Naphthenic Oil Boosts Synthetic Fertilizers

Naphthenic Oil Advances Synthetic Fertilizer Development Fertilizer use is vital for increasing agricultural production worldwide, yet it remains under constant critical scrutiny. Developing products that provide optimum benefits—both economically and ecologically—is a significant challenge for synthetic fertilizer manufacturers. Only small quantities of oil are used in fertilizer production. The market demands optimal products, and every link in the chain, including the properties of the oil used, requires careful attention. Choosing NYTEX® or NYFLEX® oil as an anti-caking system for fertilizer pellets can lead to a more attractive product. This oil possesses extraordinary capabilities for dissolving substances and is obtained through high-level refining that provides distinct advantages compared to most other oils currently in use. Fertilizers consist of various combinations of nitrogen, phosphorus, and potassium compounds. Depending on their composition and application, synthetic fertilizers are typically supplied in liquid or solid form—that is, as granules or pellets. This article addresses only solid fertilizers, which are most preferred in Europe, Asia, and Africa and are also prominent in North America.

Effectively Dissolves Amines

The use of these fertilizers in solid form facilitates handling and means that the nutrients are released into the soil more slowly. This reduces the risk of nutrient leaching. However, to prevent individual granules from sticking together or becoming dusty, the surface of each granule must be treated. A free-flowing, dust-free fertilizer is important for handling at all stages from production to end use. While some fertilizer manufacturers develop their own anti-caking systems, others prefer to purchase ready-made blends. An anti-caking system basically consists of two components: an additive and an oil. During granule processing, talc powder or clay may sometimes also be used. The additive, which mostly contains amines, plays the most important role and is also the most expensive component. The oil serves as a carrier for the additive. Oil is sprayed onto the granules and the required amount of powder sprinkled adheres to the surface. As an alternative to this process, a ready-made mixture containing oil, amine, and, for example, beeswax can also be used. Such mixtures are typically used without powder. The oil must have good solubility properties to effectively dissolve amines. This means that naphthenic oil—a highly refined oil with low aromatic content—would perform well in this respect. A highly refined paraffinic oil has weaker solubility properties and is therefore less effective for this function.

Lower Environmental Impact

In practice, if the oil is to function in the mixing process, it must also be pumpable at low temperatures. This is possible with naphthenic oils, whereas the corresponding paraffinic oils would need to be heated to higher temperatures. Additionally, naphthenic oils require less heating during the spraying process for the anti-caking agent. The viscosity of sprayed naphthenic oils rises rapidly and remains on the surface, protecting the fertilizer granule. Highly refined naphthenic base oil and highly refined paraffinic base oil are not currently the first choice for anti-caking system manufacturers and users. Many different types of oil are used, ranging from vegetable oils to diesel and less refined fuel oils. It is not as strange as it may seem that less refined oils can be added to products spread on fields because extremely small quantities of oil are used. You should bear in mind that regulatory requirements are not always directly related to actual environmental outcomes. However, beyond lower environmental impact, there are other advantages to using a highly refined oil. One of these is that a highly refined product is virtually odorless. The psychological effect of the strong oily odor emitted by fertilizers in hot silos where anti-caking systems containing less refined oil are used cannot be ignored.

Minimal Amounts of Unwanted Substances

High refining of an oil means that the material has low aromatic content and polycyclic aromatic content—that is, PCA—is extremely low. Additionally, the sulfur content is also very low. When toxicity is a concern, polycyclic aromatics are the primary cause of undesirable properties. However, aromatics offer good solubility properties. As long as aromatic content is high, it matters little whether the oil is naphthenic or paraffinic. When searching for a highly refined alternative, the good solubility properties of naphthenic molecules become the focus.

Tests Reveal Oil Properties

Nynas has long had customers using specialized naphthenic oils for anti-caking systems. To achieve the desired properties, the oil is refined to a high degree, thereby obtaining a DMSO extractable content of less than 3 percent by weight according to IP 346. This means low PCA content and that the oil does not require labeling. Nynas Naphthenics offers oils in a wide range of viscosity grades. Depending on the type of problem encountered and the type of fertilizer being worked with, different oils may be suitable. To demonstrate the function of the oils, we conducted tests using Nynas oils NYTEX 810 and NYTEX 840 (Table 1) together with amine-functionalized talc. Caking tendency (Figure 1), dusting tendency (Figure 2), moisture absorption (Figures 3 and 4), and flow properties (Figure 5) were addressed as main parameters. Four systems were tested: 1 = No treatment, 2 = Talc functionalized with paraffinic oil, 3 = Talc functionalized with NYTEX 840, 4 = Talc functionalized with NYTEX 810, NPK fertilizer type NPK 24/6/12 (showing composition) and CAN type CAN 23 (MgO) were used. Oil was first sprayed onto the fertilizer pellets followed by talc. A hot spray gun was used for oil application.

Caking Tendency

Pellets were held in 100 percent humidity for one hour, then pressed at 1 kg/cm² pressure for 24 hours. Following this, the energy required to break apart the solidified pellets was measured. The stated result is the average of five measurements with a standard deviation of 2.

Dusting Tendency

Pellets were stored at 55 percent humidity at 23°C. Samples were taken from the product once a week and sieved for four minutes. The weight difference in the pellets before and after sieving is a measure of the amount of dust produced.

Moisture Absorption

Fertilizer pellets weighing 10 to 15 grams were stored at 100 percent humidity at room temperature. Samples were weighed after 5, 24, 48, and 72 hours.

Flow Properties

Fertilizer pellets were spread on a plate and then gradually inclined. The inclination at which all pellets flowed was measured. This value indicates the ease with which pellets flow. The addition of functionalized talc and oil significantly improved the flow properties of the pellets.

Conclusion

The tests clearly demonstrate that the addition of an anti-caking system significantly improves the storage behavior of the fertilizer. When the effect of the oil is compared, the use of Nynas NYTEX 840 yields better results across all parameters in this test compared to the paraffinic oil used. A higher viscosity oil exhibits lower dusting and caking tendencies. Nynas NYTEX 810 improves the storage behavior of the fertilizer and has lower viscosity, which offers easier handling. Emma Öberg Development Engineer Nynas