Bed Reactor Research Articles

Numerical simulation of fluidized bed reactor for calcium looping energy release process in thermochemical storage: Influence of key conditions

The thermochemical energy storage technology applied to concentrating solar power is expected to realize the large-scale deployment of solar power. Reactor design is recognized as a key challenge. In this study, the calcium looping energy release process in a bubbling fluidized bed reactor was numerically simulated using an Eulerian-Eulerian Two-fluid Model. The effects of immersed tubes, particle size, CO2 concentration, and flow velocity on the multi-physical coupling characteristics during the carbonation process were explored. The result indicated that the presence of immersed tubes improves flow characteristics and effectively controls the bed temperature. Particle size had no significant effect on the carbonation process during the kinetically controlled stage. Increasing CO2 concentration significantly enhanced the conversion rate; however, it could lead to a reduction in particle renewal frequency, thereby deteriorating the heat transfer coefficient (HTC). The study on flow velocity indicated that a balance should be struck between bed stability and reaction conversion rate, with the model identifying 0.48 m/s to 0.74 m/s as the suitable operating gas velocity. Additionally, the study compared two methods for calculating HTC and analyzed the energy utilization efficiency during the carbonation process, providing recommendations for industrial applications.

Design and experimental study of solar-driven biomass gasification based on direct irradiation solar thermochemical reactor

Solar-driven biomass steam gasification is a promising technology to produce H2-rich syngas, meanwhile achieve flexible storage of renewable energy. However, the solar gasification application also faces numerous challenges, due to its involved complex chemical reaction characteristics and the inherent the multi-physics energy conversion processes. This work designs a novel direct irradiation solar gasification reactor, with the improved optical acceptance structure and reasonable test module, and the wheat straw particle is selected as experimental sample. Employing a 9 kWe high flux solar simulator, the maximum temperature of reaction bed in this prototype reactor reaches to 1260 °C, with the average solar flux of 1171.3 kW/m2. With adjustable radiation flux as experiment factor, under the highest total radiation of 3.35 kW, the molar fraction of H2 in the produced syngas is 47.1 % with the energy upgrade factor of 1.15, and the cellulose component completes decomposition. Increasing the mass flow rate of steam reduces the syngas output while raising the H2/CO ratio of the syngas. In addition, smaller biomass particle size facilitates the reaction, thereby improving the conversion efficiency of direct irradiation gasification. The investigation results provide a meaningful reference for the efficient utilization of abundant solar and biomass energy.

Continuous production of chitooligosaccharides in a column reactor by the PUF-immobilized whole cell enzymes of Mucor circinelloides IBT-83

BackgroundChitosan oligosaccharides (COS) have great potential for applications in several fields, including agriculture, food industry or medicine. Nevertheless, the large-scale use of COS requires the development of cost-effective technologies for their production. The main objective of our investigation was to develop an effective method of enzymatic degradation of chitosan in a column reactor using Mucor circinelloides IBT-83 cells, immobilized in a polyurethane foam (PUF). These cells serve as a source of chitosanolytic enzymes.ResultsThe study revealed that the process of freeze-drying of immobilized mycelium increases the stability of the associated enzymes during chitosan hydrolysis. The use of stabilized preparations as an active reactor bed enables the production of COS at a constant level for 16 reactor cycles (384 h in total), i.e. 216 h longer compared to non-stabilized mycelium. In the hydrolysate, oligomers ranging in structure from dimer to hexamer as well as D-glucosamine were detected. The potential application of the obtained product in agriculture has been verified. The results of phytotests have demonstrated that the introduction of COS into the soil at a concentration of 0.01 or 0.05% w/w resulted in an increase in the growth of Lepidium sativum stem and root, respectively (extensions by 38 and 44% compared to the control sample).ConclusionsThe research has verified that the PUF-immobilized M. circinelloides IBT-83 mycelium, which has been stabilized through freeze-drying, is a promising biocatalyst for the environmentally friendly and efficient generation of COS. This biocatalyst has the potential to be used in fertilizers.

