Mixed gas separation method and mixed gas separation device

A mixed gas separation method comprising:

• a) supplying a mixed gas containing at least N2, H2, and CO2 and having a CO2 concentration of 30% or less by volume to a first separation membrane that selectively allows passage of H2 to separate said mixed gas into a first permeated gas that has permeated through said first separation membrane and a first non-permeated gas that has not permeated through said first separation membrane;
• b) supplying said first non-permeated gas to a second separation membrane that selectively allows passage of CO2 to separate said first non-permeated gas into a second permeated gas that has permeated through said second separation membrane and a second non-permeated gas that has not permeated through said second separation membrane;
• and
• c) supplying said second non-permeated gas to a CO2 collector that separates and collects CO2 by a separation method other than membrane separation to collect CO2 contained in said second non-permeated gas,
• wherein said first non-permeated gas has a CO2 concentration that is 5% or more by volume higher than or equal to the CO2 concentration in said mixed gas,
• said second non-permeated gas has an N2 concentration of 50% or more by volume, and
• said second non-permeated gas has an H2 concentration of 30% or less by volume.