Naphthenic Oil Enhances Synthetic Fertilizers

Naphthenic Oil Advancing Synthetic Fertilizer Development Fertilizer use is vital to increasing agricultural production worldwide, yet it comes under continuous critical scrutiny. Developing products that provide optimum benefit both economically and ecologically remains a significant challenge for synthetic fertilizer manufacturers. Only minimal amounts of oil are used in fertilizer production. The market demands optimum products, and every link in the chain requires careful attention, including the properties of the oil used. Fertilizer pellets' anti-caking system can benefit from selecting NYTEX® or NYFLEX® oil, allowing a more attractive product to be obtained. This oil possesses extraordinary capabilities for dissolving materials and is obtained through high-degree refining, which provides distinct advantages over 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. In this article, we will address solid fertilizers, the preferred form in Europe, Asia and Africa, and also prominent in North America.

Effectively Dissolves Amines

Using these fertilizers in solid form facilitates handling and means that nutrients are released into the soil more slowly. This reduces the risk of nutrient leaching. However, the surface of individual granules must be treated to prevent them from sticking or dusting. A free-flowing, dust-free fertilizer is important for handling throughout 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 essentially consists of two components: an additive and an oil. Talc powder or clay may sometimes also be used during granule processing. The additive, most often containing 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 dusted onto the surface adheres. 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, performs well in this regard. 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 of 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 yet the first choice for anti-caking system manufacturers and users. Many different oil types are used, from vegetable oils to diesel and less refined fuel oils. The addition of less refined oils to products spread on fields is not actually as unusual as it might seem, as extremely small quantities of oil are used. It should be borne in mind that environmental requirements are not always directly linked 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 odourless. The psychological effect of the strong oily odour emitted by fertilizers in hot silos using anti-caking systems containing less refined oil cannot be ignored.

Unwanted Substances in Minimal Amounts

High refining of an oil means that the material has low aromatic content and extremely low polycyclic aromatic content, or PCA. Sulphur content is also very low. When it comes to toxicity, polycyclic aromatics are the main culprit for undesirable properties. However, aromatics provide good solubility properties. As long as aromatic content is high, it matters little whether the oil is naphthenic or paraffinic. When seeking a highly refined alternative, the good solubility properties of naphthenic molecules become the focus.

Tests Reveal Oil Properties

Nynas has long-standing customers using naphthenic specialty oils for anti-caking systems. To achieve the desired properties, the oil is refined to a high degree, thereby achieving a DMSO extractable content of less than 3% by weight according to IP 346. This means low PCA content and that the oil does not require labelling. Nynas Naphthenics offers oils in a wide variety 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 with Nynas oils NYTEX 810 and NYTEX 840 (Table 1) using amine-functionalised talc. Caking tendency (Figure 1), dusting tendency (Figure 2), moisture absorption (Figures 3 and 4) and flow properties (Figure 5) were addressed as principal parameters. Four systems were tested: 1 = No treatment, 2 = Talc functionalised with paraffinic oil, 3 = Talc functionalised with NYTEX 840, 4 = Talc functionalised with NYTEX 810, NPK fertilizer type NPK 24/6/12 (showing composition), CAN type used as CAN 23 (MgO). Talc was first sprayed onto fertilizer pellets, then oil. A hot spray gun was used for oil spraying.

Caking Tendency

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

Dusting Tendency

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

Moisture Absorption

Fertilizer pellets of 10 to 15 grams were stored at 100% 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 angle at which all pellets flowed was measured. This value indicates the pellets' ability to flow easily. The addition of functionalised talc and oil significantly improved the flow properties of the pellets.  

Conclusion

The tests clearly show that adding an anti-caking system significantly improves the storage behaviour of the fertilizer. When the effect of the oil is compared, using Nynas NYTEX 840 yields better results across all parameters than the paraffinic oil used in this test. A higher viscosity oil exhibits lower dusting and caking tendencies. Nynas NYTEX 810 improves the fertilizer's storage behaviour and has lower viscosity, which provides easier handling.   Emma Öberg Development Engineer Nynas