GB2155360A

GB2155360A - Coating active material

Info

Publication number: GB2155360A
Application number: GB08506021A
Authority: GB
Inventors: Philippe Rivals; Georges Boquet; Henri Dayre
Original assignee: Elf France SA
Current assignee: Elf Antar France
Priority date: 1984-03-13
Filing date: 1985-03-08
Publication date: 1985-09-25
Also published as: DE3508744A1; GB2155360B; BE901914A; JPS60210589A; DK111885D0; DK111885A; FR2561133A1; GB8506021D0; IT8519763A0; IT1183475B; NL8500699A

Abstract

This invention relates to a method for coating rapidly dissolving active ingredients whose rate of release in a given medium it is desired to reduce. The coating is effected by compacting a mixture of solid particles of the active ingredient and particles of a pseudoplastic material at ambient temperature. By pseudoplastic behaviour is understood a material which is able to flow and agglomerate when subjected to pressure. Among the coating materials may be mentioned petroleum products rich in asphaltenes and polymeric materials. This method is very particularly suitable for coating inorganic fertilisers, plant protection products and products used in the treatment of industrial and urban effluents.

Description

SPECIFICATION Method for coating an active material This invention relates to a method for coating rapidly dissolving active ingredients whose rate of release in a given medium it is desired to reduce. It is very particularly suitable for the production of slow-release inorganic fertilisers.

Only 50 to 80 % of nitrogen fertiliser applied to the soil is used by the plant. One of the factors reponsible for this incomplete assimilation is the great solubility of nitrogenous fertilisers in water which results in a considerable loss of nitrogen by leaching. The fertiliser leached out in this way is not only a loss to agriculture and therefore a great waste, but it also contributes to the eutrophication of groundwater and water courses.

The slow-release fertilisers also called delay fertilisers are fertiliser products that can regulate the release of their nutrient elements and provide a better compromise between the needs of a plant and the liberation of nutrient elements in the soil.

The retarding effect is obtained by external coating or bulk coating of the active ingredient particles.

External coating consists in forming a film round the active ingredient particle. Coating in bulk is effected by intimately mixing the active ingredient with the coating material. Each active ingredient particle is isolated or even dissolved in an insoluble matrix.

With fertilisers, the external coating must form a thick, homogeneous film round each fertiliser particle.

This film filters the exchanges between the interior and exterior of the particle and slows down the release of fertiliser ions. This film must be strong enough not to burst in the soil as a result of osmotic pressure. The formation of such a coating is a difficult operation.

In the CHISSOASAHI FERT method, described in French Patent 2 255 962, external coating is effected by spraying the fertiliser granules with an organic solution of a thermoplastic resin.

The method requires the use of large quantities of organic solvents. The evaporation and the recycling of the solvents weights the method. It is the source of considerable losses of solvents and expenditure of energy.

The coating in bulk methods have in common that coating is effected at a high temperature.

Thus according to U.S. patent 3219433, coating is effected by molten bitumen either by dipping or spraying or splashing the fertiliserwith molten bitumen.

All these methods therefore make it impossible to use thermosensitive active ingredients. The decomposition temperature of inorganic fertilisers varies between 150 and 200 C. There is therefore a risk of decomposition in their case.

The object of this invention is to overcome these disadvantages and coat the active ingredients in bulk by a simple method that may be applied to thermosensitive active ingredients.

This method of coating active ingredients that can dissolve rapidly and whose release rate it is desired to reduce is characterized in that the coating is effected by compacting a mixture of solid particles of active ingredient and solid particles of a pseudoplastic material.

By pseudoplastic behaviour is understood a material which is able to flow and agglomerate when subjected to pressure.

The compacting temperature is between 0 and 500C and preferably between 15 and 30 C. The compacting pressure is between 0.1 and 100 bars, and preferably between 10 and 15 bars.

The respective grain size distribution of the active ingredient and the coating material, the active ingredient/coating material weight ratio and the nature of the coating material are the essential characteristics which determine the quality of the retarding effect obtained by coating.

If the mean diameter of the active ingredient particles and that of the coating material particles are very similar or even identical, the mixture obtained is coarse and access to the active ingredient particles in the coated product is very easy.

