Contribution to the Study of Heterogeneous Catalytic Reactions in SCFs: Hydrogenation of Sunflower Oil in Pd Catalysts at Single‐Phase Conditions.

La hidrogenación es uno de los procesos químicos industriales más importantes. Una amplia variedad de productos químicos es obtenida mediante la hidrogenación catalítica. Uno de los procesos típicos de hidrogenación catalítica heterogénea es la producción de margarina y shortenings a partir de aceites vegetales, La hidrogenación de dobles enlaces presentes en grasas y aceites tiene como objetivo proveer a los productos de una textura y un perfil de fusión de acuerdo con su uso final. El aceite hidrogenado es más estable y menos sensible a la oxidación.El proceso convencional es llevado a cabo en reactores tipo batch donde el aceite, el hidrógeno y el catalizador de níquel son mezclados intensamente a temperaturas entre 373 K y 423 K. En este caso, en el que el compuesto a ser hidrogenado y/o los productos de reacción son líquidos a las condiciones de proceso, la velocidad de reacción es limitada por la concentración de hidrógeno en la superficie del catalizador. La baja velocidad de reacción es causada por la baja solubilidad del hidrógeno y la alta resistencia a la transferencia de masa en la fase líquida, lo que conlleva al agotamiento del hidrógeno en la superficie del catalizador. En presencia de dobles enlaces, la carencia de hidrogeno promueve la migración de los dobles enlaces y la isomerización cis-trans.A pesar de que la isomerización cis-trans aumenta el punto de fusión del producto final, existen conclusiones conflictivas acerca de los ácidos grasos. En varios estudios, estos isómeros formados durante la hidrogenación han mostrado tener efectos similares a los que presentan las grasas saturadas que aumentan los niveles de colesterol en la sangre, causa principal del infarto de corazón. Por esta razón, la atención del público sobre el potencial peligro para la salud debido a la ingesta en la dieta diaria de ácidos grasos trans ha aumentado.El propósito de esta investigación es el estudio de la hidrogenación del aceite de girasol en continuo, en fase vapor sobre catalizadores soportados en Pd utilizando fluidos supercríticos como solventes de reacción. Este puede ser un proceso alternativo para producir una amplia variedad de productos finales con diferentes características (índice de yodo, contenidos de trans y saturados principalmente) de interés industrial para ser usados como materias primas "saludables" para la formulación de bases de margarinas y shortenings en los próximos años.Otro objetivo es mostrar a escala laboratorio, el potencial que poseen las reacciones heterogéneas catalíticas en una sola fase supercrítica. Esta tesis esta basada en material publicado en varios documentos técnicos y una patente, los cuales están al final del texto. La estructura de la tesis es la que sigue:1. Com a mínim 1 i com a màxim 4. Els codis els podeu trobar en la pàgina web: http://www.upc.edu/tercercicle/impresos.php 2. El resum ha de tenir un màxim de 4000 caràcters. Cal tenir present que si es supera aquest límit es tallarà automàticament el resum al caràcter 4000.El capítulo 1 presenta los antecedentes y el estado del arte, explica la idea de utilizar fluidos supercríticos en la hidrogenación de grasas aceites y plantea cuales son los objetivos de esta investigación.El capítulo 2 presenta el estudio teórico del modelado del equilibrio líquido-vapor a alta presión del sistema aceite de girasol/hidrógeno/fluido supercrítico (propano o DME) con el objetivo de determinar las condiciones de operación apropiadas (concentraciones, temperaturas y presiones) que garanticen que todos los reactivos y productos de hidrogenación estén en una sola fase. El capítulo 3 establece como las variables de operación afectan la velocidad de reacción, la conversión y la distribución final de productos en una reactor continuo de reciclo así como permite determinar las condiciones experimentales bajo las cuales el proceso potencial en CSTR debe operar para obtener productos finales con interés industrial alimentario. Como una extensión de estos resultados, la cinética de la reacción es determinada para ambos casos.El capítulo 4 es una consecuencia de los resultados del capítulo anterior y desarrolla el estudio de los mecanismos de reacción-reacción intrapartícula en la hidrogenación de aceite de girasol sobre un catalizador de Pd/C.El capítulo 5 contiene los detalles experimentales de la tesis. La parte final de la