Abstract
The present research exploits an innovative methodology for producing auto‐pressurized carbon microreactors with a precise and controlled structure analyzing the influence of their design on ...the fluid dynamics and their catalytic performance. Carbon monoliths with Tesla‐valve shape channels (Tesla, T, and modified Tesla, Tm) are synthesized through the combination of 3D printing and sol–gel process and further probed as Ni/CeO2 supports on CO2 methanation. The experimental results and mathematical modeling corroborated the improved performance obtained through the complex design compared to a conventional one. In addition to chaotic fluid flow induced by the deviation in flow direction, which improves the reagents‐active phase interaction, local pressure increases due to convergence of flows may enhance the Sabatier reaction according to Le Châtelier's principle. Conversely to straight channels, T and Tm are not affected by flow rate and presented chemical control. Tesla‐valve with curved angle (Tm) improved the mass transfer, achieving higher conversion and ≈30% reaction rate increase regarding right angle (T). Thus, this auto‐pressurized multi‐stage Tesla‐valve monolith opens the gate to design specific and advanced functional materials for multitude chemical reactions where not only the reactant‐active phase contact can be maximized but also the reaction conditions can be controlled to maximize the reaction kinetics.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Additive manufacturing (AM) presents a promising opportunity for the innovative design and production of structured catalytic materials. Given the critical role of catalysts in industrial catalytic ...processes, AM has the potential to contribute to the development of improved catalysts by reducing activation energy and enhancing selectivity. Conventional synthesis methods limit the choice of structural materials and composition for producing monoliths. Additionally, the deposition of catalytic compounds is also restricted by commonly applied techniques that may require prior coverage or treatments to improve adherence or do not achieve a homogenous coat. Moreover, production is limited to monoliths with straight and parallel channels. However, this format drives to laminar regime flow thus restricting the radial mass and heat transfer. Conversely, AM allows the production of a wider variety of compositions and more complex structures that have proven to rise their effectiveness by increasing reagents‐catalyst interaction, making catalytic processes more cost‐effective. Therefore, in this review an outline of the recent progress of AM methods in the development of monolithic catalysts is presented focusing on the requirements, advantages, and disadvantages of each technique, hence providing a practical overview of their novel opportunities to overcome current limitations in catalyst synthesis.
Additive manufacturing (AM) offers potential for designing structured catalytic materials, enhancing industrial processes. AM can improve catalysts by reducing activation energy and enhancing selectivity. Traditional methods limit material choice and coating uniformity. AM enables diverse compositions and complex structures, enhancing reagent‐catalyst interactions, and cost‐effectiveness. This review outlines AM's progress in developing monolithic catalysts, discussing advantages, disadvantages, and opportunities to overcome synthesis limitations.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Chili seeds (CS) represent one of the most abundant residues in Mexico due to the high production and consumption. In this work, CS were used as raw material for the production of low-cost adsorbents ...for the removal of methylene blue from water. The adsorbents were synthesized from a hydrothermal treatment (based on a surface response experiment design) and characterized texturally by assessing changes in their properties. The mass yield (%R), carbon content (%C), and the second order adsorption rate constant (k2) were derived in relation to a list of input variables (e.g., the reaction temperature, residence time, and water/biomass ratio). Accordingly, those output variables were affected most sensitively by temperature and/or residence time, while changes of the water/biomass ratio were insignificant. Besides, an increase in the reaction temperature favored the degradation of the lignocellulosic material with increases in the carbon fixation. The adsorption capacity of methylene blue (MB) by the hydrochars depended drastically on the oxygen/carbon ratio. As such, the maximum adsorption capacity value of 145 mg g−1 was attained at the initial MB concentration of ~3000 μM (optimal oxygen/carbon value of 0.43). On the other hand, the maximum partition coefficient (KD) was estimated as 2.96 μM−1 mg g−1 with the initial/equilibrium concentrations of 20.5/6.93 μM. The performance evaluation between different studies, when made in terms of KD, suggests that the tested hydrochar should be one of the best adsorbents to treat methylene blue, especially at near-real environmental conditions (e.g., below micromolar levels).
