Nitrogen and Methane Content

The normal specification for CO plus CO2 in the makeup gas stream to a Hydrocracker is in low two-digit mol-ppm maximum. Larger quantities can have a harmful effect on catalyst activity. CO is considered the worst impurity due to the fact that it has a limited solubility in both hydroearbon and water and will, therefore, build up in the reeyele gas. CO2, on the other hand, is much more soluble and is readily removed from the system in the high-pressure separator liquids. 

Both CO and CO2 have similar effects on the Hydrocracking catalyst they are converted on the active sites of the catalyst in the presence of hydrogen to methane and water. This methanation of CO and CO2 competes with the normal hydrocarbon reactants for the catalyst. Therefore, if CO + CO2 is allowed to build up, higher eatalyst temperatures will be required. In an extreme case where a large quantity of CO or CO2 would be introduced to the Hydrocracker in a short period of time, it is theoretically possible that a temperature excursion would result since the methanation reaction is highly exothermic. 

It is recommended practice that if the CO + CO2 content exceeds the maximum design limit, the catalyst temperature should not be increased to compensate for a resulting decrease in conversion. Catalyst temperature should be maintained at the same level or reduced until the problem causing the high CO + CO2 is eliminated. In this way the catalyst will not be harmed 

Ipatieff, V.N. Catalytic Reactions at High Pressures and Temperatures, Macmillan (New York) 1936. 

Bergius, F. Nobel Prize Lecture, Stockholm, Sweden, 1931 

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