Scielo RSS <![CDATA[Brazilian Journal of Chemical Engineering]]> http://www.scielo.br/rss.php?pid=0104-663220140002&lang=es vol. 31 num. 2 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>Biodiesel production through non-catalytic supercritical transesterification</b>: <b>current state and perspectives</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200001&lng=es&nrm=iso&tlng=es The inconveniences of the conventional method for biodiesel production by alkaline catalysis suggests research towards alternative methods, with the non-catalytic transesterification using an alcohol at supercritical conditions proposed as a promising technique for biodiesel production. The so-called supercritical method (SCM) has powerful advantages over conventional techniques, such as fast reaction rates, feedstock flexibility, production efficiency and environmentally friendly benefits. However, application of this methodology has some limitations, like operating conditions (elevated temperature and pressure and higher amounts of alcohol), which result in high energy costs and degradation of the products generated. In this review paper the state of the art in relation to the use of the SCM for biodiesel production is reported and discussed, describing the characteristics of the method, the influence of operational parameters on the ester yield, patents available in the field and the perspectives for application of the technique. <![CDATA[<b>Conversion of by-products from the vegetable oil industry into biodiesel and its use in internal combustion engines</b>: <b>a review</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200002&lng=es&nrm=iso&tlng=es Biodiesel produced from by-products and waste materials can be an economical way of reducing traditional oil consumption and environmental problems. The by-products from the vegetable oil refining industry such as soapstock, acid oil and fatty acid distillates are suitable for producing biodiesel. The present work is a survey related to the use of these by-products to obtain biodiesel, covering not only the traditional and most widely used acid/base catalysis, but also solid and enzymatic catalysis. Details of the techniques are presented and compared. The advantages and drawbacks of the different approaches are mentioned and analyzed. The synthesis and use of by-products from the vegetable oil refining industry are covered in this work. The use of the obtained biodiesel in diesel engines is also included, demonstrating the disparity between the number of papers related to biodiesel production and engine performance assessment. <![CDATA[<b>Error propagation in open respirometric assays</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200003&lng=es&nrm=iso&tlng=es This work deals with the calculation of the uncertainty of the exogenous respiration rate (Rex) and the total oxygen consumed (OCT) derived from a single open respirometric profile. Uncertainties were evaluated by applying a linear error propagation method. Results show that standard deviations (SD) of Rex and OCT depend not only on the SD of the dissolved oxygen (σC) and kLa (σkLa), but also on the SD of the derivative term (dC/dt) of the oxygen mass balance equation (σb). A Monte Carlo technique was employed to assess σb; a power law expression for the dependence of σb as a function of σC, the time window (t w) and the sampling rate (Δt) was proposed. The equations obtained in the present work are useful to calculate suitable conditions (e.g., biomass concentration, kLa) that minimize the coefficient of variation corresponding to Rex and OCT. <![CDATA[<b>Maintenance-energy-dependent dynamics of growth and poly(3-hydroxybutyrate) [P(3HB)] production by <i>Azohydromonas lata</i> MTCC 2311 using simple and renewable carbon substrates</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200004&lng=es&nrm=iso&tlng=es The dynamics of microbial growth and poly(3-hydroxybutyrate) [P(3HB)] production in growth/ non-growth phases of Azhohydromonas lata MTCC 2311 were studied using a maintenance-energy-dependent mathematical model. The values of calculated model kinetic parameters were: m s1 = 0.0005 h-1, k = 0.0965, µmax = 0.25 h-1 for glucose; m s1 = 0.003 h-1, k = 0.1229, µmax = 0.27 h-1 for fructose; and m s1 = 0.0076 h-1, k = 0.0694, µmax = 0.25 h-1 for sucrose. The experimental data of biomass growth, substrate consumption, and P(3HB) production on different carbon substrates were mathematically fitted using non-linear least square optimization technique and similar trends, but different levels were observed at varying initial carbon substrate concentration. Further, on the basis of substrate assimilation potential, cane molasses was used as an inexpensive and renewable carbon source for P(3HB) production. Besides, the physico-chemical, thermal, and material properties of synthesized P(3HB) were determined which reveal its suitability in various applications. <![CDATA[<b>Immobilization of puerarin glycosidase from <i>Microbacterium oxydans</i> CGMCC 1788 increases puerarin transformation efficiency</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200005&lng=es&nrm=iso&tlng=es For immobilization of puerarin glycosidase from Microbacterium