Artículos de publicaciones periódicas

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Optimal control of a batch bioreactor: a study on the use of an imperfect model
(2001-12) Dondo, Rodolfo G.; Marqués, Dardo
"This paper presents a numerical study on the performance degradation of a batch bioreactor optimal control strategy when the model used to compute such strategy shows wide variations from the real process. The optimal control was computed using a model that, when exposed to large variations of the control inputs, presents large departures from real process behavior. An improved model based on published experiments was proposed. A new optimal policy was calculated and the behavior of this model when controlled with the earlier policy was studied. Although the earlier control showed a performance degradation with respect to the real optimal control, degradation was modest, and the results are superior to these obtained with other control strategies."
Polymeric Membranes from Colloidal Templates with Tunable Morphology
(2010-07) Casis, Natalia; Ravaine, Serge; Reculusa, Stéphane; Colvin, Vicki L.; Wiesner, Mark R.; Estenoz, Diana; Fidalgo de Cortalezzi, María Marta
"Polymeric porous membranes were fabricated from templates made from silica particles. The templates were obtained by self-assembly and by the Langmuir-Blodgett (L-B) technique. For the self-assembly technique, suspensions of silica particles in ethanol were used to create the deposits. L-B deposition was employed to produce templates of different particle sizes for the fabrication of asymmetric membranes. Two different polymers were tested to fabricate membranes: polystyrene (PS) and the diethyleneglycol dimethacrylate (DEGDMA)/urethane dimethacrylate (UDMA) copolymer. Templates and porous films were observed by SEM in order to analyze the pore morphology. Permeability of the poly(DEGDMA/UDMA) films was comparable to commercially available membranes. Proposed applications for these ordered porous structures include, sensors, filters, and catalytic materials."
Fabrication and characterization of iron oxide ceramic membranes for arsenic removal
(2010-11) Sabbatini, Paola; Yrazu, Fernando M.; Rossi, F.; Thern, G; Marajofsky, A.; Fidalgo de Cortalezzi, María Marta
"Nanoscale iron oxide particles were synthesized and deposited on porous alumina tubes to develop tubular ceramic adsorbers for the removal of arsenic, which is an extremely toxic contaminant even in very low concentrations. Its natural presence affects rural and low-income populations in developing countries in Latin America and around the world, which makes it essential to develop a user-friendly, low energy demanding and low cost treatment technology. The fabricated ceramic membranes can be operated with minimal trans-membrane pressure difference and do not require pumping. The support tubes and final membrane have been characterized by surface area and porosity measurements, permeability tests and scanning electron microscopy (SEM) imaging. Arsenic concentrations were determined by inductively coupled plasmaeoptical emission spectroscopy (ICP-OES). Due to its low cost and simple operation, the system can be applied as a point of use device for the treatment of arsenic contaminated groundwaters in developing countries."
Imidazo[2,1-b]thiazole carbohydrate derivatives: synthesis and antiviral activity against Junin virus, agent of Argentine hemorrhagic fever
(2011-01) Barradas, José Sebastián; Errea, María Inés; D´Accorso, Norma B.; Sepúlveda, Claudia Soledad; Damonte, Elsa Beatriz
"Herein, we describe the syntheses of 3,5-disubstituted imidazo[2,1-b]thiazole. The cyclization step was performed in two different conditions by using either thermal or microwave heating. Comparing the results of both methodologies, we found that the microwave assistance is an improved alternative to obtain this family of heterocyclic compound. Compounds were first evaluated for cytotoxicity in Vero cells by MTT method and then, the antiviral activity was assayed by a virus yield inhibition assay in the range of concentrations lower than the corresponding CC50, using JUNV strain IV4454 as the model system. The most active compounds (3 and 4), showed a level of antiviral activity against JUNV in monkey Vero cells better than the reference substance ribavirin. Then, they are promising lead compound for further analysis and characterization to establish their therapeutic potential against hemorrhagic fever viruses."
Barrier properties and structural study of nanocomposite of HDPE/Montmorillonite modified with polyvinylalcohol
(2013-02) Carrera, María C.; Erdmann, Eleonora; Destéfanis, Hugo A.
