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Catalytic reactions are critical to the energy sector, being used ubiquitously to convert simple natural gases and biomass into high-energy fuels and chemicals. A solid catalyst is put into contact with gaseous reactants to speed up the formation of the desired products and dramatically enhance efficiency.
For decades, these reactions have been run in fixed bed reactors, which are filled with catalyst pellets packed in a random order. This ‘packed-bed’ design limits the reaction potential, due to a slow rate of heat transfer either into or out of the reactor.
“A critical aspect of such processes is the reaction heat management,” explains Enrico Tronconi, professor of Chemical Engineering at the Polytechnic University of Milan. “To enable new, efficient and compact process units, as is urgently needed in view of distributed energy scenarios, such obstacles need to be removed,” he adds.
In the EU-funded INTENT project, Tronconi designed a new ‘structured reactor’, able to intensify heat transfer of catalytic processes and potentially make the energy sector far more sustainable.
“We have shown both by experiment and by mathematical modelling that, if the internals are made of a highly conductive material – aluminium or copper, say – we can expect a much more efficient heat transfer than in packed beds,” says Tronconi. “For example, detrimental ‘hot spots’ or ‘cold spots’ in the reactor will be avoided.”
Introducing internal structures
By replacing the random packings of catalyst pellets with structured catalysts, like honeycombs or open-cell foams, the reactor takes advantage of a different heat transfer mechanism: heat conduction in the matrix of the structure.
These ‘internals’, which could be open-cell foams, or 3D-printed structures, can then be catalytically activated by coating them with a layer of active catalyst – a process known as ‘wash coating’. Alternatively, they could be packed with particles of catalyst of a size suitable to the desired reaction.
“In both cases, the highly conductive cellular structure ensures excellent heat transport and uniform temperature distribution across the reactor, thus removing the main bottleneck of the process,” remarks Tronconi.
Designing and testing conductive reactor internals
The INTENT team studied two generations of conductive reactor internals, starting with commercially available cellular materials and then moving to a new class of engineered, 3D printed designs. They then investigated these structures as catalyst carriers, through an innovative methodology that combines experiments with computational models.
In parallel, the researchers also studied the application of the new reactor concept experimentally at a lab scale, for two key processes: the Fischer-Tropsch (FT) synthesis, which produces clean hydrocarbon fuels; and the methane steam reforming (MSR), the most commonly used and cost-effective method to produce hydrogen.
The original INTENT plan also included an investigation of structured catalysts applied to solar reforming – using solar irradiation to supply the heat for MSR. In recent years, a new concept has emerged using electric energy from renewable sources to supply this heat. During INTENT, the team therefore steered their activities toward exploring this concept, and designed and constructed two new set-ups to run electrified MSR.
Helping create a future of clean energy
Thanks to promising results, the INTENT work on the electrification of MSR immediately attracted the attention of a major Italian energy company. The team is now jointly working on the development of an eMSR unit for small-scale, low-carbon hydrogen production.
INTENT has clearly proven that the application of thermally and electrically conductive cellular reactor internals has great potential for the intensification of catalytic processes, says Tronconi.
“In view of the current acceleration of the energy transition, the need for such an intensification is even much greater nowadays than it was when the project was originally conceived, seven years ago.”