Monolithic Reactor Research Articles

Time-of-Flight Secondary Ion Mass Spectrometry Revealing the Organocatalyst Distribution in Functionalized Silica Monoliths.

Hierarchically porous monolithic silica shows promise as a carrier material for immobilized organocatalysts. Conventional analysis usually includes physisorption, infrared spectroscopy and elemental analysis, among others, to elucidate the pore space and degree of functionalization of the material. However, these methods do not yield information about the spatial distribution of the organic species inside the monolithic reactor. In this work, time-of-flight secondary ion mass spectrometry has been applied to characterize the surface of organically functionalized silica monoliths. Cross sections of a silica monolith functionalized with 4-dimethylaminopyridine were analyzed and the results were compared with physisorption and elemental analysis experiments of the same material. This way, insight into the radial distribution of the catalyst could be achieved, which might assist in interpreting the performance of such reactors in heterogeneous flow catalysis.

Electrified reformer for syngas production – Additive manufacturing of coated microchannel monolithic reactor

Here, an electrified reformer with a bespoke design of catalyst-coated and additively manufactured monoliths with 3-D pore architecture is presented. The 2D-pore architecture of the hexagonal honeycomb monolith was compared against the 3D-pore architecture of three broad classifications - triply periodic minimal surface (Gyroid), strut-based (Octet) and stochastic lattice (Voronoi). Gyroid structured reactor, coated with NiO/Ce0.8Gd0.2O2-δ catalyst and heated to 900 °C achieved >99 % conversion of CO2 and CH4 at WHSV = 11,000 L.h−1.kgcat−1, while remaining active for >42 h with no evidence of coke deposition. Whereas Octet and Voronoi reactors showed slightly lower conversions, with 6-fold and 4-fold higher pressure drops, respectively. This study combines Computational Fluid Dynamics and experimental evidence to reveal that the Gyroid lattice provides high catalyst deposition and catalytic activity at low pressure drops. This study demonstrates the feasibility of renewable energy-powered structured reactors to provide a pathway for low carbon footprint chemical production.

Extra trees regression assisted 1D monolith reactor simulations based on microkinetic analysis and rate transformation

The incorporation of microkinetic method for surface reaction calculation is a key development direction in monolith reactor simulations, albeit posing significant computational stability and efficiency challenges. A data-driven multi-scale simulation framework is proposed to bridge the gap between macroscopic numerical model and microscopic reaction solvers. After the generating of precomputed microkinetic dataset, we utilize a tailor-designed preprocessing transformation, AD_log10, to effectively manage the common challenges of large variances and reversed directions in microkinetic rate data. A suite of machine learning regression models is developed as reaction rate solver integrated into the 1D two-phase monolith model. We employ NH3 selective catalytic oxidation on Cu(100) and Cu(111) as probe systems to validate our framework’s efficacy. In the context of on-board simulations under operating conditions, the Extra Trees Regression (with best regression performance) based model exhibits commendable accuracy and efficiency, successfully addressing complex processes previously unmanageable with interpolation-based models. This innovative approach paves the way for advanced monolith reactor modeling and sheds light on multi-scale simulation methodologies in chemical reaction engineering.

High performance nickel structured catalysts prepared using EDTA for hydrogen production

Bioethanol Steam Reforming is a sustainable and environmentally friendly way to produce hydrogen. The most promising catalysts for this reaction are deactivated by carbon deposition and sintering. It is well known that the synthesis method can affect the active phase dispersion and metal‒support interactions in catalysts. In this work, structured systems based on Ni/CeO2–MgAl2O4 were prepared by using ethylenediaminetetraacetic acid, EDTA, for Ni incorporation. An EDTA‒free structured system was also prepared, for comparison. FeCrAlloy metal monoliths were used as support, as they provide efficient heat transfer due to their high thermal conductivity. The catalysts were evaluated in the ethanol steam reforming reaction at 650 °C. The Ni precursor influences the properties and catalytic performance of the systems. The systems prepared from [Ni(EDTA)]2- complex showed good reaction performance during 25 h (5.3 and 5.7 mol H2/mol C2H5OH for systems containing 1 and 5 wt% of Ni). The EDTA‒free system showed low activity. The best performing system was subjected to a regeneration process and evaluated in a second reaction cycle, showing good performance. Finally, the best structured system was compared with a powder catalyst. The results reflect that the performance of the monolithic reactor is significantly higher than the packed bed reactor.

