Hydrogen liquefaction method and liquefier

A method of liquefying a hydrogen feed stream having both ortho-species and para-species of hydrogen, said method comprising:

• liquefying the hydrogen contained within the hydrogen feed stream within a hydrogen liquefier to produce a liquid hydrogen product stream, the hydrogen liquefier having heat exchangers operating at successively lower temperatures to cool the hydrogen;
• catalytically converting a portion of the ortho-species contained in the hydrogen feed stream to the para-species in a higher temperature catalytic converter, the portion being converted including desorbed ortho-species;
• adsorbing a further portion of the ortho-species contained in the hydrogen feed stream within an adsorbent of at least one adsorption unit to produce a para-rich stream containing unadsorbed ortho-species and regenerating the adsorbent within the at least one adsorption unit through desorption to produce the desorbed ortho-species;
• introducing the desorbed ortho-species into the higher temperature catalytic converter;
• introducing at least the para-rich stream into a lower temperature catalytic converter and catalytically converting at least the unadsorbed ortho-species to the para-species, thereby producing an ortho lean stream having a reduced content of the ortho-species as compared with that of the hydrogen feed stream;
• and
• forming the liquid hydrogen product stream from the ortho lean stream;
• the higher temperature catalytic converter, the at least one lower temperature catalytic converter and the at least one adsorption unit being in flow communication with the heat exchangers such that the higher temperature catalytic converter operates at a higher temperature level greater than that of the at least one lower temperature catalytic converter and the at least one adsorption unit has an operational temperature no greater than that of the higher temperature catalytic converter and greater than that of the lower temperature catalytic converter.