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What contaminants removal capabilities are available to expand the SAF feedstock base?

Jan-2024

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Ezequiel Vicent, Oli Systems, Ezequiel.Vicent@olisystems.com

The advent of renewable fuels has brought the necessity to change catalyst to treat the carboxylic groups in the fatty acids that make up vegetable oils (increased CO, CO₂ and H₂O production) as well as an increase in chlorides. In addition to catalyst selection, unit engineers need to focus on the production of the byproducts from these reactions.

We have seen an increase in NH₄Cl salt formation out of these feeds that can foul the feed-effluent exchangers at higher temperatures. The increase in water formation (up to five times larger than usual hydrocarbon feed) means the possibility of the salts that deposit in the feed-effluent exchangers getting wet increases dramatically. Engineers need to monitor the exchangers for the NH₄Cl formation temperature as well as the relative humidity increase due to increased water content.

The engineer should note that at relative humidity greater than 10%, ammonium chloride salts will start to absorb water from the vapour stream. This can cause under-deposit corrosion and pitting in equipment and piping. The equipment most at risk for this type of corrosion is the feed-effluent heat exchangers and the piping up to the reactor effluent air coolers inlet wash water injection.

In this case, operations will need to invest in monitoring tools (both software and hardware) that can help them calculate salt formation temperatures, water relative humidity, and sour water concentrations (especially bisulphide concentration) to maintain static asset reliability.

Jan-2024
Kandasamy Sundaram, Lummus Technology, kandasamy.sundaram@lummustech.com

SAF is addressed from different angles. Plastics pyrolysis, tyre pyrolysis, and vegetable oils are a few examples. They all have different types of contaminants compared with fossil fuels. Some adsorbents are used to remove some contaminants. However, they are not able to reduce the concentration significantly. Hydrotreating is required. Isoterra for vegetable oil uses hydrotreating. Plastic pyoil requires hydrotreating to reduce chlorides and nitrogen. For chemicals production, adsorbents meet the specification in some cases.

Jan-2024
Andres Coy, Clariant Catalysts, Andres.Coy@clariant.com

The potential feedstocks and process routes toward SAF are constantly increasing. Any SAF as a final Jet fuel blending component must meet very stringent specifications, as aviation fuels are the most delicate fuel products in terms of quality and stability. In addition, most of these processes need optimum reactant properties to achieve the most efficient SAF yields. Clariant offers a broad variety of catalysts and adsorbents technology to clean most feed and intermediate species in gas or liquid phase for these SAF processing technologies. This technology is primarily based on long-time experience in handling non-benign and demanding feed streams even in industries beyond refinery.

Jan-2024
Yvon Bernard, AXENS, Yvon.BERNARD@axens.net

For SAF production from low-carbon ethanol through Axens’ proprietary Jetanol solution, one of the key Axens features (Atol) is an innovative and profitable technology due to its flexibility in handling a wide range of feedstocks. During the technology development, Axens, along with its partners IFPEN and TotalEnergies, developed customised analytical methods for mastering the ethanol impurities that are critical for this application.

Extensive testing in pilot plants was also performed to confirm the technical ability to process virtually all kinds of ethanol: bioethanol (1G) or advanced ethanol (2G) and waste-based ethanol (from blast furnace flue gas and municipal solid waste) at various levels of dilution. Furthermore, Atol relies on its superior catalyst, which has proven to have a high tolerance to feedstock impurities and is fully regenerable. Atol catalyst provides even more flexibility by allowing the handling of feedstock quality fluctuations. In terms of ethanol, impurities are well-known and can be handled with pretreatment solutions.

For SAF production from lignocellulosic biomass via gasification route (BioTfueL), impurities are dealt with in three steps. The first is the pretreatment step, which ensures the removal of foreign contaminants such as glass, rocks, plastics, and moisture. Additionally, the pretreatment homogenises the biomass through drying and torrefaction: this step is key to enabling the utilisation of a wide array of lignocellulosic biomass, from agricultural residues to energy crops and forestry residues. In the second step, biomass gasification technology removes the inorganic (mineral, metals) and chlorine from the biomass.

The remaining S- or N-based impurities are removed in the syngas phase through well-known separation technologies. Its smart and flexible contaminant removal scheme allows BioTfueL to operate with any kind of biomass. This feature means more resilience for the project and gives significant flexibility in operation to the customers. Some additional feedstock, like municipal solid wastes, brings other opportunities but requires additional pretreatment and purification steps to deal with the heterogeneity of the feedstock and impurities.

For SAF production from CO₂ and H₂, purity requirements are often regulated by the downstream unit, mainly the Fischer-Tropsch reaction section for the e-fuel production. Axens dispatches its wide portfolio to cope with the common impurities found in CO₂ feedstock, including adsorbents for impurities trapping as well as washing sections, to bring the feed to the desired specifications. The final scheme of purification will depend on CO₂ project quality and is typically adapted on a case-by-case approach. Typical contaminants for FT catalyst are (sulphur, organic nitrogen, metal, NOx). Axens’ integrated scheme takes advantage of its expertise and know-how to optimise the sizing and positioning of such purification requirements.

For SAF production from vegetable oils with Vegan technology, pretreatment is also needed. Phospholipids and metals (Fe, Mg, K, Ca, Na) were the main contaminants present in the first-generation vegetable oil (soybean oil, palm oil, rapeseed oil) and could be abated with well-established edible oil refining technologies. The processing of second-generation waste oil (used cooking oil, animal fats) brings a wide variety of contaminants, including the same contaminants as vegetable oil, but at higher content.

Pretreatment technologies are adapting to remove contaminants to acceptable levels. Higher nitrogen, sulphur and chlorine are also observed in these new feeds: nitrogen/sulphur are partially removed by pretreatment and then converted by the hydrotreatment, inorganic chloride is completely removed by pretreatment, whereas organic chloride slips to the hydroprocessing unit, which has an impact on the unit design and metallurgy selection. Polyethylene found mostly in animal fats should be removed in a dedicated section of the lipid feed pretreatment.

Jan-2024