`
`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applicatio.ns under the PCT.
`
`AL
`AM
`AT
`AU
`AZ
`BA
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`Cl
`CM
`CN
`cu
`CZ
`DE
`DK
`EE
`
`All>ania
`Annenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Herzegovina
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
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`Canada
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`Congo
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`
`ES
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`
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`
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`Sri Lanka
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`
`LS
`LT
`LU
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`MK
`
`ML
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`MR
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`NE
`NL
`NO
`NZ
`PL
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`RO
`RU
`SD
`SE
`SG
`
`Lesotho
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`Luxembourg
`Latvia
`Monaco
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`The former Yugoslav
`Republic of Macedonia
`Mali
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`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
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`Sudan
`Sweden
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`
`SI
`SK
`SN
`sz
`TD
`TG
`TJ
`TM
`TR
`TT
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`UG
`us
`uz
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`YU
`zw
`
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`
`
`
`WO98/26656
`
`PCT/US97 /22520
`
`CHEMICALLY STABLE, INSECTICIDALLY ACTIVE
`PHOSPHOROAMIDOTHIOATE PELLET COMPOSITIONS
`AND METHODS FOR THEIR MANUFACTURE
`
`FIELD OF THE INVENTION
`The present invention is directed to chemically
`stable,
`low moisture content,
`insecticidally active
`pellet compositions and methods for their manufacture.
`
`BACKGROUND OF THE INVENTION
`phosphoroamidothioates
`and
`Certain
`phosphoroamidodithioates (collectively referred to as
`"phosphoroamidothioates" for convenience) are known in
`the art as having excellent insecticidal activity against
`a variety of insects and in a variety of environments.
`A particularly important commercial insecticide within
`this class of compounds is the insecticide acephate
`(generic name) or Orthene® (trade name), which can be
`systemically taken up by a plant so that insects which
`feed and/or live on the plant are killed, in addition to
`those insects which directly ingest or are contacted by
`the insecticide. Acephate and related compounds are
`described in U.S. Patent Nos. 3,716,600, 3,845,172 and
`3,914,417, which disclose that
`in addition to their
`insecticidal properties, the compounds possess very low
`mammalian toxicity. Orthene® is commercially produced as
`a technical grade chemical of about 97 to 99.5% purity,
`which is often referred to as acephate technical or
`acephate TG (technical grade).
`
`
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`WO98/26656
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`PCT/US97 /22520
`
`Acephate technical is commercially available as a
`powder, which has a tendency to clump or agglomerate.
`In
`the past, acephate technical has been applied to crops as
`a dust (for example, after exposure to moisture via rain,
`dew or irrigation), or in spray form as a water solution
`spray.
`Dusts are undesirable because of airborne
`contamination and handling difficulties, while liquid
`spray
`formulations
`involve
`solvent
`and packaging
`expenses,
`and container disposal
`requirements
`that
`detract from commercial desirability.
`Accordingly, in recent years, attention has turned
`to a pellet form of application for acephate and its
`related
`insecticidal compounds.
`Pellets have
`the
`practical advantages of eliminating dust problems and
`reducing offensive odors in comparison to powder forms
`because of a
`reduced surface area to weight ratio.
`However,
`problems have been encountered
`in
`these
`pelletization efforts and to date, high-strength acephate
`pellets have not been commercialized, most likely due to
`processing difficulties.
`Phosphoroamidothioate-containing pellets have been
`proposed
`in U.S. Patents 5,075,058, 5,100,667 and
`5,464,623, each of which is assigned to Chevron Research
`and Technology Company.
`Each of these three patents
`recognizes
`the difficulties
`in pelletizing acephate
`technical, and proposes certain types of pellets made,
`for example, by extrusion. For example, the '058 Chevron
`patent states in the paragraph bridging columns 2-3 that
`attempts to manufacture acephate technical pellets from
`heretofore
`acephate
`technical
`powder
`"have
`been
`unsuccessful". Similar statements are made in each of
`the '667 and '623 Chevron patents. The present inventors
`have conducted considerable experimentation in the area
`of producing high-strength acephate pellets, and have
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`WO98/26656
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`PCT/0S97/22520
`
`the
`the manufacturing difficulties which
`confirmed
`Chevron inventors apparently experienced. Furthermore,
`the pellets and methods proposed for making
`them as
`discussed in the three Chevron patents leave considerable
`room for
`improvement.
