Increasing hydrogen partial pressure in a hydrocracker will increase conversion for the same reactor temperatures.
1. Increasing hydrogen partial pressure at constant conversion requires lower reactor temperatures and thus increases the cycle length of the catalyst.
2. The higher partial pressure favors the desired reactions (cracking) and supresses the undesired reactions (coking).
3. Complete the hydrotreating reactions due to high conversion rates at the catalyst.
4. Ensure availability and physical contact of hydrogen for reactions at the catalyst bed.
For how to improve the hydrogen partial pressure view, https://thepetrosolutions.com/improving-hydrogen-partial-pressure-in-hydrotreating-units/