Note: Descriptions are shown in the official language in which they were submitted.
;53~
This invention relates to methods of preparing solid
formulations of herbicides, particularly bipyridylium ~`
herbicides.
Various herbicidal bipyridylium quaternary salts are
described ln United Kingdom Patent Specifications No.
785,732, 813,531 and 813,532. In general, these
compounds are manufactured for use in agriculture in
the form of concentrated aqueous solutions. When
required for use, these concentrated solutions are
diluted with water to form a solution which is then
sprayed upon unwanted plants. For various reasons,
for example convenience in packaging, it would be
convenient for bipyridylium herbicides to be provided
in solid form, rather than as aqueous solutions.
Various methods have been proposed for the preparation
of solid formulations of herbicidal bipyridylium
quaternary salts, but so far none of these formula-
; tions has proved suitable for wide spread commercial
use in agriculture. United Kingdom Patent Specification
813,532 for example discloses dust ormu'ations comprising ~ .
a mixture of a herbicidal bipyridylium quaternary salt
with an inert pulverulent diluent, for example, talc, :~
china clay, gypsum, or basic slag. Such formulations
are not convenient for applying bipyridylium herbicides
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6~3~
in agriculture and have not gained acceptance in
commercial use.
United Kingdom Patent Specification 1,086,937
discloses a process for the preparation of solid
herbicidal compositions in which an aqueous solution
of a herbicidal bipyridylium quaternary salt is
mixed with a hydrate-forming salt in such proportions
that the hydrate-forming salt combines with sufficient
of the water present to give a solid composition.
The compositions prepared in this way have found
acceptance in the retail market for use in domestic
gardens. However, they are not suitable for large
scale agricultural use. Thus, the proportion o~
active ingredient is relatively low, and the product
does not dissolve sufficiently rapidly. Yet another
procedure for preparing solid herbicidal compositions
is disclosed in Japanese Patent Publication 3381/73.
According to this procedure, an aqueous solutio~ of a
bipyridylium herbicide is absorbed into pre-formed
granules of a water soluble salt. As in the case of
the process of UK Specification 1,086,937, only
formulations of relatively low concentration of
active ingredient can conveniently be made.
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6~3~
A method has now been devised which is capable of
preparing a solid granular formulation containing a
relatively high proportion of the bipyridylium quaternary
salt used as the active ingredient.
According to the present i~lvention, there is provided
a process of preparing a solid granular herbicidal
composition containing a herbicidal bipyridylium
diquaternary salt in association with a solid diluent,
which comprises introducing an aqueous solution of a
herbicidal bipyridylium diquaternary salt into a fluid
bed of particles of a solid diluent maintained at an
elevated temperature, whereby the solution of the
bipyridylium salt rapidly evaporates and the bipyridylium
salt is deposited on the particles of the solid diluent
and collecting the solid granular herbicldal composition
so prepared. The term fluid bed is well known in the
chemical process art; it relates to processes in which
a gas is passed through a layer of solid particulate
material at such a velocity that the particles become
dynamically suspended in the gas stream. The layer
(i.e. "bed") of material assumes a highly turbulent
condition resembling a boiling liguid. In the present
invention it is preferred to use air as the gas for
fluidising the solid particulate material. However,
other gases (e.g., nitrogen) may be used if desired.
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~6~S3~
The fluid bed is maintained at an elevated temperatura
by heating the gas stream which fluidises the bed.
The temperature of the heated gas stream is
preferably in the range from 100 to 250C, for example
from 120 to 150C. The fluid bed temperature may
range for example from 50 to 100C. The aqueous
solution of the bipyridylium quAternary salt may be
introduced into the fluid bPd by spraying through one
or more spray nozzles. The aqueous solution may itself
be heated i desired, but no particular advantage is
gained thereby. The concentration of the bipyridylium
quaternary salt solution is preferably high, for
example at least 200 grams per lltre of bipyrldyllum
quaternary cation, so as to reduce the amount of water
which has to be evaporated.
Surprisingly, it is not necessary for the solid
particulate diluent to be insoluble in water. The
evaporation of water fxom the aqueous solution proceeds
so rapidly that even where a water-soluble diluent,
for example sodium chloride, is us~d, no difficulties
are encountered with the granules dissolving in the
aqueous solution of bipyridylium quaternary salt.
Thus both water-soluble and water-insoluble diluents
may be used. It is preferred, however, to use diluents
~.,. . ~ ~ . . .
~ ~66S3~L
which are freely water-soluble, so that when the
solid composition of the invention is to be used to
kill unwanted plants it may be completely and rapidly
dissolved in water to form a spray solution. When
; 5 an inorganic salt is used as the diluent, it is
preferred that the salt should b8 substantially free
of water of crystallisation, since hydrated salts
may decrepitate when placed in the heated air stream.
Salts which react as alkalis in agueous solution, for
example salts which have a pH o more than about 8
when dissolved in water (for example sodium carbonate)
are preferably not used as solid diluents in the
invention, because of the deleterious effects they
may have on the active ingredients of the composition,
bipyridylium quaternary salts heing less stable in
solutions of high pH.
