Abstract:
Dry flow, low compact, dust free, soluble granules of phosphoroamidothioates, preferably acephate, are produced by the process of 1) pre-mixing technical grade phosphoroamidothioate with specified adjuvants and other inert ingredients; 2) grinding to produce a ground product having a preferred particle size of 5 microns to 10 microns; 3) post-mixing; 4) granulating; 5) drying; 6) sizing to required length, preferably 1.5 to 3.0 mm; 7) and sieving to remove the fines to get the desired dust free soluble granule.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit, under 35 U.S.C. 119(e), of U.S. Provisional Application No. 60/340,272 filed Dec. 18, 2001, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for preparing insecticidally active soluble granules of phosphoroamidothioate, referred to herein as acephate. 
     2. Background Information 
     In recent years, agricultural chemicals have been most preferably formulated in the form of dusts, wettable powders, soluble powders, emulsifiable concentrates, soluble liquid/concentrates, granules, coated granules, water dispersible granules, suspension concentrates, and solutions. Occasionally, when dusts are produced by absorbing or mixing active ingredients with a finely divided inert carrier material, for example China Clay or the like, drift problems occur. With wettable powders and soluble powders the problems faced at the time of dilution are not only drift, but the final disposal of containers, for dust particles tend to stick to sides of the containers. The left over materials within the containers pose great problems to the environment, operators and users. 
     Although dusts are undesirable because of airborne contamination and handling difficulties, liquid spray formulations have not provided an acceptable alternative, for they involve solvents and packaging expenses, along with container disposal requirements that detract from their commercial desirability. 
     Water dispersible granules produced by fluidized bed spray dryers overcome the problems associated with wettable powders and soluble powders, but have high processing costs and require high value capital investment, as well as requiring highly skilled staff. These problems impose a significant barrier in widening the market acceptance of these compounds. 
     Certain phosphoroamidothioates and phosphoroamidodithioates, collectively referred to as Phosphoroamidothioates, are known to have excellent insecticidal activity against a variety of insects and in a variety of environments. Acephate, one of the important commercial insecticides within this class of compounds, is a systemic and contact insecticide of moderate persistence with residual activity lasting about 10-15 days. It is effective against a wide range of aphids, leaf-miners, lepidopterous, larvae, sawflies and thrips and it is also a non-phytotoxic on many crop plants. 
     Phosphoroamidothioate containing pellets have been proposed in the past, but difficulties have been encountered in pelletizing acephate technical, the preferred insecticide within the class of phosphoroamidothioates. Attempts to manufacture acephate technical pellets from acephate technical powders have been proposed and have been unsuccessful. 
     Considerable experimentation in the area of producing the preferred high-strength acephate granules has been conducted and confirms the manufacturing difficulties which earlier formulators have experienced. Furthermore, the pellets and methods proposed for making pellets suggested in the prior art leave considerable room for improvement. Prior extrusion processes have proposed the addition of costly surfactants, the combination of phosphoroamidothioate with a second active ingredient, or the creation of a mixture of the active ingredient with a solvent in an amount of from 3-25% by weight before extrusion, but these processes have not solved the problems encountered. 
     The formulation of acephate presently in use is acephate 75% soluble powder having acephate active ingredient 75% (w/w), surfactant 1 to 2% (w/w), inert filler (precipitated silica) to make 100% (w/w). Acephate 75% soluble powder poses the problems of dust, low pourability, high transportation costs, high capital manufacturing investment, measurement difficulties, difficulties in packing material disposal, handling problems, high risk of caking and others. 
     Because of the problems associated with producing granular forms of phosphoroamidothioates, such as the preferred acephate, there is a need in the art for a process for preparing chemically stable, dry flow, low compact, dust free, insecticidally active soluble granules of phosphoroamidothioate which are useful from a practical stand point, as well as for a low cost, practical manufacturing technique which can be practiced on a commercial scale without requiring expensive additives or solvents. 
     SUMMARY OF THE INVENTION. 
     By the present invention the above-identified major limitations have been overcome. The method for producing dry flow, low-compact, dust free, soluble phosphoroamidothioate granules, such as the preferred compound acephate, is an improvement over prior manufacturing processes. Further, the dust free soluble granules produced by this invention, which has a concentration of the insecticidally active ingredient in this formulation may vary from 40-98% of phosphoroamidothioate active ingredient, is more advantageous than prior granular products and exhibits certain very desirable characteristics as noted hereinafter. 
     Briefly, and in accordance with a preferred embodiment of the invention, dry flow, low compact, dust free, soluble granules of insecticially active phosphoroamidothioate are prepared by forming a pre-mix containing the required quantity of phosphoroamidothioate, a dispersing agent, a wetting agent, a binding agent, an antifoaming agent, a disintegrating agent, a stabilizer and filler. The specified adjuvants have a maximum of 1% water insoluble matter. This pre-mix is then ground to produce a ground product having preferred particle sizes between 5.0 microns to 10.0 microns. The ground product is fed to a post-mixer to form a mixture. The mixture is then fed through a hopper into a granulator where granules are formed. The granules are then dried, and the dried granules are sized and sieved to separate dry granules from fines, producing dry flow, low compact, dust free, soluble granules of phosphoro-amidothioate as noted above, the preferred phosphoroamidothioate is acephate. The fines may be recycled back to the post mixer. 
     This invention produces essentially dry flow, low compact, dust free soluble phosphoroamidothioate granules having a preferred granule size of 1.5 to 3.0 mm in length and 0.5 to 1.0 mm in diameter. These granules of phosphoroamidothioates are characterized by aging stability for a minimum of two years. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a flow chart of the preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The process of the present invention is best described by referring to the flow chart in FIG.  1 . An essentially dry pre-mix comprising about 95% to 99% of solids and 1% to 5% moisture and/or solvent is formed from the following ingredients: 40% to 98% of the insecticidally active compound  2 , 0.1% to 5.0% dispersing agent  4 , 0.1% to 3.0% wetting agent  6 , 0.1% to 3.0% binding agent  8 , 0.01% to 0.08% antifoaming agent  10 , 0.01% to 10.0% disintegrating agent  12 , 0.01% to 1.0% stabilizer  14 , and fillers  16  to make 100% (w/w). The insecticidally active compounds of the present invention have the following formula: 
                        