`In this regard, while
`these
`patents generally describe extrusion of solid pellets,
`few details of the actual extrusion process are set
`forth. Moreover, the Chevron patents generally propose
`the addition of costly surfactants (see '667 patent), the
`combination of the phosphoroamidothioate with a second
`active ingredient (see '058 patent), and the creation of
`a mixture of the active ingredient with a solvent in an
`amount of from 3-25% by weight before extrusion.
`To satisfy the need in the art for a
`low cost,
`chemically
`stable,
`insecticidally
`active
`phosphoroamidothioate granular formulation, one of the
`present inventors developed an insecticidally active
`composition
`comprising particles prepared by
`the
`compaction of an admixture comprising ammonium sulfate
`and
`at
`least
`one
`insecticidally
`active
`phosphoroamidothioate. This composition and methods for
`its manufacture and use are described in U.S. Patents
`5,298,501, 5,352,674, and 5,369,100. As set forth in
`these patents, it was found that the use of ammonium
`sulfate in particular leads to a compacted composition
`which provides a high degree of chemical stability.
`U.S. Patent 5,443,764 issued August 22, 1995, and
`related U.S. Patent 5,622,658 issued April 22, 1997, each
`assigned to ICI Australia Operations Proprietary Ltd.,
`disclose
`a process
`for
`the preparation of water(cid:173)
`dispersible granules. The process comprises mixing the
`desired ingredients of the granules to form an extrudable
`composition, extruding
`the mixture and rolling
`the
`extrusions to break them down into granules.
`In contrast
`
`-
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`WO 98/26656
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`
`to the pellets of the present invention, the granules
`disciosed in these ICI patents are designed to have rapid'
`dispersion and superior suspensability in water.
`The
`granules of
`the
`ICI patents
`comprise
`an active
`agricultural chemical (including, e.g., insecticides) and
`normally have a surfactant component and/or a binding
`agent. The particular class of insecticidal compounds
`included in the pellets of the present invention are not
`disclosed in the ICI patents, although a wide variety of
`insecticidal active ingredients are stated to be useful.
`Thus,
`there is a need in the art for chemically
`stable,
`high
`strength,
`insecticidally
`active
`phosphoroamidothioate pellets which are useful from a
`practical standpoint, 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
`
`One object of the present invention is to provide
`chemically stable, high strength, insecticidally active
`phosphoroamidothioate pellets.
`invention is to
`Another object of
`the present
`provide a commercially viable process for manufacturing
`chemically stable, high strength, insecticidally active
`phosphoroamidothioate pellets having a
`low moisture
`content.
`Still another object of the present invention is to
`provide an economically practical process for producing
`such insecticidal pellets , which avoids
`the use of
`organic sol vents and most other additives previously
`proposed.
`The above and other objects and advantages of the
`present
`invention can be attained by a process for
`
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`WO98/26656
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`PCT/US97 /22520
`
`low moisture content pellets comprising an
`producing
`insecticidally active compound of the formula:
`
`0
`II
`R - y 0
`C - R2
`\t
`I
`p - N
`\
`I
`RJ
`Rl - s
`
`wherein Rand R1 individually are an alkyl, alkenyl
`or alkynyl group containing up to 6 carbon atoms, R2 is
`hydrogen, an alkyl group containing 1 to 18 carbon atoms,
`a cycloalkyl group containing 3 to 8 carbon atoms, an
`alkenyl group containing 2
`to 18 carbon atoms or an
`alkynyl group containing 3 to 18 carbon atoms, R3 is
`hydrogen or an alkyl group containing 1 to 6 carbon
`atoms, and Y is oxygen or sulfur, comprising the steps of
`feeding a powder comprising at leas t about 95% by
`weight of said insecticidally active compound to an
`extruder,
`feeding water to the extruder during at least a
`portion of feeding of said powder, the water contacting
`the powder to form a mixture,
`extruding an extrusion product while controlling the
`temperature within the extruder and the rate and quantity
`of water fed to the extruder to minimize tackiness and
`clumping together of the extrusion product, and
`forming pellets having a moisture content of less
`than about 0.5% by weight from the extrusion product.
`As discussed further herein, chemically stable
`pellets can be manufactured in accordance with the above
`process.
