Quinta do Anjo, Portugal
Quinta do Anjo, Portugal

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Nogueira A.G.,University of Coimbra | Silva D.C.M.,CUF Quimicos Industriais | Baptista C.M.S.G.,University of Coimbra
Industrial and Engineering Chemistry Research | Year: 2016

The behavior of flow in an industrial adiabatic reactor was studied for assessing nonuniform regions or bypassing. Mathematical models for a continuous stirred tank reactor were developed using adjustable parameters to be obtained from residence time distribution data. Owing to reaction the flow rates of the two liquid phases change. These models combine ideal vessels in series: a plug flow followed by one or two stirred tanks. The interchange of fluid between two stirred reactors was regarded, as well as a stagnant region in the middle reactor. The experimental study was carried out by injecting a tracer in the organic phase of the liquid-liquid system and quantifying it in the outlet stream. This procedure was followed for different flow rates and RTD data used to assess the best-fit combined model for the flow in this reactor which was a plug flow followed by two stirred tanks with interchange of fluid between them. © 2015 American Chemical Society.


Paiva J.,University of Porto | Salcedo R.,University of Porto | Salcedo R.,Advanced Cyclone Systems | Araujo P.,CUF Quimicos Industriais
Chemical Engineering Journal | Year: 2010

The purpose of this work is to build a model to predict in a more realistic way the collection efficiency of gas cyclones, and in particular, of numerically optimized cyclones, that show very high collection efficiencies for sub-micrometer particles. These cyclones can be coupled to recirculation systems for further improving the collection efficiencies of these fine particles.As a first approach, in this paper a reverse-flow gas-cyclone without recirculation was studied. The model starts by solving the particle trajectory in a predetermined flow field inside the cyclone on which turbulence is superimposed by adding random fluctuating components. By employing a fixed set of parameters, it determines if a collision or an agglomeration occurs. In case of agglomeration, the initial particles will have a dynamic behavior inside the cyclone as an newly formed agglomerate, thus having a different collection efficiency from that of the original particles. In fact, the observed efficiency will increase above theoretical predictions for un-agglomerated particles and this can be observed in various experimental results.The hypothesis of particle agglomeration within the cyclone turbulent flow seems a sound justification for the higher than predicted collection efficiencies observed for smaller particles in a gas-cyclone, being expectable with recirculation that this effect will become even more significant. © 2010 Elsevier B.V.


Dias A.C.,University of Porto | Pereira M.J.,University of Porto | Brandao L.,University of Porto | Araujo P.,CUF Quimicos Industriais | Mendes A.,University of Porto
Journal of the Electrochemical Society | Year: 2010

The effect of the operating parameters current density, feed flow rate, brine and caustic concentrations, and temperature of a laboratory-scale chlor-alkali membrane cell on its overall performance (power consumption) was studied. Electrochemical impedance spectroscopy (EIS) was used to evaluate in situ the ohmic resistances of electrolytes and membrane. The cell temperature and the brine concentration were the most important variables on the cell voltage. The gas bubble evolution had a great effect on the ohmic resistance, especially at the anode side, where the gas void fraction was about 10%. © 2010 The Electrochemical Society.


Nogueira A.G.,CUF Quimicos Industriais | Nogueira A.G.,University of Coimbra | Silva D.C.M.,CUF Quimicos Industriais | Reis M.S.,University of Coimbra | Baptista C.M.S.G.,University of Coimbra
Chemical Engineering Transactions | Year: 2013

Side reactions are undesirable in most industrial processes, as they decrease process yield and selectivity. For this reason, mononitrobenzene's manufacturers set nitrophenols minimization as a critical goal, along with the MNB production targets. The mechanism of these side reactions in benzene nitration is still under debate and, so far, none of the alternatives has achieved general consensus in the scientific community. As an alternative, industrial data may provide valuable information on the contribution of inlet process variables and operating conditions upon the formation of nitrophenolic compounds in the adiabatic nitration process. In this work, Partial Least Squares regression was applied to data collected from a mononitrobenzene industrial production plant. This methodology allowed concluding that nitration temperature and mixed acid volumetric flow rate as the most influential variables in nitrophenols formation. The models developed enable proper estimates of DNP and TNP concentrations in the industrial process, although their explanation power is lower than those previously obtained by Quadros et al. (2005), in a pilot plant, and by Portugal et al. (2009) in their extended models. Copyright © 2013, AIDIC Servizi S.r.l.


Costa T.J.G.,University of Coimbra | Nogueira A.G.,University of Coimbra | Silva D.C.M.,CUF Quimicos Industriais | Ribeiro A.F.G.,CUF Quimicos Industriais | Baptista C.M.S.G.,University of Coimbra
ACS Symposium Series | Year: 2013

The High Pressure Liquid Chromatography (HPLC) method for nitrophenols measurement in the benzene nitration process has been improved. A new eluent mixture was studied using two different compositions and the 30/70 (%v/%v) ratio of acetonitrile and aqueous potassium dihydrogen phosphate solution proved sufficient in accurately quantifying every nitrophenolic compound. The influence of the pH upon peak resolution was assessed and pH 7.0 provided the best results. Once the chromatography parameters were set a reproducibility study was carried out confirming the accuracy of the method. © 2013 American Chemical Society.


Prior J.M.V.,CUF Quimicos Industriais | Almeida I.,Institute for Molecular and Cell Biology | Loureiro J.M.,University of Porto
Powder Technology | Year: 2013

This work presents a theoretical model that describes the porosity of spherical and non-spherical particles mixtures, with and without macropores. It was based on the geometry of packing of spherical particles. The description of the particles mixture porosity, without macropores, is performed by a single expression that takes into account the abundance of each particle species present in the mixture, as well as, the physical properties and the initial packaging of them. When the shape is not spherical, the model makes use of the concept of equivalent packing diameter. The published experimental values of the porosity of binary and ternary packings are compared with the values calculated with the proposed model. The results of the model are in good agreement with published experimental data. © 2013 Elsevier B.V.

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