Scielo RSS <![CDATA[Latin American applied research]]> vol. 33 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Cultivation of insect cells in airlift reactors: influence of reactor configuration and superficial gas velocity]]> Large-scale cultivation is an essential step towards the feasible production of baculovirus in insect cell cultures. Airlift reactors appear to offer considerable advantages over other insect cell culture systems. In order to evaluate the impact of reactor design on the behavior of insect cell cultures, the IPLB-Sf-21 cell line was cultivated in three different concentric tube airlift reactors that differ in their geometrical parameters. The ratio of downcomer to riser cross sectional areas, the shape of the bottom and the ratio of height to diameter of the reactor proved to be important since them produce significant differences on cell growth behavior. Modifying the reactor design the cellular growth rate could be improved from 0.016/h to 0.031/h, while the maximum viable cell density could be elevated from 9x10(5) to 2.4x10(6) cells/ml. Once selected a reactor configuration, the influence of gas flow rate was determined, finding an optimal value of superficial gas velocity that renders sufficient oxygenation without any significant effect on the cellular viability. In addition, the influence of the reactor design on fluid circulation in the reactor was tested. <![CDATA[Regional risk associated with the transport of hazardous materials]]> An increasing concern over the level of risk associated with hazardous materials transportation has led international efforts to focus on risk assessment at regional level. Following this trend, the aim of this work is to review the latest procedures for analysing the regional risks resulting from hazardous materials transportation by means of road and rail. In particular, two methodologies are reviewed and discussed, a method recently developed at Swiss Federal Institute of Technology [1] and the strategy outlined by CCPS [2]. The extent of these methodologies has been explored in order to find their advantages and disadvantages. As a case study this paper considers the transport of methanol from its production site to the port where it is going to be stored, obtaining risk results using at least one of the above mentioned methodologies. <![CDATA[Effect of ozonation on the activated carbon surface chemical properties and on 2-mercaptobenzothiazole adsorption]]> Benzothiazoles are organic compounds that may produce negative environmental impact when released into watercourses. In particular, 2-mercaptobenzothiazole (MBT) are known to be toxic and hard to biodegrade. Activated carbon adsorption and ozonation have been identified as suitable treatment for those contaminants. However, there is some controversy about the effect of carbon surface chemical composition on the MBT adsorption. This paper focuses on this issue and presents experimental adsorption isotherms for MBT on Filtrasorb-400 activated carbon treated with different ozone doses. The activated carbon surface chemical properties were assessed by acid/basic neutralization, temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and the point of zero charge (pH PZC). Results show that ozone treatment modified the oxygenated groups on the activated carbon surface, increasing the concentration of acid groups, and reducing the pH PZC. Finally, ozone treatment led to a significant reduction of the carbon's MBT adsorption capacity, due to the increase in polar hydrophilic groups. <![CDATA[Effect of amino acids and peptides on growth of pediococcus pentosaceus from wine]]> Lactic acid bacteria are characterized by numerous nutritional requirements. The influence of amino acids and peptides on the growth of Pediococcus pentosaceus c1 isolated from argentinean wines was determined. Cells were growth in synthetic media and in the same media added with the following dipeptides: leucine-leucine; leucine-proline; methionine-proline and glycine-glycine. In the complete medium, P. pentosaceus c1 reached a final biomass of 1x10(8) cfu ml-1 with a growth rate of 0.17 h-1. When leucine, methionine and glycine were independently removed from complete medium, cell biomass was lower than 90% indicating that these amino acids are essentials to bacterial growth. In absence of proline the parameters of growth were similar to those obtained on control medium, indicating that proline was not essential for bacterial growth. The growth was partially restored in the medium without methionine (80 %), after addition of the dipeptide methionine-proline, and a growth of 90 % was reached by the addition of leucine-proline to the medium without leucine. When leucine-leucine was added to the medium without leucine, 100 % of cell growth was observed and when glycine-glycine was incorporated to the medium without glycine, growth parameters were increased. Dipeptides could supply the essential amino acid requirements of P. pentosaceus c1. The lower specific growth rate (20 %) and cell biomass (70 %) obtained when the four dipeptides were added to the medium without leucine, methionine, glycine and proline, suggest that a limited uptake of amino acids by P. pentosaceus c1 could be caused by a substantial concentrations of dipeptides. <![CDATA[Influence of non-sacharomyces yeast growth on the metabolism of nitrogenous compounds in lactic acid bacteria from wine]]> A comparative study of the influence of Hanseniaspora uvarum metabolism on the growth and physiology of two lactic acid bacteria involved in vinification: Lactobacillus hilgardii 5w and Oenococcus oeni