Question
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What options are available for increasing the number of higher octane gasoline components?
Jun-2024
Answers
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Pierre-Yves Le Goff, Axens, Pierre-Yves.LE-GOFF@axens.net
Several technologies are available for generating high-octane gasoline components. We are not reviewing all options in this instance, only the most important commercial technologies available today.
Beginning with C₅/C₆ isomerisation, and depending on unit configuration, different catalysts can be proposed, ranging from zeolite to sulphated zirconia and up to the highest performance level with chlorinated alumina catalyst. For a given catalytic solution, depending on the feed and whether a high or low amount of C₅ component (vis targeted octane) is present, the ensuing process flow diagram can be significantly modified. This modification can include the addition of a deisopentaniser upstream from the reaction section or the addition of a deisohexaniser (DIH) downstream from the reaction section.
To reach the highest level of research octane number (RON), separation with a molecular sieve section can also be proposed. Going from the once-through configuration with zeolite to a unit based on chlorinated alumina with a DIH, the octane can increase from 80 RON up to 88 RON. With this technology, the RON is achieved by the production of multibranched C5/C6 paraffins and does not contain any aromatics or olefins.
Reforming is another process for generating high-octane components. Isomerisation schemes can vary from one unit to another, but reforming process flow diagrams are all quite the same, with the major difference between units being the unit pressure. The oldest units can run at high pressure (30 barg). To maximise gasoline and hydrogen production, the most recent designs run at ultra-low pressure (3 barg) with a continuous regeneration (CCR technology) to ensure the highest time on-stream factor. The highest achievable RON with isomerisation is around 90-91 and about 102 with CCR reforming due to the presence of aromatics.
A third solution to generate high-octane hydrocarbon is alkylation, which generates a chemical reaction between isobutane and C₄/C₃ olefins in the presence of an acid-type catalyst. The most common and safest alkylation units are sulphuric acid units. Indeed, hydrofluoric acid is quite a toxic and dangerous chemical. To generate an iso-C₄-rich stream, a C₄ isomerisation unit can be used. This unit uses a chlorinated alumina catalyst. A key advantage of alkylate is the absence of aromatics and its low RVP, making alkylate an attractive blending component for the gasoline pool.
A fourth solution is the use of FCC gasoline, the main constraint of this stream is the presence of sulphur. A dedicated hydroprocessing scheme such as Axens’ proprietary PrimeG technology can be used, allowing for sulphur removal while minimising the olefin saturation, thus minimising octane losses. A new solution combines Axens’ Prime-G+ and GT-BTX PluS, which offers a unique solution to reduce octane loss to a very low level for the gasoline pool. The technology is especially important in countries upgrading fuel specifications to meet environmental requirements. It can be applied in new or retrofits of existing operating units to maximise profit.
Aside from pure hydrocarbon technology, another pathway to generate high-octane molecules is to produce oxygenate components. For example, again, on an acid-type catalyst, it is possible to generate methyl/ethyl tertiarybutyl ether (MTBE, ETBE) by a reaction between methanol/ethanol and isobutane. As for alkylate, the key advantage of oxygenates is their low Reid vapor pressure (RVP), mainly for MTBE, but some regulations limit the use of oxygenates, such as the MTBE ban in the US.
PrimeG, Prime-G+ and GT-BTX PluS are marks of Axens.
Jul-2024
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