HIGHLY CONCENTRATED, SOLID ACIFLUORFEN POWDERS AND PROCESSES FOR MAKING DRY FORM SOLID ACIFLUORFEN POWDERS

Abstract: The present invention provides highly concentrated, solid acifluorfen powders and processes for making them.

Description: Highly Concentrated, Solid Acifluorfen Powders and Processes for Making Dry Form Solid Acifluorfen Powders Description The present invention relates to methods for making flowable, highly concentrated dry acifluorfen powders from an aqueous solu¬ tion of the salt form of acifluorfen. The invention moreover relates to the powder thus obtained and PVA bags comprising the powder. Herbicides may be applied to plants in a variety of methods in- eluding different formulations. Of these various methods, use of liquid and dry compositions are the most common. The particular formulation desired and resulting efficacy enhancement will greatly depend upon the species to be treated, environmental conditions, the geographical area and the climatology of the area at the time of treatment. The herbicide, known trivially as acifluorfen, is widely used to control various weeds, such as morning glory, pigweed, ragweed, velvetleaf, foxtail, Johnson grass, Florida beggarweed, cockle- bur, and others. See, for example, US Patents 3,798,276 and 3,928,416. Further patents claim enhanced herbicidal activity for acifluor¬ fen and its agronomically acceptable salt forms with the addition of one water-soluble salt from an organic or inorganic acid (see US Patent 4,508,559), and specifically by the addition of a ci¬ trate salt (see US Patent 4,549,903). Acifluorfen' s chemical name is 5- (2-chloro-4- (trifluoro- methyl)phenoxy)-2-nitrobenzoic acid and is available from BASF Corporation under the trademarks BLAZER® or TACKLE ® . These products are manufactured in the form of about a 43 to 48% active ingredient aqueous solution of the sodium acifluorfen with impu¬ rities . This product is sold by BASF Corporation under the trade- mark BLAZER ® TECHNICAL. The end user normally purchases acifluorfen either as an aqueous mixture of sodium acifluorfen, trisodium citrate, and a cosolvent butyl cellosolve (BLAZER ® ) ; or as sodium acifluorfen, a sodium lignin sulfonate-REAX 910 (from estvaco Corporation), and co ¬ solvent propylene glycol (TACKLE ® ) . Acifluorfen is preferentially sold in agronomically acceptable salt forms mentioned above because the salt form has a high water solubility which imparts convenience to the farmer who applies the product from this tractor tank. The sodium form, for example, has a water solubility of more than 119 g/L. The aqueous solution can be added directly to an application tank containing water, recirculated for a few minutes, and applied as a dilute aqueous liquid to the plant growth in the fields. The acifluorfen in its acid form is not soluble in water to any appreciable extent, and presents dispersion problems using an application tank to apply the chemical universally in the field. Until now, the high water solubility of the salt forms have given it an advantage over the water insoluble acid form for the end user. However, the high hygroscopicity of the salt form makes it difficult to dry the salt form. The water is difficult to remove during drying. Attempts to remove the water from acifluorfen formulations by spray drying have resulted in a sticky, non-flowable mass, most of which stuck to the walls, ducts, and cyclone walls of the spray dryer, rendering the process ineffective. Similarly, attempts to dry acifluorfen formulations, such as solutions of REAX 910 with BLAZER ® , by use of a double drum dryer resulted in the formation of a sticky material that could not be scraped off the drums. Furthermore, drying generally is also hindered by foaming which can result in certain dryers being ineffective. In batch drying for example, foaming can greatly hinder the rate of drying, or even eliminate the possibility of drying such a compound suffi¬ ciently to form a powder. All three commercial formulations of acifluorfen, (BLAZER ® Technical, BLAZER ® , and TACKLE ® ) could not be dried in several batch dryers. Attempts to dry these products in either a rotary dryer or a mechanical fluid bed dryer with chopping blades (for example, the Littleford FKM dryer) resulted in violent foaming, which rendered the process ineffective. Generally, solid forms of herbicides offer a number of key advan¬ tages, including convenience, increased stability and shelf life, as well as reduced packaging, storage and shipping costs. Addi¬ tionally, there is the possibility of future government regula- tion requiring solid forms of agricultural products in