Resumo em Inglês:

The objective of this research was to improve Glucose-6-phosphate dehydrogenase (G6PD) production by Saccharomyces cerevisiae W303-181, which carry the plasmid YEpPGK-G6PD, by varying the following cultivation conditions: pH value (4.8, 5.7 and 6.6); inoculum concentration (0.1, 0.6 and 1.1 g/L) and initial glucose concentration (20.0, 30.0 and 40.0 g/L). The effect of those variables on G6PD production capability was studied by the application of response surface statistical analysis. The results showed that the highest G6PD production (1594.2 U/L), specific activity (1189.7 U/g cell) and productivity (45.6 U/L.h) occurred at pH 4.8, inoculum concentration of 0.1 g/L and initial glucose concentration of 20.0 g/L, under agitation of 150 rpm at 30ºC after 36 h. In this work, the strain expressed about 21 fold more activity than the wild S. cerevisiae strain, being an attractive and promising new source of this enzyme.

Resumo em Inglês:

The alternatives used for minimizing the usage of chlorine dioxide in bleaching sequences included a hot acid hydrolysis (Ahot) stage, the use of hot chlorine dioxide (Dhot) and ozone stages at medium consistency and high consistency (Zmc and Zhc), in addition to stages with atmospheric hydrogen peroxide (P) and pressurized hydrogen peroxide (PO). The results were interpreted based on the cost of the chemical products, bleaching process yields and on minimizing the environmental impact of the bleaching process. In spite of some process restrictions, high ISO brightness levels were kept around 90 % brightness. Additionally, the inclusion of stages like acid hydrolysis, pressurized peroxide and ozone in the bleaching sequences provided an increase in operating flexibility, aimed at reducing environmental impact (ECF Light). The Dhot(EOP)D(PO) sequence presented lower operating cost for ISO brightness above 92 %. However, this kind of sequence was not allowed for closing the wastewater circuit, even partially. For ISO brightness level around 91%, the AhotZhcDP sequence presented a lower operating cost than the others.

Resumo em Inglês:

Styrene-butadiene rubber (SBR) has large applications in the shoe industry, especially as expanded sheets used to produce insoles and inner soles. According to TG analysis, the rubber content in SBR residues (SBR-r) was found to be around 26-wt%. Based on that data, a cost-effective technique for the reuse of SBR-r in Nitrile rubber (NBR) was developed. Later, the effect of SBR-r on the cure behavior, mechanical performance, swelling, and crosslink density of reused rubber was investigated, with more emphasis placed on the effect of both particle size and loading of waste filler. Cure characteristics such as optimum cure time and scorch time were then reduced by the increasing amount of SBR-r filler. Owing to the reinforced nature of the largest particle size SBR-r, the best results for the mechanical properties of NBR were those in which SBR-r was added at the end of the cure process. The study has thus shown that SBR residue (SBR-r) can be used as an economical alternative filler in NBR.

Resumo em Inglês:

In this investigation, a large number of experiments have been performed to measure the nucleate boiling heat transfer coefficients of water/diethanolamine (DEA) and water/monoethanolamine (MEA) binary solutions. Based on these experimental data, effects of physical properties such as surface tension and viscosity of mixtures on nucleate boiling heat transfer coefficients and also on bubble dynamics have been discussed. Meanwhile, some photographs have also been selected which illustrate the behaviours of bubbles near the heat transfer surface. In this article, a new correlation has been developed on the basis of the correlation of Stephan and Körner which is known as a successful correlation for the prediction of nucleate boiling heat transfer coefficients of mixtures. Comparison of the prediction of this new correlation with experimental data indicates that this modification can significantly improve the performance of the Stephan and Körner correlation.

Resumo em Inglês:

In this work, boundary layer development was investigated for a mass transfer process between a moving fluid and a slightly soluble cylinder or plane surface buried in a packed bed, in alignment with the direction of flow. The bed of inert particles is taken to have uniform voidage. For this purpose, numerical solutions of the partial differential equations describing mass concentration of the solute were undertaken to obtain the concentration boundary layer thickness as a function of the relevant parameters. Mathematical expressions that relate the dependence with the Peclet number and aspect ratio of the immersed active surfaces are proposed to describe the approximate size of the concentration boundary layer thickness.

