Scielo RSS <![CDATA[Brazilian Journal of Chemical Engineering]]> http://www.scielo.br/rss.php?pid=0104-663220140003&lang=es vol. 31 num. 3 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>An overview of heavy oil properties and its recovery and transportation methods</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300001&lng=es&nrm=iso&tlng=es Unconventional oils - mainly heavy oils, extra heavy oils and bitumens - represent a significant share of the total oil world reserves. Oil companies have expressed interest in unconventional oil as alternative resources for the energy supply. These resources are composed usually of viscous oils and, for this reason, their use requires additional efforts to guarantee the viability of the oil recovery from the reservoir and its subsequent transportation to production wells and to ports and refineries. This review describes the main properties of high-viscosity crude oils, as well as compares traditional and emergent methods for their recovery and transportation. The main characteristics of viscous oils are discussed to highlight the oil properties that affect their flowability in the processes of recovery and pipeline transportation. Chemical composition is the starting point for the oil characterization and it has major impact on other properties, including key properties for their dynamics, such as density and viscosity. Next, enhanced oil recovery (EOR) methods are presented, followed by a discussion about pipeline and transportation methods. In addition, the main challenges to achieve viable recovery and transportation of unconventional oils are compared for the different alternatives proposed. The work is especially focused on the heavy oils, while other hydrocarbon solid sources, such as oil sands and shale oil, are outside of the scope of this review. <![CDATA[<b>MgO nanoparticles as antibacterial agent</b>: <b>preparation and activity</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300002&lng=es&nrm=iso&tlng=es Bacterial pollution is a great risk for human health. Nanotechnology offers a way to develop new inorganic antibacterial agents. Nano-inorganic metal oxide has a potential to reduce bacterial contamination. MgO is an important inorganic oxide and has been widely used in many fields. Many studies have shown that MgO nanoparticles have good antibacterial activity. Therefore, in this paper, the main synthesis methods, antibacterial activity and antibacterial mechanisms of MgO nanoparticles are reviewed. <![CDATA[<b>Biohydrogen production from cassava wastewater in an anaerobic fluidized bed reactor</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300003&lng=es&nrm=iso&tlng=es The effect of hydraulic retention time (HRT) and organic loading rate (OLR) on biological hydrogen production was assessed using an anaerobic fluidized bed reactor fed with cassava wastewater. The HRT of this reactor ranged from 8 to 1 h (28 to 161 kg COD/m³-d). The inoculum was obtained from a facultative pond sludge derived from swine wastewater treatment. The effluent pH was approximately 5.00, while the influent chemical oxygen demand (COD) measured 4000 mg COD/L. The hydrogen yield production increased from 0.13 to 1.91 mol H2/mol glucose as the HRT decreased from 8 to 2 h. The hydrogen production rate significantly increased from 0.20 to 2.04 L/h/L when the HRT decreased from 8 to 1 h. The main soluble metabolites were ethanol (1.87-100%), acetic acid (0.00-84.80%), butyric acid (0.00-66.78%) and propionic acid (0.00-50.14%). Overall, we conclude that the best hydrogen yield production was obtained at an HRT of 2 h. <![CDATA[<b>Performance of a biosurfactant produced by <i>Bacillus subtilis</i> LAMI005 on the formation of oil / biosurfactant / water emulsion</b>: <b>study of the phase behaviour of emulsified systems</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300004&lng=es&nrm=iso&tlng=es In this study, the phase behaviour of emulsified systems (oil + biosurfactant + water) was analyzed. The biosurfactant was produced in a 4-L batch bioreactor by Bacillus subtilis LAMI005, using residual glycerine from biodiesel production as a carbon source. Fourier Transform Infrared Spectroscopy (FT-IR), Nuclear Magnetic Resonance (NMR), and High Performance Liquid Chromatography (HPLC) analyses demonstrated that the biosurfactant produced by Bacillus subtilis (LAMI005) consists of a lipopeptide similar to surfactin. The influences of temperature and the composition of oil + biosurfactant + water were determined by using phase diagrams. Three types of oil were used, namely: motor oil, hydrogenated naphthenic oil (NH140) and castor bean oil. The emulsified systems were analyzed using optical micrography. The results presented here indicated that the biosurfactant produced in this work presents a potential use as stabilizing agent for oil-in-water emulsions. <![CDATA[<b>Drying of </b><b>α-amylase by spray drying and freeze-drying - a comparative study</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300005&lng=es&nrm=iso&tlng=es This study is aimed at comparing two traditional