Herstellung von Oxymethylenethern anhand von alternativen Reaktionskonzepten

Gierlich, Christian Henning; Palkovits, Regina (Thesis advisor); Jupke, Andreas (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

In this dissertation, process and reaction concepts for the preparation of oxymethylene ethers (OME$_X$) are developed. OME$_X$ are oxygenated oligomers without direct covalent C-C bonds. They show a very good emission profile in diesel engines with low NO$_X$ and soot emission. OME$_X$ with a chain length of 3-5 are ideally suited for low-impact and environmentally friendly use in the transportation sector due to their diesel-like properties. The required amount of liquid fuels in the transportation sector is enormous and requires, in terms of environmentally friendly production, efficient processes for the introduction of a novel fuel that is not based on limited available fossil raw materials. This dissertation deals with the production of OME$_{3-5}$ using novel process concepts. For this purpose, the most important adjusting screws in the OME synthesis are investigated and evaluated in a differentiated manner. A decisive criterion for an efficient synthesis is the selection of the reactants. For this purpose, OME$_1$ is chosen as the smallest oligomer and aqueous formaldehyde as reactants. The reaction is carried out in a plug-flow reactor and revealed data is subsequently analyzed. For this purpose, a shaping methodology for the design of the catalyst is elaborated in the work, with which shapes and geometries can be successfully created from zeolite powders. On the one hand these geometries are predictable in their flow properties and on the other hand pressure drop and residence time can be adjusted via the geometry. Data showed that the pressure drop across the catalyst can be tailored. The reaction is subject to equilibrium, with H$_2$O being formed as a co-product. For an efficient process design, co-products and by-products are separated from OME$_2$ and OME$_{6+}$. By-products can be recycled back into the reactor. However, recirculation of co-products shifts the equilibrium in favor of the reactants and should therefore be removed from the process. Due to the similar boiling point of H$_2$O and OME$_2$, only a mixture of H$_2$O and OME$_2$ can be separated by distillation. Therefore, for further separation, adsorption is considered as a separation methodology. For this purpose, a material screening with different activated carbons as well as hypercrosslinked polymers is carried out in the work. In addition, the desorption of the materials is examined as well as the influence on the overall process in the case of a potential process recirculation of the H$_2$O-OME$_2$ mixture. Another methodology for separating or shifting the reaction equilibrium is the separation process of extraction. Here, two different approaches are considered in this dissertation. One possibility is to separate OME$_X$ from the reaction mixture after the reaction. Another possibility is to perform the extraction during the reaction to influence the equilibrium by shifting the components into different phases. In this work, a solvent screening model was successfully established, via which potentially possible extraction agents could be selected and tested for their suitability on an industrial process scale. Thus, the results of this work, especially the developed modeling, can contribute to the development of environmentally friendly and low-energy processes to produce chemical products in a fast and cost-efficient way.