Reactant Stream Research Articles

A Paper-Based Microfluidic Methanol Fuel Cell Catalyzed By Ni-Co@LTA Electrocatalyst for Micro-Nano Power Systems

Sustainable energy generation has recently gained popularity due to the rising energy demand and environmental concerns caused by conventional non-renewable energy sources. In the context of portable electronics, and microsystems all would require fully integrated, dependable power generation. In this regard, paper-based microfluidic fuel cells (PMFC), have drawn significant attention. By utilizing the inherent properties of paper substrate and microfluidic reactant streams, this fuel cell device takes away the requirement of any membranes or external pumps that are necessary for conventional FCs. In co-laminar flow, where PMFCs work, a unique diffusive mixing area serves as a pseudo-membrane by preventing the convective mixing of two reactants. The reactants flow by capillary action with the aid of an absorbent pad. While the ions transport across the channel through the mixing zone. This not only makes the pumping of fluids into paper-based systems simpler, but also provides numerous other benefits such as cost-effectiveness, simplicity in manufacturing, ease of disposal, and portability over traditional FCs. In this work, we synthesized a Ni-Co catalyst encapsulated within zeolite 4A (also known as LTA) via a hydrothermal synthesis route. The resulting catalyst exhibited better catalytic activity of 12.1 mA cm-2 at 1.12 V vs Ag/AgCl and retained remarkable stability (~77%) even after 1000 cycles CV test in 0.1 M KOH + 1 M methanol. By utilizing this catalyst as anode and Pt/AC (5 wt%) as cathode, we demonstrate a Y-shaped membraneless PMFC using Whatman filter paper grade 41 as paper substrate. It has been shown that the device can deliver power densities in the range of 2 - 10 mW cm-2 (Fuel: methanol, Oxidant: KMnO4), and can retain power output for at least 30 min. Additionally, the power of the cell can easily be raised by connecting two or more cells in series, making these PMFCs suitable for micro/nano power generation systems.Keywords: Fuel cell, Microfluidic, Paper substrate, Co-laminar flow, Zeolite 4A.

Innovators and Transformers Revisiting the gap between academia and practice: insights from the green logistics phenomenon

PurposeLogistics and supply chain management (L&SCM) scholars and practitioners have devoted extensive efforts to advancing green logistics practices (GLPs), yet the intersection between the two domains in relation to the topic remains underexplored. To accelerate GLPs’ development amid the escalating climate crisis, this research examines this intersection by comparing the responsiveness of academia and practice to the call for green logistics over time.Design/methodology/approachTo compare between academia and practice, we combined a systematic literature review on the development of GLPs in L&SCM journals (N = 122) with a content analysis of annual and sustainability reports published by the four major global logistics service providers (LSPs: DHL, DB Schenker, UPS and FedEx; N = 156) over the past three decades.FindingsThis research reveals that all the GLPs covered in the L&SCM literature have already been applied and reported by practitioners, both consistently and over a significant period of time. Academic progress, in turn, is delayed by slow-paced empirical methods, elevated research quality standards, prolonged funding and recruitment processes, and extended peer-review intervals. Further, a tendency toward reactive knowledge creation rather than proactive knowledge transfer is evident, obscuring the role of L&SCM scholars in steering the industry’s green advancement.Practical implicationsRecommendations are offered to L&SCM authors, editors, reviewers and university departments to advance pracademic endeavors in green logistics research and increase its responsiveness to global events.Originality/valueThis is one of the first studies to scrutinize the intersection between academia and practice on the evolution of GLPs. The revealed gaps prompted us to suggest a transformative paradigm for academia-practice collaborations targeting the L&SCM discipline at large, combining a bold proactive research stream aimed at knowledge transfer with a more traditional reactive stream aimed at knowledge creation.