`In certain preferred embodiments, the pellets
`comprise an insecticidal compound as described above,
`preferably acephate, in an amount of at least about 97%
`
`- 5 -
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`WO 98/26656
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`PCT/US97 /22520
`
`by weight, more preferably virtually 100% by weight, and
`water in an amount of up to about 0.5% by weight.
`the
`In other particularly preferred embodiments,
`pellets have a low moisture content sufficient to avoid
`caking or compaction upon storage. Typically, moisture
`levels of about 0.3 wt% or less, preferably 0.2 wt% or
`less, will give unexpectedly good
`long-term storage
`properties, assuring flowability of the product.
`In addition
`to
`the
`above-described process,
`chemically stable pellets can be manufactured using a low
`pressure basket extrusion process, comprising the steps
`of
`
`providing a powder comprising at least about 95% by
`weight of
`the above-described
`insecttcidally active
`compound,
`contacting the powder with water to form a damp or
`wet mixture, and thereafter
`extruding an extrusion product of predetermined
`diameter from the damp or wet mixture,
`forming pellets from the extrusion product, and
`drying the pellets to a moisture content of less
`than about 0.5% by weight.
`Preferably the drying conditions are controlled so
`that the resultant pellets have a moisture content of
`less than about 0 . 3% by weight.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`showing water content vs.
`is graph
`Figure 1
`flowability for pellet samples stored at 40°c, as
`discussed in Example 8 below.
`showing water content vs.
`is graph
`Figure 2
`flowability for pellet samples stored at 50°C, as
`discussed in Example 8 below.
`
`- 6
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`WO98/26656
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`PCT/US97 /22520
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`the
`In
`the
`present
`invention,
`term
`"phosphoroamidothioate II refers to a compound or a mixture
`of compounds of the formula:
`
`0
`II
`R - y 0
`C - R2
`\t
`I
`p - N
`I
`\
`Rl - s
`R3
`
`wherein Rand R1 individually are an . alkyl, alkenyl or
`alkynyl group containing up to 6 carbon atoms, R2 is
`hydrogen, an alkyl group containing 1 to 18 carbon atoms,
`a cycloalkyl group containing 3 to 8 carbon atoms, an
`alkenyl group containing 2
`to 18 carbon atoms or an
`alkynyl group containing 3 to 18 carbon atoms, R3 is
`hydrogen or an alkyl group containing 1 to 6 carbon
`atoms, and Y is oxygen or sulfur.
`Such ·compounds are
`sometimes characterized in the art as N-hydrocarboyl
`phosphoroamidothioatesandphosphoroamidodithioates (see,
`e.g., U.S. Patents 5,075,058, 5,100,667 and 5 , 464,623
`discussed above). It would be apparent to one skilled in
`the art that the same class of insecticides is intended
`for use in the present invention as
`in the patents
`described in the Background of the Invention .
`Particularly preferred compounds for use in the
`present
`invention are
`those
`in which R and R1 are
`independently a methyl, ethyl, allyl or alkenyl group; R2
`is Hor an alkyl group; R3 is hydrogen; and Y is oxygen.
`The most preferred compound, acephate, is that in which
`R, R1 , and R2 are methyl groups, R3 is hydrogen and Y is
`oxygen. Compounds of the above formula may be prepared
`as described in U.S. Patent Nos. 3,176,600, 3,845,172 and
`
`- 7 -
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`WO98/26656
`
`PCT/US97 /22520
`
`incorporated herein by
`
`3,914,417, each of which is
`reference in its entirety.
`Acephate is commercially available in high strength
`technical form from Chevron Chemical Company, San Ramon,
`California.
`Such high strength acephate technical is
`sold under the trade name of Orthene® 97SP,
`typically
`contains acephate in at least about 97% purity,
`the
`remainder being impurities, and is sold as a powder. It
`is preferred that the active ingredient comprise as close
`to 100% of the technical powder as possible. Acephate
`contents of about 99 to 99.5% purity are common and are
`most pref erred.
`As noted above, acephate
`technical
`powder has a tendency to clump and agglomerate over time,
`and has proven to be difficult to process, as recognized
`in the art.
`One or a mixture of the above compounds forms the
`insecticidally active component in the pellets of this
`invention.