Sustainable Heat Generation in Flow from a Molecular Solar Thermal Energy Storage System

As the global deployment of renewable technologies accelerate, finding efficient ways to store energy will aid in responding to shifting energy demands. A prospective option not only in harvesting solar energy but also in emission‐free heating is MOlecular Solar Thermal (MOST) energy storage. A central part of MOST applications is to develop methods to release the stored energy. Herein, the Quadricyclane (QC)‐to‐Norbornadiene catalyzed back reaction is explored in a specially designed packed‐bed reactor. Four distinctly sized and purposely synthesized platinum on activated carbon catalysts are studied to trigger the heat release from the energy‐dense QC isomer. The catalysts are fully characterized using a variety of structural, surface, and spectroscopic techniques. Parameters to optimize catalytic conversion and heat release in flow conditions are explored including particle size and packing behavior, flow rates, and molecular residence times. Moreover, using CO pulse chemisorption technique, site time yield values and a turnover number are reported. Complementary to the flow reactions, computational fluid dynamic simulations applying lattice Boltzmann methods to two catalytic packed beds of different size ranges are done to evaluate fluid‐dynamic behavior within the reactor bed to ascertain the ideal particle size and packing density for catalysis in MOST applications.

Performance improvement of a U-tube heat exchanger based hydrogen storage reactor by phase change materials

Solid-state hydrogen storage technology using metal hydrides as carriers has great application prospects. This study aims to optimize the heat transfer resistance and absorption kinetics issues encountered in practical applications of LaNi5-H2 storage materials in storage reactors. A mathematical model for the hydrogen absorption process in the reactors based on U-tube and straight-tube heat exchangers was built, and the advantages of U-tube structure and the flow characteristics of the heat transfer fluid on its heat transfer and absorption performance were analyzed. To further enhance the U-tube based reactor's performance, phase change materials (PCM) were subsequently introduced as an auxiliary heat transfer medium, while the amount of PCM and the thermal conductivity of the reaction bed were optimized. The results showed that the appropriate PCM dosage could overcome the inherent defects of the U-tube heat exchanger and significantly improve heat dissipation and reaction rates of the reactor, and the H2 absorption completion time was shortened by 1.4 times. In addition, the increased thermal conductivity of reaction beds is equally important for the enhancement of heat transfer and absorption rate. Nevertheless, further increase of PCM's thermal conductivity has a limited effect on the improvement of the performance.

Innovative Fixed-Bed Reactor Integrated with Heat Transfer System for Lean Methane Mixture Removal

A new type of compact, portable fixed-bed reactor integrated with a heat transfer system was developed for the removal of volatile and flammable air pollutants such as lean methane and volatile organic compounds (VOCs). The reactor may operate in catalytic or thermal combustion conditions with the purpose of achieving autothermal processes with the possibility of energy recovery. An excess heat recovery point was designed behind the reactor bed at the place where the gas temperature is the highest to enable its usage. The mathematical model is presented together with a number of simulation calculations performed for the assessment of the developed reactor. The case study in this paper was for catalytic methane oxidation at a temperature of 400 °C, a methane concentration between 0.1% and 2% by weight, a gas flow rate of 1 m3/s STP, and a heat exchange surface for the assumed plate exchanger from 10 to 200 m2. The calculations show that the thickness of the insulation is of little importance for the operation of the equipment, and a sufficient thickness was about 20–50 mm. The optimal area for the considered case is 80–100 m2. It was found that recovery of thermal energy is possible only for higher methane concentrations, above 0.3% by weight. Using an appropriate surface for the exchanger, it is possible to recover even 50% of the combustion enthalpy at a methane concentration of 0.45% by weight. For an exchanger area below 50 m2, the recoverable energy drops rapidly. It was found that the exchanger area is the most important equipment parameter under consideration.

Morphological regulation of Pt/CeO2 and its catalytic dehydrogenation of methylcyclohexane in fixed bed reactor

A series of Pt/CeO2 compounds with hollow spheres (Pt/CeO2–S), wires (Pt/CeO2–W), and particle (Pt/CeO2–P) morphologies were prepared and further used for catalytic liquid organic hydrogen carrier (LOHC) dehydrogenation. The exposure and distribution of different crystal faces affected the nucleation process of crystals and then formed different microscopic morphologies. Compared with Pt/CeO2–W and Pt/CeO2–P, Pt/CeO2–S showed hollow spherical structures with significantly higher oxygen vacancy concentrations and specific surface areas. These structural differences not only affected platinum (Pt) dispersion, but also affected the activity and stability of the catalyst, thus promoting methylcyclohexane (MCH) conversion. The fixed bed reaction showed that Pt/CeO2–S had excellent catalytic activity, with the MCH conversion rate at 97.7 % and hydrogen release rate of 350.50 mmol/g(Pt)/min, and it still maintained stable activity after 72 h. Under the same conditions, the MCH conversion rates for Pt/CeO2–W and Pt/CeO2–P were only 77.23 % and 32.02 %, respectively. Therefore, through the growth pattern and morphology controls of catalyst supports, this was an effective means for improving the dehydrogenation performance of LOHC.