oxydans CGMCC 1788 on DEAE-52 cellulose, the optimal amount of enzyme protein was 12 mg protein: 1 g DEAE-52 cellulose; the optimal pH was 6.5; and the optimal immobilization time was 6 hr. The specific activity of immobilized enzyme was 36.67 mU.g-1 carrier with an immobilization yield of 98.87% and an enzyme recovery yield of 92.43%. The molar transformation rates of puerarin by immobilized enzyme and by the relative bacterial cell amount equal to the same amount of enzyme were 53.3% and 2.2%, respectively, after 1 hr of transformation. The former molar transformation rate, which was similar to that for free enzyme, was more than 24-fold greater than the latter. The immobilized puerarin glycosidase showed improved enzymatic properties and stability. The immobilized puerarin glycosidase retained 88% of its initial activity after being reused 10 times. <![CDATA[<b>Additive effects of CuSO<sub>4 </sub>and aromatic compounds on laccase production by <i>Pleurotus sajor-caju</i> PS-2001 using sucrose as a carbon source</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200006&lng=es&nrm=iso&tlng=es Laccase enzymes are now commercially available, and a laccase/mediator combination is currently marketed for indigo dye bleaching in textile manufacturing; replacing traditional chemical-based processes with enzymatic technology reduces the need for effluent treatment. However, an inexpensive source of these enzymes will be needed to enable wider application of this technology. In the present work, the main objective was to increase laccase production by the mushroom Pleurotus sajor-caju strain PS-2001 grown on sucrose derived from sugar cane, one of most economical carbon sources known, by the addition of compounds that are known to affect laccase production. High laccase activities (45-62 U mL-1) were obtained with additions of syringaldazine, benzoic acid, gallic acid, and vanillin. When CuSO4 was used in conjunction with these aromatic compounds, the levels of laccase activity were further improved, reaching 58-80 U mL-1. These laccase activities indicate the potential of this strain as an enzyme producer, which has also been detected in media containing glucose, but with activity lower than that observed with sucrose. <![CDATA[<b>Modeling the microbial growth of two <i>Escherichia coli</i> strains in a multi-substrate environment</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200007&lng=es&nrm=iso&tlng=es The microbial growth in multi-substrate environments may be viewed as an optimal resources allocation problem. The optimization aims at maximizing some biological objective like the biomass growth. The models developed using this hypothesis are called "cybernetic" and they represent the complex cell structure as an optimizing function that regulates the intracellular enzymatic machinery. In this work, a cybernetic model was developed to represent the growth of two E. coli strains (JM 109 and BL 21 -DE3-) on a medium containing glucose and glycerol as carbon and energy sources. The model was able to accurately simulate the biomass growth, the substrates consumption and the growth-rate profiles. <![CDATA[<b>Production of fermentable sugars by combined chemo-enzymatic hydrolysis of cellulosic material for bioethanol production</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200008&lng=es&nrm=iso&tlng=es To change the recalcitrant nature of the lignocellulosic material for maximum hydrolysis yield, a comprehensive study was done by using sulphuric acid as an exclusive catalyst for the pretreatment process. The enzymatic digestibility of the biomass [Water Hyacinth: Eichhornia crassipes] after pretreatment was determined by measuring the hydrolysis yield of the pretreated material obtained from twenty four different pretreatment conditions. These included different concentrations of sulphuric acid (0.0, 1.0, 2.0 and 3.0%), at two different temperatures (108 and 121 ºC) for different residence times (1.0, 2.0 and 3.0h).The highest reducing sugar yield (36.65 g/L) from enzymatic hydrolysis was obtained when plant material was pretreated at 121 ºC for 1.0 h residence time using 3.0% (v/v) sulphuric acid and at 1:10 (w/v) solid to liquid ratio. The total reducing sugars obtained from the two-stage process (pretreatment + enzymatic hydrolysis) was 69.6g/L. The resulting sugars were fermented into ethanol by using Saccharomyces cerevisiae. The ethanol yield from the enzymatic hydrolyzate was 95.2% of the theoretical yield (0.51g/g glucose), as determined by GS-MS, and nearly 100% since no reducing sugars were detected in the fermenting media by TLC and DNS analysis. <![CDATA[<b>Electroremediation of heavy metals in sewage sludge</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200009&lng=es&nrm=iso&tlng=es This paper presents the application of electrokinetic remediation in the treatment of sludge in a sewage treatment station. The study consisted of, in a first step, the characterization of physicochemical parameters of sludge and, in a second step, the implementation of the electrokinetic remediation technique. The concentrations of Cu, Cr, Pb and Zn in sludge samples, before and after the experiment, were determined by