PTQ Q4 2025 Issue

Main operational challenges and catalytic solutions for renewables co-processing distillate hydrotreating

Operational challenges

Catalytic solutions • Trapping of solid impurities

• Increased pressure drop

• Control of polymerisation reactions • Trapping of phosphorous and alkaline metals • Selective conversion of fatty acides (HDO) • Control of polymerisation reactions • Selective conversion of fatty acids (HDO) • Tailored HDS/N/A main catalyst system

• Product yield loss

• Higher exotherm and H₂ consumption

• Higher WABT

• Worsened cold flow properties

• Deeper nitrogen removal • Dewaxing (cracking or isomerisation)

Table 2

Operational challenges and catalytic solutions Table 2 summarises the key operational challenges when co-processing renewables and their catalytic solutions. Increased dP can be caused by solid impurities, gum for- mation and coking from triglycerides, and by the accumula- tion of phospholipids. Solid impurities can be trapped at the reactor top by applying macroporous ceramic foam filters. These filters have a high void fraction and macropores that ensure particulates trapping and undisturbed feed flow. For scale, particulate, and gum management, Ketjen applies KG 56 ceramic foam disks. Stacking foam filters with increas - ing pore density is typically applied to optimise trapping efficiency and maximise reactor volume for other catalyst functionalities. Gum formation occurring in the reactor under the foam filters and throughout reactor Zone 1 can be tackled by applying dedicated catalyst grading. The extent and con - Among the three decomposition pathways of fatty acids, HDO is by far the preferred one as it does not produce CO and CO₂. By doing so, it retains carbon within the diesel pool, resulting in a higher diesel yield sequences of gum formation are exacerbated by the high exotherm and H₂ consumption from the reactions of triglyc - erides, as previously shown in Figure 7, leading to local H₂ depletion and to the condensation of gum into coke. Proper catalyst grading ensures that gum formation and coking are minimised and distributed more evenly across the entire guard bed, thereby reducing the risk of local dP build-up. Phosphorus from phospholipids deposits on the catalyst pore mouth, blocking feed access to the active sites, and reducing the ability of the guard bed to trap metals. This can result in metals from the feed reaching and deactivating the underlying main catalyst layers. Phosphorus trapping is enhanced by applying grades with large median pore diameters and a proper balance between pore accessibility

The second reaction step is the decomposition of the saturated triglycerides into fatty acids, producing propane. Also this reaction is fast and occurs at the reactor top. Both the saturation of the double bonds in the fatty acid chains and the decomposition of the saturated triglycerides into fatty acids take place in the guard bed and in operating Zone 1. These reactions occur in parallel with the ongo- ing reactions in the conventional feedstock, including the saturation of olefins, conversion of easy sulphur and easy nitrogen compounds, and the HYD of PNAs, as previously shown in Figure 1. Fatty acids formed from the decomposition of triglycer- ides or directly present in the biofeed react further to form n-paraffins through two competing paths, hydrodeoxygen - ation (HDO) and decarboxylation (DCX). The CO₂ produced in the DCX reaction can further react with H₂, forming CO and H₂O, leading to the decarbonylation (DCN) reaction. The DCX and DCN reactions are linked by the reverse water gas shift (RWGS) reaction, which is always at thermody- namic equilibrium. Additionally, CO and H₂ react to form methane through the methanation (MTN) reaction. Note that the RWGS and MTN reactions occur in the gas phase in all reactor zones. While the CO₂ formed is mostly removed by the scrubbing system (if present), CO and CH₄ tend to accumulate in the recycle gas, reducing PPH2, which lowers the perfor- mance of the main hydrotreating catalyst, especially NiMos. Lowered PPH2 can also lead to higher coke formation on the catalyst system. Among the three decomposition pathways of fatty acids, HDO is by far the preferred one as it does not produce CO and CO₂. By doing so, it retains carbon within the diesel pool, resulting in a higher diesel yield. Additionally, CO is a strong inhibitor of the direct desulphurisation (DDS) path- way of the HDS reaction, which is particularly important at moderate PPH2 and when CoMo catalysts are applied.1 At low PPH2 with a 5% biofeed intake, CO inhibition on HDS can lead to penalties of up to 10°C/18°F in WABT and a 5% loss in diesel yield. Therefore, along with applying an efficient phosphorous trapping guard system, to maintain operating efficiency and improve economics in biofeed co-processing operations, it is crucial to load a highly selec- tive and stable HDO catalyst.

PTQ Q4 2025