Production of Pesticides (Part 1)
Modern processing plants are needed to produce pesticides. The highly effective substances are not only valuable in both senses of the word, but due to their high concentration during the process, they are potentially harmful for the plant operator. For more safety, the multi-stage syntheses and formulation steps therefore take place in closed systems.
This two-part article describes why amixon equipment, with its special design features, can make a major contribution to efficiency in this challenging environment and have a decisive influence on the output quantity of a production. The first part deals with the synthesis steps in the process of pesticide production and the special challenges and their technical solutions.
Cultivated plants for nutrition
More than 7.8 billion people would be living on Earth by the end of 2020. In 2050, there will be around 9.7 billion people, according to the current UN population projection of 2019. In order to produce enough food for the growing world population, the agricultural industry worldwide cannot function without pesticides. Without crop protection products, the agricultural yields we take for granted around the world today would be nowhere near achievable.
The term pesticides is a collective term and includes active substances with different spectrum of action: to control mites (arcricides), microbial pathogens (bactericides), fungi or their spores (fungicides), multivorous weeds (herbicides), insect swarms (insecticides), nematodes (nematicides) and harmful rodents (rodenticides).
Turnover and sales in the German market for crop protection products,
used against undesirable organisms to maximise yields in agriculture. Unfortunately, their large-scale use also entails residual risks for the environment, but there is no alternative because of their high benefit for agricultural production. Their effect is so great that certain plant protection products may also be used in organic farming. This is the case when other interventions fail. - A frequently practised method is the establishment of clever crop rotations to prevent the mass reproduction of pests -. The range of pesticides that are permitted for use in organic farming, for example, is set out in the Organic Farming Regulation. "In the event of an identified threat to crops, only plant protection products authorised for use in organic production in accordance with Article 16 may be used" (Article 12 of Regulation 834/2007).
Crop protection products are a global market worth billions
The world market for crop protection products is large. Herbicides account for by far the largest production volume, followed by insecticides and fungicides. In 2018, global sales of crop protection products amounted to just under 48 billion euros - an increase of 0.5 percent compared to the previous year. In 2021, global turnover stagnated. Asia is by far the largest market, ahead of Latin America and Europe.
In Germany, turnover in the same period was 1.3 billion euros. The quantity of plant protection products sold in Germany was around 48,000 tonnes in 2016, doubling within ten years (2006: around 32,000 tonnes). Of these, about 40 per cent are herbicides (weed killers), about 25 per cent are fungicides (against fungi and their spores) and about 30 per cent are insecticides (to kill, drive away or inhibit insects and their developmental stages). The use of plant protection products in Germany declined steadily from 1.6 billion euros to 1.15 billion euros in the period 2014 to 2020. In 2021, consumption increased to 1.2 billion euros. In Germany, around 270 active substances were registered in a total of 753 different plant protection products in 2016. Researchers around the world are working at full speed to develop new, sustainable active substances that break down without leaving residues once they have taken effect.
The development of new crop protection products is lengthy and costly
It takes about ten years of intensive development work before a plant protection product can be approved and launched on the market. Promising new substances are sought in the laboratory and tested in model trials. The manufacturer is investing around 200 million euros in a new development. It conducts around 200 studies and analyzes more than 800 parameters. The actual active ingredients are already converted into agriculturally applicable products as so-called formulations for these tests. For these formulations, so-called carriers such as rock flour or organic solvents are used as excipients. Surface-active emulsifiers can also be used as wetting or adhesive agents. The task of these formulation aids is to ensure that the active ingredients are technically safe for the end use. For their part, excipients and carriers must be environmentally compatible and support efficacy.
Multi-step production process with high requirements
The synthesis steps for the production of crop protection products naturally differ depending on the active ingredient and the desired form of application. However, the basic process steps are similar for powdered starting materials. First, a solvent is introduced into the reactor, the powdery reactants are added and homogeneously dissolved or suspended. In this liquid phase, the first synthesis reaction takes place under heating. To promote the reaction kinetics, the stirring process can be supported by circulation pumps. After completion of the reaction, the new substance is now present in liquid form. It is mixed with additives to initiate crystallisation of the new intermediate. Crystallisation/flocculation can be promoted by skilful temperature control. At the moment of phase change (liquid to crystalline/solid), a particularly gentle mixing action is required, especially if the crystalline structures are to be preserved.
The suspended solids usually remain pumpable and are subjected to a multi-stage wash in the next process step. Here, the active ingredient crystals are usually freed from reagents with water or solvent. Further cleaning steps can follow. Mechanical solid-liquid separation is carried out with the aid of continuously operating centrifuges, which are the preferred method. It is not uncommon to use chamber filter presses. As a rule, gas-tight, closed systems are preferred for mechanical solid-liquid separation. The first synthesis step is completed by thermal drying in the vacuum mixer dryer. The aim is to preserve the particle structure and size. In addition, the solvents are to be recovered.
Durable synthesis reactors thanks to suitable materials
Looking at the equipment specifications for new equipment in synthesis factories in Europe, the USA and India, three observations can be made:
- the chemical synthesis processes are becoming increasingly complex
- the solvents used become more aggressive/corrosive
- the permissible operating overpressures are defined higher
- the permissible operating temperatures become higher
Conventional austenites are at best still used in powder formulation. But here, too, austenitic-ferritic stainless steels, so-called duplex and superduplex steels, are increasingly being used. For the synthesis reactors and dryers, the trend is towards high-alloy nickel-based materials (Hastelloy C22 and Alloy 59). In addition to the corrosive stress, the change between vacuum and pressure as well as between hot and cold operation leads to additional stress on the process apparatus and accelerates the ageing process. This can even lead to rapidly progressing stress corrosion cracking.
amixon® has a great deal of experience and the necessary welding qualifications to manufacture pressure equipment of all classes in accordance with international regulations. The average service life of amixon® devices is more than 30 years. In this respect, amixon® fulfils three prerequisites:
- Sophisticated design for permanent tightness under pressure and vacuum
- Excellent corrosion protection and
- good wear protection
amixon® has welding experience in dealing with high-alloy materials. Welding these materials requires, for example, strictly observed welding sequences and strict cleanliness. Even the mechanical tests and corrosion tests that accompany production, such as ASTM G48, can lead to an unwanted termination of the work that has already been done. The same applies to the Cabot corrosion test on weld seams.
The respective synthesis stage is completed with vacuum drying
Vacuum drying yields a first powdery synthesis product that can serve as an educt for a second synthesis step. Modern, highly effective powder chemicals are usually the result of several synthesis steps, which almost always end with vacuum mix-drying. In the process, the active ingredient becomes more valuable and often more sensitive with each synthesis step. During drying, it is therefore important to avoid thermal and mechanical stress.
If the synthesis product is dry and cool enough to be discharged from the vacuum dryer, simple stainless steel materials such as 1.4571 or 1.4404 are usually sufficient again.
Part of the development is the evaluation of different product formulations: One of these, for example, is the micronisation of powdered active ingredients and their subsequent agglomeration. Agglomerated products are fixed in their mixed state, low in dust and well suspendable/soluble in water. The finest particles can float permanently in the water without sedimenting. The lump-free, homogeneous suspension/solution can be evenly applied by the farmer.
Another quality aspect of many is long-term stability - no matter in which climate zone of the earth the crop protection product is used. It must not decompose and must remain readily soluble/dispersible.
In the amixon test centre, the preparation steps of synthesis, vacuum contact drying, homogenisation and build-up granulation can be demonstrated. amixon has decades of experience in designing process machines that are 10 to 50 times larger than the experimental machines.
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