Resumo em Inglês:

In this paper, direct tracking method as an image analysis based technique for measuring electrospun nanofiber diameter has been presented and compared with distance transform method. Samples with known characteristics generated using a simulation scheme known as µ-randomness were employed to evaluate the accuracy of the method. Electrospun webs of polyvinyl alcohol (PVA) were also used to verify the applicability of the method on real samples. Since direct tracking as well as distance transform require binary input images, micrographs of the electrospun webs obtained from Scanning Electron Microscopy (SEM) were first converted to black and white using local thresholding. Direct tracking resulted in more accurate estimations of fiber diameter for simulated images as well as electrospun webs suggesting the usefulness of the method for electrospun nanofiber diameter measurement.

Resumo em Inglês:

In this work, a series of perovskite-type mixed oxide LaMo xV1-xO3+δ powder catalysts (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0, with 0.5 < δ < 1.5), prepared by the sol-gel process and calcined at 750ºC, provide an attractive and effective alternative means of synthesizing materials with better control of morphology. Structures of resins obtained during the gel formation process by FT-IR spectroscopy and XRD analysis showed that all the LaMo xV1-xO3+δ samples are single phase perovskite-type solid solutions. The surface area (BET) between 2.5 - 5.0 m²/g (x = 0.1 and 1.0 respectively) increases with increasing Mo ratio in the samples. They show high purity, good chemical homogeneity, and lower calcinations temperatures as compared with the solid-state chemistry route. SEM coupled to EDS and thermogravimetric analysis/differential thermal analyses (TGA/DTA) have been carried out in order to evaluate the homogeneity of the catalyst. Finally, the experimental studies show that the calcination temperature and Mo content exhibited a significant influence on catalytic activity. Among the LaMo xV1-xO3+δ samples, LaMo0.7V0.3O4.2 showed the best catalytic activity for the topic reaction and the best activity and stability for ethane reforming at 850ºC under 8 bar.

Resumo em Inglês:

The photocatalytic degradation of phenol in aqueous suspensions of TiO2 under different salt concentrations in an annular reactor has been investigated. In all cases, complete removal of phenol and mineralization degrees above 90% were achieved. The reactor operational parameters were optimized and its hydrodynamics characterized in order to couple mass balance equations with kinetic ones. The photodegradation of the organics followed a Langmuir-Hinshelwood-Hougen-Watson lumped kinetics. From GC/MS analyses, several intermediates formed during oxidation have been identified. The main ones were catechol, hydroquinone, and 3-phenyl-2-propenal, in this order. The formation of negligible concentrations of 4-chlorophenol was observed only in high salinity medium. Acute toxicity was determined by using Artemia sp. as the test organism, which indicated that intermediate products were all less toxic than phenol and a significant abatement of the overall toxicity was accomplished, regardless of the salt concentration.

Resumo em Inglês:

A modification of Smith predictor for controlling higher order processes with integral action and long dead-time is proposed in this paper. The controller used in this Smith predictor is an Integral-Proportional Derivative controller, where the Integrator is in the forward path and the Proportional and Derivative control are in the feedback, acting on the feedback signal. The main objective of this paper is to design a dead time compensator, which has minimum tuning parameters, simple controller tuning, and robust performance of tuning formulae, and to obtain a critically damped system that is as fast as possible in its set point and load disturbance rejection performance. The controller in this paper is tuned by an adaptive method. This paper also presents a survey of various dead time compensators and their performance analysis.

Resumo em Inglês:

This paper presents an application of Artificial Neural Network (ANN) and Genetic Algorithm (GA) for system identification for controller tuning in a pH process. In this paper, the ANN based approach is applied to estimate the system parameters. Once the variations in parameters are identified frequently, GA optimally tunes the controller. The simulation results show that the proposed intelligent technique is effective in identifying the parameters and has resulted in a minimum value of the Integral Square Error, peak overshoot and minimum settling time as compared to conventional methods. The experimental results show that their performance is superior and it matches favorably with the simulation results.

Resumo em Inglês:

In this work a strategy is presented for the temperature control of the polymerization reaction of styrene in suspension in batch. A three-layer feed forward Artificial Neural Network was trained in an off-line way starting from a removed group of patterns of the experimental system and applied in the recurrent form (RNN) to a Predictive Controller based on a Nonlinear Model (NMPC). This controller presented very superior results to the classic controller PID in the maintenance of the temperature. Still to improve the performance of the model used by NMPC (RNN) that can present differences in relation to the system due to the dead time involved in the control actions, nonlinear characteristic of the system and variable dynamics; an on-line adjustment methodology of the parameters of the exit layer of the Network is implemented, presenting superior results and treating the difficulties satisfactorily in the temperature control. All the presented results are obtained for a real system.