methods of drying of enzymes and at verifying the efficiency of each one and their advantages and disadvantages. The experiments were performed with a laboratory spray dryer and freeze-dryer using α-amylase as the model enzyme. An experimental design in star revealed that spray drying is mainly influenced by the inlet air temperature and feed flow rate, which were considered to be the main factors influencing the enzymatic activity and water activity; the long period of material exposure to high temperatures causes a partial activity loss. In the experiments of freeze drying, three methods of freezing were used (freezer, acetone and dry ice, and liquid nitrogen) and samples subsequently freeze-dried for times ranging between 0-24 hours. The product obtained from the two techniques showed high enzymatic activity and low water activity. For the drying of heat-resistant enzymes, in which the product to be obtained does not have high added value, spray drying may be more economically viable because, in the freeze drying process, the process time can be considered as a limiting factor when choosing a technique. <![CDATA[<b>Stability of immobilized <i>Rhizomucor miehei</i> lipase for the synthesis of pentyl octanoate in a continuous packed bed bioreactor</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300006&lng=es&nrm=iso&tlng=es The enzymatic synthesis of organic compounds in continuous bioreactors is an efficient way to obtain industrially important chemicals. However, few works have focused on the study of the operational conditions and the bioprocess performance. In this work, the aliphatic ester pentyl octanoate was obtained by direct esterification using a continuous packed bed bioreactor containing the immobilized enzyme Lipozyme® RM IM as catalyst. Enzymatic deactivation was evaluated under different conditions for the operational parameters substrate/enzyme ratio (5.00, 1.67, 0.83 and 0.55 mmol substrate∙min-1∙g-1enzyme) and temperature (30, 40, 50 and 60 °C). The optimal condition was observed at 30 ºC, which gave the minimum enzymatic deactivation rate and the maximum conversion to the desired product, yielding approximately 60 mmols of ester for an enzyme loading of 0.5 g into the bioreactor. A first-order deactivation model showed good agreement with the experimental data. <![CDATA[<b>Antimicrobial analysis of films processed from chitosan and N,N,N-trimethylchitosan</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300007&lng=es&nrm=iso&tlng=es Chitosan and its derivatives have been proposed as bactericidal and fungicidal agents against a large numbers of gram-negative and gram-positive bacteria and fungi. Some antimicrobial mechanisms have been proposed for chitosan, with the most widely acceptable being the presence of charged-NH3+ groups in the polymer backbone and its interactions with the bacterial wall constituents. Since this mechanism is based on an electrostatic interaction, it suggests that the greater the number of cationic amines, the higher will be the antimicrobial activity. So, in the present study, the effectiveness of commercial medium molecular weight chitosan and its ionic charged derivative (quaternized N,N,N-trimethylchitosan) were evaluated. Cast films of both materials were assessed against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative) as model bacteria by inhibition zone formation. The results show positive activity against the gram-positive microorganism for both materials. The antibacterial effectiveness of the chitosan derivative was dependent on the film polymer concentration. No activity however, was observed against the gram-negative species for either material in film form. The results point to the possibility of considering different antimicrobial mechanisms acting on each type of bacteria. <![CDATA[<b>Simulation and calibration of a full-scale sequencing batch reactor for wastewater treatment</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300008&lng=es&nrm=iso&tlng=es The aim of this study is to apply the main mathematical models used in activated sludge reactors, the Activated Sludge Model No. 1 (ASM1) and its variations (ASM2d and ASM3), to predict the behavior of a full-scale sequencing batch reactor (SBR) used for the treatment of domestic wastewater employing the software ASIM®. Two cycles were studied, the step-feed cycle and conventional filling. Samples were taken from the raw influent, from the reactor and from the treated wastewater, and these data were used to calibrate the models. The ASM1 model was the best model to represent the cycle with only an input, while model ASM3 was the best for simulating the scaled filling cycle. This work presents calibrated parameters for the two kinds of filling. The results of these simulations indicate that the calibration process succeeded and can be used as a model for future studies. <![CDATA[<b>AnSBBR with circulation applied to biohydrogen production treating sucrose based wastewater</b>: <b>effects of organic loading, influent concentration and cycle length</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300009&lng=es&nrm=iso&tlng=es