tesis lista las conclusiones principales de este trabajo, discute la perspectiva de investigaciones posteriores y presenta la bibliografía junto a los anexos.Hydrogenation is a major industrial chemical process. A wide variety of chemicals is obtained by catalytic hydrogenation.One typical heterogeneous catalytic hydrogenation process is the production of margarine and shortenings from vegetable oils. The hydrogenation of double bonds in fats and oils has the purpose of providing products with the desired melting profile and texture, according to their final use. The hydrogenated oil is more stable and less sensitive to oxidation.The classic process is carried out in batch reactors where the oil, hydrogen, and catalyst nickel powder are mixed intensively at temperatures between 373 K and 423 K. In this case, the compound to be hydrogenated and or the reaction products are liquid at process conditions; the reaction rate is limited by the concentration of hydrogen on the catalyst surface. The low reaction rate is caused by the low solubility of hydrogen and the high mass transfer resistance in the liquid phase, which leads to a depletion of hydrogen at the catalyst surface. In the presence of double bonds, this lack of hydrogen also gives rise to double-bond migration and cis-trans-isomerization.Despite of the fact that isomerization of cis trans configuration increases the melting point, conflicting conclusions have resulted from studies on trans fatty acids. In several studies, these isomers formed during hydrogenation of fatty edible oils have shown to have similar effects as saturated fats increasing serum cholesterol levels in the blood, believed to be a major cause of heart desease. For this reason, apprehension and public awareness have risen regarding the potential health hazards of trans fatty acids intake in the human diet.The aim of this research is to study continuous single-phase hydrogenation of sunflower oil on supported palladium catalysts using supercritical fluids as a reaction solvent. This would be an alternative process for producing a wide variety of end products having different characteristics (iodine value, trans-fatty acid content and saturated content mainly) of industrial foodstuffs interest to be used as low cholesterol precursors for margarine and shortening bases in the next few years.In addition, the objective of the study is to show, on a lab-scale, the potential of heterogeneous catalytic reactions under supercritical single-phase conditions. This thesis is based on the material published in several technical papers and one patent, which can be found at the end of the thesis. The tesis is structured as follows:1. Com a mínim 1 i com a màxim 4. Els codis els podeu trobar en la pàgina web:http://www.upc.edu/tercercicle/impresos.php2. El resum ha de tenir un màxim de 4000 caràcters. Cal tenir present que si es supera aquest límit es tallarà automàticament el resum al caràcter 4000.Chapter 1 consists of a background, to explain the idea of use supercritical fluids in the hydrogenation of fats and oils, to describe the state of the art and what are the aims of this research.Chapter 2 presents a theoretical study for modelling the vapor-liquid high pressure equilibrium for sunflower oil/hydrogen/C3H8 system as well as for sunflower oil/hydrogen/DME in order to determine suitable operating conditions (concentrations, temperatures and pressures) which can bring all hydrogenation reactants and products into a homogeneous reactive fluid phase.Chapter 3 establishes a better understanding of how operating variables affect the rate of reaction, conversion and final product distribution in a continuous recycle reactor as well as the experimental conditions where a potential CSTR process could be operated to obtain end-products with industrial foodstuff of interest. As an extension of these results, the kinetics of the reaction is worked out. Chapter 4 it is a consequence of the results of the previous chapter and develops the study of the intraparticle diffusion-reaction mechanisms in supercritical sunflower oil hydrogenation on Pd/C catalyst.The final chapter contains the experimental details of this thesis. The last part lists the main conclusions, discusses the prospects for further investigations and presents the bibliopraphy and the appendixes

Study of implementation of the Flipped Classroom methodology (Just In Time Teaching) in the Inorganic Materials elective course of the Chemistry Degree at University of Barcelona