`The present
`invention
`is particularly
`directed
`to
`formation
`of
`"high
`strength"
`phosphoroamidothioate pellets containing a minimum of
`about 95% by weight active ingredient, preferably at
`least about 97% by weight active ingredient, and most
`preferably as close to 100% by weight active ingredient
`as possible (e.g., in the range of about 99 to 99.5% by
`weight). The pellets are characterized as having a "low
`moisture" content, which means that they can contain
`water in an amount up to about 0.5% by weight.
`In the
`present invention, the phrase "up to about 0.5% water"
`means
`from relatively small amounts on the order of
`0.001% by weight (although moisture measurements at this
`level are difficult to make, it is believed that even
`where the pellets are dried to remove moisture or where
`the pellets are stored under low humidity conditions for
`a significant time, the pellets do not become completely
`
`-
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`8
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`-
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`WO98/26656
`
`PCT/US97/22520
`
`moisture-free) up to about one-half percent by weight.
`Moist-ure amounts generally fall into the range of about.
`0.05 to about 0.5% by weight, preferably from 0.1 to 0 . 3%
`by weight.
`One of ordinary skill in the art would
`understand
`that
`the upper specified
`limit
`is not
`absolute, however, and . that under certain conditions of
`high humidity and the like, the pellets might absorb
`moisture
`in quantities
`somewhat greater
`than 0.5%.
`Nonetheless, in view of moisture's deleterious effects on
`chemical stability of the pellets, an upper limit in the
`neighborhood of 0.5% by weight has shown to provide good
`results. Also, as discussed further below, a pellet
`moisture content of about 0.3% by weight or less, even
`more pref er ably O. 2 % by weight or less, is pref erred from
`the standpoint of excellent storage properties.
`Further, if desired the pellets can contain small
`amounts of a processing aid to enhance the ability of the
`active ingredient to be extruded. For example, extrusion
`tests have been conducted in which the active ingredient
`was
`pre-mixed with
`about
`1. 5%
`by weight of
`a
`vinylpyrrolidone-vinyl acetate copolymer (sold under the
`trade name Agrimer VA-6, available from ISP), and good
`results were obtained. On the other hand, the pellets of
`the invention can be suitably manufactured without the
`need for a . surfactant or binding agent, as required in
`certain prior formulations. Thus, the pellets of this
`invention are desirable from an economical standpoint.
`Further, it has been unexpectedly discovered that the
`phosphoroamidothioate compound can be extruded
`into
`chemically stable pellets using only water as
`a
`processing aid, under the conditions discussed herein.
`Accordingly, while small quantities of processing aids
`other than water, such as Agrimer VA-6 or related vinyl
`copolymers, can be admixed with the active ingredient
`
`- 9
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`WO 98/26656
`
`PCT /US97 /22520
`
`in amounts generally
`prior to extrusion, if desired,
`rang::i:-ng from about 0.5% up to several or more percent by·
`weight,
`the present
`inventors have determined
`that
`chemically stable pellets can be obtained without such
`processing aids, using acephate technical in particular.
`One of ordinary skill in the art would readily recognize,
`however,
`that minor amounts of processing aids and/ or
`other inert ingredients could be admixed with the active
`agent,
`if desired, depending
`for example on
`the
`particular insecticidal compound selected, as long as the
`addition of such materials did not conflict with or
`adversely affect the basic characteristics of the pellets
`formed in accordance with the teachings of the present
`invention.
`In certain preferred forms of the present invention,
`the pellets consist essentially of acephate technical and
`water in an amount of up to about 0.5% by weight. Thus,
`depending on the purity of the technical reagent, it is
`possible
`in accordance with
`the
`invention
`to
`form
`chemically stable, high strength, insecticidally active
`phosphoroamidothioate pellets that contain virtually 100%
`(e.g., 99 to 99.5% or greater) active agent. To the best
`of the inventors' knowledge, chemically stable pellets of
`such
`high
`strength
`have
`heretofore
`never
`been
`manufactured.
`Such high
`strength pellets
`have
`significant advantages,
`such as permitting maximum
`concentrations of
`insecticidally active agent
`to be
`utilized in the field, and excellent stability.
`The pellets according to the present invention are
`typically cylindrically shaped, although they can take on
`any suitable shape in cross-section (e.g., hexagonal)
`depending on the shape of the extrusion die orifice. An
`average diameter of the pellet in cross-section can be
`from about 1 to about 7 mm, preferably 1. 2
`to 3 · mm.
