PTQ Q1 2026 Issue

Trust through testing: How to select the right hydroprocessing catalyst

Catalyst evaluation in pilot plants can use three distinct configurations, each offering benefits and limitations based on testing goals, feedstock type, and reactor capabilities

Rahul Singh and Xavier E Ruiz Maldonado Topsoe

H ydroprocessing is a refining process by which low-valued feedstocks are upgraded into high-value products through reactions with hydrogen and highly formulated heterogenous catalysts. These reactions are typ- ically carried out in industrial trickle-bed reactors (TBRs). In hydrotreating processes, TBRs are a class of fixed-bed reactors where hydrogen and oil phases flow co-currently downward through a packed bed of catalysts consisting of an alumina or alumina/zeolite carrier structure promoted with various concentrations of cobalt, nickel, molybdenum, and tungsten. These reactors typically operate industrially under optimal superficial velocity, liquid space velocity, and hydrogen-to-oil ratio conditions (see Figure 1 ):

Hydrogen-rich gas continuous phase

Oil thin, discontinuous lm

Volumetric flow Total cross-sectional of the reactor

• Optimal superficial velocity:

Volumetric flow Catalysts volume Total hydrogen flow Total fresh oil flow

• Liquid space velocity:

• Hydrogen-to-oil ratio:

The trickle bed regime occurs at relatively low to moder- ate liquid and gas flow rates, where the following physical behaviours dominate: • The oil phase descends through the fixed catalyst bed as a thin, discontinuous film over the surface area of the catalyst particle. • Hydrogen-rich gas acts as the continuous phase, occupy- ing the void spaces between catalyst particles and flowing co-currently (downward) with the liquid. • Both gas and liquid phases contact the solid heterogene- ous catalyst, enabling surface mediated reactions. Reactor design and operating conditions must ensure effec- tive catalyst wetting, sufficient hydrogen solubility, and opti- mal reactant access to active sites on the surface area of the catalyst, all of which directly influence catalyst performance. Although commercial units run under stable, optimised conditions, pilot plant tests often require altered flow regimes, higher hydrogen-to-oil ratios, elevated superficial velocities, or added diluents to replicate the wetting, heat transfer, and mass transfer characteristics of larger industrial hydroprocessing units. When translating pilot data to full-scale operations, it is critical to account for scale-related limitations, follow the

Solid hetrogeneous catalyst

Figure 1 Trickle-bed reactors (TBRs)

catalyst supplier’s activation protocols, and interpret perfor- mance metrics within the context of a meaningful industrial application. Pilot plant testing considerations Prior to industrial deployment, hydroprocessing catalysts are evaluated in pilot plant units to generate kinetic data and assess the influence of operating conditions. For high-profile units like hydrocrackers, FCC pretreat, and ultra-low sulphur diesel (ULSD) pilot plants testing is typically essential to vali- date catalyst performance in terms of sharp-cut point yields, selectivity, specific product properties, activity, and provide a clear definition of volume swell or true conversion/gross conversion, as well as to rank offerings from multiple cata- lyst suppliers. Pilot plant testing, when performed correctly, will provide transparency in catalyst selection and serves as a critical decision-making tool to identify the most valuable option for the refinery’s objective. Pilot testing is sometimes initiated through collaboration

PTQ Q1 2026