Question
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We’ve increased the opportunity crude content of our feed and are experiencing high calcium issues. How can we best address this?
Jun-2021
Answers
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Steven Van Vegten, Albemarle, Steven.vanVegten@Albemarle.com
Calcium may be removed through pretreatment of the feed. If such pretreatment is unavailable or insufficient, calcium will irreversibly poison the catalyst when the feed is processed in an FCC unit.
Calcium deposits on the outer surface of FCC catalyst particles, much the same as iron. Calcium is detrimental to FCC catalyst performance as it causes sintering of the surface, reducing the accessibility of the catalyst. With reduced catalyst accessibility, it is more difficult for feed molecules to reach actives sites, hampering conversion, particularly in bottoms upgrading.
Because calcium and iron contamination hardly affect Ecat activity, surface area, and pore volume, it may be overlooked. As these lab tests employ long contact/diffusion times, they do not capture the dynamic nature of diffusion. To compensate for these oversights, Albemarle developed a lab test to measure the accessibility of FCC catalysts by allowing large probe molecules to diffuse into the catalyst. The test result is known as the AAI (Albemarle Accessibility Index). A diffusion limited catalyst has a low AAI, while a catalyst whose structure allows easy rapid diffusion has a high AAI.
As calcium poisoning is irreversible, a refiner may choose to increase catalyst additions, perhaps with the use of purchased Ecat, flushing the contaminants from the unit inventory and reducing calcium contamination to a level the catalyst can cope with. Alternatively, employing a high accessibility catalyst with intrinsic tolerance to calcium may provide for a more cost-effective option, allowing for lower catalyst addition rates while maintaining conversion. Albemarle offers a suite of catalysts with high accessibility, such as ACTION for maximising butylenes and AFX for maximising propylene.
Jun-2021
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