PTQ Q1 2026 Issue

Key consideration for in-situ sulphiding during pilot test

Key parameter

Objective

Required in commercial unit

Feed final boiling point and density High LHSV and sulphur content

Control the amount of poly-aromatic and prevent hydrogen starvation Ensure proper wetting and sulphur for sulphiding and activation

Yes No No Yes Yes Yes

High hydrogen-to-oil ratio Controlled heating ramp

Overcome linear velocity and mass transfer limitations

Ensure uniform and effective sulphiding

Maximum sulphiding temperature

Promote proper metals slab formation and catalyst activation Prevent hydrogen starvation and coking while passivating the catalyst

Break-in period (48 hours) before testing

Table 3

benchmarking, it is therefore recommended that kinetic data obtained from microreactors be validated against larger bench-scale units that provide more representative and accurate hydrodynamic conditions. Topsoe recommends the following best practice for reliable catalyst benchmarking: • Initiate testing at moderate temperature and increase severity gradually. • Follow consistent sulphiding and activation procedures, according to the catalyst supplier. • Avoid overtreating catalysts to ensure real activity differ- ences are visible, unless volume swell is the target (for exam- ple, ULSD), where overtreating is, in most cases, unavoidable. • Validate any microreactor (least reliable) results with bench-scale reactor data (most reliable) to conclude. Pilot plant vs commercial in-situ activation of catalysts Catalyst development with high activity for cracking, sulphur and nitrogen removal, and aromatic saturation is essential for upgrading challenging refinery feedstocks into valua - ble products. There is sustained industry demand for pro- gressively higher-activity catalysts, enabling processing of higher refractory feed charges, increased volume swell, and/ or extended cycle lengths. However, formulation of new-generation, high-activity catalysts often necessitates more careful sulphiding proce- dures during pilot testing (see Table 3 ). This is due to hydro- dynamic limitations at smaller scales, particularly lower linear velocities and non-ideal flow regimes. These extra precau - tions are not typically required at a commercial scale, where such limitations are mitigated by higher linear velocity and better hydrogen distribution.

Highly dispersed catalysts are more sensitive to coke for- mation, which can result from hydrogen starvation during activation under pilot-scale conditions where mass trans- fer rates are lower than the surface reaction rates. In these small-scale units, non-ideal plug flow and mass transfer limitations can restrict hydrogen diffusion through the liquid phase to the catalyst surface. This is particularly critical dur- ing the initial activation stage, where hydrogen demand is high due to rapid aromatic hydrogenation. It has been observed that 80-95% of hydrogen consump- tion typically occurs within the first 10-20% of the reactor length in pilot units. This creates a steep hydrogen concen- tration gradient at the top of the bed. As readily saturable aromatics are rapidly hydrogenated, the dissolved hydrogen is quickly depleted. Consequently, catalyst particles at the top may experience internal hydrogen deficiency, increasing the risk of localised deactivation and coke formation. This can be mitigated by making the pilot plant reactor quite long (3ft or more). In this reactor design, the impacted catalyst at the top of the tube will not impact the overall result of the test because the majority of the catalyst is seeing normal process conditions. This mitigation is not possible in a high- throughput micro-scale reactor due to the extremely small catalyst volume and a reactor length of only a few inches. This artificially high deactivation rate, caused by mass transfer limitations, rapid hydrogen consumption, and sub- optimal activation, will compromise the reliability of pilot- scale results and lead to inaccurate assessments of catalyst performance. A common unit operator question is whether the high hydrogen-to-oil ratio required during pilot testing is also necessary in a commercial unit. The answer is no; the higher hydrogen-to-oil ratio is a pilot-specific requirement, implemented to compensate for mass transfer limitations phenomena present due to hydrodynamic limitations not present at the commercial scale. In commercial units, better hydrogen distribution and flow characteristics ensure effec - tive activation without the need for such adjustments. Pilot plant reactor selection Bench-scale tubular reactors have the best geometric and flow characteristics among lab reactors to minimise wall effects, mass transfer, heat transfer, and wetting effects (une- ven irrigation). Additionally, upsets from reactor plugging are avoided with wider diameter bench-scale reactors. Hence, reloading and restarting the pilot plant is avoided. This case

120

Pe = 100

100

Pe vs. L/d

L/d = 350 (recommended) p

Pe = 40

L/d = 350 p

50 100 150 200

250

300

350

400

L/d (reactor length/particle diameter) p

Figure 4 Peclet number vs reactor length/particle diameter

PTQ Q1 2026