"In this work was studied the permeation of CO2 in films of high-density polyethylene (HDPE) and organoclay modified with polyvinylalcohol () obtained from melt blending. Permeation study showed that the incorporation of the modified organoclay generates a significant effect on the barrier properties of HDPE. When a load of 2 wt% of was incorporated in the polymer matrix, the flow of CO2 decreased 43.7% compared to pure polyethylene. The results of TEM showed that clay layers were dispersed in the polymeric matrix, obtaining an exfoliated-structure nanocomposite. The thermal stability of nanocomposite was significantly enhanced with respect to the pristine HDPE. DSC results showed that the crystallinity was maintained as the pure polymeric matrix. Consequently, the decrease of permeability was attributable only to the effect of tortuosity generated by the dispersion of . Notably the mechanical properties remain equal to those of pure polyethylene, but with an increase in barrier properties to CO2. This procedure allows obtaining nanocomposites of HDPE with a good barrier property to CO2 which would make it competitive in the use of packaging."
Virus removal by iron oxide ceramic membranes
(2014) Fidalgo de Cortalezzi, María M.; Gallardo, María V.; Yrazu, Fernando; Gentile, Guillermina J.; Opezzo, Oscar; Pizarro, Ramon; Poma, Hugo R.; Rajal, Verónica B.
Nanoporous iron oxide ceramics were studied for the removal of virus contamination from water. Supported and unsupported iron oxide nanostructured hematite was fabricated by a green chemistry route from ferroxane nanoparticles. The material had a surface area of approximately 30 m2 /g and a mean pore size of 65 nm. Bacteriophage P22 was chosen as a model for human virus. The kinetics and equilibrium of the attachment process was investigated. P22 adsorption isotherms on iron oxide were described by the Freundlich equation. Batch experiments resulted in 1.5 LRVs. Removal proceeded rapidly for the first 7 h; next, a diffusion-limited stage occurred. Dynamic attachment experiments demanded extensive recirculation to achieve significant reduction levels. Up to 3 LRV were observed. The enhanced performance can be explained by the higher iron oxide area available and the facilitated access to inner porosity sites that were previously unavailable due to slow diffusion. The role of electrostatic interactions in the attachment mechanisms was confirmed by the dependence of the isotherm on the ionic strength of the suspension medium. P22 bacteriophage is expected to attach to the iron oxide by electrostatic forces up to a pH of 6.5. DLVO theory predicts moderately well the interaction energies between P22 particles themselves and between the phage and the ceramic. However, a slight underestimation of the P22–P22 repulsive forces was evident by comparison to the experimental data.
Virus removal by iron oxide ceramic membranes
(2014-09) Fidalgo de Cortalezzi, María Marta; Gallardo, María V.; Yrazu, Fernando M.; Gentile, Guillermina José; Opezzo, Oscar; Pizarro, Ramón A.; Poma, Hugo R.; Rajal, Verónica Beatriz
"Nanoporous iron oxide ceramics were studied for the removal of virus contamination from water. Supported and unsupported iron oxide nanostructured hematite was fabricated by a green chemistry route from ferroxane nanoparticles. The material had a surface area of approximately 30 m2/g and a mean pore size of 65 nm. Bacteriophage P22 was chosen as a model for human virus. The kinetics and equilibrium of the attachment process was investigated. P22 adsorption isotherms on iron oxide were described by the Freundlich equation. Batch experiments resulted in 1.5 LRVs. Removal proceeded rapidly for the first 7 h; next, a diffusion-limited stage occurred. Dynamic attachment experiments demanded extensive recirculation to achieve significant reduction levels. Up to 3 LRV were observed. The enhanced performance can be explained by the higher iron oxide area available and the facilitated access to inner porosity sites that were previously unavailable due to slow diffusion. The role of electrostatic interactions in the attachment mechanisms was confirmed by the dependence of the isotherm on the ionic strength of the suspension medium. P22 bacteriophage is expected to attach to the iron oxide by electrostatic forces up to a pH of 6.5. DLVO theory predicts moderately well the interaction energies between P22 particles themselves and between the phage and the ceramic. However, a slight underestimation of the P22–P22 repulsive forces was evident by comparison to the experimental data."
