http://www.recercat.cat:80/handle/2072/152140 Tue, 21 May 2013 09:17:20 GMT 2013-05-21T09:17:20Z http://www.recercat.cat:80/bitstream/id/34212/ http://www.recercat.cat:80/handle/2072/152140 http://www.recercat.cat:80/handle/2072/210691 Modelling and Experiments for Application of Catalytic Distillation to TAME Synthesis Bonet-Ruiz, Alexandra E.; Bonet, Jordi (Bonet Ruiz); Bozga, Grigore; Llorens Llacuna, Joan; Plesu, Valentin; Tuluc, Alexandru; Bumbac, Gheorghe; Muscalu, Constantin In the early stages of distillation process analysis, the residue curve maps are used to check its feasibility. The residue curve map represents the composition that follows the residue in the still of a Rayleigh distillation for several initial conditions. It is demonstrated in the literature by several authors that the compositions followed by a residue curve matches a column composition profile of a packed column operated at infinite reflux flow-rate. In the present work, it is demonstrated that the dimensionless time used to calculate the residue curves corresponds to the number of transfer units by applying mass balances in a section of a packed column operated at infinite reflux flow rate. However, when there is a reaction, the number of moles changes due to the reaction stoichiometry, a different expression is obtained by the residue curves than by the infinite reflux flow rate packed column. It is important to notice that when there is no reaction or the number of stages does not change by the reaction stoichiometry. This expression becomes equal to the Rayleigh distillation expression. http://www.recercat.cat:80/handle/2072/210691 http://www.recercat.cat:80/handle/2072/209913 Minimum Number of Transfer Units and reboiler duty for multicomponent distillation columns Plesu, Valentin; Bonet Ruiz, Alexandra Elena; Bonet, Jordi (Bonet Ruiz); Llorens Llacuna, Joan; Iancu, Petrica Some guidelines to evaluate distillation columns, considering only basic thermodynamic data and principles, are provided in this paper. The method allows a first insight to the problem by simple calculations, without requiring column variables to ensure rational use of energy and low environmental impact. The separation system is approached by two complementary ways: minimum and infinite reflux flow rate. The minimum reflux provides the minimum energy requirements, and the infinite reflux provides the feasibility conditions. The difficulty of separation can be expressed in terms of number of transfer units (NTU). The applicability of the method is not mathematically limited by the number of components in the mixture. Several mixtures are rigorously simulated as illustrative examples, to verify the applicability of the approach. The separation of the mixtures, performed by distillation columns, is feasible if a minimum NTU can be calculated between the distillate and bottom compositions. Once verified the feasibility of the separation, the maximum thermal efficiency depends only on boiling point of bottom and distillate streams. The minimum energy requirements corresponding to the reboiler can be calculated from the maximum thermal efficiency, and the variation of entropy and enthalpy of mixing the distillate and bottom streams. http://www.recercat.cat:80/handle/2072/209913 http://www.recercat.cat:80/handle/2072/209646 Effects of inorganic nitrogen (NH4Cl) and biodegradable organic carbon (CH3COONa) additions on a pilot-scale seawater biofilter Simón, Francesc Xavier; Rudé i Payró, Elisabet; Berdalet i Andrés, Elisa; Llorens Llacuna, Joan; Baig, Sylvie Biofilters degrade only a small fraction of the natural organic matter (NOM) contained in seawater which is the leading cause of biofouling in downstream processes. This work studies the effects of chemical additions on NOM biodegradation by biofilters. In this work, biofiltration of seawater with an empty bed contact time (EBCT) of 6 min and a hydraulic loading rate of 10 m h-1 reduces the biological oxygen demand (BOD7) by 8%, the dissolved organic carbon (DOC) by 6% and the UV absorbance at 254 nm (A254) by 7%. Different amounts of ammonium chloride are added to the seawater (up to twice the total dissolved nitrogen in untreated seawater) to study its possible effect on the removal of NOM by a pilot-scale biofilter. Seawater is amended with different amounts of easily biodegradable dissolved organic carbon (BDOC) supplied as sodium acetate (up to twice the DOC) for the same purpose. The results of this work reveal that the ammonium chloride additions do not significantly affect NOM removal and the sodium acetate is completely consumed by the biofiltration process. For both types of chemical additions, the BOD7, DOC and A254 in the outlet stream of the biofilter are similar to the values for the untreated control. These results indicate that this biofilter easily removes the BDOC from the seawater when the EBCT is not above 6 min. Furthermore, nitrogen does not limit the NOM biodegradation in seawater under these experimental conditions. http://www.recercat.cat:80/handle/2072/209646 http://www.recercat.cat:80/handle/2072/200687 Seguimiento continuo del proceso de gelificacion de alcoxidos de silicio y titanio mediante ensayos reologicos Rudé i Payró, Elisabet; Llorens Llacuna, Joan; Mans Teixidó, Claudi, 1948- En este trabajo se ha estudiado el proceso de gelificación desde un nuevo punto de vista: el seguimiento de la transición solgel mediante la evolución con el tiempo de la distribución de tiempos de relajación, que está directamente relacionada con la distribución de pesos moleculares. La técnica utilizada para la determinación de la distribución de tiempos de relajación es la reología. El proceso de gelificación se ha seguido de forma continua mediante dos ensayos reológicos