Cleaning up natural gas to make the most of its methane typically entails using aqueous solutions of alkylamines to remove hydrogen sulfide and carbon dioxide from the gaseous mix. Known as sweetening because the gas smells better after H2S is removed, this process produces elemental sulfur as a by-product. Although sulfur is used to make gunpowder and sulfuric acid, it has relatively few large-scale applications. Chemists at Korea Advanced Institute of Science & Technology have found a way to use sulfur to help scrub CO2 from natural gas. Ali Coskun and colleagues used elemental sulfur to synthesize ultramicroporous benzothiazole polymers in a catalyst- and solvent-free synthesis. These sulfur-containing polymers (part of the polymer structure is shown) can separate CO2 from methane in natural gas, flue gas, and landfill gas (Chem 2016, DOI: 10.1016/j.chempr.2016.08.003). Such polymers could be used in a two-step sweetening process, Coskun suggests, where H2S is first removed from natural gas via an amine solution and then CO2 is eliminated with the polymer. Sulfur, the chemists note, can be effectively recycled back to the natural gas purification process, offering the potential for a high-value, large-scale application for a low-value commodity.