Catalytic transformations of glycerol via hydroxyacetone into nitrogen heterocycles of industrial interest
- Autores: Jaime Mazarío Santa Pau
- Directores de la Tesis: Marcelo Eduardo Domine (dir. tes.), Sara Iborra Chornet (tut. tes.)
- Lectura: En la Universitat Politècnica de València ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Dirk De Vos (presid.), Benjamín Eduardo Solsona Espriu (secret.), Pedro J. Maireles Torres (voc.)
- Programa de doctorado: Programa de Doctorado en Química Sostenible por la Universidad de Castilla-La Mancha; la Universidad de Extremadura; la Universidad Jaume I de Castellón; la Universitat de València (Estudi General) y la Universitat Politècnica de València
- Materias:
- Enlaces
- Tesis en acceso abierto en: RiuNet
- Resumen
This doctoral thesis addresses the development of new catalytic processes centered on glycerol valorization, which is the main by-product of biodiesel synthesis. In this sense, the main aim focused on using it as a carbon source to generate nitrogen heterocycles of industrial interest, specifically, to produce 2-methylpiperazine and 2-methylpyrazine.
Due to the low reactivity of glycerol and the severe reaction conditions necessary to carry out the transformations towards these N-heterocycles, previous detailed research to optimize and understand the selective dehydration process of glycerol to hydroxyacetone (or acetol) was undertaken. Through obtaining this intermediate compound, it has been possible to develop efficient and selective nitrogen heterocycles production processes, under moderate reaction conditions.
In this regard, Cu-Mg-Al hydrotalcite precursors give rise to a family of materials based on Cu-Mg-Al mixed oxides capable of carrying out the selective dehydration of glycerol to acetol continuously with yields of 40%. In addition, these catalysts are stable for more than 8 hours under operational conditions, showing excellent regeneration capacity and reusability.
In the same way, through the combination of catalytic and characterization studies, the interesting mix of acid-base and redox centers exhibited by these materials has allowed for advancing significantly in the state of the art regarding understanding this glycerol catalytic dehydration reaction. Hence, it has been possible to verify the fundamental role of Cu species and, specifically, Cu(I) species present in the catalysts, in the generation of glyceraldehyde as a critical reaction intermediate for acetol production. Similarly, the acid centers of the catalyst facilitate the first adsorption of glycerol, thus accelerating the reaction.
However, the need to achieve higher acetol productivities from glycerol to stand a chance to succeed in the overall strategy motivated the development and study of a second family of catalysts based on copper oxide supported on different metal oxides (SiO2, Al2O3 and ZrO2) combining Lewis acid centers and high Cu exposure. The proper selection and optimization of these materials lead to reaching, with several of them, yields of 60% to acetol with much higher glycerol concentrations in the starting feed.
Once several catalytic systems had been established to produce acetol, the generation of the nitrogen heterocycles of interest from the combination of this molecule with ethylenediamine was investigated. Specifically, the Pd/TiO2-Al2O3 catalyst presents high specific activity when forming 2-methylpiperazine (80% yield). These excellent results could be attributed to the enhanced exposure of unsaturated Pd centers observed in this material, critical for activating the C=N double bond and thus proceeding to the hydrogenation of the intermediate imines. Secondly, the CuO/Al2O3-npw catalyst yields 50% to 2-methylpyrazine, reaching values close to 60% when the precipitation-deposition method by micelles in reverse phase is used to incorporate the CuO nanoparticles. Finally, a proof of concept of 2-methylpyrazine synthesis starting from glycerol by using a specially designed multi-bed catalytic reactor to perform the two-steps process in one-pot with the same CuO-supported catalyst was assayed, with promising results.
In summary, two new catalytic routes have been established to produce nitrogen heterocycles with glycerol as the main carbon source through its derivative hydroxyacetone, thus opening new perspectives in the field of sustainable valorization of biomass-derived molecules.
