Molecular sieve sorts ethylene from crude oil

Of all the hydrocarbons composing crude oil, ethylene is one of the most valued by industry. With a low molecular weight and relatively simple structure, it’s an unassuming compound, but contains one crucial feature: a double-bond between its two carbon atoms, which can be broken to attach other atoms and groups. This makes it a basic building block for many more complex hydrocarbon structures, including the common polymer polyethylene.

However, separating ethylene from the complex mixture that is crude oil is a costly business, requiring the crude to be chilled below -100°C. Ethylene can be produced by “cracking” larger molecules using heat, steam and catalysts, but this is also a costly process. Finding a cheaper way of obtaining ethylene directly from crude has been a major goal for the hydrocarbons industry for many years.

Researchers from the University of Texas San Antonio (UTSA) and China’s Taiyuan University of Technology have announced a step forward in this search in the current issue of Science. Working with a team at the US National Institute of Standards and Technology Centre for Neutron Research, the chemists have been studying materials known as metal-organic frameworks (MOFs). These consist of a framework of organic chains joined together with metal atoms, usually iron, which is “decorated” with more organic groups. MOFs have been of interest to the plastics and petroleum industry for some time because their ability to separate individual hydrocarbons from complex mixtures.