The velocity of the air stream required to
fluidise the solid particulate diluent will depend
upon a number of factors, for example upon the
:
particle size of the dilu~nt and upon its density.
A suitable velocity i5 readily established by operation
of the process, the technology of fluid bed processes being
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6531
well known to those skilled in thc~ art, but by way of
example~ a linear air velocity of 0.9 to 1.1 metres
per second has been found suitable to maintain a bed
of sodium chloride in a fluid condition.
S Herbicidal bipyridylium quaternary salts which
may be used as the active ingredients of the
compositions o~ the invention include those of the
following formulae:-
Rl- N ~ N- R2 2 ~X~ n and ~ 2 ~X] n-
+ CH2CH2 +
wherein Rland R2,which may be the same or different,
each stand for an alkyl or alkenyl radical of 1 to 4
carbon atoms, which may be substituted by a hydroxy,
carboxy, alkoxy, alkylcarbonyl, alkoxycarbonyl, carbamoyl,
or N-alkyl-substituted carbamoyl radical, or a halogen
atom; X n represents an anion and n is 1, 2, 3 or 4.
Preferred alkoxy groups are those containing 1 to 4
carbon atoms. Preferred alkylcarbonyl and alkoxycarbonyl
groups are those containing from 2 to 5 carbon atoms.
Preferred N-alkyl substituted carbamoyl radicals are
those in which the N-alkyl substituent or substituents
contain from 1 to 4 carbon atoms.
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` 1~36653~
Examples of herbicidal bipyridylium diquaternary
salts include those listed below:-
: 1,1'-ethylene-2,2'-bipyridylium dibromide (diquat dibromide)
1,1'-dimethyl-4,4'-bipyridylium dichloride (paraquat
: 5 dichloride)
1,1'-di-2-hydroxyethyl-4,4'-bipyridylium dichloride
1,1'-bis-3,5-dimethylmorpholinocarbonylmethyl-4,4'-
bipyridylium dichloride (morfamquat dichloride)
1-(2-hydroxyethyl)-1'-methyl-4,4'-bipyridylium dichloride
1,1'-di-carbamoylmethyl-4 3 4'~bipyridylium dichloride
1,1'-bis-N,N-dimethylcarbamoylmethyl-4,4'-bipyridylium '~
dichloride
1,1'-bis-N,N-diethylcarbamoylmethyl-4,4'-bipyridylium
dichloride
1,1-di-(piperidinocarbonylmethyl)-4,4'-bipyridylium ~ '
dichloride " ~ :
1,1'-diacetonyl-4,4'-bipyridylium dichloride
1,1'-diethoxycarbonylmethyl-4~4'-bipyridylium dibromide
1,1'-diallyl-4'-bipyridylium dibromide
The names in brackets alongside some of the compounds
in the above list are the accepted common names for the
;. cationic portion of the compounds. Thus 'paraquat' is ~
`' the common name for the l.,l'-dimethyl-4,4'-bipyridylium '
' cation. Paraquat is a particularly preferred bipyridylium
"' 25 compound for use in the compositions of the invention.
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~ ~366S3~
Since the herbicidal effect of a bipyridylium
quaternary cation is independent of the nature of
the associated anion, the choice of the anion is a
matter of convenience, depending, for example, on cost.
Preferably the anion is one which gives rise to a salt
of convenient water solubility. Examples of anions,
which may be mono- or poly-valent, include acetate,
benzenesulphonate, benzoate, bromide, butyrate,
chloride, citrate, fluorosilicate, fumarate 3 fluoroborate,
iodide, lactate, malate, maleate, methylsulphate,
nitrate, propionate, phosphate, salicylate, succinate~
sulphate, thiocyanate, tartrate, and ~toluenesulphonate.
The salt of the herbicidal bipyridylium cation may be
formed from a number of similar anions or mixtures of
di~ferent ones. A salt having any particular desired
anion may be prepared either by direct synthesis from
reactants which include the desired anion, or by
exchanging the anion of a previously prepared salt for
the preferred anion by methods well known in the art,
for example by passage of a solution of the previously
prepared salt through an ion-exchange resin. For ~ -
reasons of convenience and economy, the chloride anion
- is a particularly preferred anion.
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~6~53~
Since the characteristic herbicidal activity of
a salt of a herbicidal bipyridylium quaternary cation
resides in the cation only, it is customary to quote
concentrations of active ingreclient and rates of
application in terms of the amount of bipyridylium
qùaternary cation used, thus avoiding the inconvenience
of having to quote different application rates for
different salts of the same bipyridylium quaternary
cation. Application rates and concentrations quoted
in this specification therefore relate to the amount
of bipyridylium quaternary cation unless otherwise
stated.
As noted above, in operating the process of the
invention, it is preferred to use an aqueous solution
containing a high concentration of bipyridylium quaternary
cation, for example at least 200 grams per litres.