Multimodal Insights of Regeneration Dynamics of Spent Bimetallic Catalysts by Full Field Hyperspectral Quick‐EXAFS Imaging and Environmental Transmission Electron Microscopy

AbstractMultimodal measurements involving time‐resolved Ni and Cu K edges Quick‐EXAFS, time‐resolved hyperspectral Full Field Quick‐EXAFS imaging with micrometer spatial resolution and aberration‐corrected Environmental Scanning Transmission Electron Microscopy have been performed over a NiCu catalyst used for the ethanol steam reforming reaction to establish structure‐activity relationships after regeneration. Activated catalysts are composed of 5–10 nm monometallic nickel nanoparticles and larger bimetallic randomly alloyed NiCu nanoparticles (NPs). After 3 h time on reactive stream, the monitoring of the regeneration of the coked deactivated catalyst at 500 °C by Full Field hyperspectral XAS imaging evidences that the oxidative propagation front affects faster metallic Ni species than metallic Cu ones as a result of the stronger oxophilic character of the former compared to the latter. Furthermore, ESTEM characterization of the deactivated catalyst when passing from H2 to O2 atmosphere at 500 °C for burning coke deposits evidences the fragmentation of the Ni and NiCu‐NPs driven by the Kirkendall effect in the encapsulated coked catalyst. The resulting increase of specific surface of active species is assumed to be responsible for the activity boost observed after regeneration.

Synthesis of zeolite X from fly ash in an impinging stream reactor and its mechanisms

The conventional hydrothermal method with magnetic stirring for the synthesis of zeolite X from fly ash has some problems, such as low micromixing efficiency, low mass transfer rate, and long synthesis time. In this study, impinging stream reactor is used to improve the mass transfer and micromixing and the mechanism how the nucleation and crystallization of zeolite is accelerated is explored. The results show that premixing in the impinging stream reactor can reduce the stirring and aging time from 4 h to 20 min because the hydroxyl free radicals resulting from the cavitation effect can accelerate the crystallization of zeolite. After collision, the viscosity of the system is increased from 0.22 Pa·s to 3 Pa·s, which can increase the residence time of cavitation bubbles in the gel solution and effectively inhibit the aggregation of crystal nuclei. As a result, the crystal nuclei in the system are well dispersed. The impinging stream reactor can also accelerate the mass transfer between liquid and solid phases and improve the micromixing of raw materials, so that the polymerization between Si and Al is increased and the nucleation of zeolite X is accelerated. The degree of order of zeolite X samples obtained by premixing in the impinging stream reactor is much higher than that obtained by magnetic stirring. The relative crystallinity after crystallization for 12 h (100 %) is higher than that obtained by magnetic stirring (94.93 %); and the n(Si/Al) is lower than that obtained by magnetic stirring. It is concluded that premixing in the impinging stream reactor can improve the polymerization of aluminosilicate and accelerate the nucleation and crystallization of zeolite X. Under the same conditions, zeolite X synthesized by premixing in the impinging stream reactor has better CO2 adsorption capacity than those synthesized by magnetic stirring and industrial synthesis.

Optimizing refuse-derived fuel production from scheduled wastes through Aspen plus simulation

This study aims to improve the quality of fuel with high calorific value namely Sfuel – a commercial high-quality refuse-derived fuel (RDF) from hazardous waste via modifying the process design and operating parameters of thermal conversion process. The study analyses key parameters of RDF quality, such as calorific value and heavy metal content, before and after process modifications based on the combination of experimental and simulation using Aspen Plus. In this study, the temperature and pressure of the simulation system are varied from 100 to 700 °C and from 1 to 5 bar, respectively. Findings indicate that there are a total of eleven heavy metals and 179 volatile compounds in the “Sfuels”. The quality of the targeted product is greatly improved by the metal evaporation at high temperatures and pressures. However, the calorific value of RDF significantly decreases at 700 °C due to a large amount of the carbon content being evaporated. Although the carbon content at high temperatures is significantly lost, the heat from the vapour stream reactor outlet, which is reused to preheat the nitrogen gas stream supplied to the system, reduces energy consumption while improving the thermal conversion efficiency of the system. Besides, low pressure along with high temperature are not the optimal conditions for quality Sfuels improvement by thermal conversion. Results also indicate that electric heating is more economically efficient than natural gas heating.