`
`- 10 -
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`WO98/26656
`
`PCT/US97 /22520
`
`Certain pref erred pellets recently extruded using the
`high- pressure axial extrusion method described herein
`were cylindrically shaped and had a cross-sectional
`diameter of about 5/64 11
`(about 2 mm). The length of the
`pellets is variable, but typically is in the range of
`from about 3 mm up to about 25 mm, preferably from about
`3 up to about 6 mm.
`the present
`to
`The pellets produced according
`invention are chemically stable, and have a commercially
`satisfactory shelf life on the order of about 2-4 years,
`during which time they generally remain free-flowing and
`avoid the raw powder's
`tendency to agglomerate.
`As
`discussed further below, it has now been discovered that
`excellent flowability can be mainitained over time when
`the pellets are produced so as to have a moisture content
`of about 0.3 wt% or less. The pellets generally have a
`white appearance but may have a yellowish tint, and are
`of sufficient hardness to avoid creation of significant
`quantities of dust during handling due
`to pellet
`crumbling and the like. For pellets produced by the high
`pressure axial extrusion process described herein,
`average bulk density has been determined to range from
`about 36 to about 40 lbs/cubic foot, and typically is
`about 37 lbs/cubic foot. Using the low pressure type of
`basket extrusion process also described herein,
`the
`average bulk density of the pellets typically ranges from
`about 28 to about 31 lbs/cubic foot.
`A significant
`advantage is that the pellets are preferably formed
`without the use of organic solvents, as discussed below,
`and without the use of conventional formulating agents
`which is not only advantageous economically, but which
`results in higher strength pellets, while still retaining
`sufficient physical properties such as hardness and
`
`- 11 -
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`WO98/26656
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`PCT/US97 /22520
`
`reducing the offensive odors associated with prior powder
`appltcations.
`Once formulated, the pellets are useful in a method
`for controlling insects by application of the pellets
`onto the insects' habitat.
`In general, the pellets can
`be applied onto the habitat in an amount sufficient to
`provide acceptable control of
`the
`insects.
`In a
`preferred embodiment, the pellets are applied at a rate
`of at least about 0.5 lbs. active ingredient per acre and
`more preferably at a rate of from about 0.5 lbs. to about
`one lbs. active ingredient per acre.
`
`High Pressure Extrusion
`The pellets according to the present invention can
`be manufactured by a high pressure axial extrusion
`process as follows, using acephate
`technical as an
`exemplary insecticidal compound within the scope of the
`present invention.
`Acephate technical powder having a minimum purity of
`about 97% by weight (preferably 98% or greater, more
`preferably 99% or greater and most preferably 99.5% or
`greater purity) is first subjected to a delumping step in
`a conventional mill or the like, if necessary to reduce
`or eliminate clumps of material that may have formed due
`to the material's agglomeration tendency described above.
`Delumped technical powder provides for better flowability
`during extrusion.
`Next, the delumped acephate technical powder can be
`blended with a small quantity (e.g., from about 0.5 to
`about 3.0% by weight) of a processing aid (other than
`water) , such as the Agrimer VA- 6 copolymer described
`above. However, such a step is not necessary to achieve
`pellets in accordance with the present invention, but may
`assist flowability during extrusion, particularly for
`
`- 12 -
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`WO 98/26656
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`PCT/US97/22520
`
`In some examples described
`some insecticidal compounds.
`below, a mixture of Orthene® 97SP (lot# Rl2095, targe~
`active ingredient= 97.5%, assayed at 99%) and Agrimer
`VA-6 (lot# CCS0907S) was prepared by blending in a mixer
`at a weight ratio of 2000 lbs/30 lbs= 98.5% / 1.5%. As
`described above, however, such processing aids are not
`essential
`in practicing the present
`invention.
`If
`desired, however, other processing aids besides Agrimer
`VA-6 can be used, as would be apparent to one of ordinary
`skill in the art. The blend thus formed, or the delumped
`technical,
`can be
`stored
`in drums until needed.
`Alternatively, delumping and blending, if carried out,
`can be part of a continuous in-line process.
`The acephate technical powder is then placed into a
`suitable apparatus for supplying
`the powder
`to
`the
`extruder. The supply can either be continuous over the
`course of a desired production run, or alternatively,
`measured batches can be supplied.