X2L was carried out. At different yeast growth times in grape juice medium, fermented broth was inoculated with L. hilgardii or O. oeni and incubated for 48 h at 30ºC. When O. oeni grown in the culture supernatant after 0, 3 and 8 hours of yeast growth (M1, M2 and M3 respectively), the growth rate and final biomass were not modified. With L. hilgardii a decrease of both parameters was observed. After 12, 24 and 34 h of yeast growth (M4, M5 and M6 respectively), the results for both microorganisms were similar: the growth rate increased and the final cellular mass decreased. When O. oeni was inoculated in M1, M2 and M3 media, an initial decrease of proteins directly related to amino acids production was observed. With L. hilgardii the amino acid and proteins concentrations diminished. In M4, M5 and M6 media O. oeni showed that the protein concentrations remained constant and the amino acid concentrations diminished. The results obtained with L. hilgardii were different with a higher protein consumption rate without significative amino acids modification. The amino acids increment in the first hours of O. oeni growth could regulate the protease production achieving the equilibrium between amino acids production and utilization. The high proteolytic activity in L. hilgardii could be responsible of the amino acids increase despite its consumption. <![CDATA[Study of operative variable influence on the vegetable oil extraction process]]> In the vegetable oil extraction process it is possible to identify a sequence of process units that deal with solids: extractor, desolventizer and meal drier, the so-called ¨solid line¨. Such unit operations are rarely included in available commercial process simulators, so it was necessary to develop a simulation tool for this particular application. The model obtained by using mass and energy conservation equations is represented by a differential equation system. In each process unit, heat and mass transfer flows were written in terms of lumped parameter constitutive equations. Industrial data were collected in a soybean extraction facility and the parameters of the model were estimated by using the Marquardt method. This simulation tool allows to analyze the influence of operative variables on solid line performance. It was found that the main variables that affect extraction efficiency are operation temperature, solid material preparation characteristics and residence time. In the desolventizer, the direct steam flow and the amount of indirect heat affect final meal solvent and moisture content. Inlet air flow, temperature and humidity have an important effect on the degree of meal moisture elimination in the drier. Effects of changes in the amount of solid material treated in the extractor is shown in this work. <![CDATA[Modeling molecular weight distribution, vinyl content and branching in the reactive extrusion of high density polyethylene]]> We study reactive modification of high density polyethylene by organic peroxides. We improve a previous model capable of describing average molecular weights and vinyl content to incorporate the calculation of long-chain branching and complete molecular weight distributions. We calculate average molecular weights and long-chain branching indexes for molecules with a given number of vinyls, by applying a double moment technique over those variables. No moment technique was applied to the vinyl content so the model has the capability of calculating those average quantities for every vinyl content. To calculate molecular weight distribution we apply probability generating function definitions with respect to the molecular size, to the mass balances of radical and polymer species of a given number of vinyls. We use two distinct definitions of probability generating functions, each one directly applicable either to the number or weight distributions. These probability generating functions are numerically inverted to obtain the corresponding calculated molecular weight distribution. Results give a deeper insight into the evolution of vinyl groups and branching points formation. MWD and vinyl content predictions are compared with qualitative experimental data showing the model capabilities. <![CDATA[Use of back-off computation in multilevel MPC]]> The desired operating point in Model Predictive Control is determined by a local steady-state optimization, which may be based on an eco-nomic objective. In this paper we proposes the solu-tion of a linear dynamic back-off problem to obtain a hierarchical scheme that ensures feasible operation in despite of disturbances. This is performed by computing the critical disturbances and expanding the optimization problem to ensure the existence of a control action that ensures the rejection of each perturbation. <![CDATA[Infinite dilution activity coefficients of solvents in fatty oil derivatives]]> Inverse gas-liquid chromatography has been applied to measure infinite dilution activity coefficients (g¥ ) of different solutes in low and high molecular weight triacylglycerides (TAGs) and in mixtures of carboxylic acids with TAGs. The g¥ data obtained were used to determine binary interaction and size related parameters for the GCA-EOS group contribution with association equation of sate. <![CDATA[Modeling the electropherogram of small charged molecules in capillary zone electrophoresis]]> A model for capillary zone electrophoresis (CZE) is presented to carry out the method development of practical separations involving small charged molecules. The model is based on principles and dynamic equations that contain true physicochemical properties