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Biblioteca Digital do IPB (53.442 recursos)

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DTQB - Actas de Congressos Indexados ao ISI

Mostrando recursos 1 - 20 de 24

  1. Sorption of carbon dioxide on binderless beads of 13X

    Silva, José A.C.; Schumann, Kristin; Rodrigues, A.E.
    The sorption equilibrium of CO2 and CH4 in binderless beads of 13X zeolite has been investigated between 313 and 373 K and pressure up to 4 atm. The amount adsorbed of CO2 and CH4 is around 5.2 mmol/gads and 1.2 mmol/gads, respectively, at 313 K and 4 atm. Comparing these values with the ones in literature the value of CO2 is 20% higher than in CECA 13X binder pellets. The crystal diffusivity of CO2 measured experimentally by the ZLC technique is 5.8×10-15 m2/s and 1.3×10-15 m 2/s at 373 and 313 K, respectively. These values are in the same order...

  2. Modeling studies on the synthesis of superabsorbent hydrogels using population balance equations

    Gonçalves, Miguel; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui
    The synthesis of super-absorbent hydrogels is simulated using a kinetic model based upon population balance equations of generating functions. Dynamics in a batch reactor of properties such as the weight fraction of gel or average molecular weights of the soluble fraction can be predicted. This kinetic model neglects intramolecular cyclization reactions for simplicity (hence predictions can be valid only for very small amounts of crosslinker) but it can accommodate the operation with different kinds of crosslinking agents, namely bifunctional (e.g. N,N0- methylenebisacrylamide), trifunctional (e.g. trimethylolpropane triacrylate) and tetrafunctional (e.g. tetraallyloxyethane). The influence of the use of such different kinds of crosslinkers on the dynamics of gelation is discussed. It...

  3. The use of model samples to estimate the level of fraudulent addition of pork meat in poultry meat by real-time PCR

    Soares, Sónia; Amaral, J.S.; Mafra, I.; Oliveira, M.B.P.P.
    The undeclared presence of meat species in grounded and comminuted meat products is a concern because it represents an economic fraud, but also for public health, ethical and religious reasons. Meat species identification allows detecting adulterations such as the fraudulent substitution of cheaper meats for more expensive ones. In this work, model samples were prepared at the laboratory containing poultry meat added with known amounts of pork meat. DNA was extracted from the model samples and a real-time polymerase chain reaction (PCR) technique using the SYBR Green I fluorescent dye coupled to melting curve analysis was proposed to obtain a...

  4. A segmentation approach for the identification of hazelnut cultivars

    Rodrigues, Pedro; Amaral, J.S.; Santos, Alberto; Igrejas, Getúlio
    The development of a methodology for cultivar discrimination and selection during on-line quality selection could be a relevant tool for certain industries that use hazelnuts as ingredients in processed food products. The aim of this work was to obtain a computer vision system that enables an automatic recognition of six hazelnuts cultivars from 3 different origins (US, Italy and Spain). To achieve this objective, an algorithm for tuning the segmentation between the hazelnut shell and crown was developed. Important morphological features that allow the correct identification of the cultivar present in an image were obtained from the segmentation process. Finally,...

  5. A T-S fuzzy model based on initial FCM partition to estimate the composition of commercial blended vegetable oils

    Igrejas, Getúlio; Amaral, J.S.; Rodrigues, Pedro; Oliveira, M.B.P.P.
    Several samples of four types of vegetable oils (sunflower, soybean, corn and peanut oils) produced and/or refined in Portugal were analyzed for their fatty acid composition. Data obtained was used to build a fuzzy model to predict the amounts of different vegetable oils (VO) in commercial blends. The strategy used was a combination of a fuzzy clustering method (Fuzzy C-means) and a Takagi-Sugeno fuzzy model. Model was tested with the data from the analysis of simulated blended VO prepared in the laboratory. Results proved the ability of the model in predicting the blend composition. The model was then used to...

  6. Bioleaching of hexavalent chromium from soils using Acidithiobacillus thiooxidans

    Fonseca, Bruna; Rodrigues, Joana; Queiroz, A.M.; Tavares, Teresa

  7. Liquid phase stability via global optimization

    Rodrigues, Vânia; Pereira, Ana I.; Ferreira, Olga; Pinho, Simão
    In this work, the Penalty Stretched Simulated Annealing Method and the Multilocal Branch and Bound method were applied to identify the stationary points of the tangent plane distance function defined for the Gibbs energy. The classic excess Gibbs energy Non Random Two Liquid model was used for these studies in several multicomponent mixtures, for which specific numerical difficulties were shown. The preliminary results obtained by applying the methodology developed in this work were satisfactory.