At the other extreme, if the ratio of the mean diameter of the active ingredient particles to that of the coating particles is about 10, there is a flow of coating material fines between the coarse particles of the active ingredient leading to the destabilisation of the mixture with separation into two solid phases. Finally, the active ingredient particles form an easily accessible uncoated continuous phase. The release of the active ingredient is still rapid.

On the other hand, if the mean ratio of active ingredient particles to coating particles is between 2 and 8 and preferably between 3 and 4, the mixture is stable and a good dispersion of the active ingredient is obtained.

The sizes of active ingredient particles can be between 10 and 1500 microns, and preferably between 100 and 300 microns, that of the coating particles between 1 and 500 microns, and preferably between 30 and 100 microns. The coated active ingredient particles are in the form of pellets, tablets, granules, plugs, small rods whose sizes vary between 1 and 40 mm and preferably between 2 and 6 mm.

The coated material contains between 20 and 70 % by weight preferably between 40 and 50 % of coating material and between 30 and 80 % by weight preferably between 50 and 60 % of active ingredient.

The method is suitable for coating active ingredients that can dissolve rapidly and whose release rate it is desired to reduce, on condition that they are in the form of solids that may be ground.

All inorganic fertilisers and their mixtures are suitable for this method as for example potassium or ammonium nitrate, soluble phosphates and ammonium chloride.

Among the active ingredients can further be cited plant protection products, such as fungicides, insecticides and herbicides and products, such as bactericides, neutralizing agents and complexants used in the treatment of industrial and urban effluents.

Suitable materials are grindable pseudoplastic solids. By pseudoplastic behaviour is understood the ability of a material to flow and agglomerate when subjected to pressure.

Among the coating materials may be mentioned petroleum products rich in asphaltenes, like asphalts obtained by deasphalting residues under vacuum, atmospheric residues or heavy crudes residues. As deasphalting solvent can be used C3 to about C7 paraffinic hydrocarbons. The best results are obtained with asphalts extracted with butane or pentane.

Other solid products, like polymeric materials are also suitable coating materials. Coating can be an important use for polymeric residues.

It may be useful to incorporate inorganic substances such as talcum, bentonie or dry clay to prevent coated materials from agglomerating. There also exist organic products such as polymeric anti-caking agents for this purpose.

Coating does not alter the chemical nature of the active ingredient. In fertilisers, the nutritive value is retained. Only the effect of a fertiliser is retarded. The fertiliser is applied to the surface of the soil or in it under normal agricultural usage conditions. The active ingredient is released over 3-4 months. The coating method generally consists of three principal stages: grinding, mixing and compacting.

All the known types of mills from ball mills to hammer mills may be used for grinding the active ingredient and the coating material.

It is possible to grind the constituents separately but sometimes, because of a difference in hardness between the active ingredient and the coating material, joint grinding gives mixtures of suitable grain size distribution ratio. If the products are ground together, the mixing stage becomes superfluous.

If ground separately, the constituents must be mixed before compaction. All the types of mixers already used for mixing solid particles or powders are suitable, as also drum, screw or helicoidal counter-vane pug mills, or else a gutter with an endless screw.

The time required to obtain a homogeneous mixture can vary between a few seconds and a few minutes, depending on the nature of the products and the type of mixer. This operation can be carried out continuously or batch-wise.

The most important operation is compaction. In general, this is achieved by pressing or extrusion.

Depending on the compacting mode selected, the finished product is in the form of pellets, tablets, granules, plugs, small rods, etc... whose sizes variy between 1 and 40 mm and preferably between 2 and 6 mm.

Rotary compressor or excentric presses (KILIAN) give tablets. Cylindrical presses (ALEXANDERWERK) give plates which require additional crushing, followed by sorting according to grain size. Sorting is carried out by screening or if necessary with a cyclone.

According to a particular embodiment of the method the mixing and compacting operations can be performed in an extruder. The extruder is fed with a ground product. It is preferable in this case to use a mill jointly for the material and the active ingredient.

The grinding and compacting operations can be performed at between 0 and 50 C but preferably at ambient temperature between 15 and 30 C.

By way of non-limitative example, a unique figure in the Annex shows the flowsheet of an installation according to the invention.

The starting materials arrive from the active ingredient hopper (1) and the coating material hopper (2).

