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Open-cell foams are promising catalyst supports as they provide a low pressure drop, radial mixing, and exceptional heat transport properties. Even though their large potential for the design of small-scale, dynamically operated reactors with strongly exothermic reactions is known, their application is not yet common. To design efficient and safe structured reactors in the future, the understanding of structure-heat transport relations is key. Fully resolved CFD simulations of non-isothermal structured reactors including chemical surface reactions require a high modeling effort and are computationally expensive. In a previous study we therefore implemented volumetrically distributed heat sources in the solid to mimic the heat production during an exothermal reaction, and evaluated the resulting heat flows and temperature distributions via CFD. The previous analysis, however, was limited to one specific open-cell foam geometry. In this study, we extend the conjugate heat transfer problem including heat production in the solid to five periodic open-cell foams (Kelvin cell-lattices) with defined but different structural parameters to establish structure-heat transport relations. We confirmed conduction being the dominant heat removal mechanism and found the strut diameter and the solid thermal conductivity being the key parameters to improve heat transport and reduce hot spots.

Membranes showing monomodal pore size distributions with mean pore diameters of 23, 33, and 60 nm are chemically functionalized using silanes with varying chain length and functional groups like amino, alkyl, phenyl, sulfonate, and succinic anhydrides. Their influence on the morphology, pore structure, and gas flow is investigated. For this, single-gas permeation measurements at pressures around 0.1 MPa are performed at temperatures ranging from 273 to 353 K using He, Ne, Ar, N2, CO, CO2, CH4, C2H4, C2H6, and C3H8. Results show pore size and pore volume linearly depending on the length of functional molecules, as expected for monolayer deposition. However, the gas flow through functionalized membranes is disproportionally decreased up to a factor of around 10. Hence, the decreased pore size and pore volume cannot explain the large decrease in flow. Furthermore, there is no specific dependency between the decrease in flow and temperature or gas type other than the relation proposed by Knudsen (√RTM)-1. Considering the large variety of functional molecules used, it is very surprising that no correlations between the type of functional group and the flow have been found. The decrease in flow, however, is strongly dependent on the chain length of the silanes (factor of 10 at ∼2 nm length). This leads to the conclusion that the observed effect is not caused by sorption driven processes. It is proposed that steric interactions between functional groups and gas molecules lead to increased residence times on the surface and longer molecular trajectories, which, in turn, lead to a decrease in flow. In membrane design, any surface modification should, therefore, make use of functionalizing agents with chain length as short as possible.

Martensitic stainless steels are widely used materials. Their mechanical and corrosion properties are strongly influenced by their microstructure and thereby can be affected by heat treatment. In the present study, the effect of different austenitizing temperatures on the passive film growth kinetics of martensitic stainless steel is studied by electrochemical impedance spectroscopy. The data was further fitted by the point defect model to determine kinetic parameters. We show that an increasing austenitizing temperature leads to a more protective passive film and slows down passive film dissolution in sulfuric acid.

In situ thermometry of catalytic gas phase reactions allows the determination of temperature profiles in catalyst beds. In NMR imaging systems used for measuring the chemical composition of species in model reactors, temperature measurements by NMR spectroscopy are technically challenging and confined to a rather low temperature range. In this study, an optimized NMR in situ technique is proposed, which will allow the determination of the temperature distribution in highly exothermic reactions on structured catalysts. Diffusion weighted magnetic resonance imaging (DW-MRI) was successfully applied as an alternative method for temperature measurements commonly performed by chemical shift measurements using ethylene glycol. DW-MRI applied with different diffusion sensitizing gradients allows high-resolution imaging of the temperature dependent diffusion coefficient, without the need for high spatial homogeneity of the magnetic field. Using 3D DW-MRI on ethylene glycol, glycerol, and the temperature stable ionic liquid Pyr13 [TFSI] (decomposition temperature of 400 °C) as NMR thermometers, measurements were performed in a temperature range from 20 to 160 °C. The proposed method can be used in reaction engineering approaches performed in NMR systems.

Combining low pressure drop and remarkable heat transport properties, open-cell foams offer a combination that makes them a highly attractive option as monolithic catalyst support. The coupled thermal behavior of foams and fluids during heat production, e.g., exothermic chemical reactions, is still not thoroughly described despite their potential to optimize temperature control in fixed-bed reactors. Hence, the aim of this study is to get deeper insight into coupled conjugate heat transfer and heat production in open-cell foams used in a tubular reactor with constant wall temperature. Therefore, we conducted - μ CT-based CFD simulations of open-cell foams with artificial heat sources that mimic the heat of reaction during an exothermal chemical reaction and allow to study the effect of heat production on heat transfer while requiring lower computational cost than simulating actual chemical reactions. We implemented a range of heat source intensities, that covers typical exothermic reactions, to study their effect on heat flows as well as temperature fields and used CO 2 methanation as a case study. We further quantified the influence of superficial velocity, heat source intensity, and material on the temperature fields inside the foam and found conduction being the dominant heat transport mechanism. We further evaluated the feasible range of even more simplified pseudo-homogeneous models and found high thermal conductivities and low superficial velocities to be appropriate. In conclusion, the presented approach offers the possibility to study thermal effects regarding catalytic supports and give valuable insight in heat transport mechanisms under relevant process conditions in heterogeneous catalysis (heat sources: 5–150 W for a reaction volume of 1.2 × 10−5 m3, superficial velocities 0–0.51 m s−1, thermal conductivities 5–50 W m−1 K−1).