Modeling and optimizing gas solid distribution in fluidized beds

In fluidized bed reactors, uniform distribution of gas and solids is critical to achieve the desired hydrodynamic and kinetic performance. For FCC units, Technip Energies uses a proprietary distributor design to terminate both reactor risers and spent catalyst lift lines to distribute the exiting gas-solid stream into a fluidized bed.In Technip Energies' Resid FCC unit, air and spent catalyst are distributed from an upward flowing stream into a catalyst bed for coke combustion on catalyst. Proper distribution is key to achieve a uniform coke burn and an even temperature profile throughout the bed. In PropyleneMax™ Catalytic Cracking (PMcc™) technology, the reactor riser also terminates in a fluidized bed, requiring proper distribution of the hydrocarbon vapor and solid mixture into the reactor bed, which is key to providing adequate contact for further cracking to valuable products. This paper discusses Technip Energies' gas-solid distribution technology and the recent work performed to develop an improved distributor for use as a riser termination device in both the PMcc reactor and the RFCC regenerator to achieve improved performance. The use of CFD modeling to screen and evaluate the initial concepts and optimize the final selected concept are presented here. The performance matrices used to quantify the benefits of the optimized distributor design with respect to the existing one in the reactor application are highlighted, showing the benefits of improved gas solid distribution on hydrodynamic and kinetic performance. The paper presents a systematic approach to develop a novel industrial device using physics-based computational tools.

A novel decoupled triple-fluidized bed reaction system for polyvinyl chloride (PVC) disposal: (I) Thermodynamic simulation and experimental investigation

ABSTRACT In this work, a novel decoupled triple-fluidized bed reaction system was proposed to dispose of polyvinyl chloride (PVC). Thermodynamic simulation and thermogravimetric experiments were conducted to examine the dechlorination feasibility and analyze the effects of CaO and CaCl2 on PVC pyrolysis. Besides, the quantitative removal efficiency of HCl was investigated in a lab-scale bubbling fluidized bed. Results indicated that HCl hardly interacted with the silica−alumina catalyst and Fe2O3 adsorbent, while for Na2O and CaO adsorbents, HCl could convert into corresponding stable chlorides, demonstrating the theoretical feasibility of the system. Next, PVC pyrolysis was a multi-stage process, and CaO spontaneously reacted with the released HCl but simultaneously inhibited its alkylation reaction; moreover, CaCl2 could act as a catalyst to facilitate its HCl release and alkylation reaction. Finally, as the temperature rose, the dechlorination efficiency first increased and then decreased, reaching a peak value of 87.6% at 700°C in the N2 atmosphere. In addition, the dechlorination efficiency in the CO2 atmosphere was higher at 400–900°C.

Holistic Hydraulic Simulation for Pebble Bed Using Porous Media Approach

The porous media approach is regarded as an appropriate methodology for hydraulic simulations of complex pebble beds in fusion reactors. In order to determine the parameters (permeability α and inertial loss coefficient C) of the porous media accurately, two methods are proposed: the correction method and the fitting method. In this paper, a single-channel model with sequentially packed pebbles is constructed in order to obtain the pressure drop gradient against superficial velocities. Two methods, the correction method and fitting method, are employed to determine the permeability and inertial loss coefficient, and the results are evaluated with comparisons. Based on the results, both the correction method and fitting method are deemed feasible for the parameter determinations. In consideration of the consumption of resources and time for simulation, the fitting method is recommended during the preliminary design phase to shorten the duration of design, while the correction method is suggested to obtain precise results when the design is accomplished. Both of the methods would be evaluated with the data obtained from experiments in the future.