An anaerobic sequencing batch biofilm reactor (AnSBBR) containing immobilized biomass and operating with recirculation of the liquid phase (total liquid volume 4.5 L; treated volume per cycle 1.9 L) was used to treat sucrose-based wastewater at 30 ºC and produce biohydrogen. The influence of applied volumetric organic load was studied by varying the influent concentration at 3600 and 5400 mgCOD.L-1 and using cycle lengths of 4, 3 and 2 hours, obtaining in this manner volumetric organic loads of 9, 12, 13.5, 18 and 27 gCOD.L-1.d-1. Different performance indicators were used: productivity and yield of biohydrogen per applied and removed load, reactor stability and efficiency based on the applied and removed organic loads, both in terms of organic matter (measured as COD) and carbohydrate (sucrose). The results revealed system stability (32-37% of H2 in biogas) during biohydrogen production, as well as substrate consumption (12-19% COD; 97-99% sucrose). Conversion efficiencies decreased when the influent concentration was increased (at constant cycle length) and when cycle lengths were reduced (at constant influent concentrations). The best yield was 4.16 mol-H2.kg-SUC-1 (sucrose load) at 9 gCOD.L-1.d-1 (3600 mgCOD.L-1 and 4 h) with H2 content in the biogas of 36% (64% CO2 and 0% CH4). However, the best specific molar productivity of hydrogen was 8.5 molH2.kgTVS-1.d-1 (32% H2; 68% CO2; 0% CH4), at 18 gCOD.L-1.d-1 (5400 mgCOD.L-1 and 3 h), indicating that the best productivity tends to occur at higher organic loads, as this parameter involves the "biochemical generation" of biogas, whereas the best yield tends to occur at lower and/or intermediate organic loads, as this parameter involves "biochemical consumption" of the substrate. The most significant metabolites were ethanol, acetic acid and butyric acid. Microbiological analyses revealed that the biomass contained bacilli and endospore filaments and showed no significant variations in morphology between different experimental conditions. <![CDATA[<b>Alkaline extraction of humic substances from peat applied to organic-mineral fertilizer production</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300010&lng=es&nrm=iso&tlng=es An organic-mineral fertilizer based on humic substances (HSs) and potassium was developed based on the alkaline extraction of HSs from peat. The HSs have interesting properties for use as a fertilizer since they improve the physical and chemical structure of the soil and provide a source of organic carbon which is readily absorbable by the plants, whereas potassium is a primary nutrient for plants. It was found that highly decomposed peats containing a small inorganic fraction are more favorable for the extraction of HSs. Using these peats, organic-mineral fertilizers that meet the Brazilian legislation have been obtained for a peat-extractant mixture containing 2.57 wt% total organic content (TOC), a K2O/TOC ratio of 1 wt% and an extraction time of 12 hours. <![CDATA[<b>Comparison between a conventional membrane bioreactor (C-MBR) and a biofilm membrane bioreactor (BF-MBR) for domestic wastewater treatment</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300011&lng=es&nrm=iso&tlng=es In this paper, the influence of biofilm carriers in a MBR on the performance of organic matter and nitrogen removal and the influence on membrane fouling were evaluated. The configurations studied included a Conventional Membrane Bioreactor (C-MBR) and a Biofilm Membrane Bioreactor (BF-MBR) operated in parallel, both fed with domestic wastewater. Regarding organic matter removal, no statistically significant differences were observed between C-MBR and BF-MBR, producing an effluent with a Soluble COD concentration of 27 ± 9.0 mgO2/L and 26 ±1.0 mgO2/L and BOD concentration of 6.0 ± 2.5 mgO2/L and 6.2 ± 2.1 mgO2/L, respectively. On the other hand, the BF-MBR produced a permeate with lower ammonia and total nitrogen concentrations, which resulted in a removal efficiency of 98% and 73%, respectively. It was also observed that the fouling rate was about 35% higher in the C-MBR than that for the BF-MBR, which also presented a reduction of total membrane resistance, about 29%, and increased operational cycle length around 7 days, compared to C-MBR. <![CDATA[<b>Effects of direct and alternating current on the treatment of oily water in an electroflocculation process</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300012&lng=es&nrm=iso&tlng=es In the direct current mode (DC), widely used in electroflocculation (EC), the formation of an impermeable oxide layer on the cathode causes the declining of the efficiency of this process. This disadvantage has been reduced by adopting alternating current (AC). In this study, the effects of AC and DC on operational parameters such as the removal of oils and greases (O&G), color and turbidity from oil-in-water (O/W) emulsions of the petroleum industry using aluminum electrodes were investigated. Removal efficiencies of 95%, 97% and 99% of O&G, color and turbidity with energy consumption of 