Decarbonisation Technology - November 2024 Issue

hte customer reported using hte technology for intensive testing of bifunctional FTS catalysts ( Kibby, et al., 2013 ). FTS is considered to be very promising for CO 2 emissions abatement when used in the production of SAF. The sustainability of FTS would be ensured by integrating reverse water gas shift (rWGS) of captured CO 2 with the use of green H 2 as feedstock for the process. Direct coupling of both processes can be realised by operating the rWGS reactor at 30-40 bar, which requires high temperatures to convert CO 2 into CO. To address this challenge at laboratory scale, it is essential to have a suitable reactor concept that allows the catalyst activity to be isolated from any potential reactor wall activity. hte technology ensures data reliability and accuracy by using reactors with a ceramic inlay tube that can operate at conditions such as 780°C and 50 bar, thus combining high temperatures and “ As an alternative route towards hydrocarbons, CO 2 can be directly used to synthesise methanol, which can then be further converted within the methanol-to-olefins process ” elevated pressures. Such reactors can be used to carry out different types of chemical reactions and are suitable for both low-conversion kinetic studies and high-conversion stability tests ( Mutz, et al., 2022 ). Once the FTS waxes are obtained, they require hydroprocessing, carried out in trickle bed units, to ensure they meet the specifications for SAF. With the use of both gas phase and trickle bed high-throughput units, hte has enabled its customers to carry out FTS first, followed by wax hydroprocessing ( Roberts, et al., 2020 ). Details about the latter process step are provided in the following sections. The direct conversion of CO 2 as FTS feedstock without the use of a separate reactor to operate rWGS can be achieved using shift-active Fe-based catalysts. However, it presents additional challenges and limitations requiring a rethinking of the process. As an alternative route towards hydrocarbons, CO 2

can be directly used to synthesise methanol, which can then be further converted within the methanol-to-olefins (MTO) process. Screening of the activity for different catalytic systems and testing of the different operating conditions for this type of reaction can be readily achieved by using hte’s catalyst- testing technology ( Haas, et al., 2019 ). Finally, the olefins produced via MTO can be further processed by means of oligomerisation to produce SAF. Oligomerisation of renewable ethylene The process of converting alcohol to jet fuel (alcohol-to-jet) is another promising route to meeting the necessary blend mandates in the coming years. Such a process is currently being commercialised by a variety of companies. The upgrading of ethanol to SAF first requires a dehydration step to produce ethylene, followed by a purification step and oligomerisation to produce long-chain alkanes. The production of SAF is achieved by employing a two-step oligomerisation route rather than direct ethylene oligomerisation to better control the selectivity to C 8 -C 16 alkenes. Accordingly, ethylene is first converted to butenes and hexenes on Ni-based catalysts at low temperatures, and subsequently the olefin mixtures produced are further upgraded over an acidic catalyst at higher temperatures. Finally, the products are hydrogenated to transform all the olefins into alkanes and meet the SAF specifications, as defined by ASTM D7566. While olefin hydrogenation is a well- known process, the testing and scale-up of oligomerisation catalysts and process conditions require both catalyst and process optimisation. hte operates various gas-to-liquid high- throughput units, which could be used to rapidly screen a large number of potential catalysts. One of the major concerns with oligomerisation is controlling the large amount of heat generated by the reaction. hte’s technology can handle this issue by loading a limited amount of catalyst (up to 3 mL) diluted with inert material as well as diluting the olefinic feed with inert gas. Once the optimal catalyst is selected, it is possible to move on to the process optimisation stage. This part typically requires the use of