of electrolyte solutions and analytes. The basic variables considered in the model are: injection and detection lengths of analytes, electrical field strength, hydration radius and diffusion coefficient of analytes, pK of analyte terminal groups, pH and ionic strength of electrolyte solution, capillary diameter and length, capillary zeta potential, test temperature and relative mass fractions of analytes. The model is solved numerically to predict the separation of analytes through the resulting electropherogram, which is then compared with experimental data. <![CDATA[Molecular solvent design and near critical solvents optimization with ECOFAC]]> In this work an efficient analysis tool for separation process design and property predictions is presented. ECOFAC can estimate pure compound and solution properties, specially some of environmental interest, generate the best potential solvents for a specific liquid-liquid extraction or extractive distillation problem through molecular design, or find the optimal operating conditions for a given supercritical extraction process. <![CDATA[Corrosion mechanism of Al-Zn-In alloys in chloride solutions]]> The electrochemical behavior of Al-Zn-In alloys was investigated in chloride media by means of potentiodynamic techniques, complemented by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDX) and Transmission Electron Microscopy (TEM). The influence of local alkalization produced by previous cathodization was analyzed at potentials more negative than the rest potential. The electrochemical response of alloys is given by the sum of those corresponding to the different present phases. Thus, the electrochemical behavior of each metal and bimetallic alloy (Al-In, In-Al and Zn-In) was analyzed in the same solution conditions at a potential region near the corrosion potential of the ternary alloy. The low solubility of In in Al favors its segregation at grain boundaries, where the formation of Zn-In alloys was detected. The initiation of the attack in the Al-Zn-In alloy is mainly localized in these zones. This is a consequence of the enhanced adsorption and surface accumulation of Cl- promoted by In at potentials more positive than - 1.1 V SCE. Close similarities of the anodic behaviors of the Al-In and ternary alloys lead us to propose a mechanism where the In distribution plays the major role. The In dissolution from homogeneous solid solution phases allows an enrichment of this element at the Al and Zn rich phases by displacement reactions. (Al,Zn)In + Cl- ® InCl2+ + 3 e- 2 InCl2+ + 3 Zn ® 2 In0 + 3 Zn2+ + 2 Cl- This, in turn, assures an accumulation of adsorbed Cl-, which maintains an active state of the Al matrix. Thus, the rapid Zn dissolution reaction ensures a better redistribution of In, so bringing the system towards potentials near those for Cl- adsorption on In. The attack morphology was also analyzed in order to explain the smooth wide cavities embracing many grains. <![CDATA[Fortification of mushroom with calcium by vacuum impregnation]]> Foods with added physiologically-active food components (PAC) are receiving special attention by their potential in disease prevention and health promotion. Additional intake of any nutrient might be achieved by the application of vacuum impregnation technique to fruits and vegetables. Viability of mushroom as matrix for the incorporation of calcium was then evaluated. It was found that, due to the high impregnated liquid fraction observed (17 - 40 %), the calcium incorporated in 100 g of mushroom would satisfy about 24 - 32 % of the Adequate Intake (AI). Thus, there would seem to be much potential for the introduction of high Ca2+ concentration in mushroom tissue through vacuum impregnation, combating the widespread Ca2+ deficiencies that occur in human populations. Although mechanical properties are affected by the vacuum treatment, similar or greater mushroom softening is produced during post-harvest storage or commercial thermal processing. <![CDATA[The influence of heat treatment on the corrosion behaviour of Fe<SUB>69.5</SUB>Cu<SUB>1</SUB>Nb<SUB>3</SUB>B<SUB>9</SUB>Si<SUB>13.5</SUB>Cr<SUB>4</SUB> FINEMET type alloy]]> The influence of the annealing treatment on the passivating ability of the Fe65.5Cu1Nb3B9Si13,5Cr4 nanocrystalline alloy in 2 M HCl solution was studied by differential scanning calorimetry (DSC), atomic force microscopy (AFM), scanning electron microscopy (SEM) and conventional electrochemical techniques. The samples were isothermally annealed at 525 C (onset of nanocrystallization) and 600 C during different times and the fraction of transformation was determined by DSC. The initial stages of crystallization could be well characterized by AFM and the images have showed hemispherical features related to the first stage of nanocrystallization. These features, interpreted as a -Fe(Si) nanocrystallites embedded in the residual amorphous matrix, increased in number depending on the time or temperature of the thermal treatment, in agreement with the DSC studies. The results indicate that the nanocrystallization of the alloy produced an improvement in their passivating ability. The current density in the active-passive transition have a minimum value when the fraction crystallized reached a maximum and the nanocrystallites formed have not started to coalesce. <![CDATA[Performance analysis of pilot rotary kiln for activated carbon manufacture, using a steady state mathematical model]]> The physical activation of charcoal from eucalyptus wood has produced excellent results in laboratory tests. The obtained activated carbons have good adsorbent