr feed solution without weeping to occur by checking condition at bottom cone of the spray dryer. Details are tabulated as below.
Sno Atomizer Speed Feed flow in kg/hr Observation
1 12000.00 1050 No weeping
2 11500.00 1050 No weeping
3 11000.00 1050 No weeping
4 10500.00 1050 No weeping
5 10000.00 1050 No weeping
6 9500.00 1050 No weeping
7 9000.00 1050 No weeping
8 8500.00 1050 Weeping observed at bottom cone of the spray chamber
9 8000.00 1050 Weeping observed at bottom cone of the spray chamber
10 7500.00 1050 Weeping observed at bottom cone of the spray chamber
11 7000.00 1050 Weeping observed at bottom cone of the spray chamber
12 6500.00 1050 Weeping observed at bottom cone of the spray chamber
13 6000.00 1050 Weeping observed at bottom cone of the spray chamber

Feed solution is weeping from the bottom of the spray dryer cone when we operated at lower atomizer rate.

Based on the experiments conducted at different set of conditions it is concluded that ZnEDTA powder with an improved physical properties can be produced at 50% feed concentration, 1050 Kg/hr feed rate and atomizer speed at 9000RPM.

Fig.5 is the photo micrograph of ZnEDTA produced at above conditions.

The inventive step of the invention lies on:

1. A method of reducing the hygroscopicity of ZnEDTA powder by increasing the particle size to 100 microns average while producing in spray dryer.
2. A method to produce free flowable powder of ZnEDTA with an average particle size of 100 microns in spray drying process.

The applicant relies upon the provisional specification filed in this application and shall be considered as part and parcel of complete specification.

The examples and embodiments are provided only for the purpose of understanding and none of them shall limit the scope of the invention. All variants and modifications as will be envisaged by skilled person are within the spirit and scope of the invention. ,CLAIMS:WE CLAIM :

1. A process of spray dry method of preparing ZnEDTA powder comprising the steps of :
a. preparing Disodium EDTA solution with PH value in the range 6.0 to 6.5 PH,
b. selecting an atomizer chamber having solids dia as 0.21m and nozzle diameter as 0.015m with 24 nozzles,
c. providing a draft inside the atomizer chamber at -30 mmwc with chamber inlet air temperature at 210°C and inlet air flow equal to 15000 m3/hr,
d. maintaining feed temperature at 65°C and feed solution pressure at 0.5Ksc,
e. maintaining feed concentration at 50% and feed flow rate at 1050 kg/hr, and
f. maintaining atomizer speed at 9000 RPM to prepare a ZnEDTA powder which particle size is atleast 100 microns average.

2. The process of preparing ZnEDTA powder as claimed in claim 1(a), the step includes reacting with reactants (15) which are Disodium EDTA and ZnO alongwith DM water (16) as aqueous media with steam (17) in a steam jacketed reactor at around 70-80°C for neutralisation reaction and until PH of the solution is around 6.0 to 6.5 Ph.

3. The process of preparing ZnEDTA powder as claimed in claim 1 and claim 2, further includes step of transferring the prepared solution of claim 2 with a solution transfer pump (2) to a feed tank (3), and pumping the solution further to the atomizer chamber of spray dryer (6) with a progressive cavity screw pump (4) with a flow ranging from 800 to 1000 kg/h through a centrifugal atomizer (5).

4. The process of preparing ZnEDTA powder as claimed in claim 1, further includes a step of supplying hot air (19) to the atomizer chamber of spray dryer (6) by heating ambient air drawn through air filter (7) by a force draft fan (8) with controlled supply steam (18) in a pre-heater (9) thereby drying the atomised feed solution.

5. The process of preparing ZnEDTA powder as claimed in claim 1, further includes a step of supplying induced draft air from an induced draft (13) across the atomizer chamber of spray dryer (6), for eliminatory flushing out of the powder and increasing residence time of the particle in the spray dryer (6).

6. The process of preparing ZnEDTA powder as claimed in claim 1, further includes a step of passing the prepared powder exiting out from spray dryer (6) through a cyclone separator (1) for separating the powder from the hot air.

7. The process of preparing ZnEDTA powder as claimed in claim 1 and claim 6, includes a step of scrubbing the exhaust hot air with a scrubber (11) to separate powder dust and exist only dust free air through a stack (14).