FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See Section 10)
"SAFE AND STABLE DUST FREE ALUMINIUM PHOSPHIDE FORMULATION AND THE PROCESS OF PREPARATION"
We , UNITED PHOSPHORUS LIMITED,
a company incorporated under the Companies Act,
1956 and having its registered office at 3-11, GIDC,
Vapi-396 195,
State of Gujarat, India ,
INDIAN.
The following specification particularly describes the nature of this invention and the manner in which it is to be performed :-
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TITLE
SAFE AND STABLE DUST FREE ALUMINIUM PHOSPHIDE FORMULATION
AND THE PROCESS OF PREPARATION
FIELD OF INVENTION:
The present invention relates to a continuous process for the manufacture of a safe and stable formulation of Aluminium Phosphide.
BACKGROUND OF THE INVENTION:
Phosphine (PH3) is one of the widely used gaseous fumigants for protecting the stored grains and other agricultural products from the harmful insects and rodents. Phosphine is generated by action of moist air on Aluminium phosphide or similar metal phosphides. Though phosphine is one of the preferred fumigants, there are some significant problems with its use.
Potential problems with the use of phosphine is its toxicity to mammals including human beings when it is present in higher concentration. The presence of Aluminium phosphide residues in the food after fumigation is another health hazard to be taken care of. The powder remaining after the use of Aluminium phosphide as fumigant is mainly aluminium hydroxide but may contain a small amount of (upto 5%) the original content of aluminium phosphide, (ref: data Sheet on pesticides, no.46, Phosphine, Organisation Mondale De La Sante) Another problem encountered with phosphine gas is self ignition. When the concentration of phosphine in the air reaches certain values, the gas mixture is inflammable and potentially explosive ("Controlled atmosphere and fumigation in Grain storages" Edited by B E Ripp et al. Amsterdam, Elsevier 1983; 433-
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449). It is known that phosphine when accumulates in a concentration of more than 17900 ppm has a tendency to self ignite resulting in explosion. Attempts have been made to overcome these problems by incorporating some organic or inorganic substances during the formulation of metal phosphides like Aluminium phosphide. Substances which thermally decompose to liberate ammonia and carbon dioxide such as ammonium bicarbonate , ammonium carbamate, etc. have been used successfully for suppressing the tendency to auto-ignite Phosphine formed hydrolytically from phosphides. Other inhibitors have also been described recently which even in low concentration inhibit or retard the spontaneous reaction between phosphine and atmospheric oxygen .To suppress the violent reaction of metal phosphide with moisture or water it has been proposed to hydrophobise the phosphides or the phosphide particles. Paraffins, waxes, stearates silicones, synthetic resins have been used as hydrophobing agents.
Conventional hydrophobic agents such as paraffins, waxes and stearates etc. Besides their hydrophobic effect also act as lubricants and binding agents in the context of making compressed bodies. Conventionally Aluminium Phosphide formulation containing Active Ingredient content of 56% is made by mixing with ammonium carbonate or carbamate or a bicarbonate, a stearate like aluminium stearate or zinc stearate ,wax as a binder. Urea is also added as filler. This formulation is made in to a tablet or pellet, basically a compacted form to make it safe for handling. The tablet reacts with moisture to form phosphine gas which fumigates the grains or other commodity.
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Generally 2.5 -3.5% wax is added at a stretch to the formulation as a binder to form and retain the shape of the tablet and as the moisture repellent. However it is known that these conventional formulations can ignite when in contact with water. Even in the cases, when the humidity is higher in the commodity being fumigated, the rate of rapid generation of phosphine gas can lead to a fire & / or even an explosion. Higher paraffin wax content may afford better protection but may not be feasible due to problems in compaction operation to make tablets or pellets and problems in handling and sticky nature of the formulated product. More over in conventional formulation method, wax is added to aluminium Phosphide in a pot /blender/ ball mill and mixed. This is not a continuous process but a batch process. Other ingredients Like carbamate, carbonate, stearate and other ingredients are added in a blender. This is also a batch mixing process. The time for manufacture of Aluminium Phosphide, formulating & packing takes up to 2-3 days. The continued exposure of the product to atmosphere, dust and atmospheric moisture for such long duration would lead to decomposition of the product, and generation of phosphine gas. More care and accuracy is required for longer duration. When the tablets / pellets are applied to commodity for fumigation, the operator / fumigator is exposed to toxic dust which is present invariably in tablets & pellets
The object of the present invention is to provide a continuous process of manufacturing stable and dust-free Aluminium phosphide formulation which is faster, relatively inexpensive and environmentally safe. Another objective of the present invention is to provide a safe, stable, and dust-free Aluminium phosphide formulation with longer shelf
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life and containing higher concentration of wax and with higher content of Aluminium phosphide..
