(478b) Decomposition of H2S and CH4 in Pulsed Corona Discharge Reactors

Decomposition of H₂S and CH₄ in
Pulsed Corona Discharge Reactors

Natural gas typically contains
70-90% methane (CH₄) and 0-5% hydrogen sulfide (H₂S). The
conversion of CH₄ to hydrogen and more valuable hydrocarbons, like ethylene,
is of great importance to the petrochemical industry.  Direct decomposition of
H₂S to yield hydrogen and sulfur is desirable compared to the
conventional Claus process, which converts H₂S into sulfur and water.
 CH₄ and H₂S have been separately decomposed in our
experiments in a wire-in-tube pulsed corona discharge reactor.  The pulsed
corona discharge is a good source for generating chemically active species at
room temperature, which initiate chemical reactions leading to CH₄ and
H₂S conversion.

A corona discharge was achieved
with our present reactor configuration after pure H₂S was diluted
with argon.  The effects of charge voltage, capacitance and frequency on
reaction rate and energy efficiency were studied for different concentrations
of H₂S in argon.  At constant power input (100 W), low capacitance
(720 pF) operation gave the highest conversion and lowest energy consumption
for H₂S decomposition.  The effect of mixed argon-nitrogen diluents
on H₂S conversion is being studied.

The effect of capacitance,
cathode material, gas flow rate and specific energy input on conversion, energy
efficiency, and product selectivity on CH₄ decomposition was also
studied.  Ethane and acetylene appear to be formed from dimerization of CH₃
radicals and CH radicals, respectively, while ethylene is formed mainly from
the dehydrogenation of ethane.  At a given power input, low capacitance (1280
pF) with high pulse frequency (1000 Hz) results in higher CH₄
conversion and energy efficiency than operation at high capacitance (1920 pF)
with low pulse frequency (200 Hz).  Platinum coated stainless steel cathodes
slightly enhance CH₄ conversion relative to stainless steel
cathodes, perhaps due to a weak catalytic effect.  As specific energy input
increases, energy efficiency for CH₄ conversion goes through a
minimum, while the selectivity of acetylene has a maximum value.