Concentrations as high as 360 grams per litre may
conveniently be employed. The product of the process
may also contain a relatively high proportion of the
bipyridylium cation used as the active ingredient; for
example, concentrations of 20% by weight of bipyridylium
cation are readily achieved and higher concentrations
for example up to 28% by weight or more can be
conveniently prepared. Pre~erably the product contains
at least 10% by weight of bipyridylium cation.
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;6531
The process of the inventlon may be operated
either batchwise or as a continuous process.
The time taken to complete the preparation of
the product will be dependent for example upon the
temperature and velocity of the heated air stream.
By way of example, in a typica:L batch preparation,
5 kilograms of sodium chloride were fluidised in an
airstream having a velocity of 60 mPtres per mi~ute
and a temperature of 130C on the inlet side o the
fluidised bed. A solution of paraquat dichlorlde
(6 litres; 360 grams paraquat per litre) was injected
into the fluidised bed through a spray nozzle over a
period of 1 hour. The product collected at the end of
this time was a non-dusty, free-flowing granular solid
containing 27% by weight of paraquat, and was moisture-
free. The average particle size of the granules was
in the range 1 to 2 millimetres and the bulk de~sity
was 0.88 grams per millilitre.
If desired, further ingredients may be incorporated
in the composition of the invention, for example
surface-active agents. This may be done in various
ways; for example a surface-active agent may be
incorporated into the aqueous solution of bipyridylium
salt which is introduced lnto the fluid bed.
Alternatively the bipyridylium solution and the
solution of the surface-active agent may be introduced
separately from one another into the fluidised bed.
,
The amount of surface-active agent used may be,
106~
for exampl~ from 10 to 20% by weight of the amount
of bipyridylium cation in the composition,
although larger or smaller amounts may be
appropriate depending upon the applica~ion intended
- 5 for the product.
- Preferably, the surface-ac:tive agent used is a
cationic or non-ionic surface-active aæent. The choice
of a particular surface-active agent is within the
competence of one skilled in the art of pesticide
formulation. By way of example, howeverg non-ionic
surface active agents useful in the compositions of the
invention include the condensation products of ethylene
oxide with fatty alcohols such as oleyl alcohol and ;~
cetyl alcohol, or with alkyl phenols such as octylphenol,
nonylphenol and octylcresol. Other non-ionic agents
are the partial esters derived from long chain fatty
acids and hexitol anhydrides, for example sorbitan
monolaurate; the condensation products of the said
partial esters with ethylene oxide; and the lecithins.
Examples of cationic surface active agents include
quaternary salts and condensates of ethylene oxide
with amines 3 for example the substances sold under the
Trade Mark "Ethomeen" "Ethoduomeen" "Duoquad" and .
.. "Arquad".
The process of the invention may be carried out in
conventional fluid bed reactor apparatus. Fluid bed
technology is well known to those skilled in the chemical
process art. The reactor itself comprises a generally
,
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~066~3~
tubular or cylindrical vessel mounted with its long
axis vertical, and having a perforated plate closing its
lower end. The solid particulate material to be
fluidised is filled into the reactor and lies on the
perforated plate. The gas which is used to fluidise
the material is forced through the perforated plate
under pressure and passes upwards through the material.
It is preferred to maintain the pressure on the downstream
side of the perforated plate at slightly below the
atmospheric pressure outside the apparatus, for example by
means of a fan arranged to exhaust the effluent air
from the reactor. In this way, escape of fine particles
from the apparatus is prevented should a leak develop
in the walls thereof. In the process of the present
invention it is preferred to pass the effluent air from
the reactor through apparatus (for example, a cyclone)
to collect fine dusty particles which are too small to
remain in the fluid bed and which are swept through the
reactor by the air-stream. As mentioned above the aqueous
solution of the bipyridylium salt may be introduced into
the fluid bed by spraying through one or more spray
nozzles. These may be mounted, for example, in the wall -
of the fluid bed reactor or in the centre of the perforated
plate. Conveniently the solution may be pumped through a
metering pump to enable measurement of the quantity
introduced to be regulated.
1~6653~
The apparatus is shown schematically in a block
diagram in the accompanying drawing.
~ he following Example illustrates the invention.
EXAMPLE
The process of the invention was operated using
S granular calcium chloride and sodium chloride as solid
particulate diluents. The bipyridylium salt used was
paraquat dichloride, at a concentration of 360 grams
of paraquat per litre. In the run with sodium chloride,
a surface-active agent comprising a condensate of from
7 to 8 molar proportions of ethylene oxide with
~-nonylphenol and sold under the Trade Mark "Lissapol" NX
was mixed with the paraquat dichloride solution in the
proportion of 4 parts paraquat to 1 part of "Lissapol" NX,
and sprayed as a homogeneous mixture. The products
from the two runs were uniform, free-flowing, non-dusty
granules havlng an average particle size in the range
from 1 to 2 milllmetres. The operating conditions are ~-
summarised in Table I.
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