Untersuchung der metallkatalysierten Hydrierung von biogener Itaconsäure
Aachen (2019) [Dissertation / PhD Thesis]
The development of a biogenous value chain is a current challenge of society. Fermentatively preparable carboxylic acids, such as itaconic acid (IA), are potential platform chemicals that can be converted by a catalytic reaction into high-value fuels, solvents or fine chemicals. In the present work, the reaction network of itaconic acid dehydrogenation with the commercial Ru (5 wt.-%)/C catalyst was first examined in more detail. After optimization of the reaction parameters, supported noble metal catalysts based on acidic or basic support materials were developed for the selective synthesis of methyl-γ-butyrolactone (MGBL), methyl-1,4-butanediol (MBDO) and 3-methyltetrahydrofuran (MTHF).The conversion of IA to MGBL proceeds through a series of hydrogenation and dehydration reactions. An effective catalyst must therefore have a transition metal for hydrogenation and acidic sites for dehydration. The synthesis of the metal in the form of nanoparticles could be achieved in this work by the electrostatic adsorption. Smaller metal particles had the largest possible surface area relative to their particle mass, resulting in higher activity. Especially by using a WO3-ZrO2 mixed oxide, the MGBL yield could be increased. From the NH3 and CO2 TPD profiles it was found that for a good MGBL selectivity, especially medium-strong acid centers were needed in the absence of strongly basic centers. These acid sites activated the carbonyl group, facilitating a nucleophilic attack on the C=O bond. To investigate the influence of metals on IA hydrogenation, alternative metals were tested as ruthenium. Although it had a high activity, but the MGBL yield was due to occurring follow and side reactions very low. A better alternative was the Pt (5 wt.-%) / C catalyst, which did not catalyze any side reactions, resulting in a better MGBL yield. For selective MBDO synthesis, catalysts based on Pd, Pt and Rh were tested. For the Pd and Pt catalysts in the aqueous reaction medium, especially the subsequent reaction to the MTHF led to a reduction of the MBDO yield. To prevent the acid-catalyzed cyclization to MTHF, working in a basic reaction medium was necessary. MTHF itself could be obtained from the MBDO by acid additives with almost no yield loss at 190°C.A major cost factor in the synthesis of fermentation products is the downstream processing. Therefore, in the last part of this work, Pd (4 wt.-%) - Ru (1 wt.-%)/C was tested in the IA direct hydrogenation of a filtered fermentation solution in the presence of fermentation salts and residual glucose. The influence of different nutrient salts on IA hydrogenation was investigated. A high salt content in the reaction solution was not generally problematic. The only decisive factor was which ions were involved. Glucose residues in the fermentation solution dramatically reduced catalyst activity, presumably due to blocking of the pore system due to formed oligomers. Based on this, IA direct hydrogenation with high MGBL yields without pretreatment of the fermentation solution was not possible. A more effective approach to processing the fermentation solution was the combination of ion exchange and carbon filtration. The acidic or basic Amberlyst could separate the remaining nutrient salts and thus prevent irreversible adsorption on the precious metal. Filtration through an activated charcoal packed column removed the oligomeric impurities which resulted in blockage of the pore system.