Resumo em Inglês:

In this study, activated sludge was used as a precursor to prepare activated carbon using sulfuric acid as a chemical activation agent. The effect of preparation conditions on the produced activated carbon characteristics as an adsorbent was investigated. The results indicate that the produced activated carbon has a highly porous structure and a specific surface area of 580 m²/g. The FT-IR analysis depicts the presence of a variety of functional groups which explain its improved adsorption behavior against pesticides. The XRD analysis reveals that the produced activated carbon has low content of inorganic constituents compared with the precursor. The adsorption isotherm data were fitted to three adsorption isotherm models and found to closely fit the BET model with R² equal 0.948 at pH 3, indicating a multilayer of pesticide adsorption. The maximum loading capacity of the produced activated carbon was 110 mg pesticides/g adsorbent and was obtained at this pH value. This maximum loading was found experimentally to steeply decrease as the solution pH increases. The obtained results show that activated sludge is a promising low cost precursor for the production of activated carbon.

Resumo em Inglês:

The knowledge of the phase equilibrium is one of the most important factors to study the design of separation processes controlled by the equilibrium. Fatty acids are present in high concentration as by-products in vegetable oils but the equilibrium data involving these components is scarce. The objective of this work is the experimental determination of the liquid-vapor equilibrium of five binary different systems formed by carbon dioxide and palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3). The equilibrium experimental data was collected at 40, 60 and 80ºC at 60, 90 and 120 bar, at the extract and raffinate phases, using an experimental apparatus containing an extractor, a gas cylinder and pressure and temperature controllers. The data was modeled using the cubic equation of state of Peng-Robinson with the mixing rule of van der Waals with binary interaction parameters. The model was adequate to treat the experimental data at each temperature and at all the temperatures together. The best model that includes the van der Waals mixing rule with two parameters has maximum deviation of 17%. The distribution coefficients were also analyzed and it was concluded that the fractionation of the fatty acids is possible using supercritical carbon dioxide.

Resumo em Inglês:

This work focuses on the adsorption of Bromelain in expanded bed conditions, such as the adsorption kinetics parameters. The adsorption kinetics parameters showed that after 40 minutes equilibrium was achieved and maximum adsorption capacity was 6.11 U per resin mL. However, the maximum adsorption capacity was only determined by measuring the adsorption isotherm. Only by the Langmuir model the maximum adsorption capacity, Qm, and dissociation constant, kd, values could be estimated as 9.18 U/mL and 0.591, respectively, at 25 ºC and 0.1 mol/L phosphate buffer pH 7.5. A column made of glass with an inner diameter of 1 cm was used for the expanded bed adsorption (EBA). The residence time was reduced 10 fold by increasing the expansion degree 2.5 times; nonetheless, the plate number (N) value was reduced only 2 fold. After adsorption, the bromelain was eluted in packed bed mode, with a downward flow. The purification factor was about 13 fold and the total protein was reduced 4 fold. EBA showed to be feasible for purification of bromelain.

Resumo em Inglês:

This work presents a method to analyze hydrogen production by biomass gasification, as well as electric power generation in small scale fuel cells. The proposed methodology is the thermodynamic modeling of a reaction system for the conversion of methane and carbon monoxide (steam reforming), as well as the energy balance of gaseous flow purification in PSA (Pressure Swing Adsorption) is used with eight types of gasification gases in this study. The electric power is generated by electrochemical hydrogen conversion in fuel cell type PEMFC (Proton Exchange Membrane Fuel Cell). Energy and exergy analyses are applied to evaluate the performance of the system model. The simulation demonstrates that hydrogen production varies with the operation temperature of the reforming reactor and with the composition of the gas mixture. The maximum H2 mole fraction (0.6-0.64 mol.mol-1) and exergetic efficiency of 91- 92.5% for the reforming reactor are achieved when gas mixtures of higher quality such as: GGAS2, GGAS4 and GGAS5 are used. The use of those gas mixtures for electric power generation results in lower irreversibility and higher exergetic efficiency of 30-30.5%.

Resumo em Inglês:

Liquid-Liquid equilibrium data were obtained for the polyethylene glycol2000(PEG2000)-sodium citrate-water system at 298.15, 308.15 and 318.15 K. The effect of temperature on binodal and tie line data was studied and published in a previous article (Murugesan and Perumalsamy, 2005). The interaction parameters of ASOG and UNIFAC models were estimated using the LLE data of PEG2000-sodium citrate-water system and are used to predict the LLE data for PEG6000-sodium citrate-water system at 298.15, 308.15 and 318.15 K (literature data). The predicted LLE data by both ASOG and UNIFAC models showed good agreement with the experimental and literature data.