Modeling the dynamic operation of a monolithic CO2 methanation reactor. Evaluation of the response to H2 load fluctuation

A full-scale, 2-D, axially symmetric, heterogeneous, and transient mathematical model is utilized to evaluate the dynamic operation of a honeycomb monolithic reactor during CO2 methanation. A base case is defined, which considers a step-type functionality for H2 load reduction (−20%) and a Ni catalyst. The impacts of the catalyst type (Ni vs Ru), the functionality of the H2 load disturbance, and the monolith's diameter on reactor performance are studied and compared to the base case. Results show that the use of Ru as catalyst, a ramp-type disturbance and a smaller reactor diameter generate a superior dynamic response to the H2 feed disturbance as well as favorable effects on thermal behavior. This is despite the higher temperature gradient generated when using Ru. These findings suggest that the monolithic reactor is a viable technological option for CO2 methanation under flow variations, such as those encountered when employing green hydrogen.

Development of an immobilized laccases - CDI CIMmultus® monolithic reactor for ecofriendly producing gallic acid-dextran conjugate

Enzymatic modification of polysaccharides is an efficient and environmentally friendly method to enhance their bioactivities. Immobilized enzymes represent a technology that enables the reuse of enzymes and increase their stability. In this study, laccases from Trametes versicolor were covalently immobilized on CIMmultus® CDI monolithic column, which was employed to graft gallic acid (GA) onto the backbone of T40 dextran. 1.43 mg laccases were successfully immobilized, yielding a mass conversion rate of 32.17 %. The kinetic parameters of free and immobilized laccases were respectively 0.0056 and 0.1770 U for Vmax and 0.0121 and 0.7510 mmol·l−1 for Km. Remarkably, 91.29 % of the enzymatic activity of immobilized laccases was preserved after catalyzing 1200 ml of reactant. A central composite design was carried out to investigate the influence of T40 dextran concentration and flow rate on the phenolization. Response surface methodology was used for predicting the optimal conditions, showed that a 2.07 % mass ratio of phenolization could be achieved with 2 % dextran and a flow rate of 0.89 ml·min−1. The GA-dextran conjugate, produced under the best conditions, revealed a DPPH radical inhibition activity of 63.97 % and an IC50 of 73.39 µg·ml−1. This work describes a new IMER for ecofriendly producing phenolized polysaccharides.

CFD simulation of a laboratory-scale monolithic reactor for the combustion of VOC

This study presents initial findings from simulating a laboratory-scale monolithic reactor for VOC (Volatile Organic Compounds) combustion. The reactor, made of stainless steel, measures 45 cm (height) and 2.3 cm (diameter). It contains a catalyst supported by a ceramic structure, tested for toluene combustion. Using ANSYS CFD simulation software, fluid dynamics inside the reactor were accurately modeled. The simulation then focused on a specific channel within the monolith, based on comprehensive reactor data. The final stage simulated toluene combustion using the Mars-Van Krevelen mechanism. ANSYS CFD results for toluene combustion, measured by CO2 yield, closely matched experimental outcomes. The average CO2 yield of 1.16 showed a strong alignment between the simulation and the experiment. ANSYS CFD not only aids in obtaining hard-to-gather information about fluid dynamics and chemical reactions but also enables simulations of geometry changes and catalyst types once validated. It also supports exploring more complex reactions.

