Experimental diffusivities are scarcely available, though their knowledge is essential to model rate-controlled processes. In this work various machine learning models to estimate diffusivities in ...polar and nonpolar solvents (except water and supercritical CO
) were developed. Such models were trained on a database of 90 polar systems (1431 points) and 154 nonpolar systems (1129 points) with data on 20 properties. Five machine learning algorithms were evaluated: multilinear regression,
-nearest neighbors, decision tree, and two ensemble methods (random forest and gradient boosted). For both polar and nonpolar data, the best results were found using the gradient boosted algorithm. The model for polar systems contains 6 variables/parameters (temperature, solvent viscosity, solute molar mass, solute critical pressure, solvent molar mass, and solvent Lennard-Jones energy constant) and showed an average deviation (AARD) of 5.07%. The nonpolar model requires five variables/parameters (the same of polar systems except the Lennard-Jones constant) and presents AARD = 5.86%. These results were compared with four classic models, including the 2-parameter correlation of Magalhães et al. (AARD = 5.19/6.19% for polar/nonpolar) and the predictive Wilke-Chang equation (AARD = 40.92/29.19%). Nonetheless Magalhães et al. requires two parameters per system that must be previously fitted to data. The developed models are coded and provided as command line program.
Biomass residues are a potential renewable source for the sustainable production of chemicals, materials, fuels, and energy embodying the so‐called biorefinery concept. In this context, agro‐forestry ...and agro‐food industry by‐products have attracted considerable interest of researchers in academia and industry as a renewable source of polymeric materials. The research developed to date on the valorization of biomass residues by converting them into polyols through oxypropylation is the subject of this review. These bio‐based polyols exhibit properties similar to their petrochemical counterparts and, as such, can be used with economical advantage in the production of polyurethanes. The operating conditions of the oxypropylation reaction depend on the biomass and on the desired polyol properties. The discussion of their influence and the economic viability of the process are also presented.
Liquefying and foaming biomass waste: The oxypropylation of biomass residues, reviewed in this paper, is connected to sustainability as a biorefinery process for the synthesis of bio‐based polyols, allowing partial substitution of the propylene oxide utilized by the conventional route. Such polyols exhibit similar properties to their petrochemical counterparts, making polyols an economical alternative for the production of, for example, polyurethane foams.
The presence of some anionic species, such as nitrate, nitrite, chloride, sulfide, fluoride, and cyanide, in water supplies may represent a serious environmental problem. In this work, the main ...sources and harmful effects of their bioaccumulation on living organisms are reviewed, as well as the most adopted technologies for their uptake. The major advantages and disadvantages of each methodology are also listed. In general, ion-exchange has been elucidated as the most suitable removal process. In view of that the most promising materials used to remove anionic pollutants from aqueous solutions are highlighted in this review. In particular, the major efforts towards the development of low-cost and easily available effective sorbents for water decontamination are covered. For instance, natural waste solid materials and derivatives have emerged as promising low-cost exchangers for selective anions uptake. Besides, a number of structural modifications including the introduction of more suitable surface functional groups or compensation species into the sorbent matrix have been investigated in order to enhance sorbents selectivity and capacity for anionic pollutants. The influence of speciation and removal conditions is also focused.
Weyl metrics and Wiener-Hopf factorization Aniceto, P.; Câmara, M.C.; Cardoso, G.L. ...
The journal of high energy physics,
05/2020, Letnik:
2020, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A
bstract
We consider the Riemann-Hilbert factorization approach to the construction of Weyl metrics in four space-time dimensions. We present, for the first time, a rigorous proof of the remarkable ...fact that the canonical Wiener-Hopf factorization of a matrix obtained from a general (possibly unbounded) monodromy matrix, with respect to an appropriately chosen contour, yields a solution to the non-linear gravitational field equations. This holds regardless of whether the dimensionally reduced metric in two dimensions has Minkowski or Euclidean signature. We show moreover that, by taking advantage of a certain degree of freedom in the choice of the contour, the same monodromy matrix generally yields various distinct solutions to the field equations. Our proof, which fills various gaps in the existing literature, is based on the solution of a second Riemann-Hilbert problem and highlights the deep role of the spectral curve, the normalization condition in the factorization and the choice of the contour. This approach allows us to construct explicit solutions, including new ones, to the non-linear gravitational field equations, using simple complex analytic results.
Winemaking is one of the main Portuguese industries and has significantly grown in recent years, thus increasing the quantity of obtained residues. These wastes have a complex chemical composition ...and structure, and, for this reason, their treatment and valorisation are simultaneously a challenge and an opportunity. After an overview of the wine industry and its wastes, this article intends to review the different solid winemaking wastes, highlighting their chemical composition and structural characteristics, as well as their main potential applications. These wastes, such as grape stalks, can be directly applied as a source of bioenergy in the form of pellets or subjected to chemical/biological processing, resulting in valuable food additives, materials, or chemicals. Grape seeds provide food grade oil with potential biomedical applications. Grape skins are a promising source of biologically active substances. The sugar fraction of grape pomace can be biologically converted to a wide variety of bioproducts, like bioethanol, biogas, polyhydroxyalkanoates, and bacterial cellulose. The integration of the different processes into a biorefinery is also discussed, considering the characteristics of the Portuguese wine industry and pointing out solutions to valorise their wastes.