`In one embodiment, the
`powder feed system to the extruder was an Acrison Auger
`type feeder, modified with a large feed hopper into which
`the powder is placed. Using this apparatus the powder
`feed rate can be controlled as desired by calibrating a
`variable speed drive before start-up, and controlling the
`feed rate during operation. During pilot plant tests,
`the unit was calibrated to allow for a variable flow rate ·
`of from about 90 lb/hour to about 250 lb/hour, although
`it would be understood that actual flow rates during
`commercial production runs would depend on the particular
`equipment in use.
`for
`a process
`embodiment of
`In
`this
`first
`manufacturing pellets according to the present invention,
`'the extruder is preferably an axial extruder, of which
`various types are known.
`In the tests using the modified
`Acrison Auger type feeder, the extruder was a Bepex 6-
`
`- 13 -
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`WO98/26656
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`PCT/US97 /22520
`
`inch diameter Extrud-o-mixer extructor, a pilot scale
`model-of which larger versions exist (including one with,
`a 12-inch diameter). The six-inch diameter refers to the
`diameter of the barrel or screw housing. The extructor
`includes an outer orifice plate or die located on the
`front end through which the screw pushes the material
`through multiple orifices under pressure.
`If desired,
`the extructor can also contain an internal orifice plate
`to improve mixing inside the barrel of the extruder. The
`holes in the outer orifice plates determine the shape of
`the extrusion product or extrudate.
`In most of the tests
`described herein, the holes were circular of about 2 mm
`(about 5/64") diameter, which provided extrudate in the
`form of "noodles" or cylindrical pellets depending on
`their length.
`City tap water can be used as the water source for
`the process.
`In the pilot plant runs using the above(cid:173)
`described equipment,
`the water was supplied to
`the
`extruder using a tap off of a city-feed line. A flow
`regulator was
`installed in
`the
`line which allowed
`regulation and monitoring of the water feed within ranges
`of from 4 cc/minute (about 0.5 lb/hour) to 50 cc/minute
`(about 6. 6
`lb/hour) .
`The point at which the water
`contacted the powder in the extruder was about six inches
`downstream from where the powder entered the extruder.
`An important aspect of this particular embodiment of
`the present invention relates to the actual extrusion
`step. It has been unexpectedly discovered that both the
`temperature of the extruder barrel during extrusion as
`well as the rate of water flow are key factors which
`determine whether commercially viable, high strength
`acephate pellets can be produced. During extrusion,
`temperatures inside the barrel tend to increase due to
`The amount of
`pressure build-up and material mixing.
`
`- 14 -
`
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`WO98/26656
`
`PCT/0S97 /22520
`
`in the extruder directly
`water added to the powder
`affects the temperature inside the barrel. Further, test'
`results have established
`that
`the most preferred
`temperature range within the barrel during extrusion of
`acephate technical is from about 145° to about 160° F;
`within such a range,
`the acephate material reaches a
`semi-molten state which has been determined
`to be
`important
`to
`successful
`extrusion.
`At
`higher
`temperatures within the extruder, the extruded noodles
`have a tendency to become too mushy and tacky, and thus
`stick and
`clump
`together.
`Within
`the preferred
`temperature range of about 145-160° F, a preferred rate
`of water addition was determined to be in the range of
`about 0.4 up to about 1.0% by weight water, and even more
`preferably around 0.5% by weight water.
`Neither the above-identified preferred temperature
`ranges or rates of water addition are absolute values.
`The important concept is one of controlling each of these
`variables, in tandem, to achieve the desired extrudate
`which is practically workable.
`For example, during
`start-up of the extruder, a higher amount of water should
`be used until the internal temperature reaches a desired
`level, at which point the rate of water addition can be
`decreased to be within the preferred ranges. Further, at
`higher
`temperatures
`it will be
`seen
`that
`lesser
`quantities of water are needed to give the desired noodle
`consistency, although at some point the temperature can
`exceed that at which the extrudate is practically useful
`because of undue tackiness. Such a point is believed to
`be reached when the acephate (or other active agent)
`exceeds its semi-molten state and melts. Of course, the
`extrusion
`temperature
`range pref erred
`for other
`insecticidal compounds within the scope of the invention
`
`- 15 -
`
`
`
`WO98/26656
`
`PCT/US97 /22520
`
`will vary depending on the melting point of specific
`compGunds and the quantities of water employed. At lower
`temperatures within the extruder,
`the powder is less
`molten; conversely, a higher rate of water addition is
`typically required.
