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ispartof: ULTRASONICS SONOCHEMISTRY vol:93 status: published

Cooling towers are a primary and vital component of the cooling cycle in a chemical plant. The heat and mass transfer inside a cooling tower is governed by the complex geometry of the fill, flow conditions and turbulence degree of the air and liquid phases. These aspects of a cooling tower are generally modelled using computational fluid dynamics, which is time consuming and computationally intensive. The cur-rent study illustrates a methodology for modeling the heat and mass transfer of a full-scale hybrid-draft cooling tower and an induced draft cooling tower located in two separate plants. A convenient method was devised to account for the resistance encountered by the air stream passing through a full-scale hybrid-draft cooling tower. The devised method is notably simpler than engaging computational fluid dy-namics. The model constitutes a mechanistic component that computes the variation of liquid and air properties along the height of the tower. The variation of the mass transfer coefficient with the contact area between the liquid and gas phases was predicted using an artificial neural network. As the model utilizes a mechanistic component developed based on heat and mass transfer principles, that borrows values for the mass transfer coefficient predicted by a neural network to simulate liquid and air proper-ties, the entirety functions as a hybrid model. The developed neural network predicted the mass transfer coefficient with an R-2 > 0.94 for both cases. The overall model demonstrated a prediction accuracy ( R-2 ) of 0.99 in the year-round thermal performance of both towers. Therefore, the high prediction accuracy and simplicity of the model enables applications in real time monitoring of the thermal performance and optimization of operational parameters.(C) 2022 The Authors. Published by Elsevier Ltd.

The enzymatic esterification of oleic acid and 1-butanol to butyl oleate was performed in an aqueous-organic system in capillary microreactors with various inner diameters operated under slug flow. The free Rhizomucor miehei lipase in the aqueous phase was used as catalyst and n-heptane as the organic solvent. A close to 100% yield of butyl oleate could be achieved in the microreactor made of polytetrafluoroethylene within 30 min residence time at 30 °C. The reaction rate is well described by the existing kinetic model based on a Ping Pong Bi Bi mechanism with competitive inhibition of 1-butanol. This model was extended to describe the effect of the interfacial area and aqueous to organic flow ratio in microreactors. By performing the reaction at low aqueous to organic flow ratios in hydrophilic microreactors (e.g., made of stainless steel), the enzyme turnover number could be enhanced significantly making it promising for process intensification.

As organic porous soil, peat is prone to self-heating ignition, a type of spontaneous initiation of fire that can take place at ambient temperatures without an external source. Despite the urgency to tackle peat fires, the understanding of the self-heating ignition of peat is insufficient. In this study, a computational model that integrates the mechanisms of heat transfer, mass transfer and chemistry is incorporated with a three-step reaction scheme that includes drying, biological reaction and oxidative oxidation to simulate the self-heating ignition of smouldering peat. The model is first validated against 13 laboratory-scale experiments from literature. For critical ignition temperature (Tig), the model gives accurate predictions for all experiments with a maximum error of 5°C. The validated model is then upscaled to predict Tig for field-size peat soil layers and compared with the predictions using a one-step scheme. The three-step scheme is shown to give more reliable predictions of Tig than the one-step scheme. According to the simulation results, for a 1.5-m-deep peat layer, self-heating ignition can occur at an average ambient temperature above 40°C. This is the first time that a multi-step scheme is used to simulate the self-heating ignition of peat, aiming to help in the prevention and mitigation of these wildfires.

Liquid-phase adsorption has hardly been established in micro-flow, although this constitutes an industrially vital method for product separation. A micro-flow UV-photo isomerization process converts cis-cyclooctene partly into trans-cyclooctene, leaving an isomeric mixture. Trans-cyclooctene adsorption and thus separation was achieved in a fixed-bed micro-flow reactor, packed with AgNO3/SiO2 powder, while the cis-isomer stays in the flow. The closed-loop recycling-flow has been presented as systemic approach to enrich the trans-cyclooctene from its cis-isomer. In-flow adsorption in recycling-mode has hardly been reported so that a full theoretical study has been conducted. This insight is used to evaluate three process design options to reach an optimum yield of trans-cyclooctene. These differ firstly in the variation of the individual residence times in the reactor and separator, the additional process option of refreshing the adsorption column under use, and the periodicity of the recycle flow. ispartof: AICHE JOURNAL vol:67 issue:1 ispartof: location:United States status: published

Spin freeze-drying, as a part of a continuous freeze-drying technology, is associated with a much higher drying rate and a higher level of process control in comparison with batch freeze-drying. However, the impact of the spin freezing rate on the dried product layer characteristics is not well understood at present. This research focuses on the relation between spin-freezing and pore size, pore shape, dried product mass transfer resistance and solid state of the dried product layer. This was thoroughly investigated via high-resolution X-ray micro-computed tomography (µCT), scanning electron microscopy (SEM), thermal imaging and solid state X-ray diffraction (XRD). It was concluded that slow spin-freezing rates resulted in the formation of highly tortuous structures with a high dried-product mass-transfer resistance, while fast spin-freezing rates resulted in lamellar structures with a low tortuosity and low dried-product mass-transfer resistance.

