hide
Free keywords:
-
Abstract:
The growing demand of fossil fuel resources comes at a time of diminishing reserves of these non-renewable resources. To sustain modern civilization an alternative resource must be found to continue the supply of energy and chemicals. In addition, implementation of an alternative feedstock implies the development of new catalyst systems and processes.
Being renewable, biomass is the only sustainable source of energy and organic carbon. Utilizing straightforward chemical methods, biomass can be transformed into 5-hydroxymethylfurfural (HMF), a platform chemical that can serve as an important intermediate to biofuels and commodity chemicals. This thesis describes the reaction systems for the selective conversion of carbohydrates to HMF and its further upgrading to potential biofuels via aldol condensation and subsequent hydrogenation reactions.
Dehydration of sugars to HMF was conducted in a two-phase solvent system based on environmentally benign solvents. Thereby, the employment of novel acidic resin catalysts was demonstrated. Varying the physico-chemical properties of the catalysts makes it possible to identify factors governing the dehydration reaction. Accordingly, a high density of accessible acid sites and low cross-linker content facilitated the highest selectivity towards the desired HMF product. Recycling experiments were performed to prove the stability of polymeric materials as solid acid catalyst. With the aim to produce a variety of potential biofuels, upgrading of HMF via a C-C bond forming reaction was chosen. Here, liquid-phase aldol condensation of HMF and acetone catalyzed over solid bases was investigated. Thereby, Mg-Al hydrotalcites with different Mg/Al molar ratios and spinel oxides such as MgAl2O4 , ZnAl2O4 and CoAl2O4 were synthesized and characterized. Temperature-programmed CO2 desorption measurements verified the Brønsted OH- groups as the active basic sites. Moreover, in the case of Mg-Al hydrotalcites calcination and subsequent rehydration were required to generate suitable active sites. The larger surface area of mesoporous spinels provided more accessible active sites leading to higher catalytic activity. To investigate the reusability of the materials as solid base catalyst recycling tests were performed. Furthermore, with the aim to design a multifunctional catalyst and with respect to process integration, metal was introduced into a mesoporous spinel. Noble as well as non-noble metal loaded spinel oxides showed high activity in both aldol condensation and subsequent hydrogenation into potential biofuels. Thereby, Cu/MgAl2O4 enabled selective formation of previously unreleased product. Noteworthy, transfer hydrogenation was successfully employed utilizing Cu/MgAl2O4 and isopropanol as a hydrogen donor.