`In some cases, after start-up and
`with a relatively slow material feed, it may be possible
`to maintain
`the
`temperature within
`these preferred
`parameters while reducing water addition to a drip, or
`stopping it altogether for a portion of a run.
`In this
`regard, it will be apparent that the rate at which the
`powder is fed to
`the extruder will also
`impact
`the
`internal
`temperature of the extruder, with a slower
`rate/lesser quantity developing less internal heat, and
`a higher rate/greater quantity generating more internal
`heat.
`Thus, a key aspect of the invention is to carry out
`the extrusion step while controlling the temperature
`within the extruder and the rate and quantity of water
`fed to the extruder such that the extrusion product or
`extrudate has a consistency with minimal stickiness and
`clumping together. Also, an extrudate which is too wet
`due to excessive water addition is not preferred because
`it can lead to stickiness and/or a
`requirement for
`excessive drying of the extrudate for a period sufficient
`to achieve the target moisture level of about 0.5% or
`less.
`To aid in avoiding noodle clumping as the extrudate
`exits the extrusion die orifice, cooled air can be blown
`across
`the outer orifice to accelerate cooling and
`hardening of the noodles, with resulting decrease in
`tackiness as they harden. Alternatively, the throughput
`rate of the material being extruded can be
`lowered,
`giving the noodles more time to cool before corning into
`contact with each other.
`
`- 16 -
`
`
`
`WO 98/26656
`
`PCT/US97 /22520
`
`The extrusion product formed in the above manner is
`formed into pellets. This can be done by simply allowing·
`the extrusion product to cool and harden, which will lead
`to
`formation
`of
`pellets
`of
`variable
`lengths.
`Alternatively, as the extrusion product exits the die
`plate, the product can be cut to appropriate size -- for
`example, into more uniformly sized pellets of from 3-10
`mm in length.
`Drying of the extrusion product can be performed, if
`desired or as necessary to obtain pellets having a
`low
`moisture content. For example, drying is more likely to
`be carried out on extrusion product formed at or shortly
`after start-up during which higher quantities of water
`are generally used and the noodles are wetter.
`The dryer can be a vibratory fluid-bed of suitable
`dimensions with steam-supplied heat.
`The exhaust is
`provided by a baghouse that pulls moisture and heat from
`the extrusion product. Temperature, airflow into, and
`amount of pull are all variable. The airflow and exhaust
`are adjusted to provide a fluidized bed of pellets and a
`slight negative pressure inside the dryer. Temperature
`is monitored at both the inlet and the outlet of air.
`The vibrating motion of the drying bed aids in reducing
`the length of the noodles, which can initially be quite
`long, but which break down upon cooling and hardening.
`In some instances a separate mechanical force (e.g., a
`Stokes delumper) could be applied to assist in.breaking
`down the noodles into shorter pellets as well as breaking
`up clumps of noodles excessively stuck together, if it is
`desired to reduce the amount of overs.
`The dried pellets can be screened to eliminate fines
`and overs, if desired. Pellets within the size ranges
`generally described above can be obtained using an 18-
`inch Sweco fitted with 6-mesh and 10-mesh screens. Overs
`
`- 17 -
`
`
`
`WO98/26656
`
`PCT/US97 /22520
`
`and fines can be recycled to the raw material hopper to
`be fed through the extruder again, if desired.
`The
`following
`Examples
`illustrate
`specific
`embodiments of the invention but should not be construed
`as limiting the scope of the claims in any way.
`In the
`Examples as well as other parts of this application, all
`parts, percents, ratios and the like are by weight unless
`otherwise indicated.
`
`Example 1
`
`RUN 9623201
`Powder feed was started before the water at a rate
`of 90 lb/hr.
`The powder was a 98. 5%/1. 5% mixture of
`acephate technical and Agrimer VA-6, as described above .
`In the past it has proven best to begin extrusion a
`little on the wet side and slowly decrease the water to
`the desired rate.
`The desired rate ( 1. 5%) for the 90
`lb/hr of powder was 10 cc/m, or 1.3 lb/hr. The rate used
`at start-up was between 20 and 30 cc/m (2.6 - 4.0 lb/hr
`or 2.8% - 4.3%) until noodles were formed. As soon as it
`was determined the extrusion process (forming noodles)
`was stable, the water was slowly cut back to betwe
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