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was performed in perfluoroalkoxy alkane capillary microreactors packed with a carbon-supported ruthenium (Ru/C) catalyst with an average particle diameter of 0.3 or 0.45 mm. The reaction was executed under an upstream gas–liquid slug flow with 1,4-dioxane as the solvent and H2 as the hydrogen donor in the gas phase. Operating conditions (i.e., flow rate and gas to liquid flow ratio, pressure, temperature and catalyst particle size) were varied in the microreactor to determine the influence of mass transfer and kinetic characteristics on the reaction performance. At 130 °C, 12 bar H2 and a weight hourly space velocity of the liquid feed (WHSV) of 3.0 gfeed/(gcat·h), 100% LA conversion and 84% GVL yield were obtained. Under the conditions tested (70–130 °C and 9–15 bar) the reaction rate was affected by mass transfer, given the notable effect of the mixture flow rate and catalyst particle size on the LA conversion and GVL yield at a certain WHSV. A microreactor model was developed by considering gas–liquid–solid mass transfer therein and the reaction kinetics estimated from the literature correlations and data. This model well describes the measured LA conversion for varying operating conditions, provided that the internal diffusion and kinetic rates were not considered rate limiting. Liquid–solid mass transfer of hydrogen towards the external catalyst surface was thus found dominant in most experiments. The developed model can aid in the further optimization of the Ru/C catalyzed levulinic acid hydrogenation in packed bed microreactors.

ispartof: CHEMPHOTOCHEM vol:4 issue:10 pages:5193-5200 status: published

Reducing the cost of redox flow batteries (RFBs) is critical to achieving broad commercial deployment of large-scale energy storage systems. This can be addressed in a variety of ways, such as reducing component costs or improving electrode design. The aim of this work is to better understand the relationship between electrode microstructure and performance. Four different commercially available carbon electrodes were examined – two cloths and two papers (from AvCarb® and Freudenberg Performance Materials) – and a comprehensive study of the different pore-scale and mass-transport processes is presented to elucidate their effect on the overall cell performance. Electrochemical measurements were carried out in a non-aqueous organic flow-through RFB with these different electrodes, using two supporting solvents (propylene carbonate and acetonitrile) and at a variety of flow rates. Electrode samples were scanned using X-ray computed tomography, and a customised segmentation technique was employed to extract several microstructural parameters. A pore network model was used to calculate the pressure drops and permeabilities, which were found to be within 1.26 × 10−11 and 1.65 × 10−11 m2 for the papers and between 8.61 × 10−11 and 10.6 × 10−11 m2 for the cloths. A one-dimensional model was developed and fit to polarisation measurements to obtain mass-transfer coefficients, km, which were found to be between 1.01 × 10−6 and 5.97 × 10−4 m s−1 with a subsequent discussion on Reynolds and Sherwood number correlations. This work suggests that, for these fibrous materials, permeability correlates best with electrochemical cell performance. Consequently, the carbon cloths with the highest permeability and highest mass-transfer coefficients, displayed better performances.

We reported experimental measurements of the diffusion coefficient of methane at effectively infinite dilution in methylbenzene and in heptane at temperatures ranging from (323 to 398) K and at pressures up to 65 MPa. The Taylor dispersion method was used and the overall combined standard relative uncertainty was 2.3%. The experimental diffusion coefficients were correlated with a simple empirical model as well as the Stokes–Einstein model with the effective hydrodynamic radius of methane depending linearly upon the solvent density. The new data address key gaps in the literature and may facilitate the development of an improved predictive model for the diffusion coefficients of dilute gaseous solutes in hydrocarbon liquids.

A useful aerosol model must be able to adequately resolve the chemical complexity and phase state of the wide particle size range arising from the many different secondary aerosol growth processes to assess their environmental and health impacts. Over the past two decades, significant advances in understanding of gas-aerosol partitioning have occurred, particularly with respect to the role of organic compounds, yet aerosol representations have changed little in air quality and climate models since the late 1990s and early 2000s. The gas-aerosol partitioning models which are still commonly used in air quality models are separate inorganics-only thermodynamics and secondary organic aerosol (SOA) formation based on absorptive partitioning theory with an assumption of well-mixed liquid-like particles that continuously maintain equilibrium with the gas phase. These widely used approaches in air quality models for secondary aerosol composition and growth based on separated inorganic and organic processes are inadequate. This review summarizes some of the important developments during the past two decades in understanding of gas aerosol mass transfer processes. Substantial increases in computer performance in the last decade justify increasing the process detail in aerosol models. Organics play a central role during post-nucleation growth into the accumulation mode and change the hygroscopic properties of sulfate aerosol. At present, combined inorganic-organic aerosol thermodynamics models are too computationally expensive to be used online in 3-D simulations without high levels of aggregation of organics into a small number of functional surrogates. However, there has been progress in simplified modeling of liquid-liquid phase separation (LLPS) and distinct chemical regimes within organic-rich and inorganic-rich phases. Additional limitations of commonly used thermodynamics models are related to lack of surface tension data for various aerosol compositions in the small size limit, and lack of a comprehensive representation of surface interaction terms such as disjoining pressure in the Gibbs free energy which become significant in the small size limit and which affect both chemical composition and particle growth. As a result, there are significant errors in modeling of hygroscopic growth and phase transitions for particles in the nucleation and Aitken modes. There is also increasing evidence of reduced bulk diffusivity in viscous organic particles and, therefore, traditional secondary organic aerosol models, which are typically based on the assumption of instantaneous equilibrium gas-particle partitioning and neglect the kinetic effects, are no longer tenable.

A catalyst preparation method, consisting of slurry washcoating with γ-Al2O3 followed by impregnating platinum on the microreactor walls, has been investigated. The effect of various factors in the preparation procedures on the adhesion of the washcoated γ-Al2O3 was studied, including the slurry property (i.e., the binder type, concentration and molecular weight, γ-Al2O3 concentration and particle size, pH), and the (micro)reactor substrate and channel shape. The results show that the adhesion of γ-Al2O3 washcoat strongly depended on the slurry rheological characteristics. A good adhesion on FeCrAlloy substrates was obtained using the slurry with polyvinyl alcohol as the binder (typical concentration at 3–5 wt% and molecular weight of 57,000–186,000), 20 wt% γ-Al2O3 (particle size being around 3 µm) and pH = 3.5. FeCrAlloy as the substrate exhibited an excellent coating adhesion in rectangular or round channels, primarily due to the formation of alumina film over the surface during thermal pretreatment. The aluminum-free stainless steel as the substrate only showed a good adhesion in a round channel. Well-adhered Pt/γ-Al2O3 catalysts were then applied in a microreactor comprising parallelized microchannels made of FeCrAlloy under the optimized coating procedures, and investigated in terms of its performance in the catalytic methane combustion. It is shown that the reaction temperature has a greater influence on the methane conversion than the flow rate, and a favorable coverage of methane and oxygen on the catalyst surface is essential to obtain a good catalytic performance. These reaction results are in line with the temperature behavior measured along the microreactor.