They are ground separately in a mill (3) from which the ground product passes into the active ingredient hopper (4) or the ground coating material hopper (5). From the feed and mixture hopper (6), the active ingredient and coating material mixture passes to the endless screw (7) which provides final mixing and predensification. This endless screw feeds cylinders (8). The plates formed are crushed in a crusher (9) and then ground in mill (10). The product passes into a three-compartment separator screener (11). Coarse particles are sent back to the crusher (9) and the finest particles return to the feed hopper (6). The product of desired grain size distribution passes to the bagger (12) and then to storage (13).

EXAMPLE A pentane deasphalted asphalt and previously dried ammonium nitrate are ground separately. The fertiliserfraction between 400 and 625 microns and an asphalt fraction between 1 and 100 microns are collected by screening. 12.5 g of asphalt and 12.5 g of ammonium nitrate are mixed. The mixture is homogenized by malaxing, using a roller bench. When the mixture is homogeneous, it is pelleted in a laboratory hydraulic press. The operation is performed under a pressure of 20 bars for 30 seconds, the decompression time being 20 seconds. 4 pellets of about 6 g each are obtained. To compare the resistance to leaching of the coated fertiliser with an ammonium nitrate control, a leaching test is performed. After having filled two columns, one with a measured quantity of coated fertiliser, the other with pure ammonium nitrate of the same grain size distribution, 60 ml/hour of demineralized water are passed through the colums for 3 h 45 minutes.

The leached fertiliser is collected and weighed after evaporation of the water.

The percentage of fertiliser retained (Xr) is calculated from the formula:

m, = leached weight mj = initial weight The percentage of fertiliser retained (Xr) is 40.28 % for the coated fertiliser, and 2.3% for the pure ammonium nitrate.

Claims

1. A method for coating active ingredients that can dissolve rapidly and whose release rate it is desired to reduce characterized in that the coating is effected by compacting a mixture of solid particles of active material and solid particles of a pseudoplastic material.

2. A method according to claim 1 characterized in that the compacting temperature is between 0 and 500C and preferably between 15 and 30 C.

3. A method according to claims 1 and 2 characterized in that the compacting pressure varies between 0.1 and 100 bars and preferably between 10 and 50 bars.

4. A method according to one of claims 1 to 3, characterized in that the ratio of the mean diameter of the active ingredient particles to that of the coating particles is between 2 and 8 and preferably between 3 and 4.

5. A method according to one of the claims 1 to 4 characterized in that the size of the active ingredient particles is between 10 and 1500 microns and preferably between 100 and 300 microns.

6. A method according to one of the claims 1 to 5 characterized in that the size of the coated solid particles is between 1 and 500 microns and preferably between 30 and 100 microns.

7. A method according to one of the claims 1 to 6 characterized in that the size of the coated material is between 1 and 40 mm and preferably between 2 and 6 mm.

8. A method according to one of the claims 1 to 7 characterized in that the coating material contains between 30 % and 80 % by weight and preferably 50 and 60 % by weight of active ingredient and between 20 % and 70 % by weight and preferably between 40 and 50 % by weight of coating material.

9. A method according to one of the claims 1 to 8 characterized in that the mixture is made by jointly grinding the active ingredient and the coating material.

10. A method according to one of the claims 1 to 9 characterized in that compacting is effected by pressing a mixture of active ingredient particles and coating material particles.

11. A method according to one of the claims 1 to 9 characterized in that compacting is effected by extruding a mixture of active ingredient particles and coating particles.

12. A method according to one of the claims 1 to 11 characterized in that the coating material is an asphalt obtained by deasphalting with paraffinic solvents.

13. A method according to claim 12 characterized in that the deasphalting is effected with a paraffinic solvent of between C3 and C7 and preferably between C4 and C5.

14. A method according to one of the claims 1 to 14 characterized in that the coating material is a polymeric material.

15. A method according to one of the claims 1 to 14 characterized in that the active material is an inorganic fertiliser.

16. A method according to claims 1 to 14 characterized in that the active ingredient if a product used is a plant protection product such a fungicide, insecticide or herbicide.

17. A method according to one of the claims 1 to 14 characterized in that the active ingredient is a product such as bactericides, neutralizing agents or complexants used in the treatment of effluents.

18. Coated materials obtained by the method according to one of the claims 1 to 17.