distintos: (1) ensayos dinámicos u oscilatorios y (2) ensayos de retardo y recuperación, con el objetivo de caracterizar de forma completa la viscoelasticidad del sistema a lo largo de todo el proceso. El estudio ha abarcado todos los estadios de la gelificación: (a) el estadio pre-gel, (b) el propio estadio gel y (c) el estadio post-gel. Los procesos estudiados corresponden a soles poliméricos de titanio y de silicio. Los resultados obtenidos permiten evaluar la influencia de la composición de los soles, así como comparar los dos tipos de soles analizados. Además, permiten describir el tiempo de gelificación desde una nueva perspectiva, basada en la distribución de tiempos de relajación, ya que se observa que este momento corresponde a una distribución de polidispersidad máxima. http://www.recercat.cat:80/handle/2072/200687 http://www.recercat.cat:80/handle/2072/184071 Designing and testing of a sensor based on a magnetoresistive manganese perovskite thick film Balcells i Argemí, Lluís; Enrich i Sard, Regina; Calleja Lázaro, Alberto; Fontcuberta i Griñó, Josep; Obradors, Xavier In this paper we report on the growth of thick films of magnetoresistive La2/3Sr1/3MnO3 by using spray and screen printing techniques on various substrates (Al2O3 and ZrO2). The growth conditions are explored in order to optimize the microstructure of the films. The films display a room-temperature magnetoresistance of 0.0012%/Oe in the 1 kOe field region. A magnetic sensor is described and tested. http://www.recercat.cat:80/handle/2072/184071 http://www.recercat.cat:80/handle/2072/183952 Shear thinning and thixotropy of HMHEC and HEC water solutions Maestro Garriga, Alicia; González García, Ma. Concepción; Gutiérrez González, José María, 1953- Steady state viscosity and thixotropy of hydrophobically modified hydroxyethyl cellulose HMHEC and nonassociative cellulose water solutions are studied. Although all the samples are shear thinning, only the HMHEC is thixotropic, since the migration of hydrophobes to micelles is controlled by diffusion. The Cross model fits steady state curves. The Mewis model, a phenomenological model that proposes that the rate of change of viscosity when the shear rate is suddenly changed is related to the difference between the steady state and current values of viscosity raised to an exponent, fits structure construction experiments when the exponent, n, is estimated to be around 2. The Newtonian assumption used by Mewis cannot be used here, however. This seems to be related to the fact that the thickening is due to bridged micelle formation, which is a slow process, and also to topological constraints and entanglements, which are rapid processes. The kinetic parameter was redefined to kn in order to make it independent of initial conditions. So, kn depends only on how the shear affects the structure. kn reaches a plateau at shear rates too low to produce structure destruction and decreases at higher shear rates. http://www.recercat.cat:80/handle/2072/183952 http://www.recercat.cat:80/handle/2072/183951 Rheological behavior of hydrophobically modified hydroxyethyl cellulose solutions: A linear viscoelastic model Maestro, A.; González, C.; Gutiérrez, José Ma. (José Maria), 1949- The rheological behavior of hydrophobically modified hydroxyethyl cellulose HMHEC, an associative thickener, was studied and compared with that of hydrophobically modified ethoxylated urethanes HEURs and nonassociative celluloses. In contrast to HEURs, a simple Maxwell model does not fit the linear viscoelastic behavior of HMHEC. Differences are attributed to the stiffness and comb structure of HMHEC. A generalized Maxwell model with a logarithmic distribution of relaxation times is proposed, and another parameter that includes Rouse-like relaxation is added to fit behavior at high frequencies. Four parameters are needed to describe HMHEC viscoelasticity: a mean relaxation time, lM ; its corresponding standard deviation, s; a plateau modulus, GN ; and a viscosity at infinite frequency, h ` . Satisfactory fitting is obtained for all concentrations and temperatures in the range of frequencies studied. The sharp increase of GN with concentration indicates loop-to-bridge transitions. Temperature does not influence GN , since the reduction in the number density of elastically effective chains caused by Brownian motion masks the direct effect of temperature. The dependence of lM on temperature follows the Arrhenius equation, as does the relaxation time of HEURs, but it does not change with concentration, presumably because the comb structure of HMHEC prevents the formation of long superchains. http://www.recercat.cat:80/handle/2072/183951 http://www.recercat.cat:80/handle/2072/183950 Vortex shedding from a spinning cylinder Díaz, Francesc; Gavaldà, Josefina; Kawall, J. G.; Keffer, J. F.; Giralt, Francesc An experimental investigation of a two-dimensional turbulent wake behind a spinning cylinder at Re=9000 is carried out to determine the influence of the rotation on the initial development of the flow. Spectral analysis of the velocity data measured in the near wake shows that for peripheral velocities up to the value of the free¿stream velocity, a distinct Kármán vortex activity exists within the wake, whereas for greater peripheral velocities, the Kármán activity deteriorates and disappears for values in excess of twice the free-stream velocity. http://www.recercat.cat:80/handle/2072/183950 http://www.recercat.cat:80/handle/2072/152146 Reliability of the density functional approximation to describe the charge transfer of electrostatic complexes involved in the modeling of organic conducting polymers Alemán, Carlos; Curcó Cantarell, David; Casanovas Salas, Jordi http://www.recercat.cat:80/handle/2072/152146