An optimized design for a 210 kg alloy, Ti-Mn alloy based hydrogen storage system for stationary application is presented. A majority of the studies on metal hydride hydrogen systems reported in literature are based on system scale less than 10 kg, leaving questions on the design and performance of large-scale systems unanswered. On the basis of sensitivity to various design and operating parameters such as thermal conductivity, porosity, heat transfer coefficient etc., a comprehensive design methodology is suggested. Following a series of performance analyses, a multi-tubular shell and tube type storage system is selected for the present application which completes the absorption process in 900 s and the desorption process in 2000 s at a system gravimetric capacity of 0.7% which is a vast improvement over similar studies. The study also indicates that after fifty percent reaction completion, heat transfer ceases to be the major controlling factor in the reaction. This could help prevent over-designing systems on the basis of heat transfer, and ensure optimum system weight. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

International audience; A fixed volume packed column was simulated for the absorption at counter-current of four more or less hydrophobic volatile organic compounds (VOCs) in water and in two heavy organic solvents (PDMS 50, a silicone oil) and DEHA (Bis(2-ethylhexyl) adipate). Reliable values of the mass-transfer coefficients were deduced allowing to calculate the VOCs removal efficiency. Disappointing performances in heavy solvents, lower than 60% for isopropanol and acetone, were computed in a 3 m height column and using mild conditions (atmospheric pressure and a liquid-to-gas mass flow rate ratio around 2). However, toluene removal efficiencies higher than 90% were simulated. (C) 2017 The Korean Society of Industrial and Engineering Chemistry.

Product yield optimization in bimodal reaction sequences including degradation has been performed considering three-phase reactors such as the jet loop and trickle bed reactors. The considered reaction network comprises two consecutive homogeneous reaction steps toward intermediates which are converted to the corresponding final products by heterogeneously catalyzed reactions, while the reactant and these intermediates are susceptible to irreversible degradation. In the jet loop reactor, the so-called “homogeneous product” is the main product; hence, the remaining challenge is the reduction of degradation. For the trickle bed reactor, gas−liquid mass phase transfer plays a very pronounced role in its ultimate performance. Higher gas flow rates may be employed in the trickle bed reactor to overcome potential mass-transfer limitations and selectively form the “heterogeneous product”. Lower gas flow rates result in a less effective gas dissolution, and product selectivities change toward the homogeneous product, rendering avoiding degradation difficult.

The use of capillary microreactors for enantioselective liquid-liquid extraction (ELLE) was successfully demonstrated using a model system consisting of a buffered aqueous amino acid derivative (3,5-dinitrobenzoyl-(R,S)-leucine) solution (phosphate buffer, pH 6.58) and a chiral cinchona alkaloid (CA) host in an organic solvent. It was shown that 1-octanol is a suitable replacement for the commonly used chlorinated solvents like 1,2-dichloroethane. Experiments were conducted in a capillary microreactor set-up (0.8 mm internal diameter) operated in the slug flow regime at 294 K (residence times between 12 and 900 s, 1 : 1 flow ratio of the aqueous to organic phases, 1 mM of host and 1 mM of amino acid derivative). The enantiomeric excess (ee) was shown to be a function of the solvent and residence time and varied between 37% and 49% in 1,2-DCE and 28 and 46% in 1-octanol in the organic phase. The ee values in the organic phase at shorter residence times were higher than the independently determined equilibrium ee values (41% in 1,2-DCE and 31% in 1-octanol at a host concentration of 1 mM). This is an unprecedented observation with large implications for ELLE, as it implies that operation in the kinetic regime may lead to improved enantioseparation performance.

Measurements for the density and viscosity of partially carbonated solutions containing water, piperazine (PZ), and a tertiary amine, which was either dimethylaminoethanol (DMAE) or 2-diethylaminoethanol (DEAE), were conducted with total amine mass fractions of 30% and 40% over a temperature range from 298.15 to 353.15 K. Density and viscosity correlations of these mixtures were developed as functions of amine mass fraction, CO2 loading, and temperature. For both systems investigated, the average absolute relative deviations of the experimental data from these correlation are approximately 0.2% for density and 3% for viscosity. The correlations will be useful for thermodynamic analysis and computer simulations of carbon capture processes utilizing these promising blended amine systems.

Heterogeneous catalytic epoxidation of propene to propene oxide with hydrogen peroxide as oxidant was investigated in a confined Taylor flow (CTF) reactor, a continuous monolith reactor, containing a long alumina rod coated with titanium silicalite (TS-1) catalyst in the centre of the reactor column. The effect of gas and liquid superficial velocity on the hydrodynamics of CTF reactor was also investigated under Taylor flow regime at atmospheric pressure. The variation of hydrodynamics had a profound impact on the production of propene oxide. When liquid superficial velocity was constant, the concentration of propene oxide produced decreased with increasing gas superficial velocity as Taylor bubble length and bubble rise velocity increase. However, when gas superficial velocity was constant, the concentration of propene oxide produced had no linear dependency on liquid superficial velocity as Taylor bubble length decreases but bubble rise velocity increases.

