A New Look at an Old Problem

Learning about clathrate hydrates could deliver a range of benefits

Given today's energy environment, researchers are looking for answers everywhere - including areas that have long been overlooked.

Clathrate hydrates are an excellent example. These common structures have long been considered as annoying, and even harmful, by the oil and gas industry because of their tendency to clog oil drill holes and gas pipelines. But in fact, leaving aside their less-than-esteemed reputation, they could hold answers to some significant challenges.

Getting past old barriers

Indeed, even the origin of their name - the Greek word khlatron, meaning barrier - suggests how scientists have been focused primarily on their negative qualities. However, all of that is changing, and today clathrate hydrates are attracting renewed interest in many fields.

Take, for example, the work of Camille Jones, Ph.D., assistant professor of chemistry at Hamilton College in Clinton, NY. With the support of a grant from the American Chemical Society's Petroleum Research Fund, Dr. Jones and a team of undergraduate chemistry majors are studying these little-understood structures using experimental physical chemistry and computational chemistry.

A host of possibilities

"Clathrate hydrates," observes Jones, "contain mostly water molecules, which gives them an appearance and many properties similar to ice. But they differ in that their water molecules are arranged into hydrogen-bonded cavities that are just large enough to hold guests, small molecules or atoms of inert gases."

Moreover, clathrate hydrates occurring naturally in the earth's deep seas and permafrost regions can contain large amounts of methane, and thus could be an attractive source of energy, provided that the environmental impact is controlled effectively. Small wonder then, that clathrate hydrates are becoming an increasingly popular material for study.

The Jones group is primarily interested in how the arrangements and motions of water and trapped organic molecules in clathrate hydrates relate to their special structures and properties. To that end, the team is synthesizing hydrates using heavy water under modest pressures and low temperatures, and transporting them to research facilities such as the NIST Center for Neutron Scattering in Gaithersburg, MD to perform powder diffraction experiments.

New findings, new potential

Recent results obtained by Jones and undergraduate researchers Thomas Nevers and Sarah Cryer show that hydrate host frameworks accommodate a great deal of distortion to achieve minimum-energy configurations with different types of guest molecules. These results have inspired the team to make modifications in upcoming neutron scattering experiments and data analysis techniques in order to distinguish static and dynamic disorder in the hydrogen-bonded water host. And, led by clues from these structural studies, Jones and senior undergraduate researcher Divij Mathew are now moving beyond mere determinations of the structures to use ab initio calculations and molecular dynamics to investigate the nature of the self-assembly process by which hydrates are formed.

Dr. Jones sees a number of potential implications of the insights her group is gathering. "Research on gas hydrates has been largely motivated by their potential as an energy source and the detrimental effects of their growth in pipelines. In general, we know what their structures look like on an atomic level," she notes. "But by obtaining even more detailed structural information about them from our neutron diffraction experiments, we can gain a far more thorough understanding, and perhaps improve our ability to predict and control their properties."

Other positive applications of clathrate hydrates include industrial processes such as carbon dioxide sequestration, separation and natural gas storage and transportation. And, in an era of global warming, there may also be new ways to apply their dissociation energy in refrigeration processes, cool storage and air conditioning.

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