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• What options are available for increasing the number of higher octane gasoline components?

  Jun-2024

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Answers

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• Heather Blair, Johnson Matthey, Heather.blair@matthey.com

  There are a few operational methods available to increase higher-octane gasoline components. The first is to increase FCC riser temperature; an increase of ~13-15°F yields an octane increase of 1.0 RON, and a 25°F riser increase yields a MON increase of 1.0. Decreasing FCC feed gravity will also increase gasoline octane; a decrease of -1.7 API (+0.1 g/cc density) will increase gasoline RON by 0.6. Reducing the rare earth content of the base catalyst will also increase gasoline octane, but it comes at the expense of gasoline yield. The ability to change feed quality, adjust riser temperature, or change catalyst properties is not always possible. An alternative method to increase gasoline octane is to utilise a ZSM-5-type additive.

  ZSM-5 additives increase the octane first by cracking C6 to C10 straight-chain gasoline olefins into LPG olefins. This increases the propylene and butylene feed to the alkylation unit, increasing alkylate as a high-octane blending component. The cracking of the lower-octane gasoline species also concentrates the gasoline stream to higher-octane material.
  ZSM-5 has a secondary effect of increasing the gasoline octane. As ZSM-5 deactivates and loses cracking activity, older ZSM-5 particles isomerise straight-chain gasoline molecules to more highly branched molecules, increasing the octane of the gasoline stream. When ZSM-5 is used long term a significant boost in gasoline octane is observed.
  Johnson Matthey provides multiple types of ZSM-5, such as the standard Super Z family that cracks into both propylene and butylene, with more selectivity towards propylene. The second family is ZMX-B-HP, which has more selectivity towards butylene than a standard ZSM-5 product. propylene processing or sales outlets, but there is a significant economic benefit for butylene.

  The last ZSM-5 product with the unique ability to increase gasoline octane with minimal LPG increase is Johnson Matthey’s Isocat HP additive. Standard ZSM-5 additives have a low silica:alumina (Si:Al) ratio. By increasing the alumina content of the ZSM-5 particle, there are more acid sites for catalytic cracking reactions. Independent of the alumina content, the shape selectivity of the ZSM-5 crystal also promotes isomerisation reactions to increase branching and, hence, octane in the gasoline stream. Isocat HP additive is designed to have a very high Si:Al ratio, so it has a lower activity for cracking but maintains the shape selectivity of the ZSM-5 crystal to promote isomerisation and increase gasoline octane. This additive is used in FCCs where LPG processing is limited, but an increase in gasoline octane is still required.

  SUPER Z, ZMX-B-HP, and ISOCAT HP are marks of Johnson Matthey.

   

  Jul-2024