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Description  |
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Dispersions of plant protection agents can be in the form of aqueous
systems or alternatively, in rarer cases, in the form of oil dispersions.
It is known to prepare dispersions of plant protection agents by wet
grinding. In this process, the active ingredient is first precomminuted
with the aid of so-called crushers and converted to powder form. The
powdered active ingredient, together with the appropriate formulation
aids, is then mixed in water or an organic solvent to give a premix. This
premix is then ground by means of suitable wet grinding units to give the
desired dispersions.
However, this process of preparation has the disadvantage of being very
costly in terms of apparatus technology and being very energy-intensive.
Boilers and mills of a very wide variety of types are required. In
particular, the pulverizing, which affords an average particle size of ca.
2 .mu.m or less, represents a very energy-intensive process.
Surprisingly, it has now been found that dispersions of plant protection
agents can be prepared by metering at least one molten active ingredient
into a turbulent stream, produced by means of a jet, of a solution of the
formulation aids.
The present invention therefore relatcs to a process for the preparation of
dispersions of plant protection agents which contain one or more active
ingredients and customary formulation aids, wherein at least one active
ingredient is metered, in the molten form, into the outlet stream of a
jet, which stream contains an aqueous or organic solution of the
formulation aids, and the temperature difference between the active
ingredient melt and the solution of formulation aids being at least
150.degree. C.
In principle, all active ingredients which do not decompose on melting are
suitable. As regards the stability of the resulting dispersions, however,
active ingredients with a melting point above 70.degree. C. are
particularly suitable since, in the case of active ingredients with a
lower melting point, agglomerates can occasionally be formed if the
product is exposed to elevated storage temperatures above the melting
point of the active ingredient.
The process according to the invention makes it possible to prepare aqueous
dispersions and oil dispersions. For the latter dispersions, the
formulation aids are dissolved not in water but in high-boiling organic
solvents such as white oils (long-chain paraffin oils), high-boiling
aromatic solvents such as xylenes, methylnaphthalenes or the .RTM.Solvesso
types from ESSO, or high-boiling aliphatic or aromatic esters. The boiling
point of these organic solvents should not be below 150.degree. C.
However, it is preferred to prepare water-based dispersions of plant
protection agents by the process according to the invention.
The temperature difference between the active ingredient melt and the
solution of formulation aids should preferably be more than 40.degree. C.
The upper limit of the temperature difference is determined by the melting
point of the active ingredients used. In general, the active ingredient
melts used are those whose temperature is only slightly above the melting
point of the active ingredient, preferably 1.degree. to 10.degree. C.
above the melting point. The temperature of the solution of formulation
aids should appropriately be between 10.degree. and 50.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of the system according to the invention for carrying
out the process,
FIG. 2 is a sectional view of an example of the construction of a jet
device.
The process according to the invention is advantageously carried out
according to FIG. 1, in which the solution of formulation aids is
circulated.
According to FIG. 1, the active ingredient is introduced in the molten
state into a container (1). From the receiver (1), the active ingredient
melt is conveyed to the jet (4) via a heated line (2) of the shortest
possible length, by means of a suitable heatable pump (3), for example a
piston pump, gear pump or centrifugal pump. This jet (4) is located in a
circuit composed of a pump (5), a deflector (6) and an intensive cooling
system (7). In this circuit, water or organic solvent, which contains the
auxiliary substances required for the plant protection agent formulations,
is circulated in the line (8) by means of the pump (5), for example a
centrifugal pump or pressure piston pump. The auxiliary substances are
introduced into the circuit via a line (9). A line (10) is used to
ventilate the unit. The finished dispersion is removed from the circuit
via a line (11).
The active ingredient melt is metered into this circuit via the jet (4). By
means of the pump (5), a pressure of more than 0.3 bar is set up in the
region between the pump (5) and the jet (4); pressures of between 3 bar
and 40 bar are advantageous and pressures of between 4 and 35 bar are
particularly preferred. The upper pressure limit is governed by the design
of the unit. At a pressure above 40 bar, the cost of apparatus is too
great. The pressure level is regulated by appropriate choice of the
diameter of the line (8) and the choice of the jet (4) and also by the
output of the pump (5), which can be adjustable. The jet (4) and the
diameter of the line (8) are advantageously designed to have a constant
relationship. The pressure is monitored by the manometer (12).
