22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Plasma assisted direct liquefaction of shale gas
A. Rabinovich, A. Fridman and D. Dobrynin
A.J. Drexel Plasma Institute, Drexel University, Camden, NJ, U.S.A.
Abstract: Plasma assisted direct liquefaction of shale gas is based on non-thermal plasma
stimulation of natural gas with direct incorporation into crude oil and its distillation
products, "drop­ in" fuels, and other liquid hydrocarbons, producing improved and
expanded volumes of such products. The key difference of this approach with respect to
other plasma stimulated methods is selective CH 4 (NG) vibrational excitation which allows
exothermic plasma catalytic incorporation with extremely low energy cost.
Keywords: direct liquefaction, gliding arc, non-thermal plasma
1. Introduction
The recent development of shale gas resources has
made available abundant supplies of natural gas (NG) in
the U.S. Currently crude oil and liquid fuels have been
selling for substantial premiums to natural gas, with
prices for crude oil trading approximately 70% higher.
Availability of such low-cost NG is expected to be at least
to the year 2040. Traditionally, the technology used to
convert natural gas into high-value oils and "drop-in"
fuels is very costly technology of reforming of methane to
syngas followed by Fischer-Tropsch synthesis (FTS). As
such, there is a clear need in development of a scalable
novel direct process of shale gas liquefaction with
minimal capital expenditures and operating costs.
The breakthrough solution has been suggested by
Drexel Plasma Institute and its industrial partners. The
novel approach is based on non-thermal plasma
stimulation of natural gas with direct incorporation into
crude oil and its distillation products, "drop­ in" fuels, and
other liquid hydrocarbons, producing improved and
expanded volumes of such products. The key difference
of this approach with respect to other plasma stimulated
methods is selective CH 4 (NG) vibrational excitation
which allows exothermic plasma catalytic incorporation
with extremely low energy cost. The process occurs
according to reactions [1-4]:
CH 4 *+ RH  CH 3 R(H)H,
(1)
CH 4 *+ ROH  RCH 3 + H 2 O,
(2)
CH 4 *+ R 1 =R 2 H  CH 3 R 1 R 2 H,
(3)
CH 4 *+ Armt  CH 3 RH
(4)
In reactions (1-4) - CH 4 * - VT activated molecule of
methane; RH – general formula of hydrocarbons; Armt –
aromatic hydrocarbons.
The CH 4 incorporation energy cost in this case
theoretically doesn’t exceed 0.3 eV/mol (7 kcal/mole),
which corresponds to OPEX cost 0.3 kWh per 1 m3 of
incorporated natural gas. This is about 4 times cheaper
than conventional GTL FTS process Gas-to-Liquid Fisher
Tropsch Synthesis.
Effective organization of such
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technology is possible only using plasmas providing
significant vibrational-translational (VT) non-equilibrium
at atmospheric pressure, which can be achieved only in
high gas flow gliding arc discharges (GA), microwave
discharges (MW), and atmospheric pressure glow
discharges (APG). In the above mentioned discharge
systems CH4 vibrational temperature is 2000 - 4000 K.
To guarantee effective CH 4 incorporation into liquid fuel
(with low energy cost 0.3 - 0.5 eV/mol) gas temperature
in the cold plasma reactor should be not higher than
700 - 900 K, which is already achieved in Drexel Plasma
Institute experimental systems.
2. Preliminary experimental results proved feasibility
of this approach.
0.5 L of methanol has been treated for 9 minutes by
gliding arc plasmatron (Fig. 1). The nozzle of the
plasmatron has been submerged into methanol. Plasma
power was ~200 W. Plasma gas was N 2 with 10% of
CH 4 . GC analysis showed that during experiments ~25%
of CH 4 disappeared. At the same time analysis of liquid
methanol performed by spectrophotometry showed
increased
quantity
of
unidentified
compounds
(presumably hydrocarbons) in the liquid (see Fig. 2).
Fig. 1. Schematic of gliding arc plasma liquefaction
system with NG recirculation.
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Fig. 2. Top: change of methanol composition during
gliding arc treatment with N 2 + CH 4 mixture. Bottom:
control treatment with N 2 only plasma.
3. Conclusion
It should be mentioned that numerous researchers tried
to convert CH 4 into liquid hydrocarbons using plasma
dissociation processes with production of H 2 , CH radicals
and other active species. This process proved to be very
energy consuming and not feasible for industrial
applications. The most efficient process should include
stages of plasma vibrational excitation of methane with
following surface chemisorption and incorporation into
liquid hydrocarbons. This process require significantly
less (at least 4 times) energy consumption than formation
of radicals.
Currently lab scale experiments carried out with
2 non-thermal plasma systems: gliding arc Tornado
plasma and pulsed nano-second DBD discharge. Based
on experimental results the optimal plasma system will be
selected for pilot plant scale design and fabrication.
Successful large scale implementation of direct plasma
assisted NG liquefaction will open a pathway to solve
most of modern energy challenges.
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