RT info:eu-repo/semantics/masterThesis
T1 Hydrogenation of selected carbohydrate molecules in the presence of solid foam catalysts in a stirred tank reactor
A1 Araujo Barahona, Germán Rodrigo
A2 Universidad de Valladolid. Escuela de Ingenierías Industriales
K1 Hydrogenation
K1 Heterogeneous catalysis
K1 Structured catalysts
K1 Ruthenium
K1 L-arabinose, D-galactose
K1 Binary sugar mixtures
K1 Sugar alcohols
K1 3303 Ingeniería y Tecnología Químicas
AB This research work was carried out at the Laboratory of Industrial Chemistry and Reaction Engineering (TKR) at Åbo Akademi University (Turku/Åbo, Finland) in collaboration with the University of Valladolid (Valladolid, Spain) under the supervision of Tapio Salmi (Professor of the Academy of Finland) and Juan García Serna (Full Professor at the University of Valladolid) as part of the Erasmus Plus exchange program.The growing concern about the short and long-term consequences caused by climate change is driving humankind towards a more sustainable development, which requires adequate diversification of feedstock and industrial production processes. In this context, the use of lignocellulosic biomass as raw material for chemical industry is a promising option on which a lot of research effort has been focused in recent years, such as the production of sugar alcohols. These compounds can be obtained by catalytic hydrogenation of mono and disaccharides present in the cellulose and hemicelluloses fractions of biomass. Sugar alcohols have a wide range of applications e.g., in the alimentary industry as healthier sweeteners or in the pharmaceutical industry as excipients and anti-caries agents.The research effort of this thesis was focused on the development of a novel solid foam catalyst based on ruthenium supported on carbon. This heterogeneous catalyst was used to perform kinetic experiments on the hydrogenation of L-arabinose and D-galactose at different temperatures (90˚C, 100˚C, and 120˚C) and hydrogen pressures (20 and 40 bar) to investigate the effect of these parameters on the hydrogenation rate. Furthermore, kinetic experiments were carried out with binary sugar mixtures at different D-galactose to L-arabinose molar ratios to study the interactions of these sugars during the reaction in the presence of the prepared catalyst.The solid foam catalyst preparation comprised the following steps: cutting of the open-cell foam aluminum pieces, anodic oxidation pretreatment, carbon coating, acid pretreatment, ruthenium incorporation, and ex-situ reduction. The carbon coating method comprised the polymerization of furfuryl alcohol, followed by a pyrolysis process and activation with oxygen. The degree of crosslinking of polyfurfuryl alcohol was identified as a relevant parameter to obtain a carbon coating with appropriate properties to act as catalyst support; thus, the polymerization conditions were optimized to obtain the desired catalyst properties.Incorporation of ruthenium on the carbon-coated foam was done by two different methods, homogeneous deposition precipitation (HDP) and incipient wetness impregnation (IWI), using in both cases ruthenium(III) nitrosyl nitrate as the precursor solution. In the HDP method, the carbon content of the foams and the molar ratio of urea-to-ruthenium were the most relevant parameters to obtain an active catalyst. On the other hand, for the IWI method, the carbon content and the concentration of the precursor solution were identified as the most relevant parameters. Using IWI, it was possible to prepare an active catalyst with a ruthenium load of 1.1 wt. % for the conversion of the sugars to the corresponding sugar alcohol. This catalyst was used in the systematic kinetic experiments for both the individual sugars and sugar mixtures.Several catalyst characterization techniques such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Temperature-Programmed Reduction (TPR), and Inductively Coupled Plasma Atomic Optical Emission Spectroscopy (ICP-OES) were used to interpret the behavior of the catalyst in terms of activity, durability and critical parameters for the catalyst preparation.Extensive kinetic experiments were carried out in an isothermal laboratory-scale semibatch reactor to which gaseous hydrogen was constantly added. Two pieces of solid foam catalysts were placed at the endpoint of an agitating shaft and rotated at a constant speed during the experiments. From the individual kinetic experiments, high selectivities towards sugar alcohols, exceeding 98% were obtained for both sugars, in fact, the conversions were within the range of 60-98%, depending on the temperature. The temperature effect on the reaction rate was very strong, while the effect of the hydrogen pressure was rather minor. Regarding the sugar mixtures, in general, the L-arabinose presented a higher reaction rate, and an acceleration of the hydrogenation process was observed for both sugars as the ratio of D-galactose to L-arabinose increased, evidently as a result of competitive interaction on the catalyst surface.A kinetic model based on a non-competitive adsorption mechanism between sugar molecules and hydrogen was tested with extensive experimental data by applying non-linear regression. A good description of the concentration profiles and the temperature effect on the reaction kinetics was achieved with the mathematical model. Furthermore, a detailed sensitivity analysis revealed that the estimated parameters were very well defined and all of them had an important contribution to the model.The obtained results demonstrate the feasibility of converting primary sugars from biomass such as L-arabinose and D-galactose and their mixtures into the corresponding sugar alcohols using ruthenium as the active metal on an active carbon support implemented in an open foam structure. A possible next step would be the use of this catalyst in continuous three-phase reactors that allow taking the advantage of the properties associated with structured catalysts, such as high flow rates, high external heat and mass transfer rates and low diffusion resistance in the active catalyst layer.
YR 2021
FD 2021
LK https://uvadoc.uva.es/handle/10324/47145
UL https://uvadoc.uva.es/handle/10324/47145
LA eng
NO Departamento de Ingeniería Química y Tecnología del Medio Ambiente
DS UVaDOC
RD 21-dic-2024