Apr-2022

Data quality obtained in refinery catalyst testing

With high data quality (repeatability, reproducibility, and scalability) refiners can confidently determine the most efficient catalyst for their process units.

Tiago Vilela
Avantium Catalysis

Article Summary

Accurate evaluation of catalysts performance is crucial in optimising catalytic refinery processes with respect to product yields, run length, energy efficiency, and overall product quality. Utilising high-throughput multiple parallel reactors with excellent reactor-to-reactor repeatability is key to achieving the desired high data quality.¹

High data quality means that the test results are reproducible and thus reliable to evaluate the best performing catalysts. To guarantee high data quality in a parallel system, we need to obtain a good reactor-to-reactor repeatability where duplicate reactors within a run (loaded with the same catalyst system) yield the same results (within the experimental error margins). We also need to obtain good run-to-run reproducibility where the same catalyst system tested in different runs yields comparable results. As the catalyst packing in the reactors is straightforward (single-pellet string-reactor, or SPSR, loading) and does not require any special procedures, we avoid typical packing issues like wall effect or channelling. This results in excellent reactor loading repeatability, which translates into the high quality of the test results.

Avantium developed small-scale parallel fixed bed reactor systems designed for catalyst intake of up to 1 ml, trade name Flowrence, to enhance catalyst development and selection for refinery applications. Flowrence high-throughput technology with 16 reactors in parallel is extensively used to simulate refinery catalytic processes, such as hydrotreating, hydrocracking, reforming, isomerisation, and dewaxing, over a wide range of process conditions and applications.

These small-scale reactors are ideal in terms of heat transfer and hydrodynamics compared to larger reactors and therefore provide data that is reliable and intrinsically easier to translate to an industrial scale.²

It is intuitive to expect that larger reactors are less susceptible to size-related limitations. However, recent research by Moonen et al. shows that SPSRs are no more susceptible to wall effects, channelling, and back mixing than properly utilised bench-scale reactors. Through an experimental programme, Moonen et al. showed an excellent correspondence for gas oil hydrodesulphurisation (HDS) between an Avantium SPSR unit and a bench-scale unit with a catalyst volume of 225 ml — more than 300 times the volume of an SPSR. With rigorous modelling of the corresponding hydrodynamics, they explained why results from the smaller unit are so similar to the larger one.³

In addition, a recent paper for a lubricant base-oil hydrotreater showed that comparable results are obtained when using the Flowrence unit with 16 parallel SPSRs and a conventional pilot plant with a single-reactor pilot plant with a catalyst volume between 0.5L and 1L. For both catalyst systems, the relative average deviations were less than 1 wt% for HDS and HDN.⁴

In the Flowrence unit, the schemes were evaluated in parallel — at two different space velocities and in quadruplicate for increased accuracy — while in the conventional unit the catalyst schemes were tested one at a time without replication. Due to excellent hydrodynamics of the SPSR and sophisticated process control, Avantium’s unit achieves high repeatability, resulting in average deviations of less than 0.2 wt ppm for HDS and HDN across the quadruple reactors with the same loading scheme^.5

The engineering concepts of the Flowrence parallel small-scale reactor systems are discussed in the book chapter by van der Waal et al. This includes the influence of catalyst particle size, flow patterns, pressure drop, and temperature profiles on the quality of catalytic performance results and is exemplified by multiple case studies on Fischer-Tropsch, oxidative coupling of methane, hydrocracking, and hydrotreating applications.

Parallel testing allows for replication — determining the statistical significance of results obtained — and simply evaluating more catalyst options simultaneously (side-by-side. In addition, smaller volumes will reduce the amount of feed required, avoiding the typical issues associated with obtaining large quantities such as handling, shipping, and storage (also for longer term availability of reference feed material).

The catalyst testing data presented in this article were obtained in collaboration with the major catalyst suppliers Albemarle, ART, Axens/IFPEN, Haldor Topsoe, Shell, and UOP. All catalyst suppliers have validated the resulting data quality (repeatability, reproducibility, and scalability).

Technology
Micro-pilot plant
Figure 1 shows a schematic overview of the 16 parallel reactors micro-pilot plant. This unit employs Flowrence technology, which enables the tight control of process conditions — temperature, flow rates, and pressure.
The Flowrence high-throughput systems employ a series of patented technologies to ensure the highest precision in controlling the flow, temperature, and pressure. Five key constituents’ technologies play a crucial role in the overall performance of the parallel reactors system.¹

Tube-in-tube reactor system with effluent dilution
The tube-in-tube design (Figure 2) offers several advantages. The reactors can be quickly and easily replaced without the need for any connections. Each reactor block has a large and accurate isothermal zone where we can ensure a correct plug flow regime with reactor-to-reactor temperature uniformity ≤0.5°C (≤0.9°F).

The use of an inert diluent gas to maintain the reactor pressure is used to stop undesirable reactions directly after the catalyst bed, serving as a carrier gas for the gas products analysed in the GC.

Single-pellet-string-reactor loading
Catalyst packing in the SPSR is straightforward and does not require special procedures. A single string of catalyst particles is loaded in the reactors with an internal diameter (ID) that closely matches the average particle diameter. This applies to single catalyst systems, as well as stacked bed systems. An inert non-porous diluent material (with a defined average particle size distribution) is used as a filler to enhance hydrodynamics. Before final loading in a steel reactor tube, we often perform a trial loading in quartz reactors to confirm the packing (Figure 3). The extrudates are used as delivered by the vendors.