0.280 kWh/m³ and electrode consumption of 0.12 g and 0.18 g were achieved at a current density of 3 A, operation time of 3 minutes and initial pH of 9.0 using AC and DC, respectively. In continuous flow tests performed with the same experimental conditions, the electrode consumption at times up to 60 minutes were 1.6 g and 3.4 g using AC and DC, respectively. <![CDATA[<b>Degradation of organic pollutants and characteristics of activated sludge in an anaerobic/anoxic/oxic reactor treating chemical industrial wastewater</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300013&lng=es&nrm=iso&tlng=es A laboratory-scale anaerobic/anoxic/oxic system operated at the hydraulic retention times (HRT) of 20, 40, and 60 h with mixed liquor suspended solids (MLSS) concentrations of 3 g/L and 6 g/L was considered for treating chemical industrial wastewater rich in complex organic compounds and total dissolved solids. Extending the HRT and increasing the MLSS concentration resulted in higher removal efficiency for chemical oxygen demand at 72%. Organic compounds in wastewater could be classified into easily-removed and refractory compounds during treatment. The easily-removed compounds consisted primarily of ethers, alcohols, and aldehydes, whereas the refractory compounds included mainly oxygen-containing heterocyclic and benzene-containing compounds. Results from energy-dispersive X-ray spectroscopy showed that several metal ions accumulated in activated sludge, particularly Fe(III). Fe accumulated mainly on the surface of sludge floc pellets and resulted in the compactness of activated sludge, which caused the values of mixed liquor volatile suspended solids /MLSS and sludge volume index to decrease. <![CDATA[<b>UASB reactor startup for the treatment of municipal wastewater followed by advanced oxidation process</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300014&lng=es&nrm=iso&tlng=es The present study was done to shorten the start-up time of up-flow anaerobic sludge blanket (UASB) reactor. Two different nutrients were used during the UASB start-up period, which was designed to decrease the hydraulic retention time (HRT) from 48 to 24 and 12 to 6 hrs at average temperatures of 25-34 ºC. In the first stage, start-up was with glucose for 14 days and then the reactor was also fed with macro- and micronutrients as a synthetic nutrient influent (SNI) from 15 to 45 days as the second stage. For the control, a second reactor was kept on glucose feeding from day 1 to 45. The removal efficiencies of the chemical oxygen demand (COD) were 80% and 98% on the 6th and 32nd day of the first and second stage, respectively. The maximum substrate removal rate of 0.08 mg COD mg-1 VSS d-1 was observed for glucose and synthetic nutrient influent (SNI) on the 8th and 40th days, respectively. When the reactor reached the maximum COD removal efficiency it was then shifted to municipal wastewater (MWW) mixed with industrial wastewater. The HRT was reduced gradually with a one week gap while treating MWW. For further cleaning, the UASB effluent was treated with 40% waste hydrogen peroxide. The whole integrated treatment process was successful to reduce the COD by 99%, total suspended solids (TSS) by 73%, total nitrogen (TN) by 84% and turbidity by 67%. <![CDATA[<b>Continuous catalyst-free production of esters from <i>Jatropha curcas</i> L. oil under supercritical ethanol</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300015&lng=es&nrm=iso&tlng=es In the present study, the transesterification of Jatropha oil in a continuous catalyst-free process using supercritical ethanol was investigated. Experiments were performed in a packed-bed tubular reactor by studying the effect on the reaction of temperature, pressure, water and cosolvent (n-hexane) concentrations, keeping the oil:ethanol mass ratio fixed at 1:1 for different residence times. The results demonstrated that temperature and pressure had a positive effect on fatty acid ethyl ester (FAEE) production and it was observed that the free fatty acids present in vegetable oil promote faster reaction kinetics due to simultaneous esterification and transesterification reactions. The addition of water and a cosolvent increased the FAEE yields at 573 K and 20 MPa. Within the experimental ranges investigated, water and the cosolvent decreased the decomposition of fatty acids. Appreciable reaction yields (~90 wt%) were achieved at 573 K, 20 MPa, with an oil:ethanol mass ratio of 1:1 and 10 wt% water. <![CDATA[<b>Synthesis and physicochemical characterization of titanium oxide and sulfated titanium oxide obtained by thermal hydrolysis of titanium tetrachloride</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300016&lng=es&nrm=iso&tlng=es This work reports the synthesis of titanium oxide (TiO2) and sulfated titanium oxide (TiO2-SO4(2-)) obtained by thermal hydrolysis of titanium tetrachloride. Titanium hydroxide synthesized by this method was impregnated with a 1 N H2SO4 solution, to give amounts of sulfate ions (SO4(2-)) of 3 and 7 wt%. The synthesized samples were dried at 120 °C during 24 h and then calcined for 3 h at 400 °C. Thermal analyses, X-ray diffraction, nitrogen physisorption, infrared spectroscopy, potentiometric titration with n-butylamine, U.V.