Catalysis 2025 Issue

catalysis q&a

More answers to these questions can be found at www.digitalrefining.com/qanda

Q What evolving methanol-to-olefins configurations are feasible for SAF production? A Scott Sayles , Manager, Renewable Fuels and Alternate Feeds, Becht, ssayles@becht.com Methanol processes that emit a minimal amount of green- house 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) fol - lowed 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 technol - ogies 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 pro - duction is an exothermic reaction requiring heat removal. The catalyst also deactivates, requiring regeneration. Fixed-bed designs use a cyclic design, with some reactors in regenera - tion 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 (naph - thene), and a smaller concentration of naphthene/aromat- ics. FT synthesis allows for customising the hydrocarbon chain length range to the jet fuel range of C 9 to C 1₆. 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 simi - lar 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 pos - sible 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 lead - ing 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 blend - stock with fossil jet, the results of the work would update ASTM D7566. A Woody Shiflett, President, 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 associ - ated carbon intensity of existing MTO processes that utilise fluidised bed reactors and associated regeneration configu - rations 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 distri - bution 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

MeOH to Olens

MeOH

C–C Olens

Figure 1 Converting methanol to olefins is a proven technol - ogy with many licence providers

Catalysis 2025