Nov-2024

Accelerate SAF R&D with high-throughput catalyst testing

The required ramp-up in SAF production can be achieved more easily and efficiently with the support of high-throughput catalyst testing technology

Giada Innocenti, Benjamin Mutz, Christoph Hauber, Jean-Claude Adelbrecht, Ioan-Teodor Trotus
hte GmbH

Article Summary

Rising CO₂ emissions are a constant source of concern for both the public and government agencies due to their implications for global warming. Regulators have been setting stringent specifications to decarbonise every industrial sector, triggering a rethink of the refining and petrochemical industries. The European Green Deal has set the very ambitious target of decreasing the European Union’s greenhouse gas emissions by at least 55% by 2030 to reach climate neutrality by 2050. The European Union has launched the ReFuelEU initiative, which progressively increases the target amount of sustainable aviation fuel (SAF) that must be used to ensure that the aviation sector also reaches carbon neutrality. The goal of 70% SAF by 2050 can only be achieved if a ramp-up in SAF production from different sources is pursued.

The technologies for producing SAF are at different technology readiness levels depending on the type of raw material used (syngas, used cooking oils, animal fats, alcohols, algae, and so on). It is clear that state-of-the-art tools are needed to provide the requisite momentum for the development and optimisation work required to enable a quick increase in SAF production. SAF production efficiency can be accelerated through the use of high-throughput experimentation. This technology enables the rapid collection of large datasets to develop kinetic models, test the impact of upsets, or identify the most efficient catalyst in a benchmarking study. By providing a large amount of data in a short timeframe, high-throughput technology can support the retrofit of existing facilities or the choice of either the best catalyst or the optimal operational conditions for newer dedicated production plants.

The most technologically advanced routes to SAF are shown in Figure 1 and will be discussed in this article.

Syngas to liquid hydrocarbons via Fischer- Tropsch synthesis
Fischer-Tropsch synthesis (FTS), which produces liquid hydrocarbons from CO/H2 mixtures, is the central process of the SAF route via syngas. FTS technology was originally developed for the conversion of natural gas or coal into fuels. Recently, however, FTS has been attracting more attention as a way to produce value-added fuels and chemicals from unconventional feedstocks such as biomass or municipal solid waste.

The hydrocarbon product spectrum from FTS follows an Anderson-Schultz-Flory distribution, which can be influenced by process conditions and catalyst selection. To target the highest yield of SAF, the formation of long-chain paraffinic hydrocarbons has to be favoured. Downstream hydroprocessing is then required to reach the desired fuel specifications.

Sustainable syngas composition and purity vary widely; it is, therefore, necessary to enhance process efficiency by improving the catalyst and selecting the right reaction parameters to achieve a targeted product distribution. Catalyst and parameter screening, kinetic studies, quality control, and catalyst upscaling towards extrudate testing can be accelerated by high-throughput technology featuring a robust and reliable gas-to-liquid workflow, as detailed in an earlier publication (Knobloch, et al., 2015).

hte’s well-established reactor packing protocols ensure stable plug flow conditions and prevent thermal runaways, enabling a broad range of conversion rates and reproducible performance data. The fully integrated data warehouse allows accurate quantification and real-time calculation of conversion, product formation rates, and mass balance (see Figure 2). The mass balance can be closed to 100±2% by combining the products generated in both the gas and liquid phases, each quantified via fast online detection and integral wax analysis, respectively. hte’s multicolumn/multidetector gas chromatography (GC), configured in-house, makes it possible to reliably discern paraffins, olefins, isomers, and alcohols.

The great flexibility of high-throughput experimentation allows ranking among possible candidate catalysts with a one-to-one comparison. For example, the effect of the pore structures in different samples of Co/TiO2 was highlighted by running 48 experiments within a five-week timeframe. This was achieved using 32 reactors in parallel to explore the parameter space of the kinetically controlled regime (Schulz, et al., 2021). As another example, an 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 CO2 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 CO2 with the use of green H2 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 CO2 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 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 CO2 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, CO2 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.