A thermodynamic comparison of membrane-assisted processes for hydrogen production with integrated CO2 capture

The energy efficiency of two novel process designs for the production of ultra-pure hydrogen with simultaneous capture of CO2 using CH4 as the feedstock, namely membrane-assisted chemical looping reforming (MA-CLR) and membrane-assisted sorption-enhanced reforming (MA-SER) has been compared. The modelling of the integrated network for mass and heat balances has been carried out using the ASPEN® Plus V10 process simulation tool to quantify the benefits and disadvantages of integrating hydrogen perm-selective membranes with either chemical looping or sorption-enhanced reforming. The evaluation of the MA-CLR process is carried out for a range of the following operating conditions: 10 < pR < 60 bar, 500 < TR < 900°C, and 1.5 < H2O/CH4 < 3.0. On the other hand, for the MA-SER process the operation ranges of 1.0 < pR < 10 bar, 400 < TR < 900°C, and 2.5 < H2O/CH4 < 4.0 were considered. Within the operation window of the MA-SER process, no carbon formation is observed, as any carbon present in the system reacts with CaO in the form of CO2. However, in the case of the MA-CLR process, carbon formation can occur during the pre-reforming stage, particularly at low H2O/CH4 ratios. In terms of hydrogen yield, energy utilization and carbon capture, the MA-CLR outperforms the MA-SER plant. However, the MA-SER plant offers certain advantages over the MA-CLR system, such as a pure CO2 product stream and lower reactor design temperatures. In the MA-CLR system, a carbon capture rate of 99.8% and a hydrogen product yield of 74.4% are achieved, whereas the MA-SER plant achieves a carbon capture rate of 98.5% and a hydrogen product yield of 69.7%.

Narrow middle channel design in counter-flow microfluidic fuel cell with flow-through electrodes

Output performance of counter-flow microfluidic fuel cell is hampered by its significant internal ohmic resistance. In this work, narrow middle channel design is introduced to the counter-flow microfluidic fuel cell with flow-through electrodes to ease the internal ohmic resistance issue and realize increased fuel utilization and improved power density simultaneously. Systematically numerical investigations are performed to validate the feasibility and evaluate the prospect of the narrow middle channel design. Meanwhile, in-depth analyses are provided to explore the mechanisms behind the distinctive cell characteristics. Corresponding results demonstrate that the width of the middle channel in the counter-flow microfluidic fuel cell with flow-through electrodes can be safely reduced from the commonly used 1–2 mm–0.3 mm without reactant crossover and obvious increase in the energy consumption for the pumping of the reactant streams. Superiority of the narrow middle channel design is more significant in the high reactant concentration and high flow rate case where an increase of 30.29 % is observed in the peak power density when the middle channel width reduces from 1 mm to 0.3 mm under the reactant concentrations of 4 M and flow rate of 120 μLmin−1.

Predicting the size of silver nanoparticles synthesised in flow reactors: Coupling population balance models with fluid dynamic simulations

Achieving size control during nanomaterial synthesis is critical for their deployment in numerous applications due to their strong size-properties relationships. However, it remains a challenge in the field due to multi-step mechanisms in nanoparticle synthesis. In this paper, we present an experimentally-validated model able to predict the particle size and distribution of silver nanoparticles synthesised in flow reactors by coupling time-resolved fluid dynamic simulations with population balance. The model reveals fundamental correlations between reactor design and the corresponding size of the nanoparticles. It shows that increasing mixing rate, increases the overall rate of nanoparticle formation, where nanoparticle synthesis takes place homogeneously in the whole of the reaction volume. In contrast, when there is a distinguishable interface between reactant streams (i.e. low mixing rate), nucleation and growth take place in a small fraction of the reaction volume in the interface between the inlet streams. The combination of fast mixing and high average nucleation rate can lead to a burst of nuclei formation translated in small size and narrow size distribution. This work presents a new approach for the use of computational-guided design of reactors for the synthesis of nanomaterials to move the field away from current trial-and-error strategies.

Preparation of C-S-H-PCE composites using an impinging stream reactor

The C-S-H-PCE composites (CPCs) serve as an accelerator for cement hydration. This work presents a novel approach for synthesizing CPCs using an impinging stream reactor (ISR). The resulting CPCs exhibited an average particle size of approximately 21 nm and significantly enhanced the compressive strength of mortar when used as an additive. The compressive strength value of the mortar after curing for 6 h is 18.7 N/mm2, which is 503 % higher than the control group. Moreover, the ISR method was superior to the conventional stirred tank reactor method in terms of product particle size and acceleration efficiency.

