Key operational differences between pilot plant and commercial unit
Key parameter
Pilot plant
Commercial unit
Temperature control
Isothermal operation
Adiabatic
Catalyst density Hydrogen purity
ASTM
Sock/Dense
99.99 vol%
Typical 75-95%
Hydrogen partial pressure
Adjusted to match average H₂ partial pressure, accounting for pressure drop Sharp cut points without overlap Improved via diluent addition and small
Average H₂ partial pressure considered directly
Fractionation
Typically, broader cuts with some product overlap
Catalyst wetting
Enhanced by reactor internals, geometry,
reactor geometry
and flow distribution LHSV considered
Space velocity Particle size
WHSV matching considered
Small particle size is preferred to minimise
Determined by pressure drop and
internal diffusion resistance
activity considerations
Table 4
v Refinery-focused units (customisable evaluation) : Topsoe uses comprehensive, refinery-oriented pilot units with large catalyst volumes, offering advanced configurabil- ity for catalyst comparison, long-term performance studies, and process optimisation. These customisable evaluations support: • Once-through, recycle, and two-stage flow schemes. • Real feedstocks, including cracked or contaminated streams. • Online fractionation for recycle/two-stage; offline for once-through. These units deliver robust insights into catalyst activity, product quality, and selectivity, closely simulating commer- cial operating conditions. w Third-party pilot plants: Commonly employed by refin- ers for catalyst benchmarking, third-party pilot plant units are typically once-through microreactors or bench-scale sys- tems. While convenient for independent comparison, they present notable limitations: • Inability of high-throughput microreactor facilities to follow vendor-specific sulphiding protocols due to equipment con- straints, requiring standardised (non-optimised) activation procedures, which leads to inconclusive performance data. • Increased risk of data ambiguity, especially for activity/ selectivity comparisons. • Poor ‘closure’ of the mass balance, meaning that the feed and product quantities do not match. In other words, mole- cules are lost and cannot be accounted for. • Insufficient lineout of the catalyst activity due to a too short testing time. • Microreactors also have frequent catalyst reloads due to fouling and microchannel blockage, interrupting the test campaign and losing data, making an inaccurate perfor- mance comparison. • Use of doped interstage feeds to simulate recycle units, requiring careful data interpretation to extract reliable con- clusions about yields and activity. • Lack of two-stage and recycle configurations. Conclusion When engaging a third-party pilot facility, always include a well-characterised incumbent catalyst as a reference to quantify performance differentials between the unit and the facility’s reactor. During each run, monitor key operating
parameters, such as conversion, selectivity, and pressure drop, by trending time-on-stream curves to verify steady- state conditions and promptly identify deviations. Should an upset occur, assess its potential impact on catalyst integrity and liaise with both the vendor and the refinery to define corrective actions. Clarify your mass balance closure meth- odology, raw versus elemental, and evaluate how this choice influences accuracy. Establish clear performance expectations with the catalyst supplier and ensure that the test feedstock closely matches RFP specifications; if necessary, forward samples for inde- pendent verification. It is also important to bear in mind that many third-party microreactor setups employ a single, uniform sulphiding protocol rather than vendor-specific pro- cedures, masking true catalyst behaviour. Additionally, their small channels can be susceptible to fouling, interrupting continuous operation. While microreactors offer valuable screening capabilities, they are not suitable for an accu- rate catalyst comparison; a properly designed larger pilot plant test unit is required for a proper quantitative catalyst comparison. References 1 Mears, D.E., Chemical Engineering Science , 26, 1971, 1361. 2 Levenspiel, O., Bischoff, K.B., Advanced Chemical Engineering, 4, 1963, 95. 3 Sie, S.T., Revue de l’Institut Français du Pétrole, 46, 1991, 501. 4 A Practical Guide To Catalyst Testing, Catalytica , 1987. 5 Delgado, J., Heat and Mass Transfer, 42, 2006. 6 Mederos, F.S., Ancheyta, J., Chen J., Applied Catalysis, 355, 2009, 1. Rahul Singh is Technical Service Manager for the hydrocracking catalyst segment for the US and Canada at Topsoe. He has been responsible for the overall technical service, sales and support to the hydrocracking cli- ents in North America for more than 10 years. He holds an MS and PhD in chemical engineering with a focus on heterogenous catalysis from the University of Akron, Ohio. Email: rsin@topsoe.com Xavier E Ruiz Maldonado is Technical Service Manager at Topsoe North America and has more than 19 years of experience in technical support in hydrotreating and hydrocracking industrial operations for both the Americas and European refinery business. He holds an MS in chemical engineering from Simon Bolivar University in Venezuela and a petro- leum studies degree from the French Institute of Petroleum. Email: xerm@topsoe.com
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PTQ Q1 2026
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