order to reduce handling of contaminated packaging of these products dur¬ ing field application and during disposal. These dry flowable hy- groscopic herbicidal compounds would be safer for the farmer to use and dispose of, and also result in a smaller volume of haz¬ ardous waste being produced. If the dry herbicide can be filled into dissolvable bags which are added to the tractor tank, then exposure during loading and the hazardous waste generated can be virtually eliminated. There is a need for a dry, flowable, highly concentrated powder form of hygroscopic acifluorfen suitable for filling water dis- solvable bags. The ideal dry powder would not only include the active ingredient, but also a sequestering agent such as a ci¬ trate salt . Surprisingly, a free-flowing, non-caking solid salt form aci- fluorfen (such as sodium acifluorfen) containing a citrate salt sequesterant can be produced by spray drying such a solution. The citrate salt is dissolved in acifluorfen (BLAZER® TECHNICAL) solution, and the resulting solution spray dried to form a free flowing, dry powder, with about 73% active sodium acifluorfen. Optionally, suitable inerts such as silica can be added to the spray tower as anti-caking agents. Additionally, a dry powder acifluorfen with citrate salt can also be produced on a drum dryer. The preferred forms of acifluorfen of the present invention in¬ clude all agronomically acceptable salts of the acifluorfen, most preferably sodium acifluorfen. It is an object of the present invention to provide an agricul¬ turally acceptable acifluorfen formulation in a solid form. It is an object of the present invention to provide a dry, flow¬ able powder form of acifluorfen suitable for filling into and use in water soluble bags. It is an object of the present invention to provide a spray dry¬ ing process to produce an acifluorfen dry powder. It is an object of this invention to provide a drum drying pro¬ cess to produce an acifluorfen dry powder. Figure 1 illustrates a spray dryer used in a method of the pres¬ ent invention. Figure 2 illustrates a double drum dryer used in a method of the present invention. Figure 3 illustrates a Littleford ® vacuum dryer used in Examples 8-10. As used herein, the term "agriculturally acceptable" includes the present agricultural, industrial and residential use. As used herein, acifluorfen formulations of the present invention may be used to form both package and tank mix compositions. The present preferred invention comprises herbicide compositions comprising an agriculturally and plant growth regulating effec¬ tive amount of acifluorfen, or any of its herbicidally effective derivatives or salts, in a dry flowable highly concentrated pow¬ der. The most preferred acifluorfen form is sodium acifluorfen. This product is commercially available under the registered trademark BLAZER ® (BASF Corporation) . For convenience of description, sodium acifluorfen will be used as an example. However, the methods described apply equally to other salt forms of acifluorfen. Suitable sequestrants are citrates, preferably ammonium citrates and/or potassium citrates and particularly preferred are sodium citrates, especially tri-sodium citrate. In general it is preferred that the weight of a sequestrant, such as a citrate salt, per weight of acifluorfen is about 0.1:100 to about 35:1. While the ratios of the concentrations of the various components of the present invention hereinafter suggested, those skilled in the art will recognize that minor variations may be necessary to accommodate particular characteristics of acceptable formulations of the various salt forms of acifluorfen which may be employed in this invention. A preferred embodiment of the present invention consists of a spray dryer of the type illustrated in Figure 1 may be used. As can be shown from Figure 1, a sequestrant, tri-sodium citrate is combined in the sodium acifluorfen aqueous solution in an agi¬ tated feed tank (2) and fed through a line (4) via a feed pump (6) into the spray dryer unit (8) . The aqueous acifluorfen feed solution is introduced into the spray dryer unit (8) by an atom¬ izing means (10) . An inlet air heating means (12) provides heat to the dryer at a temperature of about 150 to about 250°C. The formed droplets are heated by the hot air, and the water in the droplet is evaporated, forming a solid particle containing the acifluorfen salt and the sequestrant. The dry particles are swept by the air stream to the exit duct (24) and finally to the cy- clone (26) where the particles are separated from the air by cen¬ trifugal action. The collection system may also include a