Study on the Turbulent Vortex Structure Characteristics of a Two‐Layer Impinging Stream Reactor

AbstractThe structure of the turbulent vortex in a two‐layer impinging stream reactor was studied by large eddy simulation. The distributions of vortex intensity, turbulent kinetic energy, and shear stress at different Reynolds numbers Re, nozzle spacings L, and nozzle layer spacings are discussed. The relationship between vortex structure and mixing effect in the flow field is revealed. The effects of longitudinal swirls and shear flow characteristics are analyzed. Finally, the field synergy theory is used for evaluation. With increasing Re, the vortex intensity and average shear stress increase. The nozzle spacing and layer spacing affect the mixing effect in the reactor by controlling the change of vortex structure in the flow field. When L/D = 3, where D is the nozzle diameter, the energy loss is the smallest and the mixing effect is the best. The research results provide a theoretical reference for the structural optimization of the impinging stream reactor.

DEVELOPING A NON-BLOCKING WEB APPLICATION USING REACTIVE STACK IN KOTLIN LANGUAGE

As the number of users of services on the Internet grows, the importance of scaling web applications increases. The system performance problem becomes more acute in a highly loaded state. There are various ways to optimize the performance of an application, including at the stage of architecture design. The purpose of this article is to develop a non-blocking web application on a reactive stack of technologies to solve the problem of performance under high load. In the course of the work, the principles of processing requests in the reactive model were considered. To organize the reactive approach, the Project Reactor library was used and a diagram of its operation was given. In addition to the Project Reactor library, the Spring WebFlux framework was considered, which allows you to develop full-fledged non-blocking web applications at all system levels. Examples of the program code of services using the described technologies are given. Further, an alternative implementation of the specification of reactive streams based on coroutines from the kotlinx.coroutines library is proposed, and some possibilities of their application are demonstrated. In conclusion, general conclusions are formulated regarding the effectiveness of using the reactive approach to solve the performance problem in modern web applications, and a comparative characteristic is given in relation to classical blocking applications.

Complexity analysis of multiscale flow field of dynamic impinging stream based on chaos theory and Stockwell transform

The complexity analysis of the flow field is of great significance for studying the flow mechanism and strengthening the mixing. The multiscale flow field of dynamic impinging stream reactors is studied by experimental and theoretical methods. The chaotic characteristic parameters (correlation dimension, K entropy, the largest Lyapunov exponent) are investigated under different nozzle spacing L, different outlet velocity difference vd, and different outlet average velocity vp. The flow mechanism of dynamic impinging stream mesoscale flow field is revealed. The results show that the flow field of dynamic impinging stream reactor presents chaotic characteristics, and the chaotic characteristic parameters firstly increases and then decreases with the increase of nozzle spacing L. With the increase of outlet velocity difference and average outlet velocity, the chaotic characteristic parameters show an increasing trend. The time-frequency analysis of the microscale flow field in the dynamic impinging stream reactor is carried by Stockwell transform to obtain the energy evolution, the flow mechanism is further revealed. With the increase of outlet velocity difference and average outlet velocity, the energy of flow field gradually accumulates to the low frequency region, and the flow field energy enlarges. The radial flow field of dynamic impinging stream impact center is divided into radial jet region and radial vortex region by the energy characteristic. According to the analysis of chaotic characteristics and energy evolution of dynamic impinging stream, the optimal working condition is that nozzle spacing L=4d, outlet velocity difference is 1m/s, and outlet average velocity is 1.7m/s.

Flow Pattern and Mixing Performance of a Dynamic Impinging Stream Reactor

AbstractThe mixing process of a dynamic impinging stream reactor was measured by planar laser induced fluorescence. The fluid flow pattern and mixing characteristics were studied under different conditions. The flow field was divided into the following regions by flow pattern: free jet region, impingement region, radial jet region, and radial vortex region. The mixing characteristics were analyzed under different operational conditions. The mixing time first decreased and then increased with increasing nozzle spacing. The mixing time decreased with increasing outlet velocity difference and outlet average velocity, and the optimal working conditions were nozzle spacing L = 4d, where d is nozzle diameter, outlet velocity difference vd = 1 m s−1, and outlet average velocity vp = 1.7 m s−1.

