Aufwertung von aus Biomasse gewonnenen Plattformmolekülen in der Gasphase : von Lävulinsäure zu biobasierten Chemikalien

• Upgrading bio-platform molecules in the gas-phase : from levulinic acid to bio-chemicals

Blair Vasquez, Paola; Cavani, Fabrizio (Thesis advisor); Palkovits, Regina (Thesis advisor); Albonetti, Stefania (Thesis advisor); Tabanelli, Tommaso (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021. - Dissertation, Università di Bologna, 2021

Abstract

Levulinic acid (LA) is a polyfunctional molecule obtained from biomass. Because of its structure, the United States Department of energy has classified LA as one of the top 12 building block chemicals. Most commonly, it is valorized through chemical reduction to obtain γ-valerolactone (GVL). It is typically done with molecular hydrogen (H2) in batch systems, with high H2 pressures and noble metal catalysts, making it expensive and less applicable. Hence, alternative approaches such as the catalytic transfer hydrogenation (CTH) through the Meerwein-Ponndorf-Verley (MPV) reaction using heterogeneous transition metal oxide catalysts have been studied. This uses organic molecules, such as alcohols, which are capable of acting as a hydride transfer agent (H-donor), in order to reduce molecules containing carbonyl groups. Studies have reported the batch liquid-phase CTH of levulinate esters with secondary alcohols, given the stability of the carbocationic intermediate. Remarkable results have been obtained (in terms of GVL yield) over ZrO2, given the need of a Lewis acid and base pair in order for CTH to take place. However, there were no studies in the literature reporting the continuous gas-phase CTH of levulinate esters. Therefore, high surface area ZrO2 was tested for the gas-phase CTH of methyl levulinate (ML) at different temperatures using ethanol, methanol and isopropanol as H-donors. Under optimized conditions with ethanol (250 ℃), the reaction is selective toward the formation of GVL (yield 70%). However, the deposition of heavy compounds over the catalysts surface progressively blocked Lewis acid sites leading to a progressive change in the chemoselectivity. The in situ regeneration of the catalyst permitted a partial recovery of the Lewis acid sites and an almost total recovery of the initial catalytic behavior, proving that the deactivation is reversible. Results obtained with methanol were not promising (conversion of 35% and GVL yield of 4%). However, as expected, using isopropanol a complete conversion was achieved with a GVL yield of 80%. The reaction was also tested using bioethanol derived from agricultural waste. In addition, a preliminary study was performed for the hydrogenolysis of polyols for the production of bioethanol. Pd-Fe catalyst was found to be active for the hydrogenolysis of glycerol, being quite selective towards ethanol (37%).