1. Field of the Invention
The present invention relates to a dust control composition for fertilizer for the purpose of reducing the dust levels present in the fertilizer, reducing subsequent dust formation, and to reduce the tendency of the fertilizer particles to agglomerate or cake during storage and transportation.
2. Description of Related Art
Methods for the manufacture of fertilizers (inorganic, organic, or micronutrient) as well as methods for processing these fertilizers into particles via prilling, granulating, compaction or other techniques are well known. The resulting fertilizers often contain an undesirable level of particles fine enough to become airborne dust. This dust is produced during the manufacture, storage and transportation of the fertilizer particles. The dust can be the result of mechanical abrasion encountered during movement of the fertilizer particles, continued chemical reactions or curing processes after the initial particle formation, the action of moisture migration through the fertilizer during storage or ambient temperature and humidity conditions.
Fertilizer dust dissemination poses safety, health, environmental, housekeeping and maintenance problems for fertilizer producers, distributors and consumers. For instance fertilizer dust has raised health concerns due to human and animal inhalation thereof. It is also a concern when fertilizer dust becomes airborne which can lead to the loss of agronomic and economic value, while potentially contributing to the contamination of surface water ecosystems.
The use of oils, waxes, blends of oil and wax, and emulsions based on these products have been known for a long time. These oils and waxes can be petroleum or vegetable based. For instance, in 1977 Frick suggested that petroleum based products be used to control dust from agricultural fertilizers, See xe2x80x9cPetroleum Based DCA""s to Control Fugitive Dustxe2x80x9d, Frick, Proceedings of the Annual Meeting of the Fertilizer Industry Round Table, Series 27, pages 94-96. However there are disadvantages involved in using these treatment methods. Over time oils tend to volatilize and/or be adsorbed into the fertilizer particle and loose their effectiveness. Waxes are also ineffective and difficult to handle because they absorb into the fertilizer particle at temperatures above their melt point and do not spread or coat the fertilizer particle surface at temperatures below their melt point. In addition, both oils and waxes have limited binding properties that are essential for long term fertilizer dust control.
Other proposed dust control methods include application of other liquids such as lignosulfonate solutions, molasses solutions, urea solutions, mixtures of these solutions, other fertilizer solutions, amines, surfactants, polymers and even water. Examples are U.S. Pat. No. 5,360,465 to Buckholtz et al. and U.S. Pat. No. 5,328,497 to Hazlett. These methods have a number of disadvantages as well. Due to the water present, aqueous solutions and emulsions tend to accelerate the formation of fertilizer dust and exacerbate the fertilizer particles caking tendencies. These treatments also tend to loose their binding properties as the solutions and emulsions dry, thereby becoming ineffective as long term dust control agents.
European Patent 0320987 discloses the use of a conditioning agent comprising 10-60% wax, 30-90% oil and 0.3-10% by weight of a high-molecular weight viscoelastic elastomer such as polyisobutylene. U.S. Pat. No. 5,603,745 to Pettersen et al. discloses the use of a conditioning agent comprising 10-50% wax, 40-90% oil and 1-30% of a oil soluble and wax miscible resin such as esters of polymerized resin, esters of stabilized resin acids or non-crystallized tall oil resin. While these conditioning agents provided an improvement in dust control over oils, waxes, and oil/wax blends, they do not provide the degree of binding required for effective long-term dust control. This is because the majority of these conditioning agents still consist of poor performing oils and waxes.
The vast majority of commercially produced fertilizers are treated with a conditioning agent of some type to reduce dust levels. For instance, in 1995 Ogzewalla suggested several characteristics needed for an effective dust control conditioning agent in xe2x80x9cFertilizer Dust and Dust Control Coating Agentsxe2x80x9d, Ogzewalla, Proceedings of the Annual Meeting of the Fertilizer Round Table, 45th Meeting, 1995, pages 95-100. These characteristics included the ability to bind dust back to the surface of the fertilizer granule, resist absorption into the fertilizer granule surface, and the ability to spread or coat the fertilizer granule surface. The example given in this article shows that several commercially available conditioning agents were able to reduce dust levels in a diammonium phosphate fertilizer from 600 ppm to between 170-70 ppm. In addition, the xe2x80x9cSixth Annual 1996 Granular Fertilizer Surveyxe2x80x9d, 1996, ARR-MAZ Products, L.P., shows the dust levels found in twenty two samples of diammonium phosphate collected from fertilizer production facilities across North America. The producers, during manufacture, had treated all of these fertilizer samples with a conditioning agent. Dust levels were shown to range from 425 ppm to 55 ppm and averaged 125 ppm.