Nonclassical Crystallization Causes Dendritic and Band-Like Microscale Patterns in Inorganic Precipitates.

The self-organization of complex solids can create patterns extending hierarchically from the atomic to the macroscopic scale. A frequently studied model is the chemical garden system which consists of life-like precipitate shapes. In this study, we examine the thin walls of chemical gardens using microfluidic devices that yield linear Ni(OH)2 precipitate membranes. We observe distinct light-scattering patterns within the compositionally pure membranes, including disorganized spots, dendrites, and parallel bands. The bands are tilted with respect to the membrane axis and their spacing (20-100 μm) increases with increasing flow rates. Scanning electron microscopy reveals that the bands consist of submicron particles embedded in a denser material and these particles are also found in the reactant stream. We propose that dendrites and bands arise from the attachment of solution-borne nanoparticles. The bands are generated by particle-aggregation zones moving upstream along the slowly advancing membrane surface. The speed of the aggregation zones is proportional to the band distance and defines the system's dispersion relation. This speed-wavelength dependence and the flow-opposing motion of the aggregation zones are likely caused by low particle concentrations in the wake of the zones that only slowly recover due to Brownian motion and particle nucleation.

Nonclassical Crystallization Causes Dendritic and Band‐Like Microscale Patterns in Inorganic Precipitates

AbstractThe self‐organization of complex solids can create patterns extending hierarchically from the atomic to the macroscopic scale. A frequently studied model is the chemical garden system which consists of life‐like precipitate shapes. In this study, we examine the thin walls of chemical gardens using microfluidic devices that yield linear Ni(OH)2 precipitate membranes. We observe distinct light‐scattering patterns within the compositionally pure membranes, including disorganized spots, dendrites, and parallel bands. The bands are tilted with respect to the membrane axis and their spacing (20–100 μm) increases with increasing flow rates. Scanning electron microscopy reveals that the bands consist of submicron particles embedded in a denser material and these particles are also found in the reactant stream. We propose that dendrites and bands arise from the attachment of solution‐borne nanoparticles. The bands are generated by particle‐aggregation zones moving upstream along the slowly advancing membrane surface. The speed of the aggregation zones is proportional to the band distance and defines the system's dispersion relation. This speed‐wavelength dependence and the flow‐opposing motion of the aggregation zones are likely caused by low particle concentrations in the wake of the zones that only slowly recover due to Brownian motion and particle nucleation.

Synergistic degradation and degradation pathways of methylene blue by plasma process combined with cavitation impinging stream reactor based on hydrodynamic cavitation

The plasma process is an advanced oxidation technique that boasts high efficiency and low cost. A combination of the plasma process with a cavitation impinging stream (CIS) reactor has been developed to investigate the degradation characteristics of methylene blue dye wastewater. The results indicate that under a pressure of 1.40 MPa and an impinging distance of 40 mm, the CIS reactor achieved a degradation rate of 52.83%, which was twice as much as self-excited oscillation cavitation alone. Furthermore, it was found that the optimum solution concentration for this reaction was 5.70 mg/L. Combining a plasma apparatus with a CIS reactor resulted in a degradation rate of 94.06% within 60 min, with a synergy index of 3.13. Intermediate products generated during the HC+plasma treatment were analyzed using liquid chromatography-mass spectrometry. Based on experimental and theoretical analyses, two possible pathways for methylene blue degradation were proposed. This study presents novel insights into the degradation pathway of methylene blue. The CIS+Plasma technology exhibits superior efficiency, higher cavitation yield, and lower operational costs, rendering it a viable option for large-scale wastewater treatment applications.

Chemical Titration of Promoted Ag/α‐Al2O3 Ethylene Epoxidation Catalysts

AbstractWe enumerate the active site density for a promoted Ag/α‐Al2O3 ethylene epoxidation catalyst (35 wt.% Ag) by using trifluoroethanol as a chemical titrant. Trifluoroethanol, when introduced into the reactant stream, deprotonates to deposit stable trifluoroethoxy or trifluoromethyl groups on the Ag surface and inhibits ethylene oxide (EO) rates, thus enabling us to assess catalytic site densities. Active site densities vary between 52 and 69 μmolTFE gcat−1 across different chlorine coverages (0–0.4 monolayers) and different oxygen concentrations (2.5–7.7 mol%) in the reactor feed. Site densities measured by in situ trifluoroethanol chemical titration are distinct compared to those evaluated using ex‐situ N2O decomposition (12.3 μmolN2O gcat−1) suggesting that dynamic restructuring of the Ag surface under reaction conditions may render pre‐reaction chemisorption measurements insufficient to accurately enumerate the active sites relevant for ethylene epoxidation.

