The research suggests that filtering out acetylene using MOFs would produce ethylene at the high purity that industry demands while sidestepping the current need to convert acetylene to ethylene via a costly catalytic process.
The chemical name for the plastic you see every day – from water bottles and grocery bags to household appliances — is polyethylene, a pliable material made by stringing together long chains of a simpler molecule called ethylene.
Worldwide demand for plastic makes ethylene the most widely produced organic compound in the world, with well over 100 million tons of it manufactured each year, largely by refining crude oil.
Newly made ethylene is not pure enough to become plastic because the refinement process also creates a substantial amount of acetylene, which can ruin the catalysts that enable ethylene molecules to be strung together.
The conventional industrial solution is to convert this undesirable acetylene into ethylene as well, but this step requires the use of palladium, an expensive and rare metal, as a catalyst and consumes a significant amount of energy.
The research team, which includes scientists from the NIST Center for Neutron Research (NCNR) and five universities from around the world, found that a family of MOF materials called SIFSIX, discovered in the 1990s, might provide a better alternative for removing the acetylene.
The team found that when they passed ethylene through the MOFs, the fluorine attracted and captured most of the acetylene contaminant, letting the now-purified ethylene to pass unhindered. Varying the size of the pores by changing the length of the girders allowed the MOFs to filter ethylene-containing acetylene in concentrations of anywhere from 1 percent to 50 percent, which are typical in industry.
The SIFSIX MOFs set records among adsorbent materials for both selectivity and adsorption capacity. According to the research team, the results show that the SIFSIX group offers a viable alternative to standard industrial practice.
