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What evolving methanol-to-olefins configurations are feasible for SAF production?

Mar-2025

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Rob Snoeijs, Zeopore, rob.snoeijs@zeopore.com

A variety of conversions are available to convert methanol (or other alcohols) to olefinic products, which, through further upgrading, may be used as SAF.

The first option relates to methanol conversion to ethylene and propylene using zeolite-based catalyst in an MTP (ZSM-5-based) or MTO-type (SAPO-34-based) configuration. The resulting small olefins may then be oligomerised towards larger carbon numbers suitable for the SAF boiling range, a conversion for which zeolite catalysts have shown selectivity and lifetime benefits (particularly based on ZSM-23 zeolites). Finally, the resulting stream may be hydrogenated using a standard hydrogenation catalyst towards the required levels to suit SAF.

An alternative pathway relates to the conversion of methanol directly towards larger olefinic species, for example using a ZSM-5-based catalyst in an MTG-type configuration. Here, too, the ZSM-23 zeolite has shown remarkable selectivity and lifetime benefits. Also, after this reaction, hydrogenation is required to yield an acceptable SAF.

Importantly, reactions involving small alcohols and olefins tend to coke and deactivate the zeolite catalysts rapidly, hampering selectivity and catalyst lifetime. To overcome this challenge, various solutions have been developed, such as diluting the reactive feed, adding additives to the zeolite, and importantly increasing the external surface of zeolite, giving rise to the family of more accessible (mesoporous) zeolites.

Mesoporous zeolites have suffered a bad reputation when it comes to industrial applications based on the high cost commonly associated with their production. However, efforts at Zeopore have demonstrated that these cost challenges can be overcome through capitalising on the synergy between conventional hydrothermal zeolite and post-synthetic workup. This can be seen in the associated Zeopore article in this issue of PTQ Catalysis 2025, that sizeable benefits can be attained in this domain (specifically for ZSM-5 and ZSM-23 zeolites), and that combining mesoporisation with simultaneous additive addition yields sizeable benefits (PTQ Catalysis 2023, pp55-58 which you can VIEW HERE).

Mar-2025
Woody Shiflett, Blue Ridge Consulting, blueridgeconsulting2020@outlook.com

The framing of the question precludes any discussion of the various methanol feed source processes that can ultimately yield net-zero or even sub-net-zero carbon footprints, so in this instance the focus will be on the MTO process itself as well as the necessary oligomerisation and hydrogenation steps required for viable SAF production. Until very recent years, MTO processes were geared towards light olefin production, with ethylene and propylene, and development work followed that path toward petrochemical applications. Oligomerisation as a fuels production process is nearly 90 years old, and innovation in that process has been at a pace commensurate with such a mature process until recently. So, with respect to SAF, what is needed, and what are recent developments?

Several opportunities exist under the needs list:
• MTO process selectivity to higher carbon chain products beyond light olefins.
• Oligomerisation processes that are specifically selective to the carbon chain molecules required in the jet fuel range.
• Some means to reduce the energy required and associated carbon intensity of existing MTO processes that utilise fluidised bed reactors and associated regeneration configurations to deal with the coke fouling issues of existing MTO catalysts.
• Process consolidation and optimisation to mitigate the heritage path to jet fuel involving MTO, oligomerisation, hydrogenation, hydrocracking, and hydroisomerisation required for drop-in SAF with appropriate molecular distribution and cold flow properties.

The perusal of recent patent applications and grants shows progress in a number of these areas. It is no surprise that innovation is based on catalysis in most cases. Catalyst development in MTO focuses on shape-selective catalysts of varying structure and acidity to promote larger carbon chain olefins to be produced as well as even isoparaffins. More coke-resistant catalysts promise to offer less energy input for regeneration. They could even stretch to a departure from the complexity of operation and energy needed in the current fluidised bed/regenerator configurations. Changes in the mode of MTO operation have revealed certain unexpected benefits in product distributions and operating conditions.

The oligomerisation area has likewise seen catalyst development expand the selectivity envelope to home in on SAF yield maximisation. Technology to combine both oligomerisation and hydrogenation functions in a single reactor is demonstrated in the laboratory at a minimum. In more conventional process flows, consolidation of hydrocracking and hydroisomerisation functions in a single step are outlined.

The key enabler will be to efficiently marry the MTO and oligomerisation selectivities as a combined process that ideally produces the isoparaffin content and molecular chain length to meet SAF requirements. Predominant technology providers are clearly active in these efforts.

Mar-2025
Scott Sayles, Becht, ssayles@becht.com

Methanol processes that emit a minimal amount of greenhouse gas (GHG) are bio-methanol (sustainable biomass) and e-methanol (CO₂ and renewable hydrogen). eMeOH or BioMeOH are viable synthetic liquid fuels. Both are used directly for transportation fuel, mainly in maritime service today.

The concept of converting methanol-to-olefins (MTO) followed by polymerisation to sustainable aviation fuel (SAF) is referred to as methanol-to-jet (MTJ). The individual steps are commercially proven, while the combination of technologies to produce MTJ is new (see Figure 1).

Converting eMeOH to olefins is a proven technology with many licence providers. Each licensor is readily improving their technologies to increase yield and selectivity. The eMeOH production is an exothermic reaction requiring heat removal. The catalyst also deactivates, requiring regeneration. Fixed-bed designs use a cyclic design, with some reactors in regeneration while others are in service. Newer reactor system designs utilise a fluidised bed reactor with integrated regeneration.

MTJ is a mixture of oxygen-free hydrocarbon chains and is a ‘drop-in fuel’. The blend is typical of a Fischer-Tropsch (FT) synthesis consisting of paraffins, cycloparaffins (naphthene), and a smaller concentration of naphthene/aromatics. FT synthesis allows for customising the hydrocarbon chain length range to the jet fuel range of C9 to C1₆. The chemical composition is different from fossil fuel, and the performance in jet engines requires ASTM certification. The unit designs are focused on energy and carbon efficiency to maximise renewable carbon in SAF.

Commercial fixed-bed reactors designed for methanol-to-gasoline (MTG) have been in operation in New Zealand (now shut down) and China. Catalyst is regenerated in a batch process, in situ. Heat removal is via recycled gas exchange, and the exchangers are large as gases are exchanged. An improved MTG reactor design is a fluidised bed reactor similar to a fluid catalytic cracker (FCC). The fluidised process allows continuous catalyst addition and regeneration. Heat removal is accomplished by generating steam. Extension of this technology to methanol-to-jet (MTJ) production is possible with changes in operating conditions and fractionation.

The emerging technology is directional, progressing from MTG to MTJ, and focused on lower investment cost. Using fluidised bed reactors allows smaller systems and lower investment. Approval for MTJ as aircraft fuel is being evaluated by ASTM to ensure safe performance. ASTM International’s aviation fuel subcommittee developed the ASTM D4054 standard practice to outline the data needed to assess a fuel’s performance and composition. ASTM is fast-tracking the approval, but at the time of writing it had still not been approved. The ASTM subcommittee approved the establishment of a task force to oversee the work leading to the qualification of new SAF. In addition to chairing the ASTM MTJ Task Force, ExxonMobil has produced and submitted test batches of MTJ for evaluation by the ASTM D4054 Clearinghouse. Provided the fuel passes as a blendstock with fossil jet, the results of the work would update ASTM D7566.

Mar-2025