Transforming Catalyst Activation in Refineries with Safer Alternatives
Abstract: Sulfiding, the process of activating hydroprocessing catalysts in refineries, traditionally relied on dimethyl disulfide (DMDS). While effective, DMDS presents safety, handling, and environmental challenges. Di-tert-butyl polysulfide (DTBPS) emerges as a superior alternative, offering increased safety due to a higher flashpoint, a less offensive odor, nonregulated transportation, and reduced SOx emissions. Pilot studies confirm that DTBPS performs on par with DMDS while enabling quicker sulfiding at lower temperatures. Despite minor differences in sulfur content, DTBPS is endorsed by catalyst manufacturers as a safer, efficient, and environmentally favorable sulfiding agent.
Keywords: Sulfiding, hydroprocessing catalysts, DTBPS, DMDS, refinery safety, SOx emissions, catalyst activation.
This article explores the key factors in the sulfiding process of hydroprocessing catalysts and their impact on catalyst performance. By analyzing the types of sulfiding agents, sulfiding conditions (e.g., temperature, pressure, time), and catalyst support properties, effective strategies for optimizing the sulfiding process are proposed. The article highlights Di-tert-butyl Polysulfide (DTBPS) as a novel sulfiding agent, which offers superior safety, lower odor, and easier transportation and storage compared to the traditional Dimethyl Disulfide (DMDS). Laboratory and industrial-scale studies demonstrate that DTBPS performs equally to DMDS in terms of sulfiding efficiency and catalyst performance, while significantly reducing environmental risks and operational costs. The article concludes with future research directions, emphasizing the need for further advancements in sulfiding technology driven by both environmental and economic benefits.
Key Terms:
- Hydroprocessing catalysts
- Sulfiding process
- Di-tert-butyl Polysulfide (DTBPS)
- Dimethyl Disulfide (DMDS)
- Catalyst performance
- Optimization strategies
- Industrial applications
- Environmental technology
Main Content
1. Importance of the Sulfiding Process
Hydroprocessing catalysts are widely used in refineries for hydrotreating, hydrodesulfurization, and hydrocracking units. Initially, catalysts are in an inert/inactive state, with active metals in oxide form. Sulfiding activates the catalyst by reacting the active metals with hydrogen sulfide, which is typically generated in situ from sulfur in the feedstock or provided by a sulfiding agent.
2. Limitations of Traditional Sulfiding Agent DMDS
Dimethyl Disulfide (DMDS) has been widely used as a sulfiding agent for many years, but it has several drawbacks:
- Safety Hazards: DMDS has a low flash point (16°C), posing fire risks during transportation, storage, and use.
- Odor Issues: DMDS has a strong, unpleasant odor, which can be a nuisance to workers and surrounding communities.
- Transportation Restrictions: Due to its low flash point, DMDS is subject to strict transportation regulations, potentially leading to additional demurrage charges.
- Environmental Emissions: The methane produced during DMDS decomposition dilutes hydrogen in the recycle gas, increasing sulfur dioxide (SOₓ) emissions.
3. Advantages of the New Sulfiding Agent DTBPS
Di-tert-butyl Polysulfide (DTBPS) is a novel sulfiding agent with the following advantages:
- Enhanced Safety: DTBPS has a high flash point (100°C), significantly reducing fire risks.
- Low Odor: DTBPS has a mild, diesel-like odor, making it more tolerable for workers and communities.
- Easier Transportation: Classified as non-hazardous, DTBPS offers greater flexibility in transportation and storage.
- Environmental Benefits: The isobutane byproduct from DTBPS decomposition does not dilute hydrogen in the recycle gas, reducing SOₓ emissions.
4. Pilot-Plant and Industrial Applications
Pilot-plant studies confirmed that DTBPS performs equally to DMDS in terms of sulfiding efficiency and catalyst performance. DTBPS decomposes at a lower temperature (160°C) compared to DMDS (200°C), allowing sulfiding to begin at lower catalyst bed temperatures. This reduces the risk of catalyst damage due to high-temperature reduction and shortens the sulfiding process time.
5. Limitations of DTBPS
DTBPS has a slightly lower sulfur content (56%) compared to DMDS (68%), requiring a slightly higher dosage to achieve the same sulfiding effect. However, this drawback is outweighed by its safety, environmental benefits, and operational convenience.
