Abstract

Hydrogen bound in organic liquid hydrogen carriers (LOHC) such as dibenzyl-toluene enables simple and safe handling as well as long-term storage. This idea is particularly interesting in the context of the energy transition, where hydrogen is considered a key energy carrier. The LOHC technology serves as a storage between volatile energy and locally and timely independent consumption. Depending on the type of application, decisive specifications are placed on the hydrogen purity. In the product gas from dehydrogenation, however, concentrations of 100 to a few 1000 ppm can be found from low boiling substances, which partly originate from the production of the LOHC material, but also from the decomposition and evaporation of the LOHC molecules in the course of the enormous volume expansion due to hydrogen release. For the removal of undesired traces in the LOHC material, a pre-treatment and storage under protective gas is necessary. For purification, the use of Pd-based membranes might be useful, which makes these steps less important or even redundant. Heat supply and phase contacting of the liquid LOHC and catalyst is also crucial for the process. Within the contribution, the first results from a coupled microstructured system—consisting of a radial flow reactor unit and membrane separation unit—are shown. In a first step, the 5 µm thick PdAg-membrane was characterized and a high Sieverts exponent of 0.9 was determined, indicating adsorption/desorption driven permeation. It can be demonstrated that hydrogen is first released with high catalyst-related productivity in the reactor system and afterwards separated and purified. Within the framework of limited analytics, we found that by using a Pd-based membrane, a quality of 5.0 (99.999% purity) or higher can be achieved. Furthermore, it was found that after only 8 hours, the membrane can lose up to 30% of its performance when exposed to the slightly contaminated product gas from the dehydrogenation process. However, the separation efficiency can almost completely be restored by the treatment with pure hydrogen.

Highlights

  • The call for a change, caused by climate change, is gaining importance in our society

  • Within the framework of limited analytics, we found that by using a Pd-based membrane, a quality of 5.0 (99.999% purity) or higher can be achieved

  • Its potential as fuel is enormous; in the medium to long term, the mobility sector can be fed with hydrogen for applications such as Materials 2020, 13, 277; doi:10.3390/ma13020277

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Summary

Introduction

The call for a change, caused by climate change, is gaining importance in our society. Young people and scientists demonstrate for climate protection on a regular basis. Sustainable technologies and renewable energy sources are the key to a healthy ecosystem for future generations. Hydrogen plays an important role in this development, as the molecule can be produced and converted in a climate-friendly way—meaning without greenhouse gas emissions. With the use of renewable energy, hydrogen can be produced by the electrochemical splitting of water. Its potential as fuel is enormous; in the medium to long term, the mobility sector can be fed with hydrogen for applications such as Materials 2020, 13, 277; doi:10.3390/ma13020277 www.mdpi.com/journal/materials

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