The mixture leaving the jet (4) is expanded in the deflector (6) and then
led over the intensive cooling system (7) (heat exchanger) in order to
keep the temperature of the circulation within a constant range. The
suitable temperature of the circulated product varies with the type of
active ingredient used; it is advantageously in the range between
10.degree. and 50.degree. C.
The jet (4) to be used is shown diagrammatically in FIG. 2, it being
possible to use any commercially available jets which correspond to the
diagram of FIG. 2. The circulated aqueous solution enters the left-hand
part of the jet under slight pressure and is accelerated more strongly
through the jet restriction. At this stage, the ratio of the diameter of
the inlet tube (8) to the diameter of the jet passage (13) (narrowest
point of the jet) can vary in the range between 2:1 and 100:1, especially
between 3:1 and 30:1. The data on the diameters of the devices according
to FIGS. 1 and 2, given here and in the following text, all refer to
internal diameters. The diameter of the inlet tube (8) for the circulated
product is dependent on the flow rate of the circulation. The flow rate of
the circulation is in turn in a particular ratio to the quantity of active
ingredient metered in, this ratio being 1:1 to 500:1, preferably 1:1 to
100:1, particularly preferably between 5:1 and 50:1.
Underneath the jet restriction, the active ingredient is pumped as a melt
through the heated inlet tube (2) directly into the strongly turbulent
outlet stream. The diameter of the exit of the inlet tube (8), namely the
jet passage (13), can be between 2 and 30 mm, advantageously 4 to 10 mm,
according to the design of the unit. In the outlet piece of the whole jet,
namely in the jet exit (14), the melt is immediately micronized and
quenched because of the high turbulences or shear forces present, this
giving particles preferably having a diameter of 0.2 to 50 .mu.m. The size
of the particles can be regulated in particular via the pressure
prevailing in the circuit: the higher the chosen pressure, the finer the
resulting particles can become.
The receiver (1) of FIG. (1) represents any desired storage vessel
containing the desired quantity of active ingredient. For some active
ingredients, it can be advantageous to blanket the storage vessel with
inert gas, for example nitrogen under a pressure of between 0.1 and 10
bar, in order to be able to meter the active ingredient into the circuit
even better. In principle, it is possible to meter the active ingredient
without the pump (3) and only with the aid of this inert gas pressure. The
metering rate is variable and depends on the size of the unit.
The process according to the invention, described here as a batch process,
can also be carried out continuously, the portion of the product removed
from the circuit being replaced immediately, in a known manner, by
metering in the corresponding quantity of starting materials. This can be
regulated by known technical measuring and monitoring procedures.
Likewise, the process according to the invention makes it possible to
prepare a dispersion with several active ingredients to be dispersed, by
taking the appropriate active ingredients in the form of a mixture,
converting this to a melt and metering it into the unit, or by connecting
several storage vessels in parallel with the jet (4) or several jets.
With regard to the nature of the active ingredients, the process according
to the invention is not limited to specific types. Thus, it is possible to
use all known active ingredients of plant protection agents, such as, for
example, fungicides, herbicides, insecticides and acaricides, which, as
explained above, should have a melting point in particular above
70.degree. C. This also applies to other substances which do not have a
pesticidal activity but which can be processed to form dispersions.
Possible active ingredients are, in particular, sulfur, linuron,
endosulfan, binapacryl, monolinuron, chlortoluron, isoproturon and diuron.
Likewise, it is also possible to use the customary auxiliary substances
suitable for dispersions, such as the customary wetting and dispersing
agents, emulsifiers, thickeners and antifoams.
