Res. Chem. Intermed.
, Vol. 27, No. 6, pp. 643–658 (2001)
Activation of methane in microwave plasmas
at high pressure
, STEVEN SUIB
, JEFFREY B. HARRISON
and FRANK KNIGHT
Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA
Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA
Department of Chemical Engineering, University of Connecticut, Storrs, CT, USA
Texaco Research Center, Texaco, Inc., PO Box 509, Beacon, NY 12508, USA
Texaco Ltd., Information and Technology, 1 Westferry Circus, Canary Wharf, London,
E14 4HA, UK
Received 8 November 2000; accepted 5 December 2000
Abstract—Methane is converted to C2 products in a microwave plasma under pressure up to 400 torr
at maximum plasma power of 100 W. Steam is introduced with methane into the plasma zone in order
to suppress coke formation. Major products are C2 hydrocarbons. Small amounts of benzene are
also formed. Very small amounts of some unusual highly unsaturated hydrocarbons are also formed.
Oxygenated products are CO and CO
. The conversion and yields are related to experimental variables
by an empirical second order linear model. The conversion of methane ranges from 10 to 60%. The
yield of C2 products ranges from 5 to 68%. The major C2 product is acetylene.
Activation of methane via plasmas may be a possible method for upgrading methane
to more useful products. A key step in this process is the selective activation of
the carbon– hydrogen bond. Unlike traditional thermal catalytic reactions where a
highly selective and effective catalyst is needed to lower the activation energy of
breaking carbon – hydrogen bonds, in plasma reactions this bond is easily broken
by the collision of energetic ions or electrons with methane. Further reactions of
methyl radicals created by this collision produce the products.
High methane conversion can be achieved in plasma reactions [1– 7]. The
bond-breaking process involves indiscriminately collisions of electrons and ions
with methane. The selectivity can be low. However, by manipulation of reactant
concentrations good selectivity in methane conversion is obtainable. For instance,