Structure optimization and flow field characteristics of baffle-type impinging stream reactor

The impinging stream reactor is an efficient equipment for fluid mixing that strengthens the mass and heat transfer in two fluids mixing processes, with potential for many chemical engineering and industrial applications. In this paper, the flow characteristics and concentration distribution of baffle-type impinging stream reactor are analyzed by numerical simulation to optimize the reactor. The influence of different baffle spacing W and baffle aspect ratio λ on the velocity, turbulent kinetic energy and mixing effect of the reactor are explored. It is indicated that the flow regime changed with the inserted baffle in reactor. With the decrease of the baffle spacing and the baffle aspect ratio, the velocity, turbulent kinetic energy and the fluid mixing intensity firstly increase and then decrease. The mixing intensity of the flow field with different baffle spacing is compared, it is found that W = 40mm>W = 60mm>W = 30mm>W = 80 mm. The mixing intensity with different baffle aspect ratios are found that λ=1>λ=1.5>λ=0.75. The baffle-type impinging stream reactors with W = 40 mm and λ=1 have the best mixing effect.

Reaction performance in T-, X- and arrow-shaped microdevices

Microreactors are widely used for continuous flow operations. The assessment of their performance has a crucial role in determining the optimal geometries and working conditions. Among the most common geometries, we compare T-, X- and arrow-shaped devices to highlight how flow features, mixing degree and residence time affect the reaction yield and productivity. We focus on the steady flow regimes occurring in the three devices fed with reactive streams for varying Reynolds numbers. The Reynolds number, Rei, is herein based on the bulk velocity and the inlet-channel hydraulic diameter. The flow regimes presenting a central vortex in the mixing channel, found in X- and arrow-microreactors, lead to the best mixing and reaction yield. For Rei≤ 120 the maximum productivity is obtained with the X-microreactor, whereas above Rei = 120, with the arrow-reactor. Conversely, lower reaction yields and productivities are found in the T-microreactor, which exhibits an engulfment regime with two co-rotating vortices in the mixing channel. It is thus evident that the spiral pattern induced by a single central vortex extends the contact area between the reactants and leads to better performance. In terms of reaction cost, for the lower productivity values, the associated pressure drops are similar for all three geometries. For higher productivities, the best performance, i.e., the lowest pressure drops, is reached in the arrow-microreactor, followed by the T- and, then, by the X-device.

Design of an integrated CO2 methanation system with CO2 capture from flue gas and H2 production from water electrolysis

As one of the important Power to X technologies, CO2 methanation realizes the storage of green hydrogen and the emission reduction of flue gas CO2. In this study, process modeling was applied for CO2 methanation coupled with CO2 capture and water electrolysis. Aspen Plus and HYSYS models of 400 kW water electrolysis were set up for integration. The heat exchange network and the reaction temperature and catalyst usage of two methanation reactors are optimized. The effects of step-wise evolution of H2 flow on stream flows and reactors are also studied. The results show a system energy efficiency of 42.3% using a high-temperature solid oxide electrolysis cell (SOEC) and 30% monoethanolamide solution (MEA). The heat-exchange network significantly improves the efficiency to 61.5%. Optimizing two-stage methanation reactors realizes 98% CO2 conversion at 10018 h-1 gas hourly space velocity. The optimized reaction temperatures are 390 and 325 °C, respectively. The Aspen HYSYS dynamic modeling shows that the flows reach stability within 10 min under 1 kmol/h step-wise evolution of H2 flow. Longer time is required to approach the stability of the methanation reactor. Sharp evolutions of H2 flow cause higher amplitudes and a longer time to reach stability. The H2 flow lower than 35% of the initial value would result in the unstable behavior of the methanation reactor.