-visible diffuse reflectance spectroscopy and scanning electron microscopy were used to characterize the materials. The results of physicochemical characterization revealed that a mixture of crystalline structures, anatase, brookite and rutile developed in the titanium oxide, stabilizing the anatase structure in the sulfated titanium oxides, and coexisting with a small amount of brookite structure. The synthesized mesoporous materials developed specific surface areas between 62 and 70 m² g-1, without detecting an important influence of sulfation on this parameter. The presence of sulfate ions improved the acidity of titanium oxide and modified the characteristics of light absorption in the 425-600 nm region, which suggests the possibility of using these materials in reactions assisted by visible light. <![CDATA[<b>Myoglobin entrapment in poly(vinyl alcohol) dense membranes</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300017&lng=es&nrm=iso&tlng=es Our goal in this study was the immobilization of myoglobin in poly(vinyl alcohol) dense membranes. Glutaraldehyde was investigated both as the crosslinking agent, aiming to increase the membrane stability in aqueous medium, and as the vehicle to bind myoglobin and PVA. Reaction and membrane synthesis were carried simultaneously in mild operating conditions in order to maintain the native protein folding. Membrane characterization comprised the water swelling degree, DSC, TGA, UV-visible spectroscopy, FTIR analysis and oxygen transport in a dialysis cell. The incorporation of myoglobin in the film decreased the water swelling degree and improved the membrane thermal properties compared to unmodified PVA membrane. The reduction of ferric iron in the prosthetic group of the protein to the ferrous form was observed. The increased affinity between oxygen and the immobilized myoglobin did not favor the release of this solute from the biocarrier. <![CDATA[<b>Catalytic oxidation of volatile organic compounds (n-hexane, benzene, toluene, o-xylene) promoted by cobalt catalysts supported on </b><b>γ-Al<sub>2</sub>O<sub>3</sub>-CeO<sub>2</sub></b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300018&lng=es&nrm=iso&tlng=es Cobalt catalysts supported on γ-alumina, ceria and γ-alumina-ceria, with 10 or 20%wt of cobalt load, prepared by the wet impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission transmission electron microscopy (FETEM), N2 adsorption-desorption isotherms (BET/BJH methods), energy-dispersive X-ray spectroscopy (EDX), X-ray photoemission spectroscopy (XPS), O2-chemisorption and temperature programmed reduction (TPR) were used to promote the oxidation of volatile organic compounds (n-hexane, benzene, toluene and o-xylene). For a range of low temperatures (50-350 °C), the activity of the catalysts with a higher cobalt load (20% wt) was greater than that of the catalysts with a lower cobalt load (10% wt). The Co/γ-Al2O3-CeO2 catalytic systems presented the best performances. The results obtained in the characterization suggest that the higher catalytic activity of the Co20/γ-Al2O3-CeO2 catalyst may be attributed to the higher metal content and amount of oxygen vacancies, as well as the effects of the interaction between the cobalt and the alumina and cerium oxides. <![CDATA[<b>State estimation of chemical engineering systems tending to multiple solutions</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300019&lng=es&nrm=iso&tlng=es A well-evaluated state covariance matrix avoids error propagation due to divergence issues and, thereby, it is crucial for a successful state estimator design. In this paper we investigate the performance of the state covariance matrices used in three unconstrained Extended Kalman Filter (EKF) formulations and one constrained EKF formulation (CEKF). As benchmark case studies we have chosen: a) a batch chemical reactor with reversible reactions whose system model and measurement are such that multiple states satisfy the equilibrium condition and b) a CSTR with exothermic irreversible reactions and cooling jacket energy balance whose nonlinear behavior includes multiple steady-states and limit cycles. The results have shown that CEKF is in general the best choice of EKF formulations (even if they are constrained with an ad hoc clipping strategy which avoids undesired states) for such case studies. Contrary to a clipped EKF formulation, CEKF incorporates constraints into an optimization problem, which minimizes the noise in a least square sense preventing a bad noise distribution. It is also shown that, although the Moving Horizon Estimation (MHE) provides greater robustness to a poor guess of the initial state, converging in less steps to the actual states, it is not justified for our examples due to the high additional computational effort. <![CDATA[<b>Effects of temperature-dependent viscosity on fluid flow and heat transfer in a helical rectangular duct with a