Clean up sulphur with calixarenes

Carbonyl sulphide is a common impurity in natural gas and, because it is toxic and corrosive, must be removed during processing.

Chemists from the US National Institute of Standards and Technology have found that it can be removed by treating the gas with 4-tert-butyl calixarene - a large organic molecule which binds to the sulphide.

Previously, says lead reseacher Thomas Bruno, refiners used a variety of ways of removing carbonyl sulphide, such as reacting it with mono ethanol amine or hydrolysing it over a catalyst. However, these processes tend to be slow, expensive and inefficient.

Bruno's process, developed with colleague Anthony Lagalante, involves passing the gas through a column packed with calixarene on a solid support. Each calixarene molecule can complex between four and five carbonyl molecules.

Once the column is saturated with sulphide, it can be taken off-stream. The column can be regenerated by heating the packing to 85°C. As well as being simple, the process is faster and cheaper than the alternatives, and absorbs more sulphide, Bruno claims.