Homogeneous hydrolytic degradation of poly(lactic-co-glycolic acid) microspheres: Mathematical modeling
(2015-12) Busatto, Carlos; Berkenwald, Emilio; Nicolás, Mariano; Casis, Natalia; Luna, Julio; Estenoz, Diana
"The homogeneous hydrolytic degradation of poly(lactic-co-glycolic acid) (PLGA) microspheres was investigated. A mathematical model was developed that estimates the evolutions of ester bonds concentrations and average molecular weights along the degradation process. The model is based on a detailed kinetic mechanism that includes the hydrolysis of the different types of ester bonds by random chain scission and considers the effect of polymer chemical composition and molecular structure. Novel and published experimental data were used to adjust and validate the model. The experimental work consisted of homogeneous hydrolytic degradation of PLGA microspheres. The predictions are in very good agreement with the experimental results."
Bulk polymerization of styrene using multifunctional initiators in a batch reactor: A comprehensive mathematical model
(2016-02) Berkenwald, Emilio; Laganá, María Laura; Acuña, Pablo; Morales Balado, Graciela Elizabeth; Estenoz, Diana
"A detailed, comprehensive mathematical model for bulk polymerization of styrene using multifunctional initiators - both linear and cyclic - in a batch reactor was developed. The model is based on a kinetic mechanism that considers thermal initiation and chemical initiation by sequential decomposition of labile groups, propagation, transfer to monomer, termination by combination and re-initiation reactions due to undecomposed labile groups. The model predicts the evolution of global reaction variables (e.g, concentration of reagents, products, radical species and labile groups) as well as the evolution of the detailed complete polymer molecular weight distributions, with polymer species characterized by chain length and number of undecomposed labile groups. The mathematical model was adjusted and validated using experimental data for various peroxide-type multifunctional initiators: diethyl ketone triperoxide (DEKTP, cyclic trifunctional), pinacolone diperoxide (PDP, cyclic bifunctional) and 1,1-bis(tert-butylperoxy)cyclohexane (L331, linear bifunctional). The model very adequately predicts polymerization rates and complete molecular weight distributions. The model is used to theoretically evaluate the influence of initiator structure and functionality as well as reaction conditions."
A novel combination of experimental design and artificial neural networks as an analytical tool for improving performance in thermospray flame furnace atomic absorption spectrometry
(2016-02) Morzan, Ezequiel; Stripeikis, Jorge; Goicoechea, Héctor; Tudino, Mabel Beatriz
"In this work, we present the combined effect of artificial neural networks (ANN) and experimental design as a suitable analytical tool for improving the performance of thermospray flame furnace atomic absorption spectrometry (TS-FFAAS) using Mg as leading case. To this end, mixtures of different amounts of methanol, ethanol, and i-propanol in water were assayed as carriers at different flow rates and different flame stoichiometries (air/acetylene ratios). Different levels of these variables determined the experimental domain, consisting in a cube which was divided into eight identical cubical regions that allowed increase in the number of available experimental points. A Box–Behnken design (BBD) was employed in each one of the regions. The name Multiple Box–Behnken design (MBBD) was given to this new approach. Then, the features of ANN were exploited to find the optimum conditions for conducting Mg determination by TS-FFAAS. The prediction capability of ANN was examined and compared to the least-squares (LS) fitting when applied to the response surface method (RSM). The suitability of the new approach and the implications on TS-FFAAS analytical performance are discussed."
