What Are The Optimal Operating Conditions For A Hydrodesulfurization (HDS) Unit To Achieve A Sulfur Removal Efficiency Of 99.9% While Minimizing The Formation Of Hydrogen Sulfide And Mercaptans In The Refinery's Diesel Fuel Production, Considering A Feedstock With A Sulfur Content Of 1.2 Wt% And An API Gravity Of 34°?

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To achieve 99.9% sulfur removal efficiency in a hydrodesulfurization (HDS) unit while minimizing the formation of hydrogen sulfide (H2S) and mercaptans in diesel fuel production, the following optimal operating conditions and considerations are recommended:

Operating Conditions:

  1. Temperature:

    • Operate within the range of 350°F to 380°F (175°C to 193°C). This range balances efficient sulfur removal with minimal formation of byproducts.

  2. Pressure:

    • Maintain a pressure between 500 psi to 800 psi. This pressure range enhances the reaction rate without excessively increasing H2S solubility.

  3. Hydrogen Flow:

    • Use a hydrogen flow rate of 1,000 to 2,000 standard cubic feet per barrel (SCFB). This ensures sufficient reactant availability for efficient sulfur removal.

  4. Catalyst:

    • Utilize a cobalt-molybdenum (CoMo) catalyst, which is effective for HDS. Consider catalysts with promoters to enhance selectivity and minimize byproduct formation.

  5. Space Velocity:

    • Opt for a low space velocity, specifically a liquid hourly space velocity (LHSV) of 1.0 to 2.0 hr⁻¹, to allow adequate contact time for high sulfur removal.

Additional Considerations:

  • H2S Management: Implement a separator post-reactor to remove H2S from the product stream.
  • Post-Treatment: Use a sweetening process, such as the Merox process, to further reduce mercaptans in the final product.

These conditions and processes are tailored to handle a feedstock with 1.2 wt% sulfur and an API gravity of 34°, ensuring minimal formation of H2S and mercaptans while achieving high sulfur removal efficiency.