Hydrogen storage in Liquid Organic Hydrogen Carriers (LOHC)

Whenever there is a time duration between the production of hydrogen and its use, the hydrogen needs to be stored in a certain location, preferably near the point of use. Some German companies and research institutes investigate a new way of storing hydrogen: in synthetic aromatic-based heat transfer oils that are normally used in bakery systems and other high temperature applications. Here the heat transfer oil acts as a liquid organic hydrogen carrier, LOHC.

The hydrogen is stored inside the liquid hydrogen carriers via a catalytic reaction. The liquid now has a low viscosity and looks like water. After the hydrogenation the viscosity has increased, and the liquid looks like honey.

When loaded with hydrogen, this LOHC is flame-retardant, which makes it a safe transport medium for hydrogen to the location of use where the hydrogen can be unloaded from this carrier liquid.

The loaded LOHC can be stored at ambient conditions, which is (another) advantage over gaseous hydrogen. This loading/unloading is a reversible process; hydrogenation (loading) requires higher pressures, is exothermal and therefore releases energy, whereas dehydrogenation (unloading) is an endothermal process which requires energy and therefore higher temperatures - both catalyst-driven.

Bronkhorst’s distributor, Wagner Mess- und Regeltechnik, is requested to assist the German partners in their R&D.

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Application requirements

The companies investigate at which pressure the reaction performs best for loading and unloading. To this end, accurate flows of LOHC and hydrogen must be supplied to the reactor. Tricky part here is the change of viscosity of the LOHC before and after the catalytic reaction. The mass flow instruments need to be able to cope with these viscosity changes.

Important topics

Ability to dose and pump viscous liquids
Accuracy
Mass flow instruments need to be able to cope with viscosity changes

Process solution

In one setup, the LOHC is heated up to reach the right viscosity range and is brought to a higher-pressure level by a Wadose HPLC pump with heating element. A high temperature Coriolis flow meter with suitable electronics and a control valve is used here to dose the LOHC to the reactor vessel.

In a different setup, the dosing of the LOHC at higher viscosities also works very well with HNP pumps in combination with the Coriolis mass flow meters. Here the medium does not have to be heated up very much, because the pump copes very well with high viscosities.

Flow scheme: to store hydrogen in tank for transport (loading process)

Of the hydrogen that is fed to the LOHC process, the flow is only measured. This hydrogen (that leaves the electrolyser in a previous stage prior to entering the reactor vessel) is pressure-controlled.

For this application, several Bronkhorst instruments are being used for several aspects of the process:

to apply a pressure,
for pumping,
for measuring and controlling media
to reveal the media density
to measure relevant temperatures

The combination of these devices makes it a highly functional solution.

Flow scheme: LOHC after transport (unloading of hydrogen)

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Hydrogen storage in Liquid Organic Hydrogen Carriers (LOHC)

Application requirements

Important topics

Process solution

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