Tag refinery operations

When is TBPS or DTBPS preferred over DMDS?

Refineries may select TBPS/DTBPS when:

• A lower sulfiding temperature is required.
• Methane formation (“methane make”) is a concern.
• Operators prefer less odor and improved safety profile (TBPS/DTBPS are less volatile than DMDS).
• The unit requires gradual sulfur release for temperature-sensitive catalysts.

How is the sulfiding process monitored?

A controlled sulfiding procedure includes:

1. Drying the catalyst bed (200–250°F).
2. Wetting with clean straight-run feed.
3. Injecting DMDS or DTBPS at 450–500°F in hydrogen-rich atmosphere.
4. Monitoring H₂S concentration to detect catalyst activation (“breakthrough”).
5. Holding temperature (600–660°F) until sulfiding is complete.

Modern refineries use online H₂S and hydrogen analyzers to ensure precision and safety throughout the process.

Why is sulfiding necessary?

Without sulfiding, the catalyst remains inactive and cannot drive hydrodesulfurization (HDS) or hydrodenitrification (HDN) reactions. Proper sulfiding ensures the catalyst achieves full activity and longevity, preventing deactivation and maintaining fuel quality standards (sulfur <10 ppm).

How is the sulfiding process monitored?

Modern refineries use online H₂S and hydrogen analyzers to monitor sulfiding progress. The process involves:

1. Drying and wetting the catalyst bed.
2. Gradually heating the reactor while introducing the sulfiding agent.
3. Tracking H₂S concentration in the effluent gas to detect breakthrough — the point at which the catalyst becomes fully sulfided.
4. Holding at a final temperature (typically 600–660°F) until completion.

What is sulfiding in refineries?

Sulfiding is the activation process for hydrotreating and hydrocracking catalysts. Fresh catalysts are manufactured in oxide form and must be converted into their active sulfide form before they can remove sulfur, nitrogen, and other impurities from fuels. The process involves feeding a sulfur-containing compound (sulfiding agent) with hydrogen into the reactor to form hydrogen sulfide (H₂S), which reacts with the catalyst to create the active sulfide phase.

To activate hydrotreating and hydrocracking catalysts, refineries use sulfiding agents — specialized sulfur compounds that convert metal oxides (like CoMo or NiMo) into their active sulfide forms.

The most widely used sulfiding agents today are:

Note:
In refinery practice, TBPS and DTBPS are often used interchangeably. DTBPS (Di-tert-Butyl Polysulfide) is a high-purity variant of TBPS, offering greater thermal stability and a smoother sulfiding profile.

Why Refineries Choose These Agents

• DMDS is preferred globally due to its higher sulfur concentration and cost efficiency.
• DTBPS (or TBPS) is selected where lower sulfiding temperatures or improved safety and odor control are priorities.

Both are crucial in ensuring complete and controlled activation of hydrotreating catalysts — a key step for producing ultra-low sulfur fuels.