In a method for separating a synthesis gas containing carbon monoxide and hydrogen, a synthesis gas flow from a synthesis gas source is compressed in a compressor and separated into at least three gaseous products. If there is insufficient synthesis gas, at least three separation products are recycled in the compressor in order to separate said products.

An apparatus and process for recycling hydrogen can be provided so that hydrogen is recycled during hydrogen liquefaction processing to account for an unexpected loss of feed of hydrogen so the recycled hydrogen can be provided to avoid liquefier operations having to be shut down. Embodiments can utilize a parahydrogen to ortho-hydrogen conversion unit to facilitate such recycling of hydrogen to avoid liquefaction processing problems in liquefaction of the recycled hydrogen included into the feed to account for the loss of fee hydrogen.

A process for separating a gas mixture, a first item of equipment of the process is heated by a first flow of a first heat producer and supplies heat to a first fluid, the first flow of heat producer being heated upstream of the first item of equipment by a heat source, a second item of equipment of the process heats a second fluid while consuming heat, the heat originating from a second flow of the first heat producer heated by the heat source, which heats the second flow of the first heat producer up to an intermediate temperature lower than the second temperature, and by a heater downstream of the source, which heats the second flow of the first heat producer, which has been heated by the heat source, from the intermediate temperature up to a second temperature higher than the first temperature.