6. Industry Acceptance and Future Outlook
DTBPS has been tested and approved by major catalyst manufacturers worldwide as a safe and efficient alternative to DMDS. As environmental regulations become stricter, DTBPS is expected to gain broader adoption in the refining industry.
- Table 1: Comparison of DMDS and DTBPS Sulfiding Methods
- DTBPS:
- Low odor and high flashpoint (212°F/100°C): Safer to handle with reduced fire risk, allowing for nonregulated transport.
- Low decomposition temperature (320°F/160°C): Provides a better safety margin for catalyst reduction.
- Industry acceptance: Rapidly gaining global market share and approved by catalyst manufacturers.
- Efficiency: Sulfiding process completes in 1-2 hours, which is faster than DMDS.
- DMDS:
- Strong odor: Described as “decaying cabbage,” making it unpleasant for workers and communities.
- Low flashpoint (61°F/16°C): Requires Department of Transportation (DOT)-regulated transport and specialized handling.
- Moderate decomposition temperature (392°F/200°C): Standard for current industry processes.
- Industry standard: Widely recognized and approved, but the sulfiding process takes 18-36 hours, much longer compared to DTBPS.
- Table 2: Comparison of Chemical and Physical Properties of DMDS and DTBPS
- DTBPS is a safer and more efficient alternative to DMDS in catalyst sulfiding. It offers significant advantages such as:
- Safety: A higher flashpoint and lower decomposition temperature make it safer and reduce the risks of fire.
- Environmental Impact: DTBPS minimizes SOx emissions due to its byproduct (isobutane) and prevents hydrogen dilution in the recycle gas.
- Convenience: Nonregulated transportation simplifies logistics, while low odor improves workplace conditions.
- The trade-off for DTBPS is its lower sulfur content (56% vs. DMDS’s 68%), requiring slightly more volume to achieve equivalent sulfiding.
- Pilot studies confirm DTBPS matches DMDS in catalytic activity and delivers added benefits like shorter sulfiding times (1-2 hours vs. 18-36 hours). Globally, catalyst manufacturers recognize DTBPS as an effective alternative. Overall, DTBPS’s properties make it the preferred choice for safer, faster, and environmentally favorable refinery operations.
- Additional Insights: Hydrodesulfurization Efficiency of Catalysts Sulfided with DTBPS and DMDS
- Hydrocarbon Byproducts:
- DMDS produces methane as its hydrocarbon byproduct during sulfiding. This methane tends to accumulate in the recycle gas stream, diluting hydrogen and lowering the hydrogen partial pressure. This often requires gas purging and hydrogen makeup, leading to SOx emissions and wasted resources.
- In contrast, DBPS generates isobutane, which exits with liquid hydrocarbons from the high-pressure separator. This prevents hydrogen dilution and reduces SOx emissions, making it a more environmentally responsible choice.
- Operational Efficiency:
- The lower decomposition temperature of DBPS (320°F/160°C) allows sulfiding to begin at a lower catalyst bed temperature, which reduces the risks associated with catalyst overheating (exotherms). This also shortens the sulfiding time, leading to cost savings by minimizing reactor downtime.
- Global Adoption:
- Catalyst manufacturers worldwide endorse DBPS as a viable alternative to DMDS. Its ease of use, safety advantages, and comparable effectiveness make it a promising choice for refiners aiming to optimize operations.
- Minor Considerations:
- The slightly lower sulfur content of DBPS (54% versus 68% for DMDS) requires a marginally higher volume of DBPS to achieve the same level of catalyst sulfiding. However, this minor inconvenience is outweighed by the safety, handling, and environmental benefits.
- Conclusion:
- DBPS stands out as a safer, more environmentally friendly, and efficient alternative to DMDS in the hydroprocessing catalyst sulfiding process. Its adoption reflects a move towards greener and more sustainable practices in the refining industry. While it does require a marginally larger dosage, the overall benefits—ranging from reduced SOx emissions to simplified handling—make it a compelling choice for modern refineries.
Conclusion
DTBPS, as a novel sulfiding agent, offers significant advantages in safety, environmental performance, and operational convenience, making it an ideal replacement for traditional DMDS. Despite its slightly lower sulfur content, its overall benefits make it the preferred choice for optimizing sulfiding processes in refineries.