Structured Reactors with INTensified ENergy Transfer for Breakthrough Catalytic Technologies

Periodic Reporting for period 4 - INTENT (Structured Reactors with INTensified ENergy Transfer for Breakthrough Catalytic Technologies)

Berichtszeitraum: 2021-05-01 bis 2022-04-30

Critically important heterogeneous catalytic reactions for energy conversion and chemicals production have been run for decades in fixed bed tubular reactors packed with catalyst pellets, whose operation is intrinsically limited by slow heat removal/supply. There is urgent need for a new generation of chemical reactors to address the current quest for process intensification.

In the INTENT project we propose that a game-changing alternative is provided by structured reactors wherein the catalyst is washcoated onto or packed into structured substrates, like open-cell foams or 3D printed periodic open cellular structures (POCS), fabricated with highly conductive metals (Al, Cu).
The goal of INTENT is to elucidate fundamental and engineering properties of such novel conductive structured catalysts, investigate new concepts for their design, manufacturing, catalytic activation and operation, and demonstrate their potential for a quantum leap in the intensification of crucial catalytic processes for the production of sustainable energy vectors, like the conversion of syngas to clean synthetic fuels in compact Fischer-Tropsch Synthesis reactors, and the distributed Hydrogen generation in efficient small-size methane reformers using renewable energy.

To this purpose we combine CFD modelling with lab-scale experimentation in order to identify the optimal structure-performance relationships of existing and novel substrates, use such new knowledge to design optimized prototypes, apply additive manufacturing technologies for their production, and construct a semi-pilot tubular reactor to test them at a representative scale.

The project results enable novel reactor designs based on tuning geometry, materials and configurations of the conductive internals to match the activity – selectivity demands of specific process applications. The new reactor technology will have significant influence on both the Energy and on the Environment scenarios. As an example, it will enable compact Gas-to-Liquids process technologies with potential to drastically reduce flaring of associated and remote Natural Gas.

Task 1 - The fundamental investigation of the transport properties of open-cell foams as enhanced catalyst substrates has produced an original procedure for the digital reconstruction of foams from two easily accessible pieces of information, i.e. porosity and pore size. It generates faithful virtual replicas of real foams, suitable for numerical parametric analysis and optimization.
Pressure drops, heat and mass transfer in foams and POCS have been investigated combining experiments with CFD simulations. This has generated dimensionless correlations for fluid/solid mass transfer coefficients covering an unprecedented range of geometrical and flow variables, and optimal designs that maximize the effective thermal conductivity.

Task 2 –The catalytic activation of metallic foams by washcoating was first addressed. The innovative spin coating method has been systematically compared to the conventional dip coating, revealing improved uniformity of the deposited catalytic layers and superior control of the coating characteristics. The alternative method for catalytic activation investigated in INTENT relies on packing open-cell foams and POCS with catalyst micro-particles. All the factors influencing the loading of the catalyst particles (i.e. the catalyst inventory) have been elucidated.
Additive manufacturing (3D printing) of Al POCS started early in the project thanks to a collaboration with the Department of Mechanical Engineering of Politecnico di Milano. Regular cellular materials offer additional degrees of freedom for the design of optimized catalyst substrates and look therefore very promising for process intensification. Samples with different geometrical and structural features have been produced and characterized by pressure drop, heat and mass transfer measurements, and with CFD simulations, and tested in the Fischer-Tropsch reaction.

Task 3 - Lab-scale methane steam reforming (MSR) experiments over Rh-based catalyst particles in the presence of Cu foams have pointed out significant mitigation of the radial temperature gradients in the reactor due to the enhanced effective thermal conductivity. This improves the performances of the heat-transfer limited endothermic process, which is promising for distributed hydrogen generation in compact devices. A novel aspect investigated in INTENT is the electrification of the structured internals via Joule heating: when electric energy from renewable sources (solar, wind) is used, this concept enables a substantial reduction (- 40%) of the CO2 emissions.
Along similar lines, Fischer-Tropsch (FTS) runs over Co-based catalyst particles in a lab-scale tubular reactor and eventually in a dedicated semi-pilot jacketed tubular reactor demonstrated a substantially improved temperature control when the reactor was loaded with packed conductive internals, i.e. Al foams and POCS. Unprecedented performance indicators (CO conversions per pass up to 70%, heat duties over 1 MW/m3, overall heat transfer coefficient > 1.3 kW/m2/K) were achieved using optimized structured internals (POCS with skin). These data demonstrate at a representative scale the successful application of the INTENT concepts to Gas-to-Liquids process technologies.

Significant progress beyond the state of the art has been achieved in the following areas:

- Geometrical and digital characterization of open-cell foams and other cellular substrates. We use the methodology developed in INTENT to generate "virtual digital foams": these provide a computational domain for CFD simulations but can be also 3D printed and tested under reactive flow conditions, removing any geometrical uncertainty from the comparison between simulations and experiments.

- Analysis of the transport properties of cellular substrates: the combination of experiments and CFD simulations is a methodological approach first successfully demonstrated in INTENT to analyze gas/solid heat and mass transfer and pressure drop in random open-cell foams and in regular cellular structures (POCS) uased as enhanced catalyst substrates. It has enabled to derive unprecedented engineering correlations for transport properties in foams and POCS.

- Activation of cellular substrates by packing with catalyst microparticles: packed foams and POCS are a new concept; we are the first to report data on the related transport properties and the first applications under reactive conditions.

- Application of Al foams and POCS packed with catalyst particles to the strongly exothermic, temperature-sensitive Fischer-Tropsch synthesis (FTS). This new concept enabled to run the reaction almost isothermally up to very high heat duties not accessible to conventional packed-bed reactors in a lab-scale tubular reactor and eventually in a semi-pilot reactor facility fabricated on purpose during the INTENT project, demonstrating the feasibility of compact FTS reactors for small-scale Gas-to-Liquids processes.

- Application of washcoated/packed Cu foams to the strongly endothermic Methane Steam Reforming for syngas/hydrogen production, leading to improved productivities.

- Electrification of the Reformer via direct Joule heating of the structured internals.

All these results are very promising for the intensification of key catalytic processes for energy conversion.

Intensifying heat transfer in multitubular catalytic reactors

Periodic Reporting for period 4 - INTENT (Structured Reactors with INTensified ENergy Transfer for Breakthrough Catalytic Technologies)

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