The issue of diesel flash point
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The diesel used as feed for diesel hydrogenation has a flash point of 60. After hydrodesulfurization, 5%-7% naphtha is separated out in the fractionating tower, yet the flash point of the diesel product at the bottom of the tower remains at 60. Why is that?
This post was last edited by qugd on 2020-11-5 09:12. The function of that distillation tower is to separate the light components produced during the hydrogenation process, so as to prevent significant changes in the specifications of the diesel fraction. It’s not strange, is it? Generally, after hydroprocessing oil products, a distillation tower is used to separate the light components produced, in order to ensure that the flash point and dry point of the oil products do not exceed the specified limits. This is determined by the chemical change patterns that occur after the hydrogenation of oil products.
According to the definition of flash point: it is the lowest temperature, expressed in °C, at which a mixture of vapor and air emitted when heating a petroleum product comes into contact with a flame and causes an instantaneous ignition under specified test conditions. The open flash point is used to determine heavy oils, while the closed flash point is used to determine light oils. A temperature of 45°C is used as the boundary to distinguish between combustible materials and flammable materials. The naphtha has not been completely removed; try to increase the extraction level further. Also, run a diesel process to see, but make sure the samples taken are accurate. During production, when sampling, it is possible to obtain a sample from the previous point
The most significant improvement after hydrocracking is the freezing point, while the control of the flash point is handled in the subsequent distillation stage.
Pull out insufficiently; keep pulling to raise the top temperature.
Whether 5%–7% of naphtha is considered much or not is uncertain; however, an excessively low flash point is simply due to insufficient separation or too intense reactions that result in the production of excessive amounts of light components. So, it’s necessary to check whether the temperature rise is excessive, and adjust the parameters of the fractionation tower to remove more light components.
In the hydrogenation reaction, some of the oils are cracked to produce petroleum fractions, which results in a lighter final product; meanwhile, hydrogenation or polymerization of some other oils leads to a heavier final product. The effects of lightening and heavyening are roughly equal and cancel each other out, so there is no significant change in the flash point of either the raw materials or the final products.
Do the catalysts used for the hydrogenation refining of ordinary diesel undergo cracking reactions? Catalysts are all refined products, those from NIMO
Hydrorefining catalysts can also undergo cracking reactions, although these reactions are relatively weak. Most conventional catalysts use aluminum oxide as a carrier, and aluminum oxide contains acidic sites; as a result, the catalysts exhibit some degree of cracking activity.
The liquid yield from diesel hydrorefining also does not reach 100%; a small amount of catalytic cracking occurs as well, producing some light fractions and gas. The flash point of diesel is 60 degrees, and all grades of diesel meet the flash point quality requirements. The GB252 standard for ordinary diesel specifies that the flash point of -35 grade and -50 grade diesel should be no lower than 45 degrees, while the flash point of other grades of diesel should be no lower than 55 degrees.