  8. Kinetic Modeling of the Suspension Copolymerization of Styrene/Divinylbenzene with Gel Formation

    Gonçalves, Miguel; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui
    Experimental and theoretical studies concerning the suspension copolymerization of styrene with divinylbenzene are reported. Experiments were carried out in a batch stirred reactor, at 1.2 dm3 scale, and extended beyond gelation in order to synthesize insoluble material. Looking for real time information concerning the building process of such materials, these polymerizations were In-line monitored using a FTIR-ATR immersion probe. Polymer samples collected before and after gelation were Off-line characterized using a SEC/RI/MALLS system allowing the measurement of monomer conversion, average molecular weights, MWD and also the z-average radius of gyration. The weight fraction of insoluble material (gel) was measured for...

  9. FTIR-ATR monitoring and SEC/RI/MALLS characterization of ATRP synthesized hyperbranched polyacrylates

    Gonçalves, Miguel; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui
    This work reports the synthesis at 1 L scale of hyperbranched polyacrylates based upon acrylate/diacrylate monomers such as n-butyl acrylate (nBA)/1,6-hexanediol diacrylate (HDDA) and using atom transfer radical polymerization (ATRP). A FTIR-ATR immersion probe was used to monitor the polymerization reaction. The dynamics of the build-up of polymer structure was studied by off-line analysis of samples at different reaction times by size exclusion chromatography (SEC) with detection of refractive index (RI) and multi-angle laser light scattering (MALLS) signals, leading to molecular weight distribution and z-average radius of gyration. Kinetic measurements and observed parameters of the molecular architecture are compared with...

  10. Flow of physiological fluids in microchannels: the sedimentation effect

    Garcia, Valdemar; Correia, Teresa Montenegro; Dias, Ricardo P.; Lima, R.
    Microfluidic devices are becoming one of the most promising new tools for diagnostic applications and treatment of several chronic diseases. Hence, it is increasingly important to investigate the rheological behaviour of physiological fluids in microchannels. The main purpose of the present experimental work is to investigate the flow of two different physiological fluids frequently used in microfluidic devices. The working fluids were physiological saline (PS) and dextran 40 (Dx40) containing about 6% of sheep red blood cells (RBCs), respectively. The capillaries were placed horizontally on a slide glass and the flow rate of the working fluids was kept constant by using a syringe pump. By means of a camera the images were...

  11. Kinetic modeling of the molecular architecture of cross-linked copolymers synthesized by controlled radical polymerization techniques

    Gonçalves, Miguel; Trigo, Ivone; Dias, Rolando; Costa, Mário Rui
    A recently developed general kinetic approach, based on population balances in terms of generating functions, is applied to the modeling of the molecular architecture of branched copolymers produced through controlled radical polymerization (CRP) techniques, namely nitroxide-mediated radical polymerization (NMRP) and atom-transfer radical polymerization (ATRP). Thanks to this method, it is possible to carry out dynamic predictions of distributions of molecular weights, sequence lengths and z-average mean square radius of gyration of the products, both before and after gelation (whenever it occurs) with consideration of complex kinetic schemes. The model chemical systems styrene + divinylbenzene (S/DVB) and methyl methacrylate + ethylene...

  12. Prediction and experimental characterization of the molecular architecture of FRP and ATRP synthesized polyacrylate networks

    Gonçalves, Miguel; Dias, Rolando; Costa, Mário Rui
    This work reports experimental and modeling studies concerning the conventional (FRP) and atom transfer radical polymerization (ATRP) of acrylate/diacrylate monomers. In the framework of a recently developed general approach, kinetic models including crosslinking reactions and branching by chain transfer to polymer are discussed for FRP and ATRP polymerization systems. Besides molecular weight distribution (MWD), fairly good predictions of the z-average radius of gyration could be obtained for these non-linear polymers. A set of experiments was performed at 1 L scale in a batch reactor using n-butyl acrylate (BA) or methyl acrylate (MA) as monovinyl monomers and 1,6-Hexanediol diacrylate (HDDA) or...

  13. Removal of zinc by biomass of aquatic mosses

    Martins, Ramiro; Boaventura, Rui
    The utilization of aquatic mosses for the treatment of wastewater containing heavy metals is gaining more attention as a simple, effective and economic means of pollution remediation. The effect of various parameters such as contact time, initial metal ion concentration and temperature on zinc biosorption onto the aquatic moss Fontinalis antipyretica was studied. The maximum zinc uptake by Fontinalis antipyretica in batch system at pH 5.0, adsorbent dose of 2 g l-1 and 20ºC was found to be 15.4 mg g-1. Langmuir and Freundlich isotherm models fit de experimental data. Results showed that nonliving biomass of Fontinalis antipyretica is a...

