Plant protecting and regulating compositions – Plant growth regulating compositions – Organic active compound containing
Reexamination Certificate
2002-04-15
2004-05-11
Clardy, S. Mark (Department: 1616)
Plant protecting and regulating compositions
Plant growth regulating compositions
Organic active compound containing
Reexamination Certificate
active
06734142
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to preparation of a herbicidal formulation useful in agriculture and in other situations where control of weeds or other vegetation is desired. In particular, it relates to a process for preparing a herbicidal composition containing as an active ingredient N-phosphonomethylglycine (glyphosate) in the form of the ammonium salt thereof. According to the process of the present invention, particulate glyphosate acid, ammonia, and water react to form an ammonium glyphosate paste, and as part of the process a surfactant is added to the reaction mixture to increase the reaction rate and enhance the physical properties of the resulting product.
BACKGROUND OF THE INVENTION
Glyphosate herbicides, especially herbicides comprising a water-soluble salt of glyphosate, are well known. The monoammonium salt of glyphosate is disclosed as a useful herbicide for example in U.S. Pat. No. 4,405,531 issued to Franz. Unless the context demands otherwise, “ammonium glyphosate” herein refers to the monoammonium salt of glyphosate, which has the chemical formula
Ammonium glyphosate may be produced in granular form by a continuous process in which glyphosate acid is intimately mixed with ammonia. For example, U.S. Pat. No. 5,070,197 issued to Chin et al. disclose a continuous process in which a Bronsted acid is mixed with a Bronsted base in an extruder to produce a salt. Chin et al. list glyphosate acid as one of the potential Bronsted acids that may be used and ammonia as one of the potential bases that may be used. According to Chin et al., the reaction may be carried out as a solid-state reaction essentially without addition of “extraneous solvent” such as water, although it is stated that a small amount of water (usually about 4% by weight) may be optionally added upstream for “initial lubricity”. An acid-base reaction is said to occur in the extruder, forming a dry salt which is extruded to form granules.
Ammonium glyphosate is particularly useful, however, in the preparation of dry glyphosate herbicide formulations which contain one or more surfactants in addition to the glyphosate salt. Surfactants are important components of glyphosate formulations because when a glyphosate formulation is diluted, dissolved or dispersed in water for application by spraying to foliage of plants, the surfactants enhance the herbicidal effectiveness of the glyphosate spray by assisting in: (i) the retention of droplets of the spray by the foliage; (2) the adhesion of the spray droplets to the foliar surface; and, (3) the penetration of the glyphosate through the hydrophobic cuticle that covers the foliar surface. Commercially available dry ammonium glyphosate formulations containing one or more surfactant(s) include, for example, Roundup® Dry, Roundup® Max and Rival® herbicides, marketed by Monsanto Company in several countries.
Processes for producing dry ammonium glyphosate formulations typically require combining one or more surfactant(s) with a dry ammonium glyphosate salt and granulating the mixture to form dry ammonium glyphosate granules having the desired concentration of surfactant. Numerous granulation processes have been disclosed that are suitable for preparing water-soluble or water-dispersible granules of ammonium glyphosate with a liquid surfactant. One such process is pan granulation. However, a more widely used granulation process for a dry ammonium glyphosate formulation is extrusion granulation. British Patent No. 1 433 882 (“the '882 patent”) generally describes an extrusion granulation process, and the granulation of dry ammonium glyphosate formulations are typically carried out in a similar process except that the primary active ingredient, namely ammonium glyphosate, is water-soluble rather than water-insoluble as in the process of the '882 patent. In this process, ammonium glyphosate is mixed with surfactant and a small amount of water to form an extrudable wet mix, which is then extruded to form strands of extrudate that break spontaneously at the point of extrusion or shortly thereafter to form short cylindrical granules, which are then dried.
The desired amount of surfactant for delivering the desired herbicidal effectiveness may be typically in the range of about 0.1 to about 1 part by weight of surfactant per part by weight of glyphosate, expressed as acid equivalent (a.e.), depending on the particular surfactant used. Ammonium glyphosate formulations having such a high concentration of surfactants may be difficult to achieve depending on the degree to which the surfactant is absorbed or adsorbed by the ammonium glyphosate. That is, frequently such high surfactant concentrations do not sufficiently absorb and/or adsorb to the ammonium glyphosate thereby causing the resulting formulation to become sticky, have a tendency to cake, or lack good pouring or flow properties. Thus, the absorbency and adsorbency properties of the ammonium glyphosate particles are especially important.
The process by which ammonium glyphosate is prepared has been found to affect the absorptive and/or adsorptive properties of the ammonium glyphosate particles with respect to a liquid surfactant. Recently, processes for producing a dry glyphosate powder having high absorptive and/or adsorptive characteristics suitable for producing ammonium glyphosate formulations having a high concentration of surfactant have been discovered. For example, U.S. Pat. No. 5,614,468 (“the '468 patent”), Kramer et al. disclose processes wherein particulate glyphosate acid is reacted with aqueous ammonia to produce a dry glyphosate powder having a moisture content of no greater than about 2% by weight of water. Similarly, U.S. Pat. No. 5,633,397 (“the '397 patent”), Gillespie et al., disclose a process for producing ammonium glyphosate powder wherein particulate glyphosate acid is reacted with gaseous anhydrous ammonia to produce a dry powder. As shown in Example 1 of the '397 patent, a dry powder having a moisture concentration of about 1% by weight may be produced by the process disclosed therein.
Both the process disclosed in the '468 patent and the process disclosed in the '397 patent produce a dry ammonium glyphosate powder capable of adsorbing and/or absorbing high concentrations of surfactant. However, dry solid-state reaction processes wherein the moisture content is suppressed to ensure the formation of a dry product may be more difficult to control than a process wherein glyphosate and ammonia are reacted in an aqueous medium. The exothermic nature of the reaction between ammonia and glyphosate acid gives rise to a need for the dissipation of heat, which can present problems. Since solid-state processes typically exhibit poor heat transfer properties, the dissipation of heat may become problematic.
PCT Application No. WO 01/08492, Massmann et al. disclose a process for producing ammonium glyphosate which avoids some of the difficulties encountered with processes carried out in a dry solid-state medium. Particulate glyphosate acid, ammonia in the form of either gaseous anhydrous ammonia or aqueous ammonia and water are added to a reactor to from a reaction mixture having a moisture content of about 10% to about 25% by weight. The glyphosate acid and ammonia react and a portion of the water is evaporated to produce a downstream processable ammonium glyphosate paste having a moisture content of about 5% to about 20% by weight. A surfactant is then mixed with the ammonium glyphosate paste prior to extrusion granulation, in part to condition the paste to improve the extrudability of the paste, but primarily to improve the herbicidal efficacy of the final ammonium glyphosate granules. According to Massmann et al., adding surfactant prior to or during the reaction process is detrimental to the process; thus, the entire amount of surfactant is added to the ammonium glyphosate paste after the entire reaction has been completed and preferably after the ammonium glyphosate paste has been cooled to less than 70° C.
SUMMARY OF THE INVENTION
Among the
Campbell Dwane H.
Massmann Brent D.
Wang John T.
Clardy S. Mark
Monsanto Technology LLC
Schaper Joseph A.
Senniger Powers Leavitt & Roedel
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