Mass-transfer coefficients between an electrolyte solution and the wall of a hydrocyclone were experimentally determined by using the electrochemical technique. The local mass-transfer coefficients were measured as a function of the axial distance from the entrance changing the inlet volumetric flow rate and the underflow stream. An enhancement of mass-transfer was observed in comparison to that predicted for developing axial flow in an annular duct, being the cylindrical part more active than the conical one. The global mass-transfer coefficient in the cylindrical region depends on the Reynolds number raised to an exponent of 0.79, in accordance with the mass-transfer behavior of decaying annular swirl flow. The modified hydrocyclone was also examined for the removal of copper from dilute synthetic solutions. A diminution of copper concentration from 400 ppm to 40 ppm was achieved after 60 minutes of electrolysis in a recirculating system and the contaminant was recovered as a metal powder separated by the hydrocyclone. The space time yield and the specific energy consumption were 12.5 kg m-3 h-1 and 4.9 kWh kg-1, respectively, with a cumulative current efficiency of 54%, showing that the modified hydrocyclone is a suitable reactor for the electrochemical treatment of effluents. Fil: Resio, L. C.. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Gonzalez Perez, Omar. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

A novel device was conceived and built to measure the apparent gaseous permeability of porous media over a large range of permeability values (10−10–10−18 m2) and mean pressures (from 1 bar down to ca. 40 mbar). An extensive series of experimental data are presented and analysed for various porous media: (1) Norway spruce (Picea abies) and European beech (Fagus silvatica) in the three anatomical directions, and, for comparison, (2) three simpler porous media, i.e. an autoclaved aerated concrete (AAC, light concrete) and two wood-based panels. For all porous media, the intrinsic permeability, the gas slippage factor, and the effective pore size were determined from the variations of the apparent permeability as a function of mean pressure. These results are in good agreement with those of previous studies for spruce and bring new insights for beech and wood-based materials, in general. For all products, the effective pore sizes identified with the new instrument are closely linked to the medium morphology. In particular, it was found that in spite of the huge anisotropic ratios between wood’s longitudinal and tangential directions, the identified pore size is similar and corresponds to anatomical features: openings in margo for spruce and scalariform perforation plates for beech. Besides, the pore size identified for beech in the radial direction suggests that radial permeability is most probably controlled by the openings in ray cells (either pits or intercellular voids).

openaire: EC/H2020/788489/EU//BioELCell The prediction of the morphology of wet-spun fibers has so far been only possible by complex and experimentally intensive approaches that include the construction of ternary phase diagrams. Ultimately, however, the available models give approximate information. Here we propose an alternative predictive approach that uses design principles based on the combination of (1) relative energy difference (RED) of Hansen solubility and (2) a kinetic parameter "T" that considers mass transfer effects. Such a model is applied and experimentally validated for a priori determination of the diameter and internal morphology of wet-spun fibers. Remarkably, only three. variables relevant to wet-spinning are needed, namely, the choice of polymer, solvent, and nonsolvent types. A combination of systems is tested, and the morphology of the obtained fibers is determined via electron microscopy. Aspects related to demixing, internal specific surface area (BET), and layer formation on the fibers are described qualitatively. The facile implementation of the design parameters is further confirmed through comparison with data published on the subject. Our proposed model is expected to accelerate future developments in nanomaterials, especially in the context of ongoing efforts related to fiber spinning with biopolymers.

The slag2PCC concept aims at transforming steelmaking slag into precipitated calcium carbonate (PCC) with market value. This paper reports on R&D work on two features that impact the overall performance and costs of slag2PCC as a carbon capture and utilisation (CCU) technology. Operating near ambient conditions, calcium is selectively leached from steelmaking slag using aqueous ammonium salt solvent, followed by carbonation using a CO2-containing stream. Separators for removing spent slag and PCC connect two reactors for extraction and carbonation, respectively, between which the solvent solution is cycling. One requirement is effective conversion of the CO2 fed to the system: while the dissolution of CO2 is the rate-liming step it is essential to minimise release of unreacted CO2. Mixing the solutions enhances mass transfer. High-speed video recordings were made around mixers located at various heights in a bubble column, analysing CO2 bubble swarm dissolution. A second feature studied are losses of ammonia (NH3) from the solution. An outlet for unreacted gas presents a risk of NH3 vapour release, which lowers solution alkalinity while adding costs. Multicomponent mixture mass transfer analysis showed that diffusion of NH3 into CO2 bubbles may be significant at least during initial stages of dissolution. Experimental findings were verified. (C) 2019 Elsevier Ltd. All rights reserved.

International audience; This study focuses on Butyraldehyde (C4H8O) degradation using catalytic ozonation oriented to the optimization of non-thermal plasma/photocatalytic coupled processes. After the first oxidation by non-thermal plasma coupled photocatalytic processes, a second oxidative step leading to the decomposition of the residual Butyraldehyde by Ozone is catalyzed by Mordenite, ZSM-5 and γ-alumina. The Butyraldehyde degradation in the presence of Ozone under operational parameters such as plasma energy, Butyraldehyde inlet concentration, relative humidity and the height of the catalytic bed are reported in detail. The optimum operating conditions found were Qair = 1 m3 h-1, [C4H8O] = 100 mg m-3, SIEplasma = 18 JL-1, for Butyraldehyde degradation mediated by ZSM-5. The formation of intermediate by-products was monitored during the degradation of Butyraldehyde in the presence of Ozone and ZSM-5 catalyst to suggest a degradation pathway. The coupling of catalytic ozonation by non-thermal plasma/photocatalysis lead to the total decomposition of Ozone when catalyzed by ZSM-5and presents a positive effect on the mineralization capacity. The pollutants degradation intermediates were identified by GC-MS and the oxidative states on the catalytic bed were characterized by XPS. © 2018 Elsevier B.V.

