Heavy hydrocarbon recovery from pressure swing adsorption unit tail gas

A process for the separation of nitrogen, carbon dioxide or both from a natural gas feed stream, and the recovery of C3+hydrocarbons from said feed stream, which comprises:

• passing said natural gas feed stream to a first pressure swing adsorption unit containing a crystalline titanium silicate, adsorbent so as to preferentially adsorb nitrogen and carbon dioxide and produce a first product stream containing at least 90 mol. % methane and a low pressure waste stream having a higher molar concentration of nitrogen and carbon dioxide than said feed stream, said waste stream further containing a portion of said C3+hydrocarbons contained in said feed stream and which have been co-adsorbed on said titanium silicate adsorbent;
• passing said waste stream to a second adsorption unit containing a hydrocarbon-selective adsorbent so as to preferentially adsorb said co-adsorbed C3+hydrocarbons to produce a second product stream enriched with nitrogen and carbon dioxide;
• and
• directing a methane-containing stream having a pressure intermediate the pressure of said first product stream and said waste stream to said second adsorption unit to purge said hydrocarbon-selective adsorbent and produce a combined stream of methane and said co-adsorbed C3+hydrocarbons adsorbed by said hydrocarbon-selective adsorbent.

A process for the separation of carbon dioxide from a natural gas feed stream, and the recovery of C3+hydrocarbons from said feed stream, which comprises:

• passing said natural gas feed stream to a first pressure swing adsorption unit containing a silica gel adsorbent so as to preferentially adsorb carbon dioxide and produce a first product stream containing at least 90 mol. % methane and a low pressure waste stream having a higher molar concentration of carbon dioxide than said feed stream, said waste stream further containing a portion of said C3+hydrocarbons contained in said feed stream and which have been co-adsorbed on said silica gel adsorbent;
• passing said waste stream to a second adsorption unit containing a hydrocarbon-selective adsorbent so as to preferentially adsorb said co-adsorbed C3+hydrocarbons to produce a second product stream enriched with carbon dioxide;
• and
• directing a methane-containing stream having a pressure intermediate the pressure of said first product stream and said waste stream to said swing adsorption unit to purge said hydrocarbon-selective adsorbent and produce a combined stream of methane and said co-adsorbed C3+hydrocarbons adsorbed by said hydrocarbon-selective adsorbent.