Humine : Bildung und Wertschöpfung
Maerten, Stephanie; Liauw, Marcel (Thesis advisor); Klankermayer, Jürgen (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2018
Humins are dark colored, solid polymers that occur during various processes of acid catalyzed biomass valorization. Humins are only soluble in strong bases and thus so far not industrially used as feedstock. The structure and the mechanism of the humin formation are not well known. The academic research so far focuses mainly on avoiding or minimizing the humin formation. However, using kinetic tools this is impossible. To handle the humins knowledge-based, the kinetics and the mechanism of the humin formation was studied in this thesis. The reaction of glucose to levulinic acid and formic acid via 5-HMF catalyzed with homogeneous acids was used as an example for the system where humins occur as side products. The results were compared with data from the literature and subsequently evaluated with detailed data analysis. For that a new method to use the elemental analysis of polymers in general was developed for this thesis and applied to the humins. Additionally, the kinetics of the reaction were analyzed with extensive model discrimination. For the first time the reaction was carried out in a microwave reactor and subsequently analyzed. By using design of experiments, valuable information about the kinetics was obtained from these experiments. Based on all combined information the process was for the first time transformed into a continuous plant. For that purpose, an already existing plant was transformed. To extract all humins from the reactor, a cleaning step was integrated into the process, making the continuous reaction possible. The combined data from the experiments and literature were fed into a Markov-Chain-simulation (hybrid Monte-Carlo) of the humin structure. The simulation of the polymeric structure includes the results of the spectroscopic measurements and mechanistical assumptions. The result of the simulation is a polymeric structure of the humins and the segment length distribution of the linear polymer units. The simulated polymeric structure of the humins explains the analytical data. These new findings can be used to develop ways of using humins as starting material. One new method to use humins as starting material was developed in cooperation with the university of Erlangen-Nuremberg. The humins from the levulinic acid formation process were used as starting material to produce formic acid and acetic acid with polyoxometalate catalysts. The used catalyst can be recycled. Although the process was already known for other biomass material, the specialty of the humin starting material is the formation of acetic acid at low reaction temperature.