Reasons for the green color of hydrogenated refined diesel
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The new unit has just started operation; it is a coal tar hydrogenation plant. A few days before the products were ready for delivery, their color was good. As the temperature in the reforming section increased, the color of the diesel product turned light green; when the temperature decreased slightly, the green color faded. Could it be that excessive hydrogenation is responsible for this green color? Apart from the color, all other parameters were within acceptable limits. Let’s discuss this
Changes in raw materials or excessive hydrogenation~~~~~
The raw materials have not changed; please explain in detail the concept of over-hydrogenation
It’s due to the aromatic compounds; it’s not the amount of aromatics, but rather some of these compounds give off a green color. It’s not clear what exactly it is.
An increase in temperature leads to a decrease in the degree of hydrogenation, which is caused by insufficient hydrogenation. The hydrogenation of unsaturated hydrocarbons is an exothermic reaction, and increasing the temperature is not conducive to hydrogenation. Also, the catalyst’s activity may be poor. The greenish color of oils is caused by polycyclic aromatic hydrocarbons and heterocyclic hydrocarbons present in them; moreover, polycyclic aromatic hydrocarbons exhibit a significant fluorescent effect. If over-hydrogenation occurs, the color intensity of the product should decrease. Appropriately reduce the hydrogenation temperature and increase hydrogen purity, while paying attention to whether catalyst activity is affected by carbon deposition on the catalyst caused by an excessive amount of unsaturated hydrocarbons in the oil.
Hydrogenation reactions are all exothermic; increasing the temperature at lower stages speeds up the reaction rate. However, once the temperature reaches a certain level, it reduces the degree of reaction. The change in the color of the oil is caused by insufficient hydrogenation of polycyclic aromatic hydrocarbons, and this can be addressed by reducing the temperature, increasing the reaction pressure, and improving the purity of the recycle hydrogen.