Purpose of Sulfiding a Catalyst
In petroleum refining and petrochemical processes, sulfiding is the essential activation step for hydrotreating (HDS), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrocracking catalysts that contain nickel (Ni), cobalt (Co), and molybdenum (Mo) or tungsten (W) on alumina.
Fresh catalysts are typically in their oxide form (NiO, CoO, MoO₃, etc.), which are inactive for removing sulfur, nitrogen, or metals.
Sulfiding converts these oxides into active sulfide phases such as:
These metal sulfides are the true active sites that drive hydrodesulfurization and hydrogenation reactions.
Role of DTBPS (Di-tert-Butyl Polysulfide)
DTBPS is a liquid sulfiding agent used to pre-sulfide or in-situ sulfide hydrotreating catalysts in a controlled, safe, and efficient way.
Key points:
- Chemical formula: (t-C₄H₉)₂Sₓ (x ≈ 2–5)
- Sulfur content: ~54–58%
- Boiling range: around 220–300 °C
- Flash point: high, making it safer to handle than H₂S or dimethyl disulfide (DMDS)
How DTBPS Works
When DTBPS is introduced into the reactor (usually co-fed with hydrogen and a hydrocarbon solvent), it decomposes gradually at moderate temperatures (around 200–350 °C) to release sulfur species (H₂S and organosulfur intermediates).
These sulfur species react with the metal oxides on the catalyst to form the desired sulfide phases: MOx+H2S→MS+H2OMO_x + H_2S → MS + H_2OMOx+H2S→MS+H2O
Advantages of DTBPS
✅ Safer than DMDS (less toxic, less volatile, higher flash point)
✅ Controlled sulfur release, minimizing temperature runaway
✅ Cleaner operation — less odor and corrosion
✅ No need for external H₂S injection
✅ Compatible with various refinery units — hydrotreaters, hydrocrackers, reforming pretreatment
In Summary
| Aspect | DTBPS Function / Benefit |
|---|
| Main Purpose | Converts oxide catalyst to active sulfide form |
| Active Sulfur Source | Releases H₂S in situ |
| Typical Use | Start-up or activation of NiMo, CoMo, NiW catalysts |
| Benefit | Safe, efficient, and environmentally friendly sulfiding |