Due to the finite nature and scarcity of crude oil-based fuels, increasing attention is being directed towards various forms of renewable energy. To obtain a fully functional renewable energy system, some compensation for the spatiotemporal fluctuations in renewable energy sources is necessary. In this context, the so-called liquid organic hydrogen carrier (LOHC) systems are promising from a technological perspective, although their impact on the environment and on animal/human health has not been considered in great detail. Hence, we present a proactive, comparative environmental hazard assessment of LOHC systems based on three alkylcarbazoles and quinaldine, including H2-rich, H2-lean and intermediate (i.e., partially hydrogenated) forms as well as on benzene and toluene, also including H2-rich forms (cyclohexane and methylcyclohexane, respectively). Specifically, the present study reports on the enzyme inhibitory (acetylcholinesterase), mutagenic (Ames test) and cytotoxic (IPC-81 cell line) activities of the above-mentioned compounds. Furthermore, the aquatic toxicity of the test compounds to marine bacteria (Vibrio fischeri), green algae (Raphidocelis subcapitata), aquatic plants (Lemna minor) and water fleas (Daphnia magna) was assessed in addition to their biodegradability, using inocula from a wastewater treatment plant. To complete the picture, we compared the effects of the LOHCs investigated herein with those of diesel oil. In this context, our results suggest that the quinaldine-based LOHC system is comparable with diesel oil in terms of ecotoxicity but is less biodegradable. The alkylcarbazoles appear to be more toxic and poorly biodegradable. Lastly, the benzene and toluene-based LOHC systems give serious reasons for concern in terms of human and aquatic toxicity. Nevertheless, due to their less complex composition, the assessment of the LOHC systems carries much lower levels of uncertainty regarding adverse effects. Additionally, because of more favourable physicochemical properties (e.g., higher boiling points), some LOHCs are safer for handling and transportation. Finally, the possibility of storing and using renewable energy offers a significant environmental and economic benefit.

Monolithic sponges combine low pressure losses and excellent heat transport properties and are consequently considered as promising catalyst carriers for fixed-bed reactors. Insights on how to design porosity and window size of monolithic sponges to resolve conflicting relations between low pressure losses, high thermal conductivities, and high space-time-yields (STY), i.e., a high catalyst inventory, are still unknown, especially at pilot or production scales. This study quantifies the outlined tradeoffs and assesses the potential of monolithic sponges as catalyst carriers compared to conventional packed beds of pellets. A state-of-the-art heterogeneous reactor model was applied in combination with a genetic multi-objective optimization algorithm to predict Pareto-optimal sets of sponge designs (max. STY, min. Δ p , Δ T max ⩽ Δ T tol ). As example, the methanation of CO2 was chosen. The Pareto-optimal set of sponge designs shows that small windows are necessary to obtain high space-time-yields comparable to the ones of conventional packed beds. As a consequence, the expected low pressure loss cannot be achieved. Because of excellent heat transport properties, which are weakly dependent on the throughput, monolithic sponges however allow stable operation under varying gas loads. The results demonstrate that monolithic sponges will probably not replace packed pellet beds of pellets for the steady-state production of chemicals. Instead, they provide a competitive option for small-scale, decentralized production for example within chemical energy storage and CO2 utilization.

Abstract Pattern of fluid flow through open-cell foams is important because of its influence on the performance of processes such as filtration, adsorption and heterogeneous catalysis that make use of such foams. So far, however, the experimental verification of velocity profiles obtained by computational fluid dynamics (CFD) simulation was insufficient. Here, the effect of morphology of ceramic foams on local gas flow patterns is observed via the noninvasive magnetic resonance velocimetry (MRV) technique. In order to cross-validate the simulations with the experimental flow mapping results, micro-computed tomography (µCT) data of the entire foams were used for generating the computational network required for 3D CFD simulations of velocity fields within the pores. The results of CFD simulations and MRV measurements of gas flow showed a remarkable agreement with deviations mainly below 10 percent if the whole foam structure was utilized in CFD simulations. The qualitative and quantitative agreement between CFD and MRV results underlines the reliability of CFD simulations that are based on µCT data and underpins the capability of NMR-based measurements for in situ velocity measurements. Graphic abstract