This work investigates the effect of current density on the hydrogen gas bubble formation during electrolysis on a platinum electrode. Local detection of bubble evolution was performed electrochemically by using a hydrogen-collecting microelectrode placed in close proximity of a larger hydrogen-generating platinum electrode. The micro-electrode probe locally measured the concentration of dissolved molecular hydrogen produced during electrolysis. In acidic conditions, it was found that at low electrolysis currents the concentration of dissolved hydrogen could temporarily rise up to 50 times the saturation level, while once a large current was reached, the concentration dropped, increasing the concentration of hydrogen inside gas bubbles, and became independent of the current. Through laser reflectance, the onset of bubble formation was found (similar to-0.7 mA/cm(2)), which was lower than the first bubble observable by naked eye or detected by the microelectrode probe.

The conversion rate of the mass transfer controlled oxidation of CO over a Pt/?-alumina catalyst (d = 65 ?m) has been studied in a fluidized bed (internal diameter = 0.05 m) p operated close to and in the turbulent fluid bed regime. The objectives were to investigate the gas-solids contacting efficiency to evaluate the conversion data in terms of overall mass transfer coefficients and define the apparent contact efficiency. At high superficial gas velocities, the concept of formation of particle agglomerates and voids is more realistic than the two-phase model considering discrete bubbles and a dense phase. The two-phase model is not useless but has hardly any relation with the real flow pattern in the turbulent regime.

Results of unique heat transfer measurement in beds of fine, cracking catalyst particles, fluidized by air or helium gas, are compared with predictions from a theoretical model presented in the literature [1], and also with an earlier established empirical correlation [2]. Moreover, the results have been related to dense phase flow conditions around a silver heat transfer probe by a simple turbulence model. A maximum heat transfer coefficient of h = 2300 Wm-2K-1 has been measured in a bed of 14μm (average diameter) particles, fluidized by helium gas. The data collected, and the model developed, can be used for the design of heat transfer tubes in fluidized beds of fine particles as for instance in Fluid Catalytic Cracking of crude oil heavy residues. FCC is one of the most important conversion process in the petroleum refineries.

The oxidation of ferrous ions in acidic sulfate solutions in the presence of cupric ions at elevated air pressures was investigated in a high-intensity gas-liquid contactor. The study was required for the design of the regeneration steps of the novel Vitrisol((R)) desulphurization process. The effects of the Fe2+ concentration, Cu2+ concentration, Fe3+ concentration, initial H2SO4 concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, i.e., T=50 degrees C, 70 degrees C, and 90 degrees C. Most of the experiments were determined to be affected by the mass transfer of oxygen, and therefore true intrinsic kinetics could not be fully determined. An increase in Fe2+ and Cu2+ concentrations, as well as the partial pressure of oxygen and temperature, increased the Fe2+ oxidation rate. H2SO4 did not influence the Fe2+ oxidation rate. An increase in Fe3+ concentration decreased the Fe2+ oxidation rate. Although determined from experiments partially affected by mass transfer, a first order of reaction in Fe2+ was observed, fractional orders in both Cu2+ and O-2 were measured, a zero order in H2SO4 was determined, and a negative, fractional order in Fe3+ was obtained. The activation energy was estimated to be 31.3kJ/mol.

Oral lyophilizates also called orally disintegrating tablets (ODTs) are a patient friendly and convenient dosage form. They are manufactured by dosing a suspension in blister cups and subsequently freeze-drying these blisters to achieve porous tablets that disintegrate quickly (< 10 s) when placed upon the tongue. This paper proposes a mechanistic model of the primary drying phase of these oral lyophilizates processed in cold-form blisters. A heat transfer coefficient (Kv) and dried layer resistance (Rp) are regressed and applied in a dynamic optimization of the primary drying phase. The optimization exercise showed the possibility of ultra-short sublimation times for polyvinyl acetate (PVA) based formulations with a primary drying time of 3.68 h for a 500 mg acetaminophen tablet., Graphical abstract Image 1

Models proposed to describe the liquid side mass transfer coefficient in absorption processes differ widely in such basic questions as on which of the local flow variables they are based. Comparison of different alternatives with experimental data taken from the literature suggests that there are two basic mechanisms, a laminar and a turbulent one, each of which dominates under suitable conditions. A dimensionless number that allows to identify the corresponding regimes is suggested together with a preliminary model encompassing both. New experiments will be needed to come to a final conclusion.

Solvent extraction is a key principle for separations of components often requiring relatively large separation times due to large droplet size distributions. A continuous mesoflow reactor setup was evaluated for solvent extraction and phase separation in terms of efficiency of Co/Ni separation with cyanex 272 as extractant in a kerosene mixture. Several mixer types have been evaluated for the solvent extraction capability combined with a thin film coalescer/separator, expediting separation times, resulting in a settling volume that was only 1-2 times the volume of the mixer effectively reducing total residence time compared to classic mixer-settlers, where the ratio is 4-8 times higher. This was mainly attributed to the droplet homogeneity generated in the mixer, resulting is a short separation time. The thin film coalescer partitions in the settler expedited the phase separation further reducing the required settler volume. This paper shows that continuous mesoflow reactor setups can be utilized for small-scale liquid extractions with narrowly defined droplet sizes, enhancing the phase separation time, making it a viable screening utility. It also shows that the useful volume is much higher than those for conventional mixer-settler with a phase-separation-volume-to-equilibrium-volume ratio of 1-2 compared to 4-8 for the conventional mixer-settler expediting parameter screening. (C) 2016 Elsevier B.V. All rights reserved.

