Researchers from The Scripps Research Institute (TSRI) and Brigham Young University have devised a new and more efficient method to convert natural gas into liquid products at much lower temperatures than conventional methods.
Their work, reported in the journal Science, uses main-group metals such as thallium and lead to oxidize methane and the other alkanes contained in natural gas (ethane and propane) to liquid alcohols at about 180 °C instead of the more than 500 °C used in current processes, said SRI Professor Roy Periana, who led the research. This creates the potential to produce fuels and chemicals at much lower cost.
… we report that the electrophilic main-group cations thallium(III) and lead(IV) stoichiometrically oxidize methane, ethane, and propane, separately or as a one-pot mixture, to corresponding alcohol esters in trifluoroacetic acid solvent. Esters of methanol, ethanol, ethylene glycol, isopropanol, and propylene glycol are obtained with greater than 95% selectivity in concentrations up to 1.48 molar within 3 hours at 180°C.—Hashiguchi et al.
Methane, ethane and propane, the major components in natural gas, belong to a class of molecules named alkanes that are the simplest hydrocarbons and one of the most abundant, cleanest sources of energy and materials. However, transportation can be expensive and converting these alkanes into other useful forms such as gasoline, alcohols or olefins is expensive and often inefficient.
At the core of technologies for converting the alkanes in natural gas is the chemistry of the carbon-hydrogen bond. Because of the high strength of these bonds, current processes for converting these alkanes employ high temperatures (more than 500 °C) that lead to high costs, high emissions and lower efficiencies.
The development of lower temperature (less than 250 °C), selective, alkane carbon-hydrogen bond conversion chemistry could lead to a major shift in energy and materials production technology.
Periana has designed some of the most efficient systems (Periana et. al., Science 1993, 1998 and 2003) for alkane conversion that operate at lower temperatures. However, when Periana and his team examined these first-generation systems they realized that the precious metals they used, such as platinum, palladium, rhodium, gold, were both too expensive and rare for widespread use.
Approaching the problem both theoretically and experimentally, the team hit on inexpensive metals known as main group elements, some of which are byproducts of refining certain ores. Interesting, the new findings run contrary to their predictions from the earlier studies.
The reaction of alkanes with this class of materials we’ve identified is novel. They can react with methane, ethane as well as propane at lower temperatures with extraordinarily selectivity—and produce the corresponding alcohols as the only the desired products. These products are all major commodity chemicals and are also ideal, inexpensive sources for fuels and plastics.—Roy Periana
In addition to Periana and Hashiguchi, authors of the study, “Main-Group Compounds Selectively Oxidize Mixtures of Methane, Ethane, and Propane to Alcohol Esters,” are Michael M. Konnick, Steven M. Bischof and Niles Gunsalus of The Scripps Research Institute; and Samantha J. Gustafson, Deepa Devarajan and Daniel H. Ess of Brigham Young University.
This study was supported by the US Department of Energy (DE-SC0001298).
Brian G. Hashiguchi, Michael M. Konnick, Steven M. Bischof, Samantha J. Gustafson, Deepa Devarajan, Niles Gunsalus, Daniel H. Ess, and Roy A. Periana (2014) “Main-Group Compounds Selectively Oxidize Mixtures of Methane, Ethane, and Propane to Alcohol Esters,” Science doi: 10.1126/science.1249357