State-of-the-art dielectrophoretic (DEP) separation techniques provide unique properties to separate particles from a liquid or particles with different properties such as material or morphology from each other. Such separators do not operate at throughput that is sufficient for a vast fraction of separation tasks. This limitation exists because high electric field gradients are required to drive the separation which are generated by electrode microstructures that limit the maximum channel size. Here, we investigate DEP filtration, a technique that uses open porous microstructures instead of microfluidic devices to easily increase the filter cross section and, therefore, also the processable throughput by several orders of magnitude. Previously, we used simple microfluidic porous structures to derive design rules predicting the influence of key parameters on DEP filtration in real complex porous filters. Here, we study in depth DEP filtration in microporous ceramics and underpin the previously postulated dependencies by a broad parameter study (Lorenz et al., 2019). We will further verify our previous claim that the main separation mechanism is indeed positive DEP trapping by showing that we can switch from positive to negative DEP trapping when we increase the electric conductivity of the suspension. Two clearly separated trapping mechanisms (positive and negative DEP trapping) at different conductivities can be observed, and the transition between them matches theoretical predictions. This lays the foundation for selective particle trapping, and the results are a major step towards DEP filtration at high throughput to solve existing separation problems such as scrap recovery or cell separation in liquid biopsy. Graphical abstract Electronic supplementary material The online version of this article (10.1007/s00216-020-02557-0) contains supplementary material, which is available to authorized users.

A heterogeneously catalyzed gas phase reaction process was characterized regarding temperature and concentration profiles by means of three dimensional (3D) 1 H magnetic resonance spectroscopic imaging (MRSI), using the exothermal ethylene hydrogenation as an example. Here, temperature mapping was achieved by using specifically designed thermometers filled with ethylene glycol. The impact of heat and mass transfer on the process performance was investigated by using two different monolithic catalysts with completely different heat and mass transfer characteristics: a regularly structured honeycomb monolith and a irregularly structured open-cell foam packing. The influence of these characteristics on the reaction zones within the monolithic catalysts was demonstrated by simulations that were based on 2D reactor models. To evaluate the applicability of temperature and concentration mapping by 1 H MRSI for model validation, a predictive two dimensional model of the process was applied. The resulting simulations of temperature profiles and concentration distributions were in very good agreement with the experimental data with deviations below 9%. Conventional mass spectroscopic measurements provided further evidence of the accuracy of 3D MRSI measurements as well as the 2D reactor model.

Insulator-based dielectrophoresis (iDEP) is a powerful particle analysis technique based on electric field scattering at material boundaries which can be used, for example, for particle filtration or to achieve chromatographic separation. Typical devices consist of microchannels containing an array of posts but large scale application was also successfully tested. Distribution and magnitude of the generated field gradients and thus the possibility to trap particles depends apart from the applied field strength on the material combination between post and surrounding medium and on the boundary shape. In this study we simulate trajectories of singe particles under the influence of positive DEP that are flowing past one single post due to an external fluid flow. We analyze the influence of key parameters (excitatory field strength, fluid flow velocity, particle size, distance from the post, post size, and cross-sectional geometry) on two benchmark criteria, i.e., a critical initial distance from the post so that trapping still occurs (at fixed particle size) and a critical minimum particle size necessary for trapping (at fixed initial distance). Our approach is fundamental and not based on finding an optimal geometry of insulating structures but rather aims to understand the underlying phenomena of particle trapping. A sensitivity analysis reveals that electric field strength and particle size have the same impact, as have fluid flow velocity and post dimension. Compared to these parameters the geometry of the post's cross-section (i.e. rhomboidal or elliptical with varying width-to-height or aspect ratio) has a rather small influence but can be used to optimize the trapping efficiency at a specific distance. We hence found an ideal aspect ratio for trapping for each base geometry and initial distance to the tip which is independent of the other parameters. As a result we present design criteria which we believe to be a valuable addition to the existing literature.

The use of silver nanoparticles (AgNPs) as an antimicrobial agent has increased significantly over the past decade which potentiates their release to the environment. The antimicrobial effect of AgNPs is generally considered to be due to the release of silver ions (Ag+). Here we describe their bioavailability under environmental conditions and demonstrate its influence on (eco-)toxicity for the AgNP NM-300K and a wide variety of aquatic organisms (green algae, plants and crustaceans), terrestrial organisms (soil bacteria) and mammalian cells. Since the bioavailability of AgNPs is largely determined by Ag speciation, this paper focuses on the Ag speciation in the test media for these organisms. We predicted the Ag speciation in aqueous test media by equilibrium speciation calculation and validated the results by comparison with experimental speciation using ultracentrifugation and membrane filtration. Silver amounts were quantified using GF-AAS, ICP-OES/MS and UV-vis. The dissolved Ag concentrations were controlled by the fast initial release of a limited amount of Ag+. After this initial release, the media components, chloride and proteins, controlled the available dissolved Ag by precipitation and complexation. Further release of Ag+ due to oxidation was not observed in the time frame of our experiments, except for media with very high chloride content. Apparently, the stabilisers of these AgNPs prevented any further release accounting for an enhanced redox stability. These findings facilitated the prediction of the bioavailability of Ag in the test media and, based on literature toxicity data, also of its toxic effects (EC50) on the respective organisms. The toxic effects of the AgNP NM-300K depended solely on the amount of Ag+ that was already present in the stock dispersion and not from further release due to later oxidation processes.