In the present paper, the impact of the acid concentration, Cyanex 272 concentration, and membrane wetting properties on the stripping kinetics of loaded Cyanex 272 with cobalt is studied in a flat membrane microcontactor. To reduce the environmental impact and to be ever economically viable, the extractant needs to be regenerated. From the observed results, a model was derived to describe the stripping kinetics, enabling to maximize throughput. Like for the extraction of cobalt, also for the reversed reaction (stripping of loaded Cyanex 272 with cobalt), pseudo-first order kinetics could be assumed. However, unlike the extraction of cobalt, the reaction kinetics for the stripping of loaded Cyanex 272 had to be taken into account. As a consequence, the concentration of sulphuric acid influences the stripping kinetics and consequently throughput as well. Furthermore, it was also shown that the concentration of Cyanex 272 affected the stripping rate, in contrast to the extraction of cobalt. While for extractiondiffusion in the organic phase can be neglected, this was no longer the case for stripping. When the concentration of Cyanex 272 was increased, the stripping rate decreased severely. To increase throughput, a scale-up strategy was proposed, that could realize without inducing a loss of efficiency. This was demonstrated by increasing throughput by a tenfold. Moreover, also the separation efficiency is studied in a continuous operation set-up over a span of 5 h. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Three commercial spiral-wound membrane modules of different sizes, from 1.8″ × 12″ to 4.0″ × 40″, are used to concentrate a solution of sucrose octaacetate in ethyl acetate under different operating conditions. A mathematical model to describe the batch concentration process is developed, based on a combination of the classical solution diffusion membrane transport model and the film theory, to account for the mass transfer effects. The model was implemented using the “OSN Designer” software tool. The membrane transport model parameters as well as all parameters in the pressure drop and mass transfer correlations for the spiral-wound modules were obtained from regression on a limited number of experimental data at steady state conditions. Excellent agreement was found between the experimental and multi-scale modelling performance data under various operating conditions. The results illustrate that the performance of a large scale batch concentration process with spiral-wound membrane modules can be predicted based on laboratory crossflow flat sheet test data when the fluid dynamics and mass transfer characteristics in the module, and the necessary channel geometry are known. In addition, the effects of concentration polarisation, pressure drop through feed and permeate channels, and thermodynamic non-ideality of the solution at large scale batch concentration are also investigated.

International audience; A simple dynamic absorption procedure to assess the mass-transfer performances of a solvent toward a selected gaseous solute is presented. Absorption was operated semi-continuously at transient state until the equilibrium was reached without solvent recirculation. Four volatile organic compounds (VOC) more or less hydrophobic (toluene, acetone, dichloromethane, isopropanol) were absorbed in water and two heavy organic solvents (Bis(2-ethylhexyl) adipate DEHA and polydimethylsiloxane PDMS). A numerical resolution procedure was developed to simulate the gas-liquid mass-transfer and to deduce the VOC partition coefficients, expressed as the Henry’s law constants, as well as the overall liquid-phase mass-transfer coefficients. The overall liquid-phase mass-transfer coefficients were correlated to the diffusion coefficients using the Higbie penetration theory. The results confirm the high selectivity of water whereas the two organic solvents, especially DEHA, exhibit rather good affinity with all VOC even if the Henry’s law constants of the most soluble and the less soluble compounds for those solvents differ by 1 or 2 orders of magnitude. The liquid-film mass-transfer coefficients in the two organic solvents, even being more viscous, are larger than in water which confirms their good potential for hydrophobic VOC treatment.

Carbonate rocks are commonly utilized in Wet Flue Gas Desulfurization, WFGD, because of their capability to release calcium ions and precipitate as solid gypsum in an acidic environment. Studies on the reactivity of carbonate rocks and dissolution models can be employed for optimizing the WFGD process. The correct evaluation of limestone reactivity is therefore necessary for the design of the WFGD scrubbing process and for plant operation. In this study, after statistical considerations on evaluating the sample size threshold, a mathematical model and a detailed procedure are given for the estimation of the reaction rate constant and mass transfer coefficient. Results are reported from testing limestone and dolomite samples with different formation periods and geological backgrounds. Samples were tested in a Batch Stirred Tank Reactor (BSTR) with a stepwise titration method using hydrochloric acid and non-steady state conditions. In the experiments particles were shown to be completely immersed in a defined viscous sub-layer. A parametric evaluation for the reaction rate was performed at each titration step using an implemented software procedure that handles hundreds of pH values and more than fifty particle size ranges. The experimental data were accurately fitted to the model. The second order model for dolomite and limestone samples accounts for both mass transfer and reaction rate terms, yielding values for the mass transfer coefficients that are congruent with values estimated by fluid-dynamics inspection.

The individual factors that determine the kinetic performance (B- and C-term band broadening and bed permeability K-v) of radially elongated pillar (REP) columns are studied. To this end, columns with REPs having 4 different aspect ratios (AR = 9, 12, 15, 20) were characterized experimentally and by means of numerical simulations. A tortuosity and retention based plate height equation was established, enabling a good global fit for all studied conditions. The B-term plate height contribution appears to decrease with a factor equaling the square of the flow path tortuosity tau. Going from AR= 12 to AR= 20 (tau = 5.7 and tau = 9.0 respectively), this resulted in a shift in plate height expressed in axial coordinates from H-min =0.42 mu m to H-min = 0.25 for non-retained conditions and from H = 0.77 mu m to H = 0.57 mu m for a component with k = 1.0. The obtained parameters were combined to predict optimal time-efficiency combinations for all possible channel lengths. This revealed an efficiency limit of N = 10(7) plates for a non-retained component and N = 7-8 x 10(6) for k=1 for a channel with an AR= 20, corresponding to a channel length of 2.5 m and a void time of 2.4h. (C) 2016 Elsevier B.V. All rights reserved.

ZIF-8 is a flexible zeolitic imidazole-based metal organic framework whose narrow pore apertures swing open by reorientation of imidazolate linkers and expand when probed with guest molecules. This work reports on the crystal size dependency of both structural transitions induced by N-2 and Ar adsorption and dynamic adsorption behavior of n-butanol using well-engineered ZIF-8 crystals with identical surface area and micropore volume. It is found that the crystal downsizing of ZIP-8 regulates the structural flexibility in equilibrium adsorption and desorption of N-2 and Ar. Adsorption kinetics of n-butanol in ZIF-8 are strongly affected by the crystal size, however, not according to a, classical intracrystalline diffusion, mechanism. Our results suggest that Structural transitions and transport properties are dominated by crystal surface effects. Crystal downsizing increases the importance of such surface barriers.