Resumo em Inglês:

Sorption isotherms of castor seeds were evaluated at 30, 40, 50 and 60ºC using the static gravimetric method. Sigmoid trends were observed for isotherms obtained showing a clear effect of temperature. Experimental values were adjusted using the modified isotherms of Henderson, Halsey, Oswin and Guggenheim-Anderson-de Boer (GAB). Models were compared using four statistics parameters. The results showed that Modified Henderson model adjusted adequately the experimental values in the range of temperature evaluated. The experimental values of the safe storage moisture content for castor seeds varied between 6.1 to 8.4 % (d.b.) between 20 and 40ºC, showing lower values than those reported for other traditional oilseeds as sunflower or rapeseed. The sorption heats evaluated from the combination of Clapeyron equation and Modified Henderson equation varied between 3400 and 2373 kJ/kg for moisture contents between 1 and 28 % (d.b.). Through Othmer relationship the value of the ratio Lb/Lf varied between 1.01 and 1.34 (for 14.5 and 1% d.b. moisture content respectively). The values obtained showed an exponential relationship with moisture content, of the form Lb/Lf=1+0.44exp(-0.17M) with a determination coefficient R² of 0.97.

Resumo em Inglês:

In recent times, the microalgae Spirulina platensis has been used as a functional ingredient in several food applications; its process involving drying and storage steps. Moisture equilibrium data for adsorption isotherms of microalgae Spirulina were investigated at 10, 20 and 30ºC and for desorption, at 40, 50 and 60ºC, using the gravimetric static method. The experimental data were analyzed by GAB and BET models. The GAB equation showed the best fitting to the experimental data with R² ≈ 99% and MRE < 10%. The water surface area values calculated by GAB and BET models were very similar. The isosteric heats were determined by application of Clausius-Clapeyron equation to sorption isotherms obtained from the best-fitting equation. The isosteric heat and the entropy of desorption isotherm presented similar behavior, with a sharp change in an equilibrium moisture content of 10%. The enthalpy-entropy compensation theory was applied to the isotherms, indicating that they are enthalpy-controlled.

Resumo em Inglês:

Equations of state are useful for description of fluid properties such as pressure-volume-temperature (PVT). However, the success estimation of such correlations depends mainly on the range of data which have originated. Therefore new models are highly required. In this work a new method is proposed based on Artificial Neural Network (ANN) for estimation of PVT properties of compounds. The data sets were collected from Perry's Chemical Engineers' Handbook. Different training schemes for the back-propagation learning algorithm, such as; Scaled Conjugate Gradient (SCG), Levenberg-Marquardt (LM) and Resilient back Propagation (RP) methods were used. The accuracy and trend stability of the trained networks were tested against unseen data. The LM algorithm with sixty neurons in the hidden layer has proved to be the best suitable algorithm with the minimum Mean Square Error (MSE) of 0.000606. The ANN's capability to estimate the PVT properties is one of the best estimating method with high performance.

Resumo em Inglês:

A laboratory-scale simulated moving bed (SMB) was designed and tested for the separation of paclitaxel, a powerful anti-cancer agent known as Taxol@, from impurities of a plant tissue culture (PTC) broth. The innovative strategy of a pseudo-binary model, where mixtures A and B were treated as single solutes A and B, was used in the linear standing wave analysis to fix the SMB operating parameters for a multicomponent and complex system. Linear standing wave design was used to specify the zone flow rates and the switching time for the laboratory-scale SMB unit, with two steps of separation. The SMB consists of four packed columns, where each column is 12.5 cm in length and 1.5 cm in diameter. Two sequential separation steps were used to recover paclitaxel from a small feed batch (less than one liter). Placlitaxel was recovered from the complex plant tissue culture broth in 82% yield and 72% purity.

Resumo em Inglês:

The purpose of this work was to study the mass transfer performance of rotating packed beds applying the "Higee" process. The operations were carried out with the n-hexane/n-heptane distilling system at atmospheric pressure and under total reflux conditions. The rotating speed could be varied between 300 and 2500 rpm, which provided centrifugal forces from 5 to 316 times the Earth's gravity. The effects of concentration, vapor velocity, rotating speed and packing type (two different Raschig ring sizes and structured wire mesh packing) on mass transfer behavior were analyzed. Experimental results showed that the mass transfer coefficient depends on the liquid flow rates and rotating speed. The equipment had high separation efficiency in a reduced bed volume.