A sensitivity analysis and a comparison of two simulators performance for the process of natural gas sweetening
(2016-04) Gutiérrez, Juan Pablo; Benítez, Leonel A.; Ale Ruiz, Elisa Liliana; Erdmann, Eleonora
"Chemical processes simulation is an important instrument for the design, optimization and control of industrial plants. Simulation cases can be accomplished with relatively low costs and the absence of risks for the operators. However, the precision of the results depends on the similarity between the simulation performed and the process considered. In this article, two simulators, Aspen Hysys V8.6 and Aspen Plus V8.6, are employed to simulate the process of natural gas sweetening using diethanolamine (DEA). Additionally, a parametric sensitivity analysis is performed to define the optimal operative range for the process. The required data and the conditions of the operating units are taken from a gas conditioning plant in northern Argentina. Finally, a comparison between the block of obtained results from both simulations is also detailed."
Enhanced retention of bacteria by TiO2 nanoparticles in saturated porous media
(2016-08) Gentile, Guillermina José; Fidalgo de Cortalezzi, María Marta
"The simultaneous transport of TiO2 nanoparticles and bacteria Pseudomonas aeruginosa in saturated porous media was investigated. Nanoparticle and bacterium size and surface charge were measured as a function of electrolyte concentration. Sand column breakthrough curves were obtained for single and combined suspensions, at four different ionic strengths. DLVO and classical filtration theories were employed to model the interactions between particles and between particles and sand grains. Attachment of TiO2 to the sand was explained by electrostatic forces and these nanoparticles acted as bonds between the bacteria and the sand, leading to retention. Presence of TiO2 significantly increased the retention of bacteria in the sand bed, but microorganisms were released when nanomaterial influx ceased. The inclusion of nanomaterials in saturated porous media may have implications for the design and operation of sand filters in water treatment."
Electrostatic interactions in virus removal by ultrafiltration membranes
(2017) Gentile, Guillermina José; Cruz, Mercedes Cecilia; Rajal, Verónica Beatriz; Fidalgo de Cortalezzi, María Marta
Ultrafiltration membranes are increasingly used in potabilization to remove viral particles. This removal is controlled by electrostatic repulsion, attatchment and size exclusion. The effect of electrostatic interaction in virus filtration was investigated. Our work included characterization of bacteriophage PP7 and polyethersulfone membrane with respect to size and surface charge; the removal of this bacteriophage at laboratory scale by ultrafiltration membrane process and the mechanism and limitations were analyzed and discussed under DLVO and XDLVO theories. A partial removal of the bacteriophage was achieved; however, enhanced separation may be achieved considering that the process is affected by the aqueous matrix. The presence of divalent cations diminished the effectiveness of the procedure as opposed to monovalent cations and species with amphoteric behavior such as bicarbonate. DLVO and XDLVO predicted the interactions studied between bacteriophae PP7 and polyethersulfone membrane.
Selective determination of Cr (VI) by on-line solid phase extraction FI-SPE-FAAS using an ion exchanger resin as sorbent: an improvement treatment of the analytical signal
(2017-01) Rossi, Ezequiel; Errea, María Inés; Fidalgo de Cortalezzi, María Marta; Stripeikis, Jorge
"A flow injection (FI) technique based on an on-line solid phase extraction (SPE) coupled with flame atomic absorption spectroscopy (FAAS) to selectively quantify chromium (VI) in the presence of chromium (III) was developed. An anion exchanger was used as solid sorbent and the detection limit found was two order of magnitude lower than that expected quantifying by FAAS. Until now, quantitative determinations in FAAS were carried out by measuring the height of the peaks rather than their area. In our hands, the software was reconfigured and the area under the peaks could be measured. Considering area instead of height, the enhancement factor increases from 6.7 to 360 (approx. 54 times) giving a detection limit of 0.034 μg·L − 1 , lower than that obtained using much more expensive instruments such as electrothermal atomic absorption spectrometry (ETAAS) or inductively coupled plasma-atomic emission spectrometry (IPC-AES), greatly enhancing the potential of this methodology for future use in speciation studies. The operation conditions were: pH 3, sample loading 50 mL·min − 1 , elution flow rate 7.5 mL·min − 1 . The anion exchanger lifetime was over 100 adsorption/desorption cycles. Anions commonly present in natural aqueous systems did not interfere in the chromium retention. The accuracy was validated using a certified reference material (Fluka Analytical, QC3453)."