In-situ synthesis of V2AlC@V2O5/TiO2 immobilized over honeycomb support with vanadium oxide electron transfer mediator for stimulating selective CO2 photoreduction through bi-reforming in a monolith reactor

Photocatalytic CO2 reduction to valuable chemicals and fuels is a practical approach for climate action; however, available photocatalysts and photoreactors are less efficient. In this work, well-designed V2AlC@V2O5 supported TiO2 and immobilized over honeycomb support for CO2 photoreduction in a monolith reactor have been investigated. The catalysts were loaded over the monolithic support using the sol-gel dip-coating method and found promising for higher light absorbance and charge separation. The performance of V2AlC@V2O5/TiO2 composite for photocatalytic CO2 reduction with water and bi-reforming of methanol was performed using a fixed bed and monolith photoreactor. Using V2AlC@V2O5/TiO2 with a fixed bed reactor and methanol–water mixture, a CO yield of 13.75 mmol g−1h−1 was produced, 26.39 and 38.19-fold higher than using water and pristine TiO2, respectively. Similarly, CH4 production was 1.97 and 12.33 folds higher than using water and TiO2 only, whereas, using water, production of H2 was not detected. The higher photoactivity of the composite with methanol was due to efficient photo-induced carrier separation due to the synergistic effect of V2AlC/V2O5 and more production of protons. Using a monolith photoreactor, CH4, CO and H2 production rates of 55.44, 35.51 and 1.638 mmol g−1h−1 were obtained, 166.50, 2.58 and 3.05 times more than those produced using a fixed bed reactor. This significantly higher photoactivity with monolith photoreactor was due to higher photon flux utilization with surface reactions, resulting in more production and utilization of photoinduced charge carriers. The highest QY after five consecutive cycles was 48.374, 25.358 and 1.51 % for CH4, CO and H2, which is 200.5, 2.54 and 3.87 folds higher than using the fixed bed, respectively. This work provides a new approach to designing and fabricating higher efficient and stable photocatalytic system for CO2 recycling, and it can be further employed for other energy-related applications.

3D Printing of Integrated Metallic Reactor Catalysts: Concept and Application

AbstractSelective laser melting can be used to create custom‐made monolith reactor components with embedded microscale catalytic sites. Doping with noble metals (0.01–0.04 % of Pt, Ir, Ru, or Rh) gave clean incorporation of the active metal particles metals. Yet catalytic activity was low, due to distribution of the active particles between the surface and the bulk of the monolith. Switching to cobalt enabled doping in higher amounts (1.5–2.0 %) with corresponding increase in activity. Using borohydride hydrolysis as a test reaction, we showed that a combined stainless steel and cobalt monolith was active in both batch and continuous systems, for at least 48 h, albeit with some loss of active material. The advantages and limitations of this catalyst/reactor preparation method are discussed.

Accuracy Evaluation of Monte Carlo Simulation Results Using ENDF/B-VIII.0 and JENDL-5 Libraries for 10 MWth Micro Heat Pipe-Cooled Reactor

The micro heat pipe-cooled reactor is an innovative type of reactor that utilizes heat pipes to cool its core. It consists of a reactor core, an energy conversion system, shielding, and a heat removal system. This reactor shows great potential as a viable option for supplying electricity in remote areas. By incorporating a monolithic core with heat pipes and an efficient heat conversion system, this reactor design eliminates the need for a main pipeline, circulating pump, and auxiliary equipment, resulting in a cost-effective, compact, and transportable system. The monolithic reactor design has undergone significant advancements in neutronics and thermal hydraulics. This article focuses on evaluating the impact of the latest released nuclear data libraries, ENDF/B-VIII.0 and JENDL-5, on calculated neutronics and kinetics parameters. The total keff uncertainty was propagated and found to be significant for both recently evaluated nuclear data libraries (678.52 pcm for ENDF/B-VIII.0 and 525.91 pcm for JENDL-5, respectively). The total uncertainty originated from nuclear data was evaluated for total ν, reaction cross sections, and angular distributions in the case of JENDL-5, and for ENDF/B-VIII.0, uncertainty from angular distributions was not included because of the unavailability of its multigroup structure covariance matrices. The results reveal that the largest contributor for ENDF/B-VIII.0 is 235U total (409.18 pcm), while that for JENDL-5 is 56Fe capture cross section (361.93 pcm). For the kinetic parameter’s uncertainty, the impact on the total βeff, leff, and λeff simulation results was found to be not significant (about 1%).