 
     wherein R and R 1  individually are an alkyl, alkenyl or alkynyl group containing upto 6 carbon atoms, R 2  is hydrogen, an alkyl group containing 1 to 18 carbon atoms, a cycloalkyl group containing 3 to 8 carbon atoms, an alkenyl group containins 2 to 18 carbon atoms or an alkynyl group containing 3 to 18 carbon atoms, R 3  is hydrogen or an alkyl group containing 1 to 6 carbon atoms, and Y is oxygen or sulfur. All of the inert ingredients are preferably solids and in a powder form. In one preferred embodiment, the binding agent  8  is selected from sucrose and starch derivatives or a blend thereof, the wetting agent  6  is selected from calcium or sodium salt of alkyl aryl sulphonate, the dispersing agent  4  is selected from the derivative of sulfonated fatty alcohols, the disintegrating agent  12  is selected from swelling type clays such as Bentonite and zeolite, the antifoaming agent  10  is selected from silicon oil derivatives, the stabiliser  14  is selected from salts of higher fatty acids, and the filler  16  is selected from precipitated silica and kaoline and the like. Grinding  22  of the pre-mix  20  is then conducted, preferably in a microniser, to obtain a ground product  24  having a preferred particle size of 5 microns to 10 microns. 
     The ground product  24  is subjected to post-mixing  26  to form a mixture  28  which is then made into granules  36  by preferably charging  30 , by way of a rotary feeder, a feeding hopper which supplies the mixture to a granulator for granulation  34 . The granulator that performs the granulation  34  has a preferred inlet temperature between 30 to 35° C. and a preferred outlet temperature of between 40° C. to 45° C. The resulting granules  36  are subjected to a drying  38  process, preferably by passing the granules  36  through an air chamber, producing dry granules  40 . 
     Sizing  42  the dry granules  40  is then accomplished to produce sized granules  44  of a desired length and diameter. Sizing the granules is preferably conducted by passing the dry granules  40  through an oscillating cutter to obtain granules which are preferably between about 1.5 mm and 3.0 mm in length and 0.5 mm to 1.0 mm in diameter. After sizing, the sized granules  44  are subjected to sieving  46  to separate fines  50  generated during the sizing process from desired dust free soluble granules  51 . 
     The fines  50  from the sieving  46  process may be collected and recycled at the charging  30  stage of the process to obtain a minimum yield of 99.0% dry flowable, low compact, dust free, soluble granules  54  of phosphoroamidothioates, preferably acephate. 
     The dust free soluble granules  54  were tested for required quality specifications and packed in desired packing. This technique gives 99% of conversion yield. The dust free soluble granules  54  enjoy all the formulation advantages described above, producing dust free soluble granules  54  which are beneficial from an economic aspect and a handling aspect and which show a very good performance during use. 
     The following examples are presented to illustrate but not to restrict the present invention. Parts and percentage are by weight unless otherwise specified. 
     EXAMPLE 1 
     Acephate 97% Granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredients 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 98.48 
               
               
                   
                 Dispersing agent 
                 0.50 
               
               
                   
                 Wetting agent 
                 0.10 
               
               
                   
                 Binding agent 
                 0.10 
               
               
                   
                 Antifoaming agent 
                 0.03 
               
               
                   
                 Disintegrating agent 
                 0.50 
               
               
                   
                 Stabilizer 
                 0.05 
               
               
                   
                 Filler 
                 0.24 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 1 PROCESS 
     The constituents of the above composition are mixed in a pre-mixer, then ground in a microniser to the required size of 5 micron to 10 micron. The ground product  24  is again mixed in a post-mixer to get a uniform homogeneous mixture  28 . This homogeneous mixture  28  is then fed through a rotary feeder into a low compaction granulator, while maintaining an inlet temperature of 32 to 35° C. and an outlet temperature of 40 to 45° C. The Acephate granules  36  formed in the granulator are further dried through an air chamber, sized to 1.5 mm to 3 mm length, and are collected. The fines  50  generated during the process are recharged to get a conversion yield of 99 percent. 
     EXAMPLE 2 
     Acephate 98% granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 99.50 
               
