Thiago Peixoto de AraujoLuis Fernando CusioliHeloise Beatriz Quesada
12页
查看更多>>摘要：Caffeine in water resources has been reported, indicating the need for alternative treatments. Activated carbons (ACs) are efficient adsorbents; however, they present issues that immobilization in chitosan hydrogel (CH) can overcome. Despite the importance of both aspects, adsorption in continuous systems and different aqueous matrices are understudied. The present study developed and characterized chitosan/AC composites to improve the adsorbent properties and fill the research gap presented. The adsorbent was applied to adsorb caffeine in batch and fixed-bed experiments, using distilled and tap water and synthetic hospital wastewater. Chicha-do-cerrado shells were used to develop two different ACs (KAC and CAC) and composite beads (CH-KAC and CH-CAC). KAC and CH-KAC showed high surface area (1082 and 240 m2 g~(-1)), and FTIR indicated that CH assigned new functional groups to the composites. Batch studies revealed a maximum adsorption capacity of 391.00, 139.61, 121.90, and 39.53 mg g~(-1) for KAC, CAC, CH-KAC, and CH-CAC, respectively. The ions effect in tap water did not occur for the composites due to the bridging phenomenon. In treating the synthetic hospital wastewater, the addition of AC increased the removal efficiency. The fixed-bed maximum adsorption capacity was 83.88 mg g~(-1) for CH-KAC, and the column was reused three times. The importance of both CH and ACs has been successfully proven.
查看更多>>摘要：Here we demonstrate the influence of downstream geometric constraints on droplet breakup and subsequent distribution dynamics in a microdevice containing constricted and parallel microchannels. The microfluidic configuration consists of a sequential connection of T-junction, branching-junction, and two parallel arms with different converging-straight-diverging (CSD) sections at the downstream. Geometric asymmetry was incorporated by only varying the CSD section in terms of converging-diverging angle, throat-width, and throat-length. We observed two distinct breakup regimes, namely obstructed and tunnel for all three microdevices. We found the degree of breakup asymmetry resulting from downstream feedback to increase with increasing continuous phase Reynolds number and dispersed phase capillary number. Our results show that the droplet split asymmetry and the influence of geometric constraints are more discerning for tunnel regime than the obstructed breakup. It highlights the significance of downstream feedback in a constricted and parallel microchannel network.
查看更多>>摘要：Radial heat management is crucial for a safe and stable operation of fixed-bed reactors with small tube-to-particle diameter ratios (N). Under high temperature conditions, thermal radiation can contribute substantially to the overall heat transfer. In the present work, the influence of radiation is studied with particle resolved computational fluid dynamics (PRGFD) in a fixed-bed reactor consisting of 1000 spheres and rings with N = 5.1 over 300 < Re_p< 2000 and for three different temperature levels (300-800 ℃). Two heat transfer parameters, i.e., the wall Nusselt number Nuw and the effective radial thermal conductivity of the bed k_(eff, r), are derived directly from PRGFD. While the radiation effect is minor in k_(eff, r), it is substantial for Nu_w, which is not captured adequately in the current correlations presented in literature. Depending on the temperature level and flow conditions, thermal radiation between the hot wall and the packed bed intensifies the radial heat transfer represented by an increase of up to 170 % in Nuw and 65% in k_(eff, r). A 2D axisymmetric pseudo-homogeneous model including the derived heat transfer parameters can predict the radial temperature profile of the PRCFD with reasonable accuracy also with radiation except for the near-wall region.
