Avoiding Octane Destruction in Refinery Operations

A recent REFCOMM webinar facilitated by George Hoekstra took a deep dive into the problem of octane destruction in refinery operations. The hydrogenation of FCC gasoline olefins in the post-treater reduces a large part of the octane barrel when desulfurizing to less than 10 ppm S. Comments during the Q&A towards the end of the webinar seems to indicate a surprising number of refiners could be running “tight” on octane and may be actively reviewing options to restore octane value.

Minimize olefins saturation

Increasing temperature and severity of the post-treater/desulfurizer to achieve less than 10 ppm S destroys a disproportionate amount of product octane (due to H₂ saturation effects). Hoekstra mentioned “adaptations” for resolving octane destruction may be costly to ROI, such as foregoing sales to gasoline, downgrades, etc. Options demonstrating to be effective in preventing octane destruction include:

• FCC feed pre-treating to meet S limits while avoiding excessive saturation of the high-octane branched olefins (albeit expensive due to high pressure requirements, H₂ consumption, etc.)
• Blending gasoline from the post-treater with reformate to restore octane
• Running post-treater gasoline through a catalytic reformer to restore octane
• Improving post-treater catalyst with high sulfur & octane selectivity
• Invest in an FCC gasoline splitter to separate high-octane branched olefins from lower octane alkanes (e.g., branched C₆ alkenes vs n-C₆ alkanes)
• Invest in an upgrade that combines the latter two options with improved post-treater catalyst selectivity and splitter to further minimize H₂ saturation of olefins and branched alkanes
• Aromatics extraction to generate a separate high sulfur-rich stream that can be hydrotreated with minimum olefin saturation.

Molecular level detail

These options, such as cat feed hydrotreating come at high capital, which is why most refiners aren’t configured with an FCC feed pre-treater, even though they provide multiple benefits (e.g., allows refiners to vary crude slates). Most refiners can benefit from loading the post-treater’s reactors with high selectivity catalyst that achieves near-zero sulfur reduction in gasoline while preserving octane, such as with Haldor Topsoe’s new HyOctane™ catalyst.

But before any of these strategies can be successfully implemented, Hoekstra stressed the need for modelling and understanding the key reaction pathways to determining octane loss. For example, Hoekstra noted recent field tests on twelve different commercial post-treaters clearly showing octane destruction typically being five (5) times higher than expected.

Against this backdrop, he noted that before refiners can adopt strategies for resolving octane destruction, there needs to be a clear understanding of the detailed molecular chemistry with FCC gasoline’s 550+ compounds. Providing the necessary data for predicting octane loss as a function of FCC naphtha composition, cut points, catalyst selectivity, etc., can help plan for mitigating octane loss destruction while still supplying Tier 3 zero-sulfur gasoline.

Even though gasoline demand is flat in many markets, octane is extremely valuable in most markets, so moving RON values up by just a small amount is usually worth tens of thousands of dollars per day, according to Hoekstra.

We invite readers to register for REFCOMM’s hosted webinars in the areas of FCCU, DCU and SDA.