Reactive chromatography is a special topic in chemical reaction engineering, consisting of the combination of chemical reaction and chromatographic separation. The main idea is to avoid a further separation unit, by performing reaction and separation in one unique equipment, allowing process intensification. This technology is usually applied in hydrolysis (or esterification) reactions, that undergoes through the reaching of chemical equilibrium. The chromatographic reactor application would lead to complete conversion, by separating reactants and products as the reaction proceeds. Modelling is certainly a delicate issue for chromatographic reactor to optimize the operation conditions, thus different approaches were published. The aim of the present work is to show a novel chromatographic reactor model, were all the physical and chemical phenomena involved and described by a rigorous approach. The fluid-dynamics was treated by axial dispersion approach, and the Peclet number values were obtained from dedicated experiments. The external fluid-solid mass transfer was calculated from existing correlations, demonstrating to be negligible for the modelled chromatographic reactor. The intraparticle mass diffusion was assumed to be the sum of two parallel contributions, i.e. porous and surface diffusivity. The model was tested on literature data for methyl acetate hydrolysis experiments with satisfactory results, obtaining reliable values of the surface diffusivity. A sensitivity analysis was conducted highlighting that the model can predict complete ester conversion and product separation.

As excessive foam formation is undesirable from an operational perspective in the ammonia stripping process of anaerobic digested slurry, the effect of alkaline agents on foam production was first evaluated by comparing two pH adjusters (NaOH and CaO). Results show that increased pH via CaO addition can significantly aggravate foam production and restrain defoaming ability during the stripping of anaerobic digestion effluent. The addition of 0.75% normal silicone oil (NSO) or 0.01% polyether-modified silicone oil (PMSO) as antifoam reduced foam capacity by 56.2 ± 2.5% and 75.2 ± 2.7%, respectively, but only works in a slurry with pH adjusted by NaOH, not by CaO. Moreover, the addition of these antifoams led to 4.31% (0.75% NSO) and 5.38% (0.01% PMSO) NH4+-N removal efficiency abatement during the stripping process. Finally, a new high-temperature, neutral (without pH adjustment) stripping strategy is proposed in this study, because it can effectively mitigate the formation of foam and maintain equalized ammonia removal. The effluent discharged via this stripping concept can be handled easily and does not cause heavy negative impacts from the residual alkaline content. Furthermore, the ammonia loss in the preparation phase before stripping was only 1/3 that in the traditionally high-pH stripping, indicating the potential of this new mitigation strategy in the frame of an environmentally friendly development.

WOS:000426143100062; International audience; Because of the difficulty in resolving the large variability of N-2 fixation with current methods which rely on discrete sampling, the development of new methods for high resolution measurements is highly desirable. We present a new method for high-frequency measurements of aquatic N-2 fixation by continuous flow-through incubations and spectral monitoring of the acetylene (C2H2, a substrate analog for N-2) reduction to ethylene (C2H4). In this method, named Flow-through Incubation Acetylene Reduction Assays by Cavity Ring-Down Laser Absorption Spectroscopy (FARACAS), dissolved C2H2 is continuously admixed with seawater upstream of a continuous flow stirred-tank reactor (CFSR) in which C2H2 reduction takes place. Downstream of the flow-through incubator, the C2H4 gas is stripped using a bubble column contactor and circulated with a diaphragm pump into a wavelength-scanned cavity ring down laser absorption spectrometer (CRDS). Our method provides high-resolution and precise mapping of aquatic N-2 fixation, its diel cycle, and its response to environmental gradients, and can be adapted to measure other biological processes. The short-duration of the flow-through incubations without preconcentration of cells minimizes potential artifacts such as bottle containment effects while providing near real-time estimates for adaptive sampling. We expect that our new method will improve the characterization of the biogeography and kinetics of aquatic N-2 fixation rates.

In this paper, the liquid emulsion membrane extraction of molybdenum(VI) has been conducted in static mixer. The performance in LEM mode is compared to a conventional solvent extraction mode. The rate of extraction in LEM mode is found to be significantly higher than conventional solvent extraction. Study reveals that the optimum residence time, height of the static mixer and optimum surfactant concentration are the deciding parameters of the performance of static mixer. The effect of various parameters such as superficial velocity of aqueous phase and organic phase, residence time, initial Mo(VI) concentration in feed phase, height of column, and surfactant concentration on rate of extraction has been investigated. A mathematical model is developed to predict volumetric mass transfer coefficient (k(L)a) in a static mixer. The k(L)a value is reduced from 0.045 s(-1) to 0.015 s-1 when height of the mixer was increased from 31 cm to 93 cm respectively under the same hydrodynamic conditions. This anomalous decrease of k(L)a with increase in height is due to acid extraction by TBP which reduces driving force for extraction of Mo(VI). HTU for solvent extraction and LEM extraction are estimated as 0.67 m and 0.15 m respectively which indicates less mass transfer resistance in LEM. (C) 2015 Elsevier B.V. All rights reserved.