Development of a Novel Structured Mesh-Type Pd/γ-Al2O3/Al Catalyst on Nitrobenzene Liquid-Phase Catalytic Hydrogenation Reactions

Nitrobenzene liquid-phase catalytic hydrogenation is commonly regarded as one of the most effective technologies for aniline production. The traditional granular catalysts have the disadvantages that the reactor bed pressure drop is large and the mass transfer efficiency between gas and liquid phases is low. In this study, a novel structured mesh-type Pd/γ-Al2O3/Al catalyst was prepared by anodic oxidation and pore structures of γ-Al2O3/Al supports were constructed by acid pore-widening treatments. The results showed that acid pore-widening treatments can improve the pore size of γ-Al2O3/Al supports; the support with HNO3 pore-widening treatment exhibited the largest pore size, being enlarged from 3.7 nm to 4.6 nm. The Pd/γ-Al2O3/Al catalysts prepared with different acid pore-widening treatment supports contribute to the increased active metal Pd loading, more Pd0 content, and better dispersion of the Pd particles. The catalyst prepared with HNO3 pore-widening treatment support exhibited the largest active metal Pd loading, enlarging from 1.82% to 1.95%, the largest Pd0 content being enlarged from 52.1% to 58.5% and the smallest Pd particle size being reduced from 103 nm to 41 nm, resulting in the highest nitrobenzene conversion, increasing from 67.2% to 74.3%. Eventually, we calculated that the pressure drop of structured catalysts was 1/72 of that of granular catalysts, resulting in a better diffusion of the H2 through nitrobenzene solution to active sites on the catalyst surface and a significant increase in the catalytic activity.

Direct photo-curing 3D printed bionic multistage Mo-doped tungsten oxide catalysts for static and dynamic oxidative desulfurization of fuels

3D printed monolithic catalysts have attracted increasing attention in the petrochemical industry due to their advantages of the freedom of configuration, the rapidity of fabrication and the control of the fluid properties of the reaction medium. However, this remains challenging in constructing of micromorphology, reliable manufacturing, and adaptive functionality. Herein, inspired by the function of acicular plant fractal structure, we have developed bionic multistage monolithic catalysts based on direct photo-curing 3D printing technology. We also design two configuration strategies for static and dynamic oxidative desulfurization of fuels. Below the catalyst surface, the porous structure prepared by the hard template method can increase the specific surface area of the catalyst to disperse the active center and adsorb organic sulfur to strengthen the oxidation effect. The 3D-MoWO/PC-CE monolithic catalyst shows excellent activity in the static reaction with 100% sulfur removal. Above the catalyst surface, microcrystalline cellulose is introduced in-situ in 3D printed ink to build needle-like structures to enhance mass transfer efficiency and reduce surface pressure in dynamic fixed bed reaction. This work provides valuable ideas for the fabrication of efficient monolithic catalysts in various reactions.

Using of crushed glass supported Fe/Cu bimetallic nanoparticles for remediation of ciprofloxacin antibiotic from aqueous solution

The combination of iron and copper (Fe/Cu) loaded on glass (G-Fe/Cu) has been developed for this study. The green synthesis was used to create bimetallic nanoparticles (G-Fe/Cu) using grape leaves extract, which employed as a natural reducing agent to easily produce nZVI from iron salts. The particle size, surface morphology, elemental composition and degree of crystallinity of the resulting nanocomposite have been analyzed by means of energy-dispersive X-ray spectroscopy (EDX), scanning electronic microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). G-Fe/Cu nanocomposite were employed as adsorbent materials to eliminate ciprofloxacin (CIP) from polluted aqueous solution. Some factors affecting the adsorption function, in batch and continuous experimentations have been examined to select the optimum parameters that accomplish the maximum elimination ratio (99 %) and to investigate the efficiency of the nanoparticles as reactive bed materials. It was discovered that the ideal conditions were CIP concentration (50 ppm), pH 7, nanoparticles dosage (0.5 mg/ 50 mL) and 100 min of optimum contact time. In present paper, the response surface methodology (RSM) was applied as statistical tool used to optimize and model complex systems for elimination of CIP antibiotic from aqueous solution with selection the same four factors that mentioned above. The best appropriate isotherm model was the Freundlich model in batch study. The findings imply that hazardous compounds can be successfully eliminated from aqueous solutions using the prepared nanocomposites. The model's predictions aligned well with experimental outcomes, and the G-Fe/Cu nanocomposite effectively removed CIP from the solutions.

