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China and US Researchers Make Progress With Catalyst for Conversion of Stranded Methane to Transportable Liquid
22 May 2008
Researchers in China and the US have identified details of the structure of a known catalytic material that can turn methane into a safe and easy-to-transport liquid. The insight lays the foundation for converting stranded methane in oil fields into a variety of useful fuels and chemicals.
The catalyst—molybdenum oxide sitting on a zeolite mineral—converts methane gas into the more tractable liquid benzene. The process is not yet commercially viable, as the scientists do not yet understand enough about the molecular details to improve the catalyst. Now, researchers at Pacific Northwest National Laboratory (PNNL) and the Chinese Academy of Sciences’ Dalian Institute of Chemical Physics in Liaoning province have worked out some of the details that will help researchers zoom in on an efficient catalyst.
They reported their results 26 March in the Journal of the American Chemical Society. This work is the first publication to come out of the International Consortium for Clean Energy, a collaboration between PNNL, the DICP and China’s Institute of Coal Chemistry.
To get these results, the chemists—led by Chuck Peden at PNNL and Xinhe Bao at DICP—used the world’s largest nuclear magnetic resonance (NMR) spectrometer. The 900 MHz NMR is armed with one of the strongest magnets constructed and can be outfitted to investigate solid samples, a step above its smaller cousins.
The combination of molybdenum oxide and a zeolite mineral had been shown in 1993 to convert methane, but the catalyst has been difficult to analyze. Researchers know that the zeolite anchors molybdenum oxide in place so methane and molybdenum oxide can react chemically, either on or in the zeolite channels. But no one could tell which comprised the reactive form: a small nugget of one or two molecules, or a larger cluster of many molybdenum oxide molecules.
This uncertainty has led to a controversy in the scientific literature about the active phase and reaction mechanism of methane activation on these promising catalyst materials.
—Xinhe Bao
The technological problem lay in the molybdenum oxide. To study this particular oxide with NMR, the chemists needed to pick up the signal from one variant of molybdenum, 95Mo; the ultra-high field of the NMR, housed at the DOE’s Environmental Molecular Sciences Laboratory on the PNNL campus, allowed them to do so.
The researchers prepared catalysts with increasing concentrations of molybdenum in the zeolite scaffold and focused the 900 MHz NMR on the samples. The data revealed two different forms of the catalyst, as expected. One form contained the smaller nugget and the other form comprised the much larger clusters. When the concentration of molybdenum rose, more of these large clusters formed.
Then the team added methane and measured how much got converted into benzene by the catalysts. They found that when more smaller nuggets were present, more benzene was made, indicating the variety of one or two molybdenum oxide molecules was the reactive one.
Now, said Peden, the challenge is to design and produce the active form of the catalyst that could be used for large-scale benzene production, research that Bao and his group are already working on.
This work was supported by the Department of Energy’s Office of Basic Energy Sciences and the National Science Foundation of China.
Resources
H. Zheng, D. Ma, X. Bao, J.Z. Hu, J.H. Kwak, Y. Wang, and C.H.F. Peden, (2008) Direct Observation of the Active Center for Methane Dehydroaromatization Using an Ultra-High Field 95Mo NMR Spectroscopy, J. Am. Chem. Soc., 130 (12), 3722 -3723, DOI: 10.1021/ja7110916.
May 22, 2008 in Catalysts, Natural Gas | Permalink | Comments (6) | TrackBack (0)
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Comments
I don't know what benzene would be worthwhile for, in these quantities. It is a carcinogenic compound that is nowadays removed from gasoline to make it cleaner-burning and safer, along with other aromatics that benzene might have been a precursor for. A benzene tanker spill would not be nice. There are already other gas-to-liquids processes that work better, including DME, methanol and FT diesel, and of course there's LNG. All of which promote the use of more efficient engines or perhaps fuel cells, making the project more worthwhile.
Posted by: P Schager | May 22, 2008 1:41:37 AM
Methane is a chemical compound with the molecular formula CH4. It is the simplest alkane, and the principal component of natural gas. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean burning process makes it a very attractive fuel. However, because it is a gas at normal temperature and pressure, methane is difficult to transport from its source. In its natural gas form, it is generally transported in bulk by pipeline Methane is a relatively potent greenhouse gas with a high global warming potential. (From Wikipedia)
Methane is a biogas generated by decomposing organic matter and Cattle.
Liquid benzene is also a fuel. It is an aromatic hydrocarbon. Benzene C6H6 is normally liquid at room temperature but will evaporate on contact with air. In gasoline it is used as a substitute for lead at a concentration of 1 to 2 percent. It is released as a by-product of fuel combustion. Benzene is no longer used as a paint solvent because it's toxic.
Benzene is a “known human carcinogen.” The International Agency for Cancer Research warns that benzene has been shown to cause leukemia and other types of cancer. Long-term exposure to benzene fumes can cause nerve damage and can harm the immune system.
Finding a way to turn reasonably 'life-friendly' bio-gas into a toxic polluting chemical may not be such a great discovery, even if it is cheaper to transport.
Posted by: John Taylor | May 22, 2008 2:41:33 AM
We are thinking fuel, when in fact benzene may be more valuable to the chemical industries as a precursor to many, many other useful chemicals (polymers, plastics, nylon, rubbers, lubricants, dyes, detergents, drugs, explosives, napalm and pesticides)*
*(see wikipedia) (also, simply because I list a use doesn't mean I endorse it)
Posted by: NCyder | May 22, 2008 6:24:28 AM
The zeolite/molybdenum oxide catalytic process for converting methane to benzene is of interest because it does not involve the normal procedure of gasification to carbon monoxide and hydrogen, followed by synthesis to methanol or other products. Gasification loses a lot of the theoretical energy of methane, hence I am happy to see there is hope of converting methane to other compounds without said process step.
What I'd like to see is development of a catalyst to attach oxygen to methane, i.e. 2CH4 + O2 --> 2(CH3OH), to make methanol instead of the normal process of reforming methane to H2 + CO followed by 2H2 + CO --> CH3OH. If it proves possible to do that, we'll have a great way to utilize stranded natural gas.
Posted by: Alex Kovnat | May 22, 2008 7:33:31 AM
"Stranded methane" That's the stuff that's being burned off on remote oil platforms, right? Wasted. I'd be great to find a use for all those BTUs.
Posted by: Hybrid fan | May 22, 2008 11:33:54 AM
Simple and relatively cheap way to capture the methane for shipping:
- Dry and pump to deep water through pipeline.
- Bubble through cold seawater at high pressure, yielding methane hydrate.
- Capture hydrate, separate from remaining seawater, and chill to make stable at atmospheric pressure (expansion of methane through a turbine may be a possible source of cooling).
- Load chilled methane hydrate on refrigerated freighter.
- To reconstitute methane, add water at atmospheric pressure and ambient temperature.
Posted by: Engineer-Poet | May 23, 2008 10:41:09 PM
