Transformation of levulinic acid and intermediates thereof into potential biofuel compounds over heterogeneous catalysts
Aachen (2016, 2017) [Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (IX, 183 Seiten) : Illustrationen, Diagramme
Bio-refinery process has been considered to be a promising solution with high potential for a sustainable production of valuable chemicals. One motive is to partially substitute the conventional petroleum products and to minimize the negative effects related to their uses, for years to come. Compounds like γ-valerolactone, esters of levulinic acid, and 2-methyltetrahydrofuran were identified as key target molecules that can be derived from lignocellulosic biomass and find use as renewable fuels, fuel additives, green solvents, or precursor to other fine chemicals.Central of this thesis is the exploration of the catalytic preparation of γ-valerolactone, esters of levulinic acid, and 2-methyltetrahydrofuran starting from levulinic acid and α-angelica lactone, versatile and viable platform chemicals made efficiently from lignocellulosic biomass. Although the catalytic synthesis of γ-valerolactone was studied intensively in the last years, our effort has been directed toward developing less energy demanding protocols with lower environmental impact and higher sustainability. In this regards, the catalytic transformation of levulinic acid and α-angelica lactone to γ-valerolactone has been examined under mild conditions where high yield toward γ-valerolactone were obtainable. Secondary alcohols as an internal source of hydrogen were found to be as active as hydrogen in the hydrogenation of levulinic acid. This has been proven using conventional heating or microwave irradiations methods. Analysis of reaction network confirms the conversion of levulinic acid to γ-valerolactone through γ-hydroxyvaleric acid as an intermediate. Beside the main hydrogenation reaction of α-angelica lactone, the isomerization and ring-opening reactions have found to take place and yield by-products like valeric and pentenoic acids. Furthermore, this research was extended to the investigation of γ-valerolactone synthesis starting from different esters of levulinic acid. Examining the relationship between the ester of choice and the activity reveals higher yield of γ-valerolactone for the esters with low and linear alkyl chain.The second stage focus on the preparation of levulinic esters themselves. Starting from levulinic acid and α-angelica lactone, levulinic acid esters were prepared using different catalytic systems and under mild conditions. The use of α-angelica lactone as a substrate found to be more efficient than levulinic acid as no equilibrium is encountered in the addition of alcohols to α-angelica lactone. A mechanistic study of the addition of alcohols to α-angelica lactone reveals the presence of pseudo-esters of levulinic acid prior the rearrangement step which yields the neat esters.This dissertation is also dealing with the preparation of 2-methyltetrahydrofuran starting from levulinic acid, α-angelica lactone, levulinic acid esters, and γ-valerolactone. A prohibitive effect of water in the reaction mixture on the productivity of 2-methyltetrahydrofuran was confirmed. Additionally, the stability of 2-methyltetrahydrofuran was examined where pentanol has been observed as a degradation product of 2-methyltetrahydrofuran over time. A reaction network analysis reveals several side reactions occurring in parallel with the hydrogenation reaction of γ-valerolactone to 2-methytetrahydrofuran. The utilization of ruthenium supported on carbon has found to catalyze other reactions like dehydration, decarbonylation, and dehydrogenation reactions. This yields compounds like pentanol, pentane, butanol, butane, methane beside 2-methyltetrahydrofuran.
Al-Shaal, Mohammad G.