DETAILED DESCRIPTION:
The present invention describes a novel and continuous process for the preparation of a
stable and dust free Aluminium Phosphide formulation with higher content of the active
ingredient.
The process essentially consists of the following steps:
a. Adding gradually a weighed quantity of aluminium phosphide from a container to
peddle conveyor which is heated and maintained in an inert atmosphere.
b. Adding a measured quantity of molten wax from a heated container to the product
in the peddle conveyor.
c. Adding a predetermined quantity of castor oil to the above mixture.
d. Collecting the product obtained from the above step and transferring the same to
packing machine with addition of charcoal and Zeolite to obtain the final product
The subsequent addition of suitable oil ensures all particles of aluminium phosphide
are coated properly, because of continuous movement of aluminium phosphide
through conveyor.
This combination ensures stable product.
The stable product has Aluminium phosphide content 75-80 %, paraffin wax 9- 11%,
,castor oil 0.2-0.4% , charcoal 0.5-1.0. % and optionally Zeolite 0.1 - 0.25%, and
aluminium oxide 10 - 15 %.
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The process is conducted in the apparatus which is shown in Fig. 1 and as per the flow Chart given in Fig.2 in the specification.
The general method is described as below:
Aluminium Phosphide containing aluminium oxide is taken in hopper (1). This is added gradually to a peddle conveyor (18) through a rotary valve (2), the conveyor (18) being provided with vent (21). An inert gas like Nitrogen or Carbon dioxide is passed through the conveyor (18) from valve ( 13 ) to maintain inert atmosphere. The peddle conveyor is heated along partial length of conveyor. Peddles (19) are mounted on a shaft and driven by a motor (20). Paraffin wax is added to a container (3) which is provided with heating arrangement (4). The molten paraffin wax in the heated container (3) is added to the feeder tank (7) & (8) which are heated & are used intermittently. Each is provided with a vent (16) & (17). Valves (5) & (6) provided at the bottom of each of these pots. Molten wax from feeder tanks (7) & (8) is added alternately to the conveyor (18) containing the product through orifice plate (9) or (10) and through valves (11) & (12) to add wax at desired rate. The temperature of wax is maintained between 65 - 67 deg, Celsius to ensure right to ensure uniform rate of addition. All the lines carrying paraffin wax are heated. Nitrogen under pressure is fed through valves no.(43) & (44) under pressure to pressurize the feeder tanks (7) & (8) respectively and alternately, containing paraffin wax to maintain uniformity of the flow during addition of paraffin wax. to conveyor (18 ). During transfer of Parafin wax to the conveyor, valves (14) & ( 15) in vent ( 16) & ( 17) are closed as per requirement.
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This material is optionally transferred to another peddle conveyor (26) which is provided with a vent (30) to add predetermined quantity of castor oil depending upon the requirement of castor oil in the final formulation. Inert gas is passed through valve (29) in the conveyor (26). This has peddles (27) similar to discussed above and a motor (28). Castor oil is stored in a container (22) with heating arrangement (23) and added to the conveyor (26) through valve (24) and sprayer (25). The rate of addition of castor oil is adjusted with the flow rate of aluminium phosphide.
The uniformly coated Aluminium Phosphide is collected in container (31) and transferred through valve (32) into a hopper (33) provided with heater (36). Charcoal and Zeolite are stored separately in a hopper (34) and (35) provided with heater (37) & (38). Proportionate quantity of each product is fed to packaging machine (40) through cup feeder (39) for Zeolite & similar for Charcoal and formulated aluminium Phosphide. The formulated Aluminium Phosphide is packed into aluminium foil (41) and packed as per requirements in packets (42)
It is very important that aluminium Phosphide is formulated and packed as soon as possible.