Investigation of Combustion and NO/SO2 Emission Characteristics during the Co-Combustion Process of Torrefied Biomass and Lignite.

This paper investigates the combustion characteristics and pollutant emission patterns of the mixed combustion of lignite (L) and torrefied pine wood (TPW) under different blending ratios. Isothermal combustion experiments were conducted in a fixed bed reaction system at 800 °C, and pollutant emission concentrations were measured using a flue gas analyzer. Using scanning electron microscopy (SEM) and BET (nitrogen adsorption) experiments, it was found that torrefied pine wood (TPW) has a larger specific surface area and a more developed pore structure, which can facilitate more complete combustion of the sample. The results of the non-isothermal thermogravimetric analysis show that with the TPW blending ratio increase, the entire combustion process advances, and the ignition temperature, maximum peak temperature, and burnout temperature all show a decreasing trend. The kinetic equations of the combustion reaction process of mixed gas were calculated by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) kinetic equations. The results show that the blending of TPW reduces the activation energy of the combustion reaction of the mixed fuel. When the TPW blending ratio is 80%, the activation energy values of the mixed fuel are the lowest at 111.32 kJ/mol and 104.87 kJ/mol. The abundant alkali metal ions and porous structure in TPW reduce the conversion rates of N and S elements in the fuel to NO and SO2, thus reducing the pollutant emissions from the mixed fuel.

Updating mechanism of siderite roasting through insights into reactions between inherent oxides of iron and carbon

The roasting of siderite (FeCO3) was investigated to clarify the reaction mechanism in inert atmosphere using micro fluidized bed reaction analyzer coupled with on-line particle sampling (MFBRA-P). Thermodynamic results indicated that the reactions of 6FeO + CO2 → C + 2Fe3O4 and 3FeO + CO → C + Fe3O4 are both possible to occur in the transformation process of siderite to Fe3O4. The presence of C was identified in the final solid product through analysis scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and calcination experiment of product sample in the atmosphere containing O2. Combining thermodynamic and experimental results, an updated reaction mechanism of siderite roasting in inert atmosphere was proposed. The siderite is first decomposed to form FeO and CO2, and in turn FeO rapidly reacts with CO2 to form Fe3O4 and CO. Meantime, the released CO2 or CO during decomposition reacts with FeO to form C and Fe3O4.

A tree-based automated machine learning approach of the obstructed view factor of thermal radiation in nuclear pebble beds

For the nuclear pebble bed of the high temperature gas-cooled reactor (HTGR), a tree-based automated machine learning approach is developed to discuss the complicated thermal radiation behaviors. The AutoML model for calculating the obstructed view factor between any two particles in the pebble bed includes the gradient boosting regression tree model with the fine-tuned hyperparameters and the analytical base model. Using the discrete packing of the HTR-PM nuclear reactor and the leaped Halton sequence, a large dataset of the view factor under different conditions is generated to train the AutoML model. On the same platform, numerical results show that AutoML model is approximately 5 × 105 times faster than the traditional approach. The Pareto front of the AutoML model indicates that the mean squared error decreases with the model complexity until it reaches the optimal solution. Then, the trained AutoML model is applied to the engineering pebble bed. It is shown that the average radiation exchange factor near the wall is lower than that in the bulk region. In addition, the packing height is also an important parameter for evaluating the radiative behaviors. In particular, when the height of the nuclear pebble bed is less than 20 times particle diameter, it is necessary to consider the contribution of the packing height to the radiation effective thermal conductivity.

