naRTC 2026
Making the grade: how the right grading catalysts can maximise unit performance
Henrik Rasmussen, Xavier E. Ruiz Maldonado, and Maria J. L. Perez TOPSOE
Pressure drop and catalyst contamination can escalate rapidly in hydroprocessing units, turning smooth operations into costly unplanned shutdowns. This article exam- ines the common challenges facing refin- eries and the solutions offered by Topsoe’s versatile graded-bed catalyst technology portfolio, developed over several decades and applied in more than 10,000 hydro- treating unit replacements worldwide.
2.0”
TK-18 Top Trap™
TK-22 Top Trap™
TK-24 Top Trap™
1.5”
TK-15
5/8”
TK-10
0.5”
TK-26 Top Trap™
3/16”
TK-711
TK-30
TK-45
TK-709
TK-447 Silicon Trap™
1/8”
Feedstock and reactor operating challenges related to contaminants
TK-30
TK-831
TK-711
TK-337
TK-41
TK-335
1/10”QL
Fouling and contaminant issues present significant operational challenges across hydroprocessing units. In addition, scale formation can migrate to distribution trays and catalyst beds, leading to increased pressure drop and reduced catalyst utilisa- tion. Topsoe offers a broad, science-backed grading catalyst and scale catcher portfo- lio designed to mitigate the impact of these challenges and protect unit performance. Its grading portfolio is shown in Figure 1 . A scale catcher prevents these scales from reaching the catalyst, while a distribu- tion tray, such as the Topsoe BoxVLT™, with drip points that are self-cleaning and unaf- fected by scales collecting on the tray is key to maintaining even distribution throughout the catalyst cycle. In high-fouling environ- ments, where corrosion products and solids challenge conventional grading layers, sed- imentation-based systems installed above the tangent line enable suspended solids to settle before reaching distribution trays. Suspended or precipitated particulates, such as iron sulphide, corrosion prod- ucts, asphaltenes and polymerised spe- cies, deposit between catalyst particles or within internal pore structures. While hydro- processing feed filters typically remove particles above 15-25 μm, smaller con- taminants bypass filtration and accumulate within the graded bed, driving premature pressure drop build-up and flow maldistri- bution. High-void, macroporous inert mate- rials with void fractions above 85% address this challenge in the upper sections of cat- alyst beds. Reticulated foam discs capture both coarse and sub-micron foulants while maintaining minimal flow resistance. Topsoe’s TK-18 TopTrap™, TK-22 TopTrap™, TK-24 TopTrap™ and TK-26 TopTrap™ are engineered to capture large volumes of fine and coarse contaminants, retaining more than their own weight in corrosion particu- lates, iron sulphide, polymerised gums, and other heavy foulants. These systems target contaminants from sub-25 μm fines to frag- ments above 1,000 μm, as shown in Figure 2 , capturing multiple contaminant classes, including corrosion byproducts and metal- laden particles, such as magnesium, sodium, calcium, chromium, silicon, and phosphorus, in a single high-capacity filtration layer. Milling control and solids precipitation with a high-void material Particle displacement, or ‘milling’, occurs
TK-30
TK-341 TK-743
TK-461 Silicon Trap™
TK-773
TK-453 Silicon Trap™
TK-445 MultiTrap™
TK-467 Silicon Trap™
TK-339
TK-347
1/15”QL
TK-51
TK-3001
TK-449 Silicon Trap™
TK-3000 PhosTrap™
TK-49
TK-330
TK-343 Silicon Trap™
1/20”TL
Activity
Figure 1 Topsoe grading portfolio
tha and renewable fractions. TK-453 SiliconTrap™ is designed for heavier hydro- carbons, while TK-343 SiliconTrap™ targets the circular plastics industry. These cata- lyst guard products provide higher alumina surface utilisation and silicon uptake on a per-volume basis, capturing silicon species before they reach the main bed catalysts. Beyond trapping capacity, these catalysts also exhibit high hydrodenitrogenation and hydrodesulphurisation activity. Managing phosphorus-based contaminants in conventional and renewable feedstocks Phosphorus appears in both renewable and conventional feedstocks as hydrogenated phospholipids, phosphorus-based chem- icals from anticorrosion and antifouling agents, zinc dialkyldithiophosphate from spent lubricants, and other phosphorus- containing species. In hydrotreaters, these compounds decompose and react with alu- mina catalyst supports, irreversibly block- ing the active sites. Specialised guard materials capture phosphorus and other multi-contaminant species from biofeedstocks, spent lube oils, renewable feeds, and opportunity crudes. Topsoe’s TK-3000 PhosTrap™ and TK-455 MultiTrap™ feature proprietary pore struc- tures that enable phosphorus compounds to diffuse deeply into catalyst pellets, ensuring full pore volume utilisation, as shown in Figure 3 . This design creates uni- form phosphorus distribution throughout the material cross-section rather than sur- face saturation, thus maintaining low pres- sure drop across the guard bed. Arsenic trap Arsenic ranks among the most severe poi- sons in crude oil, commonly present in syncrudes from Canada and crudes from California, Mexico, and South America. It typically exists as arsenic trisulphide (As₂S₃) on CoMo and arsenic sulphide (AsS) on NiMo catalyst active sites, causing rapid deactivation. Even at concentrations of 20-1,000 ppb, arsenic causes more severe
TK-26 Top Trap™
<25 μm
TK-24 Top Trap™
20 - 200 μm
TK-22 Top Trap™
100 - 750 μm
TK-18 Top Trap™
500 - 2,000 μm
1
10
100
1,000
Target particle size (microns)
Figure 2 Nominal particle size for each TopTrap
Without TK-3000 With TK-3000
Run days
Figure 3 TK-3000 PhosTrap deposition and pressure drop control
designs. These catalysts use the same high surface area alumina and metal loading as main bed catalysts and are manufactured to ISO 9001:2015 quality standards. Combating organic silicon in conventional and renewable feedstocks Silicon contamination has emerged as a crit- ical challenge in processing coker-derived streams, renewable feedstocks, and dur- ing co-processing operations. Silicon com- pounds enter through antifoam additives in coker units and chemicals used as drag reducers during crude transport or tertiary recovery. High surface area, alumina-based guard materials effectively address silicon contamination. Topsoe’s TK-447 SiliconTrap™, TK-461 SiliconTrap™, TK-467 SiliconTrap™, and TK-449 SiliconTrap™ are optimised for lighter boiling-range feeds such as naph-
when horizontal forces across the catalyst bed exceed frictional resistance. High-void inert materials such as Topsoe’s TK-10 sta- bilise flow in the top of gas-phase reactors by absorbing horizontal momentum from inlet nozzles and promoting uniform veloc- ity profiles across the reactor cross-section. Olefin saturation control and radial temperature spread Uneven olefin saturation and localised temperature gradients contribute to radial temperature maldistribution, excessive pressure drop, and shortened catalyst life in hydroprocessing reactors. Ring-shaped grading catalysts with optimised pore sizes and surface areas enhance bed poros- ity and improve radial flow distribution. Topsoe’s TK-709, TK-711, and TK-831 fea- ture engineered ring shapes that provide a higher total void compared to conventional
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