This report describes the results of the activity related to the study of ceramic membranes for separation of pure hydrogen produced by biomass gasification processes.

The decarbonization goals set out in the European directives for 2050 encourage the use of renewable energy sources and aim to phase out the use of fossil fuels. Hence the interest in hydrogen, which, when produced by using renewable sources, is a clean and low-carbon fuel over its life cycle. H2 production from biomass gasification could therefore be an interesting alternative to traditional processes (e.g., steam reforming), as it is a “zero-emission” process.

The syngas produced by biomass conversion, in addition to common uses, can be considered as a resource for H2 production with innovative ceramic membrane systems, which operate at high temperature (>700 °C): in fact, pure H2 can be produced from the syngas itself by means of a membrane separation stage, or the syngas can be reacted in a membrane reactor to facilitate H2 production and simultaneous separation.

A literature study was then conducted to analyze the typical thermodynamic and compositional conditions of syngas, identify the operating conditions under which the membranes would operate, and direct the identification of ceramic materials for component development. In particular, this study revealed the presence of impurities (e.g., H2S, HCl, SO2, NH3), as well as high amounts of solid residues, in addition to the basic syngas components, which could be a critical issue for membrane processes. If ceramic materials become unstable under these conditions, syngas purification systems, preferably at high temperature, may be necessary.

Literature review has shown that hydrogen separation membranes based on ceramic materials have lower permeation performance than the more established palladium membranes,but provide greater chemical stability in the presence of pollutants. The most promising compounds are Ln6-xWO12-δ oxides, where Ln is an element belonging to the lanthanide group, or dual-phase composite materials obtained by combining a proton conductor and an electron conductor.

Therefore, preliminary solid-state synthesis tests of La6-xWO12-δ (LWO) powders and subsequent membrane fabrication by uniaxial pressing and sintering were conducted. The tests gave membranes consisting of pure phase LWO with sufficiently dense microstructure.

In addition, after an analysis of the configurations available in the literature and the test procedures adopted, a test protocol was prepared and the plant for the high-temperature hydrogen permeation tests was designed.

The Report is available on the Italian site