Sorption-enhanced intensified CO2 hydrogenation via reverse water–gas shift reaction: Kinetics and modelling

Intensification of CO2 hydrogenation via the reverse water–gas shift (RWGS) reaction for CO production can be achieved through in situ removal of water when hydrophilic adsorbents are incorporated alongside the catalyst in the reaction bed. In this work, seeking to move a step closer to the industrial implementation of this innovative CO2 valorization process, a comprehensive reactor model, validated by experimental data obtained in a fixed-bed reactor, was developed to simulate the behavior of this sorption-enhanced (SE) RWGS process. Simulation and experimental data matched with good accuracy, demonstrating the striking benefits brought by the adsorbent addition, such as an almost doubling of the CO production rate at 300 °C. The kinetics of RWGS reaction over a Cu-based catalyst and H2O adsorption on a 13X zeolite adsorbent were studied both experimentally and theoretically and the kinetic models were integrated into the reactor model to assess the performance of SE-RWGS process. Fitting of the RWGS reaction rates by a Langmuir-Hinschelwood-Hougen-Watson-type heterogeneous kinetic model suggested that the rate-determining step of the reaction is the surface interaction between an adsorbed CO2 molecule and a H* species on catalytic sites of different nature. Meanwhile, the dynamic behavior of water adsorption was effectively simulated by a semi-empirical double-stretched exponential model combined with the Sips isotherm model. The results of this work could be applied to the design and scale-up of the SE-RWGS process, which offers considerable improvements over the thermodynamically constrained conventional process. The intensified approach represents a promising avenue for the effective conversion of carbon dioxide into CO, as well as into other value-added chemicals as part of a multi-stage CO2 reduction process.

Enantioselective Synthesis in Continuous Flow: Polymer-Supported Isothiourea-Catalyzed Enantioselective Michael Addition-Cyclization with α-Azol-2-ylacetophenones.

A packed reactor bed incorporating a polymer-supported isothiourea HyperBTM catalyst derivative has been used to promote the enantioselective synthesis of a range of heterocyclic products derived from α-azol-2-ylacetophenones and -acetamides combined with alkyl, aryl, and heterocyclic α,β-unsaturated homoanhydrides in continuous flow via an α,β-unsaturated acyl-ammonium intermediate. The products are generated in good to excellent yields and generally in excellent enantiopurity (up to 97:3 er). Scale-up is demonstrated on a 15 mmol scale, giving the heterocyclic product in 68% overall yield with 98:2 er after recrystallization.

Optimizing membrane reactor structures for enhanced hydrogen yield in CH4 tri-reforming: Insights from sensitivity analysis and machine learning approaches

This study explores the optimization of membrane reactor configurations to enhance hydrogen production through CH4 tri-reforming. The investigation employs ceramic membranes for oxygen, vapor, and carbon dioxide distribution within the reactor bed. A differential evolution algorithm is utilized alongside cuckoo search algorithm (CSA) and support vector regression (SVR) to determine optimal values for O2/CH4, H2O/CH4, and CO2/CH4 ratios, membrane thickness, and shell pressure, with hydrogen yield as the objective function. Results demonstrate that the oxygen membrane reactor achieves the highest hydrogen yield, reaching 2.02 and 1.75 for direct methanol synthesis and Fischer–Tropsch processes, respectively, representing a 7.98 % and 10.03 % increase compared to the conventional tri-reforming reactor. Furthermore, CSA and SVR emerge as invaluable tools, facilitating robust optimization and predictive modeling. The CSA efficiently navigates complex solution spaces to identify optimal parameters, while SVR accurately models relationships between input variables and hydrogen yield. Incorporating these methodologies enhances the effectiveness of membrane reactor design and synthesis gas production. This study contributes to advancements in clean energy technologies by providing insights into efficient hydrogen production methods using membrane reactors.

Insights into reaction–diffusion behaviors of acetylene selective hydrogenation on pellet catalysts

AbstractIn this work, a particle‐resolved computational fluid dynamics model of the acetylene hydrogenation process is developed to investigate the effects of catalyst particle structures on the reaction–diffusion behaviors aiming to improve selectivity toward target ethylene. The effects of packing structures on mass and heat transfer are explored by employing particles with varying shapes, wall thicknesses, and external diameters. The simulation results reveal that decreasing diffusion paths and elevating reactor bed temperature will enhance ethylene selectivity, and cylinder and Raschig ring packing structures exhibit the lowest and highest ethylene selectivity of 35.6% and 48.9% at 70% of acetylene conversion, respectively. Reducing wall thicknesses of Raschig ring particles facilitates the diffusion of generated ethylene from the interior zone of catalysts but concurrently inhibits the conversion of acetylene to ethylene. The Raschig ring catalyst particle with 1.9 mm of wall thickness and 3.5 mm of external diameter is finally revealed to exhibit the highest ethylene selectivity.