properties with surface areas over 500 m²/g, low density and moderate attrition resistance. The activation process is strongly endothermic and involves gasification of the carbonaceous char by oxidation with either water vapor or carbon dioxide in the temperature range of 1073 - 1373 K. This process is carried out in either directly or indirectly fired activators, such as rotary kilns. The goal of this work is to describe the performance analysis carried out on a pilot rotary kiln, using a previously developed steady state mathematical model. The comparison between simulated and experimentally data has been reported in a previous paper. The model accounts for the complex transfer and reaction phenomena, which occur inside the kiln. The model was solved by a finite difference method. The solution predicts solid, freeboard gas, and wall temperature axial profiles, as well as the mass variations in the solid and freeboard gas, due to activation reaction and solid drying. The performance of the activator can be measured through its production rate, burn off, and solid temperature profile. To analyze the influence of different operating conditions on the equipment performance, the main operating variables (i.e., gas, steam, and solid flow rate, residence time, and solid temperature) have been studied. The results obtained from the sensitivity analysis allow for the identification of the operation variables that can be optimized. <![CDATA[Optimizing load policy in anaerobic biofilm reactors for wastewater treatment]]> A rigorous dynamic model of anaerobic biofilm reactor (Mussati et al., 1998) is used to optimize and evaluate different loading strategies in anaerobic wastewater treatment systems. This work includes variations in the original model so that the results of process simulation also represent the initial events of the start up operation as regards the biofilm growth. The model was implemented in gPROMS (General Process Modeling System). Different dynamic optimization formulations are evaluated. Start up strategies are considered and discussed. A sensitivity analysis regarding kinetic data on optimal start up policies under two different conditions is included. The first condition consists of a fixed maximum load, and the other one is the maximum load supported by the system, which varies according to the kinetic data being used. Changes in maximum specific growth rate, half saturation constant and specific death rate of Monod's model generate different optimal start up periods; whereas optimal start up time did not change when the maximum allowed load for each reactor is considered. <![CDATA[Modeling of association effects in mixtures of carboxylic acids with associating and non-associating components]]> The group contribution with association equation of state GCA-EOS has been applied to calculate thermodynamic properties of pure compounds and mixtures of carboxylic acids with paraffins, alcohols, water and gases, at low and high pressures. Two associating groups, OH and COOH, were defined. Self- and cross-association in these mixtures were quantified through two parallel COOH/COOH and OH/OH associations. The validity of this approach is supported by an excellent representation of pure compound properties (vapor pressures and compressibility factors) and phase equilibria in mixtures of (associating + inert) and (associating + associating) components at low and high pressures. <![CDATA[Phase equilibria for quaternary mixtures in esterification reaction systems]]> This paper examines the effect of the simultaneous chemical and phase equilibrium on the conceptual design of reactive distillation processes. Esterification of acetic acid with methanol, ethanol and butanol are examined. Using commercial software, azeotropic points, residue curve maps and distillation line diagrams having been calculated. The analyzed systems have showed different behavior when phase equilibrium parameters and chemical equilibrium constants are changed. The methyl acetate system does not change the topological features of residue curve maps and distillation line diagrams. The ethyl acetate system and the butyl acetate system change the topological features of the graphs when different chemical equilibrium constants are used. <![CDATA[Separation of natural colorants using a combined high pressure extraction-adsorption process]]> The goal of this work was to find a process to extract and separate carotene from natural sources using supercritical carbon dioxide. A high pressure extraction process was compared with a combined extraction-adsorption process. The experiments were performed with a pilot plant which can be operated up to 50 MPa and 100ºC. A technique using an on-line photometer, was used to estimate the concentration of carotenoids in the fluid phase, to monitor the different steps of the process. During the extraction of paprika powder, a time fractionation of pigments was observed: a low concentration fraction of free carotenoids at the beginning of the process and an enriched esterified carotenoid fraction at the end. With the combined extraction-adsorption process, using silica gel as adsorbent, a selective adsorption occurred. Red pigments (mainly esterified carotenoid) were adsorbed but the yellow ones (mainly free carotenoid) remained in supercritical phase which were collected in a separation step at lower pressure. <![CDATA[Geometry effect on water diffusivity estimation in PROINTA-Isla Verde and broom wheat cultivars]]> The effect of geometry representation of the grain kernel in the estimation of the effective diffusion coefficient of water in