One of the main objectives of the invention was to develop a superior agricultural composition comprising of fertilizer particles having low dust levels and a reduced tendency to cake during the long term storage and handling conditions normally encountered by commercial fertilizer products. Another objective was to develop a superior conditioning agent that is fluid at application temperatures and can be applied by conventional coating or conditioning equipment. A further objective was to arrive at a conditioning agent that would not effect the fertilizers handling characteristics or flowability.
The main problem to be solved was to obtain a superior conditioning or dust control agent that is fluid and flexible enough to spread over the surface of the fertilizer granules during the coating process, and yet still had enough binding properties to adhere ambient dust to the surface of the granule and reduce dust formation during subsequent storage and handling. Further, it was important that the resulting treated fertilizer granules can not become too sticky for handling by conventional means, even when treated at relatively high application rates. In addition, the resultant conditioning agent should be easy to apply on the fertilizer particles and be non-toxic to the soil and plants. This latter requirement implies that the various components must be environmentally acceptable. It is also desirable that the conditioning of the fertilizer particles be accomplished in one step with the required protection obtained during this step. A further requirement was that the treated fertilizer be completely soluble a few days after to the soil, and that the conditioning agent be degradable in the soil.
In view of the above stated requirements, an investigation was started for an improved conditioning or dust control agent by studying ways to improve the properties of the oils and waxes used as major components of the most common conditioning agents. Both petroleum and vegetable based oils and waxes have some value in these conditioning agent formulations. The effectiveness of any specific oil was found to be determined by the oils physical properties, in particular the combination of viscosity and tackiness. Accordingly, this component, the oil/wax, could be substituted with a new component, another oil/wax, having somewhat different properties. Further investigation showed that selection of optimal components could be of importance.
The search for optimal components resulted in investigation of methods that could change or modify these components. The selection of a vegetable oil or wax and then subjecting this vegetable oil or wax to an oxidation process was found to have a measurable effect on reducing fertilizer dust and dust formation.
Typical examples of materials which can be oxidized and used as starting points for the oxidized component include, but are not limited to, crude oils such as corn oil, canola oil, cottonseed oil, sunflower oil, soy oil, linseed oil, castor oil, and tall oil as well as their distillation products and distillation residues such as distilled tall oil, tall oil pitch and tall oil bottoms or mixtures thereof.
The compounding or mixing of lower viscosity oils or waxes into the oxidized oil are useful, but not required, to standardize the physical properties of the finished conditioning agent such as viscosity, melt point and tackiness. This insures that the conditioning agent has the desired properties at application temperatures which provide for improved dust control abilities and also allows for application by conventional coating or conditioning equipment.
Non-oxidized oils useful for compounding with the oxidized oils include, but are not limited to, white oil, refined mineral oils, and vegetable oils such as corn oil, canola oil, cottonseed oil, sunflower oil, soy oil, linseed oil, castor oil and tall oil. Oils having moderate viscosity, low volatility, and high flash point are preferred.
Waxes useful for compounding with the oxidized oils include but are not limited to intermediate waxes, paraffin waxes, micro-crystalline waxes, carnauba wax, vegetable waxes and mixtures thereof. Waxes with low congealing points are preferred for low temperature applications, while waxes with high congealing points can be useful in high temperature applications.
The oxidized oil component of the novel conditioning agent must be soluble or miscible with the oil and/or wax components. Further, it must result in a coating with the viscosity and tackiness required for dust control while maintaining the fluidity required ease of application. The resulting coating should control ambient dust levels, reduce dust formation and reduce caking tendencies without adversely effecting the fertilizers handling characteristics. These components should also be environmentally acceptable and degrade in the soil as explained above. Within this framework, it was then found that effective relative amounts in weight % of these components should be:
Oxidized Oil: 10-100%, preferably 30-90% typically
Oil: 0-90%, preferably 10-70% typically
Wax: 0-90%, preferably 10-70% typically
The present invention is therefore a dust control composition for fertilizer particles, the composition comprising 10-100% by weight oxidized oil, 0-90% by weight non-oxidized oil, and 0-90% by weight wax. The fertilizer particle is selected from the group consisting of ammonium phosphate, potash, granulated single super phosphate, granular triple super phosphate, NP-fertilizer and NPK-fertilizer.
In a typical preferred application, the composition comprises 30-90% by weight oxidized oil, 10-70% by weight non-oxidized oil, and 10-70% by weight wax.
The oxidized oil is selected from the group consisting of corn oil, canola oil, cottonseed oil, sunflower oil, soy oil, linseed oil, castor oil, tall oil, mixtures thereof, and distillation products and distillation residues thereof; the non-oxidized oil is selected from the group consisting of white oil, refined mineral oil, vegetable oil, and mixtures thereof; and the wax is selected from the group consisting of intermediate waxes, paraffin waxes, micro-crystalline waxes, carnauba waxes, vegetable waxes and mixtures thereof.
The present invention is also a method of controlling dust from fertilizer particles which comprises treating the fertilizer particles with a composition as described above.