Gregor D. WehingerMatteo AmbrosettiRaffaele Cheula
20页
查看更多>>摘要：This work reports the results of a perspective workshop held in summer 2021 discussing the current status and future needs for multiscale modeling in reaction engineering. This research topic is one of the most challenging and likewise most interdisciplinary in the chemical engineering community, today. Although it is progressing fast in terms of methods development, it is only slowly applied by most reaction engineers. Therefore, this perspective is aimed to promote this field and facilitate research and a common understanding. It involves the following areas: (1) reactors and cells with surface changes focusing on Density Functional Theory and Monte-Carlo simulations; (2) hierarchically-based microkmetic analysis of heterogeneous catalytic processes including structure sensitivity, microkmetic mechanism development, and parameter estimation; (3) coupling first-principles kinetic models and CFD simulations of catalytic reactors covering chemistry acceleration strategies and surrogate models; and finally (4) catalyst-reactor-plant systems with details on linking CFD with plant simulations, respectively. It therefore highlights recent achievements, challenges, and future needs for fueling this urgent research topic in reaction engineering.
查看更多>>摘要：To improve used cooking oil (UCO) reclaiming, this work focused on the characterization and optimization of an existing UCO collection chain in Bogota, Colombia. First, based upon historical data from a major collector, production sites were identified, classified, and available volumes were quantified. Also, collection practices, routes, and frequencies were characterized, and inventory of resources consumed during the process were determined. Afterwards, a computational model of the existing collection chain was constructed and implemented in Python~(TM). In this case, a vehicle routing problem approximation was used by mean of weighted Hamiltonian paths. Weights were defined according to economic and environmental indicators calculated as collection costs and equivalent CO2 emissions, respectively. Routes and traveling times were estimated by correlation of geometrical distances between locations and real-time distances from Google Maps~(TM) routes, identifying a dilation factor of 1.33 and an average speed of 9.6 km/h. Finally, an optimization of the collection routes was made using a genetic algorithm inside an integer search. As a result, it was possible to identify the set of routes that minimize costs and CO2 emissions for the collection scheme. Average collection costs of 0.37 USD/kg UCO and average equivalent CO2 emissions of 117.2 g CO2/kg were obtained.
查看更多>>摘要：The electrochemical and physicochemical properties of the anode catalyst used in alcohol fuel cells affect the efficiency of the fuel cell due to both its effect on the cell potential and its direct relationship with the reaction stoichiometry. It is possible to determine these parameters from polarization curves (current vs. cell potential) of the cells. At low potentials, Tafel plots offer kinetic information, whereas currents at high potentials reveal the average number of electrons released per ethanol molecule and their potential dependency. Herein, bearing the chemical engineering research and design aspects, it was aimed to model the kinetics of ethanol electrooxidation reaction catalyzed by PANI-MnFe2O4/Pt/Ru nanocomposite by an artificial neural network (ANN) approach, specifically by Differential Evolution (DE) algorithm for the first time. The different parts of the Tafel plots were condensed into a single and efficient model to illustrate the generalization potential of ANN. The findings demonstrated that the best model with a single hidden layer with 18 neurons offered the highest correlation metrics of 0.997476, and the lowest mean-square-error value of 0.000428 at the testing phase. Furthermore, the average absolute error was calculated, with 0.773% in the training phase and 0.66% in the testing phase. These outstanding results indicated that the best model is capable of accurately capturing the dynamics of all instances analyzed.
Diana Berenice Vega-GuerreroFernando Israel Gomez-CastroAntioco Lopez-Molina
11页
查看更多>>摘要：Biodiesel can be produced by using supercritical alcohols as reactants. Among the main advantages of such approach is that the mass transfer between the alcohol and the oils is considerably enhanced, and the reaction is not affected by the presence of free fatty acids in the raw materials. Nevertheless, the high pressure and temperature under which the reactions occur may cause safety concerns, making difficult the application of such processes on an industrial scale. In this work, the risks of the supercritical processes are assessed using indexes. Moreover, strategies are proposed to minimize the risk in such processes by selecting the optimal layout and the safeguards configuration. The analysis is performed for three production scales to assess its effect on process safety. The results indicate that layout optimization with safety criteria can improve safety in all production scales, reducing the risk of a catastrophic accident without significantly increasing costs. Additionally, it has been observed that increasing the production scale does not imply an important variation of the emissions of carbon dioxide per unit mass of product.
