Separation techniques to produce
high purity hydrogen in LOHC processes
Christoph Krieger, Karsten Müller, Wolfgang Arlt
Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
Institute of Separation Science and Technology
The storage of electrical energy with hydrogen has drawn rising attention in recent years. In this application hydrogen is produced in an electrolyzer, stored and in times of energy demand the chemical energy can be converted to electrical energy. However, hydrogen has a very low volumetric density. The reaction with a liquid organic hydrogen carrier (LOHC) in a hydrogenation reaction increases the volumetric density. However, after the storage the hydrogen has to be released in a dehydrogenation reaction.
Dibenzyltoluene as a LOHC has been examined for this study. Although dibenzyltoluene is a high boiling molecule, a certain proportion is evaporated and has to be separated from hydrogen after the dehydrogenation reactor. By cooling and separation of phases (demister) most of the dibenzyltoluene can be separated from hydrogen. However, certain power generation technologies, such as PEM fuel cells, requires for extremely high purified hydrogen: The purity requirements of hydrogen in PEM fuel cells according to ISO 14687 are 2 ppm for organic compounds. Due to the efficiency of the phase separator this purity cannot be fulfilled by just cooling and separation of phases.
The suitability of different separation technologies has been examined to determine the best separation technique to provide purified hydrogen. The focus is set on energetic assessment, size of the apparatuses and the practical feasibility. Within this study both modelling and experimental results will be compared.
Preliminary investigation shows that absorption and membranes as separation techniques cannot compete with adsorption, due to the energy demand of these separation processes. Therefore, the emphasis of this study is laid on adsorption processes.
See more of this Group/Topical: Separations Division