Tag: clathrate hydrates

Research on ice-forming compound could improve pipeline safety, carbon capture and storage

Research on ice-forming compound could improve pipeline safety, carbon capture and storage

Canadians may think they’re intimately familiar with ice in all its forms, but there is one kind that most have probably never heard of. Clathrate hydrates are tiny crystalline cages of ice that can trap other gases or liquids inside them.

These hydrates can form in natural gas pipelines and cause explosions if they block the line. The BP Deepwater Horizon disaster in the Gulf of Mexico in 2010 was caused by hydrate formation, says John Tse, Canada Research Chair of Materials Science and a professor in the Department of Physics and Engineering Physics at the University of Saskatchewan (USask).

That’s one of the reasons Tse and his colleagues “want to understand more about how this compound forms, and how the gas and water interact with each other.”

Because the reactions that form hydrates happen so quickly, the researchers needed a way to both slow them down and observe them in progress. So Tse cooled down a mixture of water and a chemical called tetrahydrofuran (THF) to -263oC in a vacuum, then used the powerful X-ray beamlines of the Canadian Light Source at USask to watch how the molecules moved and changed shape as he slowly warmed up the mixture.

Tse found that, as the temperature rose, the THF separated out and formed crystals while the frozen water remained in a non-crystal form. Then, around -163oC, the THF suddenly melted and mixed with the water to form clathrate hydrates, crystalline cages of ice with THF trapped inside.

Understanding more about how hydrates behave could lead to many different practical applications beyond just protecting against pipeline explosions. They could also be used in natural gas transport and storage – a single cubic foot of hydrate can store up to 150 cubic feet of gas – or for carbon capture and storage projects. Tse hopes that his fundamental science work will be used by more applications-minded engineers to develop helpful new technologies.

Read more on CLS website

High-pressure synthesis of carbonic acid polymorphs from carbon dioxide clathrate hydrate

High-pressure synthesis of carbonic acid polymorphs from carbon dioxide clathrate hydrate

Carbon dioxide (CO2) is largely present in diverse astrochemically relevant environments, quite often co-existing with water (H2O) ices. Their simultaneous presence has triggered a great interest regarding the stabilization of CO2 clathrate hydrates and the possible formation of adducts under various thermodynamic conditions. Amongst these adducts, solid carbonic acid (H2CO3) remains elusive. All the synthetic routes followed up to now for its production required quite drastic conditions (from high energy protonation of solid CO2 to laser heating at high pressure on fluid mixtures of CO2 and H2O).

In our study, we discovered a highly reproducible, simpler and effective way to synthesize two diverse carbonic acid crystal structures upon the fast, cold compression of pristine CO2 clathrate hydrates. We found that the products of this reaction strictly depend on the starting pressures, resulting in three different reaction pathways. In the first pathway, for pressures lower than 2.7 GPa, pristine CO2 clathrate hydrate simply decomposes into its constituents, as expected from previous studies. For intermediate pressures (between 2.7 and 4.8 GPa), a first crystalline phase is observed, characterized by a well-defined lattice phonon region (see Figure 1a, green spectrum) and a specific diffraction pattern. For pressures exceeding 4.8 GPa, the formation of an amorphous product is observed, characterized by a broad, unstructured band in the lattice phonon region (see Figure 1a, black spectrum). Both the two products feature an intense, quite broad Raman band at about 1050 cm-1, a reported signature band for carbonate-based systems and, also, carbonic acid (see Figure 1b). We found that the high pressure, amorphous product (called a-ε) transformed upon decompression down to 4.8 GPa or heating at higher pressures into a distinct, much more structured crystalline phase characterized by 10 lattice phonons (see Figure 1a, red spectrum) and sharper internal Raman bands (Figure 1b, red spectrum). This structure was found to be that already reported by Abramson and co-authors in a recent paper, where it was obtained in much more drastic conditions (from fluid CO2 and H2O upon resistive heating): we called this phase ε-H2CO3.

Read more on Elettra website