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On the Morphological Characterization Procedures of Multilayer Hydrophobic Ceramic Membranes for Membrane Distillation Operations
Full text linkThe paper introduces some aspects of the characterization of hydrophobized multilayer ceramic membranes intended for use in membrane distillation (MD) operations. Four-layer hydrophobic carbon-based titania membranes, manufactured by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS, Hermsdorf, Germany), were tested according to the gas permeation technique. Gas permeance data were elaborated following the premises of the dusty gas model, to calculate the average pore size and the porosity-tortuosity ratio of each layer. Membrane testing was the opportunity to discuss which characterization method is more appropriate to obtain the membrane parameters necessary for the simulation of membranes in MD processes. In the case of multilayer membranes, the calculation of the morphological parameters should be performed for each layer. The "layer-by-layer gas permeation" method, previously introduced by other authors and completed in this work, is more appropriate for obtaining representative parameters of the membrane. Conversely, the calculation of morphological parameters, averaged over the entire membrane, might lead to heavy underestimations of the total membrane resistance and then to a heavy error on the transmembrane flux simulation
Recovery of VFAs from anaerobic digestion of dephenolized olive mill wastewaters by electrodialysis
Full text linkElectrodialysis (ED) is applied for the first time as a separation-concentration step of the Volatile Fatty Acids (VFAs) enriched effluent resulting from fermentation of olive mill wastewaters. The process would represent a key step of an integrated multi-purpose biorefinery scheme including the biotechnological production of polyhydroxyalkanoates from acidified bioresidues.
A feasibility study is introduced by testing separation efficiency of membranes with synthetic model solutions of different compositions (sodium acetate and NaCl, or acetic-propionic-butyric acids with NaCl) and with actual OMW (a complex mixture of sodium salts of acetic, propionic, isobutyric, butyric, isovaleric, valeric, isocaproic, caproic, eptanoic acids, NaCl and other electrolytes).
Experiments were performed at room temperature in a lab-scale 2-compartments ED stack, containing Neosepta AMX-CMX membranes, at constant current density (31 A/m2). Membrane resistance was tested by performing additional ED experiments according to a proper protocol developed in this work.
Removal of VFAs from actual OMW is feasible; no evidence of remarkable damages nor losses of membrane performance were observed after dedicated trials. Under the operative conditions investigated, VFAs removals ranged from 30 to 35%, resulting in a concentration factor between 1.2 and 1.5 with respect to the initial mother solution.
Chloride removal was remarkably high and it was greatly favoured at the beginning of operation; competition between chloride and acidic anions was remarkable as far as chloride concentration was high, whereas acidic anions transport across the membrane increased after NaCl removal overcame 50%.
Removal and concomitant concentration of VFAs were accomplished by a slight fractionation of acids with respect to the initial solution; the main outcome of which was an enrichment of acetate in the concentrate. Transport of each acidic anion across the membranes was affected by the concomitant role of concentration and diffusivity, which can shift the natural order imposed by the steric hindrance of the species
The Role of the Morphological Characterization of Multilayer Hydrophobized Ceramic Membranes on the Prediction of Sweeping Gas Membrane Distillation Performances
Full text linkThis paper shows which morphological characterization method is most appropriate to simulating membrane performance in sweeping gas membrane distillation in the case of multilayer hydrophobized ceramic membranes. As a case study, capillary four-layer hydrophobic carbon-based titania membranes arranged in bundles in a shell-and-tube configuration were tested with NaCl-water solutions using air as sweeping gas, operating at temperatures from 40 to 110 °C and at pressures up to 5.3 bar. Contrary to what is generally performed for polymeric membranes and also suggested by other authors for ceramic membranes, the mass transfer across the membrane should be simulated using the corresponding values of the mean pore diameter and the porosity-tortuosity ratio of each layer and measured by the layer-by-layer (LBL) method. Comparison of the modeling results with experimental data highlights that the use of parameters averaged over the entire membrane leads to an overestimation by a factor of two to eight of the modeled fluxes, with respect to the experimental values. In contrast, the agreement between the modeled fluxes and the experimental values is very interesting when the LBL parameters are used, with a discrepancy on the order of +/−30%. Finally, the model has been used to investigate the role of operative parameters on process performances. Process efficiency should be the optimal balance between the concomitant effects of temperature and velocity of the liquid phase and pressure and velocity of the gas phase
Membrane Contactors for High Temperature Applications
Full text linkIt is going to be evaluated the availability of the MC process, particularly the Sweeping Gas Membrane Distillation (SGMD), to perform the regeneration of ammonium dihydrogen phosphate (ADP) from diammonium phosphate (DAP) and the study of the main parameters to perform the scale up of the process to an industrial level. Making focus on the selection and characterization of suitable membranes for the process and the design-development of SGMD pilot plant and test for the evaluation of the operative parameters.
The main requirement for the MC technology application is bank on suitable membranes for the process. This must act as a barrier for one of the phases on contact and should enable the mass transport of volatile components. For operative reasons is preferable to hold back the aqueous phase, making the use of hydrophobic membranes imperative.
The hydrophobic membrane character of the membranes is a critical argument for the MC process and is one of the main drawback for the massive application of this technology. Many studies to evaluate the hydrophobic character have been performed and continues to be a trend topic on the MC scenario. However few studies have been done to evaluate the variation of the hydrophobicity with the temperature and none of them to evaluate the effect of temperature above the normal water boiling point
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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