The chemical name of glyphosate is N-phosphonomethyl glycine, which has the following molecular formula.

Glyphosate is a broad-spectrum sterile herbicide highly effective in the prevention and control of various malignant deep-rooted weeds due to good systemic conduction performance. Recently, its sales volume is gradually increased. The application field thereof is further extended with the gradual popularization of glyphosate-resisting transgenosis crops. Now, it has become a herbicide with the highest sales volume and the quickest speed increased in its production in the world.
Because the solubility of glyphosate in water is very low (1.2 g per 100 g water at 25° C.), as for practical application, the glyphosate is usually processed into water-soluble salts, and is commercially available as an aqueous formulation of glyphosate isopropylamine salt, an aqueous formulation of glyphosate trimesium, an aqueous formulation or a water-soluble powder (granula) of ammonium (sodium) glyphosate. Because the aqueous formulation of glyphosate salt contains a great amount of water as a solvent and its package has an increased weight and volume, the water-soluble solid formulation has a relatively low cost. As for the end users, the products with lower price and better performance are required. It is obvious that the water-soluble solid formulation of ammonium glyphosate is more competitive than the aqueous formulation thereof.
Chinese Patent Application No. CN-96196134.1, which was published on Sep. 9, 1998 and was issued to Monsanto Company of American on Jul. 18, 2001, shows that great efforts have been made for the preparation and use of compositions of dry glyphosate formulation, and for related methods. Herein, the related patents and references are used as the references for the present invention. The patent discloses a process for preparing ammonium glyphosate by the reaction of an aqueous ammonium hydroxide solution (ammonia water) with glyphosate in a liquid-solid reaction system. Since the concentration of ammonia water is only 29%, namely, it contains a large amount of water, continuous drying is required so as to keep an appropriate water content during the process. Further, the rate for introducing ammonia water is required to control strictly so as to ensure the rate for introducing water into the system less than that for removing it from the system during the reaction. The water content should be periodically measured, and the product should be dried and then pulverized. Furthermore, sodium sulfite as an antioxidant (oxidation inhibitor) is required further to add during the reaction in order to decrease the oxidization of glyphosate by hot air because the oxidation causes formation nitrosamine which content needs to be controlled. Therefore, the technology and control are relatively complicated to some extent, and a large amount of water has to be removed by hot wind, so the energy consumption is higher.
Chinese Patent Application No. CN-96196133.3, which was published on Sep. 9, 1998 and was grant on Jul. 4, 2001, discloses a process for preparing ammonium glyphosate by the reaction of glyphosate and anhydrous ammonia. The process needs to use a “self-cleaning type” of autoclave equipped a “propeller” which has a precision dimension and is able to scrape continuously the products deposited on the reactor wall, otherwise, the solid deposition formed will affect the removal of reaction heat. Furthermore, the rate for introducing ammonia is strictly controlled in order to ensure introducing the ammonia and glyphosate into the reactor in a manner that they are completely homogeneous dispersed. If the inlet for ammonia is not set in an appropriate position, fouling and clogging will easily occur at the inlet and solid aggregations will also be formed. The disadvantages of the process are that it is difficult to removal the reaction heat from the gas-solid reaction system and the reaction rate is slow.
Chinese Patent Application No. CN-99119971.5, which was published on Jul. 19, 2000 and was grant on Oct. 10, 2001, discloses a commercial process for preparing ammonium glyphosate by the reaction of glyphosate with liquid ammonia. Because the process is carried out directly through the liquid-solid reaction of liquid ammonia with glyphosate, it is required to be carried out under a pressure of 1.0-2.8 MPa while the reaction heat is required to remove timely during the reaction to avoid resulting in danger under too high pressure. The process has disadvantages in that the reaction has to be conducted at a higher pressure and bigger equipment is further required to install for recovering ammonia.
Although the aforementioned inventions provide the process for preparing dry ammonium glyphosate salt that can be used in the preparation of the water-soluble solid formulation, the processes suffer from deficiencies such as slow reaction rate, high cost or complicated technology and the like. That is, the prior arts are such unsatisfactory that there is still a need for a further invention. In this regard, the present invention solves the problems associated with the process in the prior arts and meets requirements that are not yet realized in aforementioned inventions or well-know technologies.