bag filter to recover the solid particles. A flow aid, such as silica, may optionally be stored in a feed hopper (14) and injected into the spray dryer unit (8) via a screw feeder (16) through a line by an air eductor (18) . Alterna¬ tively, the flow aid can be introduced in the heating duct or top of the chamber at a point of negative pressure. The flow aid ad¬ heres to the forming droplets or partially dried particles and reduces the tendency of the partially dry particles to stick on the walls of the drying chamber. Furthermore, the flow aid also aids the product in storage by reducing the tendency to cake or lump, particularly when exposed to atmospheric moisture. It is preferred that the sodium acifluorfen solution be initially heated to about 60°C before adding the sequestrant. This greatly reduces the tendency of the acifluorfen solution to foam on addi¬ tion of the sequestrant. The rate at which the aqueous acifluorfen feed solution is fed into the spray dryer is not critical and is dependent upon the size of the spray dryer used. This rate is easily determined by those skilled in the art. A preferred method dries the acifluorfen/sequestrant solution with a double drum dryer as illustrated in Figure 2. The double drum dryer has a pair of hollow, rotating drums (28, 30) whose surfaces are scraped by a knife (32) . High pressure steam is introduced to the interior of the drums and acifluorfen solution added continuously via a feed line (34) to the nip between the drums (36) . The acifluorfen solution must be prepared by adding sequestrant to an agitated tank, as in the spray drying example. The drums turn toward one another, by means of a conveyor (38) depositing a portion of the liquid, boiling acifluorfen solution on the drum surface (28, 30) where boiling is initiated. Prefer¬ ably the solution is charged into the double drum dryer at a rate of about 5 gm/min to about 200 gm/min per square foot of heated surface. Upon further rotation, the thin film of acifluorfen's water boils of into the vapor hood (40) and a solid film remains that is scraped by sharp knifes (32) from the turning drum surfaces (28, 30) . The material is then collected and optionally, a flow aid may be added to improve flowability and impart anti- caking properties prior to filling water soluble bags. Option¬ ally, the flakes from this process may be ground to improve flow¬ ability. The methods described optionally use one or several inerts such as silica or other flow aids to reduce caking in the drum or water soluble bag, and to reduce adherence to equipment and which is added as a rule prior to the drying process, to the solution of the acifluorfen salt. Other inert additives include any form of silica including fumed silicas, precipitated silicas, aluminum silicates, magnesium sil¬ icates, and the like, zeolites, bentonites, montmorillonites, and attapulgites, and mixtures thereof. The preferred silica is known commercially as Sipernat ® 50S. The weight of the optional inert per weight of the acifluorfen formulation in all these drying processes is about 0.2:100 to about 3:100, and more preferably about 2:100. This ratio is based on the overall formula, not just the active ingredient. Optionally, to further improve flowability, reduce sticking ten- dency or caking, or to increase the dissolution rate, binders, fillers, and/or disintegrants can be dissolved in the feed solu¬ tion before drying. Suitable binders, fillers, and/or disintegrants include water- soluble cellulose derivatives, cellulose derivatives, carboxy- methyl cellulose, hydroxypropyl methylcellulose, water soluble gums such as gum arabic, gum tragacanth, alginates, gelatin, and polyvinylpyrrolidone, cross-linked polyvinylpyrollidone, micro- crystalline cellulose, modified starches such as sodium carboxy- methyl starch, and mixtures thereof. Other suitable fillers, binders, and/or disintegrants include any water soluble starch, corn syrup, dextrin or pregelatinized starch which is at least partially soluble in water at ambient temperature. For example, there can be used as a binder the pre¬ gelatinized, modified and stabilized waxy maize starch (commer¬ cially available from National Starch and Chemical Corporation under the trade name Instant Celar Gel) . In addition, pregelati¬ nized corn starch (commercially available from Hubinger Company under the trade name OK Pre-Gel) may be used. Other binders suitable for use are pregelatinized food starch, refined from tapioca and marketed under the trade name Instant Gel; stable, modified amylopectin marketed under the trade name Kosol; a low viscosity tapioca dextrin marketed under the