Decrease in flash point during vacuum distillation of used lubricating oil
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In production, a batch of used lubricating oil is processed through vacuum distillation. Initially, light oil is obtained, followed by oil with a flash point of 210°C. At this point, the temperature inside the reactor has reached 330°C; raising the temperature further aims to increase the oil production rate. As a result, the flash point of the oil decreases, from 210°C to 190°C, and then to 160°C. What’s going on here? Some people say it’s due to air leaking in, which then participates in the reaction ； Some say it is due to the waste lubricating oil itself. Please help point out what the problem is; thank you.
You haven’t controlled your light oil at the top properly
It is likely that uneven heating during the heating process of the oil, combined with a prolonged duration, caused the oil to crack.
It is likely that uneven heating during the heating process of the oil, combined with a prolonged duration, caused the oil to crack.
In used lubricating oil, there are usually some mechanical impurities present. The metal ions and metal fragments in these impurities act as catalysts when the oil is heated to high temperatures, leading to increased cracking of the heavy fractions in the oil. As a result of this cracking, the flash point of the oil inevitably decreases. Furthermore, additives in used lubricating oil that contain components such as sulfur and nitrogen also decompose at high temperatures, which further increases the production of light components.