Algae-derived N-doped porous carbons with ultrahigh specific surface area for highly selective separation of light hydrocarbons

•Low-cost and facile one-pot method for porous carbon preparation.•Ultrahigh specific surface area, large pore volume, and rich N-contents.•Outstanding C3 and C2 adsorption capacity.•High IAST selectivity and adsorbent S value in VSA process for C3H8/CH4 and C2H6/CH4 separation.•C2H6-selective adsorbent for C2H6/C2H4 separation.