Green Hydrogen

Linde continues to research ways of producing hydrogen from biogenic raw materials that are readily available and do not compromise food supplies.

We are looking primarily at raw materials which are already sophisticated enough to generate commercially viable hydrogen.

Following extensive studies to explore suitable raw materials and in-depth laboratory tests, work is now underway on a landmark demo plant at our Leuna site. This facility will pyroreform glycerol to create a hydrogen-rich synthesis gas.

Crude glycerol is a biogenic raw material, available throughout the year. It is a cost-effective, easy to handle and does not conflict with food production. 

Salt is first removed from the crude glycerol by means of vacuum distillation before it is thermally treated. The standard distillation process is further simplified as only salt needs to be removed. Other substances such as water, methanol and organic matter do not interfere with the downstream process, and may even have a desirable effect.

This simplified purification step also marks an innovation in the overall process chain. 

The next step involves diluting the purified glycerol with water, compressing it to 30 bars, preheating it, mixing it with compressed steam in a special chamber and feeding it to the pyrolysis reactor where it is superheated.

This completely breaks up the glycerol into hydrogen, carbon monoxide, carbon dioxide, methane and other hydrocarbons. Although this type of process is normally very prone to soot, this can be eliminated by carefully selecting the operating parameters and separating the catalytic stage. 

The pyrolysis gas is fed at a high temperature (600-750°C) to a reformer where the hydrocarbons (methane in particular) contained in the gas are reformed in a special catalytic reaction. This catalytic step greatly increases the hydrogen yield. 

With smaller volumes, the reformate gas flows to a quench chamber, for example, where it is water-cooled from 850°C to 250-330°C. With larger volumes, steam is released to cool the gas, which is then fed directly to the CO shift reactor at 28 bars.

As the subsequent CO shift and H2 purification steps are already well-established, the synthesis gas from this glycerol demo system is fed into an existing steam reforming pipeline in Leuna.

Together with the reformate gas, it passes through the CO shift and pressure swing adsorption (PSA) stages to create pure hydrogen. 

The glycerol demo plant produces hydrogen at a rate of around 50 Nm³/h. Depending on the final application, the hydrogen can be fed to a liquefaction plant, resulting in a total stream of 4.4 kg/h of liquid hydrogen from biogenic sources.

This landmark project marks the first plant to enable industrial-scale production of “green” hydrogen at a commercially viable cost, allowing automotive manufacturers to deliver on their “clean energy” promise from 2010 onwards.