Nickel-loaded zeolite snags small alkynes from mixtures with olefins

When making polymers from lower olefins like ethylene, propylene, and 1,3-butadiene, it’s important to ensure no alkynes are in the mix. These small hydrocarbons—acetylene, propyne, and butyne—are by-products of the steam-cracking process that produces lower olefins, but they can poison polymerization catalysts if they’re present in levels above 5 ppm. To eliminate alkynes, polymer makers typically partially hydrogenate them using palladium catalysts. But this method is expensive and can result in fully hydrogenated hydrocarbons. Looking for a less costly and more reliable method for separating alkynes from olefins, researchers led by Nankai University’s Landong Li and the University of Manchester’s Sihai Yang found that inexpensive zeolites loaded with nickel can selectively adsorb alkynes mixed with olefins (Science 2020, DOI: 10.1126/science.aay8447). The zeolite they used, faujasite, acts as a scaffold for Ni(II). The researchers fill the faujasite’s pores with Ni(II), which forms complexes with alkynes when a gaseous olefin-alkyne mix passes through it. Using this material, the scientists were able to purify lower olefins so that less than 1 ppm of alkyne was present. Using nickel is key: zeolites loaded with copper or zinc didn’t work as well. They also showed they could regenerate the nickel-zeolite material over 10 cycles by heating it to 150 °C. This ability suggests the material could be used industrially.