Chemistry: fertilizers – Processes and products – Forms or conditioning
Reexamination Certificate
1999-10-29
2002-11-05
Silverman, Stanley S. (Department: 1754)
Chemistry: fertilizers
Processes and products
Forms or conditioning
C071S059000
Reexamination Certificate
active
06475259
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to particulate materials with a protective water vapor-barrier coating. More specifically, the invention relates to coated particulate fertilizers such as ammonium nitrate with a blend of amines and microcrystalline and/or synthetic waxes.
2. Discussion of the Background
Particulate fertilizers, stored in bulk, will absorb moisture from the atmosphere at rates depending on the composition of the chemical salt, temperature of the solid and the vapor pressure of water in air (Physical Properties of Fertilizers and Methods for Measuring Them, Bulletin Y-147, National Fertilizer Development Center, October 1979). It is generally understood that the quality of particulate fertilizers can be improved by reducing their moisture content during production and by preventing moisture absorption during storage. This is especially true for fertilizers stored in large bulk piles where no dehumidification is provided.
Various coatings have been proposed for fertilizers. Obrestad et al, U.S. Pat. No. 5,472,530, disclose coatings designed to produce free flowing ammonium nitrate particles. Simms et al, U.S. Pat. No. 4,521,239, disclose protective coatings for ammonium nitrate comprising a combination of an amine and a polysiloxane. Other coatings for fertilizers are disclosed by Novascues et al, EP 00574306; Kjohl et al EP 00255665; and Ureng et al U.S. Pat. No. 5,294,251. These coatings are taught to provide limited uptake of water by the fertilizer stored in bulk in the open air in a wet atmosphere, limit the formation of significant encrustation, reduced dust formation and hygroscopicity, corrosion resistance properties and water proofing properties.
Most commercially available coating technologies for fertilizers such as ammonium nitrate claim to provide anti-caking properties and even moisture barrier properties. However, the mechanism for their efficacy is generally not discussed other than saying that the materials are hydrophobic. Common commercially available coating agents include Galoryl alkyl-aryl sulphonates, anionic and nonionic surfactants (sold by Lobeco Industries), Lilamine and Armoflo fatty amine coatings (sold by Akzo Nobel), Petro-Ag (an amine based coating marketed by Witco Corporation), Perflow (another amine based coating marketed by IWC Stockhausen) and Radiamine (sold by Fina Chemicals).
Solid fertilizers, and particularly ammonium nitrate, are usually coated with active anti-caking agents. These anti-caking agents serve to reduce the contact area between particles where fertilizer salts are soluble and where these salts may recrystallize from saturated aqueous film layers between particles (D. C. Thompson, 1972). However, commercially available anti-caking agents tend to be poor water vapor barriers.
In the case of ammonium nitrate, the anti-caking agent may serve to prevent significant caking in storage, but moisture will continue to be absorbed through the coating layer, causing saturation of internal additives and desiccant phases. Once these desiccant phases become saturated, undesirable crystal phase transitions can occur during thermal cycling resulting in product degradation. This is evidenced by fluff formation over the surface of bulk piles, crust layer formation beneath the fluff layer and deep pile caking as moisture migrates vertically in the bulk pile.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide a suitable anti-caking agent that also has superior water vapor barrier properties.
Another object of the present invention is to provide a coated particulate fertilizer that is protected from caking and from moisture absorption by the coating.
This object and other objects of the present invention have been satisfied by the discovery of a process for application of amines or blends of amines and at least one of microcrystalline waxes, paraffins and/or synthetic waxes to particulate fertilizers which provide excellent resistance to caking in bag and bulk storage and the resulting coated particles provided. Furthermore, these blends provide resistance to water vapor absorption by the fertilizer thus increasing the storage life of the product.
DETAILED DESCRIPTION OF THE INVENTION
Any material which is to be successful as a coating agent for particulate fertilizers must possess several desirable characteristics. The coating agent must be compatible with the fertilizer material, i.e., it must not cause deterioration of the fertilizer nor render it hazardous, which is a particular concern with ammonium nitrate. Since the coated fertilizer is frequently handled by unprotected personnel and is applied to crop land, the coating agent must be nontoxic. In some instances where a hygroscopic salt is being coated such as in the case of ammonium nitrate, the fertilizer readily absorbs water from the ambient air. This results in caking and breakdown of the prilled fertilizer. Accordingly, an acceptable coating agent must substantially impede or eliminate moisture absorption by the particulate hygroscopic fertilizer. Another important aspect of the coating is that the coating on the particles must be sufficiently uniform to prevent particle-to-particle contact in uncoated areas of the particles. If this type of contact is not prevented during storage of the ammonium nitrate, caking of the fertilizer particles will result as bonding occurs between particles where there is insufficient coating material to prevent exposed surfaces of the particles from contacting each other. The raw materials for the coating agent must be in abundant supply so that production of coated fertilizer product in volume is not impeded. The coating agent must firmly bond to the fertilizer particles from the time it is applied until the coated fertilizer is applied to the crop land.
Other beneficial characteristics which the coating agent should possess, but which are not mandatory, are that the cost of the ingredients on a per ton fertilizer basis should be reasonable and it should be able to be easily handled from an operational standpoint. However, with regard to both of these factors, some expense and inconvenience can be tolerated as long as a superior coated fertilizer product is produced.
The coating agent of the present invention has been found to satisfy all of the above-described characteristics. The present coating agent is a mixture of an amine and a microcrystalline and/or synthetic wax.
The amine component of the present coating composition is a material which is semisolid or solid at room temperature. The amine should melt at a temperature of about 43° C. to about 93° C. and should not decompose at these temperatures. Suitable amines include primary, secondary and tertiary, straight and branched chain amines of 12 to 18 carbon atoms per carbon chain, as well as amines containing cyclic hydrocarbon radicals of 5 to 8 carbons. Saturated cyclic amines and saturated polyamines may also be used as long as they possess the above-desired physical properties. Mixtures of amine may also be used, and in fact, long chain fatty amines as obtained industrially are frequently a mixture of amine compounds and are quite suitable for use in the present invention. Amines containing unsaturated hydrocarbon and aromatic hydrocarbon radicals should be avoided when coating the likes of ammonium nitrate because of the increased danger of forming hazardous compositions. This is substantially much less of a factor when relatively less hazardous substrates are to be coated. A preferred amine composition is a mixture of amines having the formula:
CH
3
—(CH
2
—CH
2
)
x
—CH
2
—NH
2
wherein x is 6, 7 and 8. This particular mixture is characterized as follows:
(a) Solid at 24° C.
(b) Melting point (° C.): 49°-54° C.
(c) Freezing point (° C): 43° C.
(d) Specific gravity (150/60), g/cc: 0.794
(e) Viscosity (66° C.) cp:3
(f) Colorless
(g) 97% purity
The wax component of the coating composition should be a soft or hard microcrystalline wax, a paraffin wax or a soft synthetic wax. The wax component must
Ciaccio Corinne Grady
Collins Kerry
Thomas Donald Ray
Mississippi Chemical Corporation
Nave Eileen E.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Silverman Stanley S.
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