The Flipped Classroom (FC) strategy was implemented in an elective course of the Chemistry Degree at UB under its Just In Time Teaching approach. The methodology includes a self-studying activity, an assessment of students' initial level, the on-site FC session, and a verification of their achievements. The results evidenced some deficiencies in the assessment of student's achievements. Nevertheless, students highly appreciated the methodology, which helped them to develop self-learning skills

Catalysts: Advances in the Catalytic Behavior of Ion-Exchange Resins

This article is the editorial of the Special Issue Advances in the Catalytic Behavior of Ion-Exchange Resin

Influence of acid ion-exchange resins morphology in swollen state on the synthesis of ethyl octyl ether from ethanol and 1-octanol

Ethyl-octyl ether (EOE) liquid phase synthesis from ethanol and 1-octanol over ion-exchange resins is feasible at 423K, though di-ethyl ether and di-n-octyl ether were also formed. The influence of the catalyst morphology on the reaction was checked by testing twenty-two acidic resins. Gel-type resins of low crosslinking degree yielded the higher amounts of EOE, whereas macroreticular ones of high crosslinking degree gave mainly di-ethyl ether. Ethanol conversion highly depends on the resin acid capacity, [H+], whereas 1-octanol conversion and selectivity to EOE depends on the specific volume of swollen polymer, Vsp, and porosity. The variation of ethanol and 1-octanol conversion, selectivity to EOE with respect to both alcohols as well as ethers TOF as a function of [H+]/Vsp suggests that a part of the active sites does not take part in the EOE synthesis reaction on highly cross-linked resins. Amberlyst 70 could be interesting in industry due to its selectivity to EOE and higher thermal stabilit

Kinetics of 1-hexanol etherification on Amberlyst 70

The kinetics of the liquid-phase etherification of 1-hexanol to di-n-ethyl ether and water on the ion-exchange resin Amberlyst 70 in the temperature range 423-463 K is studied. The strong inhibition effect of water is considered following two approaches. First, a model stemming from a Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism was used, wherein the inhibitor effect of water was explained by the competitive adsorption of water and hexanol. Secondly, a modified Eley-Rideal (ER) model that includes an inhibition factor, in which a Freundlich-like function is used to explain the inhibitor effect of water by blocking the access of hexanol to the active centers. Both models fitted data quite well, although the best fitting results were obtained with the modified ER model. The activation energy was 125 ± 3 kJ/mol for the LHHW model and 121 ± 3 kJ/mol for the modified ER on

Liquid-phase synthesis of butyl levulinate with simultaneous water removal catalyzed by ion exchange resins

The liquid-phase synthesis of butyl levulinate by esterification of levulinic with an excess of 1-butanol (initial molar ratio 1:3) and simultaneous water removal has been studied at atmospheric pressure and at the boiling point of the reacting medium. The catalytic performance of ten commercial sulfonic resins has been compared: four gel-type and six macroreticular. For both type of resins the levulinic acid conversion was complete after 4-6h and no byproducts derived from the acid were detected. Selectivity of 1-butanol towards the ester was about 95%, di-butyl ether and butenes being the detected 1-butanol-derived byproducts. Among the tested catalysts, gel-type resins with low crosslinking degree showed the highest activity, what could be attributed to a higher accessibility to active centers in polar medium. In additional experiments where initial reactants content was at stoichiometric relation, the levulinic acid conversion was lower (82-85%), while selectivity of 1-butanol towards the ester was slightly higher, because of the lower 1-butanol concentration

Equilibrium conversion, selectivity and yield optimization of the simultaneous liquid-phase etherification of isobutene and isoamylenes with ethanol over Amberlyst 35

