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Raney Ni stability and characterization upon different systems and solvents

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Mendes Burak,  Jorge Augusto
Research Group Rinaldi, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Mendes Burak, J. A. (2017). Raney Ni stability and characterization upon different systems and solvents. Thesis, Ruhr-Universität Bochum, Bochum.


Cite as: http://hdl.handle.net/21.11116/0000-0001-165B-1
Abstract
This work shows the versatility of Raney Ni under different conditions and systems, many answers about the behavior of Raney Ni are given here, making this work a significant base for studies or applications of Raney Ni in chemical processes. The reactions using the model compounds from lignin show how each group is converted differently by Raney Ni helping to understand the catalytic upgrading process. Some functional groups are converted easily, e.g. ether bonds, simple phenols, ketones and allylic bonds. For guaiacol and aldehyde groups, longer reaction times and higher active Raney Ni is required for significant conversion. These differences between singles model compounds illustrate the heterogeneity of natural lignin, clarifying the challenge to upgrade natural feedstock. The system Raney Ni and 2-propanol present outstanding results applied to the biorefining process through several runs. The partial deactivation of Raney Ni after catalyzing the biorefining process, which is detected using the model compounds from lignin as probe molecules, is not strong being easily reversed under a new and uncomplicated regeneration process developed here. A simple heating process in 2-propanol is able to regenerate Raney Ni, this new catalyst presents the best results regarding the quality of model compounds upgrade. The Raney Ni properties also Raney Ni stability and characterization upon different systems and solvents change during these processes, the changes are shown by the characterizations. The increase in the particle size and oxidation of the surface species are the strongest changes observed. The new approach using a sustainable and renewable feedstock, limonene, is presented for the production of p-cymene. The new process has high conversion and selectivity towards the p-cymene production. These results are superior to the traditional method used nowadays in industry. Raney Ni employed in this process in the presence of acetone/2-propanol retains the activity and the product distribution for several runs, proving to be a competitive process. Also the characterizations showed how the acetone interacts and affects Raney Ni, leaching aluminum, removing the hydrogen, breaking the domain particles and reducing the magnetic properties. During the biorefining and the model compound reactions, the characterizations have shown the influence of the biorefining process on the material. An organic film is deposited on the surface and subsequently removed after the regeneration process. However, the most interesting are the comparison of the processes using 2-propanol and acetone. Although both solvents have shown high quality results in each process, 2-propanol has a protective and regenerative nature instead of a degenerative character like acetone. In addition, monitoring reactions to investigate the impact of the different solvents used to store of Raney Ni as a function of time and hydrogen storage show how different functionalities develop different characteristics in the Raney Ni. Keto groups lead to a quick removal of the hydrogen content. Water remains the H-storage even after prolonged storage periods but favors the oxidation of the catalyst. Still, alcohols are the most appropriate solvents to store Raney Ni and Raney Ni stability and characterization upon different systems and solvents keep the H-content, presenting a promotion in the activity in the first hours and as the carbon chain grows.