trade name Crystal Gum; dextrinized corn starch marketed under the trade name Purity Glaze; maltodextrin marketed under the trade name Maltrin, such as M040 by Grain Processing Corporation. It is preferred that the binders, fillers, and disintegrants be present in an amount of about 0.1 to about 99.7%. All of the above-described powders, with and without fillers, binders, and/or disintegrating agents can then be filled in water soluble bags . In general the formulations of the present invention contain from about 0.1 to about 80% active ingredient, and preferably from about 40 to about 70% active sodium acifluorfen. Typically, for the herbicide concentrate of the present invention, the con- centration of regulator active ingredient (based on sodium aci¬ fluorfen) is about 65 to about 500 gms/acre. In addition to the above-described components, the compositions of the present invention may also include other ingredients or adjuvants commonly employed in the art. Examples of such ingredients include drift control agents, de- foaming agents, preservatives, surfactants, fertilizers, phyto- toxicants, plant growth regulators, pesticides, insecticides, fungicides, wetting agents, adherents, nematocides, bactericides, trace elements, synergists, antidotes, mixtures thereof and other such adjuvants well known in the herbicidal art. However, it is preferred to employ the compositions of the pres- ent invention along with sequential treatments with these other components for optimal effect. The compositions of the present invention may be applied to plants. The application of liquid and particulate solid herbicide compositions to above ground portions of plants may be carried out by conventional methods, for example, boom and hand application, including sprayers or dusters. The composition may be applied aerially as a spray, if desired. The mixtures of the present invention are preferably used in the form of aqueous solutions. The mixtures are applied in a conventional manner, for example, by spraying, atomizing, watering or disinfecting seed. The forms of application depend entirely on the purpose for which the compositions are being used. In any event, they should ensure a fine distribution of the active ingredients in the composition. The above herbicide formulations may then be dispersed in water and sprayed onto plants according to the method of the present invention. Powders, dusts and broadcasting agents may be prepared by mixing or grinding the active ingredients with a solid carrier. Granules, for example, coated, impregnated or homogeneous gran¬ ules, may be prepared by bonding the active ingredients to solid carriers. Examples of solid carriers are mineral earths such as silicic acid, silica gels, silicates, talc, kaolin, Attaclay, limestone, lime, chalk, bole, loess, clay, dolomite, diatomaceous earth, calcium sulfate, magnesium sulfate, magnesium oxide, ground plastics, fertilizers such as ammonium sulfate, ammonium phosphate, ammonium nitrate, and ureas, and vegetable products such as grain flours, bark meal, wood meal, and nutshell meal, cellulosic powders, and the like. The action of the compositions of the present invention are opti¬ mal even at low application rates. For a given herbicide composi¬ tion, the skilled artisan will readily arrive at a composition having the optimum ratio of the ingredients by routine exper¬ imentation. The compositions of this invention may be prepared, for example, by adding, in any order, the various components of the composi- tion of the present invention. For example, one may start with a commercial formulation of acifluorfen, which is an aqueous con¬ centrate containing about 43 to about 48% active sodium acifluor¬ fen. Thereafter, in any order, one mixes suitable amounts of any optional adjuvants or ingredients. The following examples serve to illustrate the invention and should in no way be construed as limiting the scope thereof. Example 1 12,884 grams of a sodium acifluorfen solution (BLAZER ® Technical) of 44.76% active sodium acifluorfen was added to an agitated jacketed spray dryer feed tank and heated to 66°C with tempered water. To this solution was added 2,116 g of trisodium citrate (moisture content 14%) and mixed until the citrate was dissolved. The resulting solution had a viscosity of 110 centipoise at 66°C. This solution was pumped at 111 to 128 g/min. to a 5 inch slotted atomizing wheel rotating at about 17,000 rpm in a Niro Utility spray dryer. The droplets formed by this method were dried by 175°C inlet air, with a resulting outlet temperature of about 117 to about 126°C. 5 The resultant powder was collected in a cyclone separator. The powder was flowable and produced minimal wall deposits. Analysis of the powder showed that the powder had 0.99% moisture, untapped bulk density of 0.41 g/cc, a tapped bulk density of 0.52 g/cc. 10 The ash content was measured at 7.15%. This demonstrates that a flowable dry powder of normal bulk density and moisture content for a spray dried powder was produced. The powder was suitable for filling water soluble bags . 