Methods, apparatuses and systems for processing fluid streams having multiple constituents are provided including embodiments utilizing ascending temperature separation processes as well as combined ascending and descending temperature separation processes. For example, in one embodiment, a mixed gas stream may be processed by flowing the stream through multiple heat exchangers, expanding the stream, and then separating the stream into a liquid portion and a vapor portion. The vapor portion, having an increased or decreased concentration of an identified constituent may then pass through the heat exchangers again in reverse order and collected. The liquid portion may then be subjected to further, sequential separation acts which each take place at increasing temperatures. In another embodiment, numerous, sequential separation acts take place in, for example, at decreasing temperatures and, subsequently, at increasing temperatures. Such a mixed fluid stream, for example, may include constituents such as hydrogen, carbon monoxide and methane.
 The United States Government has certain rights in this invention pursuant to Contract No. DE-AC07-05ID14517 between the United States Department of Energy and Battelle Energy Alliance, LLC.