The key reactions in the NHT unit are:
✔ Hydrodesulfurization (HDS)

$$R-S + H₂ → R-H + H₂S$$

(Sulfur removal as hydrogen sulfide)

✔ Hydrodenitrogenation (HDN)

$$R-NH₂ + H₂ → R-H + NH₃$$

(Nitrogen removal as ammonia)

✔ Hydrodemetallization (HDM)

$$R-Me + H₂ → R-H + Me$$

(Removal of metals like nickel & vanadium)

✔ Saturation of Olefins & Aromatics

$$C=C + H₂ → C-C-H₂$$

(Olefins are hydrogenated to paraffins, reducing gum formation)