wheat, cv. Broom, is studied. Isothermal thin layer drying is assumed. The two-dimensional diffusive mass transport equation is solved for spherical and ellipsoidal geometries. The effective diffusion coefficient was estimated for drying air temperatures of 64, 70 and 75ºC and initial grain moistures of 0.22, 0.25 and 0.28 db. Results were correlated by means of Arrhenius-type functions, varying from 2.953x10-11 to 6.687x10-11 m²/s for ellipsoidal geometry and from 3.336x10-11 to 7.772x10-11 m²/s for spheres. An average ratio of diffusion coefficients for ellipsoid to those for spheres was calculated to be about 0.85, very close to the value of 0.86 obtained in a previous work for the "PROINTA-Isla Verde" wheat cultivar. This ratio can be considered to be equal to the wheat sphericity squared. <![CDATA[Superheated steam drying of parsley: a fixed bed model for predicting drying performance]]> Superheated steam drying technique has been known for a long time, but its application to food drying has received little attention. In this work, superheated steam was applied to dry fresh parsley (Petroselinum Cripsum). A mathematical model to simulate this drying process was developed by using mass and energy conservation equations for solid and steam phases. The resulting partial differential equation system was solved by means of a finite difference method. Software Matlab 5.3 for Windows was used for programming the algorithm. The development of the drying kinetics equation, required in the model, was based on thin layer experimental results. The simulation model was used to analyze the influence of different variables (bed height, operating pressure, steam velocity and steam temperature) on solid moisture content, as well as on solid and steam temperature profiles along the bed. Experimental determinations in a fixed bed arrangement were done at different operating pressures (0.07-0.17 kgf/cm²), steam temperatures (70-100ºC), steam velocities (5-12 m/sec.) and bed heights (thin layer, 2 cm and 10 cm). Solid temperature at the top of the bed and average solid moisture content were measured as drying proceeded. An acceptable agreement between experimental and theoretical average solid moisture contents was obtained. <![CDATA[Multicomponent ion exchange isotherms in NaX zeolite]]> In this work the ion exchange isotherms of Cr3+, Mg2+, Ca2+ and K+ in single solutions and in binary mixtures (Cr/K, Cr/Ca, Cr/Mg) using NaX zeolite at 30ºC, 45ºC and 60ºC were reported. NaX isotherms were very favorable for all metal cations studied. The respective isotherms had some differences in shape, a consequence of competition for the exchange sites. The Kielland plots of all systems were non linear, which is a characteristic of sites of different energies involved in the exchange process. Temperature influenced the ion exchange as it could alter the hydration sphere of the in-going ions. Consequently, differences in thermodynamic properties and also in the selectivity were seen. It was concluded that NaX did not have a pronounced selectivity towards chromium. <![CDATA[Catalytic abatement jof pollutants from diesel exhausts]]> K and Co,K supported catalysts were studied to determine the mechanism of the soot combustion. The thermal stability of these catalysts and the resistance to water and sulfur are also addressed. The support plays an important role. La2O3 contributes through the formation of carbonate-type intermediates and CeO2 supplies the oxygen necessary for the redox mechanism to take place. However, the addition of Co to the catalyst supported on La2O3, to supply the redox function, leads to a loss of the thermal stability as a consequence of the formation of a perovskite structure. The soot-catalyst contacting phenomenon was also addressed. A synergic La-K effect was observed, by which mechanical mixtures of soot with K-La2O3 showed higher rates than those observed when K and La were deposited on soot. Preliminary experiments using barium as a catalytic trap for NOx and the simultaneous removal of NOx and soot are also presented. <![CDATA[Non-invasive methods for monitoring biofilm growth in industrial water systems]]> Microbiological control in industrial environments is frequently restricted to monitor the number of planktonic (suspended) cells. However, this number is not often related with the microorganisms attached to the surfaces (sessile bacteria). The aim of this research work was to develop a method for monitoring biofilm growth and the biocidal efficacy through simple non-invasive ways. With this purpose, biofilms were formed on stainless steel coupons and after preset periods were removed and immersed in sterile solutions with and without biocide. The number of sessile cells attached on the metal surface and of planktonic cells that were shed from the biofilmed coupons (pcb) and grow in the initially sterile solutions were determined. Sessile cells were scrapped from the metal surface to be enumerated. The relation between the degree of growth of pcb and the reactivation capacity of the biofilm was evaluated. It could be observed that pcb growing in a nutrient non aggressive medium was related to the number of sessile cells that remain alive after the biocidal treatment. The early stages of the biofilm growth, the thickness of the biofilms and their microstructural characteristics before and after the biocidal treatment could be followed through optical microscopy using a non-invasive technique recently developed in the laboratory. Microscopic observations showed that the biofilm thickness varied to obliterate the unevenness of rough surfaces.