Energy requirements, GHG emissions and investment costs in natural gas sweetening processes
(2017-01) Gutiérrez, Juan Pablo; Ale Ruiz, Elisa Liliana; Erdmann, Eleonora
"Currently, different technologies are being employed to remove CO2 and H2S from the natural gas. Based on chemical phenomenon, the absorption using alkanolamines is probably the most extended process for the acid gas removal. However, membrane technologies are considered as an alternative in specific cases for their better performances, cleanness, energy requirements, operative costs and location flexibility. The aim of this article is to estimate, compare and analyze the energy requirements, greenhouse gases (GHG) emissions and investment costs of three Natural Gas Sweetening processes. For the study, a regular process using methyldiethanolamine (MDEA), the absorption process using recompressed vapor and a membrane system were simulated using Aspen Hysys v8.8. For the first case, real data from the gas plant Aguaragüe (Argentina) was used to validate the model. To establish a proper comparison, a natural gas with 4 mol.% of CO2 is considered as the inlet stream of each configuration. Specifically, compression and pump power, specific total heat, removed CO2, CH4 wastes and capital costs were estimated and compared for each case. Additionally, a discussion including different aspects in regard to the energy efficiency of the processes was conducted. Although the proposed membrane system demonstrated to reduce the energy requirements (77% and 72%) and emissions (80% and 76%) in respect to both absorption processes, the CH4 losses were higher by more than 6 factor. Moreover, the investment cost of the technology is 12% higher than the required capital of a conventional amine process."
Sulfated polysaccharides in the freshwater green macroalga cladophora surera not linked to salinity adaptation
(2017-11) Arata, Paula X.; Alberghina, Josefina; Confalonieri, Viviana; Errea, María Inés; Estévez, José M.; Ciancia, Marina
"The presence of sulfated polysaccharides in cell walls of seaweeds is considered to be a consequence of the physiological adaptation to the high salinity of the marine environment. Recently, it was found that sulfated polysaccharides were present in certain freshwater Cladophora species and some vascular plants. Cladophora (Ulvophyceae, Chlorophyta) is one of the largest genera of green algae that are able to grow in both, seas and freshwater courses. Previous studies carried out on the water-soluble polysaccharides of the marine species C. falklandica established the presence of sulfated xylogalactoarabinans constituted by a backbone of 4-linked b-L-arabinopyranose units partially sulfated mainly on C3 and also on C2 with partial glycosylation, mostly on C2, with terminal b-D-xylopyranose or b-D-galactofuranose units. Besides, minor amounts of 3-, 6- and/or 3,6-linked b-D-galactan structures, with galactose in the pyranosic form were detected. In this work, the main water soluble cell wall polysaccharides from the freshwater alga Cladophora surera were characterized. It was found that this green alga biosynthesizes sulfated polysaccharides, with a structure similar to those found in marine species of this genus. Calibration of molecular clock with fossil data suggests that colonization of freshwater environments occurred during the Miocene by its ancestor. Therefore, the presence of sulfated polysaccharides in the freshwater green macroalga C. surera could be, in this case, an adaptation to transient desiccation and changes in ionic strength. Retention of sulfated polysaccharides at the cell walls may represent a snapshot of an evolutionary event, and, thus constitutes an excellent model for further studies on the mechanisms of sulfation on cell wall polysaccharides and environmental stress co-evolution."
Experimental and theoretical study of the use of multifunctional initiators in the high impact polystyrene bulk process
(2018-02) Berkenwald, Emilio; Laganá, María Laura; Maffi, Juan M.; Acuña, Pablo; Morales Balado, Graciela Elizabeth; Estenoz, Diana
"The performance of three multifunctional peroxide initiators in a bulk high impact polystyrene (HIPS) process was experimentally and theoretically investigated. For the experimental work, a series of batch reactions was carried out, comprising the main stages of an industrial HIPS bulk process using multifunctional initiators with varying functionality and structure: DEKTP (cyclic trifunctional), PDP (cyclic bifunctional) and L331 (linear bifunctional). The theoretical work consisted of the development of a comprehensive, generic yet detailed mathematical model for bulk HIPS polymerization using multifunctional initiators. The model predicts the evolution of the main polymerization variables (including conversion, molecular weights, grafting efficiency) as well as the detailed molecular structure of the polymeric species (free polystyrene, residual polybutadiene and graft copolymer), and the melt flow index of the obtained HIPS. The model was adjusted and validated using experimental results, obtaining a good agreement between measured and predicted values. The model was used to theoretically evaluate the effect of the operating conditions on the molecular and physical characteristics of the obtained polymer. It was found that the use of multifunctional initiators leads to high polymerization rates and high molecular weights simultaneously, while promoting the grafting of styrene onto butadiene, generating a microstructure with salami-type morphologies."
