The raw gas, e.g., from the steam reforming of natural gas, is freed from CO, by scrubbing with ethanolamine solution until the CO, concentration reaches ca. 50 ppm. The remaining CO, and H,O are removed by molecular sieve adsorbents. Both products would cause blockages due to ice formation.
Moreover, the gas mixture should be free from N2, as, due to similar vapor pressures, a separation would be very involved and expensive. The N, separation from the natural gas thus occurs before the steam reforming.