Valorización de etanol y acetona mediante procesos catalíticos

Abstract

ABSTRACT This Doctoral Thesis deals with the valorization of two interesting platform molecules, ethanol and acetone. Their upgrading implies an increase in the length of their carbon chain, typically carried out by condensation catalytic reactions. 1-Butanol is highlighted among the ethanol products because of its different uses, so it is considered as the target compound for this reaction. In the case of acetone, there are several compounds of interest, so reaction conditions are tuned as function of the requirements. In a first approach to the ethanol gas phase condensation, two mixed oxides (Mg Al and Mg Zr) were studied following both the activity and stability. Deactivation is discarded under 400 ºC, whereas ethanol conversion decreases in 14 and 22 % at 450 ºC with Mg Al and Mg Zr, respectively. The main cause of this deactivation is attributed to the blockage of the active sites due to the adsorption of heavy species, mainly on acid ones. So, the Mg-Zr catalyst, with the highest concentration of acid sites, exhibits the lowest stability. The role of dehydrogenation and hydrogenations steps were deeply studied in order to enhance the 1-butanol production. For this purpose, reducing conditions and bifunctional catalysts (with metal nanoparticles) were considered (M/Mg Al, M: Ni, Co, Pd, Ru and Cu). The M/Mg Al catalysts improve the results obtained with the original support, especially at the lowest temperatures, at which side reactions are prevented. The Cu/Mg Al catalyst, in presence of H2, reaches a 1-butanol yield up to 30 times higher than the parent Mg Al does. These results confirm a key role of the dehydrogenation step in the whole process. Furthermore, the use of a mixture of Mg Al and Cu/SiO2 confirms that coexistence of both metallic and acid basic sites in the same surface ensures the optimum results. Likewise, in an additional work on TiO2 base catalysts, Au nanoparticles showed an excellent hydrogenation capacity, observing a clear improvement in 1-butanol productivity at soft temperature under reducing conditions. Concerning the acetone valorization, a similar study was performed. The Mg Zr catalyst exhibits deactivation despite the reaction conditions, being more relevant at high temperatures. The stability loss is due to the deposition of different species formed in reaction (from C6 to coke). Bifunctional TiO2 base catalysts (M/TiO2, M: Pt, Ni) in presence of H2 were tested with the purpose of producing MIBK and DIBK. An outstanding combined selectivity to both saturated ketones higher than 95 % (63.7 and 31.5 % to MIBK and DIBK, respectively) is obtained at 42 % of acetone conversion with Pt/TiO2. However, almost no hydrogenation is observed with Ni/TiO2 catalyst (MIBK selectivity ≤1.2 %), since the only detected species are unsaturated C6 and C9 ketones. No deactivation is noticed with the reaction time with both catalysts. Acid catalysis was essayed to improve the mesitylene yield via isophorones dehydration. Both, MCM 41 aluminosilicate and BEA zeolite show a high selectivity to mesitylene regarding the other C9. Nevertheless, acetic acid and isobutene formation by the C6 β scission limits the results. The H2 feeding improves the stability and, especially, the activity of these materials. A two bed configuration consisted of TiO2 + MCM 41 or BEA was proposed with the aim of converting the C9 ketones produced on TiO2 to mesitylene by the aluminosilicates. The TiO2 + BEA system shows a similar behavior to both beds working sequentially, whereas the TiO2 + MCM 41 system shows the desired synergic effects (higher mesitylene relative selectivity).