What is the difference between “hydrogenation” and “hydrogen treatment”?
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Sometimes I hear people mention “hydrocracking,” and other times I hear “hydrodesulfurization”; it’s a bit confusing. What is the difference between “hydrogenation” and “hydrogen treatment”?
During hydrogenation, hydrogen is consumed； Hydrogen exposure is intended to protect the stability of the catalyst. There is hydrocracking, but no hydrohydrocracking. There are hydroammoniation processes, or hydroalkylation processes, and hydrocracking processes.
There’s a problem with this: there is no hydrogen consumption in the hydrogen-rich environment. How can catalyst stability be maintained without any hydrogen consumption? Also, what is the difference between hydrocracking and hydrodecomposition?
From a material balance perspective, there is no hydrogen consumption. However, from the perspective of the reaction mechanism, there are basic reactions of dehydrogenation and hydrogenation; in order to suppress deep dehydrogenation and the resulting increase in heavy components, the pores are blocked and the surface active sites are occupied. And hydrogen has to be introduced. As an example: ethanolamine and ammonia are used to produce ethylenediamine; this is a hydrogen-adjacent process, with no net consumption of hydrogen, and if any consumption does occur, it is due to process losses in very small proportions. Some are less than 3% (v/v)
So what kind of catalytic reactions can rely on hydrogen to maintain catalyst activity?
There are also reaction processes that can produce hydrogen on their own, such as aromatization reactions, also known as hydrogenation; therefore, hydrogenation should refer to a certain type of environment. And hydrogenation refers to the process conditions. Hydrogenation reactions definitely take place in a hydrogen-rich environment, but a hydrogen-rich environment is not necessarily involved in hydrogenation reactions.
Agreed. During aromatization on certain molecular sieve catalysts, such as ZSM-5 zeolites, a dehydrogenation reaction occurs. For some isomerization reactions, hydrogen is also required to prevent carbon deposition from covering the metal active sites on the catalyst. What kind of catalysts can be used for dehydrogenation? It can generally be understood in this way: hydrogenation and dehydrogenation are reversible reactions, and a catalyst with hydrogenation capabilities also has dehydrogenation capabilities. Here, it generally refers to metal catalysts or metal-supported catalysts. Some oxide catalysts or acidic catalysts also possess dehydrogenation capabilities, but their mechanism differs from that of metal-based dehydrogenation. To prevent the deactivation of such catalysts, a small amount of metal is intentionally loaded onto them.
Hydrogenation is required by the process; being in a hydrogen-rich environment means that hydrogen is present in that system. Since hydrogen is quite dangerous, extra care is taken
I’ve learned it; I used to think they were the same thing
Good question, **the explanation was also very thorough. Thank you everyone, keep learning :)