Decarbonisation Technology November 2026 issue

Liquid-suspended (slurry) catalyst (even heat distribution tight band)

Solid catalyst bed (uneven heat removal

hot spots)

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Position along reactor bed

Figure 2 Illustrative local-temperature profile along the reactor bed: solid catalyst beds show wide swings from uneven heat removal, while liquid-suspended catalyst holds a tight band around the target set-point

two waste-derived gas streams into syngas- equivalent building blocks suitable for chain- growth synthesis, setting up the carbon backbone that will ultimately form the SAF molecule. Fischer-Tropsch synthesis: Building the C 1 -C 16 chain The converted syngas enters a Fischer-Tropsch (FT) synthesis reactor, where catalytic chain- growth reactions build hydrocarbons spanning the C1 to C16 range. SAF-grade jet fuel sits within this carbon-number range, meaning reactor selectivity, not just conversion rate, determines how much of the output lands in the usable fuel range (C 9-C16 ) versus lighter gases or heavier waxes that require further processing. A central engineering challenge addressed by ZCT is operating this synthesis under cold catalyst conditions. Cold catalyst FT synthesis reduces thermal degradation of the catalyst bed, improves selectivity towards the desired decide the outcome more than any other: the physical phase of the catalyst bed, and the precision of temperature control across the synthesis reactor ” “ Operating the GTL step at pilot scale has shown that two variables

carbon-chain distribution, and, critically, lowers the parasitic energy load of the reactor itself. Combined with heat integration across the wider plant, this is where ZCT departs most clearly from classical FT plant design. Experience in GTL conversion: Catalyst phase and temperature control Operating the GTL step at pilot scale has shown that two variables decide the outcome more than any other: the physical phase of the catalyst bed, and the precision of temperature control across the synthesis reactor. Both determine not just how much CO₂ and syngas convert, but what the converted carbon becomes: jet-range SAF, diesel-range product, or unusable light gas and wax. Solid catalyst vs liquid catalyst systems Conventional FT plants run fixed-bed or fluidised-bed reactors with a solid, typically cobalt- or iron-based catalyst, held in a static or circulating bed. This is well understood and easy to operate at large scale. However, it has a structural weakness: heat removal is uneven. Chain-growth FT reactions are strongly exothermic, and in a solid bed, hot spots form around active catalyst particles faster than the surrounding gas can carry the heat away. Hot spots push the reaction towards over-cracking and methane formation, eroding both yield and selectivity in the target carbon range.