Mesoporous inorganic structures with mean pore diameters of 26 nm are prepared by extrusion based on a yttria stabilized zirconia nanopowder. The sintered capillary membranes serve as model structures to investigate the influence of an alkyl-chain (C 16 ) surface functionalization on the gas diffusion kinetics of argon (Ar), nitrogen (N 2 ) and carbon dioxide (CO 2 ) in mesopores. The density of the C 16 alkyl-chains immobilized on the membrane surface has an effect on both, gas flow as well as gas selectivity. For low functional group densities ( −2 ), the gas flow is reduced without having an effect on the selectivity. In contrast, for high alkyl-chain densities (>4 groups nm −2 ) the mean distance between the C 16 -chains is reduced to the order of magnitude of the gas molecules leading to a reduction in gas flow and a significant change of the gas selectivity. The selectivity is found to be influenced depending on the molecular diameter of the gas species, being more evident for CO 2 compared to Ar and N 2 , suggesting a separation mechanism more comparable to molecular sieving than to surface diffusion.

Insulator-based dielectrophoresis (iDEP) has become a powerful tool for biomicrofluidic separation and analysis because it is capable to selectively separate biological particle systems according to properties like size, material, and shape. However, it has rarely been used to solve challenging separation problems involving nonbiological particles, namely, for systems that are prone to particle agglomeration. Here, we demonstrate material-selective separation of nonbiological systems, i.e., polystyrene and gold-coated polystyrene particles of two different sizes, using iDEP at high accuracy. For this purpose, we present a method to generate fluorescent gold-coated particles. We further introduce a method to reduce the static backpressure that builds up between in- and outlet reservoir due to electroosmotic flow. Moreover, we found that particle agglomeration makes their separation impossible when conventional iDEP routines are applied. Therefore, two solutions to reduce particle agglomeration are presented: A combination of AC and DC potentials and adjustment of pH and conductivity of the suspending medium. Both approaches allow separating particles under challenging conditions such as initially low absolute particle zeta potentials and high particle concentrations. Since those conditions can also be present in biological iDEP separation processes, the results are of general value for biological and nonbiological iDEP operations.

Within the last decade microscopic multiphase flows have gained broad interest. An exact understanding of the underlying hydrodynamic interrelations is the key for successful reactor layout and reaction control. To examine the local hydrodynamic behavior, non-invasive optical measurements techniques like particle tracking velocimetry (PTV) or (micro)particle image velocimetry ((\textmu)PIV) are the method of choice, since they provide precise velocity measurement with excellent spatial resolution. Such optical approaches require refractive index matching (RIM) of the involved flow phases to prevent optical distortion due to light refraction and reflection at the interfaces. Established RIM approaches often provide a single one degree of freedom which is sufficient to match the RI of the flow phases solely. With that, the material properties ($Oh$ number) are fixed and the relevant dimensionless numbers ($Ca$, $Re$) may only be altered hydrodynamically or geometrically. To avoid expansive geometric scaling of the microchannels, we propose an approach using two binary mixtures (double-binary mixtures) to introduce an additional degree of freedom. The approach allows examining liquid-liquid two-phase flows at a distinct velocity while being able to change the material combination ($Oh$-Number). Therefore $Ca$ and $Re$ can be chosen individually and the RIM provides undisturbed optical access. We present 4 different binary mixtures to be used, e.g. with Taylor droplets. The relevant material parameters are successfully correlated to measurement data, which delivers a system of equations that determines the mass fractions and the velocities to address $Re$ and $Ca$ individually. A proof-of-principle for the proposed double binary mixture RIM-approach is successfully established using \textmu PIV raw images., 21 pages, 12 figures

The application of insulator-based dielectrophoresis (iDEP) has the potential to enhance membrane fouling suppression in submerged membrane bioreactors without extra energy consumption. In this study, the effect of the insulators shapes and sizes within the interidigitated electrodes (IDE) configuration was investigated for a better dielectrophoresis (DEP) force with a better membrane fouling suppression. Three circular insulators CS 1, CS 1.5 and CS 2 with diameters of 1 mm, 1.5 mm and 2 mm, respectively, were tested. A 2 mm side square section insulator SS 2 was also examined. The numerical simulation results show that the DEP force extension is greater with a similar diameter as the excited electrodes (2 mm in this study) when using circular insulators. The use of square section insulator (SS 2) increases the overall electric field gradient squared (?|E|2) by 16% compared to the 2 mm circular insulator (CS 2). The square section insulator also extends the dielectrophoresis (DEP) force field more uniformly across the membrane surface while generating sufficient force to move the suspended solids away from the membrane. The experimental investigation verified the theoretical simulation prediction and demonstrated that SS 2 membrane modules provide longer membrane service time by maintaining a normalized permeate flux of 55% more than the circular section membrane modules, with a maximum intensification factor of 14 at a 220 V voltage and 50 Hz with a transmembrane pressure of 0.1 bar. This research is made possible by NPRP award (NPRP7-089-2-044) from Qatar National Research Fund (QNRF) Scopus

Continuous, contact-free fractionation of sensitive microparticles at high throughput is a challenge. For this purpose, we developed a sheath flow assisted dielectrophoretic (DEP) field-flow separator with a tailored arrangement of cylindrical interdigitated electrodes (cIDE) and observed size-dependent trajectories of dispersed particles. Using a voltage input of 200 V eff at a frequency of 200 kHz, polystyrene particles (45, 25, and 11 µm in diameter) levitated to different heights along the channel length due to a negative DEP force. Experimental observations agree well with simulated particle trajectories that were obtained by a modified Lagrangian particle tracking model in combination with Laplace's and Navier–Stokes equations. By exploiting the size-dependent levitation height difference the desired particle size fraction can be collected at a specific channel length. The required channel length of the proposed cIDE separator increases with decreasing particle size to be separated. The quality of theoretical fractionation, which we quantify by resolution, improves strongly with reduced collector width, reduced volume flow rate and increased voltage input. The sensitivity of these dependencies increases with decreasing particle size. We calculated a theoretical throughput of up to 47 mL min −1 when trading-off design and operation parameters, allowing for contact-free fractionation of sensitive microparticles with negligible shear stress.

