In this NIST illustration of the HKUST-1 metal-organic framework, copper atoms (green) are exposed to the open air within the lattice-like structure.

Atomic-Level Research Heralds Safer Acetylene Shipments

Scientists working at the National Institute of Standards and Technology found that one gram of a lattice structure of copper oxide and benzene stores as much acetylene as today's high-pressure cylinder can hold.

A potential breakthrough by scientists working for the National Institute of Standards and Technology may make it easier to move large amounts of acetylene safely. NIST announced that the research team has figured out why a metal-organic framework (MOF), a lattice-like structure made of copper oxide and benzene, can safely store at low pressure up to 100 times as much acetylene as today's conventional methods accomplish. The lattice "soaks up acetylene like a sponge," according to NIST.

Yun Liu, a physicist at the NIST Center for Neutron Research, said the discovery "could provide substantial savings in acetylene transportation costs." The research team included scientists from the University of Texas at San Antonio.

Acetylene has long been used for welding, and it is also used as a starting point for synthesizing chemicals used in plastics and explosives, according to NISH. Several hundred thousand tons of acetylene are produced annually in the United States, "but its volatility renders it difficult to transport: It becomes dangerously explosive at about 30 psi (207 kilopascal), only about twice normal atmospheric pressure. To safely store acetylene, storage cylinders have to be filled with both porous material and liquid solvents such as acetone," the agency's news release explains. "The research team used neutron powder diffraction and computer calculations at the NCNR to investigate an MOF called HKUST-1, which has a sponge-like interior in which copper atoms are exposed to the air. The analysis showed that the acetylene attaches to the exposed copper by virtue of weak electrical charges, allowing the MOF to store 201 cubic centimeters of acetylene per gram of lattice at ambient pressure -— comparable to the amount of similar chemicals that can be contained within a high pressure storage cylinder.

MOFs may be useful for storing other materials, Liu said. "More than a thousand of these metal—organic frameworks have been created so far," he said. "We hope our technique will turn out to be a good way to check such materials' properties in advance." The team -- S. Xiang, W. Zhou, J.M. Gallegos, Y. Liu, and B. Chen -- published its results, "Exceptionally High Acetylene Uptake in a Microporous Metal–Organic Framework With Open Metal Sites," in the Journal of the American Chemical Society.

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