Enhancement of biohydrogen production and low coke formation by applying Ni/ZrxCe1-xO2 catalyst in steam gasification of spent coffee ground in monolithic reactor

To produce H2-rich gas, steam gasification of spent coffee grounds is performed in this study by applying ZrxCe1-xO2 supports (x = 0.2, 0.6) in a monolithic reactor. Compared with conventional Ni/γ-Al2O3, Ni/ZrxCe1-xO2 catalysts offer higher gas yields and H2 generation. In particular, Ni/Zr0.6Ce0.4O2 exhibits the highest gas yield (86.32 wt%), H2 selectivity (56 vol%), and low coke formation owing to its favorable Ni dispersion, high oxygen mobility, and completely homogeneous nanometer-sized morphology. A significant increase in gas yield was observed in the monolith reactor (M@Ni/Zr0.6Ce0.4O2) compared to the fixed bed reactor (F@Ni/Zr0.6Ce0.4O2), from 74.85 wt% to 86.32 wt%. H2 selectivity (56.87 vol%) is also increased, which can be associated with the unique properties of the monolithic reactor. This phenomenon is attributed to the increase in residence time and the amount of mass and heat transfer between the catalyst and vapor, which favorably direct the selectivity toward H2. The use of metal-oxide composite supports, especially Ni/Zr0.6Ce0.4O2 catalyst, effectively alleviated coke formation (0.7 wt%), whereas the amount of coke produced by Ni/γ-Al2O3 (2.4 wt%) was more than three times higher. Overall, exploiting the remarkable benefits of ZrxCe1-xO2 (x = 0.2, 0.6) composite oxides as supports for Ni catalyst and monolithic reactors would have an emerging outlook for H2 generation via gasification technology.

Monoliths enabling biocatalysis in flow chemistry

Biocatalysis in flow improves space time yields and enables straightforward downstream processing. The underlying principles of monolithic flow reactors and their application in mono- and bi-phasic biocatalytic systems are discussed.

A multifunctional tube reactor for catalytic oxidization of dioxins and its pilot-scale application

Dioxins are hazardous pollutants and catalytic oxidization is an effective technology for the treatment, and more works needs to set up the monolithic reactor to promote the industrial application. In this work, a catalyst formula was optimized and used to prepared tube reactor (Φ60 mm*1500 mm) for the pilot investigation. As a result, the powdered catalyst removed 90% of chlorobenzene (430 ppm) at 200 °C. 6-tube reactor removed 80% of chlorobenzene (330 ppm, 24 m3·h−1) at 200–210 °C in a lab-scale pilot experiment. 96-tube reactor removed 90% of real dioxins (0.26 ng TEG·Nm−3, 1000 m3·h−1) at 230 °C in an incineration plant. Simultaneously, the tube reactor removed 99% of NOx (78.9 mg·Nm−3) and particle matters with an average size of 6 µm. Acidic gases were removed by dry deacidification. Considering this, dioxins, NOx, acidic gases, and particle matters were removed at the same time. This result is in favor of simplifying and integrating flue-gas treatment system to reach “treating all pollutants by one equipment” concept.