Catalyst pores are typically non-uniform along their longitudinal axis, and the transport of gaseous reactants and products takes place in a somehow tapered confinement. In a previous study we observed a diffusion delay in single tapered pores by means of a transient two-bulb-diffusion-cell (Veltzke et al., 2015). Processes in heterogeneous catalysis, however, are typically operated under steady state conditions. Hence also the diffusion processes are non-transient and reactant species are permanently consumed while product species steadily emerge. To mimic steady-state multicomponent diffusion in a cone, we developed a novel two-pipe-diffusion-cell and described the mass transport by an analytical model. Here we can show that the delay effect, which is caused by volumetric changes in longitudinal direction, also exists for steady-state binary and multicomponent diffusion. It is experimentally confirmed that the diffusion hindrance increases with conicity of the test tube. Also the results are transferable to those of the transient two-bulb-diffusion-cell. The measurement of steady-state experiments, however, is much faster.

A micro-scale analysis of mass transport in ceramic foams that are used as catalyst supports in gas phase reactions is of high interest. Although the effects of flow rate and foam parameters on the radial and axial dispersion are known for liquid flows, no pore-scale experimental analysis has been yet reported to correlate the mechanical and diffusional dispersion of gas flows to the geometry of open-cell foams. Here, a spatially resolved Pulsed Field Gradient NMR method is applied to determine dispersion coefficients of thermally polarized gas along axial and transversal directions of open-cell foams. The comparative study of three commercial foam samples with different morphologies shows the effect of open porosity, window size, and flow rate on gas dispersion. Additionally, the influence of mechanical and diffusional dispersion at each flow rate is investigated for individual samples. By observing the transition from diffusional dispersion to mechanically driven dispersion of gas, it is found that diffusional dispersion plays an important role, even at higher flow rates after a transition from Darcy to Darcy-Forchheimer regime occurs. The measured values for dispersion coefficients of methane can be directly used in pseudo-heterogeneous models for the methanation reaction.

This study aims to investigate the effect of dielectrophoretic (DEP) force on microorganisms' viability in a membrane bioreactor (MBR). The impact of different electrical potentials (5-150 V) and different exposure durations (20-120 min) on the viability of microorganisms were studied. An interdigitated cylindrical electrode (IDE) configuration was used in the membrane module. Each electrical potential application was operated intermittently with 10 s of the electric field on and 15 s of the electric field off. It was found that the bacteria were able to withstand voltage up to 50 V, and their activity even increased with time with the application of 5 V. At high electrical potentials (100 and 150 V), the microbial activity decreased as a result of the increased current flow and temperature build up due to the Joule heating effect. The decrease of the microbial activity caused the increase of the total organic carbon (TOC) and ammonium (NH4+) concentrations in the bulk solution. A comparison between the continuous and intermittent voltage supply for the 50 V further proved the Joule heating impact on the bacteria viability. This research is made possible by NPRP award (NPRP7-089-2-044) from Qatar National Research Fund (QNRF). The statements made herein are solely the responsibility of the authors. The support from Mr. Naveen Francis and Mr. Steve Green from Doha South Waste Water Treatment Plant is also gratefully acknowledged. Scopus

Submerged membrane bioreactor (MBR) is currently believed to be an efficient biological treatment for reusing and recovering wastewater to extenuate the ever increasing water scarcity crisis. To mitigate the main problem, membrane fouling, in MBR systems, we propose a solution that avoids usage of chemicals, and allows uninterrupted operation using a novel concept of obstacle dielectrophoresis (oDEP). The utilization of obstacles, insulator or metal (floating) electrodes, between electrically excited electrodes, can extend the DEP force field to move suspended particles away from membranes without having to increase voltage, for suppressing fouling with low energy consumption. Experimental investigation verified our theoretical simulation prediction and demonstrated that insulator membrane modules provide longer membrane service time for maintaining normalized permeate flux of 55% than those by floating electrode membrane modules, with a maximum intensification factor of 7.8 when applied 220 V voltage and 50 Hz as well as the transmembrane pressure of 0.1 bar. Although stronger DEP force and hence better performance of fouling suppression can be generated by higher voltage, 50 V insulator membrane module demonstrated to be the most energy efficient process with a specific energy consumption of 0.295 kWh/m3 product and 13 times higher efficient factor than the 220 V. - 2017 This research is made possible by NPRP award ( NPRP7-089-2-044 ) from Qatar National Research Fund (QNRF). The statements made herein are solely the responsibility of the authors. Scopus