Tomato processing leads to the production of considerable amounts of residues, mainly in the form of tomato skins, seeds and vascular tissues, which still contain bioactive molecules of interest for ...food, pharmaceutical and nutraceutical industries. These include carotenoids, such as lycopene and β-carotene, tocopherols and sitosterols, among others. Supercritical fluid extraction is well positioned for the valorization of tomato residues prior to disposal, because it remains an environmentally safe extraction process, especially when using carbon dioxide as the solvent. In this article, we provide an extensive literature overview of the research on the supercritical fluid extraction of tomato residues. We start by identifying the most relevant extractables present in tomatoes (e.g., lycopene) and their main bioactivities. Then, the main aspects affecting the extraction performance are covered, starting with the differences between tomato matrixes (e.g., seeds, skins and pulp) and possible pretreatments to enhance extraction (e.g., milling, drying and enzymatic digestion). Finally, the effects of extraction conditions, such as pressure, temperature, cosolvent, flow rate and time, are discussed.
The simulated moving bed (SMB) technology has evolved significantly since its inception. The appearance of several variants to conventional SMB has led to better performance in productivity and ...product purity, and lower operating costs, thus creating new opportunities for different applications. This trend is clearly visible in the increasing number of papers and patents published in this field in recent years. This review aims to gather and discuss several modifications and operation modes that have been proposed, from the most well-known Varicol and PowerFeed to the latest Intermittent-SMB and variable external stream systems, giving particular emphasis to innovations and applications of each SMB strategy. SMB valve designs are also covered in this article for their importance in the application of the operation modes discussed, which require ever more flexible units capable of variable switch times, column expandability, zone bypasses, and reduced solvent consumption while still avoiding contamination through line sharing.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The modeling of the ion exchange equilibrium requires the knowledge of non-idealities in both liquid and solid phases, the ion association effects that take place in solution, and non-correlated ...equilibrium constants and activity coefficients parameters for the exchanger. The resulting model is invariably complex and induces researchers to select empirical expressions that generally possess no predictive ability. In such cases, other approaches like the artificial neural networks (ANNs) studied in this work are highly advantageous. In order to investigate their application, 15 binary systems and 7 ternary systems were collected. The global and the maximum deviations found (when only experimental data were used) were 2.09% and 6.38% for binary systems, and 4.32% and 7.28% for ternary systems, respectively. In comparison to the analytical results obtained with mass action law, (4.27% and 40.46% for binaries, and 16.50% and 56.47% for ternaries, respectively), the ANNs approach proved to be very reliable and accurate for the ion exchange equilibrium representation.
► Ternary ion exchange isotherms are modeled with artificial neural networks (ANN). ► Very good ANN representations are achieved using only binary and ternary data. ► Accurate ANN results are obtained in comparison with mass action law approach. ► ANN can be a reliable modeling method when only experimental data is available.
In this Article the ion exchange equilibrium of binary and multicomponent systems was modeled with homogeneous mass action law using activities and taking account of the partial dissociation of salts ...according to Kester and Pytkowicz's approach. The activity coefficients in the solution were estimated by the Pitzer model and in the sorbent by Wilson, nonrandom two-liquid (NRTL), and universal quasichemical (UNIQUAC) models. Wilson has already been adopted in the literature, while NRTL and UNIQUAC were investigated here for the first time. The modeling procedure relied on the analysis of experimental data for the constitutive binary systems to fit the equilibrium constants and the binary parameters of the activity coefficients for the sorbent, which were then applied to predict the multicomponent isotherms. The models were tested with 22 binary, 14 ternary, 5 quaternary, and 1 quinary systems, totalizing 1494 points. The results showed that NRTL and Wilson provide reliable and very similar predictions (average deviations equal to 11.35 % and 11.53 %, respectively) while UNIQUAC performs poorly (16.02 %). The ideal model, which assumes unitary activity coefficients, achieved the largest error (34.20 %), thus emphasizing the chief importance of nonidealities. The extension of ion association also proved to be very important, attaining values near 60 %.
•A simple simulated moving bed optimization strategy based on DoE and RSM is proposed.•This approach is compared with Triangle Theory and the concept of separation volume.•The new DoE-RSM strategy ...provides accurate results with small number of simulations.•SMB separation of trans-stilbene oxide enantiomers is used as a case study.•The proposed optimization strategy allowed purities above 99.6% for both enantiomers.
The optimization of simulated moving bed (SMB) units is often performed through detailed phenomenological models and require extensive computation time. Hence several optimization methods like the Triangle Theory, and the concept of separation volume have been proposed. However, they do not provide accurate results, when mass transfer limitations are significant, or require a large number of simulations.
In this work, a combined Design of Experiments and Response Surface Methodology (DoE-RSM) approach is proposed for SMB optimization, aimed at providing good results with simplicity and reduced number of simulations. The separation of trans-stilbene oxide enantiomers is selected as case study in order to compare DoE-RSM with previous approaches. In the whole, accurate results are obtained with a few number of simulations, allowing for purities above 99.60% for both enantiomers, and productivity of 65.41kg/(m3adsorbentday). The versatility of DoE-RSM tool is also discussed, emphasising their advantages and general applicability.
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