finite pitch</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300020&lng=es&nrm=iso&tlng=es An incompressible fully developed laminar flow in a helical rectangular duct having finite pitch and curvature with temperature-dependent viscosity under heating condition is studied in this work. Both the cases of one wall heated and four walls heated are studied. The cross-sectional dimensions of the rectangular duct are 2a and 2b. The aspect ratio n=2b/2a is 0.5. Water is used as the fluid and Reynolds number (Re) is varied in the range of 100 to 400. The secondary flow with temperature-dependent viscosity is enhanced markedly as compared to constant viscosity. An additional pair of vortices is obtained near the center of the outer wall at Re=400 for the model of four walls heated with temperature-dependent viscosity, y, while for constant viscosity, the appearance of two additional vortices near the outer wall cannot be found. Besides, the axial velocity decreases and the temperature increases at the central region of the rectangular duct when the temperature-dependent viscosity is considered. Due to the decrease of the viscosity near the walls, the friction factor obtained with temperature-dependent viscosity is lower than that of constant viscosity, while the convective heat transfer for temperature-dependent viscosity is significantly enhanced owing to the strengthened secondary flow. Especially for four heated walls, the effects of viscosity variation on the flow resistance and heat transfer are more significant. <![CDATA[<b>Biosorption of Mn (II), Co (II) and Cr (VI) in a horizontal rotating tubular bioreactor</b>: <b>experiments and evaluation of the integral bioprocess model</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300021&lng=es&nrm=iso&tlng=es In this research, a multi heavy metals removal process with mixed microbial culture was examined in a horizontal rotating tubular bioreactor (HRTB) with different combinations of process parameters. Three metals were selected as examples of cations (manganese and cobalt) and oxy-anion (hexavalent chromium). Hydrodynamic conditions and biomass sorption capacity in the HRTB had the main impact on the heavy metals removal efficiencies, which were for Mn2+ 87.0-93.6%, Co2+ 89.0-95.7% and Cr6+ 99.7-100%, respectively. For the bioprocess description in the HRTB, the integral bioprocess model that combines hydrodynamics, mass transfer and kinetics was used. This model was evaluated for the new experimental conditions and average variances between experimental and simulated data were in the range of 0.12 - 3.21·10-3. The results obtained clearly show that the integral bioprocess model is able to describe the heavy metal removal process in the HRTB. <![CDATA[<b>Measurement and correlation of isobaric vapor-liquid equilibrium for the binary system of cyclopentane and tetrahydrofuran</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300022&lng=es&nrm=iso&tlng=es Isobaric vapor-liquid equilibrium (VLE) data for the cyclopentane and tetrahydrofuran (THF) system were measured at 101.3 kPa by using an equilibrium still. Thermodynamic consistency of the experimental data was confirmed by means of the Herington method. The experimental data were correlated and calculated by the Margules, Van Laar and Wilson activity-coefficient models, respectively. The Wilson and Van Laar activity-coefficient models are better than the Margules activity-coefficient model based on the average absolute deviations of temperature and the vapor-phase composition. For the Wilson and Van Laar activity-coefficient models the average absolute deviations between the experimental and the calculated values were 0.24 K and 0.23 K for the boiling point, and 0.0040 for vapor-phase composition, respectively. These agree well with the experimental data. Therefore, it was shown that the Wilson and Van Laar activity-coefficient models satisfactorily correlate the experimental results of the cyclopentane and tetrahydrofuran system. <![CDATA[<b>A study of parameters affecting the solvent extraction of lactic acid from fermentation broth</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322014000300023&lng=es&nrm=iso&tlng=es Lactic acid has recently been drawing much interest as a raw material for biodegradable polymer. One of the promising technologies for recovery of lactic acid from fermentation broth is reactive liquid - liquid extraction. Equilibrium studies on the reactive extraction of lactic acid with trioctylamine (TOA) in various organic phases and its re-extraction into aqueous solutions were carried out. In this study distribution coefficient, extractability, stripping efficiency of various active and inert diluents with TOA as extractant were investigated, which were higher for active diluents. The effects of operating temperature, speed of agitation, agitation time and diluent composition on extraction efficiency were also studied. Temperature and extraction efficiency were inversely proportional to each other, whereas extraction efficiency was little affected by speed of agitation and agitation time.