atomic absorption spectroscopy. After 40 hours of experiment, considering an electrolyte flow-rate of 1.34 L.h-1 at a voltage of 20 V, the removal rate of all the metals accompanied was over 50%; the highest removal efficiency was for Pb, with 72.49%. The results show the feasibility of using the electrochemical technique of electrokinetic remediation for metal removal from a sludge sewage treatment station. <![CDATA[<b>Methane production in anaerobic digestion of organic waste from Recife (Brazil) landfill</b>: <b>evaluation in refuse of diferent ages</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200010&lng=es&nrm=iso&tlng=es This work focuses on monitoring the generation of biogas by biochemical methane potential (BMP) assays, commonly used to assess anaerobic biodegradability of solid and liquid wastes under controlled conditions. The experiment employed 5 g of substrate of both refuses (fresh and one-year-old wastes), digested with 250 mL of inoculum in 1 L flasks as bioreactors (all of them in triplicate, operating under batch conditions at ± 35 ºC). Despite the difference of age of both refuses evaluated, there was no significant differences in volume (near 1800 mL) and composition (55% methane) of biogas generated in 80 days of incubation under mesophilic conditions. The important parameters of both refuses (such as moisture content, volatile solids and chemical oxygen demand) also showed very similar initial values. <![CDATA[<b>Activated sludge inhibition capacity index</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200011&lng=es&nrm=iso&tlng=es Toxic compounds in sewage or industrial wastewater may inhibit the biological activity of activated sludge impairing the treatment process. This paper evaluates the Inhibition Capacity Index (ICI) for the assessment of activated sludge in the presence of toxicants. In this study, activated sludge was obtained from industrial treatment plants and was also synthetically produced. Continuous respirometric measurements were carried out in a reactor, and the oxygen uptake rate profile obtained was used to evaluate the impact of inhibiting toxicants, such as dissolved copper, phenol, sodium alkylbenzene sulfonate and amoxicillin, on activated sludge. The results indicate that ICI is an efficient tool to quantify the intoxication capacity. The activated sludge from the pharmaceutical industry showed higher resistance than the sludge from other sources, since toxicants are widely discharged in the biological treatment system. The ICI range was from 58 to 81% when compared to the synthetic effluent with no toxic substances. <![CDATA[<b>Enhancement of anaerobic digestion of microcrystalline cellulose (MCC) using natural micronutrient sources</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200012&lng=es&nrm=iso&tlng=es The effect of adding four minerals as micronutrient sources to stimulate the anaerobic process of microcrystalline cellulose (MCC) was investigated. Three mineral doses (5, 10 and 15 mg/L) were evaluated and the response to trace metal addition was monitored by the methane yield (Y CH4) and specific methanogenic activity (SMA). A clear stimulation of the Y CH4 and SMA on MCC due to the presence of minerals with a high content of trace elements was observed, respectively: the Y CH4 and SMA of the sludge with 5 mg/L of high-Fe-Mg mineral increased to 397 NmLCH4/gVSsubstrate and 0.267 gCOD NmLCH4/gVSinoculum/d compared to 303 NmLCH4/gVSsubstrate and 0.205 gCOD NmLCH4/gVSinoculum/d in a medium without adding mineral. An increase in the doses of high-Ca mineral highly decreased methane production and process stability, due to a possible inhibition of the anaerobic digestion by calcium ions. <![CDATA[<b>Comparison of carrot (<i>Daucus carota</i>) drying in microwave and in vacuum microwave</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200013&lng=es&nrm=iso&tlng=es Drying is a single operation employed to prolong the life of a large quantity of vegetables. Carrot (Daucus carota) drying has been the subject of many studies. This plant has been highlighted in the human diet for having high nutritional value, mainly due to the high content of β-carotene. In this work, carrot drying behavior was studied in a regular microwave dryer and a vacuum microwave dryer. A vacuum of 450 mmHg was applied for drying of carrot in different geometrical shapes (cubes, discs and sticks). The samples were dried at power ratings of 1.0 W/g, 1.5 W/g and 2.0 W/g for both methods of drying. The evolution of physical properties such as density, volume and porosity was monitored and related to the moisture content of the sample and to the method of drying and power rating used. The geometric shape of the sample influenced the drying kinetics and it was verified that the cubic form was responsible for a slower drying. The application of vacuum showed no major changes in the drying kinetics in microwave but influenced the physical properties of the material. The influence of power ratings on the content of β-carotene was also evaluated and discussed. The main difference observed was the lower shrinkage of the samples dried in the vacuum microwave compared to those dried only in