Process for separating methane and nitrogen

Claim 1

A process for the separation of methane and nitrogen comprising providing added refrigeration to the process at required column temperature levels by a recirculating fluid heat pump, while precluding the need for significant amounts of outside added refrigeration or large expansion of process streams, by the steps of: (a) introducing a feed comprising methane and nitrogen into a rectification column operating at a pressure in the range of from 200 to 450 psia; (b) separating the feed in said column into a nitrogen-enriched vapor and a methane-enriched liquid; (c) partially condensing nitrogen-enriched vapor by indirect heat exchange with heat pump fluid to warm the heat pump fluid; (d) employing at least some of the resulting liquid of step (c) as reflux liquid for the column; (e) partially vaporizing methane-enriched liquid by indirect heat exchange with warm heat pump fluid; (f) employing at least some of the resulting vapor of step (e) as reflux vapor for the column; (g) warming remaining methane-enriched liquid of step (e) by indirect heat exchange with warm heat pump fluid wherein not more than 75 percent of said remaining methane-enriched liquid is vaporized; (h) further warming the warmed methane-enriched fluid of step (g) by indirect heat exchange with feed prior to the introduction of said feed into the column; and (i) recovering resulting methane-enriched fluid as product methane, thereby providing refrigeration to the column at or below column temperature levels.