Transformación de intermedios lignocelulósicos en gamma-valerolactana: hacia un proceso catalítico eficiente

• Autores: Clara López Aguado Sánchez
• Directores de la Tesis: Juan Antonio Melero Hernández (dir. tes.), Gabriel Morales Sánchez (codir. tes.)
• Lectura: En la Universidad Rey Juan Carlos ( España ) en 2019
• Idioma: español
• Tribunal Calificador de la Tesis: Javier Dufour Andía (presid.), Jovita Moreno Vozmediano (secret.), María Pires (voc.), Rafael Mariscal López (voc.), Ricardo Bermejo de Val (voc.), Araceli Rodríguez Rodríguez (voc.), José María Fraile Dolado (voc.)
• Programa de doctorado: Programa de Doctorado en Tecnologías Industriales: Química, Ambiental, Energética, Electrónica, Mecánica y de los Materiales por la Universidad Rey Juan Carlos
• Materias:
  • Ciencias tecnológicas
    • Ingeniería y tecnología químicas
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• Resumen

  • The current productive system is characterized by the shortage of raw materials and the high environmental impact generated in their extraction and processing, as well as the impact resulting from massive CO2 emissions to the atmosphere. Hence, it is widely considered as not sustainable in the medium and even short-term. In this context, great efforts are being performed for the transition from a "linear economy" to a "circular economy", where all the wastes generated by the productive system must be reused and ultimately transformed back into raw materials that enter again in multiple points of the productive system chain of value, promoting energy savings, the use of renewable energy sources and reducing greenhouse gasses emissions. Within the framework of the circular economy, the development of an economy based on the optimal utilization of renewable biological resources and wastes, and their conversion into bioenergy and bioproducts (known as bioeconomy) is one of the pursued objectives.

    Biorefineries, based on the conversion of residual biomass for the production of bioenergy and chemical products, are shown as a key strategic element for the development of this bioeconomy. Lignocellulosic biomass is the cheapest and most abundant form of terrestrial biomass and, consequently, its cost-effective exploitation to obtain a wide variety of chemical products with potential use in many different industrial sectors would be very attractive. Starting from lignocellulpse, there are different chemical strategies for its valorisation, leading to a range of valuable platform molecules which can be subsequently transformed into value-added products.

    Platform molecules are recognized as pillars in biorefineries, since they are intermediates between the raw material and the final product. In a biorefinery, 5- and 6-carbon sugars (pentoses and hexoses, respectively) obtained from hydrolysis of lignocellulosic biomass can be converted into intermediate compounds (furfural and levulinic acid), which in turn can be further transformed to final chemical compounds (levulinates, lactones or GVL).

    In this context, the direct and selective transformation through a one-pot approach would be highly desirable, as the overall investment and operational costs would be potentially reduced. Sorne of the steps require the use of Br0nsted acid sites, like those typically displayed by aluminium-containing acid zeolites, such as H-Beta, H-ZSM-5, or H-Y zeolites. On the other hand, MPV-type hydrogen transfer reactions in the presence of an alcohol as solvent and hydrogen donar are typically promoted by solid Lewis acid sites, among others, such as those in Ti-, Sn-, and Zr-containing catalysts. Therefore, an interesting approach for such a cascade process is the use of multifunctional catalysts, carrying different active sites on the same material. This enables the possibility of fulfilling the requirements for the individual steps to achieve a single-step process in which ali the chemical transformations occur in the same reaction vessel. The simultaneous incorporation of both functionalities within the same zeolite framework would favour the sequential conversion to the final product, specially in the current study gamma-valerolactone (GVL). This operating mode avoids the use of intermediate separation and purification steps, which would potentially reduce the overall costs and energy demand of the process.

    Recently, this strategy has been described in several works, aiming to combine Lewis and Bnzmsted acid sites within the same zeolite framework (bifunctional catalysts). Bui et al. presented a zeolite with Br0nsted and Lewis acid sites