Yuanhai Su and Volker HesselMicro Flow Chemistry and Process Technology, Dept. of Chemical Engineering and Chemistry, EindhovenUniversity of Technology, Den Dolech 2, 5600 MB Eindhoven, The NetherlandsTimothy No€elMicro Flow Chemistry and Process Technology, Dept. of Chemical Engineering and Chemistry, EindhovenUniversity of Technology, Den Dolech 2, 5600 MB Eindhoven, The NetherlandsDept. of Organic Chemistry, Ghent University, Krijgslaan 281 (S4), 9000 Gent, BelgiumDOI 10.1002/aic.14813Published online in Wiley Online Library (wileyonlinelibrary.com)A compact photomicroreactor assembly consisting of a capillary microreactor and small-scale light emitting diodes wasdeveloped for the study of reaction kinetics in the gas-liquid photocatalytic oxidation of thiophenol to phenyl disulfidewithin Taylor flow. The importance of photons was convincingly shown by a suction phenomenon due to the fast con-sumption of oxygen. Mass transfer limitations were evaluated and an operational zone without mass transfer effects waschosen to study reaction kinetics. Effects of photocatalyst loading and light sources on the reaction performance wereinvestigated. Reaction kinetic analysis was performed to obtain reaction orders with respect to both thiophenol and oxy-gen based on heterogeneous and homogeneous experimental results, respectively. The Hatta number further indicatedelimination of mass transfer limitations. Reaction rate constants at different photocatalyst loadings and different photonflux were calculated. Furthermore, the advantages of this photomicroreactor assembly for studying gas-liquid photocata-lytic reaction kinetics were demonstrated as compared with batch reactors.

This review presents recent developments for effective heat management systems to be integrated in metal hydride storage tanks, and investigates the performance improvements and limitations of each particular solution. High pressures and high temperatures metal hydrides can lead to different design considerations, which are discussed in the paper. Studies analyzing design procedures based upon different geometrical solutions and/or operation strategies are considered, and their related advantages are explained. Restrictions to the validity of particular results are also evaluated.Major attention is here given to metal hydride storage tanks for light duty vehicles, since this application is the most promising one for such storage materials and has been widely studied in the literature. Enhancing cooling/heating during hydrogen uptake and discharge has found to be essential to improve storage systems capacities and minimize time requirements. Various fueling strategies are widely explained differing by the particular system approach taken into account.At the end, optimization criteria and outcomes for both geometry-oriented and operative strategies-oriented methods are analyzed and presented to the reader as a helpful tool for future design considerations. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

International audience; The purpose of this paper is to study the butyraldehyde (Buty) conversion using dielectric barrier discharge (DBD) in a continuous reactor at pilot scale. One of the focused-on parameters in this study is relative humidity, which effect on (i) butyraldehyde removal (ii) selectivity of CO2 and CO, and (iii) intermediate byproducts and ozone formation was investigated using a DBD reactor with planar configuration. The results showed that at pilot scale, adding a small amount of water vapor in air enhances the processes performance and 10% increase in Buty removal efficiency was observed. A kinetic degradation model was also proposed, which takes into account the relative humidity influence. Active species due to water dissociation are integrated in the model. To represent the chemical degradation pathway, we supposed, in a first step, that an equivalent intermediate compound (EI) is formed directly from Buty. Then, in a second step, this EI is oxidized by active species into CO2 and CO in the discharge zone. This approach that also considers the competition effect between actives species improved the concordance between simulated results and experiments with a satisfactory overall description of the degradation and byproducts formation. (C) 2016 Elsevier B.V. All rights reserved.

International audience; In this study, a continuous process combining plasma and photocatalysis, at pilot scale, has been investigated on pollution treatment. The degradation efficiency and by-products formation has been monitored through the variation of multiple parameters such as inlet concentration, specific energy, and residence time. Results show that process combination leads to an enhancement of pollutant degradation compared to the separate systems even at high flow rate (250 m(3) h(-1)). Synergy factor due to this association ranged from 1.10 to 1.17. Furthermore, CO2 selectivity has significantly improved when comparing the combined system to that with plasma alone. Moreover, we note that adding a photocatalyst in the discharge zone leads to a reduction of ozone and CO formation compared to plasma process alone. Based on this investigation, a methodology of scaling up the combined system was proposed. Indeed, as a practical application, an industrial reactor has been developed and tested for treating a real pollution from animal quartering centers. This investigation indicates that the combined system of photocatalysis with plasma is a promising method for removing air pollutants.

Made available in DSpace on 2018-12-11T17:09:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01 Petrobras Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios – water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion. Laborat�rio de Estudos de Bacias Centro de Estudos Ambientais UNESP – Universidade Estadual Paulista, Av. 24A, 1515 Departamento de Geologia Aplicada Centro de Estudos Ambientais UNESP – Universidade Estadual Paulista, Av. 24A, 1515 Laborat�rio de Estudos de Bacias Centro de Estudos Ambientais UNESP – Universidade Estadual Paulista, Av. 24A, 1515 Departamento de Geologia Aplicada Centro de Estudos Ambientais UNESP – Universidade Estadual Paulista, Av. 24A, 1515 Petrobras: 2052/2012

Ammonia (NH3) emission can cause acidification and eutrophication of the environment, is an indirect source of nitrous oxide, and is a precursor of fine dust. The current mechanistic NH3 emission base model for explaining and predicting NH3 emissions from dairy cow houses with cubicles, a floor and slurry pit is based on measured data from a limited number of studies. It requires input values for numerous variables, but the empirical equations for the model parameters in the literature vary. Furthermore, many of the input variables cannot be assessed accurately, and their actual influence on the prediction is unknown. We aimed to improve NH3 emission modelling, by assessing the contribution to the variation in NH3 emission of each input variable and each model parameter related to a single urine puddle. We did so for 27 candidate models, created by each possible combination of three equations per model parameter: the acid dissociation constant, Henry’s law constant, and the mass transfer coefficient. After analysing each candidate model with a Global Sensitivity Analysis we found that at least 71% of the model variation in NH3 emission for each candidate model was explained by five puddle related input variables: pH, depth, area, initial urea concentration and temperature. NH3 emission was not sensitive to the other four variables: air temperature, air velocity, maximum rate of urea conversion and the MichaeliseMenten constant for urea conversion. Based on these results we recommend simplifying the model structurally and reducing the number of input variables.