microwave. <![CDATA[<b>Natural convection of nanofluids over a convectively heated vertical plate embedded in a porous medium</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200014&lng=es&nrm=iso&tlng=es In this paper, the natural convective flow of nanofluids over a convectively heated vertical plate in a saturated Darcy porous medium is studied numerically. The governing equations are transformed into a set of ordinary differential equations by using appropriate similarity variables, and they are numerically solved using the fourth-order Runge-Kutta method associated with the Gauss-Newton method. The effects of parametric variation of the Brownian motion parameter (Nb), thermophoresis parameter (Nt) and the convective heating parameter (Nc) on the boundary layer profiles are investigated. Furthermore, the variation of the reduced Nusselt number and reduced Sherwood number, as important parameters of heat and mass transfer, as a function of the Brownian motion, thermophoresis and convective heating parameters is discussed in detail. The results show that the thickness of the concentration profiles is much lower than the temperature and velocity profiles. For low values of the convective heating parameter (Nc), as the Brownian motion parameter increases, the non-dimensional wall temperature increases. However, for high values of Nc, the effect of the Brownian motion parameter on the non-dimensional wall temperature is not significant. As the Brownian motion parameter increases, the reduced Sherwood number increases and the reduced Nusselt number decreases. <![CDATA[<b>Emulsifying properties of maillard conjugates produced from sodium caseinate and locust bean gum</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200015&lng=es&nrm=iso&tlng=es Emulsifying properties of sodium caseinate -locust bean gum Maillard conjugates produced at different temperatures (54 - 96 ºC), protein/polysaccharide ratios (0.3 - 1.0) and reaction times (1 - 24 hours) were evaluated. Conjugate formation was confirmed by formation of color and high molecular weight fractions and the decrease of the αs- and β-casein bands. The emulsions stabilized by Maillard conjugates showed good stability. The mean droplet diameter (d32) tended to decrease with the increase of incubation time and temperature, except at extreme conditions (24 hours and 90 ºC or 96 ºC) when the partial degradation of the conjugates was probably favored, resulting in phase separation of emulsions. The emulsion viscosity decreased with the increase in the protein/polysaccharide ratio and with the degradation of the conjugates. The conditions used in the experimental design made the optimization of the conjugate production viable, which showed greater emulsifier properties than the pure protein under acid conditions. <![CDATA[<b>A Mixed-Integer convex formulation for production optimization of gas</b><b>-</b><b>lifted oil fields with routing and pressure constraints</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200016&lng=es&nrm=iso&tlng=es Production optimization of gas-lifted oil fields under facility, routing, and pressure constraints has attracted the attention of researchers and practitioners for its scientific challenges and economic impact. The available methods fall into one of two categories: nonlinear or piecewise-linear approaches. The nonlinear methods optimize simulation models directly or use surrogates obtained by curve fitting. The piecewise-linear methods represent the nonlinear functions using a convex combination of sample points, thereby generating a Mixed-Integer Linear Programming (MILP) problem. The nonlinear methods rely on compact models, but can get stuck in local minima, whereas the piecewise-linear methods can reach globally optimal solutions, but their models tend to get very large. This work combines these methods, whereby piecewise-linear models are used to approximate production functions, which are then composed with convex-quadratic models that approximate pressure drops. The end result is a Mixed-Integer Convex Programming (MICP) problem which is more compact than the MILP model and for which globally optimal solutions can be reached. <![CDATA[<b>A supervision and control tool based on artificial intelligence for high cell density cultivations</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200017&lng=es&nrm=iso&tlng=es High cell density cultivations of recombinant E. coli have been increasingly used for the production of heterologous proteins. However, it is a challenge to maintain these cultivations within the desired conditions, given that some variables such as dissolved oxygen concentration (DOC) and feed flow rate are difficult to control. This paper describes the software SUPERSYS_HCDC, a tool developed to supervise fed-batch cultures of rE. coli with biomass concentrations up to 150 gDCW/L and cell productivities up to 9 gDCW.L-1.h-1. The tool includes automatic control of the DOC by integrated action of the stirrer speed as well as of the air and oxygen flow rates; automatic start-up of the feed flow of fresh medium (system based on a neural network committee); and automatic slowdown of feeding when oxygen consumption exceeds the maximum capacity