               
                   
                 Dispersing agent 
                 0.25 
               
               
                   
                 Wetting agent 
                 0.03 
               
               
                   
                 Binding agent 
                 0.05 
               
               
                   
                 Antifoaming agent 
                 0.02 
               
               
                   
                 Disintegrating agent 
                 0.05 
               
               
                   
                 Stabilizer 
                 0.05 
               
               
                   
                 Filler 
                 0.05 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 98% granules with above composition can be prepared by following the process described in EXAMPLE 1. 
     EXAMPLE 3 
     Acephate 97.5% granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 98.99 
               
               
                   
                 Dispersing agent 
                 0.40 
               
               
                   
                 Wetting agent 
                 0.10 
               
               
                   
                 Binding agent 
                 0.10 
               
               
                   
                 Antifoaming agent 
                 0.03 
               
               
                   
                 Disintegrating agent 
                 0.20 
               
               
                   
                 Stabilizer 
                 0.05 
               
               
                   
                 Filler 
                 0.13 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 97.5% granules with above composition can be prepared by following the process described in EXAMPLE 1. 
     EXAMPLE 4 
     Acephate 90% Granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 91.38 
               
               
                   
                 Dispersing agent 
                 00.75 
               
               
                   
                 Wetting agent 
                 00.10 
               
               
                   
                 Binding agent 
                 00.20 
               
               
                   
                 Antifoaming agent 
                 00.03 
               
               
                   
                 Disintegrating agent 
                 01.00 
               
               
                   
                 Stabilizer 
                 00.50 
               
               
                   
                 Filler 
                 06.04 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 90% granules with above composition can be prepared by following the process described in EXAMPLE 1. 
     EXAMPLE 5 
     Acephate 85% granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 86.30 
               
               
                   
                 Dispersing agent 
                 01.50 
               
               
                   
                 Wetting agent 
                 00.50 
               
               
                   
                 Binding agent 
                 01.00 
               
               
                   
                 Antifoamer 
                 00.05 
               
               
                   
                 Disintegrating agent 
                 02.00 
               
               
                   
                 Stabilizer 
                 00.60 
               
               
                   
                 Filler 
                 08.05 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 85% granules with above composition can be prepared by following the process described in EXAMPLE 1. 
     EXAMPLE 6 
     Acephate 75% Granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 76.15 
               
               
                   
                 Dispersing agent 
                 2.00 
               
               
                   
                 Wetting agent 
                 1.50 
               
               
                   
                 Binding agent 
                 1.50 
               
               
                   
                 Antifoaming agent 
                 0.06 
               
               
                   
                 Disintegrating agent 
                 5.00 
               
               
                   
                 Stabilizer 
                 0.75 
               
               
                   
                 Filler 
                 13.04 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 75% Granules with above composition can be prepared by following the process described in EXAMPLE 1. 
     EXAMPLE 7 
     Acephate 50% Granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredients 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 50.77 
               
               
                   
                 Dispersing agent 
                 3.00 
               
               
                   
                 Wetting agent 
                 2.00 
               
               
                   
                 Binding agent 
                 3.00 
               
               
                   
                 Antifoaming agent 
                 0.08 
               
               
                   
                 Disintegrating agent 
                 10.00 
               
               
                   
                 Stabilizer 
                 1.00 
               
               
                   
                 Filler 
                 30.15 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 50% Granules with above composition can be prepared by following the process described in EXAMPLE 1. 
     EXAMPLE 8 
     Acephate 40% granules can be prepared as follows: 
     Composition 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Quantity (% w/w) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acephate Technical 98.5% purity 
                 40.61 
               
               
                   
                 Dispersing agent 
                 4.50 
               
               
                   
                 Wetting agent 
                 3.00 
               
               
                   
                 Binding agent 
                 3.00 
               
               
                   
                 Antifoaming agent 
                 0.08 
               
               
                   
                 Disintegrating agent 
                 12.00 
               
               
                   
                 Stabilizer 
                 1.50 
               
               
                   
                 Filler 
                 35.31 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Acephate 40% Granules of above composition can be prepared by following the process described in EXAMPLE 1. 
     Tests 
     The physical properties of Acephate granules were determined before and after aging at 45° C. for 500 hrs and for flowability, wetting time, attrition test, disintegration rate, tap density, suspensibility, sedimentation and persistent foam. No noticeable difference in all the above properties was observed. The dynamic wetting time and solubility test was measured as per MT-167 of CIPAC. The flowability was measured as per MT-172 of CIPAC. The dry sieve analysis was measured as per MT-170 of CIPAC. The sedimentation was measured as per MT-15.1 of CIPAC. Dustiness of granules was measured as per MT-171 of CIPAC. The tap density was measured as per MT-58.4 and MT-33 of CIPAC. The Acephate technical was determined by the GLC method published in AOAC. 
     Although the present invention has been disclosed in terms of a preferred embodiment, it will be understood that numerous additional modifications and variations can be made without departing from the scope of the invention as defined by the following claims.