15 Example 2 The experiment of Example 1 was repeated, but Sipernat® 50S silica from a loss-in-weight screw feeder was injected via an air eductor into the air plenum to mix with the heated air entering 20 the drying chamber. The silica was fed at a rate of 3%, based on the dry basis feed rate of the acifluorfen feed solution. The silica/air mixture was maintained at 175°C, then the mixture en¬ tered the drying chamber, intermixing with the droplets formed by the atomizer. The resultant outlet temperature was about 109 to 25 125°C. On drying, the powder exited the drying chamber and was separated by a cyclone separator. The powder was flowable and produced minimal wall deposits. Analysis of the powder showed that the 30 powder had 0.50% moisture, a bulk density of 0.42 gm/cc untapped, and 0.53 g/cc tapped, with an ash content of 8.10%. This ash con¬ tent implies a silica content, as compared to Example 1, of 0.95%. This powder was also suitable for filling water soluble bags. 35 Example 3 A hot solution of 5000 gms of BLAZER ® Technical liquid with 835 gms of trisodium citrate was prepared as in Example 1. The solu- 40 tion was dripped onto the rolls between the nip of a lab scale double drum dryer, with the hot rolls rotating at about 6 rpm. The rolls were heated with 5.5 bar steam. The material adhered to the rolls and the moisture evaporated while the drums rotated. The solid film was scraped off the rolls by blades and collected. 45 The resulting sheets of dried solid broke easily into a granular, flowable powder with a bulk density of 0.39 gm/cc untapped, 0.56 gm/cc tapped, and moisture of 1.0 %. These results were judged acceptable for filling water soluble bags. Example 4 A greenhouse trial was conducted to assess the weed killing effi¬ cacy and crop injury potential of various surfactants and aci¬ fluorfen, compared with two intermediate dry, flowable formula¬ tions of acifluorfen and trisodium citrate (Examples 1 and 2) . The two formulation of Examples 1 and 2 demonstrated weed effi¬ cacy and crop phytotoxicity similar to the control formulation. The results in this test showed that the dry flowable formula¬ tions of Examples 1 and 2 worked as well as the other control formulas. In contrast to the above examples, the following examples illus¬ trate the difficulty of drying acifluorfen formulations. Example 5 A solution of 5000 gms of BLAZER ® Technical liquid with 81 grams of Reax 910 was prepared (simulating the TACKLE ® formulation) in the same equipment used to prepare the feed solution of Example 1. The spray dryer again was operated at 175°C inlet temperature, and the atomizing wheel revolved at 17,000 rpm and the feed added as in Example 1. The resultant powder was an extremely fine, sticky dust the bulk of which adhered to the walls of the spray dryer. The powder which was recovered would not flow, and because of this was not suitable for filling water soluble bags. Example 6 BLAZER ® Technical liquid was heated to 60°C and dripped on the nips of the double drum dryer rolls at the conditions of Example 3. Even when the rolls were slowed down, the material was too gummy to be flaked with the blades. It was concluded that a flow¬ able powder could not be formed by this method. Example 7 A solution of BLAZER ® Technical and Reax 910 was prepared in the method of Example 5. The 60°C liquid was dripped on the nip of the double drum dryer rolls at the conditions of Example 3. Even when the rolls slowed down, the material was too gummy to be flaked with the blades. It was concluded that a flowable powder could not be formed by this method. Example 8 Another method of drying the acifluorfen was made using a batch vacuum dryer with chopping blades, described as a "mechanical fluidized bed", a typical example of which is the Littleford ® type (or Lδdige) vacuum dryer, as shown in Figure 3. As is seen from Figure 3, the vacuum dryer unit (52) consists of double jacket (42, 44) . Inside the double jacket is a hollow ro¬ tating shaft (46) with attached plough shaped mixing elements (48) . Feed solution is fed via a line (50) into the vacuum dryer unit (52) . Steam or hot water (54) is fed via a line (56) into a jacket (42) which surrounds