Electrostatic interactions in virus removal by ultrafiltration membranes
(2018-02) Gentile, Guillermina José; Cruz, Mercedes Cecilia; Rajal, Verónica Beatriz; Fidalgo de Cortalezzi, María Marta
"Ultrafiltration membranes are increasingly used in potabilization to remove viral particles. This removal is controlled by electrostatic repulsion, attachment and size exclusion. The effect of electrostatic interaction in virus filtration was investigated. Our work included characterization of bacteriophage PP7 and polyethersulfone membrane with respect to size and surface charge; the removal of this bacteriophage at laboratory scale by ultrafiltration membrane process and the mechanism and limitations were analyzed and discussed under DLVO and XDLVO theories. A partial removal of the bacteriophage was achieved; however, enhanced separation may be achieved considering that the process is affected by the aqueous matrix. The presence of divalent cations diminished the effectiveness of the procedure as opposed to monovalent cations and species with amphoteric behavior such as bicarbonate. DLVO and XDLVO predicted the interactions studied between bacteriophage PP7 and polyethersulfone membrane."
Absorption of siderite within a chemically modified poly(lactic acid) based composite material for agricultural applications
(2018-05) García, Nancy L.; Fascio, Mirta; Errea, María Inés; Dufresne, Alain; Goyanes, Silvia Nair; D'Accorso, Norma Beatriz
"Iron is an essential micronutrient for higher plants. Although abundant in most soils, Fe3+ is not available for plant uptake, because of its poor solubility. Ferrous sulfate is a fertilizer used for crops but, Fe2+ is readily oxidized to the plant-unavailable ferric form. It is therefore important to provide Fe2+ to plants, minimizing the loss of this nutrient by oxidation in Fe3+. This paper reports the development of a composite material consisting of a matrix (PLARAM), obtained by the chemical modification of poly(lactic acid), capable of retaining ferrous carbonate (siderite) within PLARAM (PLARAMFe). From the matrix, Fe2+ is released into the soil, enhancing its bioavailability. PLARAM and PLARAMFe films were obtained and their water wettability was studied. One side of the films was more hydrophilic than the other, turning this material attractive as a protective film when it is necessary to avoid loss of humidity."
Adsorption with catalytic oxidation in a recirculating bed reactor for contaminated groundwater
(2018-06) Russo, Analia; De Angelis, Laura; Jacobo, Silvia E.
"A novel nanoremediation concept, which is based on in situ trapping of organic contaminants by adsorption and catalytic oxidation in combination with oxidants such as hydrogen peroxide is presented. In earlier works we explored the porous structure of a modified natural clinoptilolite loaded with iron as a supported catalyst (NZ -AFe). The supported catalyst prevents iron release during all the process. This paper presents novel results for BTX (Benzene, Toluene and Xylene) removal from aqueous solution considering that adsorption and oxidation processes are taking place simultaneously. The experiment was achieved by fluxing an aqueous solution of BTX 3.3 mM and hydrogen peroxide, at neutral pH, using the same reservoir. After 870 min, C/C0 reaches near 10% for each pollutant. The system removed 65 mg BTX in the present conditions (13 mg/g NZ-A-Fe). The results indicate that the recirculation bed reactor is an excellent system to remove by adsorption and oxidation processes BTX from water due to high mass transfer coefficients and other advantages when compare to batch reactor experiments."

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