A prospective study on the product distribution at chemical equilibrium for the simultaneous liquid-phase etherification of isobutene and isoamylenes with ethanol over Amberlyst¿ 35 is presented. Experiments were performed isothermally in a 200 cm3 stirred tank batch reactor operating at 2.0 MPa. Initial molar ratios of alcohol/olefins and isobutene/isoamylenes ranged both from 0.5 to 2, and temperature from 323 to 353 K. Reactants equilibrium conversion, selectivities and yields toward products were clearly affected by the experimental conditions. Experimental etherification yields have been modeled using the response surface methodology (RSM), combined with the stepwise regression method to include only the statistically significant variables into the model. The multiobjective optimization (MOO) of etherification yields has been carried out numerically, by means of the desirability function approach, and graphically, by using the overlaid contour plots (OCP). Optimal conditions for the simultaneous production of ethyl tert-butyl ether (ETBE) and tert-amyl ethyl ether (TAEE) have been found to be at low temperatures (323 to 337 K) and initial molar ratio alcohol/olefins close to 0.9 and isobutene/isoamylenes close to 0.5

Catalytic activity dependence on morphological properties of acidic ion-exchange resins for the simultaneous ETBE and TAEE liquid-phase synthesis

The simultaneous liquid-phase synthesis of 2-ethoxy-2-methylpropane (ETBE) and 2-ethoxy-2-methylbutane (TAEE) has been studied over fifteen commercial acidic ion-exchange resins. Kinetic experiments were carried out in a batch reactor at T = 335 K and initial molar ratios of alcohol to olefins (R°A/O) and between olefins (R°C4/C5) of 1.1 and 1, respectively. The catalytic activity, measured as intrinsic initial etherification rates, has been found to decrease in the order: Amberlyst¿ 35 > Amberlyst¿ 48 > Purolite® CT-275 > Amberlyst¿ 15 > Purolite® CT-175 > Amberlyst¿ 40 > Amberlyst¿ 36 > Amberlyst¿ 16 > Purolite® CT-482 > Amberlyst¿ 39 > Amberlyst¿ DT > Amberlyst¿ 45 > Purolite® CT-124 > Purolite® MN-500 > Amberlyst¿ 46. This catalytic activity rank is related to the morphological properties of the resins in both dry and swollen states. The ratio of acid capacity to specific volume of the swollen polymer has been found to be the main catalyst properties that determine their activity: the higher the ratio, the higher the activity

Kinetic modeling of the simultaneous etherification of ethanol with C4 and C5 olefins over Amberlyst 35 using model averaging

A kinetic study on the simultaneous liquid-phase etherification of ethanol with isobutene (IB), 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B) catalyzed by Amberlyst¿ 35 to form ethyl tert-butyl ether (ETBE) and tert-amyl ethyl ether (TAEE) is presented. Isothermal experimental runs were carried out in a stirred tank batch reactor in the temperature range 323-353 K at 2.0 MPa, starting from different initial concentrations. Obtained reaction rates were free of catalyst load, internal, and external mass transfer effects. Mathematical fitting of a series of systematically originated models, model selection, and model averaging procedures were applied to find the best model and to draw conclusions about the reaction mechanism. The selected model involves a saturated catalytic surface with the participation of two active sites in etherification reactions and one active site in isoamylenes isomerization. Apparent activation energies for ETBE formation from IB and EtOH, TAEE formation from 2M1B and EtOH, TAEE formation from 2M2B and EtOH, and double bond isomerization between 2M1B and 2M2B were 72.8±1.4, 74.9±2.8, 81.2±2.2 and, 76.5±7.2 kJ/mol, respectively. The alkenes with the double bond in terminal position were more reactive towards EtOH than 2M2B, with the double bond in internal position

Implementing the flipped classroom methodology to the subject "Applied computing" of two engineering degrees at the University of Barcelona

This work is focused on the implementation, development, documentation, analysis, and assessment of the flipped classroom methodology, by means of the just-in-time teaching strategy, for a pilot group (1 out of 6) in the subject “Applied Computing” of both the Chemical and Materials Engineering Undergraduate Degrees of the University of Barcelona. Results show that this technique promotes self-learning, autonomy, time management as well as an increase in the effectiveness of classroom hoursPeer Reviewe