Liquid chemicals and fuels from natural gas

Natural gas is mostly methane, but it also contains significant amounts of ethane and propane. Those three hydrocarbons are raw materials for easily transportable liquid commodities such as methanol. A key step in making those compounds is to break a strong carbon–hydrogen bond and attach an oxygen atom to the carbon. Current processes require high temperatures (up to 900 °C) that lead to low reaction efficiencies and high carbon dioxide emissions. For decades now, chemists have worked to enable oxygenation at lower temperatures, mostly using scarce and expensive precious metals such as platinum or palladium. Now scientists from the Scripps Research Institute and Brigham Young University, led by Roy Periana, have discovered that salts of abundant elements like thallium and lead can activate and oxygenate C–H bonds of methane, ethane, and propane. The work could be the first step toward an inexpensive and practical conversion of natural gas into other fuels and chemicals. In experiments run under a variety of conditions but always at temperatures below 200 °C, the Periana group achieved oxygenated product yields often exceeding 70%. The figure (courtesy of the Scripps Energy and Materials Center) shows an intermediate state for the reaction of methane with thallium trifluoroacetate [TI(CF₃COO)₃]. As the thallium (orange) grabs onto the methane carbon atom above it (gray), an oxygen (red) from an acetate group prepares to pluck off one of the methane’s hydrogen atoms (white). An acetate group from the reaction solvent replaces the removed hydrogen; then the newly oxygenated methane disengages from the complex. (B. G. Hashiguchi et al., Science 343, 1232, 2014, doi:10.1126/science.1249357 .)