The concentration of hydrogen gas in the hydrocracking reaction
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Hydrogen is added in the hydrocracking reaction – is there any requirement regarding the concentration of the hydrogen added? What is the minimum required level?
The higher the purity of the new hydrogen, the better; usually >99.9%
As far as I know, there are two types of hydrogen that enter the reactor: one is the hydrogen added for cooling purposes (recycled hydrogen), and the other is the hydrogen that enters the reactor along with the oil (this hydrogen is a mixture of fresh hydrogen and recycled hydrogen). Is there any requirement regarding the hydrogen concentration resulting from the mixture of fresh hydrogen and recycled hydrogen? If so, what is it? Second, I would like to ask what the requirements are for the concentration of recycled hydrogen?
We only require fresh hydrogen and recycled hydrogen. For fresh hydrogen, we pay attention to levels of substances such as CO; the purity of recycled hydrogen is around 90%. No analysis has been done on mixed hydrogen. The purity of our fresh hydrogen is 99.99%, and the recycled hydrogen meets the required standards, so no analysis is necessary for mixed hydrogen
How can we ensure that the concentration of recycled hydrogen is maintained at around 90%?
The purity of recycled hydrogen is a direct indicator of the hydrogen partial pressure in the system. The required purity level in petroleum refining is generally no less than 85%, but as the density of the hydroprocessing feedstock increases and its composition becomes more complex, the hydrogen partial pressure also rises accordingly. Processes such as coal tar hydrogenation with a purity of not less than 90% and the direct or indirect liquefaction of coal require a higher purity of recycled hydrogen. Since the hydrogenation reaction involves a series of hydrogen addition or substitution reactions, along with some polymerization reactions, the gaseous products mainly consist of saturated alkanes with 4 carbon atoms or fewer, in addition to some hydrogen sulfide gas, which is used to maintain the activity of the catalyst. The concentration of these gases can also reflect the degree of reaction in the system; to ensure their purity, it is necessary to maintain it by introducing fresh hydrogen and removing waste hydrogen.
Laboratory analysis: Low concentration; hydrogen waste is discharged