Back

Question

Submit an Answer

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

Jun-2024

Answers

Subramani Ramachandran, Ketjen, subramani.ramachandran@ketjen.com

Refiners have a multitude of options for increasing overall octane barrels output from the refinery, either by increasing FCC gasoline RON and/or by increasing the output of high-octane blend components such as reformate, alkylate, and isomerate. Typically, FCC operators have multiple operational handles to further maximise overall octane barrels from their FCC asset. While short-term operational moves like maximising riser outlet temperature (ROT), maximising CTO (impact depends on conversion level), and deployment of ZSM-5 additives can provide a short-term boost, they tend to move a carefully optimised FCC operation/catalyst system to an overall sub-optimal operating point. Our approach in such cases is to work closely with the refiner to design and implement a catalyst reformulation that can provide the necessary octane barrel shifts that the refiner is seeking while maximising overall profitability. Two such case studies of maximising overall octane barrels with differing yield objectives include:
• Maximising net octane barrels
• Maximising alkylation (alky) barrels.

Maximising net octane barrels
An existing customer using the Denali catalyst was looking to further maximise C₄= yields without significant penalty in gasoline volume from their FCC unit along with improved bottoms yields. The Denali family of catalysts incorporates our latest ZT-600 zeolite technology. It provides enhanced coke selectivity and superior activity retention, which directionally lowers hydrogen transfer at similar activity. A reformulated Denali catalyst was designed with directionally lower RE content while compensating for the lower resultant activity by enhancing the active-matrix content in the catalyst. Figures 1 and 2 show the key benefits of the reformulated Denali compared to the base. Not only was the reformulation able to provide the desired C₄= increase at minimal gasoline volume loss, but the overall octane barrels increase was achieved at lower slurry yields. Traditional approaches to light olefins selectivity optimisation have typically centred around RE-level optimisation, incorporating different shape-selective activity with varying molecular selectivities. In addition to these levers, optimisation of active-matrix content and type is an additional handle from a catalyst formulation standpoint to tailor the system hydrogen transfer index. While matrix components provide bottoms cracking along with activity enhancement, their ability to provide these benefits without enhancing hydrogen transfer increase (HTI) provides an additional degree of freedom to achieve targeted molecular selectivities.

Maximising alky barrels
Alternatively, depending on individual refinery configurations and economics, maximising alky barrels might be an overriding objective in certain regions. In this case study, the refiner was employing an Action catalyst, which is proven in the industry for its capability to maximise C₄= and C₄ olefinicity while providing excellent bottoms cracking. To meet their need, they were supplementing it with conventional ZSM-5 additive additions to increase the desired C₄ olefins. Action+ catalyst was proposed to Ketjen’s refinery partner, which employs a novel stabilisation technology (ZT-500). This new stabilisation technology provides a superior balance between activity increase and HTI compared to conventional rare earth modification. This approach allows refiners to maximise C₄= yields at similar C₃= yields at comparable activity (see Figure 3), effectively maximising alky barrels more than conventional catalyst (plus additive) approaches would allow. For conventional FCC units operating in maximum fuels mode, tailored approaches such as Action+ result in a significant increase in alkylate octane barrels due to a higher octane potential of C₄= relative to C₃= in an alkylation unit while achieving the above at a net lower wet gas volume, compared to conventional approaches.

In summary, the FCC unit remains an important vehicle for maximising high-octane gasoline components. Optimal solutions will be refinery-specific, depending on economic drivers, and there is no one-size-fits-all. As the prior two case studies demonstrate, approaching the challenge holistically and partnering with a catalyst technology provider will provide the best outcomes in terms of achieving the desired yield and product quality shifts while maximising overall unit profitability. Various catalytic handles are available with advances in catalyst technology, and a partnership approach is the key to sustained success in a dynamic environment.

DENALI and ACTION are marks of Ketjen.

