The H2/CH4 ratio issue in catalytic cracking units
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This post was last edited by tristadeng on 2010-8-25 at 16:02. I would like to ask everyone: in catalytic cracking, apart from reflecting the catalyst’s resistance to metal contamination, what other information can be obtained from the H2/CH4 ratio? Under normal conditions, what is the approximate range for the H2/CH4 ratio? Is there a specific value beyond which it indicates that the catalyst has been severely contaminated by heavy metals? Is there such a requirement regarding metal passivators? What is the maximum allowable ratio for H2/CH4 in metal passivators? I would be greatly grateful for your advice!
Heavy metals and alkaline earth metals in the raw materials can poison the catalyst and cause its permanent deactivation. The use of passivators can suppress the dehydrogenation reactions of heavy metals on the catalyst as well as coking, thereby reducing the damage to the catalyst. For metal passivators, the H2/CH4 ratio is required to be no higher than 2.
A sensitive indicator that directly reflects heavy metal contamination in catalysts in industrial plants is the molar ratio of H2/CH4 or H2/(C1+C2) in the catalytic dry gas. In plants with mild contamination, the H2/CH4 ratio ranges from 0.2 to 0.3; however, in plants that use residue oil as a feedstock, this ratio exceeds 1, and can even reach 3.
Professional books state that empirical values range from 0.5 to 3.0
You don’t need to ask others for this ratio; just look at yourself. What is the CH4 level of the device under normal conditions? We require that the H2 content in the dry gas be no more than 30% (V); just calculate the ratio. It might be 1.2-1.3.