Enhanced liquid–liquid mass transfer in a monolithic reactor with multi-jet-channel in the circumferential array

A monolithic reactor with multi-jet-channel in the circumferential array (MR-MJCCA) is designed to intensify mass transfer. Effects of operating conditions and geometric parameters on the mass transfer efficiency E and overall volumetric mass transfer coefficient KLa are illustrated through experimental and numerical methods. Results show that the increased jet impingement intensity due to a higher flow rate and smaller jet diameter Dp effectively enhances mass transfer. E and KLa in the MR-MJCCA possessing eight channels increase with reducing the channel depth De and helical pitch p, yet first rise and then decline with enlarging the jet unaligned-impinging distance w. A higher two-phase interfacial area and energy dissipation rate are conducive to improving mass transfer performance in configurations with Dp = 0.3 mm, De = 1 mm, p = 5 mm, and w = 1.5 mm. Increasing the axial length of reactor elevates E whereas KLa diminishes. A reliable artificial neural network model was used to correlate KLa with key parameters. MR-MJCCA exhibits a higher KLa compared to most microreactors and the throughput increases by over tenfold, demonstrating its scalability and broader industrial applications.

Effect of TiO2 on Pd/La2O3-CeO2-Al2O3 Systems during Catalytic Oxidation of Methane in the Presence of H2O and SO2.

New results on the effect of TiO2 on Pd/La2O3-CeO2-Al2O3 systems for catalytic oxidation of methane in the presence of H2O and SO2 have been received. Low-temperature N2-adsorption, XRD, SEM, HRTEM, XPS, EPR and FTIR techniques were used to characterize the catalyst. The presence of Ce3+ on the catalytic surface and in the volume near the lantana was revealed by EPR and XPS. After aging, the following changes are observed: (i) agglomeration of the Pd-clusters (from 8 nm to 12 nm); (ii) transformation of part of the TiO2 from anatase to larger particles of rutile; and (iii)-the increase in PdO/Pd-ratio above its optimum. The modification by Ti of the La2O3-CeO2-Al2O3 system leads to higher resistance towards the presence of SO2 most likely due to the prevailing formation of unstable surface sulfites instead of thermally stable sulfates. Based on kinetic model calculations, the reaction pathway over the Pd/La2O3-CeO2-TiO2-Al2O3 catalyst follows the Mars-van Krevelen mechanism. For evaluation of the possible practical application of the obtained material, a sample of Pd/La2O3-CeO2-TiO2-Al2O3, supported on rolled aluminum-containing stainless steel (Aluchrom VDM®), was prepared and tested. Methane oxidation in an industrial-scale monolithic reactor was simulated using a two-dimensional heterogeneous reactor model.

Improving solar fuel production performance from H2O and CO2 thermochemical dissociation using custom-made reticulated porous ceria

Thermochemical CO2- and H2O-splitting cycles for sustainable fuel generation were investigated by using custom-made reticulated ceria foams integrated in a solar-heated cavity reactor. A parametric study revealed the suitable conditions to produce H2/CO with maximum fuel rates and yields per unit mass of redox material. Various operating parameters such as the total pressure during the reduction step, the gas inlet flowrates, the temperature, or the reactive gas content during the oxidation step were studied in detail. A series of on-sun experiments including more than 20 cycles under different cycling conditions were carried out with relevant performance repeatability and stability. With a ceria foam reduction temperature in the range 1400–1470 °C and a reduction pressure of 103 mbar, the ceria foams produced 281 μmol of H2 and 332 μmol of CO per gram of material during oxidation below 1000 °C under cooling with a maximum production rate of 3.0 mL/min.g and 10.2 mL/min.g, respectively. Direct syngas production was also evidenced during on-sun experiments with simultaneous H2O- and CO2-splitting, which yielded a H2:CO ratio ranging from 0.7 to 1.14. The dual-scale porous ceria structures were characterized using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis to confirm material thermal stability during cycling. Finally, optimization of fuel production capacity was achieved by maximizing the total amount of ceria foam loaded into the reactor, yielding 667 mL of CO (409 μmol/g) and 513 mL of H2 (314 μmol/g) per cycle. A maximum solar-to-fuel efficiency of 10.1% was calculated for CO2-splitting vs. 4.9% for H2O-splitting cycle. This study thus demonstrated noteworthy fuel production performance in an efficient monolithic reactor under real concentrated solar radiation, from highly reactive customized ceria foams.