  14. Uptake and release of divalent zinc ions from aqueous solutions by aquatic moss Fontinalis antipyretica.

    Martins, Ramiro; Boaventura, Rui
    Aquatic mosses are able to accumulate zinc and some other heavy metal ions from aqueous solutions and partially release them when exposed to metal-free water. They play an important role in the assessment of toxic elements in water. The advantage of mosses over direct water sampling is that the use of the former lessens spatial and temporal variations, enhances the level of contaminant identification by concentrating toxic elements, and provides information relative to the bioavailable species. However, to make the concentration of metals that can be measured in mosses a reliable indicator of the concentration of toxic elements in the water, we need to model...

  15. Modeling and operation of a simulated moving bed for the separation of optical isomers

    Rodrigues, A.E.; Lu, Z.P.; Loureiro, José M.; Pais, L.S.
    A model for predicting the steady state behavior of the simulated moving bed (SMB) is developed. SMB performance is characterized by purity, recovery, solvent consumption and productivity. The effect of switching time (rotation period), extract flowrate and section length on the SMB performance is discussed. A pilot plant for the separation of optical isomers is operated and tested with two systems: “Sandoz epoxide” and “bi-naphthol”.

  16. Simulated moving bed adsorptive reactor

    Leão, C.P.; Pais, L.S.; Santos, M.; Rodrigues, A.E.
    The Simulated Moving Bed (SMB) technology is a mature one with above 100 applications in chemical industry (UOP Sorbex processes). Now it is finding applications in fine chemistry and pharmaceuticals (chiral separations). In this work, separation is coupled with reaction. The test system is enzymatic inversion of sucrose coupled with glucose/fructose separation using Ca2+ resin as adsorbent. Modeling, simulation and operation of a pilot plant is addressed.

  17. Rigid polyurethane foams from lignin based polyols

    Cateto, C.A.; Barreiro, M.F.; Rodrigues, A.E.; Belgacem, M.N.
    Rigid polyurethane (RPU) foams were synthesized using lignin-based polyols obtained by an oxypropylation process. Alcell, Indulin AT, Curan 27-11P and Sarkanda lignins have been oxypropylated using formulations deduced from an optimization study with Alcell. L/PO/C (ratio between lignin, PO and catalyst content) of 30/70/2 and 20/80/5 were used to obtain the desired polyols. The resulting RPU foams were characterized in terms of density, mechanical properties, conductivity and morphology. All Sarkanda lignin based polyols and the 30/70/2 Curan 27-11P polyol were found inadequate for RPU formulations. Alcell and Indulin AT based polyols and the 20/80/5 Curan 27-11P polyol resulted in RPU...

  18. Heat transfer to Newtonian and non-Newtonian fluids in cross-corrugated chevron-type plate heat exchangers: numerical approach

    Fernandes, Carla S.; Dias, Ricardo P.; Nóbrega, João M.; Maia, João M.
    Food fluids are frequently processed in plate heat exchangers (PHEs) and usually behave as non-Newtonian fluids, this behaviour being scarcely considered for PHEs design purposes. Moreover, many food fluids processed in PHEs have a high viscosity and, therefore, data obtained in laminar flow regime is useful to practical applications. The thermal-hydraulic performance of PHEs is strongly dependent on the physical properties of the fluid and on the geometrical properties of the plates namely, on the corrugation angle and on the channel aspect ratio. The mostly widely used PHEs have corrugations of the chevron type with an area enlargement factor defined...

  19. Modelling and simulation of Fe2O3/aluminum thermite combustion: experimental validation

    Durães, Luísa; Brito, Paulo; Campos, José; Portugal, António
    A one-dimensional model was built to simulate the non-steady radial combustion propagation on thin circular samples of Fe2O3/Aluminum thermite mixtures. The model considers zero order kinetics and conductive/radiative heat transfer. All the properties of the system are assumed to vary with the temperature and composition during the propagation and phase transitions are also contemplated. These features, not yet considered in the literature, allowed the obtainment of realistic solutions, readily comparable with experimental values measured in an earlier work. The experimental combustion velocities were used to adjust the kinetic constant of the model, in order to give it a good predictive capability. The predicted combustion temperatures and reaction extents were...

  20. Molecular architecture of non-linear polymers: kinetic modeling and experimental characterization of the system methyl methacrylate + Ethylene Glycol Dimethacrylate

    Trigo, Ivone; Gonçalves, Miguel; Dias, Rolando; Costa, Mário Rui
    A general kinetic approach allowing the prediction of the molecular architecture of non-linear polymers is applied to the study of the copolymerization of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA). Dynamic predictions of molecular weight distributions, sequence length distributions and mean square radius of gyration are possible before and after gelation. A set of experiments concerning the copolymerization of MMA and EGDMA was carried out in toluene solution at 60 8C for which classic radical kinetics is a good approximation. The time evolution of key polymer properties was followed using a SEC system with a refractive index detector coupled with MALLS...

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