Decarbonisation Technology May 2025 Issue

applications. Notably, the core of the catalyst extrudate, where only a low concentration of P is deposited, represents just 24% of the catalyst volume, indicating that the effective use of the catalyst is nearly 76%. Another important aspect of an HDO catalyst is its ability to selectively remove oxygen via the hydrodeoxygenation pathway, splitting off oxygen as H 2 O instead of CO or CO 2 during the HDO step. Besides reaction conditions, such as temperature (T) and pressure (P), the HDO selectivity is determined by the catalyst applied. The use of a selective HDO catalyst minimises the formation of CO, which can cause issues in off-gas handling and results in maximum carbon yield as valuable products. This HDO selectivity can be derived from the ratio of C 17 and C 18 n-paraffins in the HDO product since fatty acid chains with an uneven C-number do not naturally occur in biogenic triglycerides. Ketjen’s ReNewFine 204 catalyst was designed to deliver optimal HDO selectivity. As illustrated in Figure 3 , compared to previous- generation HDO catalysts, a 15% higher selectivity can be achieved using ReNewFine 204 over a broad temperature range, which translates to almost 1% higher carbon yield in the final product. This catalyst provides supreme stability towards the deposition of phosphorus (P), ensuring that the high HDO selectivity can be maintained throughout the HDO cycle. By targeting the use of this catalyst grade in the reactor zone where triglycerides are converted, a small layer of this catalyst is required to improve the HDO selectivity of the entire reactor loading. N-compounds, such as fatty amines and amides, form another class of heteroatom compounds that require special attention in the HDO reactor. If N-compounds are not effectively removed by the HDO catalyst system, this may significantly lower the performance of the downstream HI catalyst. This is particularly critical when the goal is to produce SAF, which requires deep isomerisation. N-slip from the HDO reactor can lead to sub-optimal performance. While deep hydrodenitrogenation (HDN) is important, care must be taken to prevent the oligomerisation of n-paraffins in the final zone of the HDO

+15%

310

330

345

Temperature (˚C)

Conventional HDO catalyst

ReNewFine 204

50% ReNewFine 204 50% Conventional HDO

reactor, as this would result in the formation of high molecular weight compounds that can severely impact the properties of the final product. Considering the range of different reactions that need to be catalysed in the HDO reactor, it is inevitable that an optimal HDO reactor Figure 3 HDO selectivity (defined as the ratio between C 17 and C 17 +C 18 n-paraffins in the HDO product) for ReNewFine 204 catalyst applied as a full load (yellow) and as a 50/50 load with a conventional catalyst (green), as a function of operating T as compared to operation with a conventional HDO catalyst (grey) loading consists of several different HDO catalysts, each with a specific function. For this reason, Ketjen has developed its ReNewFine portfolio, which includes guard bed catalysts (ReNewFine 100 series), HDO catalysts (ReNewFine 200 series), and HDN catalysts (ReNewFine 300 series). By combining the catalysts in this portfolio, an optimal ReNewSTAX reactor loading can be designed for each HDO unit, tailored to the unique operational requirements to ensure minimum N-slip and oligomerisation, as well as maximum cycle length. “ Another important aspect of an HDO catalyst is its ability to selectively remove oxygen via the hydrodeoxygenation pathway splitting off oxygen as H 2 O instead of CO or CO 2 during the HDO step ”