查看更多>>摘要：Hydrogen production is an active area of research with a vast amount of available scientific literature. However, this data is unstructured and scattered, making its utilization difficult from an academic and industrial point of view. This work aims to develop a recommendation system to identify optimal process conditions and catalyst information using Natural Language Processing (NLP) tools. To this end, full-text articles were extracted using the Elsevier API key followed by a custom XML parser. Latent Dirichlet allocation (LDA) was applied on this dataset to form clusters of topics. The experimental section of each article is annotated using state-of-the-art sentiment analysis techniques and divided into four categories based on the presence of catalyst and process information. This dataset is used to develop a dedicated NLP model, 'Ex-SciBERT' by performing transfer learning on the 'Sci-BERT' model. This model performs classification followed by Named Entity Recognition (NER) to extract catalyst and process parameters. Ex-SciBERT model produces an accuracy score of 0.915 (train dataset) and 0.890 (test dataset) for the classification of sentences task and an excellent accuracy score of 0.998 (train dataset) and 0.997 (test dataset) for the NER task. Deployment of this model will automate and accelerate the screening of relevant information from literature by reducing manual efforts.
查看更多>>摘要：This paper concerns the removal of arsenic and hydrated silica (HS) from groundwater (32.45 μg L~(-1) As, 5.70 mg L~(-1) F~-, 155.5 mg L~(-1) HS, 30.0 mg L~(-1) SO_4~(2-), 0.77 mg L~(-1) PO_4~(3-), pH 8.36, and conductivity of 533 μS cm~(-1)) by electrocoagulation (EC) using an up-flow continuous reactor. Iron electrodes were used as sacrificial anodes. The EC efficiency on pollutants removal at current densities from 4 to 8 mA cm~(-2) and mean linear flow velocities ranging from 1.1 to 4.5 cm s~(-1) were analyzed. The best EC trial was obtained at 8 mA cm~(-2) and 1.1 cm s~(-1), where the residual concentrations of As and HS were 1.1 μg L~(-1), and 33 mg L~(-1), respectively, giving values of electrolytic energy consumption (E_(cons)) and overall costs (OC) of 1.96 kWh m~(-3) and 0.28 USD m~(-3). The proposed EC process agrees with the WHO guideline for the concentration of As (< 10 μg L~(-1)). XRF, SEM-EDS, XRD, FTIR, and Raman analyzes indicate that HS reacts with coagulant forming iron silicates. Arsenic was removed by adsorption on iron hydroxides, iron oxyhydroxides, and iron silicates flocs. Sulfate and phosphate are trapped and swept within the sedimentation of the flocs. The removal of fluorides (17%) is attributed to weak adsorption on the iron agglomerates.
查看更多>>摘要：The monodisperse pseudo-boehmite (PB) is an essential raw material for the preparation of the hydrogenation catalyst carrier, γ-Al2O3, which is of great significance for the efficient conversion of heavy crude oil and the development of the residue hydrotreating technology. The introduction of hydrocyclone has been proved to better improve the grade efficiency of PB particles. However, in the actual production process, it is found that the change of slurry viscosity will have a serious impact on particle size control and centrifugal classification of PB particles. Therefore, in this paper, based on the computational fluid dynamics (CFD), the internal flow field characteristics of the hydrocyclone and the effect of continuous phase viscosity on particle classification efficiency were systematically studied. The results demonstrated that hydrocyclone not only participated in particles classification, but also indirectly promoted particle growth. Satisfied classification efficiency was obtained in practical industrial applications by adopting the optimized condition parameter (Na2CO3 concentration of slurry 5 wt%). The average PB particles size increased from 12.9 μm to 40.3 μm, and the corresponding separation efficiency was improved to 74.9%. The obtained results can provide a feasible reference and theoretical basis for optimization of continuous-carbonization preparation process of PB particles.
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