In this article, we introduce a novel approach to retrieve spatial- and time-resolved Taylor slug flow information from a single non-invasive photometric flow sensor. The presented approach uses disperse phase surface properties to retrieve the instantaneous velocity information from a single sensor’s time-scaled signal. For this purpose, a photometric sensor system is simulated using a ray-tracing algorithm to calculate spatially resolved near-infrared transmission signals. At the signal position corresponding to the rear droplet cap, a correlation factor of the droplet’s geometric properties is retrieved and used to extract the instantaneous droplet velocity from the real sensor’s temporal transmission signal. Furthermore, a correlation for the rear cap geometry based on the a priori known total superficial flow velocity is developed, because the cap curvature is velocity sensitive itself. Our model for velocity derivation is validated, and measurements of a first prototype showcase the capability of the device. Long-term measurements visualize systematic fluctuations in droplet lengths, velocities, and frequencies that could otherwise, without the observation on a larger timescale, have been identified as measurement errors and not systematic phenomenas.

The safe implementation of nanotechnology requires nanomaterial hazard assessment in accordance with the material physicochemical properties that trigger the injury response at the nano/bio interface. Since CuO nanoparticles (NPs) are widely used industrially and their dissolution properties play a major role in hazard potential, we hypothesized that tighter bonding of Cu to Fe by particle doping could constitute a safer-by-design approach through decreased dissolution. Accordingly, we designed a combinatorial library in which CuO was doped with 1–10% Fe in a flame spray pyrolysis (FSP) reactor. The morphology and structural properties were determined by XRD, BET, Raman spectroscopy, HRTEM, EFTEM and EELS, which demonstrated a significant reduction in the apical Cu-O bond length while simultaneously increasing the planar bond length (Jahn-Teller distortion). Hazard screening was performed in tissue culture cell lines and zebrafish embryos to discern the change in the hazardous effects of doped vs. non-doped particles. This demonstrated that with increased levels of doping, there was a progressive decrease in cytotoxicity in BEAS-2B and THP-1 cells, as well as an incremental decrease in the rate of hatching interference in zebrafish embryos. The dissolution profiles were determined and the surface reactions taking place in Holtfreter’s solution were validated using cyclic voltammetry (CV) measurements to demonstrate the Cu+/Cu2+ and Fe2+/Fe3+ redox species playing a major role in the dissolution process of pure and Fe doped CuO. Altogether, a safe-by-design strategy was implemented for the toxic CuO particles via Fe doping and has been demonstrated for their safe use in the environment.

A new electrode configuration based on dielectrophoresis (DEP) for a Submerged Membrane Bioreactors was suggested. The intensification of the permeate flux with the new system was examined experimentally using a pulsed DEP of 10 s on and 15 s off. In comparison with the test without DEP effect, the normalized permeate is 3.5; 3.9 and 4.5 times higher when applying 105 Veff, 144 Veff, and 220 Veff respectively. The membrane working time is found to be 10 times higher when using DEP. The impact of electrodes spacing was also examined experimentally and numerically. It was demonstrated that a large electrodes spacing is not able to intensify the permeate flux, but it could increase the membrane lifespan by stabilising the permeate flux. This publication was made possible by NPRP grant (NPRP7-089-2-044) from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors. Also the authors would like to thank the public works authority of Qatar (ASHGAL) for their supply of the activated sludge samples. Scopus

Membrane bioreactors (MBRs) present a unique opportunity in waste water treatment by combining the activated sludge process with membrane filtration. Although MBRs require less area, produce less volume of sludge and have high purification efficiency, they suffer from high membrane fouling. Membrane fouling can be reduced by applying aeration and Dep voltage. However, application of these two anti-fouling mechanisms would make the process expensive. Thus, a new aeration and DEP scheme of 5 min on – 5 min off is being suggested in this study. With this scheme, it was found that through application of DEP at 100 V and 0.3 L/min.m2 aeration flowrate and reduced lumen size of 6 mm, the membrane permeate flux can be increased by 58% compared to MBR without DEP and aeration. However, through energy analysis the optimum operating parameters were found to be at 0.3 L/min.m2 aeration flowrate and 50 V DEP using the suggested 5 min on-5 min off scheme. At the optimum operating condition, the permeability flux is 54% higher than MBR without DEP and aeration. This research project is made possible by NPRP award (NPRP7-089-2-044) from Qatar National Research Fund (QNRF) (grant ID NPRP7-089-2-044 ). The statements made herein are solely the responsibility of the authors. The authors would also like to acknowledge the help provided by Qatar Works Authority (Ashghal) for providing the wastewater and sludge samples. Scopus

Heat Treatment of martensitic stainless steels is used to increase the hardness that is caused by several microstructure changes. But such a treatment does affect both mechanical properties and corrosion resistance. Existing studies about the effect of austenitizing on the material properties and the corrosion resistance show contradictory results. Here we reveal the different effects of austenitizing on the passive layer of stainless steel and thus the corrosion resistance, thermodynamic phase calculations, microstructure investigations and various electrochemical measurements are performed. By potentiodynamic polarization scans the pitting potential, the critical pitting potential and the corrosion current are determined. Impedance spectroscopy are used to gain deeper insight into the passive layer properties. The results show a strong dependency of the corrosion behavior on the heat treatment where the governing corrosion mechanism are affected differently.