the vacuum dryer unit (52), and op¬ tionally through the hollow rotating shaft (46) . Agitating means (57) in the interior of the vacuum dryer unit (52) agitates the feed solution. A vacuum means (58), which may be a pump or vacuum jet unit is introduced into and applied to the vacuum dryer unit (52) . The vacuum and applied jacket heat causes the evaporation of the solvent from the feed sulution. The evaporated solvent boils up, passes through a bag collector means (60) , and is re¬ covered by a condenser (62) and collected in a condensate tank (64) . When a sufficient amount of solvent has been evaporated, a paste begins to form. Mixing elements (48) are used to divide the paste, breaking it up, and bringing the interior moisture to the surface so as to expose it to the vacuum to increase the drying rate. As the material solidifies, the chopping means breaks the material into small particles to maintain the high drying rate. The feed solutions of the composition of Example 1, Example 5, and Example 6 were fed to a 130 liter Littleford ® dryer (Model FKM-130 with chopping blade). 77,6 kg of trisodium citrate/sodium acifluorfen solution of the formula in Example 1 was charged to the Littleford ® and heat-up begun, running the plough agitator at 80 rpm. No appreciable moisture was removed between 60 and 100°C with vacuums of 0.21 bar absolute in the vessel. As it approached 100°C the solution foamed violently, and the foaming could not be controlled. Example 9 An experiment similar to Example 8, using a solution of 69.4 kg of Reax 910/sodium acifluorfen was attempted using the Littleford dryer. At 80 rpm, and 60-70°C in the dryer, moisture could be slowly removed, but when the pasty state was reached, moisture could no longer be evaporated, even with the chopping blade run¬ ning, 0.07 bar absolute vacuum, and at temperatures exceeding 120°C. An examination of the interior of the dryer indicated that the material was in one large lump, and had to be chipped out. Example 10 An experiment was attempted using the feed of Example 7, BLAZER ® Technical. 68 kg of this liquid was charged and heat-up begun. A vacuum of 0.6 bar was pulled. Even at temperatures below 60°C, the batch foamed badly, and moisture could not be removed to any ap¬ preciable extent. Examples 8-10 illustrate the disadvantages of using a Littleford vacuum dryer as a means to dry these materials to a flowable pow¬ der. Whereas particular embodiments of the invention have been de- scribed above for purposes of illustration, it will be appre¬ ciated by those skilled in the art that numerous variations of the details may be made without departing from the invention as described in the appended claims.

Claims: CLAIMS : 1. A method of making a dry, flowable powder of acifluorfen or 5 its agronomically acceptable salts using a spray dryer com¬ prising dissolving a sequestrant in an aqueous solution of acifluorfen salt at an elevated temperature and drying said acifluorfen. 10 2. The method of claim 1, wherein the acifluorfen form is sodium acifluorfen. 3. A method of making a dry, flowable powder of acifluorfen using a spray dryer comprising: 15 a) injecting aqueous acifluorfen feed solution containing tri-sodium citrate into said spray dryer at a controlled rate; and 20 b) injecting an inert in the inlet air stream of said spray dryer at a controlled rate. 4. A method of making a dry, flowable powder of agronomically acceptable salts of acifluorfen using a double drum dryer 25 comprising two rotating drums with interior pressurizing means and scraping means and a nip between the two rotating drums, comprising: a) dissolving a sequestrant in an aqueous solution compri- 30 sing acifluorfen at an elevated temperature; b) charging the sequestrant/acifluorfen feed solution into said double drum dryer at a continuous rate; , 35 c) rotating each drum of said double drum dryer toward the other thereby depositing a portion of the aqueous seques¬ trant/acifluorfen feed solution on the interior drum surface, thereby forming a solid film of acifluorfen; 40 d) removing said solid film by scraping means. 5. A powder formed by the method of claim 1. 6. A powder formed by the method of claim 3. 45 7. A powder formed by the method of claim . 8. A PVA bag comprising the powder of claim 1. 9. A PVA bag comprising the powder of claim 3. 10. A PVA bag comprising the powder of claim 4.

Inventors: KILBRIDE TERENCE K JR, LISA RUDOLPH E, KILBRIDE, TERENCE, K., JR., LISA, RUDOLPH, E.
Applicants: BASF AG, BASF CORP, BASF AKTIENGESELLSCHAFT, BASF CORPORATION
Application year: 1995
Main classification: A01N37
IPC codes: A01N25, A01N37, A01P13