See, for example, Sandoz brochure 9151/82 Surfactants for Pesticides,
Soprosoie brochure (1981/82) from Rhone Poulenc, Dehydag brochure Raw
Materials for the Chemical Engineering Industry, 2nd edition (1982) from
Henkel, and Atlas-Surfactants brochure EC-G34-80 from Atlas Chemie.
The invention is illustrated in greater detail by means of the examples
which follow.
EXAMPLES 1 to 6
The apparatus shown in FIG. 1 was used with the jet according to FIG. 2.
The jet inlet tube (8) for the aqueous solution had a diameter of 14 mm
and the inlet tube (2) for the active ingredient melt had a diameter of 4
mm. The jet passage (13) had a diameter of 4.5 mm and the jet exit (14)
had a diameter of 10 mm. The ratio of the flow rate in circulation to the
quantity of active ingredient melt metered in was regulated by the
metering rate of the active ingredient melt, given below, at the
corresponding adjusted pressure in the circulation (given below). The
temperature of the circulation varied between 20.degree. and 50.degree. C.
The temperature of the active ingredient melt is given in the examples.
EXAMPLE 1
Active ingredient: 3.5 kg of endosulfan (technical grade) with a
temperature of 95.degree. C.
Auxiliary substances: 0.7 kg, consisting of the Na salt of sulfosuccinic
acid half-ester (0.4 kg), alumosilicate (.RTM.Darvan No. 3) (0.05 kg),
ethylene glycol (0.2 kg) and silicone antifoam SE2 (0.05 kg)
Water: 5.8 kg
Pressure in the circulation: 4 bar
Metering rate of the active ingredient: 7.2 kg/hour.
A stable dispersion with an average particle size of 1.5.mu. was obtained.
EXAMPLE 2
The same composition and temperature as in Example 1 were chosen. At a
pressure of 10 bar in the circulation and a metering rate of 9 kg/hour, a
stable dispersion with a particle size of 1.2.mu. was obtained.
EXAMPLE 3
Active ingredient: 4.0 kg of linuron (technical-grade) with a temperature
of 90.degree. C.
Auxiliary substances: 0.6 kg, consisting of ligninsulfonate (0.45 kg),
alumosilicate (.RTM.Darvan No. 3) (0.1 kg) and silicone anti-foam (0.05
kg)
Water: 5.4 kg
Pressure in the circulation: 7 bar
Metering rate of the active ingredient: 12 kg/hour.
A stable dispersion with a particle size of 1.6.mu. was obtained.
EXAMPLE 4
Active ingredient: 3.0 kg of linuron (technical-grade), temperature:
90.degree. C.
Auxiliary substances: 0.75 kg, consisting of 0.1 kg of .RTM.Darvan No. 3,
0.4 kg of ligninsulfonate, 0.2 kg of the Na salt of sulfosuccinic acid
half-ester and 0.05 kg of silicone antifoam
Water: 6.25 kg
Pressure in the circulation: 25 bar
Metering rate of the active ingredient: 2 kg/hour.
A stable dispersion with an average particle size of 1.1.mu. was obtained.
EXAMPLE 5
Active ingredient: 5 kg of sulfur, temperature: 120.degree. C.
Auxiliary substances: 0.5 kg, consisting of 0.25 kg of ligninsulfonate, 0.2
kg of nonylphenol ethoxylated with 30 EO and 0.05 kg of alumosilicate
(.RTM.Darvan No. 3)
Water: 4.5 kg
Pressure in the circulation: 6 bar
Metering rate: 5 kg/hour.
A stable dispersion with an average particle size of 1.6.mu. was obtained.
EXAMPLE 6
Active ingredient: 12.0 kg of sulfur, temperature: 120.degree. C.
Auxiliary substances: 2.7 kg, consisting of 1.35 kg of ligninsulfonate, 0.9
kg of nonylphenol ethoxylated with 30 EO, 0.3 kg of antifoam and 0.15 kg
of .RTM.Darvan No. 3
Water: 15.3 kg
Pressure in the circulation: 8 bar
Metering rate: 6 kg/hour.
A stable dispersion with an average particle size of 1.5.mu. was obtained.
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