Tailored monolithic catalyst and reactor by direct photo-curing 3D printing for oxidative desulfurization of fuels

Structured monolithic catalysts have attracted growing attention in the petrochemical industry due to significant advantages of reusability, easy scale-up, and high heat and mass transfer rate. 3D printing offers enormous flexibility in accurately regulating the configuration of monolithic catalysts to realize the strengthening of the reaction process. However, this remains challenging in terms of reliable manufacturing, high resolution, and the distribution of active sites. Here, we report a direct photo-curing 3D printing based method for manufacturing precise monolithic catalysts for oxidative desulfurization of fuels. Numerous molybdenum oxide nanoparticles with a high density of oxygen vacancies are spatially distributed in three-dimensional Al2O3 by 3D printing technology and post-treatment, thus favoring the catalytic reaction. This 3D-MoOx/Al2O3 exhibits excellent catalytic performance with a 99.2 % conversion of dibenzothiophene. Furthermore, this tailored catalyst is 3D-printed to manufacture a monolithic agitating impeller as a stirring reactor, which plays a dual role in mixing and catalysis. The study provides an effective strategy for precisely manufacturing structured catalysts with excellent catalytic activity and can be readily applied to a range of chemical reactions.

Theoretical Investigation on Syngas Production by Catalytic Partial Oxidation of Methane in a Reverse-Flow Microchannel Monolithic Reactor

Theoretical Investigation on Syngas Production by Catalytic Partial Oxidation of Methane in a Reverse-Flow Microchannel Monolithic Reactor

Transition of the Flow Regime Inside of Monolith Microchannel Reactors Fed with Highly Turbulent Flow

This paper investigates the flow behaviour of monolith microchannels. Specifically, the study characterizes the flow regime within in-series monolith channels where highly turbulent flow approaches them but inside of the channels, the Reynolds number is subcritical. Results from LES and a transitional RANS model are compared to those obtained when directly assuming laminar flow inside of the channels. A space-resolved model of channels placed in series and channel Reynolds numbers ranging from 50 to 300 are considered. The results show that the flow pattern in is almost identical in the two channels and that the frequency of fluctuations tends to increase with the Reynolds number. The flow regime in both channels is unsteady laminar, containing a wide spectrum of frequencies. The tested transitional RANS model (k-kL-ω) is unable to capture the velocity fluctuations predicted by LES. Despite the differences in the velocity field prediction, the pressure drop estimation from all models is practically the same. This study provides insights into the flow behaviour of monolith reactors and is useful for reactor design and optimization.

Novel Control System Strategy for the Catalytic Oxidation of VOCs with Heat Recovery

A theoretical study of the dynamic closed-loop behaviour of a reactor/feed-effluent heat exchanger (FEHE)/furnace system for the catalytic combustion of volatile organic compounds (VOCs) is presented. A 1D pseudohomogeneous plug-flow model is proposed to simulate the non-steady-state operation of the monolith reactor and the FEHE, while the furnace behaviour is described by means of a heterogeneous model of lumped parameters. Positive energy feedback is a source of instability that leads to strong thermal oscillations (limit cycles) and may cause damage to the equipment and sintering of the catalyst. The design of a robust and flexible control system and an efficient control strategy are, therefore, required to ensure safe and stable operation. The response of the system under three different control strategies to the most frequent disturbance variables—the feed flowrate (FV0) and feed concentration of VOCs (C0Et)—was evaluated. One of the control strategies consisted of a single-loop feedback system with servomechanism changes in the reactor inlet temperature (T0) that manipulated the bypass valve and, sequentially, the natural gas flowrate in the furnace (FNG). This approach made it possible to meet the control objective (reducing VOCs) without losing controllability and while minimizing the use of external fuel.