October 22, 2012
Produce benzene from methane with this catalyst. The abundance of shale gas in North America significantly influences the way ethylene producers operate their steam crackers. Cracker operators that have the flexibility to crack ethane are choosing to do so to take advantage of extraordinarily low ethane prices. This choice, however, has unintended consequences.
For example, as more and more ethane is cracked, less and less propylene, butadiene, and pyrolysis gasoline are coproduced. Much of the world’s benzene comes from pyrolysis gasoline, so decreasing its production means that the United States must import more benzene.
A potential new benzene source is inexpensive methane from shale gas. Methane can be converted directly to benzene if the right catalyst systems are developed.
To this end, S. Yamada and co-inventors disclose catalysts and operating conditions that allow the conversion of methane to aromatics, particularly relatively high levels of benzene. The catalysts are based on ZSM-5 zeolite impregnated with varying ratios of copper and molybdenum.
In the patent’s first example, 14 g catalyst is loaded into a reaction pipe of 18 mm diam. Methane gas is allowed to flow over the catalyst at a rate of 3 L/(g catalyst·h) at 780 °C and 0.3 MPa pressure. After a 24-h run time with a catalyst containing a Cu/Mo mol ratio of 0.1:1, methane conversion is 12.4%, and benzene production is 1.9 mol/(g catalyst·s). The total benzene–toluene–xylene (BTX) production rate is 2.0 mol/(g catalyst·s).
When a catalyst with a Cu/Mo mol ratio of 0.8:1 is used, methane conversion and aromatics productivity are reduced by half. (Meidensha Corp. [Tokyo]. US Patent 8,278,237, Oct. 2, 2012; Jeffrey S. Plotkin)