For hydrogen fuelling stations, Linde has developed a 5-stage ionic compressor. The pistons of the machine move up and down hydraulically. On the top of the pistons there is the ionic liquid which is compressed through the compressor cylinder as a "liquid piston" together with the hydrogen. At the end of the compression process the ionic liquid is separated from the hydrogen by the separators and returned to circulation. This design results in less wear and tear as well as much higher energy efficiency thanks to optimized cooling and avoidance of parasitic volume during the compression process. Compared to a conventional piston compressor, energy savings is around 40 %.
(Source: You Tube)