Asymmetric polymer-derived ceramic membranes

Recent calls for the development of more sustainable processes and the implementation of alternative energy generation methods have led to an increased demand for membrane-assisted gas separation as an alternative to conventional, primarily thermal separation techniques. While membranes present increased energy efficiency in combination with low instrumental expenditure during operation, the applicability of conventional polymer-based membranes is limited considering their thermal and chemical constraints. Owing to their unique chemical, mechanical, and thermal properties, ceramic membranes can be used in harsh thermal and chemical operation environments. Porous ceramic membranes are generally implemented asymmetrically: a gas-selective micro- /mesoporous functional layer is deposited on a macroporous, mechanically stable support, often combined with intermediate layers. However, the complex structure results in increased processing expenditure and a high implementation threshold. The objective of this project is the development of novel asymmetric ceramic membranes employing a polymer pyrolysis approach, i.e. the thermal conversion of preceramic organosilicon polymers into amorphous ceramics. The rationale for choosing this route stems from the wide variety of processing and pore tailoring strategies available. For the first time, the membrane support as well as the selective layer will be prepared from preceramic poly(carbosilane) or poly(methylvinylsilazane). The resulting membranes will be structurally tailored and evaluated for a potential use in gas separation applications. In order to achieve these goals, the tailoring of pore structures on dimensions spanning several orders of magnitude is necessary. Therefore, the problem will be approached gradually. The first part of the project consists of the development of the macroporous support employing a sacrificial template approach. After infiltration of a densely packed assembly of sacrificial polystyrene or poly(methylmethacrylate) microspheres with the preceramic polymer, the templates will be removed during the thermal conversion process. The structural and mechanical properties of the remaining macroporous ceramic structures will be investigated, enabling a correlation with the process parameters. The second part is focused on the polymer-derived selective layer. In addition to the systematic development of the dip coating deposition technique, the micro-/mesopore structure, relevant for the gas separation properties, will be tailored by controlling the pyrolysis parameters during the polymer-to-ceramic conversion, as well as with the use of molecular porogens. In the final part of the project, the previous findings will be combined in order to develop an integrative processing approach for the preparation of asymmetric polymer-derived ceramic membranes. The resulting materials will be characterized with respect to their gas permeances and permselectivities for different model gases at operation temperatures up to 800 C. As a result, the correlation between process parameters, pore structural development and gas separation performance shall be clarified.

The use of porous ceramic membranes for the separation of gases from gas mixtures represents an important step towards an increase in energy efficiency of a multitude of energy production and transformation processes. However, the complex structuring of these materials results in high expenditure in processing and, subsequently, an increased threshold of implementation. In this project, a novel approach to the preparation of correspondingly structured ceramics is developed by using preceramic, silicon-based polymers as precursors to high-temperature ceramic materials. The successfully achieved objective of the project was the preparation and characterization of novel, single-material based asymmetric membranes, as well as the proof of their applicability as gas separation membranes at elevated temperatures.In this project, multilayer materials made of polysilazane-derived SiCN-based ceramics with graded pore structures were generated. The tailored pore sizes ranged from below one nanometer to several micrometers. The stepwise preparation of the membrane structures included the generation of a macroporous support structure by a sacrificial filler approach, the coating of the support by an intermediate layer, and finally the deposition of a nanoporous selective layer with a thickness of several micrometers. The generation of the nanopores was accomplished by a controlled thermal treatment of the precursor material. Based on this methodology, flat-disc-type membranes were successfully prepared. A self-constructed single gas permeance test rig was used to determine the permeance of these materials for a variety of gases (He, N2, Ar, C2H6, CO2), thus demonstrating the feasibility of the suggested processing approach for the production of asymmetric polymer-derived gas separation membranes.The success of this project is not only a starting point for further scientific activities in this field, but demonstrates the potential of novel methodologies for the preparation of membrane materials with corresponding technological, ecological, and economic advantages.