Jul-2024
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
Jignesh Fifadara, Evonik Catalysts,

Jignesh Fifadara, Evonik Catalysts, Global Business Executive, HPC Catalysts and Sustainability, Evonik
There are several methods to increase the octane rating of gasoline. However, each has its own advantages and limitations. Some of the methods include:
υ Blending of higher-octane components (alkylates, isomerates, or reformates) with lower-octane gasoline to increase gasoline pool octane rating.
ϖ Blending with an alcohol-based additive (ethanol) since it has higher octane ratings than gasoline and can be blended in certain proportions.
ω Addition of aromatics (benzene, toluene, and xylene) in small amounts, which have higher octane ratings compared to straight-chain hydrocarbons.
ξ Investment in an isomerisation process that converts straight-run hydrocarbons into branched chain hydrocarbons, which typically have higher octane ratings.
ψ Addition of fuel additives focused on boosting octane can also be utilised but can be restrictive due to environmental concerns.
ζ Optimising catalyst systems within an FCC gasoline hydrotreater to minimise octane loss while operating at higher severities to meet sulphur specifications.

While blending is a common method used to increase the octane rating of gasoline, there are usually concerns about high costs, availability, and environmental concerns. Due to that, optimising your catalyst system in the gasoline hydrotreater provides the most control to produce high-quality octane gasoline.

Jul-2024
Grant Severyn, BASF Refining Catalysts,

Multiple strategies can be utilised to increase FCC gasoline octane. First, increasing the octane of the ‘as-produced’ naphtha is an obvious choice, either by formulating a base catalyst with reduced hydrogen transfer to preserve high octane molecules, adding ZSM-5 additives also, or a combination of both. Of course, process condition adjustments, such as increasing reactor outlet temperature (ROT), can also increase the as-produced octane.

Second, producing high octane blending components is another common choice. The desired blending component is alkylate, having a RON value typically ranging between 92 and 98 (a function of feedstock used between – C₃, C₄, or C₅).

Historically, refiners have used an olefins additive, including ZSM-5, in FCC units to capture value from the market’s demand for increased light olefins for alkylation and higher-octane gasoline components. The ZSM-5 zeolite is designed to selectively crack gasoline-range molecules into propylene (C₃=) and, to a lesser extent, butylenes (C₄=). In general, C₄= alkylate has a higher road octane ([RONC + MONC] / 2) value than C₃= alkylate, and C₄= alkylate is less cost intensive to produce. As an example, alkylate made from C₃= and isobutane can have a road octane of up to 92, whereas alkylate from C₄= can have a road octane of up to 98. Therefore, C₄= alkylation is the preferred method for most refiners operating alkylation units.

Since ZSM-5 zeolite tends to generate more propylene than butylenes (see Figure 1), there are strong incentives for FCCs, which feed to alkylation units, to increase C₄=/C₃= selectivity through the base catalyst technology to generate higher-octane alkylate species. FCC catalysts can be tuned to effect such change. Recent technical advancements have made this even more possible, with some refiners having taken it upon themselves to expand their alkylation units to fully utilise the benefits that improved technologies can offer.

Fourtune and Fourtitude FCC catalysts for vacuum gasoil (VGO) and resid applications, respectively, utilise BASF’s Multiple Framework Topologies (MFT) technology (Figure 1) to maximise butylenes yield and selectivity over propylene.

The multiple zeolite frameworks have optimised acid site density and strength to ensure selective butylenes yield over propylene, as well as enhanced porosity to reduce diffusion limitations and minimise saturation reactions. The mechanism behind the success of such butylenes-maximising catalysts involves both generation and preservation (avoiding saturation) of C₄ olefins while preserving high-octane molecules in the gasoline range.

Fourtune and Fourtitude catalysts have been used in multiple commercial FCC units with stand-out performance in C₄=/C₃= selectivity (up to 1% volume increase in butylenes yield at constant propylene yield) and FCC naphtha octane for gasoline blending (up to 2 RONC increase) compared to alternative suppliers in unit operating data. These changes have allowed refiners to increase their refinery gasoline octane by two methods: improved octane of FCC-generated naphtha and an increase in alkylate production.

Fourtune and Fourtitude are marks of BASF.

Jul-2024
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