Linde North America, a member of The Linde Group, a world-leading gases and engineering company, is introducing ionic compression systems for hydrogen for lift refueling in North America. Linde has used the Ionic Compressor system extensively in Europe for cars and buses. Unlike conventional mechanical systems, the Ionic Compressor uses an ionic liquid in direct contact with hydrogen instead of a piston in the pressurizing process. (Earlier post.)
Linde has been working on the use of ionic compressors for hydrogen and natural gas for a number of years. Fixed metal piston compressors, used for pressures between 200 and 1,000 bar, have many moving parts, and the guides and bearings have to have good lubrication in order to prevent wear. For a fixed-piston compressor to be efficient for natural gas of hydrogen fuel, however, the gas-side space must be absolutely tight; otherwise, lubricant could get in and contaminate the gas. To avoid this problem, Linde developed the ionic compressor.
In contrast to ordinary molecular liquids, ionic liquids consist entirely of particles with negative and positive electric charges. The ionic liquid media developed by Linde are organic salts with melting points between below 100 °C. Ionic liquids have no vapor pressure; the medium cannot mix with the ambient atmosphere provided it does not reach its decomposition temperature.
An ionic liquid compressor replaces the metal piston of a conventional compressor with a specially designed, nearly incompressible ionic liquid. The gas in the cylinder is compressed by the up-and-down motion of the liquid column, similar to the reciprocating motion of an ordinary piston. Because the ionic liquid does not mix with the gas, there is no need for seals and bearings in the compressor.
Linde will also introduce another high-performance hydrogen fueler to the North American market: the HF-KTA hydrogen fueling station. This transportable system, first developed and commercialized in Europe, is easy to deploy and can efficiently supply 350 bar and 700 bar hydrogen to vehicles.
Linde has equipped more than 70 hydrogen fueling stations in 15 countries, supplying hydrogen for projects large and small. Amounts supplied range from a few hundred cubic feet of compressed hydrogen in cylinders to thousands of tons of liquid and gaseous hydrogen delivered by tank truck or pipeline