What components are present in the recycle hydrogen of a hydrogenation unit?
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The purity of the recycle hydrogen in the hydrogenation unit is normally maintained at over 85%. What other components are present in this recycle hydrogen?
In my opinion, there should be more C1-C4 gases, with trace amounts of everything else.
Methane, hydrogen sulfide, carbon dioxide, carbon monoxide, and light hydrocarbons
Firstly, it contains hydrogen, which is the most abundant component. The other components are related to the composition of the material being hydrogenated. For petrochemical plants, the components in recycled hydrogen other than hydrogen mainly include: methane, ethane, propane, butane, C5 and C6 hydrocarbons (in small amounts), hydrogen sulfide (formed by the hydrogenation of sulfides), ammonia (formed by the hydrogenation of nitrides), and water (formed by the hydrogenation of oxides). It was mentioned earlier that carbon monoxide and carbon dioxide are also present, but I think their amounts are even smaller than those of C5 hydrocarbons, as in recycled hydrogen, carbon monoxide and carbon dioxide are converted into methane under hydrogenation conditions. There is also some nitrogen and argon. For some other hydrogenation processes, the composition may be simpler; when butyryldiol is hydrogenated to butanediol, the impurities in the recycle hydrogen are much fewer, typically consisting mainly of methane, C4 hydrocarbons, and water. Another very important hydrogenation process is (ammonia synthesis); the circulating hydrogen (it would be more appropriate to call it circulating gas) usually consists only of hydrogen, nitrogen, argon, and methane.
This post was last edited by qugd on 2017-3-10 18:49. Not necessarily. During the hydrogenation of some coker oil and catalytic cracked oil, the hydrogen sulfide content is quite high, as the hydrogenation process for such products is primarily aimed at desulfurization. Moreover, the catalysts used are generally in a sulfided state; hydrogen sulfide, in addition to being an impurity that needs to be removed from the recycled hydrogen, is also an important component for maintaining the catalyst’s activity within a reasonable range.
Methane Nitrogen Carbon monoxide Methanol
Apart from hydrogen, there are the cracking products generated during the hydrogenation process such as light hydrocarbons and hydrogen sulfide, as well as methane, nitrogen, etc., which come from the hydrogen feedstock.