•Chili seeds were used as a precursors of adsorbents using hydrothermal treatment (HTC).•H/C and O/C relationships indicate that primary reaction of HTC was dehydration.•Hydrochars were employed for the removal of methylene blue (MB) in aqueous phase.•Maximum adsorption capacity (q = 145 mg g−1) was obtained with a O/C ratio of 0.43.•The proposed hydrochar is one of the best adsorbents to treat MB blue from water.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, the effect of the cell density of monolithic catalysts was investigated and further mathematically modeled on cordierite supports used in CO
2
methanation. Commercial cordierite ...monoliths with 200, 400, and 500 cpsi cell densities were coated by immersion into an ethanolic suspension of Ni/CeO
2
active phase. SEM–EDS analysis confirmed that, owing to the low porosity of cordierite (surface area < 1 m
2
g
−1
), the Ni/CeO
2
diffusion into the walls was limited, especially in the case of low and intermediate cell density monoliths; thus, active phase was predominantly loaded onto the channels’ external surface. Nevertheless, despite the larger exposed surface area in the monolith with high cell density, which would allow for better distribution and accessibility of Ni/CeO
2
, its higher macro-pore volume resulted in some introduction of the active phase into the walls. As a result, the catalytic evaluation showed that it was more influenced by increments in volumetric flow rates. The low cell density monolith displayed diffusional control at flow rates below 500 mL min
−1
. In contrast, intermediate and high cell density monoliths presented this behavior up to 300 mL min
−1
. These findings suggest that the interaction reactants-catalyst is considerably more affected by a forced non-uniform flow when increasing the injection rate. This condition reduced the transport of reactants and products within the catalyst channels and, in turn, increased the minimum temperature required for the reaction. Moreover, a slight diminution of selectivity to CH
4
was observed and ascribed to the possible formation of hot spots that activate the reverse water–gas shift reaction. Finally, a mathematical model based on fundamental momentum and mass transfer equations coupled with the kinetics of CO
2
methanation was successfully derived and solved to analyze the fluid dynamics of the monolithic support. The results showed a radial profile with maximum fluid velocity located at the center of the channel. A reactive zone close to the inlet was obtained, and maximum methane production (4.5 mol m
−3
) throughout the monolith was attained at 350 °C. Then, linear streamlines of the chemical species were developed along the channel.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This work proposes a rigorous mathematical model capable of reproducing the adsorption process in dynamic regime on advanced monoliths geometries. For this, four bed geometries with axisymmetric ...distribution of channels and similar solid mass were proposed. In each geometry a different distribution of channels was suggested, maintaining constant the bed dimensions of 15 cm high and 5 cm radius. The mathematical modeling includes mass and momentum transfer phenomena, and it was solved with the COMSOL Multiphysics software using mass transfer parameters published in the literature. The overall performance of the column was evaluated in terms of breakthrough (CA/CA0 = 0.1) and saturation times (CA/CA0 = 0.9). The mass and velocity distributions obtained from the proposed model show good physical consistency with what is expected in real systems. In addition, the model proved to be easy to solve given the short convergence times required (2–4 h). Modifications were made to the bed geometry to achieve a better use of the adsorbent material which reached up to 80%. The proposed bed geometries allow obtaining different mixing distributions, in such a way that inside the bed a thinning of the boundary layer is caused, thus reducing diffusive effects at the adsorbent solid-fluid interface, given dissipation rates of about 323 × 10−11 m2/s3. The bed geometry composed of intersecting rings deployed the best performance in terms of usage of the material adsorbent, and acceptable hydrodynamical behavior inside the channels (maximum fluid velocity = 35.4 × 10−5 m/s and drop pressure = 0.19 Pa). Based on these results, it was found that it is possible to reduce diffusional effects and delimit the mass transfer zone inside the monoliths, thus increasing the efficiency of adsorbent fixed beds.
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•A strategy for obtaining breakthrough curves for adsorption in fixed beds is presented.•This strategy is applied to non-conventional fixed-bed adsorber designs•Breakthrough curves are obtained by solution of mass and momentum transfer equations.•This strategy allows to reduce unused height of the adsorbent, increasing its efficiency.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, the effect of the cell density of monolithic catalysts was investigated and further mathematically modeled on cordierite supports used in CO
methanation. Commercial cordierite ...monoliths with 200, 400, and 500 cpsi cell densities were coated by immersion into an ethanolic suspension of Ni/CeO
active phase. SEM-EDS analysis confirmed that, owing to the low porosity of cordierite (surface area < 1 m
g
), the Ni/CeO
diffusion into the walls was limited, especially in the case of low and intermediate cell density monoliths; thus, active phase was predominantly loaded onto the channels' external surface. Nevertheless, despite the larger exposed surface area in the monolith with high cell density, which would allow for better distribution and accessibility of Ni/CeO
, its higher macro-pore volume resulted in some introduction of the active phase into the walls. As a result, the catalytic evaluation showed that it was more influenced by increments in volumetric flow rates. The low cell density monolith displayed diffusional control at flow rates below 500 mL min
. In contrast, intermediate and high cell density monoliths presented this behavior up to 300 mL min
. These findings suggest that the interaction reactants-catalyst is considerably more affected by a forced non-uniform flow when increasing the injection rate. This condition reduced the transport of reactants and products within the catalyst channels and, in turn, increased the minimum temperature required for the reaction. Moreover, a slight diminution of selectivity to CH
was observed and ascribed to the possible formation of hot spots that activate the reverse water-gas shift reaction. Finally, a mathematical model based on fundamental momentum and mass transfer equations coupled with the kinetics of CO
methanation was successfully derived and solved to analyze the fluid dynamics of the monolithic support. The results showed a radial profile with maximum fluid velocity located at the center of the channel. A reactive zone close to the inlet was obtained, and maximum methane production (4.5 mol m
) throughout the monolith was attained at 350 °C. Then, linear streamlines of the chemical species were developed along the channel.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