Wax having a melting point of 60 - 62 deg. was used. Wax with higher or lower melting point can also be used. The passing of the Aluminium Phosphide through the peddle conveyor ensures rapid mixing. The desired uniformity is not achieved in the wax coating on aluminium phosphide. This is also added continuously to match the process requirement. The rate of addition of wax is maintained proportional to the flow rate of aluminium Phosphide. Fairly uniform mix is achieved when the product comes out of the first peddle conveyor.
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However when the product comes out of the peddle conveyor castor oil is added to the product to ensure complete & uniform coating on the product and to make it absolutely dust free.
A peddle conveyor is selected to ensure that least amount of paraffin wax sticks on the conveyor blades when the technical product is conveyed in the conveyor, when paraffin wax is added. A screw conveyor or any other similar conveyor can also be used. The peddle conveyor is heated in the initial part along the length to avoid sticking of paraffin wax to the surface of the blades of conveyor. The latter part of conveyor is not heated to ensure that the wax added does not separate out. The addition of paraffin wax is done in one conveyor and castor oil in the other to avoid a very long conveyor. All the processes can also be done in one long conveyor without loosing efficiency in coating. Inert gas like nitrogen / carbon dioxide which are most commonly available can be used. Carbon dioxide is generally used to avoid any build up of phosphine gas concentration above the lower explosive limit of 17,800 ppm or 1.8%
The process is made continuous to ensure that the product is made rapidly and product is packed rapidly to reduce exposure of aluminium Phosphide to atmospheric moisture. Exposure decreases the Active ingredient content and deteriorates the product quality. It also generates toxic phosphine gas which is harmful to people working with the product and people using the product. The time for manufacturing and packing is reduced to less
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than 24 hrs instead of current time of 2 to 3 days with conventional method of manufacture and formulation. This is particularly important in humid atmospheres.
The higher is the quantity of paraffin wax, lesser is the exposure of the aluminium Phosphide to atmosphere leading to higher stability, lesser deterioration of product thereby resulting in lesser generation of toxic gas.
Formulation with the composition containing 77.5 % of aluminium Phosphide, 11.4% aluminium oxide, 10 % paraffin wax , 0.2 % castor oil, 0.75 % charcoal, 0.15 % Zeolite is found to be preferred formulation in terms of stability .
Castor oil is used to ensure coating is complete and to ensure that the oil does not separate from the formulation on long storage.
Charcoal & or zeolite are added to the formulation to absorb the moisture and phosphine from the product.
EXAMPLE:
100 kgs of aluminum Phosphide containing 11.4 kg Aluminium Oxide is taken in a hopper . The bottom of the hopper is connected with a rotary valve. The outlet of rotary valve is connected to the peddle conveyor, is fed at rate of 100 kgs/ hour.
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A peddle conveyor of diameter of 150 mm and 1040 mm long, with peddles of size 50 mm long X 40 mm wide welded on a 40 mm shaft, located 60 degrees periphery along the length of the shaft located at an angle of 10 deg towards the flow of material. Half the length of the screw conveyor is kept hot by heating.. The screw is driven to ensure flow rate of 1.67 kg per minute.
Pieces / block of solid paraffin wax block is added to the hopper and melted. Wax is maintained at a temperature of 62 - 65° C. Two feeder tanks each of 5 kg capacity of molten wax is connected to this tank. Ball valve is operated to allow the paraffin wax to flow into the tank. The motorized, ball valve underneath the calibrated tank is opened when molten paraffin wax flows through the orifice plate 2.5 mm in diameter, at a rate of 187 gms/minute.
Compressed nitrogen under presure at 0.2 kgs / Sq.cms is fed to maintain uniformity of flow through out the addition time. At the end of 15 minutes, nitrogen is changed over to the second feeder tank to continue the addition of paraffin wax at the same rate. The contents from the first conveyor are dropped into the second conveyor where the castor oil is sprayed through a heated vessel at the rate of 3.66 gms / min. Carbon dioxide is purged through the peddle conveyor to maintain inert atmosphere. The coated product is discharged into containers of 30 kg capacity.
