Production of ultra-pure hydrogen from wood

To produce hydrogen on the basis of wood in small, decentralised facilities, the researchers modified the conventional iron-steam-process and added a gasification process. To avoid a reduction in the reactivity of the iron oxide based oxygen carriers after a few cycles, iron oxide has to be stabilised, e.g. through the addition of high Tammann temperature metal oxides such as alumina. One challenge to overcome was that the synthesis gas produced contained impurities, such as tars and sulphur containing compounds. The project team developed novel oxygen carrier formulations that showed a high tolerance to impurities of the synthesis gas and that minimized the extent of carbon deposition.

Hydrogen, when produced sustainably, could contribute to a reduction in anthropogenic CO2 emissions and reduce the dependence of Switzerland on importing energy. Hence the efficient production of hydrogen from renewable resources such as wood is an active area of research. Furthermore, hydrogen can only be used in low-temperature fuel cells if it is highly pure. The prevailing method of hydrogen production involves the steam reforming of methane, a process that produces also carbon dioxide. Hydrogen produced through a reforming process needsto be subjected to costly gas purification operations in order to reduce the content of carbon monoxide to the relevant standard levels.

The main goal of this research project is to develop innovative, iron-based redox materials with the following properties:

• high content of active material;
• fast kinetics;
• mechanical stability;
• the capability to crack tars (i.e. to split them into hydrocarbons with shorter chains);
• resistance to hydrogen sulphide and components of wood ash;

The researchers produced such materials using a sol-gel method, which allows for the synthesis of nano-structured redox materials. The materials were tested a fixed-bed reactor. Another important facet of this project aimed a coupling directly the fixed-bed reactor to a wood gasifier. Such a process operation might be interesting for industrial application.

The results of this project can contribute to a more sustainable and efficient production of hydrogen and help in reducing Switzerland's dependency on fossil fuel.

The project included two separate studies that utilize either conventional oxygen carriers or novel oxygen carriers that are enriched with copper oxide. Both studies showed that hydrogen impurities such as carbon monoxide could be minimized through advances in the formulations of the oxygen carriers, e.g. though the addition of copper oxide. Another important factor is the selection of appropriate contacting and reaction times.

Distributed production of ultrapure hydrogen from woody biomass