of the oxygen supply. <![CDATA[<b>CFD and experimental investigation on the heat transfer characteristics of alumina nanofluids under the laminar flow regime</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200018&lng=es&nrm=iso&tlng=es This study reports experimental and Computational Fluid Dynamics (CFD) investigations of the laminar convective heat transfer coefficient of Al2O3/water nanofluids in a circular tube under uniform and constant heat flux on the wall. Three different models including a constant physical properties single-phase (CP-SP) model, a variable physical properties single-phase (VP-SP) model and a discrete particles two-phase model were developed. Particle agglomeration and cluster size distribution were considered in the two-phase model. Experimental and simulation results showed that the thermal performance of nanofluids is higher than that of the base fluid and the heat transfer enhancement increases with the particle volume concentration and Reynolds number. Furthermore, higher heat transfer coefficients were detected in the case of the VP-SP model and the two-phase model. The results demonstrated that the two-phase model prediction and experimental data match significantly and that the model can be employed with confidence for the prediction of any type of nanofluid. <![CDATA[<b>Local linear model tree and Neuro-Fuzzy system for modelling and control of an experimental pH neutralization process</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200019&lng=es&nrm=iso&tlng=es This paper describes the modelling and control of a pH neutralization process using a Local Linear Model Tree (LOLIMOT) and an adaptive neuro-fuzzy inference system (ANFIS). The Direct and Inverse model building using LOLIMOT and ANFIS structures is described and compared. The direct and inverse models of the pH system are identified based on experimental data for the LOLIMOT and ANFIS structures. The identified models are implemented in the experimental pH system with IMC structure using a GUI developed in the MATLAB -SIMULINK platform. The main aim is to illustrate the online modelling and control of the experimental setup. The results of real-time control of an experimental pH process using the Internal Model Control (IMC) strategy are also presented. <![CDATA[<b>Separation and effect of residual moisture in liquid phase adsorption of xylene on y zeolites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200020&lng=es&nrm=iso&tlng=es The separation of p-xylene and m-xylene from C8 aromatic hydrocarbon feed using Y zeolites is investigated. Effect of residual moisture on p-xylene adsorption on BaY was measured in order to optimize the activation temperature of the adsorbent. The results show that with an increase in temperature the moisture on the adsorbent decreases. An optimum loading of moisture is required for adsorption of xylene on the adsorbents. The Everett equation is used to determine the adsorption capacity and selectivity. It has been found that the adsorbents best suited for the separation of p-xylene, m-xylene, o-xylene and ethyl benzene from the mixture of C8 aromatics are NaY, NaY, BaY and KY, respectively. The XRD results show that the crystallinity of the adsorbent decreases upon exchanging the zeolites to K+ and Ba2+ ions. <![CDATA[<b>Fouling behavior and performance of microfiltration membranes for whey treatment in steady and unsteady-state conditions</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200021&lng=es&nrm=iso&tlng=es Whey pretreatment for protein purification is one of the main applications of cross-flow microfiltration before an ultrafiltration process. In this paper, the effects of the operating pressure and crossflow velocity on the membrane performance and the individual resistances in microfiltration of whey for both unsteady and steady-state conditions were investigated for two 0.45 µm mean pore size polymeric membranes, Polyethersulfone (PES) and Polyvinylidene fluoride (PVDF). A laboratory-scale microfiltration setup with a flat rectangular module was used. The Reynolds number and operating pressure showed positive and negative effects on the amount of all resistances, respectively. The dominant effect of the concentration polarization and cake resistances was demonstrated by using a "Resistance-in-Series" model for unsteadystate investigations, which could vary during the filtration time. An empirical model revealed a linear relationship between the Reynolds number and permeate flux and a second-order polynomial relationship between the transmembrane pressure and the permeate flux. This empirical correlation, implemented for the limited range of MF operating parameters tested in this article for whey protein, was validated with experimental data and showed good agreement between calculated and experimental data. <![CDATA[<b>Adsorption of lead and copper ions from aqueous effluents on rice husk ash in a dynamic system</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200022&lng=es&nrm=iso&tlng=es This study evaluated the kinetic adsorption of Pb and Cu ions using rice husk ash as adsorbent in a fixed bed. The maximum adsorption capacities obtained for lead and copper ions in