Porous inorganic capillary membranes are prepared to serve as model structures for the experimental investigation of the gas transport in functionalized mesopores. The porous structures possess a mean pore diameter of 23 nm which is slightly reduced to 20 nm after immobilizing C16-alkyl chains on the surface. Gas permeation measurements are performed at temperatures ranging from 0 to 80 °C using Ar, N2, and CO2. Nonfunctionalized structures feature a gas transport according to Knudsen diffusion with regard to gas flow and selectivity. After C16-functionalization, the gas flow is reduced by a factor of 10, and the ideal selectivities deviate from the Knudsen theory. CO2 adsorption measurements show a decrease in total amount of adsorbed gas and isosteric heat of adsorption. It is hypothesized that the immobilized C16-chains sterically influence the gas transport behavior without a contribution from adsorption effects. The reduced gas flow derives from an additional surface resistance caused by the C16-chai...

International audience; Gas flow properties in channels with slightly varying cross section have a dependency on the direction of channel perfusion when the gas is in the slip and transitional flow regimes. In the past, it was observed that the flow rate in converging direction is higher compared to the case where the channel diverges alongside. This gas flow diode effect does neither exist in the continuum regime nor in the free molecular regime, and it has its maximum at the same level of gaseous rarefaction as the well-known Knudsen minimum. However, no comprehensive study on the physics of this diode effect is carried out yet. In order to overcome this knowledge gap, the current paper proceeds our previous works by an appropriate experimental study. Here we can show that the diode effect crucially depends on the proportion of inclined walls to the overall channel inner surface. Also the inclination of the wall itself determines the strength of the diode effect meaning that the diodicity increases with the opening angle. Furthermore, we found indication that the diodicity also depends on the molar mass and the internal structure of the impinging gas molecules. Finally, we propose an explanation of the diode effect that is mainly based on the tangential reflection process of gas molecules colliding with the inclined walls of a tapered channel.

Insulator-based (electrodeless) dielectrophoresis (iDEP) is a promising particle manipulation technique, based on movement of matter in inhomogeneous fields. The inhomogeneity of the field arises because the excitatory field distorts at obstacles (posts). This effect is caused by accumulation of polarization charges at material interfaces. In this study, we utilize a multipole expansion method to investigate the influence of geometry and material on field distortion of posts with arbitrary cross-sections in homogeneous electric fields applied perpendicular to the longitudinal axis of the post. The post then develops a multipole parallel or anti parallel to the excitatory field. The multipoles intensity is defined by the post's structure and material properties and directly influences the DEP particle trapping potential. We analyzed posts with circular and rhombus-shaped cross-sections with different cross-sectional width-to-height ratios and permittivities for their polarization intensity, multipole position, and their particle trapping behavior. A trade-off between high maximum field gradient and high coverage range of the gradient is presented, which is determined by the sharpness of the post's edges. We contribute to the overall understanding of the post polarization mechanism and expect that the results presented will help optimizing the structure of microchannels with arrays of posts for electrodeless DEP application.

Measuring spatially resolved concentration distributions in gas phase reaction systems is an important tool to validate simulation calculations, improve the understanding of transport processes within the catalyst, and identify potentials for improvements of monolithic catalyst supports. The commonly used measurement methods for such opaque systems are invasive and, thus, might be misleading due to alteration of the system. To overcome this issue, a 3D magnetic resonance spectroscopic imaging (MRSI) method was developed and implemented on a 7-Tesla NMR imaging system to map the concentration distributions within opaque monolithic catalysts using the ethylene hydrogenation process as case study. The reaction was catalyzed by a coated sponge packing or a honeycomb monolith within an NMR compatible packed bed reactor. Temperatures at the inlet and the outlet of the catalyst beds were simultaneously determined by analyzing the spectra of inserted ethylene glycol filled glass capsules. Steady state concentration profiles and temperature levels were measured at different reaction conditions. In order to prove the plausibility of the measured spatial distributions of compound concentrations, the experimental results were compared to a 1D model of the reactor based on kinetic data from literature. Furthermore, a comparison with integral concentration measurements using a mass spectrometer demonstrated deviations below 5%. The results show that 3D MRSI is a valuable and reliable tool to non-invasively measure spatially resolved process parameters within optically and/or mechanically inaccessible structured monolithic catalyst supports, even if only standard thermal polarization is exploited and the use of expensive and technically challenging signal enhancement techniques (hyperpolarization) is avoided. We expect that 3D MRSI can pave the way toward deeper insight into the interactions between catalyst, catalyst support, and gas phase.

