Making Plastic Production More Energy Efficient – With MOFs

A team of scientists at the National Institute of Standards and Technology (NIST) USA, created an innovative metal-organic framework (MOF), that can extract ethylene used to make polythene, the most common form of plastic from a mixture of other hydrocaarbons—while consuming far less energy than usual.

Ethylene usually needs to be highly purified for the manufacturing process to work, but with the current industrial technology for separating ethylene from all the other hydrocarbons is a chilly but high-energy process that cools down the crude to more than 100 degrees below zero Celsius. Ethylene and ethane constitute the bulk of the hydrocarbons in the mixture, and separating these two is by far the most energy-intensive step.

In the search for an alternative, scientists have found MOF’s to be promising. On a microscopic level, MOF’s look a bit like a half-built skyscraper of girders and no walls. The girders have surfaces that certain hydrocarbon molecules will stick to firmly, so pouring a mixture of two hydrocarbons through the right MOF can pull one kind of molecule out of the mix, letting the other hydrocarbon emerge in pure form. But the difficulty lay in developing a MOF that grabs ethane by-product and allows ethylene to pass through.

The research team has now built a modified MOF that separates the purified ethylene from a mixture containing ethane. The MOF was built at the University of Texas at San Antonio (UTSA) USA and China’s Taiyuan University of Technology and studied at National Institute of Standards and Technology (NIST). It was in 2012 that an earlier research team found that a frame work called MOF-74 was good in separating a variety of hydrocarbons, including ethylene. In the latest work the new research team modified MOF-74’s walls which managed to adsorb the ethane while allowing the purified ethylene to pass through. The scientists now want to dramatically increase the selectivity. If this alternative method is finally commercialized it would reduce the energy needed to make the 170 million tons of ethylene manufactured worldwide each year.