Today’s high agricultural yields would not be achievable without pesticides. They are indispensable for feeding the world’s growing population. To manufacture pesticides, modern processing facilities are necessary. For greater safety, the multi-stage syntheses and formulation steps therefore take place in enclosed systems. What contribution our devices can make in this challenging process environment based on their special design features is described in this article.
The term pesticides groups together substances with different effectiveness levels (see Table 1). These are chemical or biological high-tech active ingredients, which are used against undesirable organisms found in the agriculture sector with the aim of maximising yield.
The global market for pesticides is huge. Herbicides reach the largest production volume, followed by insecticides and fungicides. Worldwide sales of pesticides hit almost 48 billion euros in 2018 - a plus of 0.5 per cent compared to the previous year (Figure 1). Asia is by far the most important market, ahead of Latin America and Europe. Sales in Germany over the same period amounted to 1.3 billion euros. The figure has been declining in this country since 2015.
The amount of pesticide sold in Germany was around 48,000 tonnes in 2016 and thus increased by half over ten years (2006: approx. 32,000 tonnes). Herbicides make up around 40 % of this, fungicides around 25 % and insecticides around 30 %.
In Germany, approximately 270 active ingredients were approved in a total of 753 different pesticides in 2016. The research sector is working on sustainable active ingredients, which ideally decompose after being spread and unfolding their targeted effect, leaving no residue.
It takes about ten years of intensive development work, however, before an approved pesticide can be launched on the market. During this period, a manufacturer will invest about 200 million euros, conduct around 200 studies and perform tests using more than 800 parameters.
First of all, a search for suitable substances takes place and pilot projects are tested in the laboratory. Even for these tests, the active ingredients are converted from formulations into products that can be ap- plied in agriculture. For this purpose, so-called carriers – powdered minerals or organic solvents – as well as additives (usually surfactants acting as emulsifiers, wetting or adhesive agents) are used. The job of the coformulants is to make the active ingredients technically safe and usable so that spreading them is safe and their effectiveness is optimal.
Different preparation technologies are then weighed up against each other: for example, micronisation – grinding very finely for a uniform suspension in water and then later safely spraying or dripping it on the crop plants – or encapsulation, which automatically regulates the availability and effect of the substance.
Once all parameters and other attributes relating to the application have been optimised, pilot trials are
carried out in the test centre. The aim is to synthesise the active ingredient
in a way that makes it pure, stable, highly concentrated and reproducible. This project phase is particularly challenging from a process engineering point of view, because the piloted apparatus must be adequately capable of being scaled up in order to overcome the subsequent mass flows and batch sizes, which are larger by a factor of 20 to 100 as a rule.
The synthesis steps for manufacturing pesticides differ depending on the active ingredient and preferred spreading method. The basic process steps are similar, however, for the basic powdered substances.
First of all, a solvent is placed in the reactor, powdered reagents are added and dissolved or homogeneously suspended. The first reaction step takes place during this liquid phase. The stirring process can be supported by circulation pumps to enhance the reaction kinetics. Once the reaction has completely finished, the new substance is present in liquid form. It is mixed with additives to trigger a crystallisation of the active ingredient, which is promoted by skilful temperature changes. At the moment of the phase transition, a particularly effective mixing effect is necessary – especially when very rapid, even and gentle cooling is required.
The still suspended solids mostly remain capable of being pumped and are now subjected to a multi-stage washing process. The cleaned product is mechanically separated into a solid and liquid phase. Continuously working centrifuges or even filter presses are also used. As a rule, gastight, sealed systems are preferred. Finally, the thermal drying process takes place.
The concluding vacuum drying produces an initial synthesis result, which can act as a starting material for a second synthesis step. Highly effective, modern powdered chemicals are usually the result of several synthesis steps, which nearly always finish with a vacuum mixer drying stage. During the process, the active ingredient becomes more valuable and often more sensitive with each synthesis step. Thermal and mechanical stress must therefore be avoided during drying.