The application of catalytically coated metallic foams in catalytic processes has a high potential for exothermic catalytic reactions such as CO2 methanation or Fischer-Tropsch synthesis due to good heat conductivity, improved turbulent flow properties and high catalyst efficiencies. But the preparation of homogenous catalyst coats without pore blocking is challenging with conventional wash coating techniques. Here, we report on a stable and additive free colloidal CoAlOOH suspension (sol) for the preparation of catalytically active Co/Al2O3 xerogel catalysts and coatings. Powders with 18 wt% Co3O4 prepared from this additive free synthesis route show a catalytic activity in Fischer-Tropsch synthesis and CO2 methanation which is similar to a catalyst prepared by incipient wetness impregnation (IWI) after activating the material under flowing hydrogen at 430 °C. Yet, the xerogel catalyst exhibits a much higher thermal stability as compared to the IWI catalyst, as demonstrated in catalytic tests after different heat agings between 430 °C and 580 °C. It was also found that the addition of polyethylene glycol (PEG) to the sol influences the catalytic properties of the formed xerogels negatively. Only non-reducible cobalt spinels were formed from a CoAlOOH sol with 20 wt% PEG. Metallic foams with pores sizes between 450 and 1200 μm were coated with the additive free CoAlOOH sol, which resulted in homogenous xerogel layers. First catalytic tests of the coated metal foams (1200 μm) showed good performance in CO2 methanation.

International audience; Moderately rarefied gas flows are clearly distinguished from viscous flow in the continuum regime and from free molecular flow at high rarefaction. Being of relevance for various technical applications, the understanding of such flow processes is crucial for considerable enhancement in micro electromechanical systems (MEMS) and vacuum techniques. In this work, we focus on the isothermal rarefied gas flow through long channels with longitudinally varying cross section. We apply two approaches, an analytical one and a numerical one that is based on the solution of the linearized S-model, both allowing us to predict the mass flow rate in diverging and converging flow directions for arbitrary pressure gradients. Both approaches are validated by CO2, N-2 and Ar permeation experiments on tapered microchannels manufactured by means of micromilling. The local Knudsen numbers ranged from 0.0471 to 0.2263. All the numerical and analytical results are in good agreement to the experimental data and show that the mass flow rate is significantly higher when the duct is perfused in converging direction. The understanding of the physical phenomenon of this gas flow diode effect might pave the way for novel components in MEMS such as static one-way valves.

This paper reports on the (eco)toxicity and biodegradability of ionic liquids considered for application as lubricants or lubrication additives. Ammonium- and pyrrolidinium-based cations combined with methylsulphate, methylsulphonate and/or (CF 3 SO 2 ) 2 N − anions were investigated in tests to determine their aquatic toxicity using water fleas Daphnia magna , green algae Selenastrum capricornutum and marine bacteria ( Vibrio fischeri ). Additional test systems with an isolated enzyme (acetylcholinesterase) and isolated leukaemia cells from rats (IPC-81) were used to assess the biological activity of the ionic liquids. These compounds generally exhibit low acute toxicity and biological activity. Their biodegradability was screened according to OECD test procedures 301 B and 301 F. For choline and methoxy-choline ionic liquids ready biodegradability was observed within 5 or 10 d, respectively. Some of the compounds selected have a considerable potential to contribute to the development of more sustainable products and processes.

Most bio-technological applications such as enzyme immobilization for biocatalysis or biosensing require highly suitable carriers that offer high accessible surface area and good liquid flow permeability at the same time. Porous monolithic adsorbents (MAds), combining large specific surface areas with high liquid flow permeabilities, are prepared in a fast and versatile two step synthesis via the ionotropic gelation route. The obtained MAds consist of 3-dimensionally assembled porous microbeads with tailorable specific surface areas up to 50 m2 g−1 after sintering. The pores inside microbeads and MAds are highly interconnected with hierarchical pore diameters between 15 nm and 105 μm. MAds permeability constants are: k1 = 6 × 10−9 m2 and k2 = 4 × 10−4 m. The obtained MAds are excellent platforms for further bio-chemical surface modifications applying established silanization protocols. We perform an amino functionalization of the MAds which is subsequently used to covalently link the model enzyme laccase to the MAds. The applied amino molecules are situated across the whole cross-sectional area of each microbead, and enzymes like laccase with a mass of approximately 70 kDa are able to completely access the intra-bead pores. The maximum effectiveness factor η is 0.90 for freshly immobilized laccase. Furthermore, laccase keeps about 85% of its activity as compared to the free enzyme in solution, and after 9 days of storage the activity is still 80%. An additional flux test confirms that the immobilized enzyme remains active under continuous flux conditions for at least 16 h.

The electrochemical behavior of copper oxide nanoparticles is investigated at both the single particle and at the ensemble level in neutral aqueous solutions through the electrode-particle collision method and cyclic voltammetry, respectively. The influence of Cl- and NO3- anions on the electrochemical processes occurring at the nanoparticles is further evaluated. The electroactivity of CuO nanoparticles is found to differ between the two types of experiments. At the single-particle scale, the reduction of the CuO nanoparticles proceeds to a higher extent in the presence of chloride ion than of nitrate ion containing solutions. However, at the multiparticle scale the CuO reduction proceeds to the same extent regardless of the type of anions present in solution. The implications for assessing realistically the environmental fate and therefore the toxicity of metal-based nanoparticles in general, and copper-based nanoparticles in particular, are discussed.