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Browsing Facultad Ciencias by Subject "5-Hydroxymethylfurfural (HMF)"

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    Estudio de sistemas bifuncionales para la obtención de 5-(Hidroximetil)-2-Furaldehído y Acido 5-(Hidroximetil)Furan-2-Carboxílico
    (Universidad Pedagógica y Tecnológica de Colombia, 2017) Aguilera Palacios, Edna Ximena; Rojas Sarmiento, Hugo Alfonso; Martínez Zambrano, José Jobanny
    In this work the dehydration of fructose and glucose to 5-(hydroxymethyl)-2-furaldehyde (HMF) was studied on a bifunctional system based on LaOCl/Nb2O5 catalysts and hot compressed water. The catalysts were prepared by impregnation of LaCl3 over Nb2O5 with different loads. The solids were characterized by X-ray energy dispersion spectroscopy (EDX), thermogravimetry (TGA), N2 physisorption, pyridine and CO2 adsorption followed by Fourier transform infrared spectroscopy with diffuse reflectance (FT-IR); the acid and basic force was determined by NH3 and CO2 desorption at programmed temperature, respectively. The use of acid-base systems for the production of HMF mainly from glucose requires weak basic sites and conditions of moderate acidity which is reached with LaOCl/Nb2O5 as was confirmed by the acidity and basicity analyzes. The presence of Nb2O5 in the solids increased the yield to HMF (> 50%) and prevented the formation of undesirable products under compressed hot water conditions. With the same objective to produce HMF, a bifunctional system was developed; this is based on the design of solids with acid-basic characteristics to convert glucose to the HMF in which a step of isomerization of the glucose to the fructose supplied by the effect of the basic sites of oxides such as CeO2, La2O3 and SiO2 and a dehydration step in which the participation of acid sites derived from the functionalization of oxides with sulfonic groups -SO3H is required. The oxides were functionalized with 3-mercaptopropyltrimethoxysilane in relation to the density of hydroxyl groups chemically bound to the surface, for that purpose the amount of hydroxyl groups was determined by analysis of physisorption, thermogravimetric analysis and infrared spectroscopy by Fourier transform. The catalysts obtained were characterized by N2 physisorption, pyridine and CO2 adsorption by diffuse reflectance infrared spectroscopy with Fourier transform; desorption analysis at programmed temperature of NH3 and CO2. The results showed that the functionalization process with groups -SO3H decreases the volume of the pores and therefore their surface area due to the interaction of the oxides with organosilanes. Analyzes of the nature of the acidic sites of the solids by adsorption of pyridine showed that in all the solids there are both types of acidity; Lewis and Brönsted, the latter attributed to the acid sulfonic groups anchored to the oxides. As for its catalytic activity, the highest conversion of glucose was found when La2O3-SO3H was used as the catalyst, achieving an HMF yield of 58%. Given the importance of HMF as a platform molecule to obtain high added value compounds with pharmaceutical and polymer applications, a bifunctional system involving the use of Rh catalysts supported in reducible and non-reducible oxides and an aqueous alkaline medium to produce 5-(hydroxymethyl)furan-2-carboxylic acid (HMFCA). Synthesized catalysts were characterized by EDX, transmission electron microscopy (TEM), chemisorption and FT-IR pyridine. The results revealed that the reaction pathway did not follow the typical HMF oxidation path but followed the Cannizzaro reaction path so the main products were (furan-2,5-diyl) dimethanol (DHMF), salt of the HMFCA and some degradation products such as levulinic and formic acids as a consequence of the degradation of HMF by the effect of the alkaline medium. The oxide with the best activity was CeO2, based on these results the possible reaction mechanism was elucidated when Rh/CeO2 was used as catalyst in the presence of molecular oxygen. In addition it was shown that at lower particle sizes HMFCA yield increased.