Application Reports

Manufacture of Pesticides

Pesticides can be categorized into several groups - Fungicide, Herbicide, Insecticide, etc. There are many different methods of application and use and products are available in a number of formulation types, e.g. powder, granules, liquid concentrates and sprays. 

Pesticides are typically suspensions of insoluble active ingredients in water; aqueous or oil based solutions are also used. Small amounts of ingredients such as thickeners, antifreeze, antiforming agents and dispersion and wetting additives complete the formulation. The active ingredient content varies considerably, although this is typically around 50%.

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The Process

Typical processing methods can be summarized as follows: 

The premixing system must be capable of meeting the following process requirements:

  • Incorporating and dispersing large volumes and high proportions of powders.
  • Some degree of particle size reduction is required.
  • Each formulation has its own set of process conditions - the system must be versatile and adaptable to the many variations in product type.

The Problem

  • High speed dispersers used for the premixing stage have a high energy requirement.
  • Similarly, ball milling is a slow, energy intensive process.
  • Agitators are not capable of readily breaking down agglomerates and have difficulty in wetting out light powders which tend to “raft” or float on the liquid surface.
  • Some ingredients, e.g. thickening agents, only make up a very small proportion of the formulation, but must be correctly dispersed to obtain functionality.
  • A poorly dispersed premix will require more passes through the mill, further increasing process time and energy requirements.
  • Active ingredients can be harmful to the operator. Powders must therefore be incorporated into the base liquid as hygienically and safely as possible, with minimized handling and dust emissions. 

The Solution

The above problems can be overcome by premixing with a Silverson High Shear mixer. The three stage action of the rotor/stator workhead draws liquid and solid ingredients into the mixing zone, subjects them to intense hydraulic and mechanical shear, then projects them back into the mix. In a short mixing cycle all the material passes through the workhead many times, progressively reducing particle size. This produces a uniform low particle size premix for the milling stage. 

The Advantages

This offers a number of advantages: 

  • Rapid dispersion of the powders.
  • The intense shearing action of the rotor/stator workhead breaks down agglomerates.
  • Guaranteed particle separation of pre-micronized powders.
  • Reduced energy requirements.
  • Improved process hygiene.
  • The shorter processing time required to incorporate the powders reduces dust emissions.
  • A single machine can carry out several different mixing operations on a wide range of product types.
  • Improved consistency and uniformity of premix dramatically reduces the time taken in subsequent milling stages. In some cases a single pass is sufficient to obtain the required particle size after premixing with a Silverson. 

 

The batch size, formulation, type of ingredients and the viscosity of the product dictates which machine from the Silverson range is suited to individual premixing requirements: 

High Shear Bottom Entry Mixers

  • No immersed shaft - reduces cleaning requirements
  • An In-Line mixer can be added in a recirculation system to further reduce process time
  • For larger batches or higher viscosity products an agitator may be required to maintain in-tank uniformity

High Shear Batch Mixers

  • Vessel mounted batch mixers are suitable for volumes of up to 2600 US gallons. These can be used in conjunction with supplementary in-tank agitators if required
  • Small/medium units are suitable for batches of up to 260 US gallons. They can be vessel mounted on mobile floor stands and easily moved from vessel to vessel
  • Laboratory and pilot scale units available

Silverson Flashmix

  • Ideal for large batches
  • Capable of rapidly incorporating large volumes of powders
  • Minimized aeration
  • Minimized cleaning requirements
  • Suitable for higher viscosity mixes
  • Suitable for operation at higher temperatures
  • Dust extraction systems available
  • Ultra Sanitary models available
  • Minimum operator input required

High Shear In-Line Mixers

  • Ideal for large batches
  • Aeration free
  • Easily retrofitted to existing plant
  • Self-pumping
  • Can be used to discharge vessel
  • Ultra Sanitary models available
  • Multistage units available
  • High Viscosity models available 

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