The containers are on the packaging machine and discharged into feeding hopper. The feeding hopper is purged with inert gas. There are two additional hoppers which are
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heated to store charcoal and Zeolite of suitable grade. These ingredients are added to each pouch in desired proportion, packed . and sealed.
The final composition of the granules so packed is as follows:
Aluminium Phosphide — 77.5 %
Paraffin Wax — 10.0%
Castor Oil — 0.2%
Charcoal — 0.75%
Zeolite — 0.15%
Aluminium oxide — 11.4 %

Total — 100%

The novel process results in a new formulation of Aluminium Phosphide with higher active content compared to the conventionally known formulations. This ensures better coating on Aluminium Phopshide. The formulation of the present invention is preferably used with phosphine generator.
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CLAIMS:
1. A novel process of manufacturing a stable formulation of Aluminium Phosphide preferably in granular form, by a continuous process maintained under inert atmosphere and comprising the steps of
a) Adding gradually a known quantity of Aluminium Phosphide to preferably a peddle conveyor
b) Adding a proportionate quantity of molten wax from a heated container to the product of step (a), in the conveyor at a controlled rate.
c) Adding a predetermined quantity of castor oil to the product of (b).
d) The product obtained from step (c) is packed in packets with proportionate quantity of charcoal and / or Zeolite.
2. A process as claimed in claim 1 wherein the Aluminium Phosphide is added to the
conveyor at a predetermined rate.
3. A process as claimed in claim 1 where in the addition of molten wax from the heated
container is done at a constant rate.
4. A process as claimed in claim 1 wherein the inert atmosphere is maintained by
passing nitrogen..
5. A process as claimed in claim 1 wherein the inert atmosphere is maintained by passing
Carbon dioxide.
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6. A process as claimed in claim 1 wherein the paraffin wax is added at a constant rate in liquid form. .
7. A process as claimed in claim 1 wherein the final product obtained is in the form of granules.
8. A process as claimed in claim 1 wherein the concentration of Aluminium Phosphide in
the formulation obtained is minimum 75%.
9. A novel process as claimed in claim 1 wherein the concentrations of the active
ingredient and the additives in the final product is
Aluminium Phosphide (AI ): 75-80%
Paraffin Wax : 9-11 %
Castor Oil : 0.2 - 0.4 %
Charcoal : 0.5-1.0%
Zeolite : 0.1-0.25%
Aluminium Oxide : 10 - 15 %
10. A novel process as claimed in claim no.l where in the concentration of the active
ingredients and the additives in the final product is
Aluminium Phosphide (Active Ingredient): 77.5 %
Paraffin Wax : 10.0%
Castor Oil : 0.2 %
Charcoal : 0.75 %
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Zeolite : 0.15%
Aluminium Oxide : 11.4 %
11. A stable and dust free formulation of aluminium phosphide preferably in granular
form comprising of
Aluminium Phosphide (Active Ingredient): 75 - 80%
Paraffin Wax : 9 -11 %
Castor Oil : 0.2 - 0.4%
Charcoal : 0.5-1.0%
Zeolite : 0.1-0.25%
Aluminium Oxide : 10-15%)
12. A stable and dust free formulation of Aluminium Phosphide as per claim no.ll.
wherein the preferred concentration of ingredients are:
Aluminium Phosphide (Active ingredient): 11.5%
Paraffin Wax : 10.0%
Castor oil : 0.2 %
Charcoal : 0.75%
Zeolite : 0.15 %
Aluminium oxide : 11.4 %
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13. Method of generating phosphine gas in a phosphine gas generator using the stable and dust free formulation as claimed in claim no 9, claim no. 10, claim no 11 and claim no 12
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ABSTRACT:
The present invention deals with a stable, dust-free, formulation of aluminium Phosphide and the novel process of obtaining the same. Unlike the conventional batch methods the present invention describes a continuous process comprising of sequential addition of additives such as paraffin wax, castor oil to the active ingredient -Aluminium phosphide using a peddle conveyor maintained in an inert atmosphere. Further addition of charcoal and Zeolite to the formulation provides added advantages.

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