the fixed bed were 0.0561 and 0.0682 mmol/g (at 20 ºC), respectively. The thermodynamic studies indicated that the lead adsorption process was exothermic and spontaneous, while the copper adsorption process was endothermic and spontaneous. Characterization results indicated the presence of several functional groups, amorphous silica and a fibrous and longitudinal structure of rice husks. Rice husk ash (RHA) from northern Brazil can be used as a bioadsorbent for the individual removal of Pb(II) and Cu(II) ions from metal-containing effluents. <![CDATA[<b>Simple multicomponent batch distillation procedure with a variable reflux policy</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200023&lng=es&nrm=iso&tlng=es This paper describes a shortcut procedure for batch distillation simulation with a variable reflux policy. The procedure starts from a shortcut method developed by Sundaram and Evans in 1993 and uses an iterative cycle to calculate the reflux ratio at each moment. The functional relationship between the concentrations at the bottom and the dome is evaluated using the Fenske equation and is complemented with the equations proposed by Underwood and Gilliland. The results of this procedure are consistent with those obtained using a fast method widely validated in the relevant literature. <![CDATA[<b>Experimental density data and excess molar volumes of coconut biodiesel + n-hexadecane and coconut biodiesel + diesel at different temperatures</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200024&lng=es&nrm=iso&tlng=es The density of the pure component (n-hexadecane), pure pseudo-components (coconut biodiesel and diesel) and pseudo-binary mixtures of coconut biodiesel with n-hexadecane (or + diesel) were measured at temperatures 293.15, 313.15, 333.15, 353.15 and 373.15 K and atmospheric pressure, over the entire composition range (mole fractions from 0.1 to 0.9, with a step de 0.1). Densities were determined using an Anton Paar SVM 3000 viscodensimeter. Experimental density values decreased with the increase of the temperature. The excess molar volumes of the pseudo-binary mixtures were calculated by using the experimental values of density. Excess molar volumes were correlated with the Redlich-Kister polynomial expansions. Excess molar volumes show positive and negative values in the two systems studied. Excess partial volumes at infinite dilution were calculated for coconut biodiesel, n-hexadecane and diesel in the mixtures studied. <![CDATA[<b>Comparison of safflower oil extraction kinetics under two characteristic moisture conditions</b>: <b>statistical analysis of non-linear model parameters</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200025&lng=es&nrm=iso&tlng=es In this study the kinetics of oil extraction from partially dehulled safflower seeds under two moisture conditions (7 and 9% dry basis) was investigated. The extraction assays were performed using a stirred batch system, thermostated at 50 ºC, using n-hexane as solvent. The data obtained were fitted to a modified diffusion model in order to represent the extraction kinetics. The model took into account a washing and a diffusive step. Fitting parameters were compared statistically for both moisture conditions. The oil yield increased with the extraction time in both cases, although the oil was released at different rates. A comparison of the parameters showed that both the portion extracted in the washing phase and the effective diffusion coefficient were moisture-dependent. The effective diffusivities were 2.81 10-12 and 8.06 10-13 m²s-1 for moisture contents of 7% and 9%, respectively. <![CDATA[<b>Solubility measurement and solid-liquid equilibrium model for the ternary system MgBr<sub>2</sub> + MgSO<sub>4</sub> + H<sub>2</sub>O at 288.15 K</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000200026&lng=es&nrm=iso&tlng=es The solubility of magnesium minerals and the refractive index of the ternary system MgBr2 + MgSO4 + H2O at 288.15 K were investigated using an isothermal dissolution method. It was found that there are two invariant points in the phase diagram and the solubility isotherm of this ternary system consists of three branches, corresponding to equilibrium crystallization of Epsomite (MgSO4·7H2O, Eps), hexahydrite (MgSO4·6H2O, Hex) and magnesium bromide hexahydrate (MgBr2·6H2O, Mb). Neither solid solutions nor double salts were found. The refractive indices calculated from empirical equation are in good agreement with the experimental data. Combining the results from solubility measurements with the single-salt parameters for MgBr2 and MgSO4, and the mixed ion-interaction parameter θBr,S0(4), the parameter ψMg,Br,S0(4) at 288.15 K was fitted using the Pitzer theory and Harvie-Weare (HW) approach. In addition, the average equilibrium constants of the stable equilibrium solids at 288.15 K were obtained by a method using the activity product constant. A chemical model, which combined the Pitzer parameters and the average equilibrium constants, was constructed to calculate the solid + liquid equilibria in the ternary system MgBr2 + MgSO4 + H2O at 288.15 K. The model agreed well with the equilibrium solubility data for the magnesium salts.